Case Studies of Building Rehabilitation and Design 3030712362, 9783030712365

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Building Pathology and Rehabilitation

João M. P. Q. Delgado Editor

Case Studies of Building Rehabilitation and Design

Building Pathology and Rehabilitation Volume 19

Series Editors Vasco Peixoto de Freitas, University of Porto, Porto, Portugal Aníbal Costa, Aveiro, Portugal João M. P. Q. Delgado , University of Porto, Porto, Portugal

This book series addresses the areas of building pathologies and rehabilitation of the constructed heritage, strategies, diagnostic and design methodologies, the appropriately of existing regulations for rehabilitation, energy efficiency, adaptive rehabilitation, rehabilitation technologies and analysis of case studies. The topics of Building Pathology and Rehabilitation include but are not limited to - hygrothermal behaviour - structural pathologies (e.g. stone, wood, mortar, concrete, etc…) - diagnostic techniques - costs of pathology - responsibilities, guarantees and insurance - analysis of case studies - construction code - rehabilitation technologies - architecture and rehabilitation project - materials and their suitability - building performance simulation and energy efficiency - durability and service life.

More information about this series at http://www.springer.com/series/10019

João M. P. Q. Delgado Editor

Case Studies of Building Rehabilitation and Design

Editor João M. P. Q. Delgado CONSTRUCT-LFC Department of Civil Engineering Faculty of Engineering University of Porto Porto, Portugal

ISSN 2194-9832 ISSN 2194-9840 (electronic) Building Pathology and Rehabilitation ISBN 978-3-030-71236-5 ISBN 978-3-030-71237-2 (eBook) https://doi.org/10.1007/978-3-030-71237-2 © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Switzerland AG 2021 This work is subject to copyright. All rights are solely and exclusively licensed by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, expressed or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publisher remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. This Springer imprint is published by the registered company Springer Nature Switzerland AG The registered company address is: Gewerbestrasse 11, 6330 Cham, Switzerland

Preface

Building designers’ decisions affect long-term quality and the life cycle cost of buildings. Designers’ decisions are usually latent and hard to detect at the early stage of construction. Eliminating building defects is a difficult task, as the defects generally appear only during the occupancy stage. Over the time, several works showed that many of these pathologies are due the use of inappropriate materials, poor expert decisions, environmental conditions, workmanship, maintenance issues, soil impact, poor structural design, etc. Building pathology is a holistic approach to studying and understanding buildings, and in particular, building defects or problems and associated rehabilitation actions. The main purpose of this book, Case Studies of Building Rehabilitation and Design, is to provide a collection of recent research works related to blast resistant buildings, green roofs and sustainability, retrofit interventions with C-FRP fibers, analysis of compressive strength of concrete by artificial neural networks and ultrasonic wave propagation tests, and acoustic performance in buildings. The book is divided into five chapters that intend to be a resume of the current state of knowledge for benefit of professional colleagues, scientists, students, practitioners, lecturers and other interested parties to network. At the same time, these topics will be going to the encounter of a variety of scientific and engineering disciplines, such as civil, mechanical and materials engineering. Porto, Portugal

João M. P. Q. Delgado

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Contents

Design of Blast Resistant Buildings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Prafulla Parlewar

1

Green Roof as a Sustainable and Energy Efficient Construction Tool . . . . 13 J. G. Borràs, Á. Mas, and C. Lerma Seismic Analysis and Retrofitting by C-FRP of Reinforced Concrete Bell Towers Within Masonry Churches: A Case Study . . . . . . . . . . . . . . . . . 29 Antonio Formisano and Antonio Davino Compressive Strength of Concrete Estimated by Artificial Neural Networks and a Non-destructive Testing of Ultrasound . . . . . . . . . . . . . . . . . 57 R. S. Cavalcanti, F. A. N. Silva, J. M. P. Q. Delgado, and A. C. Azevedo Acoustic Performance Criteria in Internal Vertical Partitions: Numerical Simulations and In-Field Measurements . . . . . . . . . . . . . . . . . . . . 71 E. C. L. Rezende, A. J. Costa e Silva, A. C. Azevedo, and J. M. P. Q. Delgado

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Design of Blast Resistant Buildings Prafulla Parlewar

Abstract The design of blast resistant buildings is required for safety of operations and humans in petroleum refineries. These refineries require blast resistant buildings for the operations near the possible ground zero of the explosive unit. This chapter explains the design for blast resistant building in petroleum refinery in Mumbai, India. This chapter investigates the present research in blast resistant building. Then, it explains a case study of blast resistant operation building designed near Diesel Hydrodesulphurisation unit. Some of the important design parameter includes the loading, concrete retaining wall design and aesthetic. The research looks into important question for blast resistant buildings like How does the building behave during the explosion? How to design a Reinforced Cement Concrete structure for blast resistant design? What are architectural criteria for design of blast resistant buildings? How to design a facade that resist the blast as well as looks appealing aesthetically? The application of similar design can be adapted for the blast resistant buildings under threat from terrorist attack and for military installations. Furthermore, this chapter illustrated an innovative design of facade for bast resistant buildings. Keywords Blast resistant design · Blast design code · Blast facade design

1 Introduction The design of blast resistant buildings is required for operation and human safety in hazardous industrial complexes. Particularly, in the petrochemical refinery, it is expected to have a blast at an intensity of 50–100 kg. It is indeed important in petrochemical refineries to design blast resistant buildings for protecting operation system and humans working inside the building. To design the blast resistant buildings, IS Code 4991 provides the guidelines and explains the loads, behaviours of structure during blasts and dynamic design criteria. Some of the important questions in the design of blast resistant buildings are How the structure perform during the blast? P. Parlewar (B) City Development Corporation (P) Ltd., Mumbai, India e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Switzerland AG 2021 J. M. P. Q. Delgado (ed.), Case Studies of Building Rehabilitation and Design, Building Pathology and Rehabilitation 19, https://doi.org/10.1007/978-3-030-71237-2_1

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P. Parlewar

What are the major force affecting dynamic of blast resistant structure? How shock wave affect the structure? These questions are explained in this chapter with case studies on completed project in Mumbai, India. The blast is sudden release of energy due to the explosion of operating units in a petrochemical refinery. Different types of effects can occur due to an explosion which can cause damage to the nearby building. Major causes of damage are overpressure, thermal effects, energised projectiles, debris damage, cratering and ground shock (Mukherjee 2017). The blast resistant building at Diesel Hydrodesulphurisation unit in Mumbai is a building of length 37.32 and 11.49 m in width. It was designed as two storey blast resistant building with Reinforced Cement Concrete (R. C. C.) retaining walls and raft foundation. The internal profile of building included facilities for offices, console room, dining, rest rooms and changing rooms. In stage one, only the ground floor is constructed. However, provision is kept in the design for an additional one floor. The exterior design of the facade of blast resistance building requires careful selection of the materials. Various researches indicate the importance of facade design in the blast resistance building. A research on fuzzy evaluation based method was applied in order to assess various materials used in building facades from the perspective of resiliency (Hasheminasab 2019). The reinforced concrete to be the principal material of choice for blast-resistant design (Brebbia et al. 2002). So, one of the important question of the architectural design is how to design a blast resistant facade? It is indeed important to make innovation in exterior design to minimise damages. The project is located in prime location inside the campus. So, an innovative exterior design was proposed to make the building landmark inside the refinery. The idea was to use concrete as a material for aesthetic, as well as a material for blast forces. Recekli formliner was proposed on the concrete retaining wall to design the exterior of the building. Recekli formliner are manufactured in Germany which designs the concrete exterior. This chapter explains the process of design of blast resistant building and aesthetic integration of concrete wall for making the building landmark.

2 Blast Resistant Design Code The blast resistant loading on the concrete structure is completely different than the conventional structure of concrete design. The concrete structures are hit with rapidly moving shock waves which may exert pressure many times higher. Importantly, the peak intensity lasts for a very small duration only at the time of the blast. The exposed surface of the structure faces the main load. Then this load is transmitted on the other elements of the building. Thus, the response of each individual element is important, unlike the ground motion. In short period, structural system is simultaneously causing inertia effects on all parts (IS 4991, 1968). Hence, the building has to be designed as a cohesive unit than the design for a conventional structure. It is important to design a structure capable of resisting these intense but short duration loads. In the design of the blast resistant load, the members are permitted to deflection and strain than

Design of Blast Resistant Buildings

3

the usual static loads. However, this range is within the plastic range of the material. Moreover, studies have shown that deflection at different gauges on the building decrease with increasing the distance of the blast load from the building (Shallan et al. 2014). Generally, small sizes of room limit the blast to a smaller area due to the screening action on the internal wall. However, the room sizes depend on the planning of the building. The room sizes were designed such that the blast of the building will be confined to the smaller area (Table 1). The rooms were separated to reduce the intensity of the blast due to the screening reaction. Importantly, irregular buildings are vulnerable. Because it shows high value of inter-storey drift (Pooja 2017). In blast resistant buildings, narrows corridors are avoided to reduce the damage. This damage is increased to the extent of along the length of the corridors because of the multiple reflections. These multiple reflection of the blast waves affects multiples surfaces or complex surfaces. Thus, it increases the damages to the building and inhabitants. To avoid these multiple reflections a passage of 1.45 m wide was planned in the center of the building to provide easy access to all the rooms. Also, this planning created a natural barrier to reduce the intensity of the blast. Projections, parapets and balconies made of brittle materials are avoided in the blast resistant buildings. So, in the proposed building no projection like balcony was proposed to reduce the damages. Also, parapets were avoided at the top. The brittle roofing materials, like tile, roof sheets are prone to blast damage. So, innovation was done by use of concrete formliner, to shape the concrete for the aesthetic of the building. The use of the inflammable material was completely avoided in the building to catch fire in the incidental blast. The electrical wiring was kept as conduit wiring to reduce the damages with comparing to the open wiring. Moreover, the advantage of the conduit wiring is that it avoids the short circuit during the blast. Glass, wood and brittle materials are particularly avoided to reduce the impact of the blast. If the exterior building walls are capable of resisting the blast load, the shock front penetrates through window and door openings, subjecting the floors, ceilings, walls, contents, and people to sudden pressures and fragments from shattered windows, doors, etc. Building components not capable of resisting the blast wave will fracture and be further fragmented and moved by the dynamic pressure that immediately follows the shock front (Ngo 2007).

Table 1 Size of rooms S/N Name of room 1 2 3 4 5 6 7

Room no. 1 Room no. 2 Room no. 3 Room no. 4 Room no. 5 Console room Rest room

Length (M)

Width (M)

Area (Sq. M)

4.1 3.55 2.42 3.90 3.58 5.13 1.3

3.55 3.67 3.55 3.55 3.59 3.55 1.7

14.56 13.03 8.59 13.85 12.84 18.19 2.21

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3 Building Profile The blast resistant building at Diesel Hydrodesulphurisation unit is located at an important location. The building is in length 37.32 and 11.49 m in width (Fig. 1). It was designed as two storey blast resistant building with Reinforce Cement Concrete (R. C. C.) retaining walls and raft foundation. The charge of 100 kg was consider as per the IS code 4991 (Table 2). In case of design of blast resistant buildings, the barge charge of blast and the intensity of pressure on the building are the two important factors estimated along with dead load, live load, wind load and earthquake load. The building was designed under these loading conditions with ductility within the range of the material. Blast resistant design is element-focused. It enhances toughness ductility, strength and dynamic characteristic of individual structural element for resistance to air blast induced loading (Dennis 2007) (Fig. 2). The building was designed into a cohesive box type design with R. C. C. retaining wall on side and slab at top and bottom. This reduces the impact on the internal surface of the building. Bitarafan and other (2013) indicated that building spaces that are closed and separate from the other spaces are compatible solutions. The building is internally planned with uses like office, control room, dining and pantry, changing rooms, rest rooms, and retiring room. All these rooms were designed with size to reduce the impact of the blast. A corridor in center provides the access to the rooms. This corridor acts as a barrier to the impact of the blast. The total height of the building was planned a 4.0 M in height. A raft of 1.5 M wide and 0.38 M wide retaining wall (Table 2) was provided in the building based on the design of loading. Door and windows leads to the spread the blast waves inside the building. So, no windows were provided in the building. Architectural space factors, such as ergonomics, can facilitate access to secure spaces (Mahdi 2013). The interior design of the building was incorporated with ergonomics. The solutions to the building services in blast

Fig. 1 Plan of building Table 2 Minimum wall thickness in cm S/N Material of wall 1 2

R. C. C. P. C. C.

Charge of 50 Kg

Charge of 100 Kg

30 34

38 45

Design of Blast Resistant Buildings

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Fig. 2 Retaining wall

resistant building are challenging consideration due to the lack of availability of opening. Hence, artificial ventilation was planned with Variable Refrigerant Volume (VRV) system inside the building. Most of the VRV indoor units proposed were ground mounted type to avoid the damages to the interior during impact. Moreover, false ceiling was also avoided inside the building to reduce the damages due to the impact (Fig. 3).

Fig. 3 Image without retaining wall

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4 Load and Blast Pressure The load combination for design of the blast resistant buildings requires wind load, earthquake load, live load and blast pressures. Wind or earthquake forces cannot be assumed to occur simultaneously of the building. Also, the effect of temperature and shrinkages are neglected on the buildings. Live load on the building was estimated as per the IS: 875–1964. The pressure estimation was undertaken for the 0.1 Tonne explosion with a building height of 4 m. The building was located at a distance of 20 m from ground zero. The yield of explosion and its distance from the ground zero is an important aspect in the design of blast resistant buildings. As the distance increase the intensity of the explosion is reduced on the building. The pressure increases instantly on any type of surfaces to the peak values of side-on overpressure and the dynamic pressure or reflected pressure. This peak value depends upon the size of explosion, distances from ground zero, ambient pressure and temperature in air. The peak initial over pressure is Pso . The peak dynamic pressure in represented by qo . ‘To ’ is the time for positive phase of grade on pressure. As per the above criteria the pressure estimation is illustrated below (Figs. 4 and 5).

Fig. 4 Plan showing design of foundation

Fig. 5 a Section of retaining wall b Section of raft foundation

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For 0.1 Tonne Explosion H = 4 m, Building at 20 m from ground zero Estimation for charge of blast Distance x = 20/(0.1)1/3 = 43.08 Assuming ambient pressure Pa = 1.00 Kg/cm2 Interpolation between 42 m & 45 m For scaled distance Pso = ? Pro = ? qo = ? (1) Pso = Peak side on pressure = 0.76 + (0.68 − 0.76)/(45 − 42) × (43.08 − 42) Pso = 0.7312 Kg/cm2 (2) Pro = Peak reflected overpressure Pro = 1.8584 Kg/cm2 (3) qo = Peak dynamic pressure qo = 0.170 Kg/cm2 The scaled time To (Time for positive phase of grade on pressure) To = P To = 30.2836 ms Td = Duration of equivalent irregular pulse Td = 20.704 ms Values obtained To and Td are multiplied by (0.1)1/3 to get the values of respective quantities for actual explosion at 0.1 Tonne charge To = 30.2336 × (0.1)1/3 To = 14.067 ms Td = 20.704 × (0.1)1/3 Td = 9.61 ms

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M = Mach number of incident shock front  Pso M = 1 + B7 − Pr o M = 1.275 a = 344 m/s a = Velocity of sound in air U = Shock from velocity =M×a = 438.60 m/s = 0.4386 m/ms Pressure on Building H = 4.0 B = 9.2, L = 29.80 S=

1 2

S=

B or H whichever is less 1 2

× 9.2 = 4.6 or S = 4 Hence, S = 4.0

Tc = Clearance time Tt = Transit time Tr = Pressure rise time on back face Tc =

35 U

=

3x4.0 0.4386

= 27.35 ms > Td

Tt =

L U

=

29.80 0.4386

= 67.94 ms > Td

Tr =

45 U

=

4x4.0 0.4386

= 36.48 ms > Td

For roof and side Cd = 0.4 Cd = 0.4 Pso + Cd × qo = 0.7312 + (0.4 × 0.170) = 0.6632 kg/cm2

5 Visual Integration The blast resistant building design is integrated with aesthetic design, mainly, because the building is located at a prime location. One of the important parts of the design of the blast resistant building is cohesiveness of structure. So, materials like glass, exterior panels, loose materials and large projection are avoided due the blast waves.

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The external surfaces are affected mainly by temperature, which is released and thus disrupts the structure of the individual materials (Ivanˇco et al. 2020). It is important to identify stronger materials to resist the yield of the blast to sustain during the impact. Cast-in place concrete wall and corrugate steel plates structural arrangement are most common front wall cladding in industry (Singh et al. 2015). An innovative facade design concept was developed by using the pre-cast R. C. C wall by use of Reckli formliner (Figs. 6 and 7). The concept of the design was based on making the building landmark for visibility during day and night time (Figs. 8 and 9). This concept involved proposed pre-casting in curve shapes in the front facade of the building. The objective of using a curve shape was to further develop strength in the facade during the impact. These curve shapes are layered at a distance of 1.0 M vertically to give waves pattern in design. Each layer consists of 1.0 M × 1.0 M Reckli formliner block was proposed for pre-casting the concrete front surface. A uniform curvilinear pattern was generated in the design. Moreover, to make the building appear good at night, external lighting was designed below each panel to give interesting look at night (Fig. 9). Border farming was proposed in concrete to give a framing appearance to facade of the building. The pre-cast technique for making the formwork is based on the Reckli fromliner which consist of rubber like poly urethane elastomer material. The high flexibility and elasticity allow a damage free release of the concrete and exact reproduction of the pattern. Generally, these formliner can be used up to temperatures +65◦ Celsius. Above this temperate the formliner is damaged and cannot be used further. The formwork mould is order directly and delivered in poly uterine role by the Reckli Company. Once the poly urethane role is received, it is cut to fit the formwork frame. A tight compressive fit is made on formwork. It was proposed to make 1.0 M layer of formwork. It was proposed to cast in the 1.0 M each pattern from bottom to top. Some important care was proposed to keep away the air cushion in the formliner while casting the concrete. After placing the formliner, reinforcement is tided and ready mix concrete is placed inside formwork work. Air cushions or air bubbles in the casting had to be removed by use of the vibrator. It is important to keep the frequency

Fig. 6 Elevation of building showing Reckli

Fig. 7 Plan of facade of building

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P. Parlewar

Fig. 8 View of building showing Reckli

Fig. 9 View of building during night showing Reckli

of the vibrator low. So the formliner is not damaged. This process was proposed to be followed for each layer of the casting of the concrete to get the aesthetic.

6 Conclusions The petrochemical industries are hazardous area where hydrocarbon and fuels causes high yield explosion. This can harm the building nearby and also the humans working for the operation of the plant. There can be large scale of operational and financial loss to the proposed building near Diesel Hydrodesulphurisation unit in case this

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explosion occurs. Because the building was used for the purpose of operations and controls of the petrochemical plant. Indeed, it is important that the proposed blast resistance building required to be near from ground zero. This is mainly because of operational reasons. Moreover, the building has to be in operations in event the blast occurs to continue the operations and control of the unit. Hence, the distance from ground zero is an important part of the design of the blast resistance building. To achieve an accurate design for the blast resistance, following are important aspects of the design: (1) the blast pressure during the impact on the outer wall or retaining wall of the building, (2) distance from the ground zero, (3) ductile design of building and (4) size and height of structure. As compared to the conventional structure the blast resistance building are totally different in design mainly because of the the ductility of structure and elastic behaviour. The main criteria to be followed for planning of the structure are: (1) planning of the layout and sizes to reduce the impact of the blast, (2) use of the element in building like narrow passages, glass, external panelling, false ceiling, etc. should be avoided to reduce the internal and external damages, (3) estimation of the blast pressure and (4) design and detailing of the structure as per the required codes. This, similar methodology can been adopted in design of new blast resistance building from terrorist attack or for military installations. Moreover, blast resistance building in India requires further research by comparing the design consideration undertaken in countries in counties like USA, Europe and Japan.

References Bitarafan M, Hosseini SB, Hashemi-fesharaki S, Esmailzadeh A (2013) Role of architectural space in blast-resistant buildings. Front Arch Res 2:67–73 Brebbia CA, Rajendran AM (eds) (2002) Protective design of concrete buildings under blast loading WIT Press, Paper from: structures under shock and impact VII, N Jones, pp 23–33 Dennis MM, Smith SJ (2007) Blast resitande design for reinforced concrete structures. Struct Mag 22–26 Hasheminasab H, Hashemkhani Zolfani S, Bitarafan M, Chatterjee P, Ezabadi A (2019) The role of facade materials in blast-resistant buildings: an evaluation based on fuzzy delphi and fuzzy. EDAS Algor 12:119–134 Ivanˇco M, Trajkovski J, Figuli L, Erdélyiová R (2020) Determination of blast resistance of selected structural elements. MATEC Web Confer 313 Mahdi B. Sayed Bagher H, Sayed Javad H, Armin E (2013) Role of architectural space in blastresistant buildings. Front Arch Res 2(1):67–73. https://doi.org/10.1016/j.foar.2012.11.003 Mukherjee S, Bhowmik R, Das A, Banerjee S (2017) Review paper on blast loading and blast resistant structures. Int J Civil Eng Technol 8:988–996 Ngo T, Mendis P, Gupta A, Ramsay J (2007) Blast Loading and Blast Effects on Structures–an overview. EJSE Special Issue Loading Struct 76–91 Pooja DP, Dhameliya HK, Krutarth SP (2017) A review on dynamic analysis of building under blast and seismic loading. Int J Adv Eng Res 4(11)

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Shallan O, Eraky A, Sakr T, Emad S (2014) Response of building structures to blast effects. Int J Eng Innov Technol (IJEIT) 4(2) Singh J, Roy A (2015) Thickness of concrete and steel front wall claddings for various blast pressure in blast resistant buildings. https://doi.org/10.2118/175325-MS

Green Roof as a Sustainable and Energy Efficient Construction Tool J. G. Borràs, Á. Mas, and C. Lerma

Abstract Address to the search for the necessary sustainability in today’s societies, cities and architecture become the appropriate environment in which to look for a balance between socio-economic growth and caring for the environment. The green roofs, as part of this sustainable architecture, allow, thanks to their construction and their particularities, to obtain a series of environmental, energy and thermal benefits. The magnitude of the energy improvement is influenced by several factors, among which the state of the envelope of the building in which it is installed stands out. In the field of refurbishment, where a large part of the buildings to be refurbished have little or no insulation in the envelope, the contribution of the green roofs to energy saving and the improvement of interior thermal comfort is of great relevance, being able to reach energy savings in cooling of 49%, while in already insulated structures this value drops to 6%. The different types of green roofs must be studied, therefore, considering, not only the benefits that can be achieved, but also characteristics such as weight and cost depending on the field of application. Keywords Green roofs · Energy · Sustainability

1 Introduction The green roofs have been widely studied in recent years due to the necessary environmental involvement of architecture and the improvement of the surroundings where the main current societies develop. Taking into account that sustainability is posed as the great challenge of the coming years (United Nations Sustainable Development Goals Gobierno de España 2020; Challenge 2030 of the platform Architecture 2030 J. G. Borràs · Á. Mas · C. Lerma (B) Universitat Politècnica de València, Cmno. De Vera s/n, Valencia, Spain e-mail: [email protected] J. G. Borràs e-mail: [email protected] Á. Mas e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Switzerland AG 2021 J. M. P. Q. Delgado (ed.), Case Studies of Building Rehabilitation and Design, Building Pathology and Rehabilitation 19, https://doi.org/10.1007/978-3-030-71237-2_2

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Ching and Shapiro 2015), the environment must be protected and cared for, since it is the physical scenario in which future socioeconomic growth must necessarily take place (Thwink 2020). Currently, around 55% of humanity lives in cities, megacities or conurbations (Gobierno de España 2020), a value that rises to 74% if only Europe is studied (Lesjak et al. 2020). And this value tends to rise, so more than half of the human population develops, and will develop, its day-to-day in a city. Cities with a progressive increase in pollution (Gobierno de España 2020), a high percentage of impervious surfaces and a low number of green areas, among other characteristics. Architecture, specifically its green and sustainable dimension, can, and must, play an important role in solving current problems and in the search for sustainability. The scarcity of free parcels at ground level and natural spaces make green roofs an important tool for environmental improvement of the urban surroundings (Ajuntament de Barcelona 2020). The main environmental (GT-4 Infraestructuras verdes urbanas y periurbanas 2014; Walters and Midden 2018) benefits that the use of green roofs imply are the improvement of biodiversity (GT-4 Infraestructuras verdes urbanas y periurbanas 2014; Walters and Midden 2018), reduction of the heat island effect (Santamouris 2014; Speak et al. 2013), reduction of air pollution (Ching and Shapiro 2015; Penoni´c 2016), reduction of rainwater runoff (Wong et al. 2003; Berndtsson 2010; Carter and Rasmussen 2006), improved runoff water quality (Mentens et al. 2006; Berndtsson et al. 2009) and reduced environmental noise (Köhler et al. 2002; Connelly and Hodgson 2013). But not only are its environmental improvement characteristics attractive, but also the thermal and energy benefits that its use entails. The cities that we have designed so far are allocated more than 70% of the total energy consumed by all humanity (Correa 2001) and buildings, in the case of Spain, use 20% of total final energy consumption in needs such as heating, cooling or lighting (IDAE 2020). These data lead us to consider the necessary study of the building’s thermal envelope, minimizing heat losses and air leaks (Lerma et al. 2018), and promoting a design that allows to achieve the interior thermal comfort conditions with the minimum contribution of air conditioning systems (cooling and/or heating) (Ching and Shapiro 2015; Ministerio de fomento 2019). The green roofs respond to these needs and, thanks to their constructive characteristics, allow to minimize the energy consumption of buildings, especially in those cases in which it is proposed to rehabilitate buildings with little or no previous insulation (Castleton et al. 2010). An example of the use of the green roof as a rehabilitation tool can be seen on the roof of a shopping centre in the Midtbyen neighbourhood of Aarhus (Denmark) (see Fig. 1), making the building more sustainable and the roof gains a social character and leisure to stop being a forgotten and unused space. In the following lines, a review of the literature regarding the constructive and energy characteristics of the green roofs will be carried out, paying special attention to their potential in the field of rehabilitation.

Green Roof as a Sustainable and Energy …

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Fig. 1 Green roof after the rehabilitation carried out in a shopping centre in Aarhus (Denmark) (Own elaboration)

2 Constructive Features Green roofs can be defined as a multilayer roof system with a vegetable finish. These roofs, like traditional systems, can be conventional or inverted depending on the relative order of the insulation layer and waterproof sheet (Tomás 2005). Whether the insulation is placed above the waterproof sheet (inverted system) or if the insulation is placed under the waterproof sheet (conventional system), the layers that are placed above these elements and that constructively define the green roofs are: anti roots sheet (always just above the waterproof sheet), drainage layer, filter sheet, substrate and vegetation. This type of roof can be classified into three types: extensive (see Fig. 2), semiintensive and intensive (see Fig. 3). The difference lies in the thickness and type of substrate (it can contain different layers with different amounts of organic matter and drainage power) and, therefore, in the type of vegetation they can support, the system’s own weight and the cost of the same (see Table 1). These last values are very important when considering the study of the use of green roofs in the field of rehabilitation. In Spain, the first regulation with insulation requirements dates from 1979 (Gobierno de España 1979) and a very significant proportion of buildings in the current housing stock were built during the years

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Fig. 2 Standard construction detail of a conventional extensive green roof (Elaborated by associate lecturer Vicente Blasco)

1950–1980 (Instituto Valenciano de la Edificación 2011). Deficiencies in construction quality, lack of certain basic features, continued exposure of the envelope to meteorological phenomena and lack of adequate maintenance have meant that these buildings have suffered rapid and progressive aging, being susceptible to rehabilitation (Instituto Valenciano de la Edificación 2011; Gil et al. 2017). When considering the use of a roof garden in this field, its energy efficiency must be considered, as well as subordinated, regarding its economic and structural viability as a rehabilitation tool. The structures of old buildings are not calculated to withstand excessive loads, while an attempt will be made to minimize as much as possible the extra cost of installation that involves the construction of a green roof compared to a traditional one (without vegetation). It should be noted that, even though large thicknesses of the substrate make it possible to achieve adequate thermal transmittance (U) values for the roof, in accordance with the energy regulations in force, as can happen with semi-intensive or intensive roofs, it is recommended that never get by without the layer of thermal insulating material. The variation of the humidity of the substrate, the compaction or

Green Roof as a Sustainable and Energy …

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Fig. 3 Standard construction detail of a conventional intensive green roof (Elaborated by associate lecturer Vicente Blasco)

the development of the roots of the vegetation notably influence its thermal conductivity and facilitate the possibility of the appearance of thermal bridges, a fact for which the substrate is not considered an insulating material by itself (Cascone 2019). Research by Getter et al. (2009) revealed that the amount of moisture that a 4 cm substrate was capable of storing was much less than in 7 cm thicknesses, while the difference in moisture content between 7 and 10 cm thicknesses was practically nonexistent. Therefore, it is advisable, even essential, to always have a layer of insulating material that is chemically and physically compatible with its use on green roofs.

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Table 1 Basic characteristics of the different types of green roofs and traditional roof with gravel finish Own weight (kg/m2 )

Cost (e/m2 )

Type

Substrate thickness (cm)

Vegetation

Extensive

8–15

Succulent, 120–225 herbaceous perennial, evergreen

70–90

Semi-intensive

15–30

Herbaceous perennial, grasses, evergreen, scrubs

150–450

90–130

Intensive

30–100

Herbaceous perennial, grasses, evergreen, scrubs, shrubs, trees, palms

>650

>150

Traditional (gravel finish)

–

–

≈100

≈50

(Own elaboration with data from Ajuntament de Barcelona (2015) for extensive, semi-intensive and intensive roofs)

3 Thermal and Energy Benefit In green roofs, the main mechanisms that improve thermal behaviour compared to a traditional roof are Getter et al. (2009): • The shade provided by the vegetation layer. The solar radiation incident on the vegetation layer is reflected in a small proportion (Castleton et al. 2010), while plants absorb a large part of it, using it in photosynthetic and biological processes and in evapotranspiration mechanisms to regulate its surface temperature (Correa 2001). • Evapotranspiration. Combination of evaporation and transpiration in the vegetal layer and evaporation in the substrate, which allows to cool the roof surface, limiting both heat transmissions to lower layers and the urban heat island effect. • The inertia of the substrate, increasing the thermal mass of the roof as a whole and reducing the thermal fluxes through it. • The additional thermal insulation thanks to the substrate, which in turn increases the inertia.

3.1 Evapotranspiration In the case of vegetation, evapotranspiration involves three processes: the evaporation of water within the leaves, the diffusion of vapor from the surface of said leaves (transpiration) and the transport of heat from the surface of the leaves into the air (Santamouris 2014). The combination of these processes with the evaporation of

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the water from the substrate is what we here call evapotranspiration and allows the heat to be absorbed from the nearby environment, reducing the air temperature and thus reducing the positive and negative heat fluxes through the roof (green roofs as a passive cooler element) (Van der Meulen 2019). Those flows that go from the exterior to the interior of the house will be called positive and those that go from inside the house to the outside are negative. In summer, if the air temperature close to the envelope and surface temperature of the roof are lowered, the temperature gradient between the interior and exterior decreases and, therefore, also the heat fluxes. In this phenomenon, one of the most relevant factors is the amount of humidity. Bevilacqua et al. (2020), in their investigations in Cosenza (Italy), they found that, in the period from May to September, with higher humidity values, the heat fluxes in a traditional roof were always positive, while, with the installation of a green roof, even without an insulation layer, the flows were mostly negative, demonstrating the effective power of this type of roof as a passive cooler. Other investigations determine that the most influential factor in the evapotranspirative cooling rate is the properties of the vegetation, among them the LAI (Leaf Area Index) stands out. The peaks of heat loss due to evaporation fluctuate between 250–550 W/m2 for LAI indices between 2 and 7, respectively (Santamouris 2014). The morphology of the vegetation also greatly influences the loss of heat through evaporation. According to Correa’s studies (Correa 2001), extensive, short and wellwatered vegetation can dissipate by evapotranspiration around 3 kWh/m2 on a sunny day, which represents up to 80% of the total energy received.

3.2 Reduction of Heat Flows and Energy Consumption for Air Conditioning The solar radiation incident on the green roof is balanced by the flow of sensible (convection) and latent (evapotranspiration) heat, combined with the heat conduction that occurs within the substrate and the thermal radiation of the vegetable layersubstrate towards the exterior and the lower layers of the roof (Berardi et al. 2014). The substrate, thanks to its inertia, accumulates heat and delays the transmission of it to the interior (Berardi et al. 2014). In the vegetation layer, radiation is the main heat transmission factor, followed by evapotranspiration (Correa 2001). Usually, a green roof can reflect between 20 and 30% of the incident solar radiation, while the vegetal layer is capable of absorbing 60%, leaving a percentage less than 20% that reaches the substrate directly (Berardi et al. 2014). Data from the investigations of Eumorfopoulou and Aravantinos (1998) confirm these values, with 27% of the incident solar radiation reflected, 60% absorbed by the vegetation and the substrate and 13% transmitted to the lower layers of the roof. Finally, convective heat exchanges determine the microclimate around the vegetation: in general, the green roof gains heat by convection in winter and loses heat in summer, when the average air temperature is lower than the temperature of the leaves (Correa 2001).

