2018 IBC SEAOC STRUCTURAL SEISMIC DESIGN MANUAL VOLUME 2 EXAMPLES.pdf

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2018 IBC®SEAOC STRUCTURAL/SEISMIC DESIGN MANUAL VOLUME 2 EXAMPLES FOR LIGHT -FRAME, TILT-UP, AND MASONRY BUILDINGS

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Copyright Copyright 0 2020 Structural Engtneers A~iation ofCaltfornia AJI rights reserved. This publicalJOI\

or a.1y pan thereof must not bl!' reproduced t.n any fonn without the written pemllssion of the Struc:turnl Engineers Assoctalion of California. ..The IntemalJOnal Buildmg Code'" and the ..JBC"' are registered trademarks oflhe InteJnalional Code

Council.

Publisher Structural Engtneers Assocaalion ofCahfornaa (SEAOC) 92 1 lllb Street, Suue 1100

Sac.rameruo. Califomja 95814 Telepoone: (916) 447-1198; Fax: (916)444- 1501 E-mad: [email protected]~ Web address: \VWw.seaoc.org

The Structural Engineers ASSOCiatton of CalifOrnia (SEAOC) is a pmfesstonaJ assocaauon of four regtonal member organizatttm.>(j (Southem CalifOrnia. Northem CahtOmia. San Diego. and Central CalitOmia). SEAOC represents lhe structural e-ngu~erutg c:ommuntty ll\ C.ahfornta. nus document IS published in keepang walh SEAOC's stated miSSion:

To advance lhe structural engtneering profession~ to provide the public with strucrures of depe-ndable pe.rfom'taoce through the application of state-of-the-an structural engineering pnnc.tples; to assist the public m obtaining professional strocturaJ engineering servtees; to promote natural hazard mttigation; to provtde conunutng educauon and encourage research; to provide structural engtneers wtth the most current tnformauon and tools 10 improve their practice; and to mamtatn the honor and dtgntty of the pfOfess.on.

Editor lnrernattonal Code Council

Disclaimer \Vhtle the mfocmation prese1ned tn this document is believed to be.COO'ect, neither SEAOC nor its ll'k!'.mbe-r org.anizauons, committees, writers, editor~ or indtviduals \'-ilo have contrabuted to this publication make any warranty, expressed or tmplted, or assume any legal habtlny or responslbdity for the use, application of, and/or retere-nce to optnaons. findtng~ ooncluston.'i., or recommendanons mcluded mthis publication. The material prese-nted tn thts publication should not be used for any s~t fic application wuhout compete-nt e.xamination and verification of its ac.cumcy, suitabthty, and applicabdity. Users ofinfocmation from this publtcation assume all liability arising from such use. F1rs1 Pnn11ng: July 2020 ISBN: 978-1-60983-997-0 T0251t2

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2018 IBC SEAOC Stroctu.rai!Seismic Design Manual. \lbl. 2

Suggestions for Improvement Comme-ms and suggesttons for improvements are welcome ru\d should be sent to lhe following:

Structural Engineers Association ofcaltfbmta (SEAOC)

Don Schtnske, ExecutiVe Dtree-tor 921 I lib Street, SUite I 100 Socromenro, Califbrma 95814 Telephone: (916) 447- 1 198; Fax: (916) 444- 1501

E-mad: d,.,[email protected]

Errata Notification SEAOC has made a substantral etfon to ensure that the information tn tlus docwnent is accutate. In the event that cocrecuons or elardicauons ilte needed, these will be posied on the SEAOC website at ~-w-w.staot.org and on the ICC websne at ~w.k:tsart.org.

SEAOC. at

it~ sole discreuon. may 1ssue wr itte1l

errata

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2018/BC SEAOC StrocturaVSeismic Design Manual, \01. 2

Table of Contents Preface to the2018/BC SEAOC !>intcturol/Sei.smic Design Mtmual . .....• . ... . . .. . ... . ........

VII

Preface to Volwne 2 .

IX

AcknO\vledgmenL~

.. •...•. .

XI

References .. ...... ...... .