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The combination of these characteristics of the vegetation and the substrate allows that the interior temperatures under roof have fewer annual variations. But they not only contribute to the decrease of the internal temperature (cushioning), but also to the delay (phase change) of the thermal wave. Scharf and Kraus (2019) analysed the indoor temperature under a traditional roof and two green roofs. Under the traditional roof, 27 °C was reached at 12:00 h, while in the two landscaped samples, the interior temperatures rose to 22 and 23 °C, reaching this maximum in the middle of the afternoon, with a lag of several hours. The thermal and energy contributions of the green roof are also influenced by the type of climate. In hot climates, the reduction of the interior temperature, the delay of the maximum daily temperature and the reduction of the energy consumption of air conditioning (mainly cooling) occurs mainly thanks to the filtration of solar radiation in the vegetal layer. Niachou et al. (2001) determined after their research in Greece that green roofs reduced the energy used for cooling systems by between 2 and 48%, depending on the area covered by vegetation. Del Barrio (1998) reached similar conclusions after his evaluation of the cooling potential of a green roof in Athens (Greece), clarifying that the green roof does not function as a passive cooling tool, as argued by other authors (Van der Meulen 2019; Bevilacqua et al. 2020), but as an element of isolation. The National Research Council of Canada (NRC) (Liu 2003) made comparisons of a green roof with a traditional one with a self-protected waterproof sheet finish on the Ottawa campus (Canada), verifying that, in warm months, the average daily energy demand was reduced in the spaces under the green roof, since the heat fluxes were reduced by approximately 75% compared to the traditional roof. In cold climates, the plant mass and the inertia of the substrate help mitigate the effects of cold inside the house. Research conducted by Gallardo et al. (2018) in Brazil, on the coldest day of winter, they showed a lag of 4 h between the minimum outside and inside temperatures, about 5 °C above. The thermal variation of the exterior was 17 °C, while in the model studying with a green roof the interior temperature variation remained around 6.5 °C. In this case, a possible negative factor of green roofs must be taken into account, since there is a danger that the outer surface will remain colder than with a traditional roof. In this case, the interior surface of the roof will also be colder and more heating energy will be needed for the interior to reach the comfort temperature. Sailor’s research (Sailor 2008) concluded that increasing the vegetation layer reduced the energy demand for cooling in summer, but increased the energy demand for heating in winter, because of shade. If a good design is carried out, the thermal mass and the improvement in the inertia allow the absorption of the heat produced inside, radiating it later to heat the interior, functioning as a heat store in cold climates (Jim 2017).

3.2.1

Energy Contribution in the Field of Rehabilitation

The contribution of the green roof to the reduction of the variation of the interior temperature and the reduction of the energy consumption of the air conditioning

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systems also depends, and to a large extent, on the construction of the building itself. Heat losses through roofs can represent 70% of the total energy lost by a building envelope (Shao et al. 2018), but if it is well insulated, losses are lower. In these cases, the energy savings and the improved comfort of the interior is achieved by the construction of the building itself, not by the contributions of a possible green roof. For example, the potential savings thanks to the installation of a green roof, with respect to energy for heating, is 45% in buildings without insulation in their envelope and 13% in buildings with moderate insulation (Castleton et al. 2010). That is why the use of green roofs is recommended in the rehabilitation of buildings with poor thermal and insulation conditions in the envelope. Several studies confirm the relevant role of green roofs in the field of rehabilitation, as for example in the thermal simulations of Niachou et al. (2001) using the TRNSYS program. Three green roofs were modelled in Athens (Greece) with different levels of insulation in the envelope: for the version with better insulation, the green roof implied energy savings of less than 2%, while in the option with less insulation, the green roof could achieve substantial savings. Wong et al. (2003) carried out simulations for a building in Singapore, showing that on a roof with a thermal transmittance value (U) of 0.51 W/m2 K (that is, with insulation and good thermal resistance), an extensive garden system only reduced the annual cooling energy consumption by 0.6% (compared to traditional roof with the same U value). While, in the version without insulation, this same green roof system could produce an energy saving for annual cooling of 10.5% (compared to the traditional non-insulated roof). Scharf and Kraus (2019) reached similar conclusions when they observed that the heat flux on a typical summer day was 350 W/m2 in a traditional roof without insulation, while with the installation of an extensive green roof the values were reduced at 100 W/m2 and 150 W/m2 in the two studied landscaped models. Santamouris et al. (2007) carried out simulations on a roof in Athens (Greece) in which they obtained cooling energy savings between 15 and 49% for the building without insulation, while if the envelope was insulated, the savings values fell between 6 and 33%. Jaffal et al. (2012) also studied and corroborated this behaviour. In a previously uninsulated roof, the installation of a green roof reduced the average and maximum indoor air temperature by 6.5 and 9.3 °C, respectively, while the savings in the energy demand for air conditioning was 50%. When studying the installation of the same green roof on a previous roof with 30 cm of insulation, the reduction in temperature was less than 1 °C and the reduction in energy demand was only 3%.

3.3 Reduction of Surface Temperatures The existence of vegetation as roof finish makes it possible to minimize the temperatures on the substrate surface during the day. The vegetal layer prevents the direct incidence of solar radiation on the substrate, both due to reflection and absorption by the leaves (Correa 2001). According to the investigations of Jaffal et al. (2012) the temperature of the foliage was 13.2 °C higher than the temperature of the substrate

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on the hottest day of the year, thanks to the phenomenon of absorption by the vegetation. In terms of incident solar radiation, Fioretti et al. (2010), in their research on a green roof in Ancona (Italy), determined that the peak of incident solar radiation under the vegetation was reduced, in significant days of study, between 51.03 and 89.27% with respect to incident solar radiation on the surface of a traditional roof. In terms of temperature, they also concluded that, in this case, in a study carried out in Marche (Italy), the surface of a traditional roof reached up to 60 °C, with large daily temperature fluctuations, while in the green roof the temperatures were more stable throughout the day and the maximums remained below 30 °C. Niachou et al. (2001) used infrared thermography (IRT) to determine surface temperatures on a green roof near Athens (Greece), obtaining surface temperatures of 26–29 °C in places on the roof dominated by dark and thick vegetation, while, in the case of the traditional roof, the surface temperatures varied between 42 and 48 °C, so the reduction thanks to the vegetal finish was approximately 10 °C. This effect could be considered negative in cold climates or seasons, but the foliage of the vegetal layer can also function as an insulating element and limit the transfer of heat between the roof and the exterior. Jaffal et al. (2012) also studied this phenomenon, obtaining a surface temperature of the substrate, in the cold season, 5.6 °C above the air temperature. The temperature of the foliage in the cold season was 4.9 °C lower than the surface temperature of the substrate, contrary to what has been said to occur in the warm season. Regarding the reduction of surface temperatures, it is also of relative importance the reduction of temperatures and thermal fluctuations on the waterproof sheet, thus increasing its durability by subjecting it to less thermal stress. Liu (2003) demonstrated that in a cover with 15 cm of substrate thickness, the temperature in the waterproof sheet under it reached 30 °C, compared to the 70 °C that it reached in the traditional reference roof, while temperature fluctuations were 5–7 °C on the green roof and 42–47 °C on the traditional roof. Jaffal et al. (2012) measured the temperature variation on the surface of the roof structure, reaching −6 °C in winter and 58 °C in summer in the case of traditional roofing, while in a green roof the values were reduced to −4 °C in winter and 20 °C in summer.

3.4 Reduction of Energy Consumption Associated with Materials The reduction of energy consumption in buildings can not only be achieved through less use or less load on air conditioning equipment, but energy reduction in the construction phase should also be studied, trying to minimize the energy related to the execution and transportation of construction materials (Shao et al. 2018). The energy consumption associated with the extraction, processing, preparation and transport of materials is known as embodied energy (see Fig. 4) (Ching and Shapiro 2015; European Commission 2020).

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Fig. 4 Embodied energy of construction materials (Own elaboration modified from Ching and Shapiro 2015)

In the field of green roofs, most of the layers are made with polymers, whose configuration process generates high pollution (Shafique et al. 2018), although different studies show that air pollution due to the production processes of these polymers is compensated with the ecological behaviour of the green roof in about 13 years (Bianchini and Hewage 2012), but even so it is necessary to try to reduce this negative environmental impact. Several investigations have been carried out aimed at the use of more sustainable materials, as is the case of the studies by Pérez et al. (2012) on the use of rubber crumbs used as a drainage layer for green roofs. They concluded that a large amount of energy can be saved, since other materials, such as expanded clay, require a lot of energy for the transformation processes of the raw material, apart from the rubber crumbs giving a new use to the wheels of vehicle. They verified that its draining capacity, although it depends on the size of the crumbs, does not present significant differences in terms of hydraulic conductivity, water retention capacity or vegetation development. Regarding the substrate, the use of waste materials in construction as inorganic components (such as broken bricks) is recommended, reducing the cost of installation and the embodied energy of the green roof (Van der Meulen 2019).

4 Conclusions The green roofs are proposed as a response to different objectives of today’s society, in its intention to be more sustainable and socially, economically and environmentally balanced. It is a construction tool that makes it possible to improve the urban environment in which the day-to-day life of a large part of humanity develops. Not only are the environmental benefits of its implementation important, naturalizing disused spaces in a crowded city with little space at ground level to reinvent itself from a sustainable point of view. The thermal and energy benefits are also of great relevance, as is its ability to be used as a rehabilitation tool, providing new uses to neglected and aging buildings. The green roofs are configured as a multilayer system composed of a series of characteristic elements that aim to favour the growth and development of vegetation: anti roots layer, drainage layer, filter layer, substrate and vegetation. Depending on

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the thickness of the substrate, they can be classified into extensive, semi-intensive and intensive, involving certain costs or weights depending on each type. The thermal and energetic benefits that the green roofs provide are mainly due to the incident solar radiation on the roof is reflected in values between 20% and 30%, 60% is absorbed by the vegetal layer and less than 20% reaches to be transmitted to the lower layers. Of the part of radiation absorbed, both the vegetation and the substrate release a large part to the environment through the phenomenon of evapotranspiration, being able to dissipate until 80% of this received energy, depending on the state of the vegetation or the amount of moisture in the substrate. One of the main characteristics of green roofs is their ability to reduce heat flux (both positive and negative) and energy consumption for air conditioning. This reduction is influenced by factors such as the climate or the previous insulation of the building envelope. But the green roofs are not only capable of reducing the temperature under the roof, making the space more comfortable or involving less energy consumption to reach the level of comfort through mechanical systems, but they also delay the peak of temperatures. This decrease in temperatures is also perceived in the different layers of the system, being especially relevant on the waterproof sheet, whose useful life can be significantly prolonged as it is subjected to less thermal stress. The contribution of a green roof to a better thermal and energy performance of the building will depend, mainly, on the state of its envelope, being able to reach energy savings in cooling of 49% in buildings without previous insulation, while these values are only 6% in the case that the roof structure is already isolated. The use of the green roof in the rehabilitation allows to act on the existing construction elements and introduce passive energy saving measures in buildings that, otherwise, would be very unsustainable and, if it were not for the rehabilitation works, would be in disuse. For this, it is vitally important to consider not only the thermal and energetic characteristics of the green roofs, but also issues such as their cost and weight, since the rehabilitation poses more restrictions in these two fields than the new construction. Therefore, within the types of green roofs it is necessary to reach a balance between thermal and energy benefits, cost and the system’s own weight. Furthermore, it should not be forgotten that the energy consumption of buildings also considers the embodied energy of the materials used during construction. In this regard, it is necessary that the materials used in the green roofs be studied in greater detail to make this construction solution a true sustainable tool. Acknowledgements The authors thank associate lecturer Vicente Blasco for the magnificent drawings made for this work.

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Seismic Analysis and Retrofitting by C-FRP of Reinforced Concrete Bell Towers Within Masonry Churches: A Case Study Antonio Formisano and Antonio Davino

Abstract Bell towers are slender structures of variable dimensions that are highly subjected to seismic damage due to their structural characteristics. The seismic response of bell towers and the design of potential retrofit interventions depend on their configuration, either isolated or connected to other constructions making part of ecclesiastic complexes. The different seismic behavior of bell towers depending or less from the interaction with other structures is evaluated in the current work, which analyses a case study of a RC tower inserted within a masonry church placed in the municipality of Torre del Greco, in the district of Naples (Italy). Three different macro-element models of the RC bell tower developed with the 3MURI software are considered: the tower alone, the tower together with the masonry structure just below its vertical projection and the tower including the whole volume of the church. Whereas the isolated model overestimates the bell tower seismic capacity, modelling of other structural part allows to obtain more reliable prediction of the real behavior of the tower. Based on the achieved seismic response, a suitable retrofit intervention with C-FRP fibers is planned for seismic upgrading of the tower through improvement of the performance of beams and columns under bending moment, shear and axial loads. The effectiveness of retrofit interventions is performed both locally, by performing the verification of structural sections, and globally, by analyzing the seismic behavior of the entire ecclesiastic complex. Keywords Bell tower · Seismic response · 3MURI software · Retrofit interventions · C-FRP fibers

1 Introduction Towers are constructions characterized by a prevalent vertical development in proportion to their base. Already during the Roman empire, towers were built as strategic observation points, often connected to the city walls and fortifications (Von A. Formisano (B) · A. Davino Department of Structure for Engineering and Architecture, School of Polytechnic and Basic Sciences, University of Naples, Federico II, P.Le V. Tecchio, 80125 Naples, Italy e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Switzerland AG 2021 J. M. P. Q. Delgado (ed.), Case Studies of Building Rehabilitation and Design, Building Pathology and Rehabilitation 19, https://doi.org/10.1007/978-3-030-71237-2_3

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Petrikovits 1971). The most common towers had square or rectangular plan shapes, even if there were examples of polygonal-based towers. Some great examples of such ancient constructions are the Aurelian Walls in Rome or the Nuraghi towers of the Bronze Age in Sardinia. The period of greatest diffusion was certainly the Middle Ages, in which towers were constructed with circular shapes (Priester 1993). Among the different typologies, bell towers are referred-to as tower-shaped buildings, usually adjacent to churches, which represent the architectural structure intended to support the bells. From the historical point of view, the bell tower and the annexed bells can be traced back to the Christian religion and are mainly characterized by their development in height. This need arose during the first centuries of worship freedom to attract the believers through a strong sound. It became clear that the taller the emission height of the sound waves, the more the acoustic message propagates, making itself clear and intelligible even from miles away (Cuzzoni 2016). In the 19th century, in line with the eclecticism, campaniles appeared also in connection to country houses, markets, sometimes as clock towers (Lionello 2011). In larger cities, even the city hall had elevated structures, called Civic Towers. They had the same architectural characteristics as the bell towers, but with more functional variants. The bells were intended for “civil communications”, whose specific signals were in use until the mid-XX century to mark activities, to call for a meeting, to alert in case of calamity or danger and so on. Nowadays, the bell tower represents a community in its history, not only religious, but also secular: where there is a bell tower there is a community, a town, a city, a historical and artistic identity made up of architectural works, artistic works, oral and written histories, folklore traditions, rites, crafts, languages and dialects. Towers and bell towers are constructions with high seismic vulnerability due to their structural morphology (Doglioni et al. 1994; Tuti et al. 2012). On the Italian territory, which is characterized by high seismic hazard, several churches and belfries were struck during earthquakes. The most recent seismic events occurred in EmiliaRomagna (2012) and in Central Italy (2016) (Clementi et al. 2017; Milani 2013). Although collapses were often justified by extraordinary events, in old masonry towers dangers can also arise as a consequence of daily use, either due to the progressive deterioration of particular structural elements or to the gradual deterioration of the material properties. Therefore, most of the research efforts in this field are currently focused on integrated vulnerability assessment methods of the tower (Sepe et al. 2008), non-destructive health monitoring techniques (Gentile and Saisi 2007) and suitable intervention solutions for structural repairing and strengthening (Modena et al. 2002). Although they were built according to different morphologies and technologies, bell towers can be grouped according to the architecture layout into isolated structures or aggregate ones, the latter when a bell tower is either set against one or more buildings or superimposed on worship buildings (Dolce 1991). This first classification is of fundamental importance because the configuration change alters the rigidity of the structural complex. Different ratios between stiffness and mass result in different vibration periods, which leads the seismic demand to be reduced or increased (Paz and Kim 2019).

Seismic Analysis and Retrofitting by C-FRP of Reinforced …

31

There is an extensive literature on the behavior of masonry bell towers, including experimental and numerical analyses (Acito et al. 2014; Ferrante et al. 2019; Valente and Milani 2016). Less studies concern masonry−RC composite structures. This work aims at modelling a RC bell tower built over a masonry church employing three different configurations. The first model was built neglecting the underlying wall complex. The second examines the bell tower and the wall cell inherent its vertical projection only. The third and last configuration includes the masonry church which is part of the “Maria SS. del Buonconsiglio” sanctuary complex. The comparison among the three investigated hypotheses highlights how important is to model additional structures around the tower for accurately predicting its seismic behavior. As a matter of fact, the first model excessively overestimates the seismic capacity, which is instead underestimated in the second model. In conclusion, it is believed that the third schematization optimally synthesizes the real behavior of the bell tower under earthquake. The software employed for the analysis was 3MURI (Galasco et al. 2002; STADATA 2016), which is mainly used for masonry structures. This choice was dictated by the presence of the masonry church, despite the bell tower is made of reinforced concrete. The non-linear static analyses highlighted seismic deficiencies of the bell tower, which led to the hypothesis of retrofit with C-FRP carbon fibers. The choice of this material relies on the fact that, since the typical useful life of these structures is longer than that of ordinary buildings, it can provide a durability greater than the most common repairing materials one (Cosenza and Iervolino 2007). The planned interventions foresaw the improvement of the performance of beams and columns under bending moment, shear and axial load. In addition, unidirectional carbon flakes were added on the sides of the columns that are not accessible due to the presence of beams or floors (Mazzolani et al. 2004). Finally, the flakes were also inserted in the L-shaped partitions to ensure a continuous and effective shear and confinement reinforcement. The performed post-retrofit analysis entailed both local verifications of single sections and global evaluation of the whole structural complex, which showed as the hypothesized reinforcement system is configured as a seismic upgrading intervention.

2 Case Study The case study of this paper consists of the bell tower of the “Maria SS. del Buonconsiglio” sanctuary, located in Torre del Greco, in the outskirts of Naples. The construction consists of a large and articulated building complex, which includes the church and the diocese’s lodgings. The expansion was completed only in 1926 to accommodate the numerous pilgrims and the adjoining orphanage. In 1943, during the Second World War, the complex suffered extensive damage. Therefore, it experienced an extensive reconstruction intervention, which was completed in 1954. The bell tower is located over the masonry church at an elevation of 16.98 m and extends up to 28.85 m, for a total height of 11.87 m (Fig. 1). It is characterized by a

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A. Formisano and A. Davino

Fig. 1 A picture of the RC bell tower under study

square plan of about 4.10 meters and it is placed in a lateral position with respect to the skylight overlooking the apse. The vertical bearing structure of the church is made up of tuff blocks with isodomic texture, typical of buildings of the metropolitan area of Naples. On the covering terrace, at 16.98 m, there is a base with height of about 0.9 meters above which the vertical structure of the bell tower raises. This load bearing structure is made of with reinforced concrete pylons, which were reinforced at the beginning of the 80 s of the last century with a confinement system made of either steel angles and plates or reinforced concrete plaster (Calderón et al. 2009). The structure currently shows signs of deterioration, namely concrete cover spalling and corrosion of the reinforcement and metal profiles used for confinement, affecting both the original structure and the recent reinforcement intervention. The causes are ascribable to both the material degradation caused by the marine environment and the vibrations induced by the bells’ movements, as the latter can be a fundamental cause of tower vibrations and instability (Ivorra et al. 2019). The horizontal structures of the bell tower, placed at three different levels, consists of steel I-beams incorporated in a solid RC slab. These structures support the weight of the bells and related metal support structures. The rooms of the masonry sanctuary underneath the tower projection are covered by composite steel-masonry tiles floors.

Seismic Analysis and Retrofitting by C-FRP of Reinforced …

33

Table 1 Mechanical characteristics of existing materials obtained from in situ analyses Material

E [N/mm2 ]

G [N/mm2 ]

fm [N/mm2 ]

γ [KN/m3 ]

τ [N/cm2 ]

Concrete

27984

11660

22,3

22

–

Steel

206000

79231

450

79

–

Tuff stone masonry

1135

454

1,94

15

3,5

The decay state of the structure, as well as the mechanical characteristics of masonry walls and RC pylons, are evaluated from visual inspections and on-site tests and laboratory analysis on the collected material samples (UNI 2010). Such analyses allow to reach the LC2 knowledge level in accordance with the current Italian technical regulation (Ministry of Infrastructure and Transport 2018b), which corresponds to a confidence factor FC = 1.2. Table 1 summarizes the mechanical characteristics of the existing materials. The values of the partial safety factor γM are based on the material type: 3 for masonry, 1.5 for concrete and 1.15 for steel (Ministry of Infrastructure and Transport 2018a).

2.1 Load Analysis The vertical loads are represented by the weight of the RC structures (γ = 25 kN/m3 ) and the relative slabs. The latter have a 18 cm-thickness and are made of steel I-beams and concrete filling. The corresponding permanent load Gk reaches approximately the value of 5.00 kN/m2 . The floors bear the weight of the bells and the structures designed to support them. The following loads were considered: • First floor = 1 bell of about 320 kg; • Second floor = 2 bells of about 170 kg and 130 kg (total: approx. 300 kg); • Third floor = 4 bells of about 80 kg, 75 kg, 60 kg and 45 kg (total: approx. 260 kg). Although the bell tower floors are not open to the public, an accidental load Qk = 2.00 kN/m2 was assumed for precautionary purposes. On the bell tower reinforced concrete roof there is a crucifix placed in the middle over a column. For modelling purposes, the weight was simulated as a concentrated load of 2 kN at the floor gravity center. The protected railing on the last floor is represented as a linear load equal to 0.5 kN/m applied on the perimeter. The seismic evaluation is based on the elastic response spectra, which depend on the location and the building typology. Because of the ordinary destination use and according to the NTC 2018 Italian code, the building is considered as a type 2 construction with nominal life VN ≥ 50 years and use destination II, which implies a coefficient Cu = 1. Therefore, the seismic action reference period can be calculated as:

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A. Formisano and A. Davino

VR = VN ∗ CU = 50years Depending on the local seismic parameters specific for the site of Torre del Greco, the response spectra for the Operational (OP), Immediate Occupancy (IO), Life Safety (LS), and Collapse Prevention (CP) limit states are considered for seismic analysis.

3 Numerical Modelling The structural analysis is conducted through the version 12.2.1.9 of the 3MURI software, which performs non-linear static and modal dynamic analyses of new and existing structures according to Eurocodes and the current Italian technical code NTC 2018. This program is based on an innovative computational procedure, the so-called “Frame by Macro Element” (FME) method, which is able to schematize masonry buildings with structural macro-elements (Penna et al. 2004). The modelling phase is done by inserting walls discretized into macro-elements representative of masonry piers and deformable spandrels. The structural parts connecting piers and spandrels are called nodal panels, which are usually less susceptible at seismic damage. Theoretical and experimental researches have confirmed that piers and spandrels can be represented with linear elements, although the use of shell elements could be considered as a better choice. Connecting these elements results in a framed scheme, referred-to as equivalent frame (Di Tommaso and Casacci 2013). The linear elements are schematized by means of “sandwich” finite elements, that have a non-linear behavior. The choice of a specialized software for masonry elements is given by the need to model the masonry structure below the RC bell tower. In this specific case, the bell tower RC pylons are modelled over the masonry structure as walls with perforations to simulate the presence of the real openings. Three different schematization models of the tower are used to evaluate its most reliable seismic behavior. The bell tower is supported by the base, which, in turn, rests on the underlying masonry structure. The latter is aligned with three out of four sides of the bell tower in horizontal projection, as one of the walls is set back by about 1 m (Fig. 2).

3.1 First Model The first implemented model represents the RC structure of the bell tower only, which is hypothesized as directly fixed to the ground (Fig. 3), even if it is located 17 m over the ground level. The vertical structures are made of RC pylons, which are prolonged by a height of one meter with respect to the basement level. In situ inspections have revealed

Seismic Analysis and Retrofitting by C-FRP of Reinforced …

Fig. 2 Transversal section of the bell tower above the masonry sanctuary Fig. 3 First investigated model of the RC bell tower

35

36

A. Formisano and A. Davino

that the basement level is made of a RC slab as a supporting structure of the bell, which is separated through an air chamber from the composite steel-hollow tile floor representing the roof of the sanctuary room below the tower. The vibration modes resulting from the modal analysis are characterized by t = 0.236 s in Y-direction (participating mass: 67.30%) and t = 0.233 s in X-direction (participating mass: 63.75%). The non-linear static analysis (pushover) was performed considering two distributions of forces (uniform and proportional to the first vibration mode), 24 load combinations and the mean displacements of the top story (roof of the bell tower). The results of the pushover (Table 2) have provided the seismic risk coefficients αi, which represent the ratios between PGA in terms of capacity and demand for ultimate (LS and CP) and serviceability (IO and OP) limit states. In this specific case, since all values are greater than 1, the bell tower is verified against seismic actions. Table 2 Output of the first 3D model: pushover analyses in the main directions of the bell tower Eccentricity [cm]

α CP

α LS

α OP

α IO

N.

Dir. seism

Seismic load

1

+X

Uniform

0.00

2.040

2.042

2.072

1.976

2

+X

Modal distribution

0.00

1.477

1.479

1.517

1.418

3

−X

Uniform

0.00

2.491

2.494

1.845

1.692

4

−X

Modal distribution

0.00

2.310

2.313

1.325

1.238

5

+Y

Uniform

0.00

1.935

1.923

1.837

1.754

6

+Y

Modal distribution

0.00

1.571

1.573

1.331

1.214

7

−Y

Uniform

0.00

2.177

2.179

1.684

1.608

8

−Y

Modal distribution

0.00

1.654

1.656

1.203

1.175 1.994

9

+X

Uniform

17.38

1.877

1.879

2.175

10

+X

Uniform

−17.38

1.751

1.753

1.971

1.842

11

+X

Modal distribution

17.38

1.744

1.746

1.573

1.503

12

+X

Modal distribution

−17.38

1.351

1.352

1.455

1.327

13

−X

Uniform

17.38

2.529

2.532

1.761

1.682

14

−X

Uniform

−17.38

2.377

2.380

1.659

1.551

15

−X

Modal distribution

17.38

2.529

2.532

1.325

1.266

16

−X

Modal distribution

−17.38

1.930

1.932

1.242

1.133

17

+Y

Uniform

17.42

1.804

1.804

1.755

1.640

18

+Y

Uniform

−17.42

1.920

1.898

1.922

1.762

19

+Y

Modal distribution

17.42

1.472

1.474

1.269

1.213

20

+Y

Modal distribution

−17.42

1.630

1.632

1.385

1.295

21

−Y

Uniform

17.42

2.047

2.049

1.622

1.516

22

−Y

Uniform

−17.42

2.209

2.211

1.642

1.568

23

−Y

Modal distribution

17.42

1.592

1.593

1.162

1.110

24

−Y

Modal distribution

−17.42

1.884

1.886

1.257

1.175

Seismic Analysis and Retrofitting by C-FRP of Reinforced …

37

This indicates that the bell tower would not require any intervention. This outcome, however, neglects the dynamic amplification factors of horizontal forces which occur when a structure is placed above the ground level.

3.2 Second Model The second model was carried out by considering both the RC bell tower and the underlying masonry structure (Fig. 4). The vibration modes resulting from the modal analysis are characterized by t = 1.596 s in X-direction (participant mass: 65.46%) and t = 1.106 s in Y-direction (participant mass: 59.55%). By comparing the linear dynamic analysis results obtained for the first two models, a considerable increase in the vibration periods is evidenced for the second hypothesis. The non-linear static (pushover) analyses were conducted with the same input parameters employed for the previous model. This numerical modelling returns values of α < 1 for almost all tests and different limit states (Table 3). The pushover curves were interrupted for most of the load combinations due to breaking of the walls belonging to the cell below the tower. Figure 5 shows the deformed shapes of the tower in the load combinations n.15 and n.19, which are the most burdensome analysis cases, respectively, in X- and Y-directions. Fig. 4 Second model including a wall cell below the RC bell tower

38

A. Formisano and A. Davino

Table 3 Output of the second 3D model: pushover analyses in the main directions of the bell tower N.

Dir. seism

Seismic load

α CP

α LS

α OP

α IO

1

+X

Uniform

0

0.436

0.437

0.664

0.507

2

+X

Modal distribution

0

0.377

0.378

0.487

0.399

3

−X

Uniform

0

0.402

0.402

1.102

1.235

4

−X

Modal distribution

0

0.354

0.354

0.945

0.974

5

+Y

Uniform

0

1.062

1.063

1.377

1.034

6

+Y

Modal distribution

0

0.797

0.798

0.788

0.73

7

−Y

Uniform

0

0.963

0.965

1.89

1.933

8

−Y

Modal distribution

0

0.818

0.819

1.143

1.227

9

+X

Uniform

26.08

0.435

0.436

0.618

0.506

10

+X

Uniform

−26.08

0.438

0.438

0.666

0.509

11

+X

Modal distribution

26.08

0.368

0.368

0.485

0.397

12

+X

Modal distribution

−26.08

0.387

0.388

0.523

0.4

13

−X

Uniform

26.08

0.402

0.403

1.104

1.168

14

−X

Uniform

−26.08

0.393

0.393

1.11

1.244

15

−X

Modal distribution

26.08

0.352

0.352

0.901

0.914

16

-X

Modal distribution

−26.08

0.354

0.355

0.945

0.974

17

+Y

Uniform

16.55

1.024

1.025

1.37

1.03

18

+Y

Uniform

−16.55

1.083

1.085

1.317

1.132

19

+Y

Modal distribution

16.55

0.741

0.742

0.79

0.732

20

+Y

Modal distribution

−16.55

0.831

0.832

0.786

0.729

21

−Y

Uniform

16.55

0.913

0.914

1.892

1.935

22

−Y

Uniform

−16.55

1.015

1.016

1.895

2.035

23

−Y

Modal distribution

16.55

0.784

0.785

1.145

1.23

24

−Y

Modal distribution

−16.55

0.887

0.888

1.139

1.223

Eccentricity [cm]

The extremely high values of the vibration periods and the breakage of masonry walls, that have anticipated the collapse of the RC structure, have required the development of a third model. The aim is to consider both the actual height of the tower and the contribution of a large part of the sanctuary structure on its seismic behavior, which allow to contemplate the amplifying effects of the seismic forces deriving from the real configuration of the religious structure found on-site.

3.3 Third Model The third model includes the structures examined in the second model together with a large number of church rooms all around the tower. It is fundamental to specify that this model is simplified, since it considers only the volume of the basilica that affects

Seismic Analysis and Retrofitting by C-FRP of Reinforced …

39

Fig. 5 Pushover analyses on the second model. Damage distribution for the most demanding combinations: n.15, modal distribution in X-direction (a) and n.19, modal distribution in Y-direction (b)

the behavior of the bell tower. Figure 6 shows the 3D-model of the structure used for seismic evaluation. The analyses have revealed that, compared to the previous cases, the church complex modelled represents a clear constraint at the base of the bell tower, that modify its modal frequencies. The vibration modes derived from the modal analysis (Table 4), are characterized by t = 0.320 s and t = 0.237 s in X-direction (participant mass: 46.69% and 26.48%, respectively) and t = 0.780 s in Y-direction (participant mass: 69.37%). The pushover analyses are not satisfied in 22 out of 24 cases for the LS in both analysis directions and are not satisfied in a smaller number of cases for OP and IO limit states. The pushover analyses displaying the lowest risk indicator in X- and Y-direction are n. 15 and n. 20, which present, respectively, a LS risk indicator equal to 0.13 and

40

A. Formisano and A. Davino

Fig. 6 Third investigated model (reference model)

0.36. Therefore, an intervention for seismic upgrading was designed to increase the safety level of the bell tower under earthquake. The results of such analyses both in terms of pushover curve and collapse mechanisms, are shown in Figs. 7 and 8, respectively, with respect to X- and Y-directions. As shown in Figs. 7 and 8, some shear (orange elements) and compressive-bending (red elements) collapse phenomena have occurred in the pylons, so to require proper retrofit interventions.

3.4 Comparison of Results The results obtained by the three models in terms of vibration periods and seismic risk indicators are summarized in the following diagrams (Figs. 9 and 10). The graphs show that the first model has risk indices greater than unity, which indicate that no intervention is required. Instead, the values of the risk indicators of the second model are lower than unity. These values are still considered as unrealistic, as this model is unable to correctly estimate the vibration periods. In this second step, in fact, the vibration period is particularly increased due to the extreme slenderness of tower, as the full height is considered, thereby neglecting the neighboring structures. This would imply that the structure is subject to lower seismic actions. Even if the vibration periods of the first and third model differ, they lead to the same seismic stress on the structure. This is explained by the fact that in both cases the periods fall in the plateau of the response spectrum.

Seismic Analysis and Retrofitting by C-FRP of Reinforced …

41

Table 4 Output of the third 3D model: pushover analysis in the main directions of the bell tower N.

Dir. seism

Seismic load

α CP

α LS

α OP

α IO

1

+X

Uniform

0.00

0.655

0.719

2.061

2.333

2

+X

Modal distribution

0.00

0.150

0.154

0.572

0.781

3

−X

Uniform

0.00

0.784

0.850

2.321

2.538

4

−X

Modal distribution

0.00

0.143

0.147

0.545

0.741

5

+Y

Uniform

0.00

1.373

1.459

3.146

3.319

6

+Y

Modal distribution

0.00

0.494

0.483

1.109

1.050

7

−Y

Uniform

0.00

0.857

0.943

2.417

3.245

8

−Y

Modal distribution

0.00

0.827

0.809

1.268

1.140

9

+X

Uniform

121.07

0.840

0.906

2.268

2.587

10

+X

Uniform

−121.07

0.652

0.711

2.151

2.426

11

+X

Modal distribution

121.07

0.335

0.328

0.341

0.454

12

+X

Modal distribution

−121.07

0.290

0.283

0.666

0.664

13

−X

Uniform

121.07

0.828

0.895

2.258

2.669

14

−X

Uniform

−121.07

0.731

0.792

2.070

2.574

15

−X

Modal distribution

121.07

0.126

0.130

0.479

0.650

16

−X

Modal distribution

−121.07

0.390

0.382

0.630

0.862

17

+Y

Uniform

93.55

1.382

1.465

2.286

3.068

18

+Y

Uniform

−93.55

0.000

0.000

0.000

0.000

19

+Y

Modal distribution

93.55

0.465

0.455

0.808

1.109

20

+Y

Modal distribution

−93.55

0.372

0.364

0.868

0.928

21

−Y

Uniform

93.55

0.800

0.884

2.498

3.100

22

−Y

Uniform

−93.55

0.855

0.940

2.465

3.087

23

−Y

Modal distribution

93.55

0.603

0.617

1.128

1.109

24

−Y

Modal distribution

−93.55

0.678

0.689

1.261

1.250

Eccentricity [cm]

4 Local Analyses Based on the results of the global non-linear analyses, it was possible to determine the maximum stresses acting on structural sections for the design of their reinforcement interventions. In order to identify the most suitable intervention, the different structural components were classified according to their respective geometry and altimetric location (Figs. 11 and 12). Ground floor, first floor, second floor and roof were considered as bell tower levels. As regards the first two levels, two sections (corner and central) of vertical pylons were identified. For the third level the single central opening is replaced by two lateral openings. A similar approach was applied to the beams overlying the openings: first floor, second floor and roofing beams were defined. Finally, it should be noted that a perimeter curb beam is present only at the roof level.

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A. Formisano and A. Davino

Fig. 7 Results of the most demanding ante-operam combination (n.15) in X-direction

The details of the sections, including the longitudinal and transversal reinforcements derived from the experimental investigations, are shown in Fig. 13. Top (T), Bottom (B) and Lateral (L) indicate upper, lower and lateral reinforcements, respectively. The indicated geometries are representative of the bell tower sections, geometrically regularized without the previous jacketing interventions for safety reasons.

Seismic Analysis and Retrofitting by C-FRP of Reinforced …

43

T [s]

Fig. 8 Results of the most demanding ante-operam combination (n.15) in Y-direction

1.8 1.6 1.4 1.2 1 0.8 0.6 0.4 0.2 0

1.596 1.106 0.78

X Y

0.32

0.233 0.236

First model

Second model

Third model

Fig. 9 Histogram comparing the vibration modes of the three models

44

A. Formisano and A. Davino 1.6 1.4

1.35

1.47

1.2

α [-]

1 0.74

0.8 0.6

X (LS) 0.36

0.35

0.4

0.13

0.2 0 First model

Second model

Third model

Fig. 10 Histogram comparing the risk indicators derived from pushover analyses on the three models

4.1 Acting Stresses and Local Checks For each investigated pylon and level, the greatest acting stresses were sought among those highlighted from the non-linear static analyses (n. 15 and n. 20). The employed stress and the consequent reinforcement intervention with C-FRP are summarized in Table 5. To evaluate stresses in the beams, a linear static analysis was conducted on a 2D model of the bell tower performed with the SAP2000 version 20.0.0 software. This was required since the 3MURI software considered beams as pendulums without resistance to bending moment. Table 6 summarizes the maximum stresses acting in the beams. The local verifications of the sections, considering the “L” -shaped corner pylon divided into two rectangles, are depicted in Table 7. In this table the index α < 1 (α = capacity-to-demand ratio) demonstrates that all the beams and only the CoPyGr pylon need retrofit interventions.

5 Seismic Retrofitting The results of the analyses highlighted structural deficiencies in X- and in Ydirections. To improve the seismic behavior, an appropriate intervention was designed. The latter involves a preliminary removal of the old interventions and consequent reinforcement of the RC elements with C-FRP (National Research Council 2004, 2007, 2013). The fibers, arranged in the longitudinal direction of the elements, compensate for their seismic deficiencies under compression-bending stresses. On the other hand, the “U” or winding fibers, applied where possible, improve the shear resistance of the section. The interventions were designed using products whose physical-geometric and mechanical characteristics are specified in Table 8.

Seismic Analysis and Retrofitting by C-FRP of Reinforced …

Fig. 11 Plan of the different levels with the most indicative sections

45

46

A. Formisano and A. Davino

Fig. 12 Transversal sections with most indicative sections

Tables 9 and 10 illustrate the geometric characteristics of the interventions with CFRP materials. It should be noted that an extension of reinforcement is also foreseen for the seven pylons that verified the pre-intervention checks. The aim is to avoid stiffness gaps between the different levels of the bell tower, which could give rise to dangerous soft-story mechanisms. In Table 11 an overview of the checks on the sections after retrofit intervention s is shown. In order to confirm the effectiveness of local reinforcement interventions on the individual sections, global checks on the model of the sanctuary-tower aggregate following the retrofit operations were carried out (Table 12). The pushover curves related to the most severe seismic checks (n.16 in X-direction and n.8 in Y-direction) are illustrated in Figs. 14 and 15. The verifications of the non-linear static analysis were all satisfied (except than n.16) at the IO and OP limit states. Contrary, about 50% of checks were not satisfied at the LS limit state. Therefore, the complete seismic retrofit of the bell tower was not attained. However, the obtained safety level (0.603 in X-direction and 0.601 in Ydirection) significantly improves the seismic behavior of the structure, which showed

Seismic Analysis and Retrofitting by C-FRP of Reinforced …

47

Fig. 13 Sections details Table 5 Overview of the main stresses acting on pylons Element Mxmax Ncorresponding Mymax Ncorresponding Nmax Mx,corr My,corr Vmax CoPyGr 88.2

−130

−311

−176

−617 −14

9

CePyGr 55.2

−86

96

−49

−86

20

27

CoPy1

18

0.44

−97.5

44

−238 0.73

−2.4

29.8

CePy1

−36

7.86

39.0

−12

−41

−3.34

−11.8

0.2

CoPy2

16

−60

66

4.39

−64

14

57

21

55

175

48

A. Formisano and A. Davino

Table 6 Stresses acting on beams obtained from SAP2000 software Element

Acting stress Mmax ; Ncorresponding

Nmax ; Mcorresponding

Vmax

[KNm]

[KNm]

[KN]

[KN]

−531

[KN]

First floor (Be1)

−530.7

−18

−18.4

Second floor (Be2)

−259.59

−24.769

−63.5

Roof (BeRo)

−231.4

−88

−88

227.64 −231.4

344.2 175.5 143

in the ante-operam phase αLS coefficients equal to 0.13 and 0.36 (third model). The performance improvement of the bell tower is visible in the histogram of Fig. 16. The C-FRP belts are positioned on the side of the pylons that are free from beams. The regions of pylons that are not accessible, because in contact with the beams or with the floor, were reinforced with bars of carbon flakes with a diameter of 12 mm. In these cases, two bars/side were installed to obtain an equivalent CFRP area on all sides of the columns. The flakes, treated with epoxy resin, solidify upon contact with the bar, giving rise to a rigid system. Such a system was planned for L-shaped partitions to make both the confinement and shear reinforcement as effective. In conclusions, verifications were carried out on the shear node panels. In this framework, confinement evaluation was omitted as the pylons do not require such interventions. It was necessary to apply two layers of quadriaxial fabric with a thickness of 0.331 mm. Figure 17 shows the construction details of the performed intervention with carbon flakes.

6 Conclusions This work aimed at investigating the seismic response and retrofitting of a RC bell tower located over the “Maria SS. del Buonconsiglio” masonry sanctuary in Torre del Greco, in the district of Naples. Three modelling hypotheses of the bell tower were implemented with the 3MURI software. The study goal was to highlight the importance of including or excluding portions of neighboring structures to the tower, which can potentially lead to inaccurate seismic assessment results. The first model was representative only of the RC bell tower, which was hypothesized to be located directly at the ground level. The vibration modes resulting from the modal analysis were characterized by t = 0.236 s in Y-direction and t = 0.233 s in X-direction. Risk indices greater than one indicate that no intervention was needed. The second model included the masonry structure below the bell tower. The vibration modes were characterized by t = 1.596 s in X-direction and t = 1.106 s in Y-direction. The comparison in terms of linear dynamic analyses between two models highlighted a considerable increase of vibration periods in the second modelling approach, which provided risk indices less than one for almost all analyses and different limit states. These values were still considered as unrealistic,

87.7

217.7

55.1

273.9

–

–

–

CePyGr

CoPy1

CePy1

CoPy2

Be1

Be2

BeRo

110.7

Mx.rd KN/m

–

–

–

16

36

18

55.2

88.2

Mx.sd KN/m

–

–

–

17.0

1.53

12.0

1.59

1.26

α –

Compression-bending/Bending

CoPyGr

Element

Table 7 Local verification of structural sections

216.7

111.9

519.8

273.9

92.8

217.7

106.2

91.6

My.rd KN/m

231.4

259.9

530.7

66

39

97.5

96

311

My.sd KN/m

0.94

0.43

0.98

4.15

2.38

2.23

1.11

0.29

α –

84.5

43.6

125.4

156.9

28.5

110.8

34.5

30.3

Vrd KN

Shear

143

175.5

344.2

21

0.2

29.8

27

175

Vsd KN

3.72

1.28

0.17

0.59

0.25

0.36

7.47

142.50

α –

–

–

–

61417.7

1922.8

5953.7

2223.2

3325.3

Nrcc.d KN

Confinement

–

–

–

64

41

238

96

176

Nsd KN

–

–

–

959.65

46.90

25.02

23.16

18.89

α –

Seismic Analysis and Retrofitting by C-FRP of Reinforced … 49

50

A. Formisano and A. Davino

Table 8 Physical-geometric and mechanical characteristics of C-FRP Characteristics

Value

Density

1.81 g/cm3

Total weight

616 g/m2

Equivalent area

331.49 mm2 /m

Equivalent thickness

0.331 mm

Elastic modulus in the direction of the fibers

210 GPa

Tensile resistance in the direction of the fibers

2700 MPa

Ultimate deformation

1.8–2.0%

Table 9 Geometric characteristics of C-FRP reinforcements for pylons Pylons

Bending reinforcement

Shear and confinement reinforcement

Base [mm] Thickness N. Anchoring Base Thickness N. Anchoring [mm] levels length [mm] [mm] levels length [mm] [mm] CoPyGr 400

0.331

2

250

400

0.331

1

200

CePyGr 300

0.331

1

200

300

0.331

1

200

CoPy1

300

0.331

1

200

300

0.331

1

200

CePy1

250

0.331

1

200

250

0.331

1

200

CoPy2

300

0.331

1

200

300

0.331

1

200

because, even if the full height of the tower was considered, the masonry structures close to the tower were not modelled. The extreme tower slenderness led to increase its vibration periods, so that the breakage of the masonry elements occurred before the failure of reinforced concrete members. Therefore, a third model was designed by including also the walls of church rooms near to the tower along with the previously examined structures. In this case, the vibration periods, namely t = 0.32 s in X-direction and t = 0.78 s in Y-direction, decreased compared to the second method ones. Consequently, the spectral acceleration increased from 0.146 to 0.448 g. The risk index values calculated at the LS were significantly reduced from 0.35 to 0.13 in X-direction and from 0.74 to 0.36 in Y-direction. Therefore, this model was considered to be the most realistic one, as it considered the dynamic amplification factor aging on the tower, based on its real height from the ground, and reduced the excessive tower slenderness of the second model. Even if the vibration periods of the first and third model differed to each other, they led to the same seismic stress on the structure. This was explained because in both cases the periods fell in the plateau of the response spectrum. The critical issues evidenced by the seismic assessment analyses, considering that shear and bending checks were not satisfied for many tower structural elements, directed the choice of the intervention towards the use of C-FRP materials. The

300

250

300

Be2

BeRo

0.331

0.331

0.331

2

6

3 250

400

250

Anchoring length [mm]

300

250

300 300

300

500

Height [mm]

0.331

0.331

0.331

Thickness [mm]

Base [mm]

N. levels

Base [mm]

Thickness [mm]

Shear and confinement reinforcement

Bending reinforcement

Be1

Beams

Table 10 Geometric characteristics of C-FRP reinforcements for beams

1

2

1

N. levels

200

250

200

Anchoring length [mm]

Seismic Analysis and Retrofitting by C-FRP of Reinforced … 51

52

A. Formisano and A. Davino

Table 11 Local verification of the elements after retrofit interventions Sections Compression-bending/bending Mx.rd Mx.sd α KN/m KN/m –

Shear

My.rd My.sd α KN/m KN/m –

Vrd KN

Confinement Vsd KN

α –

Nrcc.d Nsd KN KN

1.02 4144.1 176

α –

CoPyGr 163.3

88.2

1.85

312.3

311

1.00

177.8 175

Be1

–

–

–

622.4

530.7

1.17

350.1 344.2 1.02 –

–

–

Be2

–

–

–

281.6

259.9

1.08

201.9 175.5 1.15 –

–

–

BeRo

–

–

–

290.6

231.4

1.26

231.9 143

–

–

1.62 –

23.55

Table 12 Results of the verifications obtained with the 3MURI software on the structure considering both the tower and the sanctuary after retrofit interventions α LS

α OP

2.143

2.243

3.578

4.211

0.781

0.764

2.154

2.393

2.370

3.833

5.042

0.648

1.240

1.708

2.269

2.582

3.284

0.835

0.817

2.220

2.463

3.243

3.122

6.710

6.853

0.575

0.601

2.116

2.794

2.511

2.628

2.713

3.470

1.928

2.028

2.149

2.804

0.819

0.801

1.305

1.785

−121.07

0.719

0.703

1.373

1.530

121.07

1.141

1.270

3.509

4.574

−121.07

1.604

1.719

2.821

3.654

121.07

0.806

0.788

1.785

1.993

−121.07

0.617

0.603

0.865

1.176

93.55

0.896

1.053

3.169

4.067

−93.55

2.319

2.235

4.275

4.400

93.55

0.852

0.833

1.324

1.809

−93.55

0.766

0.750

1.155

1.575

93.55

1.849

1.780

6.447

8.183

−93.55

2.811

2.972

3.542

4.549

93.55

0.614

0.695

2.331

2.656

−93.55

0.963

0.929

1.169

1.577

Eccentricity [cm]

α CP

N.

Dir. seism

Seismic load

1

+X

Uniform

0.00

2

+X

Static loads

0.00

3

−X

Uniform

0.00

2.461

4

−X

Static loads

0.00

0.662

5

+Y

Uniform

0.00

2.142

6

+Y

Static loads

0.00

7

−Y

Uniform

0.00

8

−Y

Static loads

0.00

9

+X

Uniform

121.07

10

+X

Uniform

−121.07

11

+X

Static loads

121.07

12

+X

Static loads

13

−X

Uniform

14

−X

Uniform

15

−X

Static loads

16

−X

Static loads

17

+Y

Uniform

18

+Y

Uniform

19

+Y

Static loads

20

+Y

Static loads

21

−Y

Uniform

22

−Y

Uniform

23

−Y

Static loads

24

−Y

Static loads

α IO

Seismic Analysis and Retrofitting by C-FRP of Reinforced …

53

Fig. 14 Results of the most severe analysis (n.16) on the post-operam model in X-direction

intervention were designed so to ensure that local checks of the sections were satisfied. For the vertical pylons, the stresses provided by the 3MURI software were employed. On the other hand, the stresses in the beams were determined by means of a linear static analysis on a 2D-model of the bell tower with the SAP2000 version 20.0.0 calculation software. This latter modelling approach was required since the 3MURI software considered the beams as simply supported to the pylons, so to be ineffective to sustain bending moment stresses. The local verifications of both all the beams and only one pylon gave capacity-to-demand ratios less than one. This required reinforcement intervention of those RC elements by C-FRP. Finally, to confirm the effectiveness of local reinforcements on the weak sections, global checks on the sanctuary-tower aggregate model following the retrofit operations were carried out. The verifications under non-linear static analysis were all satisfied (except than n.16) at the IO and OP limit states. Contrary, about 50% of checks were not satisfied at the LS limit state. Therefore, even if the complete seismic retrofit of the bell tower was not attained, at least its seismic upgrading was reached. In particular, the obtained safety levels (0.603 in X-direction and 0.601 in Y-direction)

54

A. Formisano and A. Davino

Fig. 15 Results of the most severe analysis (n.8) on the post-operam model in Y-direction

0.70

0.603 0.601

0.60 0.50 0.36

α [-]

0.40

X (LS)

0.30 0.20

Y (LS) 0.13

0.10 0.00 Pre-retrofitting

Post-retrofitting

Fig. 16 Comparison of seismic risk coefficients α before and after retrofit interventions

Seismic Analysis and Retrofitting by C-FRP of Reinforced …

55

Fig. 17 Construction details of the planned intervention with carbon flakes (Left: corner pylon; Right: beam)

after C-FRP interventions significantly improved the seismic behaviour of the tower structure, which showed in the ante-operam phase of the third model seismic risk coefficients equal to 0.13 and 0.36 in X-direction and Y-direction, respectively. Acknowledgements The Authors would like to acknowledge the S.T.A. DATA S.r.l. company for the kind supply of the 3MURI software used for global analysis of the structure. Also the kind support of the Olympus S.r.l. company for providing the software for local verification of sections after reinforcement interventions with C-FRP materials is gratefully acknowledged.

References Acito M, Bocciarelli M, Chesi C et al (2014) Collapse of the clock tower in Finale Emilia after the May 2012 Emilia Romagna earthquake sequence: numerical insight. Eng Struct 72:70–91. https://doi.org/10.1016/j.engstruct.2014.04.026 Calderón PA, Adam JM, Ivorra S et al (2009) Design strength of axially loaded RC columns strengthened by steel caging. Mater Design 30(10):4069–4080 Clementi F, Quagliarini E, Monni F et al (2017) Cultural heritage and earthquake: the case study of “Santa Maria Della Carità” in Ascoli Piceno. Open Civic Eng J 11:1079–1105. https://doi.org/ 10.2174/1874149501711011079 Cosenza E, Iervolino I (2007) Case study: seismic retrofitting of a medieval bell tower with FRP. J Compos Constr 11(3):319–327 Cuzzoni M (2016) Structural restoration of bell towers: Practical manual for maintenance, consolidation and restoration (in Italian). Dario Flaccovio Editore Di Tommaso A, Casacci S (2013) Survival of towers and bell towers in a seismic environment (in Italian). Università ALMA MATER di Bologna Dolce M (1991) Schematic and modelling of masonry buildings subjected to seismic actions (in Italian). Constr Ind 25:44–57 Doglioni F, Moretti A, Petrini V (1994) Churches and Eathquakes (in Italian). LINT, Trieste Ferrante A, Clementi F, Milani G (2019) Dynamic Behavior of an Inclined Existing Masonry Tower in Italy. Front Built Environ 5:33. https://doi.org/10.3389/fbuil.2019.00033

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Galasco A, Lagomarsino S, Penna A (2002) TREMURI program: seismic analyser of 3D masonry buildings, University of Genoa Gentile C, Saisi A (2007) Ambient vibration testing of historic masonry towers for structural identification and damage assessment. Constr Build Mater 21(6):1311–3321 Italian National Unification Body UNI (2010) UNI EN 13670: 2010−Execution of concrete structures Ivorra S, Fotib D, Gallob V et al (2019) Bell’s dynamic interaction on a reinforced concrete bell tower. Eng Struct 183:965–975 Lionello A (2011) Construction techniques, breakdowns and consolidations of the bells of venice (in Italian) Corbo E Fiore Editori Mazzolani FM, Formisano A, Vaiano G (2004) Seismic upgrading of reiforced concrete buildings: BRB & FRP Costruzioni Metalliche, pp 25–50 Milani G (2013) Lesson learned after the Emilia-Romagna, Italy, 20–29May 2012 earthquakes: a limit analysis insight on three masonry churches. Eng Fail Anal 34:761–778 Ministry of Infrastructure and Transport (2018a) Technical standards for construction (in Italian), Official Gazette, Rome (nr. 42 of 20-2-2018) Ministry of Infrastructure and Transport (2018b) (in Italian), Instructions for the application of the new technical code for constructions, Official Gazette, Rome (nr. 35 of 11-02-2019) Modena C, Valluzzi MR, Tongini Folli R et al (2002) Design choices and intervention techniques for repairing and strengthening of the Monza cathedral bell-tower. Constr Build Mater 16(7):385–395 National Research Council (2004) Guide for the design and construction of externally bonded FRP systems for strengthing existing structures. Materials, RC and PC structures, masonry structures. CNR DT 200/2004 National Research Council (2007) CNR DT 205/2007−“Istruzioni per la Progettazione, l’Esecuzione ed il Controllo di Strutture realizzate con Profili Pultrusi di Materiale Composito Fibrorinforzato (FRP)” National Research Council (2013) CNR DT R1/2013−“Istruzioni per la Progettazione, l’Esecuzione ed il Controllo di Interventi di Consolidamento Statico mediante l’utilizzo di Compositi Fibrorinforzati−Materiali, strutture di c.a. e di c.a.p., strutture murarie” Paz M, Kim YH (2019) Structural dynamics−theory and computation. Springer International Publishing Penna A, Cattari S, Galasco A et al (2004) Seismic assessment of masonry structures by nonlinear macro-element analysis. In: Proceeding of IV international seminar “structural analysis of historical construction-possibilities of numerical and experimental techniques Priester A (1993) Bell towers and building workshops in medieval rome. J Soc Arch Histor 52(2):199–220. University of California Press Sepe V, Speranza E, Viskovic A (2008) A method for large-scale vulnerability assessment of historic towers. Struct Control Health Monit 15(3):389–415 STADATA (2016) 3Muri- Seismic calculation of masonry structures according to the Italian Ministerial Decree 14/01/2008, ‘New technical codes for constructions’ Tuti M, Ongaro R, Saccomanno L et al (2012) From one bell tower to the next (in Italian). Ap., Majano Valente M, Milani G (2016) Seismic assessment of historical masonry towers by means of simplified approaches and standard FEM. Constr Build Mater 108:74–104. https://doi.org/10.1016/j.conbui ldmat.2016.01.025 Von Petrikovits H (1971) Fortifications in the north-western roman empire from the third to the fifth centuries A.D. J Roman Stud 61:178–218

Compressive Strength of Concrete Estimated by Artificial Neural Networks and a Non-destructive Testing of Ultrasound R. S. Cavalcanti, F. A. N. Silva, J. M. P. Q. Delgado, and A. C. Azevedo

Abstract This work presents an experimental campaign with 162 specimens of cylindrical specimens of 10 × 20 cm2 and 27 prismatic specimens with 25 × 25 × 50 cm3 , in order to analyse the influence of nine different concrete mixtures on compressive strength and the propagation profile of longitudinal ultrasonic waves. A neural network is best defined as a set of simple, highly interconnected processing elements that are capable of learning information presented to them and its ability to learn and process information classifies it as a form of artificial intelligence. In this work, neural networks models were used to find out the influence of several parameters used in fabrication of concrete on the material compressive strength. The results obtained showed that the simulation with neural networks associated with ultrasound tests are important tools to evaluate the compressive strength of concrete. Keywords Artificial neural networks · Compressive strength · Concrete · Nondestructive testing · Properties of concrete

1 Introduction In the last years, several factors contribute to the emergence of faster tests that enable the evaluation of concrete properties, namely the compressive strength. Among other, should be mentioned: (1) the increase of the use of high-strength concretes in civil R. S. Cavalcanti · F. A. N. Silva Civil Engineering Department, Universidade Católica de Pernambuco, Recife, Brazil e-mail: [email protected] F. A. N. Silva e-mail: [email protected] J. M. P. Q. Delgado (B) · A. C. Azevedo CONSTRUCT-LFC, Departamento de Engenharia Civil, Universidade do Porto, Rua Dr. Roberto Frias, s/n, 4200-465 Porto, Portugal e-mail: [email protected] A. C. Azevedo e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Switzerland AG 2021 J. M. P. Q. Delgado (ed.), Case Studies of Building Rehabilitation and Design, Building Pathology and Rehabilitation 19, https://doi.org/10.1007/978-3-030-71237-2_4

57

58

R. S. Cavalcanti et al.

engineering construction; (2) the relatively long period of time required by the tests of compressive strength; (3) the insecurity related to the conservation conditions of the specimens in laboratory do not satisfactorily represent the reality of the work, causing significant deviations in the concrete strength results; and (4) the destructive character of the extraction of specimens to assess the performance of the structure in service (Shehab El-Din et al. 2017; Dinakar et al. 2013; Ray et al. 2012). Concrete technologists have always paid special attention to the possibility of determining concrete properties through non-destructive tests. According to Rose (1999), the development of the ultrasonic wave propagation method started simultaneously in Canada and England, at the beginning of 1970s. In particular, ultrasound is a truly non-destructive test, as its technique involves the propagation of ultrasonic waves that do not result in any damage to the element being tested. In concrete structures, as described by Naik and Malhotra (1991) and Güçlüer (2020), the method can have the following applications: (1) estimate the concrete compressive strength; (2) determine the dynamic modulus of the material; (3) evaluate the concrete homogeneity; (4) detection of the presence of cracks. It is well-known that there are a significant number of variables that influence the concrete compressive strength, as water cement ratio, aggregate cement ratio, age of testing, additions, curing time, cement types, etc. In order to associate this information, the use of artificial neural networks (ANN) is crucial, as ANN can present a response that reflects the influence of the parameters in the obtained result (Mohamed et al. 2018; Güçlüer 2020). In this work, the method of propagation of ultrasonic waves is used to associate the values of concrete compressive strength with the use of artificial neural network techniques. Qualitative and quantitative information about the potential of using ultrasound tests and artificial neural networks in the evaluation of the compressive strength of concretes are presented and analysed in detail.

2 Experimental Program The experimental campaign performed included the fabrication of a wide range of prismatic concrete specimens with dimensions of 25 × 25 × 50 cm as well as the preparation of standard cylindrical specimens−height of 20 cm and diameter of 10 cm−made with nine different of concrete mixtures. The tests were performed at different ages and the concrete ones were made with some previously defined parameters: the maximum size of the coarse aggregate, the amount of cement replaced by metakaolin, the water/cement ratio. To meet RILEM recommendation, ultrasonic transducer frequency was limited to 54 kHz and, for this reason, it was necessary to prepare concrete prims with the cross-section size described above to ensure that the dimension perpendicular to the ultrasonic wavelength was not less than the respective wavelength−200 mm. For each concrete mixture, it was prepared eighteen cylindrical concrete specimens to hold compressive strength tests, being six specimens for each age investigated−7, 28 and 60 days.

Compressive Strength of Concrete …

59

Ultrasonic pulse velocity tests were performed in twenty-seven concrete prisms−three prims for each concrete mixture studied−at the same ages for each concrete mixture. To produce concrete samples studies−prisms and cylindrical ones−the following materials were used: Portland Cement CP-II-F, gneiss coarse aggregates with maximum size of 12.5, 16.0 and 19.0 mm, poly-functional superplasticizer and metakaolin (see Table 1 and Fig. 1). Metakaolin is a highly reactive pozzolan, consisting basically of silica (SiO2 ) and alumina (Al2 O3 ) based compounds in the amorphous phase, which combine with the calcium hydroxide−Ca(OH)2 that improves significantly many features of most cement based products. In this work 162 cylindrical concrete test specimens and 27 prismatic specimens made with nine different concrete mixtures. Eighteen specimens of each mixture were made and divided into three groups of six units. Each group of six and was submitted to compression rupture tests according at different ages: seven, twentyeight and sixty days. At the same ages, each group of three prisms was subjected to and non-destructive ultrasound tests. Nine readings at each age were meaning 486 ultrasonic pulse velocities. Table 1 Mixture proportions of the specimens tested Mix-ture Cement Sand (kg) (kg)

Aggregate (kg)

Additive Meta-kaolin(kg) Water (kg) Gravel Gravel Gravel Gravel (kg) 19 16 25 12

1

22.0

27.126 35.86

15.40

0

0

0.11

0.0

10.12

2

20.9

27.126 35.86

15.40

0

0

0.11

1.1

10.12

3

19.8

27.126 35.86

15.40

0

0

0.11

2.2

10.12

4

22.0

27.126 0

15.40

35.86

0

0.11

0.0

10.12

5

20.9

27.126 0

15.40

35.86

0

0.11

1.1

10.12

6

19.8

27.126 0

15.40

35.86

0

0.11

2.2

10.12

7

22.0

27.126 0

0

35.86

15.40

0.11

0.0

10.12

8

20.9

27.126 0

0

35.86

15.40

0.11

1.1

10.12

9

19.8

27.126 0

0

35.86

15.40

0.11

2.2

10.12

Fig. 1 Specimens submitted to compressive strength tests

60

R. S. Cavalcanti et al.

For structuring the neural networks models, input data were ordering associating the ultrasonic velocity in the prisms with the results of concrete test specimen’s compressive strength. At each age, the average of nine ultrasonic velocities of each of the three prisms of each concrete mixture was calculated. For the six specimens at each age, three averages of two specimens were, then, calculated. Each average of nine ultrasonic velocities was associated to the average of two results of compressive tests at each. Therefore, from the treatment carried out it was obtained three input pairs per age for each concrete mixture, totalling for the three ages and nine mixtures investigated 81 epochs for the ANN models.

3 Results and Discussion The factors that affecting the ultrasonic wave propagation tests (UPV) can be divided into two categories: (a)

(b)

Factors resulting directly from concrete properties, such as: (1) aggregate sizing, grading, type and content; (2) cement type; (3) water/cement ratio; (4) admixtures and (5) and age of concrete. Other factors, such as: (1) transducter contact; (2) temperature of concrete; (3) moisture and curing conditions of concrete; (4) path length; (5) size and shape of the specimens; (6) level of stress and (7) presence of reinforcing steel.

3.1 Relation Between Compressive Strength and UPV There wasn’t a clear consensus between the compressive strength and the UPV, for example Güneyli et al. (2017) presented a linear relation between these variables and several researchers as Tharmaratnam and Tan (1990) and Musmar and Alhadi (2008) presented an exponential relation between compressive strength and UPV, i.e., f c = aV pb and f c = aebV p , respectively. Figure 2 presents an exponential relation between UPV and compressive strength with a strong correlation coefficient (R), i.e., greater than 0.94. Table 2 present the experimental average results of the compressive strength and ultrasonic pulse velocities obtained for each mixture tested. The results showed that mixture 7 presents the lowest average values and mixture 3 the highest average values, in the three concrete age time tested.