Xtli

t-10\V to Use Th1s Document. . . . . . . . . . . . . . • • • • • • • • • • • • • . . . . . . • • • • • • . . . . . . . . . . . . . • • • • . . . . x.xi

Design E.xsunplt I Four-Story Wood Ltght-Frame Structure.... .

Design E.xamplt 2 Flexible Diaphragm Design. . . . . . . . . . . . . • . • • • . • • • . . • . . • . • . • . . . . . . . . . . . . . . . . . . . . . 133 Design E.xamplt J Three-Story Light-Frame Mulufanuly Buildlng Design Ustng Cold-Formed-Steel Wall Framing and Wood Floor and Roof Fram1ng . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 155 Design E.xamplt 4

Masonry Shear Wall B01ld1ng . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 273 Design E.xamplt S

Tih·Up BU1Id1ng . . . . . . . . . . . . . . . . . • . . . • . • • • . • • . . • • • . • . • . • . . . . . . . . . . . . . . . . • . . . . 299

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2018/BC SEAOC StrocturaVSeismic Design Manual, \01. 2

Preface to the 2018 IBC SEAOC Seismic/Structural Design Manual The IBC SEAOC Selsmic/Srructural Dtsign ManU(J/, throughouttl"i many edtuons. has served the purpose of iHusuaung good seismtc destg.n aoo the correct appl icat1011 of buildtng-code provtsions. 1be l<mual has bridged the gap betv.'een lhe discursive ueaunent of topics in the SEAOC Blut Book (Rtcommtntkd La/eru/ Force Requiremenu and Commentary) and reai-YI'Orld dectstons that desagners face t.n thetr pracuce.

The examples tllusttate code-complianr designs enguleered to achttve good pe,rformance under se\•ere sei.snhc load mg. In some c.ases simply complytng walh butlding-code reqUirements does not ens·ure good seismic response. This Manual takes the approach of e.xceedtng the mtntmum code require-mems in such

cases. wnh diSC-ussion of the reasons for doing so. llus manuaJ comprises four volumes: Volume 1: Code Application Exomples

Volume 2: Examples for ltght-Frame. Tllt-Up. and Ma.:;onry Budd1ngs Volume 3: Examples for Concrete Buildings Volume 4: Examples for Steel-Framed Buildings

In general. the provisions for developing the des1gn base shear. d1sttibut1ng lhe base-shear-forces \'ertically and hori2onmlly. dled:ing for irregu1arit1es.. etc .• are illosuated m Volume I. 11te olher volumes contaJn more extens1ve design examples that address tJ1e requarernents of the mater1al standards (for example. ACI 318 and AISC 341) that ate adopted by the lBC. Bulklingdes&gn examples do not illustrate 1nany of the 1tems addressed 1n Volume I in order to perm at the inclusaon of less--redundant contenL Each volume has been produced by a small g(Oup of authors under the direction of a manager. lbe managers have assembled te\'lewers to e.nsure coordmation wnh other SEAOC work and publications. most notably me Blue Book. as well as numenca1 ac:curac:y. ThiS rnanua1 can serve as \1aluable tool for eng.i~n seektng £O design buildings and build1ng components

fOf" good seismtc response. Rafael Sabello and Katy Broggs

Project Managers

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20t8 IBC SEAOC Structurai/Seis;c Desig'J Manual, tAll 2 @Seismicisolation @Seismicisolation

Preface to Volume 2 Volume 2 oflhe 20 18/BC SEAOC SJructuro//Se,snuc De.slgn Mamw/ addresses the design of light-frames ooncrere nit-up, and masonry shear wall buildmg systems for seismic loodmg. These ln('.fude the tllus.trarjon oi the design requirements for the shear \\ails ru\d diaphragms, ao; were illustrated in previous editions, and also tmponaru mtertaces with the rest of the structure.