Compressive Strength (MPa)

Compressive Strength of Concrete …

61

50 40 y = 0.204e1.202x R² = 0.943

30 20 10

Sampes 1-9 0 4.1

4.2

4.3

4.4

4.5

4.6

UPV (km/s) Fig. 2 UPV (longitudinal) versus compressive strength

Table 2 Experimental average results of the compressive strength and ultrasonic pulse velocities each mixture tested Mix-ture

Slump (cm)

Meta-kaolin(%)

Compressive strength−MPa 7 days

28 days

Ultrasonic pulse velocity–km/s 60 days

7 days

28 days

60 days

1

12

0

34.77

36.55

41.00

4.23

4.30

4.36

2

19

5

34.96

37.27

43.90

4.28

4.34

4.45 4.50

3

10

10

39.18

44.86

45.25

4.36

4.47

4

20

0

32.24

35.86

37.00

4.22

4.33

4.36

5

18

5

35.33

35.95

40.35

4.27

4.28

4.38 4.47

6

10

10

37.61

42.67

44.26

4.36

4.45

7

18

0

30.47

34.00

35.56

4.18

4.28

4.30

8

18

5

33.60

35.95

36.47

4.24

4.30

4.32

9

17

10

36.33

40.09

41.15

4.33

4.39

4.43

3.2 Influence of Metakaolin and Aggregate on Concrete Compressive Strength Regarding the diameter of the aggregates, it can be said that the mixtures that showed greater compressive strength were those with 19 mm coarse aggregate size, granulometrically improved with 16 coarse aggregates size. Likewise, this mixture was also consistent with regard to the increase in strength related to the amount of metakaolin. In fact, metakaolin is a highly reactive pozzolan that improves significantly many features of most cement-based products in short and long term (Salimi et al. 2020). Some authors (Güneisi et al. 2008; Muthupriya et al. 2011; Ramezanianpour et al. 2012) report that with a 5% addition of metakaolin it is already possible to observe

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an increase of 12 to 15% in concrete compressive strength and for an addition of 10% the observed increase in strength varied from 9 to 28% (Madandoust and Mousavi 2012; Kirthini and Sujatha 2014). It is important to highlight that is well know that the aggregate size influences more the young’s modulus of concrete than its compressive strength (Güneyisi et al. 2012) although compressive strength might also be related with concrete pore size composition−distribution and spacing (Deo and Neithalath. 2010). Decreasing coarse aggregate size can also increases concrete compressive strength (Agar-Ozbek et al. 2013; Zhong and Wille 2016; Sun et al. 2018) mainly due to the increase in adherence generated by the effect of aggregate size reduction (Zhong and Wille 2016; Sun et al. 2018; Xu et al. 2018). The fact that concretes made with coarse aggregates size combination−19 and 16 mm−presented better performance than the mixtures made with 25 mm and 16 mm aggregate sizes and the mixture made with 25 and 12 mm aggregate sizes shows the importance of improved granulometry in the performance of concretes. It can be said that, for the mixtures investigated in this work and their respective materials, the granulometric improvement with 16 mm coarse aggregate was better used when the coarse aggregate used is 19 mm size. This happens because it creates a condition that is close to the packaging process in concrete manufacture. The combination of 25 and 12 mm aggregate size presented a greater number of voids to be filled, directly reflecting the value of the compressive strength. It is also found that the addition of metakaolin exhibited a greater effect in increasing the compressive strength at the ages of 28 and 60 days. The most significant evolution to compression occurred until the 7th day, after this period there is a very small increase in the compressive strength. As shown in Fig. 3, the addition of metakaolin in mixtures 3, 6 and 9 did not generate significant influence neither in compressive strength nor in UPV at the age of 7 days. An opposite behaviour, however, was observed at 28 and 60 days where it was observed that, with the increase of the addition, the UPV and the compression strength presented an increase. As shown in Fig. 4, for the same water/cement ratio, the same mortar content and the same amount of addition of metakaolin, the best combination between two coarse aggregates size was 16 and 19 mm. This combination for all ages showed the greatest compressive strength and the highest ultrasonic pulse velocity.

3.3 Artificial Neural Network Modelling Regression models based on experimental research results are commonly used strategies to get a qualitative assessment of a given parameter of interest, based on variables that influence its behaviour. However, depending on the field of scientific research and the phenomena under investigation, the complexity of the relationships between input and output variables may significantly limit the ability of these models to provide an adequate response. In these situations, more efficient modelling tools such as Artificial Neural Networks can be more applicable.

63 4.5

50

4.4

40 30 y = 0.381x + 34.912 R² = 0.984 y = 0.464x + 32.913 R² = 0.998 y = 0.391x + 31.162 R² = 0.950

20 10

t=7 days 0 0.0

2.0

4.0

6.0

8.0

10.0

Samples 1-3

UPV (km/s)

Compressive Strength (MPa)

Compressive Strength of Concrete …

Samples 4-6

4.2 y = 0.005x + 4.248 R² = 0.987 y = 0.004x + 4.240 R² = 1.000 y = 0.004x + 4.230 R² = 1.000

4.1 4.0 3.9

Samples 7-9 12.0

4.3

t=7 days

3.8 0.0

14.0

2.0

4.0

50

10.0

Samples 7-9 12.0

14.0

4.5 4.4

40 30 y = 0.746x + 36.713 R² = 0.908 y = 0.692x + 35.387 R² = 0.947 y = 0.609x + 32.502 R² = 0.972

20 10

t=28 days 0 0.0

2.0

4.0

6.0

8.0

10.0

Samples 1-3

UPV (km/s)

Compressive Strength (MPa)

8.0

Metakaolin (%)

Metakaolin (%)

Samples 4-6

4.3 4.2

4.0 3.9

Samples 7-9

y = 0.012x + 4.270 R² = 0.923 y = 0.010x + 4.267 R² = 0.824 y = 0.008x + 4.243 R² = 0.923

4.1

t=28 days

3.8 12.0

14.0

0.0

2.0

4.0

Metakaolin (%)

6.0

8.0

10.0

Samples 1-3 Samples 4-6 Samples 7-9 12.0

14.0

Metakaolin (%) 4.5

50

4.4

40 30 y = 0.425x + 41.022 R² = 1.000 y = 0.657x + 37.022 R² = 1.000 y = 0.459x + 35.098 R² = 0.892

20 10

t=60 days 0 0.0

2.0

4.0

6.0

8.0

Metakaolin (%)

10.0

Samples 1-3 Samples 4-6 Samples 7-9

UPV (km/s)

Compressive Strength (MPa)

6.0

Samples 1-3 Samples 4-6

4.3 4.2 y = 0.011x + 4.342 R² = 0.997 y = 0.008x + 4.317 R² = 0.980 y = 0.005x + 4.298 R² = 0.987

4.1 4.0 3.9

t=60 days

3.8 12.0

14.0

0.0

2.0

4.0

6.0

8.0

10.0

Samples 1-3 Samples 4-6 Samples 7-9 12.0

14.0

Metakaolin (%)

Fig. 3 Influence of the metakaolin on concrete compressive strength and UPV

Artificial Neural Networks use concepts associated with the massive local and distributed processing believed to occur in the human brain. These networks acquire knowledge through experience, and this knowledge is represented by their ability to map relationships between input and output parameters. A neural network is best defined as a set of simple, highly interconnected processing elements that are capable of learning information presented to them and its ability to learn and process information classifies it as a form of artificial intelligence. ANN is especially useful to deal with situations in which establishing a description of functional relationships between the variables involved in a problem is either overly complex or unavailable. The success of ANN problem modelling is directly related to the network architecture, i.e.: number of hidden layers and the amount of neurons in these layers and training strategies used. A very important task to create an ANN model is to define its hidden layer architecture. Several researches have already showed that it is always possible to get a single hidden layer solution with the same level of learning of complex solutions with several hidden layers with a large number of hidden neurons (Hecht-Nielsen 1989; Beale and Jackson 1992).

R. S. Cavalcanti et al. 50

4.5 4.4

40 30 20 10

t=7 days 0

Gravel 19-16

y = -1.675x + 36.403 R² = 0.998 y = -2.250x + 39.440 R² = 0.995 y = -1.625x + 40.423 R² = 0.949

Gravel 16-25

Samples 1,4,7

UPV (km/s)

Compressive Strength (MPa)

64

Samples 2,5,8

4.3 4.2 4.1 4.0 3.9

Samples 3,6,9

3.8

Gravel 25-12

t=7 days Gravel 19-16

30 20 10

t=28 days Gravel 19-16

y = -2.300x + 39.953 R² = 0.965 y = -2.060x + 41.427 R² = 0.941 y = -2.985x + 48.147 R² = 0.970

Gravel 16-25

Samples 1,4,7

UPV (km/s)

Compressive Strength (MPa)

4.4

Samples 2,5,8

4.3 4.2 4.1 4.0 3.9

Samples 3,6,9

3.8

Gravel 25-12

t=28 days Gravel 19-16

y = -0.015x + 4.300 R² = 0.750 y = -0.020x + 4.330 R² = 1.000 y = -0.035x + 4.440 R² = 0.942

Gravel 16-25

Samples 1,4,7 Samples 2,5,8 Samples 3,6,9

Gravel 25-12

Aggregate

Aggregate 4.5

50

4.4

40 30 20 10

t=60 days Gravel 19-16

y = -2.720x + 43.293 R² = 0.931 y = -3.360x + 46.723 R² = 0.992 y = -2.550x + 48.090 R² = 0.963

Gravel 16-25

Aggregate

Samples 1,4,7 Samples 2,5,8 Samples 3,6,9

Gravel 25-12

UPV (km/s)

Compressive Strength (MPa)

Samples 3,6,9

Gravel 25-12

4.5

40

0

Gravel 16-25

Samples 1,4,7 Samples 2,5,8

Aggregate

Aggregate 50

0

y = -0.010x + 4.260 R² = 1.000 y = -0.010x + 4.280 R² = 1.000 y = -0.015x + 4.313 R² = 0.964

4.3 4.2 4.1 4.0 3.9 3.8

t=60 days Gravel 19-16

y = -0.020x + 4.360 R² = 1.000 y = -0.040x + 4.437 R² = 0.980 y = -0.050x + 4.500 R² = 1.000

Gravel 16-25

Samples 1,4,7 Samples 2,5,8 Samples 3,6,9

Gravel 25-12

Aggregate

Fig. 4 Influence of the aggregate on concrete compressive strength and UPV

To build concrete compressive strength prediction models through non-destructive ultrasound testing combined with the network networks model, the software QNET (QNET 2000) was used. QNET is a multi-layer perceptron whose training is performed using a retro-propagation algorithm. This program allows the definition of up to eight intermediate layers of neurons and the choice of four different activation functions (sigmoid, tangent hyperbolic, hyperbolic and Gaussian) Predicting the axial compression strength of concrete is a complex problem, influenced by a number of factors, mainly the water-cement (w/c) and aggregate-cement (ag/c) ratios, testing age, amount and type of addition among others, and its modelling with ANN is a hard task to implement. To assess the potentialities to predict compressive strength of concrete, an ANN model using experiments described in Sect. 2 was created with the following features: five input variables−water cement ratio, aggregate cement ratio, age of testing, metakaolin cement ratio, measured ultrasonic velocity. The output variable is the average compression strength (f c ). For the development of the models with the AAN data normalization is necessary. This normalization is essential since the different activation functions that activate

Compressive Strength of Concrete …

65

neurons in the model provide values within a range between 0 and 1. The software used to create the ANN models allows automatic data normalization, but this normalization omits important information to the user avoiding. For that reason, input and output data values were normalized outside the software considering a linear relationship between the maximum and minimum values of each of the variables, within the range 0.25–0.85, using Eq. (1): X − X min X nor m − 0.25 = 0.85 − 0.25 X max − X min

(1)

where X norm is the normalized variable, X is the variable to be normalized, X max is the maximum value of the variable to be normalized variable and X min is minimum value of the variable to be normalized variable. After data analysis and processing, the final set used in the training and validation phases totalled 81 epochs. In order to test the developed neural network models, a separation of the input data in a training group and a test group was implemented. In the research, 15% of input data were randomly chosen to test the model while it was being trained. This means that the model was not presented to this set of data in training phase and, in fact, the model was trained using 69 epochs. The result data were exclusively used to verify the quality of the ANN along its training process. For the ANN models investigated, a specific strategy was used to avoid that the over-training process might govern model’s response. Overtraining occurs when the test set error increases while the training set error continues to descend. This indicates that memorization is the predominant learning mode. When a test set error has reached a global minimum and increases indefinitely thereafter, overtraining has occurred. Training a network after the test set error global minimum has been reached can actually hurt the predictive capabilities of the model being developed. The model elaborated in this work has the objective to obtain a good approximation for the compressive strength of concrete as a function of water cement ratio (w/c), aggregate/cement ratio (ag/c), testing age (t), metakaolin cement ratio (mk/c) and measured ultrasonic velocity represented (V) by Eq. (2):  fc = f

mk a ag , , t, ,V c c c

 (2)

After several trials, the architecture of the hidden network layers that exhibited the best error was as follows: [3–5–(1 × 8)–1]. That means an ANN with 3 layers−one input layer with 5 neurons representing the five input variables, one hidden layer with 9 neurons and one output layer neurons with one neuron representing the compressive strength. Figure 5 shows the ANN architecture used for the prediction of the concrete compressive strength of the concretes studied. Figure 6 shows the evolution of the correlation coefficient R2 along the training process of the several ANN models investigated. It can be seen that the model that presented the best overall behaviour was the model [3–5–(1 × 8)–1]−R2 of 95.42

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Fig. 5 Final ANN architecture to predict compressive strength on concrete

Fig. 6 Evolution of correlations with number of iterations in the training phase and validation of the final model with architecture [3–5–(1 × 8)–1]

and 87.24% for the training and test sets, respectively. The others model presented a good performance in training phase but not so good performance on testing phase. Scatter comparison between targets and network outputs−concrete compressive strength by the network and the values obtained with the laboratory tests is shown in Fig. 7. A good agreement can be observed which means that the ANN models was able to capture the complexity of the relationship among the several parameters involved in the problem.

Compressive Strength of Concrete …

67

Fig. 7 Scatter comparison of targets versus network outputs

Table 3 shows the comparison between targets and ANN outputs where it can be confirmed the quality of the overall behaviour of the model. Most of the data in Table 3 were obtained from points that were not used in net training. This means that it is unknown data for the model. In view of this observation, one can conclude that the model behaved very satisfactorily in predicting the concrete compressive strength from the input parameters studied. In order to investigate the influence of each input parameter on the concrete compressive strength prediction result, Table 4

68

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Table 3 Comparison between targets and ANN outputs w/c

Ag/c

Age (days)

mk/c (%)

V (m/s)

Comp. Strength (MPa) Lab Tests

ANN Model

0.511

2.589

60

10

4.31

33.18

36.50

0.460

2.330

60

–

4.37

40.51

40.33

0.511

2.589

60

10

4.33

38.33

39.36

0.511

2.589

60

10

4.47

43.53

45.02

0.484

2.453

7

5

4.28

34.96

36.21

0.511

2.589

28

10

4.47

44.82

44.13

0.484

2.453

28

5

4.35

37.77

38.14

0.460

2.330

7

–

4.22

32.24

34.73

0.460

2.330

28

–

4.40

39.61

40.23

0.511

2.589

28

10

4.25

35.33

36.29

0.484

2.453

60

5

4.28

32.09

35.41

0.460

2.330

28

4.33

35.31

37.95

0.460

2.33

7

–

4.25

35.18

35.10

0.511

2.589

28

10

4.46

42.29

44.01

0.484

2.453

28

5

4.26

37.48

36.30

0.511

2.589

60

10

4.52

45.81

45.39

0.511

2.589

7

10

4.49

43.27

43.62

0.460

2.330

28

–

4.40

39.61

40.23

0.460

2.330

7

–

0.484

2.453

28

Table 4 Contribution of input node on outputs

–

5

4.28

34.87

35.41

4.31

38.22

37.69

Input node

Contribution (%)

w/c

26.0

ag/c

22.9

t

5.6

mk/c

26.3

V

19.2

was prepared. From this table it is possible to observe that, for the concretes mixtures studied, with the exception of the testing age, the other parameters investigated showed a similar contribution in the results of the neural network model. The fact that age has not shown significant importance is consistent with expectations because concrete mixtures have studied had moderate compressive strength and their evolution over time should not be so marked for the ages studied. The water-cement ratio and the percentage of metakaolin together showed an influence of more than 50% which is equally consistent.

Compressive Strength of Concrete …

69

4 Conclusions The following conclusions can be drawn from the results obtained: • These relation between UPV and compressive strength presents a strong linear correlation; • The addition of metakaolin shows an increase of the UPV and the compression strength, at ages of 28 and 60 days, and did not generate significant influence neither in compressive strength nor in UPV at the age of 7 days: • For the same water/cement ratio, the same mortar content and the same amount of addition of metakaolin, the best combination between two coarse aggregates size was 16 and 19 mm; • Artificial neural networks have a great potential to estimate the compressive strength of concrete when combined with non-destructive ultrasound tests; • The great benefit in using artificial neural networks to solve engineering problems lies in the fact that these models can be “trained” to learn the existing relationships between input and output parameters of a given problem. This characteristic has great importance when dealing with situations in which the establishment of a description of functional relationships between the variables involved in a given problem are either excessively complex or simply not available; • Good correlation coefficients were obtained for the trained nets, an aspect that highlights the applicability of the studied models; • The great difficulty of using neural networks to solve engineering problems lies in the difficulty of establishing an adequate internal architecture for the problem being addressed; • In the present work, this difficulty was overcome by adopting a simultaneous training and validation strategy that allowed the rapid identification of the best architecture for the studied problem.

References Agar-Ozbek AS, Weerheijm J, Schlangen E, van Breugel K (2013) Investigating porous concrete with improved strength: Testing at different scales. Constr Build Mater 41:480–490 Beale R, Jackson T (1992) Neural computing, 2nd edn. Bristol, Hilger, IOP (Institute of Physics) Publication, UK Deo O, Neithalath N (2010) Compressive behavior of pervious concretes and a quantification of the influence of random pore structure features. Mater Sci Eng, A 528(1):402–412 Dinakar P, Sahoo PK, Sriram G (2013) Effect of metakaolin content on the properties of high strength concrete. Int J Concr Struct Mater 7(3):215–223 Güçlüer K (2020) Investigation of the effects of aggregate textural properties on compressive strength (CS) and ultrasonic pulse velocity (UPV) of concrete. J Build Eng 27:100949 Güneisi E, Gesoglu M, Mermerda K (2008) Improving strength, drying shrinkage, and pore structure of concrete using metakaolin. Mater Struct 41:937–949 Güneyisi E, Geso˘glu M, Karao˘glu S, Mermerda¸s K (2012) Strength, permeability and shrinkage cracking of silica fume and metakaolin concretes. Constr Build Mater 34:120–130

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Güneyli H, Karahan S, Güneyli A, Yapιcι N (2017) Water content and temperature effect on ultrasonic pulse velocity of concrete. Russian J Nondestr Testing 53(2):159–166 Hecht-Nielsen R (1989) Neurocomputying. Addison-Wesley Longman Publishing Co., Inc., Boston, MA, USA Kirthini CH, Sujatha T (2014) Effect of incorporating metakaolin on the properties of high performance concrete. Int J Eng Res Technol 3(10):1011–1014 Rose JL (1999) Ultrasonic waves in solid media. Cambridge University Press, UK Madandoust R, Mousavi SY (2012) Fresh and hardened properties of self-compacting concrete containing metakaolin. Constr Build Mater 35:752–760 Mohamed OA, Ati M, Hawat W (2018) Implementation of artificial neural networks for prediction of chloride penetration in concrete. Int J Eng Technol 7(2.28):47–52 Musmar MA, Alhadi NA (2008) Relationship between ultrasonic pulse velocity and standard concrete cube crushing strength. J Eng Sci 36(1):51–59 Muthupriya P, Subramanian K, Vishnuram BG (2011) Investigation on behaviour of high performance reinforced concrete columns with metakaolin and fly ash as admixture. Int J Adv Eng Technol 2(1):190–202 Naik TR, Malhotra VM (1991) The ultrasonic pulse velocity method. In: Malhotra VM, Carino NJ (eds) CRC handbook on nondestructive testing of concrete, chapter 7. CRC Press. Boca Raton, USA QNET (2000) Qnet 2000 Shareware. Vesta Services, Inc., 1001 Green Bay Rd, STE 196, Winnetka, IL 60093, USA Ramezanianpour AA, Bahrami Jovein H (2012) Influence of metakaolin as supplementary cementing material on strength and durability of concretes. Constr Build Mater 30:470–479 Ray I, Gong Z, Davalos JF, Kar A (2012) Shrinkage and cracking studies of high performance concrete for bridge decks. Constr Build Mater 28(1):244–254 Salimi J, Ramezanianpour AM, Moradi MJ (2020) Studying the effect of low reactivity metakaolin on free and restrained shrinkage of high performance concrete. J Build Eng 28:101053 Shehab El-Din HK, Eisa AS, Abdel Aziz BH, Ibrahim A (2017) Mechanical performance of high strength concrete made from high volume of Metakaolin and hybrid fibers. Constr Build Mater 140:203–209 Sun Z, Lin X, Vollpracht A (2018) Pervious concrete made of alkali activated slag and geopolymers. Constr Build Mater 189:797–803 Tharmaratnam K, Tan BS (1990) Attenuation of ultrasonic pulse in cement mortar. Cement Concr Res 20(3):335–345 Xu G, Shen W, Huo X et al (2018) Investigation on the properties of porous concrete as road base material. Constr Build Mater 158:141–148 Zhong R, Wille K (2016) Compression response of normal and high strength pervious concrete. Constr Build Mater 109:177–187

Acoustic Performance Criteria in Internal Vertical Partitions: Numerical Simulations and In-Field Measurements E. C. L. Rezende, A. J. Costa e Silva, A. C. Azevedo, and J. M. P. Q. Delgado

Abstract This research aims to evaluate the reliability of computational simulation by analyzing data from simulations and field measurements (MC) of 14 case studies, in relation to internal vertical partition systems (SVVI). Comparative analysis of 75 SVVI results, SC and MC data showed that more than 50% of the simulation data showed values compatible with the in-field measurement, in the sense that they were considered potentially equal, taking into account the uncertainty of the predicted field measurement. in the evaluation methodology contained in the standard, in the order of ±2 dB. This acceptability refers to the values within the ±2 dB range of the aforementioned uncertainty. The data also showed variation between SC and MC, sometimes presenting larger SC, sometimes larger MC. The predicted hypothesis was that SC would always be higher due to the ideal conditions of the simulation, which do not occur in the field. However, where situations of MC greater than SC occurred, it was deduced that deciding on the simulation means choosing to work in favor of safety, since the minimum level of the standard is projected and better results are obtained in the field. It was also verified, through variation of the input data, that the fidelity with the technical specification of the designed systems reproduces reliable values, and the opposite, results in doubtful and discrepant data. In general, the results of the comparative analysis point to the use of computer simulation as positive, since part of the percentage that is not acceptable in this study represents doubtful measurements, and therefore, the simulation is an effective predictive tool and useful in the search for acoustic quality in residential buildings. E. C. L. Rezende · A. J. Costa e Silva Civil Engineering Department, Universidade Católica de Pernambuco, Recife, Brazil e-mail: [email protected] A. J. Costa e Silva e-mail: [email protected] A. C. Azevedo · J. M. P. Q. Delgado (B) CONSTRUCT-LFC, Departamento de Engenharia Civil, Universidade do Porto, Rua Dr. Roberto Frias, s/n, 4200-465 Porto, Portugal e-mail: [email protected] A. C. Azevedo e-mail: [email protected] © The Author(s), under exclusive license to Springer Nature Switzerland AG 2021 J. M. P. Q. Delgado (ed.), Case Studies of Building Rehabilitation and Design, Building Pathology and Rehabilitation 19, https://doi.org/10.1007/978-3-030-71237-2_5

71

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Keywords Acoustics · Performance · Acoustic performance · Computer simulation · Acoustic quality

1 Introduction In urban areas and in large cities, numerous pollution problems have negative impacts on both the environment and people’s health. Noise pollution is one of the problems that have been treated with greater concern by society, due to the fact that it has already been proven, including by the United Nations, how much the issue of environmental acoustics can harm the well-being and comfort of the population, and how much excessive exposure to excessive sound levels bring from harm to health. In this sense, the technical environment and even the business environment have been consolidated, that the acoustic quality of an environment is a determining factor to promote better use and occupation of environments. In Brazil, we first considered the standardization aiming at the acoustic comfort of the population, where the issue of noise, measurement and service conditions at acceptable levels in the communities was first considered, according to the type of inhabited area and the activity performed in each environment, through, respectively, the standards NBR 10151 (2019) and NBR 10152 (2017), which emerged in 1987, respectively, and recently updated. The development of the construction sector, however, showed the need for standardization with regard to the performance of housing buildings (Tutikian 2017). This performance aims to improve the conditions of use of buildings, giving it a certain quality that can be measured. In this context, NBR 15575 (2013) emerged, which began to be studied in 2007, but only in 2013 came into force, with the purpose of establishing qualitative and quantitative requirements for the performance of the building as a whole, envisioning from the issue of structural safety to the care of use and operation of the building to ensure its building functioning. Among these requirements, acoustic performance represents the achievement of attenuation of the transmission of sound energy between environments. Thus, in the reach of good performance, sound insulation between environments, both in relation to air noise and impact noise, appears as a condition of extreme importance for the use of the building, since this requirement relates the quality to the comfort and privacy required by users. However, comfort and performance, although different concepts, complement each other. Comfort aims at achieving the harmonious sound level, within the limit of the tolerable, which involves objective and subjective definitions; performance aims at sound insulation, i.e. the significant reduction of the passage of sound from one environment to another, which guarantees the expectation of quality of the indwelling. Neto (2009) demonstrates that the comfort assessment complements the performance evaluation, mainly due to the difference between the two concepts, although

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one depends on the other. And concludes, in his research, that acoustic comfort in buildings is closely related to speech intelligibility and not only to partition bedroom. It is a fact that oral/verbal communication is recognized as a fundamental requirement in any human society, and exploring sound bedroom is presented as a device to preserve this communication within the environments, ensuring a lower intelligibility of speech between environments. The interference in oral communication not only harms the coexistence in society, but also disturbs professional, educational and even domestic activities. In relation to the discomfort caused by the excess of unpleasant sounds, this goes from simple irritability, to simple physiological reactions and long-term causes more serious damage to health. To understand the limits of physiological reactions correlated to noise levels present in the environment, Souza (2016) classifies these noises into three categories, which he calls as healthy acoustic environments, within which is the limit of sleep quality and acoustic comfort (between 30 and 50 dB), tolerable acoustic environments, where the so-called light stress (55 dB) begins., which are those in which the noise level is in the transition of civilized and educated speech (55–65 dB), and finally unhealthy acoustic environments, a classification that encompasses noise levels that begin to cause hearing damage (70 dB). This understanding of noise levels and the discussion of the damage that the lack of acoustic quality in the building causes users, raises the increasing need for a control and limitation of exposure to environmental noise, making good acoustic insulation establish itself as the main tool for improving this quality, contributing to the reduction of noise pollution and remodelling, therefore, the planning of constructive decisions. In this scenario, NBR 15575 (2013) simply called the performance standard, arrives to objectively define the maximum noise levels and the limits of classification regarding the expected behaviour of the housing building, not in order to guarantee acoustic comfort, but envisioning the minimization of transmission of external noise to the interior of the environments, allowing the minimum necessary quality of oral communication, quiet ness and privacy, requirements requested by the users. However, applying the performance standard has not been an easy task for everyone involved in the construction process. The change of construction processes implemented and already consolidated involves technological remodelling, readaptations and adjustments in construction systems used for years, new project decisions and improvement of materials employed, jointly seeking the previously defined performance. The standard also brings the methodology applied to measure this performance in the field, but even before the execution of the work, builders, designers and manufacturers have sought remodelling of their processes to ensure the execution of the quality that the standard requires. Nesse sentido, o uso da tecnologia de simulação computacional favorece um ambiente pré obra de avaliação dos sistemas construtivos e decisões projetuais adotadas para a edificação, permitindo adaptações e mudanças com a finalidade de avaliação do potencial acústico antes mesmo da execução da obra propriamente.

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Research from several scientific institutions, such as those carried out by UNB (Santos Filho et al. 2017), UNICAMP (Takahasi 2016), IFGO (Costa and Oliveira 2016), USP (Carvalho 2015), UFSCar (Giunta 2013), UFSM (Marros 2011; Pinto 2011), UFPR (Ferreira and Zannin 2007; Ferreira 2004) and UNISINOS (Siqueira 2018) have sought to prove that computer simulation programs are important tools for the calculation of performance prediction models, through which designers have the possibility to readapt the sizing of systems, the choice of materials and solutions during the design phase. The difference between each of the studies lies in the particularity of the program used, in the database considered, in the function of using the studied environment, etc., but the basis of all studies is to find a correlation between values measured in the field and simulated values in the conceptual phase, to prove the efficiency of the simulations. And if, the hypothesis that the computational simulation of the acoustic indexes of an enterprise is compatible with field measurement, this process in the pre-work phase allows, above all, the reduction of the costs of adaptations in the post-work, since, in the project phase, it is possible to adjust the solutions to ensure the minimum levels required in the standard, avoiding rework and higher costs that happen in post-work adaptations, when the measured performance is not expected. In this work, we will try to comparatively evaluate the values of sound insulation to air noise in internal vertical partition systems (SVVI), measured in in-field tests according to the methodology determined in the performance standard and described by ISO 16283-2 (2018), of 14 case studies, with the sound insulation values resulting from the computational simulation of the same enterprises, through the three-dimensional modelling of the enterprises in two programs used together, Insul and SONarchitect, allowing an evaluation of acoustic behaviour according to the geometry of the environment and the construction system adopted by the works, and prove the efficiency of the computational simulation that has been used by the local market. In parallel, it will be studied whether the simulation will always present values higher than field measurements, since in the simulation it is understood that the acoustic calculation is performed in a perfect model, as highlighted by Carvalho (2015), that is, in an environment free of imperfections, constructive failures or field influences, or otherwise, if there is any variation or tendency opposite to this hypothesis.

1.1 Justification Given the scenario of increasing search for quality of buildings, meeting the performance standard has been a challenge on the part of those involved in this process. The losses and, consequently, the costs of adaptations in the post-work or post-occupation phase are infinitely higher than adaptations that can be implemented during the design phase.

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The use of computer simulation has been the means by which it is intended to predict the acoustic behaviour that will be measured in the work, which ensures the quality standardized and sought by the user who acquires a residential building from 2013. Therefore, proving that the use of computer simulations is an efficient tool will allow us to find the path that will demystify the quality that the performance standard requires of housing buildings, demonstrating, on the one hand, the viability of this tool and, on the other, the interferences they may incur, which can lead to controversial and or illegitimate results.

1.2 Objectives 1.2.1

Main Objective

This work has as general objective to analyse the efficiency of computational simulations of acoustic performance of the building and its systems, currently used in the design phase of housing developments, through the use of the Programs SONarchitect ISO and INSUL. The specific objectives of this work are: – Collect data from field tests carried out in 14 residential developments, objects of the case study, for internal vertical partitions; – Perform computational simulations of the acoustic performance expected in the field of these enterprises raised in internal vertical partition systems (SVVI); – Compare the values of the 75 data collected from the in-field tests, related to air noise in internal vertical partition systems (SVVI); – Analyse the comparative data found, i.e. measured values versus simulated values; – Evaluate the influence of modelling procedures on the assertiveness of the values found in the simulations; – Evaluate whether computational simulation represents reliability for the acoustic performance criteria required normatively, based on the results of the case studies used.

1.3 Methodology and Limitations The methodology adopted in this research started from the survey of field measurement data from 14 case studies, performed through the performance evaluation methodology provided by NBR 15575 (2013) standard and ISO 16283-2 (2018), and continued with the numerical simulation of the acoustic behavior of such enterprises. The comparison of the simulation and field measurement data and the discussions of the variations found.

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The limitations found in the course of this work were in relation to the uncertainty of execution compliance in construction details in some of the case studies, the impossibility of confirming some measurements due to the fact that the properties are already occupied and the small amount of the sample for each type of element provided for in the standard. The input data of the simulation that were to faithfully reproduce the executive system used, generated some doubts in some enterprises that did not clearly present constructive details in their specifications, which made it difficult to evaluate the whole sample as a whole, because inaccurate data would certainly result in discrepant values in the simulation. Although comparative evaluations were made in 293 data, some studies did not include all types of separation elements mentioned in the standard. Other than that, the field measurements had been carried out in 2017 and 2018, in the delivery phase of these works, therefore, there was no way to return to the projects and confirm some measurements, the values of which presented some doubt for the discrepancy with others of similar situations. These limitations, if they could have been released in time, would allow a more homogeneous mass of data and greater assertiveness in the final analysis.

2 Theory Acoustics is the science that studies sound and the ripple phenomena related to its propagation. Classified as science, it means that it is a set of observations, explanations and systematized evidence. Almeida et al. (2006) and Prado Filho (2019) define acoustics as the branch of knowledge of physics in which the phenomena of emission, propagation and perception of sound waves are studied, an area very present in people’s day-to-day lives, from the appreciation of songs to the moments of conversation between friends. Souza et al. (2013) explain acoustics as technical knowledge of sound, a physical phenomenon capable of propagating and thus qualifying a favorable or unfavorable environment regarding acoustic comfort. In architecture, acoustic study is a tool used to achieve the quality of environments. Some spaces excel in sound quality, so that the architectural characteristics of these environments directly influence the acoustic performance required, as Takahashi and Bertoli (2012) point out when relating acoustic attributes to architectural characteristics in concert halls, where the sound is sought to propagate evenly throughout the environment, maintaining original characteristics and form. In addition, with the study of acoustics, it is intended to safeguard the environmental quality of society at the level of the noise component […] and contribute to the preservation of the quiet conditions necessary for the enjoyment of the inhabited space, with a level of comfort compatible with the type of activity developed (Almeida et al. 2006).

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According to Souza et al. (2013, since antiquity the projectvalue given to acoustics is identified. The authors note that even though visual effects are the focus of the conception of Greek, Roman and Renaissance theatres, the acoustic effect was achieved, although it is not proven that it was intentional. In the scientific field, the value of the acoustics of the environments was only more valued in the twentieth century, when studies began to deal with acoustic problems, specifically the volume, materials and reverberation time of the environments, in order to ensure that the function “listening” was contemplated, achieving what the authors call “acoustic comfort”. Takahashi and Bertoli (2012) add that, in each period of history, musical pieces were created to reflect the desire of composers to obtain a sound magnitude of their works, from the Baroque, Gothic, classical, popular and contemporary period, each performed in types of spaces of specific characteristics, both for sound quality and for noise control. Studying acoustics in the construction scan stakes not only means a matter of acoustic conditioning of the environment, but the possibility of promoting improvement in environmental quality, reduction or noise control and consequently promoting the performance of buildings.

2.1 Sound Versus Noise Before defining sound as to its origin and characterization in the field of physics, it is important to distinguish sound and noise, since both have a direct relationship with sound perception in the sensory domain. Sound can be defined as a mechanical wave that can vibrate through various means, not every sound produces pleasant sensations and this theory coincides with that advocated by Méndez (1994) that the “sound” would be the acoustic signals that produce sensations pleasing to the receiver and “noise” those that cause unpleasant sensations, that is, uncomfortable. The same concept also defined by Bistafa (2011) that relates sound to a vibration with a certain positive connotation and noise as sound without harmony, with a certain negative charge. Therefore, sound and noise are not synonymous. Although the two are related to the physical structure of a wave and the sound sensation or human perception, which can be abstract, the concept of noise is associated with the production of unpleasant and undesirable sound, or physically to an aperiodic acoustic signal, defended by Oliveira (2006), Fernandes (2005) and other authors. From the point of view of Fernandes (2005), the concept of noise, as an undesirable sound, is somewhat ambiguous, because noise is presented either as a subjective definition, in which it is related to unpleasant auditory sensation, or as a measurable physical definition where it is characterized as every non-periodic acoustic phenomenon, absent from defined harmonic components. The concept of sound as the sensation produced in the auditory system, through the vibration of air particles, brought by Bistafa (2011), appears as the basis of

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the acoustic study of several authors. However, the author clarifies that not every structure that vibrates produces sound, even because the vibration of sound waves may or may not be detectable by the human ear. The perceptible sound vibrations will be presented in the conceptualization of the physical elements of sound, such as sound pressure and frequency. The author also ponders the sensations produced by the sounds, highlighting that some of these can be qualified as noise, due to being considered unpleasant, although they transmit useful information, such as those produced by the speed indication beeps of a vehicle or those that indicate the operation of an electronic equipment or even the clicks of a hard drive performing a task, or the beeps indicative of a cardiac monitoring device, among other. Prado Filho (2019) adds by highlighting that sounds can still be classified as musical sounds, and this classification is included in the human voice, or as noises. He explains that musical sound is the result of periodic or approximately periodic sound wave overlap, while noise is the result of the superposition of random vibratory movements of different frequencies, which do not establish a relationship between each other, not periodic, brief and that may present rough physical changes in their characterization. Sound sensation of aesthetic or informative content for the listener is the definition of sound, and the opposite of this is designated as noise by Almeida et al. (2006). In practice, this conceptualization relativizes the sound sensation, because the same situation can be considered sound or noise as a function of the listener, as illustrated in Fig. 1.

Fig. 1 Difference between sound and noise (Subjective definition as a function of the listener)

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It is concluded, therefore, that the question of the difference between sound and noise, although physically defined according to the periodicity of waves, may be relative, due to the physiological difference between people and thus reveals the degree of subjectivity when talking about acoustic comfort. For this reason, the degree of discomfort cannot be scientifically measured, although the minimum levels of comfort can be defined and measured, including normalized, according to criteria in NBR 10151 (2019) and 10152 (2017). Thus, sound measurements allow to detect when sounds cause harm to people, thus establishing itself as a powerful diagnostic tool in noise control programs and, consequently, of improving people’s quality of life.

2.2 Physical Concepts of Acoustic Science Bruel and Kjaer (1984) reports that sound is something so common in people’s lives that all its functions and particularities are rarely perceived, but when it becomes a problem of conflict when it is spread and perceived that they may interfere in the quality and comfort of the environments. However, not all sounds are pleasant. Unpleasant or undesirable, which does not always mean that they are loud sounds, are called noises; and to these one can associate the sound of a creaking floor, a plane taking off, a dripping faucet, a functioning electronic equipment, a scratch on a metal, a vibrating household equipment, a walking neighbor or a child playing in an apartment on an upper floor, etc. Measuring sound brings numerous benefits, since it is through this data that it seeks to improve the acoustics of the environments, allowing accurate and scientific analysis of inconvenient sounds, that is, noises. As Bezerra et al. (2018) reports, the simple crude reading of values measured in acoustic tests does not reveal the complexity that is in the interactions of sound waves, from emission to transmission, in addition to what occurs in the encounter of these waves with the elements and with people in the environments. The understanding of the fundamental concepts about the nature of sound, the physical aspects, properties of the sound wave and differentiation of the concepts of sound and noise, comfort and acoustic performance, serve as a support for the understanding of the acoustic bedroom parameters requested by the Performance Standard that deals with the essence of this work.

2.2.1

Sound–Physical Aspects and Sound Perception

The study of sound presupposes physical, biological and psychic concepts, since the relationship of the theme with people involves characterization and measurable elements, in addition to physiological and psychic sensations in the sensory field that involve subjective definitions of comfort.

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The concept of acoustic comfort, which presupposes a certain degree of subjectivity to sound perception, since it has a close relationship with the issue of discomfort. In this section will be addressed, generically, the physical aspects related to the nature of sound constitution, propagation and transmission, discussing the main characteristics of what constitutes the classical acoustics of sound purity. Thus, to better understand the characterization of what is sound, Souza (2016), supported by the study of Everest (2001), synthesizes sound as a process that presents physical aspects, related to wave behavior; and physiological aspects, related to the characteristics of audibility and intelligibility of the receptor, in this case, the human. Souza (2016) showed that sound has cause and effect: – vibration, related to the physical aspects of sound waves, as disturbances in a medium consisting of elasticity and inertia; – and physiological or psychophysical perception or sensation, which is the result of nerve impulse stimulation to the brain. From the scientific field, sound is characterized as a result of the vibrations of elastic bodies, vibrations that are verified at defined frequency limits, which propagate as mechanical waves through a fluid or solid medium. Several authors and researchers conceptualize sound in their works, relating it to its physical characteristics and human sensory perception. Cornacchia (2009) and Santana (2016), based on the concepts of Bistafa (2011), define sound as the sensation perceived by the human ear, resulting from the variation of static pressure caused by a medium in vibration, generating sound waves, emphasizing that only a range of fluctuations of this pressure variation is noticeable by the human ear, thus limiting the sound to a range of values that highlight the authors as “audible”. Ribas (2013) highlights that sound is generated by the variation of pressure or velocity of molecules in a compressible medium that results in energy transmission in the form of waves, and highlights that perception in pleasant sounds or not is a subjective factor that varies from one person to another. Souza et al. (2013) highlight that sound vibrations originate from the vibration of an object, which causes the vibration of particles from the medium. Prado Filho (2019) complements that sound sources produce vibrations that cause pressure waves that propagate and reach the human ear, causing the eardrum to vibrate and send impulses to the brain, resulting in what is meant by sound sensation. Even varying some details, the common definition among the authors is that sound, therefore, is the result of vibrations that propagate through impulses, caused in the middle, around the sound body; impulses that cause transient deformations that move longitudinally according to the pressure created (Costa 2003). The vibration of the vocal cords that produces the human voice and the touch of a note on a musical instrument cause the air particles to oscillate through the open space until they are reached by the human ear, but it is very common to mistakenly restrict the means by which this vibration occurs only in the air way. In this sense, Souza et al. (2013) clarify that sound waves overcome physical barriers, vibrating their particles, until they are perceived soon after such barriers. This said, proves that

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the propagation of sound waves is not exclusively by vibration in the air, because the sound can be perceived between environments that have some separation obstacle, such as a wall or a slab. The vibration movement of a particle causes the oscillation of neighboring particles, one by one, and no matter how small that vibration, cause sound to be reached from one environment to another. The intensity with which the sound wave will reach the other environment will depend on the composition of the separator element, that is, the materials adopted in this element, and the shape and volume of the environment. In this case, when transpose barriers, partition is considered as a vibrant medium, illustrated in Fig. 2. Thus, it is concluded that sound can be understood as a result of any variation in pressure in air, water or other medium, except in the vacuum, through which waves propagate to perception by the human ear, as Prado Filho (2019) also points out. In other words, the sound wave results from a vibratory disturbance in a medium that is in equilibrium, whether fluid or solid, which propagates mechanically throughout it. Sound waves have propagation parallel to the vibration by which they were generated and particles repeatedly undergo compression and distension, in cycles where the vibration of a particle causes the vibration of the neighboring particle and so on. Figure 3 provides a didactic illustration of how this sound vibra-

Fig. 2 Sound and vibrant medium (by air and building element)

Fig. 3 Vibration of a particle and neighboring particles

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tion propagates, as well as in a sequence of pendulums in which the initial vibration causes successive vibrations, without the transport of point-to-point material, there is only energy transfer. During the wave movement, only energy is transferred, because the particles remain in equilibrium in the zones of compression and rarefaction/distension of wave displacement (Almeida et al. 2006). It is clearly perceived that sound pressure particles do not move, but vibrate around an axis or center of equilibrium, thus transmitting the sound energy. The sound wave carries a vibratory disturbance throughout the space that can be characterized as a pressure variation (Silva Junior 2012). This disturbance of balance can be originated in several ways, either by the difference of density, velocity or temperature, thus resulting in the variation of pressure in the wave propagation medium as described by Almeida et al. (2006) and Silva Junior (2012). This pressure variation can be understood by Eq. (1). P(t) = ρ(t) + ρ0

(1)

where P(t) is the total pressure; ρ(t) is the pressão sonora; and ρ 0 is the atmospheric pressure. The sound pressure p(t) corresponds to the difference, for a given instant of time, between the total pressure and the pressure of the medium in equilibrium, in this case the atmospheric pressure (Almeida et al. 2006). The relative zero pressure is tied to the atmospheric pressure of 105 Pa, which indicates, at this point, the means of equilibrium. The magnitude of the pressure exerted on the atmosphere determines the maximum displacement of the particle in relation to its center of equilibrium, called amplitude (Souza et al. 2013). The wave amplitude is exactly the maximum distance between the equilibrium pressure and the crest or valley of a wave. The distance between two successive vibrations, that is, the distance that sound is traveling in each vibration cycle, allows characterizing the behavior of the sound before the surfaces, revealing whether the surface has dimensions appropriate to the desired sound distribution (Souza et al. 2013). The name of the wavelength is given to the distance traveled between each complete cycle of vibration, that is, the physical distance between one peak and another or between equivalent states of pressure, such as in two consecutive states of compression or two states of rarefaction, as shown in Fig. 9. The definition of length, from the calculation of its variables, represents the relationship between velocity and sound frequency, as observed in Eq. (2). λ=

c f

(2)

where λ is the wavelength; c is the speed of sound propagation; and f is the Frequency. With the wavelength and propagation speed, you can calculate the time at which each wave travels a distance equivalent to the wavelength. This magnitude is called period (T), whose inverse is the number of times a complete vibration cycle occurs

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per unit of time, called frequency (f). That is, the name of sound frequency is given to the number of pressure variations, or complete vibrations performed by a sound wave in a second, whose measurement is cycles per second or Hertz–Hz (Costa 2003). The correlation between these two variables, length and wave frequency, is inversely proportional, so that at first it is verified that the higher the frequency, the lower the wavelength. Souza et al. (2013) and Fernandes (2005) conceptualize frequency as the number of oscillations of the vibratory movement of sound for a given reference, that is, the number of times a particle completes a cycle of compression and rarefaction in a given time interval, around its equilibrium center. Other elements of the sound wave, such as height, timbre and intensity are qualities that characterize it physically. The height of the sound is related to the sequence of sound vibrations, with the number of oscillations, that is, with the frequency (Costa 2003). The height of the sound refers to the recorded sound or high-pitched sound, according to the behavior of the sound waves as to their frequency. Bass sounds are those whose frequency is lower, that is, when wave oscillations occur slowly, are the low sounds; and high sounds, called loud, are those whose vibrations are fast, which have the highest frequency. This conceptualization of sound height is also related to the wavelength, because the slow frequencies are the ones with the lowest oscillations per unit of time and, therefore, longer length. The timbre is related to the harmonic composition of the sound wave (Costa 2003), to the way the frequencies combine. This characteristic of the wave allows identifying the origin of sound, that is, it allows the human ear to distinguish sounds of the same frequency and amplitude, but emitted by different sources, such as the sound emitted by people or musical instruments. The intensity of the sound is related to the amplitude of the sound wave, which characterizes the pressure variation of the medium in which it is propagated (Costa 2003), or to the amount of energy contained in the vibratory motion (Fernandes 2005). The measurement of sound intensity or energy intensity is performed by means of sound power, propagated by surface unit, expressed in W/m2 . Considering only direct sound, without barriers or interference, and that the wave propagates outfieldly, therefore, the intensity of the sound drops as it moves away from the source, which is the reason for the increase in the distribution area of sound energy. This said, differentiated the concepts of height and sound intensity, it is clear to understand that when talking about increasing a sound, or the volume of a sound, it is intended to increase its intensity and not its height. However, in so that a person can hear a sound, it is not enough just that the sound vibrations are within the range of audible frequencies, explained below. People have a different sensitivity to the various frequencies, but within the audible range there is a threshold that is given by the variation of the sound wave pressure (Prado Filho 2019). Souza et al. (2013) clarify that the power required to produce a sound is very small, and that the minimum perception of the human ear, for healthy people, is in the order of 10−12 W, so the variation of air pressure required for audibility is also very small, in the order of 2 × 10−5 N/m2 , equivalent to 0.00002 Pa.

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Fig. 4 Range of audible frequencies for the standard individual

However, not all sound vibrations are audible by man. For this reason, the threshold of human hearing is related to the lower intensity of the distinguishable sound, and the upper limit corresponding to the pressure from which the sound intensity causes pain, called pain limit. Thus, the pressure range that causes auditory sensation, ranges from 0.00002 to 200 N/m2 (Prado Filho 2019; Saliba 2018). In relation to frequencies, the line of reasoning is the same, being perceptible by human hearing, under normal conditions, the sounds whose frequencies are in the range of 20–20,000 Hz (Gerges 2000; Almeida et al. 2006; Bistafa 2011; Saliba 2018), characterized as the audible range of frequencies, below which are designated the infra frequencies or infrassons and above 20,000 Hz ultra frequencies or ultrasounds, as illustrated in Fig. 4. Quoting some audible frequencies to take as a reference: the note of a piano varies from a frequency of 27.5 Hz, relative to the lowest note, to the frequency of 4,186 Hz, in the highest note. The minimum intensity perceived by the human ear, in the pressure unit adopted by the International System–SI, the pascoal (Pa), corresponds to 20 μPa, and the upper limit, called the pain threshold, corresponds to the intensity of 100 Pa. To facilitate acoustic studies, the Bel unit scale (B) and later the Decibel (dB) unit scale were created to identify the sound intensity level (SIL) and sound pressure level (SPL), the latter, the most common parameter for measuring a sound signal (Oliveira 2006). This scale was created based on an international reference value of 10−12 W/m2 , which approaches the minimum audible intensity at 1,000 Hz, transforming this reference value into a starting point of the new scale, i.e. 0 dB (zero decibels) (Souza et al. 2013). The decibel scale was created because of the complexity of the measurement in Pascal (Pa). The human ear, under normal conditions, can distinguish pressure variations from a minimum value in the range of 20 millionths of a pascal, which is a factor 5 billion times lower than the normal atmospheric pressure of 1 kg/cm2 . This variation of 20 μPa is so small that the decibel scale was created from this limit of

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human hearing to be the starting point or reference pressure, i.e. 20 μPa equivalent to 0 dB. This transformation, both of the sound intensity level (SIL) and of the sound pressure level (SPL), was defined as a logarithmic relationship between the measured and reference values considered, according to Eqs. (3) and (4), in order to have integer values on the decibel scale. S I L (d B) = 10 log

I I0

(3)

where SIL is the sound intensity level; I is the sound intensity in W/m2 ; and I 0 is the reference sound intensity = 10−12 W/m2 . S P L (d B) = 20 log

p P0

(4)

where SPL is the sound pressure level; P is the sound pressure in Pa; and P0 is the reference sound pressure = 2 × 10−5 Pa. Several authors made considerations about the audible zone and pain limits, such as Everest (2001), Costa (2003), Fernandes (2005), Oliveira (2006), Cornacchia (2009), Souza et al. (2013), Santana (2016) and others, relating the auditory sensation to the perception of sound within an amplitude of the fluctuation of the range of sound pressure and frequency variation compatible with the hearing limits of the human auditory organ. Everest (2001) represents the audible area of the human ear between two boundary curves: (a) the hearing limit that outlines the lowest level sounds that the ear can detect, and (b) the pain threshold area at the upper end, noting that all our auditory experiences occur within this audible area, i.e. between the curves. Table 1 presents some correspondences of pressure values, intensity and sound pressure level of some noise sources and Fig. 5 shows the correlation between the sound pressure scale in μPa and the decibel dB scale, with variations between 20 and 200,000,000 μPa, corresponding to the range of 0 dB to approximately 140 dB, highlighting that the pain threshold at the pressure of 100 Pa corresponds to the sound pressure level of 134 dB.

2.2.2

Sound Propagation

The propagation of sound in the air is similar to the waves in the water, whose oscillation transmitted particle by particle, cause the waves to spread evenly spherically in all directions, decreasing in amplitude as they distance themselves from the source, as cited in the physical characterization of the sound wave. Souza et al. (2013) and the publication of Bruel and Kjaer (1984), highlight that the propagation of sound in the air, when the distance is doubled, causes the amplitude

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Table 1 Pressure, intensity and sound pressure level of some noise sources Sound pressure (Pa)

Sound intensity (W/m2 )

Sound pressure level (dB)

Noise sources

200 100

100

140

Firing a firearm

25.1

134

Pain threshold

63.2

10

130

Jet taking off Fireworks

20

1

120

Car horn

6.32

0.1

110

Beat-stake amplified rock set

2.0

0.01

100

0.02

0.000001

60

Normal voice talk

0.0006

0.000000001

30

Bass violin

0.0002

0.0000000001

20

Rural Quiet environment

0.00002

0.000000000001

0

Jackhammer

Hearing threshold

to decrease proportionally in half, at the ratio of 6 dB, so if the distance to the sound source goes from 1 to 2 m, the sound pressure level will decrease by 6 dB. This situation only occurs in the free field condition, where propagation is spherical and barrier-free, which would be the so-called ideal situation, when there are no objects that reflect or block this propagation. However, what we have on the field are situations where obstacles/barriers delimit environments in which there are sound sources propagating waves. Neto (2006) clarifies that the propagation of sound occurs in a spherical way from a generating source, but that these waves can be reflected, partially absorbed through the stops found in the environment and still transmitted. When this sound is perceived between environments separated by some surface, that is, when sound crosses an obstacle, the separation element acts as a vibrant medium. Thus, when the sound wave encounters an obstacle, the incident sound energy has the building of being divided into three parts, a reflected part, another part absorbed by the obstacle, degrading in the form of heat as punctuated Ribas (2013) and Costa (2003), and even a third part that is transmitted through the obstacle to the neighboring environment, with lower sound power, due to the attenuation that suffers from the parade or dividing element. From these properties, especially that of reflection of the incident energy on a surface, it is said that the behavior of sound resembles the behavior of light, because it is possible to perceive the incident sound energy directly together with the sound energy resulting from reflections that occur by surfaces. Thus, it is justified that the sound we hear is not limited only to the direct sound coming from the sound source, but to the composition of this with the sequence of reflections suffered by the sound wave in the environment, an effect known as reverberation.

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Fig. 5 Correlation between sound pressure (μPa) and sound pressure level (dB)

Gerges (2000) further clarifies that the building of sound reflection is related to the ability of solid bodies to return the sound wave in another direction to the medium; and that the absorption of sound energy is related to dissipation in thermal energy, inherent to the porous and/or fibrous surface of the elements, thus resulting in sound absorption coefficients specific to each type of material that makes up the separation element of the environments. Figure 6 illustrates the building of reflection and sound absorption in the environment, reinforcing between the two images that in an empty environment occur

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Fig. 6 Reflections and sound absorption in environments

multiple reflections, while in the busy environment, reflections become smaller due to the absorption that occurred by the furniture, in addition to that absorbed by the walls themselves.

2.2.3

Echo and Reverberation

Within the study of sound reflection, it is advisable to understand the concepts of echo and reverberation. Borges (2009) brings, didactically, a common example of the daily life of human sensations: the sensation of pain after a pin, where after removing the stimulus, that is, removed the pin, pain does not cease instantly, and relates this understanding as a key point in understanding the concepts of echo and reverberation. The author, physically explaining these concepts, admits that an auditory vibration, however short, translates an auditory sensation of one tenth of a second (0.1 s), a time interval known as remain. Thus, when the receiver receives a first sound direct from the sound source and receives a second sound, the result of reflection, before the end of the remanescence time of the first, a sound superposition occurs. The sensation is unique and longer, which is called reverberation of sound. The echo occurs when the reflected sound reaches the receiver with a delay greater than the remanescence time, that is, after one tenth of a second (0.1 s), and the sensation is of repetition of the sound, not of continuity. Knowing that the speed of propagation of sound in the air is in the order of 340 m/s, the distance at which the person must be from an obstacle so that he can hear the echo is from 17 m, illustrated in Fig. 7.

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Fig. 7 Echo and reverberation

Almeida et al. (2006) explain that when a sound source interrupts its emission inside a closed space, the component of the sound field relative to direct sound ceases at almost the same instant, but the component related to multiple reflections gradually decreases due to the degree of absorption and volume of space. This sound perception within the environment translates into an extension of the sound sensation, sometimes confused with the echo, but that it is the reverberation. The reverberation time, called t60 , t2 or simply TR is the time interval in which the sound takes to decay the sound pressure level by 60 dB after the emission through the sound source has ceased, but the sound does not cease soon after being produced, as it continues to be perceived for a few moments due to the gradual decay that is a function of the absorbent material in the environment and the multiple reflections, as punctuated by Cornachhia (2009), Almeida et al. (2006), Silva Junior (2012), etc., illustrated in Fig. 8. The sound decay will be faster the more absorbent the surfaces of the space surroundings (Almeida et al. 2006). RT can be obtained through mathematical equations and measurements with proper instrumentation (Zannin et al. 2005). The most widespread mathematical equation for the calculation of RT was developed by the American physicist Wallace Clement Sabine, a scientist considered the father of modern acoustics (Silva Junior 2012), to whom the concept of reverberation time of a space is due. Sabine obtained the relationship between reverberation time and the geometric parameters of an environment. Sabine’s equation (Eq. 5), as it

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Fig. 8 Illustration of reverberation time concept

became known, allows the calculating of reverberation time as a function of the free interior volume of the environment, the area of the surfaces and the sound absorption coefficient of the constituent material of these surfaces, to which some authors summarize in an area of equivalent sound absorption (Oliveira 2006; Almeida et al. 2006; Silva Júnior 2012; Zannin et al. 2005). TR =

0, 16 V 0, 16 V , TR = Σαnx Sn A

(5)

where TR is the reverberation time; V is the volume of the environment; α n is the sound absorption coefficient of materials; S n is the surface area; and A = Σα n x S n is the total absorption of the environment. The measurement of reverberation time is done following a determined methodology, in which a sound signal is generated, amplified until filling the entire room and then the signal is interrupted and the measurement of the time in which the sound takes to fall 60 dB. Reverberation time is the most used parameter for assessing interior acoustic quality, as it is possible for each type of environment to define recommended reverberation values depending on the use of the environment. An excess of reverberation causes confusion and lack of intelligibility, and on the other hand, the scarcity of reverberation makes the environment deaf, as Costa (2003) points out. The ideal acoustic conditions depend on the characteristics of the environment and the activities developed. This acoustic quality is extremely necessary in environments where greater purity of sound is sought, with less interference, that is, where clarity and intelligibility ensure clarity of the pronounced sounds, such as in classrooms, concert halls, theaters, cinemas, etc. Studies by Zannin et al. (2005), Oliveira (2006), Takahashi and Bertoli (2012) prove that each type of space must achieve an adequate reverberation time related to the activity performed in space and thus ensure the required acoustic quality. Almeida et al. (2006) highlight that the practical need to limit the reverberation time for each type of use to a range of values is the result of the type of changes caused in the interior sound field by this variation.

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However, according to more recent studies, mentioned by Prado Filho (2019), reverberation time is not the only indicator of the acoustic properties of the environments, since it is already reasonable to agree that other measurements, such as those of relative sound pressure levels, the ratios between initial energy and late energy, residual sound pressure levels, lateral energy fractions and other parameters, are new quantities necessary for a more complete evaluation of the acoustic quality of the environments, although reverberation remains a significant indicator.

2.2.4

Acoustic Transmission

In relation to the sound energy that penetrates the surface, as Ribas (2013) explains, part of this absorbed energy degrades into heat and another part is transmitted to the adjacent environment through irradiation. This sound energy reaches the adjacent environment with lower sound power due to the attenuation that occurs by the divisor element. Gerges (2000) communicatord that the transmitted sound energy is the result of what remains after the process of sound incidence on a given surface, that is, a portion left over after reflection and absorption of the incident sound, as shown in Fig. 9. Costa (2003) explains that this process of acoustic transmission can take place through three paths that are: 1.

through direct route, i.e. through the air and through the openings of the closing elements between the environments, such as doors, windows, ventilation grilles, gaps of the frames;

Fig. 9 Sound: transmitted part

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where 1 - Crack transfer; 2 - Transfer by vibrations of elements; 3 - Marginal transfer Fig. 10 Forms of sound transmission

2.

3.

indirectly, by means of adjacent elements, i.e. through the bordering surfaces of the enclosed environment, in this case the walls, floors, closed frames and other types of closures whose own insulation is insufficient; and through the pipes and ducts of the various construction facilities that pass through the enclosures, where vibrations are transmitted and add to the vibrations of use of such installations.

Thus, it is concluded that the portion of sound pressure transmitted from one environment to another can occur through different forms. These types of transmission are again described in the studies by Souza (2016) and Ferreira (2004), where the paths of direct transmission are presented, both through the cracks in the divisive elements, and through the vibration of the separation element between the environments, and the indirect transmission through the marginal elements, both walls and floor slabs, illustrated in Fig. 10. In addition to these means of transmission mentioned, some other studies have been done to prove that constructive failures in civil construction contribute to sound transmission, and consequently the deficit of sound insulation. Arizmendi (1980), Costa (2003), Souza (2016) and other researchers report that much of the acoustic energy transmitted through the separation between environments occurs exactly through constructive imperfections, be it joints, plumbing, miters, socket boxes, partial wedges etc. The inefficiency of the partitions, which compromises the watertightness of the environment, illustrated in Fig. 11, is, in general, caused by the failure or constructive inefficiency that becomes the easiest way to transmit acoustic energy between environments. Reinforcing that vibration transmission is the main cause of the phenomenon of acoustic transmission, Costa (2003) recalls that transmission is a very complex phenomenon, because it is still caused by refraction of the sound wave, in addition

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Fig. 11 Sound transmission due to lack of partition

to the absorption of energy through the pores of the constituent material of the walls, however the author points out that the energy transmitted by irradiation by vibration of the wall, in most cases it is higher than those caused by other causes, which is why studies on sound insulation limit considerations about vibration transmission. Lievens (2013) investigated the sources of sounds irradiated to the structure of the buildings, highlighting that typically all types of vibrational source used or installed in the buildings transmit sound energy. It is noteworthy that, in addition to the vibrations of typical use of occupants, the household equipment installed, both on the walls and floors of the buildings, are the vibrational sources that most impact the noise propagation. The creation of an acoustically pleasing environment is a theme that has been much sought and debated around the world, as Seddeq (2009) reports. In order to achieve, within an environment, a sound intensity compatible with human activities and, particularly, an intensity that is not harmful to the human ear, the author clarifies that the control of sound transmission with the use of different sound absorption techniques are the widespread strategies to obtain the acoustic attenuation effect, also said acoustic bedroom, aiming to achieve the required acoustically pleasing environment.

2.2.5

Acoustic Insulation

Sharland and Lord (1979) define insulation, whether thermal, electrical or audible, as the way to provide a barrier to an energy flow. Such a barrier, specifically sound energy, imposes a certain attenuation on the transmission of energy along the path of propagation, which is generally called sound bedroom. Insulation is a way to reduce the transmission of sound energy from one environment to another and, as Oliveira (2006) summarizes, sound insulation consists of preventing, or at least attenuating, the intensity of sound propagation between environments.

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Méndez et al. (1990) argued that the bedroom of a wall depends on the relationship between the incident energy and the transmitted energy, thus defining a sound transmission coefficient (τ) for each element type, expressed by Eq. (6). τ=

Et Ei

(6)

where τ is the sound transmission coefficient; E t is the transmitted energy; and E i is the incident energy. Ferreira (2004) clarifies that the term “sound proofing” is related to the level of loss of sound transmission of the set of building building building elements, such as walls, slabs, windows and doors, while the term “sound insulation” refers to the value of transmission loss of an isolated element. However, Souza et al. (2013) relate these terms isolation and insulation, respectively to the treatment of overhead noise and vibration/impact noises. Being insulation or sound insulation, the concept implies the existence of two spaces, one being the emitting space, which can be a closed environment or the outside environment, and a receiver space, in which the “sound” is perceived as “noise”. Therefore, Almeida et al (2006) establish two classifications in the analysis of an acoustic insulation problem. The first classification takes into account the location of the emitting space, or rather the source of the noise source. Thus, they highlight: – Sound insulation to sounds from outside (or ambient noise); – Sound insulation to sounds coming from an interior space to the building (or neighborhood noise). The second classification is established by the way in which the emission and propagation of noise is processed in the emitting space, since the transmission occurs by vibration of the building’s building building elements. For this classification as to the mode of noise generation and propagation, sound insulation is designated in: – Sound insulation to air-driving sounds; – Sound insulation to solid driving sounds or percussion sounds. These classifications, cited by Almeida et al. (2006), were taken to the performance standard as concepts worked for acoustic performance requirements. The insulation promoted by a surface, as an acoustic barrier, depends on the mass of its structure (Souza et al. 2013), in addition to its watertightness to sound propagation and the damping capacity of sound waves by the constituent material of the element. This watertightness is translated into the elimination of any openings that serve as a leakage of sound energy, such as those of constructive failures, illustrated earlier in Fig. 11. The variation of sound pressure by which the building elements are subjected, causes them to vibrate and this vibration is mainly controlled by the surface mass. Souza et al. (2013) highlight that the mass of the material influences the efficiency of the acoustic isolation of the elements, however, the importance of the mass depends

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on the sound frequency, since for low frequency sounds, the mass increase is less efficient than for high frequency sounds. In this sense, it can be said that the study of sound isolation has a close relationship with the law of the masses. In addition, researchers also relate sound insulation to the absorption capacity of the constituent elements of the environment. Almeida et al. (2006) studied acoustics in buildings and concluded that, in addition to the decrease in the level of background noise, sound absorption is the phenomenon of greatest influence for the analysis of the interior acoustics of adjacent spaces. The authors stress that the sound absorption capacity, common to all materials and building elements, but with particular indexes for each type of element, should be considered in acoustic attenuation solutions as a rule of good practice to be specified in the dividing settings of the environments. Souza et al. (2013) also highlight that, while an insulating material promotes the reduction of the sound level transmitted from one environment to another, the absorbent material regulates the amount of sound absorption within the environment itself, thus contributing to the study of acoustic attenuation between environments.

2.2.6

Aerial Driving Sounds and Impact Sounds

Conceptually, the air-driving sounds include those originated in the air and continuously propagated in it, in addition to those generated in the air, but which cause the vibration of a surface, which in turn again causes the vibration of the air adjacent to its opposite face (Souza et al. 2013). Thus, when the emission and propagation of sound takes place through the vibration of the air contained in the space of the emitting space, at the request of a certain source, as in the case of a television set, or another source of sound production, in this case there is talk of air driving sounds. When the sounds are resulting from the vibration of solid elements by the direct action of the sound source, produced by a mechanical excitation applied in a short period of time directly in the structure (Ferreira 2004), there is talk of solid driving sounds or sounds of impact or percussion, such as the dragging of furniture on the floor, the steps on a slab, the fall of objects, the use of a hammer or drill in the fixing of furniture (Almeida et al. 2006). Lievens (2013) also highlights that the vibration of impact sounds are added to the vibrations of the service equipment installed in the buildings, typically the household equipment in the housing buildings. The vibrations of solids and impacts are transmitted directly on a structure and propagate through it, vibrating and radiating energy in the receiving environment (Ferreira 2004), causing the air vibration. This vibration is perceived while movement or friction is acting (Souza et al. 2013). Almeida et al. (2006) explain that the aerial conduction of sounds and noises are typical of the acoustic conditions of the spaces adjacent to the place of sound emission; while percussion sounds can come from more distant spaces, due to the propagation of sound waves by marginal elements, whose vibration is moving throughout the connection between the building elements (see Fig. 12).

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Fig. 12 Difference between aerial driving sounds and solid driving sounds at the level of noise generation and propagation

These rigid connections of the building elements cause the vibration generated by the excitation of the impact in a room to be transferred throughout the structure, propagating with great ease through the entire mesh that defines the spaces of use, establishing eventually intense sound fields in compartments reasonably distant from the place of origin of the vibration, it is difficult, often, to detect the emission site (Patricio 2005, 2010). For this reason, this type of sound may present greater potential for inthis than air driving sounds. Figure 13 illustrates how vibration of sounds and impact noises occurs. Thus, in addition to the direct form, these vibrations can travel long paths, distant from the source of sound production, through the rigid connections of the structure, being, therefore, transmitted indirectly to several floors.

Fig. 13 Transmission of impact noise and vibrations

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The irradiation of sound energy generated by vibrations is generally proportional to the size of the structure, however the mass law is not a satisfactory measure for these cases of impact sounds. This type of sound can be minimized by the uncoupling of the construction elements, that is, by the use of resilient materials, floating slabs or other solutions that favor the discontinuity of structures. Several studies have been done to seek better methods of isolating impact noise from the floor, and the use of floating floors has been the most effective in this area (Stewart and Craik 2000; Sipari 2002; Bistafa 2011; Tutikian et al. 2017; Schiavi 2018; Siqueira 2018; Na et al. 2019). In practice, it is important to highlight that sounds, whether those transmitted by air or those transmitted by solid route, require sound insulation solutions as a determining factor in improving the conditions that favor daily relationships between people, thus considering the minimization of discomfort caused by such transmission. Although the sounds of aerial driving and percussion may come from the exterior of the building, as illustrated in Fig. 14, the focus of this work is the isolation of the sounds transmitted by the internal stops that delimit the spaces, that is, by the internal vertical partitions and horizontal partitions of residential buildings, denominated by some authors as constructive elements of contour or marginal transmission. However, both for sounds of external origin, as well as for those originated internally in buildings, the analysis of sound waves involves their behavior in relation to the medium in which propagation occurs (Prado Filho 2019). Several complex phenomena involve this interaction of sound waves with the medium, and these

Fig. 14 Examples of aerial driving and percussion sounds sourced outside buildings

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acoustic interactions interfere with the comfort and performance of the elements and enclosures. Sound absorption, diffusion, diffraction, refraction, resonance, reflection and beat, in addition to reverberation, stand out, but the performance standard does not deal with these phenomena, because it focuses exclusively on acoustic attenuation, that is, in the isolation of the transmission of airborne and transmitted noises and noises, which is why all these concepts were not explored in this work, being conceptualized only the concept of reverberation, by the fact that, in the acoustic performance field measurements this phenomenon is considered as information leads to evaluate.

2.2.7

Environmental Noise

Noise is an important environmental issue, particularly in urban areas, affecting a large number of people. To date, most environmental noise assessments have been based on the nuisance it causes humans or the extent to which it disrupts various human activities (WHO 2011). Urban noise, which characterizes urban noise pollution, is considered a complex noise because it is composed of several secondary noises from various sources of activities. Noise pollution is mixed with urban life in cities and has an influence on the environment and on the quality of life of human beings (Arndt et al. 2010). There is an important concern with the level of ambient noise, especially because excessive noise or exposure can cause irreversible damage to the hearing aid, in addition to other damage involving mental health itself (Prado Filho 2019). Urbanization, economic growth and motorized transportation are some of the driving forces for exposure to environmental noise and health effects. WHO (2011) defines environmental noise as “noise emitted from all sources except industrial workplaces”. The European Union in Directive 2002/49/EC (OJEC 2002) already defined environmental noise as “unwanted or harmful external sound created by human activities, including noise from roads, railways, airports and industrial installations”. The settings complement each other, since noise characterizes undesirable sound. These external noises enter the buildings and often impair and even make impossible some human activities, whether work, study or even rest. With the expansion and disorderly growth of cities, accompanied by density, that is, the increase in population density, and consequently the growth of the flow of vehicles, excess noise began to affect society more and more (Radavelli and Paul 2015; Park and Lee 2017). According to Souza et al. (2013), external noises, in addition to causing acoustic problems in the urban environment, are still responsible for the discomforts in the internal environments of the buildings, because these noises are able to propagate to the interior through absorption and irradiation through the materials that make up the facades of the buildings. According to Ferreira (2004), prolonged exposure to noise, especially to highpotency and lasting environmental noises, can cause serious problems to people’s health, such as increased blood pressure, headache, insomnia, stress, irritability and

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other disorders. Prado Filho (2019) also adds that the psychic and somatic consequences include nervousness, shorty and others, as well as irreversible lesions and degeneration to the cells and nerve fibers of the hearing aid. According to a publication by the World Health Organization’s Regional Office of Europe (WHO 2011), the impacts of environmental noise on health are a growing concern among the general public of the European Union, which has been systematically reflected in public policy decisions, supported by several studies summarizing the evidence on the relationship between environmental noise and specific health effects, since the onset of diseases, as well as cognitive impairment, sleep disorders, tinnitus and annoyance of the population, the latter as a negative consequence to the physical, mental and social well-being of people. In this publication, who applies this exposure-response relationship and calculates the burden of the disease in terms of years of life lost, i.e. low health or disabilities, indicating that at least one million years of healthy life are lost each year due to environmental noise. Thus, noise pollution is considered not only an environmental nuisance, but also a threat to public health (WHO 2011). Noise pollution is treated as a problem that borders on the intolerable as Costa and Oliveira (2016) highlight, since the damage to health and the environment goes beyond personal issues causing serious damage to social, educational and professional activities. A problem debated by the WHO since 2003, when it was already debated that noise pollution was the type of pollution that affected the largest number of people in the world, second only to air and water pollution (Ferreira 2004). Environmental noise pollution has raised urban noise levels to levels that have compromised the environment and quality of life, showing that the construction systems that make up the facades of buildings should allow such acoustic performance to minimize this impact. According to Sales et al. (2018), the main source of noise in large cities is the traffic of vehicles, whether air, rail or road, and in their study a method for sound mapping is proposed, using measurements of local traffic, in order to assist the planning of the city and, therefore, serve as an object of consultation adesigners in the definition of the sound insulation necessary to minimize the transmission of incident noises that enter the interior of the buildings. Nardi (2008), Guedes and Bertoli (2014) and other studies report this problem of vehicular traffic noise as the main agent of noise pollution in urban areas. The sound mapping method is a fundamental tool for the study, diagnosis and management of the sound environment, simulating noise levels external to buildings, not only to comply with legislation in projects, but especially to allow builders to offer quality products to users. The acoustic map (or noise map) has as main objective the creation of visual representations of the environmental noise of a geographical area, and noise levels are represented in a similar way to topographic curves (Guedes and Bertoli 2014), with colors varying every 5 dB, giving conditions to the general public, urban planning and planning technicians and public policy makers to understand local acoustic quality and implement legislation, zoning and noise reduction plans (Nardi 2008).

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Mapping urban noise is still starting in Brazil, because such mapping has not been carried out systematically within cities, as Guedes and Bertoli (2014) explains. Only specific examples such as São Paulo, Fortaleza (see Fig. 15) and Recife have acoustic map initiatives, although this theme has been gaining continuous space in academic works. This reality of Brazil goes against what is seen in Europe, which has the mandatory sound cartography for urban agglomerates with more than 250,000 inhabitants, since the European Directive of 2002, and even before this obligation, some European cities already had their acoustic maps, such as Lisbon, whose noise map was published since the year 2000. The hard/indisputable evidence of the relationship of excessive exposure to noise with the harmful effects on the health of the population, supports the need for sound control in the environments, both internally and externally, and in the case of noise pollution resulting from environmental noises, especially to minimize the transmission of such noise from the outside to the interior of buildings.

Fig. 15 Excerpt of acoustic chart Fortaleza

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2.3 Building Performance With regard to the criteria for evaluating the acoustic behavior of a building, i.e. the expected quantitative indices (values), the NBR 15575 (2013) standard determines the following factors: 1. 2. 3. 4. 5. 6. 7.

Sound insulation of walls between environments–criteria for in-field tests; Sound insulation of walls between environments–criteria for laboratory tests; Insulation of facades and roofing–criteria for in-field tests; Insulation of facades–criteria for laboratory tests; Air noise insulation between floors and accessible covers; Insulation of impact noisefrom accessible floors and covers; Noise insulation caused by hydrosanitary equipment.

NBR 15575 translates these criteria as required minimum values, that is, it requires the guarantee of the minimum, although it brings a minimum to the higher level classification, passing through the intermediate performance condition, where for each type of environment are determined ranges of values within this classification. Tables 2, 3, 4, 5 and 6 presented below bring these ranges of values for each situation evaluated. For the internal vertical partition system, NBR 15575 (2013) determines the attendance to the minimum sound insulation performance between environments and presents recommendations regarding intermediate and superior performance, providing the range of standardized difference values of weighted level DnTW , which must be measured through the field tests by the Engineering Method, presented in Table 2. In the case of laboratory testing, the standard presents values with an increase of 5 dB, reason that the ideal laboratory conditions are superior to the field conditions, since the environmental conditions in the laboratory are carefully controlled and measured, with no interference from the field condition. These reference values, obtained in the laboratory, serve to guide manufacturers and designers, as highlighted in the scope of NBR 15575 (2013). Table 3 indicates these sound reduction values, Rw , used for the partitions between environments. However, it is custoy to attribute to the variation of geometry and mass of walls and constituent elements, the difficulty in mathematically predicting the acoustic bedroom of some elements, so that from works and research carried out by reputable entities in the technical-scientific field (IPT, Unicamp, SOBRAC, University of Coimbra), a reference table was created with values indicative of the sound reduction index, Rw , of some wall systems usually used in civil construction, reproduced in Table 8. Although they serve as a reference, these data should not be used as definitive for the types of systems mentioned, since the internal conformation of the elements, the shape of the septa, the absorption rate of the materials, the filling of the joints, the density of the mortar, internal damping and other specificities may vary the overall acoustic behavior of the system and, therefore, field tests reveal very different values from those indicated by Table 2.

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Table 2 Standardized weighted level difference between environments, DnT,w for in-field test– engineering method Element

DnT,w (dB)

Performance levela

Wall between autonomous housing units (tasling walls), in situations where there is no bedroom environment

40–44

M

45–49

I

≥ 50

S

45–49

M

50–55

I

≥ 55

S

Blind wall of dormitories between a housing unit and ordinary areas of eventual traffic, such as corridors and staircase on the pavements

40–44

M

45–49

I

≥ 50

S

Blind wall of living rooms and kitchens between a housing unit and ordinary areas of eventual traffic, such as corridors and staircase on the pavements

30–34

M

35–39

I

≥ 40

S

Wall between autonomous housing units (tumming walls), in case at least one of the environments is a bedroom

Blind wall between a housing unit and common areas of 45–49 permanence of people, leisure activities and sports activities 50–54 such as home theater, gyms, ballroom, games room, ≥ 55 bathrooms and collective dressing rooms, kitchens and collective laundries

M

Set of walls and doors of distinct units separated by the hall (DnT,w obtained between the units)

40–44

M

45–49

I

≥ 50

S

a M:

I S

minimum level/I: intermediate level/S: Superior level

For the performance levels in the external partitions, the recommendations brought must make the externally generated noise compatible and the sound intensity recorded inside the building. Considering external noises in the order of 55 to 60 dB(A), common in residential areas or small shopping centers, the acoustic insulation values stipulated in the standard, which are the criteria, aim to provide the building of reasonable performance conditions (CBIC 2013). The standard establishes minimum attenuation values in relation to external noise, called standardized difference of weighted level, D2m,nTw , according to the location of the dwelling within the sound context of its surroundings, which the standard cites as a noise class. That is, the standard establishes minimum values of sound insulation according to the noise of the place where the housing is inserted. It means that if there is little noise in the surroundings, the performance criterion of the system is less rigorous, and on the other hand, when the external environment is noisier, the acoustic performance of the building wrap (façade and roofing) should be more demanding in order to ensure minimal acoustic comfort (ProAcústica 2017a, b).

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Table 3 Weighted sound reduction index, Rw, of building components used in fences between environments Element

DnT,w (dB)

Performance levela

Wall between autonomous housing units (tasling walls), in situations where there is no bedroom environment

45–49

M

50–54

I

≥55

S

50–54

M

55–59

I

≥60

S

Wall between autonomous housing units (tumming walls), in case at least one of the environments is bedroom

Blind wall of bedrooms between a housing unit and ordinary 45–49 areas of eventual traffic, such as corridors and staircase on 50–54 the pavements ≥55

M

Blind wall of living rooms and kitchens between a housing unit and ordinary areas of eventual traffic, such as corridors and staircase on the pavements

35–39

M

40–44

I

≥45

S

I S

Blind wall between a housing unit and common areas of 50–54 permanence of people, leisure activities and sports activities 55–59 such as home theater, gyms, ballroom, games room, ≥60 bathrooms and collective dressing rooms, kitchens and collective laundries

M

Set of walls and doors of distinct units separated by the hall

45–49

M

50–54

I

≥55

S

a M:

I S

minimum level/I: intermediate level/S: Superior level

For this reason, the survey, characterization and acoustic classification of the surroundings in a judicious manner is of paramount importance, and although the performance standard does not establish an objective methodology for determining the noise class, it presents a table subjectively indicating such classes. Table 5 reproduces the noise classes with the respective minimum acoustic insulation required, only for the situation where there are dormitories, object of interest of NBR 15575, in addition to the limit values for intermediate and higher performance levels. For buildings located in areas with high noise levels, such as near airports, stadiums and sports event venues, highways, railways or very busy avenues of urban centers, the standard suggests the elaboration of specific studies and surveys of the surroundings of the building (CBIC 2013), which reinforces the importance of rigorous study of the characteristics of this environment. Acoustic measurements in the field allow characterizing the main sources of noise and, consequently, the calculation of sound propagation up to future facades. Other than this, the computer simulations and acoustic mapping, individual or city, make it possible to estimate preliminary the incident sound levels in the partitions, allowing the definition of the noise class, including for each façade of the building, thus allowing to predict the necessary

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Table 4 Values indicative of weighted sound reduction index for some wall systems, based on studies by IPT, Unicamp, SOBRAC, University of Coimbra Type of wall

Block width/ brick

Coating

Approximate mass

RW (dBA)

Hollow blocks of concrete

9 cm

Mortar 1.5 cm on each face

180 kg/m2

41

210 kg/m2

42

kg/m2

45

120 kg/m2

38

kg/m2

40

180 kg/m2

42

260 kg/m2

45

kg/m2

47

450 kg/m2

52

120 kg/m2

38

10 cm

240

kg/m2

45

12 cm

290 kg/m2

47

22 kg/m2

41

4 plates

44 kg/m2

45

4 plates + glass wool

46 kg/m2

49

11.5 cm 14 cm

Hollow ceramic blocks

9 cm 11.5 cm

230 Mortar 1.5 cm on each face

14 cm Solid bricks of baked claya

11 cm 15 cm

Mortar 2.0 cm on each face

11 + 11 cmb Solid walls of reinforced concrete

Drywall

a Values

5 cm

2 plates + glass wool

Uncoated

Uncoated

150

320

indicated by the University of Coimbra wall 11 + 11 cm, with internal space of 4 cm filled with rock wool blanket 70 kg/m3

b Double

Table 5 Minimum values and intermediate and higher limits of standardized weighted level difference promoted by the external partition of a bedroom, by noise classes Noise class House location

D2m,nT,w (dB) Performance levela

I

≥20

M

≥25

I

≥30

S

≥25

M

≥30

I

≥35

S

II

III

Housing located far from sources of intense noise of any natures.

Housing located in areas subject to noise situations not in class I and III

Housing subject to heavy noise of means of ≥30 transport and other natures, provided that in ≥35 accordance with the ≥40

M I S

Note 1 For external partition of rooms, kitchens, laundries and bathrooms, there are no specific requirements Note 2 In regions of airports, stadiums, sports event venues, highways and railways there is a need for specific studies a M: minimum level/I: intermediate level/S: Superiortop level

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Table 6 Sound reduction index, Rw , for external partitions Noise class House location

D2m,nT,w (dB) Performance levela

I

≥25

M

≥30

I

≥35

S

≥30

M

≥35

I

≥40

S

II

III

a M:

Housing located far from sources of intense noise of any natures.

Housing located in areas subject to noise situations not in class I and III

Housing subject to heavy noise of means of ≥35 transport and other natures, provided that in ≥40 accordance with the ≥45

M I S

minimum level/I: intermediate level/S: Superiortop level

insulation that guarantees the acceptable level of acoustic performance, specifically of the bedrooms. For in-field tests, the standardized difference of weighted level of the external partition, D2m,nTW , must meet the minimum levels listed in Table 5, mentioned above For laboratory tests, NBR 15575 (2013) presents values with an increase of 5 dB in relation to the reference values of the field tests, for the same reason indicated when the standard difference of sound level for internal partitions, that is, due to the conditions of contour and execution of the construction systems estimated in ideal condition in the laboratory, which does not occur in the field, function of the various variables that can interfere in the measurements, such as gaps and inefficient partitions of the frames, failures of rejointbetween walls and frames, adoption of dry joints in the masonry, failures in the encasements and other pathologies. Table 6 presents these values, which the standard calls the sound reduction index Rw .

3 Comparative Evaluation–Methodology 3.1 General Aspects In this work of comparative analysis of computational simulations and field measurements, the inverse path of the proposed flowchart illustrated in Fig. 45 was performed, i.e. the acoustic behaviors of projects whose field measurements had already been performed in the delivery phase of these works were simulated. With the simulation in the post-work phase, it was intended to verify whether the simulated performance values were compatible with the performance results measured in-field. Thus, the compatibility between the measured and simulated acoustic performance values was evaluated, based on the data contained in the field test reports

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and the data calculated after the result of the computational modeling of the selected sample properties. As the scope of this work is restricted to the analysis of sound insulation of internal vertical partition systems (SVVI), not including in the present study the analysis of sound insulation data of external vertical partitions (SVVE-façades), although in the field reports of the properties contained such results. The methodology applied for the comparative evaluation of field data with the data from the computational simulations was developed following 8 steps listed below: 1. 2. 3. 4. 5. 6.

7. 8.

selection of residential properties with measurements made, called the selection phase of the case-studies; tabulation of the values obtained by in-field tests; analysis of the results of field trials; preparation of architectural design for simulations, through AutoCAD software; composition of materials and building elements in specific soundproofing software–Insul 9.0; modeling the building and calculating the overall sound reduction through the computational simulation of the building as a whole through soundproof calculation software–Sonarchitect ISO Professional; tabulation and analysis of the results obtained in the computer simulation; comparative evaluation of field values versus simulation values.

3.2 Experimental Campaign and Numerical Simulation 3.2.1

Selection of the Case Studies

It was selected 14 residential buildings, of which 8 used masonry of ceramic blocks as an internal partition system, 1 used concrete block masonry and 5 used internal solid concrete partitions. In relation to the type of slab, except for the buildings whose walls are solid concrete and, therefore, the slabs accompanied the type of construction system, using solid concrete slabs with a thickness of 10 cm; the other properties used ribbed slab, also called alveolar slab, varying the thickness of solid concrete covers between 5 and 7 cm. Acronyms were adopted to identify the type of construction system of the internal fences as well as the slabs of the selected properties, to facilitate further analysis. For ceramic block partitions, the acronym BCE was adopted, for concrete block partitions, the acronym BCO and for the walls in solid concrete, CON was adopted. Table 7 shows the quantity of each type of wall masonry in relation to the total sample analyzed. The buildins analysed, all from the Northeast region, are located in the cities of Maceió-AL, Camaçari-BA, Fortaleza-CE, João Pessoa-PB, Cabo de Santo Agostinho-PE, Paulista-PE, Recife-PE, São Lourenco da Mata-PE and Aracaju-SE.

Acoustic Performance Criteria in Internal Vertical Partitions … Table 7 Total samples of the case study

Wall

107 Nr.

BCE−Ceramic block

8

BCO−Concrete block

1

CON−Solid concrete

5

Table 8 Equipment used in-field tests Equipament

Manufacturer (dB)

Sound pressure level meter (Sleep gauge)−class 1

01

65279

Acoustic calibrator−class 1 01

34113649

RBC3-9649-666

Dodecahedron (Omni-12)

03/09-12/B206-012

–

01

Serial No./ Version

Calibration certificate RBC2-9646-555

Amplifier

01

03/09-12/B207-A12

–

Tapping machine

01

CALP04/08-11/193

–

–

–

Software dB Bati 01 (compilation of the results)

The field tests were carried out between the years 2017 and 2018, in the delivery phase of these works, and the company that executed them used equipment standardized and calibrated by laboratories accredited by Inmetro, adopting the recommendations of the standard regarding the procedures of the tests. The specifications of said equipment used in field tests are set out in Table 8, including calibration certificates, were within the period of validity at the time of the measurements (two years from calibration) and in each test report the copy of the respective certificates was attached. Table 9 presents the summarized description of the sample characterization, with data from the city of location of the enterprise, type of construction system of the walls and slabs, and quantity of field tests performed for each type of variable for each study case. The measurement procedures of the field tests followed the methodologies standardized by ISO 140 and 16283, with a minimum of five measurements in each environment, with the doors and windows well partitioned and the environment empty, except in the I-5 building where there was already some furniture installed by the owner at the time of the test. Figure 16 illustrates the measurement scans of the field tests for the three variables of the evaluated partition systems (SVVI–air noise).

3.2.2

Numerical Simulation

The Marshall Day Acoustics’ Insul 9.0 software was used as a soundproofing device for the elements of walls, floors and ceilings, in bedroom. This initial modeling of the components, provides the predicted values of sound reduction of the elements, which will be reported as input data then in the overall simulation of the building.

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Table 9 Sample summary, type of construction system and acoustic tests Building

Location

Code TP

Type of wall (TP) (cm)

In-field SVVI

I-1

Recife/PE

BCE-01

Ceramic block 9

2

I-2

Recife/PE

BCE-02

Ceramic block 14

7

I-3

Aracaju

BCE-03

Ceramic block 14

14

I-4

João Pessoa

BCE-04

Ceramic block 9

3

I-5

Recife/PE

BCE-05

Ceramic block 9

1

I-6

Recife/PE

BCE-06

Ceramic block 14

8

I-7

João Pessoa/PB

BCE-07

Ceramic block 9

3

I-8

Fortaleza

BCE-08

Ceramic block 14

4

I-9

Cabo Sant Agostinho

BCO-1

Concrete block 14

5

I-10

Maceió

CON-01

Solid concrete 10

6

I-11

Camaçari

CON-02

Solid concrete 10

4

I-12

Camaçari

CON-03

Solid concrete 10

8

I-13

S.Lourenço Mata

CON-04

Solid concrete 10

4

I-14

Paulista

CON-05

Solid concrete 10

6

Total

75

SVVI-R.Air

EMITTER

RECEIVER

Fig. 16 Schemes of the in-field test measurements

According to the manufacturer, Insul does not replace the measurement, however, as a prediction tool, it makes good estimates of sound transmission loss and impact sounds in bands of one-third octave and weighted sound reduction index, with accuracy and reliability within 3 dB for most types of constructions, with respect to the values measured in the field. With the program, it was also possible to evaluate the effect of material change in the projects, through adjustments in the modeling, considering, for each material, the different densities, modulus of elasticity and specific damping factor. The manufacturer further clarifies that the program is multilingual and has a database of materials from various countries of the world, such as UK, USA, Australia, Netherlands, Spain, France, Germany, Italy, Sweden, Korea and others, which can be edited if necessary. Figure 17 shows the Insul screen, which

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Fig. 17 Configuration screen of standardized calculations in Insul Software

contains part of the settings and frequencies of the acoustic calculation considered by the program. With Insul software, it was possible to simulate the sound attenuation possible by the components and building elements (walls and floors), to reach the reference values of insulation Rw and Ln’w for each composition. The insulation values of the materials calculated by Insul, Rw and Ln’w were taken to the other computer simulation program used in this work, the Sonarchitect, which simulates the acoustic behavior of the building as a whole, evaluating its performance. The modeling in Insul was structured according to the densities and thicknesses of the different layers that make up the wall systems and floor systems. As previously mentioned, the program has a database with characteristics of various types of materials to be used in the compositions of the layers of the building elements to be modeled, in this case the walls and floors, but it is possible to edit or create custom compositions. In this screen of editing and creation of new material, the information of layer thickness, density, young modulus and damping were inserted for each of the layers that make up the building elements of each project to simulate. In this work, all compositions were created in a personalized way, according to information from the project specification sheets of each project, which contain the characterization of the vertical partitions and flooring systems used. As there are no technical publications detailing the criteria for the use of the acoustic damping factor of the materials and, as the densities of most materials are known, in addition to reference values of sound reduction of some elements and components, which were the results of laboratory tests provided by the tables of the CBIC (2013) guide, data of other researches such as Neto (2009), Neto et al. (2010) and Souza et al. (2013) and the FAD Performance Evaluation Forms of the Brazilian Habitat Quality and Productivity Program–PBQP-H, we chose to adjust the

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Table 10 Characterization of simulated materials Acronym

Material

Density (Kg/m3 )

Young’s modulus (GPa)

Damping

BCE VED 90

Ceramic partition block 90 mm

616

10

0.011

BCE VED 140

Ceramic partition block 140 mm

577

10

0.011

BCO VED 140

Concrete partition block 140 mm

896

40

0.001

BGV

Cast plaster block 5 mm

800

8

0.006

CON

Solid concrete wall

1900

15

0.003

RA

Cementmortar coating

1600

30

0.003

RG

Plasterpaste coating

1100

30

0.003

RC

Ceramic coating

1800

4,68

0.001

damping values used in the simulations of this study, in order to reach these acoustic performance reference values of other studies. The information related to the properties of density, modulus of elasticity and damping factor of the materials used in the simulations of the case studies were provided by Tecomat, based on the field tests and the data of the manufacturers of the materials used in the works, compatible with the data adjusted above and are listed in Table 10. The models of the walls in the Insul program were performed as the masonry with its coating are executed in the field, that is, as being a juxtaposition of several overlapping layers as a monolithic element, which are coating and substrate layers, which in the present work were in masonry or solid concrete, with their respective thicknesses and properties of density, modulus of elasticity and declared damping factor. For each wall composition created, the software performed the calculations of sound attenuation showed an image of the element as constructed and indicated the sound reduction index in the frequency ranges requested, plotting graphs and tables, presenting the critical frequency and total density, in addition to the mean Rw value for the 100–3500 Hz band, which was used as a reference index of the acoustic behavior of the respective element. For the slabs, although the layercomposition methodology is similar to those used in the modeling of the walls, the modeling was a little more complex, because a weighting of the different materials of the floor layers was made for the purpose of commaking the slab as a mass, that is, a single equivalent component, calculating a weighted density of the set, according to the specific thicknesses and densities of each material per layer, from the following expression: 

ρ = (e1 . ρ 1 + e2 . ρ 2 + . . . + en . ρ n )/e T

(7)

Acoustic Performance Criteria in Internal Vertical Partitions …

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where ρ is the total density expressed in kg/m3 ; en is the thickness of each layer that makes up the slab, expressed in m; ρ n is the density of the material of each layer, expressed in kg/m3 and eT the total thickness of the massif, expressed in m. This weighting that transformed the various layers of the slab into an equivalent layer was made because, otherwise, the Insul program would consider that between the layers of the floor there would be an elastic joint, and thus the simulation would present much better results than those that occur in the real situation, that is, in the field trials. In the case of ribbed slabs, the simplification was even greater, because the height of the ribs was disregarded and, for the calculation of the equivalent massif, only the thickness of the slab capping was considered. This greater simplification can be justified by the fact that, ignoring the air space of the ribs, the process leads to lower levels of sound reduction, a solution adopted that “favors” safety. After modeling the slab (floor/ceiling), the Insul program performed the acoustic performance calculations and indicated the Rw sound reduction index of the ceiling element and the standard impact sound pressure level of the Ln,w floor in the Ceiling and Floor tabs of the program, respectively. For each of the Ceiling and Floor tabs, the program also presents the values of air driving noises R(dB) and percussion noises Lw (dB), at frequencies from 50 to 5000 Hz, in the Tables tab, but for the modeling we use only the values included in the standard range band (band of one third octave) whose frequencies range from 100 to 3500 Hz (values that will be exported to the other modeling program–the Sonarchitect).

3.2.3

Acoustic Performance Calculation

For the acoustic performance calculation the software Sonarchitect ISO professional was used. The program was used to simulate the acoustic behavior of the building as a whole and evaluate its performance from the conformity of the simulated results with the defined sets, according to the constants in NBR 15575 (2013), which are initially loaded into the program. The results presented by the program are detailed for each environment, partition, flank and sound transmission path and is presented the conformity or not of each environment/system. The values resulting from the simulations performed in the modeling of composition of materials and elements with the Insul software were taken to the Sonarchitect software, as reference values of the custom compositions of each of the projects, with a view to computational modeling of the acoustic performance of the building. In addition to the composition data calculated in the Insul software, we used the floor plans exported in DXF, the information of the architectural project (betweenfloor height, window indication, specifications of internal, external, floor and ceiling partitions) and the values of the minimum limits of the acoustic performance criteria for in-field tests, according NBR 15575 (2013), used as input data for computer simulation in Sonarchitect. The modeling process in Sonarchitect started with the insertion of the minimum limit settings, i.e. the minimum performance levels of NBR 15575 (2013) for the

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in-field tests, since the simulation intends to predict the acoustic behavior in relation to what will be measured in real in-field situation. As this work did not evaluate the criteria of external partition systems (SVVE), information on façade frames was not included in the program, since this information would not significantly influence the calculation of the internal transmission of noise between internal and between-floor partitions, which were the restricted criteria evaluated. After the feeding of the building characterization data, the program calculated the acoustic insulation of the entire building, indicating, for all environments, the values of aerial acoustic transmission and impact of sound pressure levels and the components and paths of noise transmission. The program also compared the result of the acoustic simulation calculated with the values of limits reported in the initial configuration, demonstrating the environments inside or outside these minimum level limits required by NBR 15575 (2013), through green and red colors that mean, respectively whether or not they met the required by the aforementioned standard. Figure 18 illustrates how acoustic performance behavior plots are at the end of this computational simulation phase using Sonarchitect. We are exemplified how the projects modeled in 3 dimensions are presented; how the floors clearly present, through the red color, the environments in which values are identified in conformity in relation to the minimum levels of the standard; as the program presents the acoustic analysis for each environment, with its relationship with the neighboring enclosures on the same floor and between floors; the values of simulated and standardized sound insulation; and the reports and figures presented for each type of noise analyzed. With the modeling of the elements, design and characterization of the project, the computational simulation of the acoustic performance of the building was made, demonstrating the acoustic behavior of the ready building, succeeding in acoustic performance results by environment, allowing the confrontation of measured values and simulated values. From the field, sound reduction values were obtained between environments, in this case the standardized difference of weighted level of air noise of vertical partitions (DnTW ) and the level of standard impact sound pressure (L nT,W ) between floors. From the computational simulations, first modeled in Insul, the acoustic behavior of reference of the construction elements was predicted individually, based on the projects and specifications of the construction systems, and the sound attenuation indexes in relation to air noise (Rw ) and the standard impact sound pressure level for impact noises (Ln W ) were calculated. The individual modeling results of the elements were used in the other program, Sonarchitect, to simulate the overall situation of acoustic performance of the building. This second modeling allows simulating the field behavior of the project, and the results present the same field indices, in this case the standardized difference of weighted level of the airnoise of vertical partitions (DnTW ) and the level of sound pressure of standard impact (L nT,W ), thus allowing confrontation of the measured values with the simulated values.

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113

(a)

(b)

(c)

(d)

(e)

(f)

Fig. 18 a Example of the 3D modeled project (Building I-9); b Plotting of the project acoustic behaviour; c Plotting by pavement with indication of non-attendance area to the minimum level of the standard; d Plotting of non-compliant enclosures throughout the building; e Aerial driving noise analysis on tinning walls; and f Impact noise analysis

Finally, the values obtained experimentally and numerically were presented according to the sketch of Table 11. According to the differences found, the simulations of some of the cases in which this difference (simulated versus measured) exceeded 2 dB were redone, with the function of evaluating whether the modeling procedures influenced the assertiveness of the values found in the simulations. These procedures included variation in thickness of coating layers, air space between slab and lining, inclusion of air space considered with expansion joint between towers, in the case between vertical partitions, in addition to adjustments of construction material building for some of the cases, where the damping factor or specific density was corrected.

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Table 11 Model used to present and calculate the difference between in-field and numerical values Environment

Criterion (dB) (NBR 15575-4 & NBR 15575-3)

In-field tests Result (dB) DnT,w (aerial noise) L nT,w (impact noise)

Numerical results  (dB) Result (dB) SC-MC DnT,w (aerial noise) L nT,w (impact noise)

Emission: Environment x Reception: Environment y

Minimum: _ to _ Intermediate:_ to _ Superior: ≥ or ≤

MC

SC

NA

NA

M

M

I

I

S

S

SC–MC

where: MC is the value measured in in-field tests; SC is the numerical value;  is the SC versus MC difference; NA = Do not meets the criterion; M = Meets at minimum level; I = Meets at intermediate level; S = Meets at superior level

3.3 Results Evaluation Criteria From the comparison of the simulated values with the measured values, and the calculation of the difference in absolute values of these results, the percentage of values whose difference between the simulation and measurement result was 0 dB, 1 dB, 2 dB, 3 dB and above 3 dB, respectively, creating a scale of optimal, good, acceptable, bad and bad, respectively, according to the classification illustrated in Fig. 19. This “acceptable” classification adopted was based on measurement uncertainty, provided by ISO 16283 (2017, 2018), whose calculations made in some samples, resulted in an average value of approximately ±2 dB for such uncertainty. Thus, taking into account that the measurement value may vary in an acceptable range of ±2 dB, the situation in which there was no difference between the absolute values of the simulation and the measurement was adopted as “optimal” when there was no difference between the absolute values of the simulation and the measurement, meaning that up to 2 dB there is a possibility that the field values are equal to the simulated, because of the uncertainty range of the measurement. With the difference of ±3 dB, the sample leaves the acceptable range, with the simulation distancing itself ±1 dB of the measurement uncertainty range, classifying the sample as “bad”, and values higher than (3 dB were identified as “poor”, in the sense that there was greater incompatibility in the simulation in relation to what would be measured in the field.

Fig. 19 Evaluation rating adopted

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115

After such analyses, we were able to filter those results whose divergences are extreme and analyze such discrepancies on a case-by-case basis, in order to find a homogeneity of the comparison data and evaluate which parameters influenced such results.

4 Description of the Case Studies In this work, 14 case studies were addressed, all multifamily housing buildings. The construction system adopted for internal partitions varied between ceramic partition block, partition concrete block and solid concrete wall; for the floor systems, the projects presented alveolar/ribbed concrete slabs or solid concrete slabs. Table 12 presents the materials and construction systems of the case studies, in addition to the number of evaluations performed; the acronyms adopted to identify the simulations of this work are identified in Table 13. As in this study, the normative criteria of acoustic performance of air noise bedroom of external partition systems (SVVE) were not evaluated, restricting the scope to the verification of the values of the insulation to the air noise of internal vertical partitions (SVVI). The characterization of external partition systems and the amount of SVVE measurements was not presented in the summary of Table 20, since such data were not analyzed, however, in the individual descriptions of the case Table 12 Simulated case study building systems Building

SVVI

Quantity

I-1

RG (15) + BCE (90) + RG (15)

I-2

RA (15) + BCE (140) + RA (15)

I-3

RG (20) + BCE (140) + RG (20) RG (20) + BCE (140) + RA (30) + RG(20)

I-4

RA (15) + BCE (90) + RA (15)

I-5

RA (15) + BCE (90) + RA (15)

1

I-6

RG (15) + BCE (140) + RG (15)

8

I-7

RA (20) + BCE (90) + RA (20)

3

I-8

RA (30) + BCE (140) + RA (30)

4

I-9

RG (20) + BCO (140) + RG (20)

5

I-10

RG (5) + CON (100) + RG (5)

6

I-11

RA (20) + CON (100) + RA (20)

4

I-12

RA (7) + CON (100) + RA (7)

8

I-13

CON (100)

4

I-14

RA (4) + CON (100) + RA (4)

6

SVVI 2 7 14 3

75

116 Table 13 Identification of simulated building materials and systems

E. C. L. Rezende et al. Acronym

Material/Systems

BCE VED 90

Ceramic partition block 90 mm

BCE VED 140

Ceramic partition block 140 mm

BCO VED 140

Partition concrete block 140 mm

BGV

Cast plaster block 5 mm

BGM/ FG

Solid plaster block/ Plaster lining

CON

Solid concrete wall

RA

Cement-mortar coating

RG

Plasterpaste coating

RC

Ceramic coating

CP

Counterfloor

LJ

Ribbed concrete slab (capping only)

LJM

Solid concrete slab

CPE

Special floor–isofloc trace

MAF

Asphalt blanket with acab. acrylic resin

AR

Air space

studies, it will be mentioned which systems of the external vertical partitions were used by the respective properties, for better overall characterization of each project and because such data were used as input information in the computer simulations, even though the acoustic performance of such systems (SVVE) was not analyzed.

4.1 Building I-1 The building I-1 is located in the city of Recife, composed of 2 residential towers, with 22 floors type per tower, being 4 apartments per floor, with an area of 62.63 m2 and 74.64 m2 per apartment. Each housing unit has 2 or 3 bedrooms, being 1 suite, living/dining room, kitchen and service area, as can be seen in the floor plan reproduced in Fig. 20. Sound insulation tests were performed in apartments of the 21st and 20th floors, in internal partitions between the kitchen and living room systems, and for the floor systems between rooms, kitchen and bedrooms, as indicated by the markings in blue and green in Fig. 20. The construction system adopted by this enterprise for the internal vertical partitions was ceramic block of 9.0 cm, with coating in gypsum paste of 1.5 cm on each side, being in the wet areas adopted ceramic coating with cementitious mortar layer of 1.5 cm. For the external vertical partition, a 9.0 cm ceramic partition block with a plaster coating of 1.5 cm on the inner side and 4.0 cm with ceramic coating on the

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Fig. 20 Plant of building I-1: Detail of the vertical partition evaluated

Table 14 Construction system of the partitions of building I-1 Internal vertical partition (between units) Gypsum paste 1.5 cm + Ceramic partition block 9.0 cm + Gypsum paste 1.5 cm Wettable environments

Gypsum paste 1.5 cm + Ceramic partition block 9.0 cm + Plaster 1.5 cm + Ceramic

External vertical partition

Gypsum paste 1.5 cm + Ceramic partition block 9.0 cm + Plaster 4.0 cm + Ceramic (0.5 cm plate + 0.5 cm adhesive mortar)

external side was adopted. The construction system of the partitions adopted by the building I-1 is presented in Table 14.

4.2 Building I-2 The building I-2 is located in the city of Recife/PE, with 27 type floors, being 4 apartments per floor, with an area of 61.20 m2 per apartment of terminations 01 and 04, and 61.08 m2 for apartments of terminals 02 and 03. Each housing unit has 2 bedrooms, 1 suite, living/dining room, kitchen/service area, social bathroom and balcony, as sketched in Fig. 21.

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Fig. 21 Plant of building I-2: Detail of the in-field tests

Sound insulation tests were performed in apartments of the 1sr, 2nd and 7th floors, in internal partitions between the kitchen and living room systems, between kitchen and staircase and between living rooms, as indicated through the markings in blue and green in Fig. 21. For the internal vertical partitions, a ceramic block of 14.0 cm was used, with cement-mortar coating of 1.5 cm on each side. For the external vertical partition, a ceramic block of 14.0 cm partition was adopted with cement mortar coating of 1.5 cm on the inner side and external side, mortar of 3.5 cm, plus ceramic coating. Finally, the construction system of building I-2 is presented in Table 15.

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Table 15 Construction system of the partitions of building I-2 Internal vertical partition (between units)

Cement mortar 1.5 cm + Ceramic partition block 14.0 cm + cement mortar 1.5 cm

External vertical partition

Cement mortar 1.5 cm + Ceramic partition block 14.0 cm + cementitious mortar 3.5 cm + ceramic 1.5 cm

4.3 Building I-3 The building I-3 is located in the city of Aracaju/SE, composed of 2 towers with 5 type floors per tower. Each type floor has 6 housing units, being 2 units with an area of 80.00 m2 , 2 units with an area of 71.83 m2 and other 2 units with 79.55 m2 . Each housing unit has 2 and 3 bedrooms, being 1 suite, living/dining room, kitchen/service area, social bathroom and balcony, as can be seen in Fig. 22. Sound insulation tests were performed in apartments of 5th and 6th floors, in internal fences between the kitchen systems, between kitchen and living room, between rooms, between kitchen and bedroom, between living room and bedroom, between bedroom and eventual common traffic area (in this case, hall) and between room and eventual transit area (in this case, hall), as indicated by the blue and green markings presented in Fig. 22. The construction system adopted by the building I-3 is presented in Table 16.

4.4 Building I-4 The building I-4 is in the city of João Pessoa/PB, with 18 type floors, being 4 housing units per floor. One of the units of the floor has an area of 75.62 m2 , another has an area of 76.44 m2 and the two remaining units of the floor has an area of 63.00 m2 . Each housing unit has 2 and 3 bedrooms, being in both cases 1 suite, living/dining room, kitchen/service area, social bathroom and balcony, as can be seen in Fig. 23. Sound insulation tests were performed in apartments of the 16th and 17th floors, in internal partitions between the living room systems, between kitchen and bedroom and between bedroom and eventual transit area (in this case, staircase), as indicated through the markings in blue and green in Fig. 23. The construction system adopted by the building I-4 is presented in Table 17.

4.5 Building I-5 The building I-5 is located in the city of Recife/ PE, composed of 1 tower with 31 floors, 3 apartments per floor, with an area of 49.24 m2 for apartment termination 01, area of 50.14 m2 for apartment of termination 02 and area of 50.20 m2 for the

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Fig. 22 Plant of building I-3: Detail of the in-field tests

termination apartment 03. Each housing unit has 2 bedrooms, one of them suite, living/dining room, kitchen/service area and social bathroom, as sketched in Fig. 24. Sound insulation tests were performed in apartments of the 1st and 2nd floors, in internal partitions between the systems of rooms, as indicated by the markings in blue and green in Fig. 24. The construction system adopted by the building I-5 is presented in Table 18.

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Table 16 Construction system of the partitions of building I-3 Internal vertical partition (between units)

Gypsum paste 2.0 cm + Ceramic partition block 14.0 cm + gypsum paste 2.0 cm

Wettable environments

Gypsum paste 2.0 cm + Ceramic partition block 14.0 cm + single cement mortar 3.0 cm + adhesive mortar 0.5 cm + ceramic 0.5 cm

External vertical partition

Gypsum paste 2.0 cm + Ceramic partition block 14.0 cm + Roughcast 0.5 cm + single structuring layer 5.5 cm + adhesive mortar 0.5 cm + ceramic 0.5 cm

4.6 Building I-6 The building I-6 is located in the city of Recife/PE, composed of 1 tower with 14 floors, being 4 apartments per floor, 2 units with an area of approximately 64.94 m2 and the other 2 units with an area of 62.54 m2 . Each housing unit has 3 bedrooms, 1 suite, living/dining room, kitchen/service area, social bathroom and balcony, as can be seen in Fig. 25. Sound insulation tests were performed in apartments of the 1st, 2nd and 3rd floors, in internal partitions between the living room systems, between kitchen and living room and between kitchen and eventual transit area (in this case, staircase), as indicated through the markings in blue and green in Fig. 25. The construction system of the building I-6 is presented in Table 19.

4.7 Building I-7 The building I-7 is located in the city of João Pessoa/PB, composed of 1 tower with 8 floors and 1 duplex floor (penthouse), being 2 housing units per floor, with an area of approximately 61.00 m2 per apartment. Each housing unit has 3 suites, 2 bathrooms, living/dining room, kitchen, service area and balcony, as can be seen in Fig. 25. The duplex apartments have a penthouse with gourmet area, swimming pool free area and bedroom with bathroom (Fig. 26). Sound insulation tests were performed in apartments of the 1st and 2nd floors, in internal partitions between the kitchen systems, in addition to a test on the upper floor of the duplex floor between the gourmet areas (considered in the analysis as kitchen areas), according to markings in blue and green in Fig. 25. The construction system of the building I-7 is presented in Table 20.

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Table 17 Construction system of the partitions of building I-4 Internal vertical partition (between units)

Cement mortar 1.5 cm + Ceramic partition block 9.0 cm + cement mortar 1.5 cm

Wettable environments

Cement mortar 1.5 cm + Ceramic partition block 9.0 cm + cementitious mortar 1.5 cm + adhesive mortar 0.5 cm + ceramic 0.5 cm

External vertical partition

Cement mortar 1.5 cm + Ceramic partition block 9.0 cm + Roughcast 0.5 cm + cementitious mortar 4.5 cm + adhesive mortar 0.5 cm + ceramic 0.5 cm

Fig. 24 Plant of building I-5: Detail of the in-field tests

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Table 18 Construction system of the partitions of building I-5 Internal vertical partition (between units)

Gypsum paste 1.5 cm + Ceramic partition block 9.0 cm + gypsum paste 1.5 cm

External vertical partition

Gypsum paste 1.5 cm + Roughcast 0.5 cm + Ceramic partition block 14.0 cm + cementitious mortar 5.0 cm + adhesive mortar 0.5 cm + ceramic 0.5 cm

Fig. 25 Plant of building I-6: Detail of the in-field tests Table 19 Construction system of the partitions of building I-6 Internal vertical partition (between units)

Gypsum paste 1.5 cm + Ceramic partition block 14.0 cm + gypsum paste 1.5 cm

External vertical partition

Gypsum paste 1.5 cm + Ceramic partition block 14.0 cm + cementitious mortar 3.0 cm + adhesive mortar 0.5 cm + ceramic 0.5 cm

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Fig. 26 Plant of building I-7: Detail of the in-field tests

Table 20 Construction system of the partitions of building I-7 Internal vertical partition (between units)

Cement mortar 2.0 cm + Ceramic partition block 9.0 cm + cementitious mortar 2.0 cm

External vertical partition

Cement mortar 2.0 cm + Ceramic partition block 9.0 cm + Roughcast 0.5 cm + cementitious mortar 6.0 cm + adhesive mortar 0.5 cm + ceramic 0.5 cm

4.8 Building I-8 The building I-8, located in the city of Fortaleza/CE, is a composed of 2 towers, with 17 floors per tower. Each floor has 4 housing units, with an area of approximately 98 and 118 m2 . The apartments have 3 suites, 1 reversible, living/dining room, kitchen, service area, bedroom and bathroom service and balcony, as can be seen in Fig. 27. Sound insulation tests were performed in apartments of the 15th and 16th floors of tower 1, in internal partitions between the systems of rooms and between bedrooms, as indicated through the markings in blue and green in Fig. 27. The construction system of the building I-8 is presented in Table 21.

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Fig. 27 Plant of building I-8: Detail of the in-field tests

Table 21 Construction system of the partitions of building I-8 Internal vertical partition (between units) Cement mortar 2.5 cm + Roughcast 0.5 cm + Ceramic partition block 14.0 cm + Roughcast 0.5 cm + cementitious mortar 2.5 cm External vertical partition

Cement mortar 2.5 cm + Roughcast 0.5 cm + Ceramic partition block 14.0 cm + Roughcast 0.5 cm + cementitious mortar 4.5 cm + adhesive mortar 1.0 cm + ceramic 0.7 cm

4.9 Building I-9 The building I-9, located in the city of Cabo de Santo Agostinho/ PE, is composed of 3 towers, having the towers 12 floors and 1 floor cover, being 4 apartments per floor, with an area of approximately 127.40 m2 per housing unit. Each apartment has 4 suites, living/dining room, kitchen/service area, toilet, service bathroom and balcony, as can be seen in Fig. 28. Sound insulation tests were performed in apartments of the

Fig. 28 Plant of building I-9: Detail of the in-field tests

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Table 22 Construction system of the partitions of building I-9 Internal vertical partition (between units) Plaster coating 2.0 cm + Partition concrete block 14.0 cm + plaster coating 2.0 cm External vertical partition

Plaster coating 2.0 cm + Roughcast + Partition concrete block 14.0 cm + Roughcast + cementitious mortar 5.0 cm + adhesive mortar 1.0 cm + ceramic 1.0 cm

1st, 2nd and 3rd floors per tower, in internal partitions between the living room and bedrooms, as indicated by the marks in blue and green in Fig. 28. The construction system of the building I-9 is presented in Table 22.

4.10 Building I-10 The building I-10, located in the city of Maceió/AL, consisting of 10 residential towers, each tower with 4 floors, being 1 ground floor and 3 more floors. Each tower has 4 apartments per floor, with an area of approximately 42 m2 per apartment. The housing unit has 2 bedrooms, star/dining room, kitchen/service area and social bathroom, as can be seen in Fig. 29. Sound insulation tests were carried out in ground floor and 1st floor apartments, in internal partitions between the kitchen systems and between rooms, as indicated by the markings in blue and green in the standard floor plan of the building in Fig. 29. The construction system adopted for its internal vertical partitions is massive wall in selfadensable concrete of 10 cm thick, with plaster paste coating of 0.5 cm on each side. Its external vertical partition follows the same system as the internal partitions, with application of acrylic textured coating and hydro-repellent layer. The construction system adopted by the building I-10 is presented in Table 23.

4.11 Building I-11 The building I-11, located in the city of Camaçari/BA, is composed of 30 towers, being 25 towers with 3 type floors and 1 ground floor and 5 towers with 4 type floors and 1 ground floor. All towers have 4 housing units per floor, with an area of approximately 43 m2 per apartment. Each housing unit has 2 bedrooms, with the option of suites in some units, living/dining room, kitchen/service area, social bathroom, service room and balcony, as sketched in Fig. 30. Sound insulation tests were carried out in ground floor and 1st floor, in internal partitions between the kitchen systems and between living rooms, as indicated by the markings in blue and green in Fig. 30. The construction system adopted by the building I-11 is presented in Table 24.

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Fig. 29 Plant of building I-10: Detail of the in-field tests

Table 23 Construction system of the partitions of building I-10 Internal vertical partition (between units) Plaster coating 0.5 cm + Self-densable concrete 10.0 cm + 0.5 cm plaster coating External vertical partition

Plaster coating 0.5 cm + Self-adhesive concrete 10.0 cm + hydro-repellent + acrylic textured coating

4.12 Building I-12 The building I-12 is located in the city of Camaçari/BA with 18 residence towers, twined every 2 towers, composed of ground floor and 3 type floors. Each tower has 4 housing units per floor, with an area of approximately 43.00 m2 per apartment. Between towers, it is included in the project that there is a 20 mm expansion joint. Each housing unit has 2 bedrooms, living/dining room, kitchen/service area and social bathroom, as sketched in Fig. 31. Sound insulation tests were performed in ground floor apartments, 1st, 2nd and 3rd floors, of towers 1, 15, 17 and 18, in internal partitions between the living systems, between bedrooms and between kitchen and eventual transit common area (in this case, hall and staircase), as indicated by the blue and green markings in Fig. 31. The construction system adopted by the building I-12 is presented in Table 25.

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Fig. 30 Plant of building I-11: Detail of the in-field tests

Table 24 Construction system of the partitions of building I-11 Internal vertical partition (between units)

Cementitious mortar of regularization 2.0 cm + Concrete 10,0 cm + cementitious mortar of regularization 2.0 cm

External vertical partition

Cementitious mortar of regularization 3,0 cm + Concrete 10,0 cm + cementitious mortar of regularization 3.0 cm + texture 2.0 cm

4.13 Building I-13 The building I-13, located in the municipality of São Lourenco da Mata/PE, is an enterprise with 21 towers of 4 floors, being 1 ground floor plus 3 types, composed of 4 apartments per floor, with an area of 45.35 m2 per apartment. The towers are twined every 2 or 3 towers, and, between the towers, is included in the 20 mm expansion joint project. Each housing unit has 2 bedrooms, 1 suite, living/dining room, kitchen/service area, social bathroom and balcony/terrace, as sketched in Fig. 32. Sound insulation tests were performed in apartments of the 1st and 2nd floors, of towers 11 and 12, in internal partitions between the living room systems and between bedrooms, as indicated by the markings in blue and green in Fig. 32. The construction system adopted by the building I-13 is presented in Table 26.

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Fig. 31 Plant of building I-12: Detail of the in-field tests

Table 25 Construction system of the partitions of building I-12 Internal vertical partition (between units)

Cement mortar 0.7 cm + Concrete 10.0 cm + cementitious mortar 0.7 cm

External vertical partition

Cementitious mortar 0.7 cm + Concrete 10.0 cm + regularization cementitious mortar + texture

4.14 Building I-14 The buildingI-14, located in the city of Paulista/PE, is a development with 20 towers, with 4 floors, being 1 ground floor and 3 types. Among twin towers, it is included in the project that there is a 20 mm expansion joint. Each tower has 4 apartments per floor, with an area of 37.49 m2 per apartment. Each housing unit has 2 bedrooms, living/dining room, kitchen/service area and social bathroom, as can be seen in Fig. 33. Sound insulation tests were performed in apartments of the 1st and 2nd floors of towers 10 and 11, in internal partitions between the systems rooms, between bedrooms and between kitchen and eventual transit area (in this case, hall/staircase), as indicated by the markings in blue and green in Fig. 33. The construction system adopted by the building I-14 is presented in Table 27.

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Fig. 32 Plant of building I-13: Detail of the in-field tests

Table 26 Construction system of the partitions of building I-13

Internal vertical partition (between units)

Cement 0.3 cm + Concrete 10.0 cm + Cement 0.3 cm

External vertical partition

Cement 0.3 cm + Concrete 10.0 cm + texture 0.3 cm

5 Results and Discussion This section presents the results of computational simulations of acoustic performance performed in the 14 case studies and the discussions about the values found in comparison to the values presented in the field trials. SVVI evaluations will be presented, followed by cases of SVH, the latter being divided into air noise–RA and impact noise–RI.

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Fig. 33 Plant of building I-14: Detail of the in-field tests

Table 27 Construction system of the partitions of building I-14 Internal vertical partition (between units) Texture and paste with cementitious mortar 0.4 cm + Concrete 10.0 cm + texture and paste with cementitious mortar 0.4 cm External vertical partition

Texture and paste with cementitious mortar 0.4 cm + Concrete 10.0 cm + texture with cementitious mortar 0.4 cm

5.1 Internal Vertical Partition Systems–SVVI For the internal vertical partition systems–SVVI, 75 simulations were performed, according to the summary presented in Table 28. Figure 34 presents the computational simulation values and field measurement values of all 75 SVVI assays, ordered by case study, including the respective uncertainty range of ± 2 dB for field measurement of these data. Figure 35 shows the dispersion of the calculated difference between the values of the computational simulation and the field measurement, in increasing order of variation of the results. Regarding the calculated values of the computational simulation versus field measurement difference (SC vs. MC), the condition of SC being greater or lower than MC was disregarded, considering the values in module for this difference, and

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Table 28 Number of SVVI tests performed Building

SVVI

I-1

RG (15) + BCE (90) + RG (15)

I-2

RA (15) + BCE (140) + RA (15)

I-3

RG (20) + BCE (140) + RG (20) RG (20) + BCE (140) + RA (30) + RG(20)a

I-4

RA (15) + BCE (90) + RA (15)

I-5

RA (15) + BCE (90) + RA (15)

1

I-6

RG (15) + BCE (140) + RG (15)

8

I-7

RA (20) + BCE (90) + RA (20)

3

I-8

RA (30) + BCE (140) + RA (30)

4

I-9

RG (20) + BCO (140) + RG (20)

5

I-10

RG (5) + CON (100) + RG (5)

6

I-11

RA (20) + CON (100) + RA (20)

4

I-12

RA (7) + CON (100) + RA (7)

8

I-13

CON (100)

4

I-14

RA (4) + CON (100) + RA (4)

6

Total a Wet

Quantity 2 7 14 3

75

areas

Fig. 34 Scatter plot of results (DnT,w) measured in field and simulated−SVVI

then a histogram of the relative frequencies of this difference SC versus MC was assembled, as shown in Fig. 36. For the SVVI total sample, that is, for the total of 75 trials, 13.33% of the sample presented equal values in SC and MC, and this part was classified as “optimal”, 22.67% presented a difference of 1 dB, for which it was classified as a “good” result and 17.33% presented a difference of 2 dB, whose classification adopted was “acceptable”, totaling 53.33% of the sample within the considered uncertainty range

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Fig. 35 Dispersion plot of SC–MC (in dB)−SVVI geral

Fig. 36 Histogram of relative frequency of SC–MC for SVVI geral

of ±2 dB, this being the acceptable margin considered for the difference between simulation and experimental tests. In addition to these percentages, 10.67% presented a difference of 3 dB, identified as a “bad” result and 36% presented results from 4 dB, reaching in this sample some values of difference of up to 20 dB between SC and MC, whose identification was of “poor” level, totaling 46.67% from bad to poor for this sample. Another analysis performed with the data of computational simulation and field measurement was the amount of results in which the SC was higher than the MC or vice versa, that is, for this sample it was verified that 52% of the 75 tests

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Fig. 37 Comparison of the SC versus MC results−SVVI

presented computational simulation results higher than the results of field measurement; 34.67% of the tests presented field measurement higher than the result of computational simulation and 13.33% of the tests presented equal values between field measurement and computational simulation, as shown in Fig. 37. This result, disregarding any range of uncertainty, confirms what is expected as an initial hypothesis that the simulation will necessarily present values higher than field measurement, since in computational simulation the conditions for calculating the acoustic insulation are predictable and considered ideal, as opposed to the conditions of the field measurement in which several unpredictable factors, such as constructive failures, gaps and external noises, can negatively interfere with the expected results of sound insulation, leading to lower values than those predicted in the project. Starting for a specific analysis by type of element if separation, it was found that of the 75 tests performed in the study of sound insulation in SVVI, 45 were in separation elements between autonomous units without one of the environments being bedroom, 15 tests were between autonomous units in which at least one of the environments was bedroom, 3 between blind wall of dormitories and common areas of circulation, and 12 tests between blind walls of housing units and common areas of circulation, thus taking into account four of the situations provided for in the performance standard regarding the type of Element SVVI. Table 29 shows the number of tests performed for each classification of the SVVI elements provided for in the performance standard.

5.1.1

Condition I–SVVI on Walls Between Autonomous Housing Units (Twinning Walls), in Situations Where There is no Bedrooms

Table 30 presents the results for SVVI of the 45 in-field measurement and computational simulation tests for the separation elements in tlotting walls in situations where there is no bedroom, with the respective calculated difference (SC–MC). Figure 38 presents the values of computational simulation and field measurement of the 45 SVVI tests on tinting walls without bedroom environment are plotted,

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Table 29 Number of tests analyzed for SVVI according to types of elements in the standard NBR 15575 (2013), Part 4 Number of tests performed 45

15

3

12

0

0

Types of SVVI elements and constant limits in NBR 15575-4 Element

DnT,w (dB)

Performance level

Wall between autonomous housing units (tasling walls), in situations where there is no bedroom environment

40–44

M

45–49

I

≥50

S

Wall between autonomous 45–49 housing units (tumming walls), 50–55 in case at least one of the ≥55 environments is a bedroom

M

Blind wall of bedrooms between a housing unit and ordinary areas of eventual traffic, as corridors and staircase on the pavements

40–44

M

45–49

I

≥50

S

I S

Blind wall of living rooms and 30–34 kitchens between a housing 35–39 unit and eventual common transit areas, as corridors and ≥40 staircase on the pavements

M

Blind wall between a housing unit and common areas of permanence of people, leisure activities and sports activities such as home theater, gyms, ballroom, games room, bathrooms and collective dressing rooms, kitchens and collective laundries

45–49

M

50–54

I

≥55

S

Set of walls and doors of distinct units separated by the hall (DnT,w obtained between the units)

40–44

M

45–49

I

≥50

S

I S

including the respective uncertainty range of ±2 dB for field measurement, arranged according to the case studies indicated in Table 30. Figure 39 shows the dispersion, in ascending order, of the calculated difference between SC and MC values for these tweded cases, named as SVVI –Condition I. In the same way as the general sample of SVVI was carried out in the analysis, for the specific cases of the types of separation element, the condition of SC being greater or lower than MC was also disregarded, considering the values in module for the computational simulation versus field measurement difference (SC × MC), in order to enable the creation of a histogram of the relative frequencies of this difference, as

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Table 30 SVVI tests on wall between autonomous housing units (twining walls), in situations where there is no bedroom environment In-field

Numerical simulation

 (dB)

Minimum: 40 to 44 Twinning wall Intermediate: 45 to 49 in situations where Superior: ≥50 there is no bedroom

Result (dB) DnT,w

Result (dB) DnT,w

SC–MC

I-01

Emission: Kitchen−Ap. 2102 Reception: Room−Ap. 2103

44

38

−6

Emission: Living room−Ap. 2103 Reception: Kitchen−Ap. 2102

42

36

−6

Emission: Kitchen−Ap. 103 Reception: Living room−Ap. 104

41

42

1

Emission: Living room−Ap. 101 Reception: Kitchen−Ap. 102

44

42

−2

Emission: Living room−Ap. 102 Reception: Living room−Ap. 103

43

42

−1

Emission: Living room−Ap. 702 Reception: Living room−Ap. 703

42

42

0

Emission: Living room−Ap. 703 Reception: Living room−Ap. 702

41

42

1

Emission: Kitchen−Ap. 503 Reception: Kitchen−Ap. 502

45

41

−4

Emission: Kitchen−Ap. 504 Reception: Kitchen−Ap. 505

43

40

−3

Emission: Kitchen−Ap. 603 Reception: Kitchen−Ap. 602

44

41

−3

Criterion (dB) (NBR 15575-4)

I-02

I-03

Ambient

(continued)

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Table 30 (continued) Ambient

In-field

Numerical simulation

 (dB)

Emission: Kitchen−Ap. 604 Reception: Kitchen−Ap. 605

40

40

0

Emission: Kitchen−Ap. 506 Reception: Living room−Ap. 505

47

45

−2

Emission: Kitchen−Ap. 606 Reception: Living room−Ap. 605

43

45

2

Emission: Living room−Ap. 601 Reception: Living room−Ap. 602

43

42

−1

Emission: Living room−Ap. 1701 Reception: Living room−Ap. 1702

38

38

0

Emission: Living room−Ap. 1702 Reception: Living room−Ap. 1701

39

38

−1

I-05

Emission: Living room−Ap. 102 Reception: Living room−Ap. 103

33

39

6

I-06

Emission: Kitchen−Ap. 101 Reception: Living room−Ap. 104

42

42

0

Emission: Kitchen−Ap. 102 Reception: Living room−Ap. 103

41

42

1

Emission: Kitchen−Ap. 202 Reception: Living room−Ap. 203

42

42

0

Criterion (dB) (NBR 15575-4)

I-04

(continued)

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Table 30 (continued) Criterion (dB) (NBR 15575-4)

I-07

I-08a

I-09 (BCO)a

I-10

Ambient

In-field

Numerical simulation

 (dB)

Emission: Living room−Ap. 101 Reception: Living room−Ap. 102

38

41

3

Emission: Living room−Ap. 102 Reception: Living room−Ap. 101

38

41

3

Emission: Área Gourmet−Ap. 01 Reception: Área Gourmet−Ap. 02

28

40

12a

Emission: Kitchen−Ap. 101 Reception: Kitchen−Ap. 102

44

43

−1

Emission: Kitchen−Ap. 102 Reception: Kitchen−Ap. 101

44

43

−1

Emission: Living room−Ap. 1502 Reception: Living room−Ap. 1501

44

46

2

Emission: Living room−Ap. 1503 Reception: Living room−Ap. 1504

43

46

3

Emission: Living room−Ap. 102S Reception: Living room−Ap. 101S

45

47

2

Emission: Living room−Ap. 102S Reception: Living room−Ap. 101S

45

47

2

Emission: Kitchen−Ap. 01 Reception: Kitchen−Ap. 03

41

43

2

(continued)

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Table 30 (continued) Criterion (dB) (NBR 15575-4)

I-11

Ambient

In-field

Numerical simulation

 (dB)

Emission: Kitchen−Ap. 02 Reception: Kitchen−Ap. 04

41

43

2

Emission: Kitchen−Ap. 104 Reception: Kitchen−Ap. 102

43

43

0

Emission: Living room−Ap. 01 Reception: Living room−Ap. 03

43

44

1

Emission: Living room−Ap. 02 Reception: Living room−Ap. 04

43

44

1

Emission: Living room−Ap. 104 Reception: Living room−Ap. 102

40

45

5

Emission: Kitchen−Ap. 01 Reception: Kitchen−Ap. 04

44

43

−1

Emission: Kitchen−Ap. 02 Reception: Kitchen−Ap. 03

45

43

−2

Emission: Living room−Ap. 01 Reception: Living room−Ap. 04

46

46

0

Emission: Living room−Ap. 02 Reception: Living room−Ap. 03

41

46

5

Emission: Living room−Ap. 04TA Recept.: Living room−Ap. 03TA

40

43

3

(continued)

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Table 30 (continued) Criterion (dB) (NBR 15575-4)

I-13 (Simple wall)

I-14

a Test

Ambient

In-field

Numerical simulation

 (dB)

Emission: Living room−Ap. 04 TB Recept.: Living room−Ap. 03 TB

42

43

1

Emission: Living room−Ap. 101 Reception: Living room−Ap. 104

41

45

4

Emission: Living room−Ap. 102 Reception: Living room−Ap. 103

40

45

5

Emission: Living room−Ap. 102 Reception: Living room−Ap. 101

42

44

2

Emission: Living room−Ap. 103 Reception: Living room−Ap. 104

43

44

1

I-7 (emission in the gourmet area of Ap.01 and reception gourmet area of Ap.02)

Fig. 38 Scatter plot of results (DnT,w) measured in field and simulated−SVVI Condition I

shown in Fig. 40, for further analysis of how far the SC and MC results are distant from each other. For condition I of the SVVI, that is, in relation to the tests of situations in which the element of separation of the environments was a tinting wall where there was no bedroom, of the 45 trials of the study cases, 15.56% of the sample presented

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Fig. 39 Dispersion plot of SC–MC (in dB)−SVVI Condition I

Fig. 40 Histogram of relative frequency of SC versus MC difference for SVVI Condition I

equal values in SC and MC, being classified as “optimal”, 28.89% of the sample presented a difference of 1 dB between SC and MC, for which it was classified as a “good” result and 22.22% presented a difference of 2 dB, whose classification adopted was “acceptable”, totaling 66.67% of the sample within the considered uncertainty range of ±2 dB for MC, which is the tolerance considered acceptable for the difference between simulation and measurement. In addition to these percentages, 13.33% presented a difference of 3 dB, therefore considered as a “bad” result and 20% presented results from 4 dB, reaching in this sample some values of up to 12 dB,

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Fig. 41 Comparison of SC versus MC−SVVI Condition I

whose classification received was of “poor” level, thus totaling 33.33% from bad to poor for the sample of SVVI–Condition I. Regarding the number of results in which cs was higher than MC or vice versa, i.e. for this sample it was verified that 53.33% of the 45 trials presented computational simulation results higher than the results of field measurement (SC > MC); 31.11% of the tests presented higher field measurement than the computational simulation result (SC < MC) and 15.56% of the tests presented equal values between field measurement and computational simulation (SC = MC), as illustrated in Fig. 41. Thus, this comparison repeats the one presented in the analysis of the results of general SVVI, in which most of the results presented simulation results superior to the result measured in the field, which proves the hypothesis that the ideal conditions of computational simulation will result in values higher than those measured in the field, a reason for the numerous interferences that the field can infer in the actual situation, and which bring damage to the soundproofing provided for in the project.

5.1.2

Condição II–SVVI on Walls Between Autonomous Housing Units (Twinning Walls), in Situations Where There is a Bedroom

Table 31 presents the results for SVVI of field measurement and computational simulation tests for the separation elements in twinning walls in situations where there is bedroom in at least one of the analyzed environments, with the respective calculated difference (SC–MC), with a total of 15 samples analysed. Figure 42 presents the values of computational simulation and field measurement of the 15 SVVI tests on tination walls with at least one bedroom environment are plotted, including the respective uncertainty range of ± 2 dB for field measurement, in the order of the study cases tested according to Table 31. Figure 43 shows the dispersion of the calculated difference between the SC and MC values for these tinting cases, which is named As SVVI–Condition II, in ascending order of variation. Repeating the form of comparative analysis of the other cases, for the comparative analysis of The SVVI values in Condition II, the fact that SC is greater or lower

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Table 31 SVVI tests on wall between autonomous housing units (twinning walls), in situations where there is a bedroom environment Criterion (dB) (NBR 15575-4)

Environment

In-field

Numerical

 (dB)

Minimum: 45 to 49 Intermediate: 50 to 54 Superior: ≥55

Tmanyting wall in situations where there is bedroom

Result (dB) DnT,w

Result (dB) DnT,w

SC−MC

I-03

Emission: Kitchen−Ap. 601 Reception: Suite−Ap. 606

43

42

−1

Emission: Living room-Ap. 504 Reception: Suite−Ap. 503

40

40

0

Emission: Living room-Ap. 604 Reception: Suite−Ap. 603

42

40

−2

Emission: Room−Ap. 1502 Reception: Room−Ap. 1503

45

42

−3

Emission: Room−Ap. 1602 Reception: Room−Ap. 1603

47

42

−5

Emiss: Couple suite–Ap. 101S Recept: Couple suite–Ap. 101 N

46

45

−1

Emiss: Couple suite−Ap. 101S Recept: daughter suite–Ap. 101 N

45

44

−1

Emiss: daughter suite–Ap. 101S Recept: daughter suite–Ap. 101 N

47

46

−1

Emission: Room 1−Ap. 02 TB Reception: Room 1−Ap. 03 TA

54

57

−4

Emission: Room 1−Ap. 03 TB Reception: Room 1−Ap. 02 TA

55

57

−5

Emission: Room 2−Ap. 03 TB Reception: Room 2−Ap. 02 TA

50

56

−2

Emission: Suite−Ap. 102 TA 43 Reception: Room−Ap. 104 TB

52

1

I-08

I-09

I-12

I-13

(continued)

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Table 31 (continued) Criterion (dB) (NBR 15575-4)

Environment

In-field

Numerical

 (dB)

Minimum: 45 to 49 Intermediate: 50 to 54 Superior: ≥55

Tmanyting wall in situations where there is bedroom

Result (dB) DnT,w

Result (dB) DnT,w

SC−MC

Emission: Room−Ap. 102 TA Reception: Suite−Ap. 104 TB

40

51

3

Emission: Room 1−Ap. 103 TA Reception: Room 1–Ap. 102 TB

51

53

−7

Emission: Room 2–Ap. 103 TA Reception: Room 2–Ap. 102 TB

48

52

−5

I-14

Fig. 42 Scatter plot of results (DnT,w) measured in field and simulated−SVVI Condition II

Fig. 43 Dispersion plot of SC–MC (in dB)−SVVI Condition II

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Fig. 44 Histogram of relative frequency of the SC versus MC difference for SVVI Condition II

than MC was disregarded, considering the values in module for the computational simulation versus field measurement difference (SC vs. MC), in order to enable the creation of a histogram of the relative frequencies of this difference, as shown in Fig. 44. In relation to the SVVI trials –Condition II, that is, in situations where the element of separation of the environments was a tinting wall with at least one of the bedroom environments, of the 15 trials of the study cases, 6.67% presented SC results equal to the mc results, being classified as “optimal”, 26.67% of the results showed a difference of 1 dB between SC and MC, for which it was classified as a “good” result and 20% of the sample presented a difference of 2 dB, whose classification was “acceptable”, totaling 53.33% within the margin called acceptable for the difference SC versus MC, corresponding to the uncertainty range of ±2 dB of the field measurement. Apart from these, 13.33% of the results showed a difference of 3 dB, classified as “bad” results and 33.33% of the results showed a difference from 4 dB, with a greater distance between CS and MC in the order of 11 dB, and this portion was classified as “poor”, thus totaling 46.67% of the sample between the “bad” and “poor” levels, according to the comparative classification of analysis. Regarding the number of results in which cs was higher than MC or vice versa, i.e. for this sample it was verified that 46.67% of the 15 trials presented computational simulation results higher than the results of field measurement (SC > MC); 46.67% of the tests presented higher field measurement than the result of computational simulation (SC < MC) and 6.67% of the tests presented equal values between field measurement and computational simulation (SC = MC), as illustrated in Fig. 45.

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Fig. 45 Comparison of SC versus MC−SVVI Condition II

5.1.3

Condition III and IV–SVVI in Blind Wall of Bedrooms Between Housing Unit and Common Areas of Eventual Traffic/ SVVI in Blind Wall of Rooms or Kitchens Between Housing Unit and Eventual Common Areas of Traffic

Tables 32 and 33 present the results for SVVI of field measurement and computational simulation tests, with the respective calculated difference (SC–MC), for the following separation elements: – blind walls of dormitories between housing unit and common areas of eventual traffic, such as corridors and staircase on the pavements, which we call SVVI– Condition III, with a total of 3 tests analyzed (see Table 32), and; Table 32 SVVI trials in blind wall of bedrooms between housing unit and common areas of eventual traffic Criterion (dB) (NBR 15575-4)

Environment

In-field

Numerical

 (dB)

Minimum: 40 to 44 Intermediate: 45 to 49 Superior: ≥50

Blind wall of bedrooms between housing unit and public use spaces

Result (dB) DnT,w

Result (dB) DnT,w

SC−MC

I-03

Emission: Hall−5º Pav. Reception: Suite−Ap. 506

41

41

0

Emission: Hall−6º Pav. Reception: Suite−Ap. 606

41

41

0

Emission: Stairs 17º Pav. Reception: Suite−Ap. 1702

48

39

−9

I-04

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Table 33 Blind wall SVVI trials of living rooms and kitchens between a housing unit and eventual common transit area Criterion (dB) (NBR 15575-4)

Environment

In-field

Numerical

 (dB)

Minimum: 30 to 34 Intermediate: 35 to 39 Superior: ≥40

Blind wall of living rooms and kitchens between a housing unit and eventual common transit area

Result (dB) DnT,w

Result (dB) DnT,w

SC−MC

I-02

Emission: Stairs Reception: Kitchen−Ap. 101

49

38

−11

Emission: Stairs Reception: Kitchen−Ap. 104

50

38

−12

Emission: Stairs−5º Pav. Reception: Sala−Ap. 503

39

44

5

Emission: Stairs−6º Pav. Reception: Sala−Ap. 603

36

44

8

Emission: Stairs 1º Pav. Reception: Kitchen−Ap. 103

42

38

−4

Emission: Stairs 1º Pav. Reception: Kitchen−Ap. 104

44

38

−6

Emission: Stairs 2º Pav. Reception: Kitchen−Ap. 203

33

38

5

Emission: Hall 24 Reception: Kitchen−Ap. 02

44

20

Emission: Hall 25 Reception: Kitchen−Ap. 03

44

19

Emission: Hall 26 Reception: Kitchen−Ap. 04

43

17

Emission: Hall Reception: Kitchen−Ap. 101

27

42

15

Emission: Hall Reception: Kitchen−Ap. 101

25

42

17

I-03

I-06

I-12

I-14

– blind walls of rooms or kitchens and common areas of eventual traffic, such as corridors and staircase on the floors, which we call SVVI–Condition IV, with a total of 12 tests analyzed (see Table 33).

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Figure 46 presents the values of the computational simulation and field measurement of the 3 SVVI tests of condition III are plotted, i.e. blind walls between dormitories and eventual transit areas, and Fig. 47 the values of the 12 SVVI tests of condition IV, that is, of situations in which the separation element is blind walls between rooms and kitchens and eventual transit areas, including with the respective uncertainty range of ±2 dB for field measurement. Taking into account that in condition III, there are only 3 results, and that in condition IV, there are 12 results, and that both situations have as contiguous environment

Fig. 46 Scatter plot of results (DnT,w) measured in field and simulated−SVVI Condition III and IV

Fig. 47 Scatter plot of results (DnT,w) measured in field and simulated−SVVI Condition III and IV

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Fig. 48 Dispersion plot of SC–MC (in dB)−SVVI in blind wall of a bedroom (condition III) and blind wall of living rooms and kitchens (condition IV) and eventual traffic areas

an area of type staircases and corridors, the analysis of the dispersion of the differences between field measurement and simulation for these 15 trials is presented in Fig. 48. The dispersion of the calculated difference between the SC and MC values are presented in Fig. 48 The first 3 points presented correspond to condition III and the following 12 points refer to condition IV. In all tests for these two conditions, the sound source was located on the staircase or in the hall space of the floors, as illustrated in situations A and B in Fig. 49. Only in case study I-03, the hall was a confined environment (sit. A in blue in Fig. 49), which is why, for these results, the measurement and simulation values are compatible, as can be seen in the points referring to data 2 and 3 of Fig. 52. In other situations, the hall environment (social or service) shares the same space with the access ladder to the pavement, and the values of the comparative simulation and measurement showed great discrepancy, with differences ranging from 5 to 20 dB, as can be seen in Fig. 48. What was evident in the evaluation of the values presented is that the computational simulation presents discrepant values when compared to those measured in the actual field situation for the stair environments where there is no confining, because there is dissipation of part of the sound emitted through the interconnected floors of the stair wells, that is, it is observed escape of portion of the sound emitted through the open/empty span between floors. For this reason, in the situation where the emission of sound occurs in stair well and reception in adjacent environment, the comparison of simulation and measurement becomes doubtful, since the program has the limitation of considering the spaces as confined, calculating a reverberation value and consequently transmitting the sound

Acoustic Performance Criteria in Internal Vertical Partitions …

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Fig. 49 Hall environment in case studies: hall confined in case study I-3 (sit. A, in blue), shared staircase with social hall or service hall in other studies (sit. B, in yellow)

different from the actual situation, because the reflections that would occur in the confined space are different in a space where open spans dissipate portion of the sound waves that would be transmitted by the separator element. Thus, because the intercommunication between the floors in stair wells and, consequently, possible partial escape of the transmitted sound, is not considered, the simulation program presents incompatible/conflicting values for the present study, demonstrating the limitation of this analysis through computational simulation, as illustrated in Fig. 50. Repeating the form of comparative analysis of the other cases, for the comparative analysis of the SVVI values in Conditions III and IV, the fact that SC is greater or lower than MC was disregarded, considering the values in module for the computational simulation versus field measurement difference (SC versus MC), in order to enable the creation of a histogram of the relative frequencies of this difference, as shown in Fig. 51. In relation to the SVVI trials–Condition III and IV, of the 15 trials of the study cases, 13.33% presented SC results equal to the MC results, being classified as “optimal”, which were specifically the tests in which the hall was confined environment, being this percentage the only one within the designated margin acceptable for the SC versus MC difference, corresponding to the uncertainty range of ±2 dB of the field measurement. The remaining 86.67% of the results showed a difference from 4 dB, with a greater distance between SC and MC in the order of 20 dB, and this portion was classified as “poor” for the present study. This result confirms the limitation of simulation for the non-confined environment.

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Fig. 50 Example of acoustic test in SVVI where the sound emission occurs in stairs or hall connected to the stairs, where sound dissipation between floors occurs

Fig. 51 Histogram of the relative frequency of SC–MC, for SVVI tests in blind wall of bedrooms and living room/kitchen with stairs/halls

Regarding the number of results in which cs was higher than MC or vice versa, i.e. for this sample it was verified that 53.33% of the 15 trials presented computational simulation results higher than the results of field measurement (SC > MC); 33.33% of the tests presented higher field measurement than the computational simulation

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Fig. 52 Comparison of the results of SC versus MC−SVVI in blind wall of a bedroom and living room/kitchen with eventual traffic area (stairs and halls)

result (SC < MC) and 13.33% of the tests presented equal values between field measurement and computational simulation (SC = MC), as illustrated in Fig. 52.

5.1.4

SVVI Geral Without Discrepancies

Removing from the general analysis of SVVI, the data referring to conditions III and IV, whose computational simulation cannot reproduce the actual situation of interconnection of floors in the stairs, because it mistakenly considers them as confined environments, we will reduce the overall SVVI data mass from 75 to 62 tests, and thus the analysis achieves greater representativeness regarding the fidelity of the simulation in relation to the actual situation of the environments. For these 62 general SVVI values without the discrepant data, 17.74% of the sample presented equal values in SC and MC, and this part was classified as “optimal”, 27.42% presented a difference of 1 dB, for which it was classified as a “good” result and 20.97% presented a difference of 2 dB, whose classification was “acceptable”, totaling 66.13% of the sample within the uncertainty range considered of ±2 dB, this being the acceptable margin considered for the difference between numerical simulation and in-field test results (see Fig. 53). In addition to these percentages, 12.90% presented a difference of 3 dB, classified as a “bad” result and 20.97% presented results from 4 dB, whose rating received was “poor”, totaling 33.87% of bad to poor for this sample, but whose highest values in the order of 9 and 11 dB between SC and MC (only 1 value of each), suggest measurement error or divergence between design and execution. Thus, removing the conflicting measurement and simulation values from the total sample referring to the general SVVI data, 66.13% were within the acceptable range and 33.87% presented results considered bad to poor.

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Fig. 53 Histogram of relative frequency of SC−MC for geral SVVI assays without discrepancies

5.2 Summary of the Results Presented Table 34 presents, synthetically, the classification adopted in the present study for all the results of the comparative SC versus MC in relation to the variation of the difference (dB) calculated SC–MC. Regarding the distancing of SC and MC, Table 35 Table 34 Classification summary of the systems studied SVVI geral

53.33%

Optimal until Acceptable 0–2 dB

46.67%

Bad to Poor: 3 dB and >4 dB

66.67%

Optimal until Acceptable 0–2 dB

33.33%

Bad to Poor: 3 dB and >4 dB

53.33%

Optimal until Acceptable 0–2 dB

46.67%

Bad to Poor: 3 dB and >4 dB

SVVI (Condition III and IV−blind wall of a bedroom and living room/kitchen with staircases or hall)

13.33%

Optimal until Acceptable 0–2 dB

86.67%

Bad to Poor: 3 dB and >4 dB

SVVI general without discrepancies

66.13%

Optimal until Acceptable 0–2 dB

33.87%

Bad to Poor: 3 dB and >4 dB

SVVI (Condition I−twinning wall without a bedroom) SVVI (Condition II−twinning wall with a bedroom)

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Table 35 Comparative summary (Distance between SC and MC) SVVI geral

52.00%

SC > MC

13.33%

SC = MC

34.67%

SC < MC

53.33%

SC > MC

15.56%

SC = MC

31.11%

SC < MC

46.67%

SC > MC

6.67%

SC = MC

46.67%

SC < MC

SVVI (Condition III and IV−blind wall of a bedroom and living room/kitchen with staircases or hall)

53.33%

SC > MC

13.33%

SC = MC

33.33%

SC < MC

SVVI general without discrepancies

48.00%

SC > MC

18.00%

SC = MC

34.00%

SC < MC

SVVI (Condition I−twinning wall without a bedroom)

SVVI (Condition II−twinning wall with a bedroom)

presents a comparison of the SC versus MC for all systems studied.

5.3 Specific Situations–Discussions of the Particularities During the computational simulation stage, some specificities were observed in the evaluation of the expected results. The most important observation concerns the input data, which is essential for the reliability of the simulation step. Input data that differs from actual execution data will produce incompatible results. In some case studies, the simulation was redone after observing a great distance between the SC and MC results, since the results of MC were already known. Now the data have been ratified, now they have been corrected. Thus, there were situations in which the new simulation did not present any difference from the initial one, but there were others in which some particularities required remodeling that generated new bedroom values, which revealed some specificities.

5.3.1

SVVI–Air Space (Expansion Joint) Between Twintowers

For the SVVI system of case studies I-12, I-13 and I-14, it was observed, in the analysis of the projects, that among the twintowers was provided for a 20 mm expansion joint, exemplified in Fig. 54, which was considered in a first simulation, which allowed variations in this input data and some conclusions regarding the acoustic behavior.

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Fig. 54 Case study I-12 with detail of expansion joint between towers

In the initial simulation of the projects of these case studies, the wall between the twintowers was considered as a simple wall, so that the result of this simulation resulted in aerial sound insulation data for the simple wall element, a situation different from that found in the field, and in this specific case, the field measurement values were well higher than the simulated values. Finally, two other situations were tested: folded wall and double wall with joint (air space) of 20 mm, in order to verify the acoustic behavior in the projects, as illustrated in Fig. 55. The variation of the input data allowed new Rw sound reduction values for this separation element and, consequently, demonstrated the relationship of the reduction of sound intensity with the thickness and composition of the studied element, confirming the study by Souza et al. (2013) that air noise bedroom has close agreement with the law of the masses. By computational modeling only of the separation element simple concrete wall without cladding, the variation showed an increase of insulation of 11 dB between the type single wall of 10 cm and folded wall of 20 cm

a) Simple Wall

b) Double wall (folded)

Fig. 55 SVVI simulation variation in twintowers

c) Double wall with 20mm gasket

Acoustic Performance Criteria in Internal Vertical Partitions …

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( = 56–45 dB), and 13 dB between folded wall of 20 cm and double wall of 10 cm each with joint (air space) of 20 mm ( = 69–56 dB). Table 36 presents the results of the computational simulation of the SVVI of these cases (I-12, I-13 and I-14) between semi-twin towers, considering the variation of single wall, folded wall and double wall with joint (air space) of 20 mm, with a total of 7 samples analyzed. According to the dispersion graph presented in Fig. 56, corresponding to the acoustic behavior tests of projects I-12, I-13 and I-14, after the modification of the input data in the simulation (from single wall to double wall and double wall with joint between towers), the increase in sound insulation in the analyzed environments is clearly perceived. Another observation pointed out is in relation to the difference between the Values SC and MC, whose new simulation, considering the simulation according to the project (including the air space referring to the i was called the expansion joint in Table 36 SVVI assays between semi-ingemated towers, varying the type of wall element Criterion (dB) (NBR 15575-4)

Environment

In-field

Numerical simulations  (dB) Single wall

Folded wall

Double wall

Minimum: 45 to 49 Intermediate: 50 to 54 Superior: ≥55

Twinning wall Result in situations where there (dB) DnT,w is a bedroom

Result (dB) DnT,w

I-12 (Single wall/Folded wall/Double wall)

Emiss: Bedroom 1−Ap 54 02 TB Recept: Bedroom 1–Ap. 03TA

45

50

57

Emiss: Bedroom 1−Ap.03 TB Recept: Bedroom 1–Ap. 02TA

55

45

50

57

Emiss: Bedroom 2−Ap. 03 TB Recept: Bedroom 2–Ap. 02TA

50

43

48

56

Emiss: Suíte−Ap. 102 TA Recept: Bedroom−Ap.104 TB

43

44

52

54

Emiss: Bedroom−Ap.102TA Recept: Suíte−Ap.104 TB

40

43

51

54

Emiss: Bedroom 51 1–Ap.103TA Recep: Bedroom 1–Ap. 102 TB

44

52

53

Emiss: Bedroom 48 2–Ap. 103TA Recep: Bedroom 2–Ap. 102 TB

43

51

52

I-13 (Single wall/Folded wall/Double wall)

I-14 (Single wall/Folded wall/Double wall)

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E. C. L. Rezende et al.

Fig. 56 Particular case−expansion joint between towers−SVVI for I-12, I-13 and I-14

the architecture project), pointed out greater proximity between SC and MC, evident in cases I-12 and I-14 (between 2 and 6 dB), which did not occur in the two trials of cases I-13, which after the inclusion of the joint, resulted in very distant values between SC and MC (between 11 and 14 dB). This specific situation in the case studies of I-13 may have occurred both due to uncertainty of compliance in the field of the project dimensions, either from the projected expansion joint, or from the partition and coating system performed, as well as by the lack of correct input data or failure in the field measurement procedure, which would need to be checked and inspected to prove the values. Figure 57 shows photos of said building in the execution phase of the work and in delivery, whose record suggests doubt as to the execution of said board. In general, it was observed that after the adjustment in the input data, the simulated values were all higher than those measured in the field, a situation that would be the initial hypothesis predicted, since in the computational simulation is the ideal

Fig. 57 Photographic record of building I-13 in the stages of execution of the work and delivery

Acoustic Performance Criteria in Internal Vertical Partitions …

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environment, whose conditions of perfection discard the potential interferences of the in loco measurement.

5.3.2

SVVI in the Cases of Solid Concrete Walls and Slabs–Calibration of the Data

For case studies I-10, I-11, I-12, I-13 and I-14, whose composition of the wall elements and floor system consisted of solid concrete, it was observed that the specific concrete density data of 2400 kg/m3 for the cases of SVVI, inserted in the Insul program for the modeling of the elements, promoted values lower than the indicative in the studies of UNICAMP (Neto 2009; Neto et al. 2010) and the CBIC Guide (2013) on 45 dB sound insulation for air noise. Calibrating the specific density of the concrete to 1900 kg/m3 , in the case of the wall elements–SVVI, the reference value of 45 dB of insulation for this type of element was reached, and hence the values modeled in The Insul were applied to the Sonar program to continue with the calculation the acoustic behavior of the studied environments. For the cases of SVVI, with the adjustment of the specific density of the concrete, the results of SC tended to be very close to MC results, as demonstrated in the dispersion presented in Fig. 58 and Table 37. It was also observed that 82.6% of the tests met the expected of the initial hypothesis of the simulation being superior to the field measurement, as shown in Fig. 59.

Fig. 58 Scatter plot of results (DnT,w ) measured in field and simulated−SVVI (Solid concrete walls)

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Table 37 SVVI results for concrete wall study cases Environment

I-10

I-11

I-12

I-12 (Double wall)

In-field

Numerical

 (dB)

Result (dB) DnT,w

Result (dB) DnT,w

SC−MC

Emiss: Kitchen−Ap. 01 41 Recept: Kitchen−Ap. 03

43

2

Emiss: Kitchen−Ap. 02 41 Recept: Kitchen−Ap. 04

43

2

Emiss: Kitchen−Ap. 104 43 Recept: Kitchen−Ap. 102

43

0

Emiss: Living room−Ap. 01 Recept: Living room−Ap. 03

43

44

1

Emiss: Living room−Ap. 02 Recept: Living room−Ap. 04

43

44

1

Emiss: Living room−Ap. 104 Recept: Living room−Ap. 102

40

45

5

Emiss: Kitchen−Ap. 01 44 Recept: Kitchen−Ap. 04

43

−1

Emiss: Kitchen−Ap. 02 45 Recept: Kitchen−Ap. 03

43

−2

Emiss: Living room−Ap. 01 Recept: Living room−Ap. 04

46

46

0

Emiss: Living room−Ap. 02 Recept: Living room−Ap. 03

41

46

5

Emiss: Living 40 room−Ap.04 TA Recept: Living room−Ap.03TA

43

3

Emiss: Living 42 room−Ap.04 TB Recept: Living room−Ap.03 TB

43

1

Emiss: Bedroom 1−Ap. 02 TB Recept: Bedroom 1−Ap. 03 TA

54

57

3

Emiss: Bedroom 1−Ap. 03 TB Recept: Bedroom 1−Ap. 02 TA

55

57

2

Emiss: Bedroom 2−Ap. 03 TB Recept: Bedroom 2−Ap. 02 TA

50

56

6

(continued)

Acoustic Performance Criteria in Internal Vertical Partitions …

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Table 37 (continued) In-field

Numerical

 (dB)

Result (dB) DnT,w

Result (dB) DnT,w

SC−MC

Emiss: Living room−Ap. 101 Recept: Living room−Ap. 104

41

45

4

Emiss: Living room−Ap. 102 Recept: Living room−Ap. 103

40

45

5

Emiss: Suite−Ap.102TA 43 Recept: Bedroom−Ap.104 TB

52

9

Emiss: Bedroom−Ap. 102 TA Recept: Suite−Ap.104 TB

40

51

11

Emiss: Living room−Ap. 102 Recept: Living room−Ap. 101

42

44

2

Emiss: Living room−Ap. 103 Recept: Living room−Ap. 104

43

44

1

Emiss: Bedroom 1−Ap.103 TA Recept: Bedroom 1−Ap.102 TB

51

53

2

Emiss: Bedroom 2−Ap. 103TA Recept: Bedroom 2−Ap.102 TB

48

52

4

Environment

I-13

I-13 (Double wall)

I-14

I-14 (Double wall)

Fig. 59 Comparison of the results of SC versus MC−SVVI (Concrete walls)

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6 Conclusions From the analyses of the results of the case study of this experimental work, it can be inferred that the computational simulation of acoustic behavior presents potential for compatibility with field measurement of more than 50% for the evaluation of vertical partition systems (SVVI). This compatibility is linked to the percentage of values of the Difference SC versus MC that were within the range classified as acceptable of ±2 dB, referring to the margin of uncertainty of the field measurement provided by ISO 16283-2 (2018) and ISO 12999-1 (2014), which induces an interpretation that the values within this range are potentially equal. It was observed that, although a portion of the comparative analysis showed a distance above 3 dB between field measurement and computational simulation, by which the criterion of classification of values of this order was adopted as bad results, since they were outside the margin of uncertainty of ±2 dB, this portion from 3 dB allowed two interpretations: – in cases where the computer simulation was lower than the SC < MC field measurement, it is admitted to suggest that when using computer simulation, it is working in favor of safety, with great possibilities of not only achieving the predicted, but of overcoming it, thus ensuring a higher quality than that required in the standard. It means that, if in the simulation the enterprise was predicted to meet a certain level of performance, that for the requirement of sound insulation the performance standard requires only the minimum level, in the field will be found a better insulation, with the potential to meet the intermediate or higher levels of said standard, thus giving a higher quality to the enterprise; – in cases where the computational simulation was greater than the SC–MC in-field measurement, it is then proven the initial hypothesis that the execution uncertainties, the construction failures and the potential field interferences decrease the acoustic bedroom potential of the building elements, which were predicted in controlled situations of the computational simulation, which are the same ideal situations of the laboratory tests. In relation to internal vertical partition systems (SVVI) in which the separation element was between eventual transit environment of the staircase type or hall conjugated to stairs, it was observed that the computational simulation can not reproduce the particularity of the interconnection of floors and possible partial leakage of the sound emitted through the empty span of the staircase, which compromises the result of the simulation. The limitation of the program in considering the confined span rather than interconnected span, will produce discrepant values to the reality of field measurement, thus demonstrating contraindication of this tool as long as there is no update that corrects such restriction. Thus, removing these conflicting cases, the percentage of acceptability of the SVVI system will rise to 66%, leading to assertiveness in the use of the tool studied.

Acoustic Performance Criteria in Internal Vertical Partitions …

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Another particularity found in the analysis performed in the SVVI systems was the cases of studies in which air spaces were predicted between twin towers (named as expansion joints in the architectural project), where it was observed how much the variation in the input data induces divergent bedroom values. It was possible to test situations of single wall, folded wall and double wall with air space between them, and it was concluded that the variation in the input data of the concrete wall element allowed an increment of 11 dB, if comparing single wall with folded wall, and 13 dB, if comparing double wall and double wall with joint of 20 mm only as air space between the walls, for this study, proving the analogy of air noise bedroom to the law of the masses.

References Almeida M, Silva S, Ferreira T (2006) Building physics. Environmental and building acoustics. Universidade do Minho, Portugal Arizmendi LJ (1980) Fundamental treaty of acoustics in la edificacion. Pamplona, Spain Arndt LT, Philips JW, Barbosa WA (2010) Geographic information system for urban noise mapping. Proceedings of the III Simpósio Brasileiro de Ciências Geodésicas e Tecnologias da Geoinformação. Recife: SIMGEO, Brazil Brazilian Association for Acoustic Quality (ProAcústica) (2017a) ProAcoustic manual on performance standard. São Paulo, Nrazil Brazilian Association for Acoustic Quality (ProAcústica) (2017b) ProAcoustic manual for noise class of housing buildings. São Paulo, Nrazil Bezerra AFD, Brito AC, Aquilino MM, Akutsu M, Vittorino FV (2018) Electrical outlet boxes and wall insulation failures. In: Proceedings of the national meeting of built environment technology, vol 17. Foz do Iguaçu, Porto Alegre: ANTAC, Brazil Bistafa SR (2011) Acoustics applied to noise control. Blucher, Brazil, São Paulo Borges PD (2009) Acoustic. In: Physics handout. Santa Maria: Universidade Federal de Santa Maria. Brazil Brazilian Association of Technical Standards (ABNT) (2013) NBR 15575: Housing buildings−performance. Rio de Janeiro, Brazil Brazilian Chamber of Construction Industry (CBIC) (2013). Performance of housing buildings: guiding guide to meet the standard ABNT NBR 15575/2013. Fortaleza: Gadioli Cipolla Comunicação, Brazil Brazilian Association of Technical Standards (ABNT) (2017) NBR 10152: Acoustics−sound pressure levels of indoor environments. Rio de Janeiro, Brazil Brazilian Association of Technical Standards (ABNT) (2019) NBR 10151: Acoustics−Measurement and evaluation of sound pressure levels in inhabited environments−application for general use. Rio de Janeiro, Brazil Bruel M, Kjaer J (1984) The sound measurement. Denmark, USA Carvalho LN (2015) Impact noise on slabs: Comparative analysis between performance of computational models and in-field tests. MSc Thesis, USP. São Paulo, Brazil Cornacchia GMM (2009) In-situ investigation of sound insulation to impact noise in residential buildings. MSc Thesis, Universidade Federal de Santa Catarina. Florianópolis, Brazil Costa EC (2003) Technical acoustics. Blucher, Brazil, São Paulo Costa JJL, Oliveira LN (2016) Semi-empirical simulations in acoustics: Technological innovation in the prediction of sound pressure levels inside buildings. Rev Geintec 6(2):3128–3142 Everest FA (2001) Master handbook of acoustics, 4th edn. McGraw-Hill, USA

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