The de:s1gn example.-; ln lhis volume represent a range of structural systems and seismtc syst·ems. The design of each of lhese systems is go,•e.rned by standards developed by the American Concrete Jnsutute (ACI) and the Amencan Wood Council (AWC). The methods tllustrated hereto represent approaches conststent w1lh the ducuhty expec.tauons for each system and wnh the des&red se1smtc response. In nlost cases there are se\'eraJ dem.Jls or mechanisms thal can be uti!ized to achieve the ducul ity and resistance requtred, arld the author or each example has selected an apptopriate opdon. In many cases alternadves are discussed. Th1s .Mauua/ tS oot imended to serve as a buildi11g code or to be an exhausuve catalogue of all valtd approaches and de-rolls.

llus ,\fa.nuli/IS prese-nted as a set of examples tn whtch lhe engineer has considered the butldtng-code requtremems in conjunction v.ith lhe opumal setsmic respon.o;e oflhe system. The examples follow the guidelines oflhe SEAOC Blut Book and other SEAOC rec.ornmendatioos. The exampl e.~ are intended to atd conscie-nlJOUS destgnetS 1n c.-raftmg destgns that are likely to achieve good sttSJtuc perfOrmance cons.stent v.1th expectations inhere1U tn lhe requtrements for the syste:.ns. Douglas Thompson

Volwne 2 Manager

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2018 ISC SEAOC Stroctu.rai!Seismic Design Manual, \lbl. 2

Acknowledgments VoJume 2 oflhe 20 18/BC SEAOC ~wmdStrucwral De.slgn .M.tmubl was wnnen by a group of highly qualified srructutal enganeers, chosen for lhear know1edge and experience with structural engu-.eertng practice and seismic destgn. The authors are: DouglasS. Thompson, S.E., S. E~C. B-Vo lumt M.anagtr and E~:amplt- I

Doug Thompson has over 40 years of expenence 1n designang of wood st.rucrures. He as the author of severaJ pubhcauons an umber desagn including the WoodWotks publications: Four-story IV()()(/{ranw StruCIUrt Ol·er Pcdlum Slab and Fn-e-story U'IHK/-frame StniCtuf? O'rtr Podmm Slab. Doug has instruc.ted

ltcense review·classes in umber destg.n for t11e PE and SE e.xams tor 20 years. He 1S a past prestdent of the Structural F..llgtneets Association of Southern C.a1iforma and holds Jteenses tn SlX states. vN;W.stbse.com John

la~'So n~

S.E..-Examplrs 2 11nd S

Professor John Lawson has provtded st.ruclutal engineenng consultlng se:rv1ces tOr 0\'et 30 years, mdudjng overseeing more than 100 mill1on square feet ofiM\'-sloped roof and uh-upconcrete engt.neenng. He now teaches m the Architectural El'lg1neenng depanment at Cal1fomia Polytechnic State Universuy 1n San ltJjs Obispo. John is lhe recipient oflhe 2006 Tth-Up Conctete Associauon·s David L Kelly DisungUtshed Engu~er Award. www.arce.calpoly.edu Mithatl Cochran, S.E., S.E~C. B.- Examp lt 3 Michael Cochran is a Vice President wnh Thonuon TomaSOCtation, 1994, Northrid~. Califorma Earthquake. Repon T-94-5. Engineered Wood Assoctalion.. Tacoma. Wa'iliington. Amencan P1ywood Association, P~rformance SJandard For Heod-Based Strucwral Use Panels. PS2-04. National 1nsutute of Standards and Technology, \Vashmgton, OC. A.tnertcan Plywood Association, 1997, Ply..-ood Design Spectjications, From Y510. Engtnee:red Wood Associauon. Tacoma, Wa.nslu'ps tn U~ in Compn!SSIOn Perpendiodar to Grow. U.S. Oepan.m.enl of Agrtculture. Forest Products Research Society (Forest Products Socie.ty) Fotest Products Journal. Madison, Wiscoostn. Brandow, Gregg E., Chul~\'\lma G. Elmueme and Gary C. Hart, 2009. Dwgn ofRtmforcttd Masomy Structurt.t. Concrete Masonry Association of California and Nevada, Sacramento, Cahforma Breyer, Donald E., Kenneth J. Fndley, David G. Pollock, Jr. and Kelly E. Colleen, 2007. Destgn of Wood Slructures ASD. McGraw-Hill Book Co., New York. NewYock. Bugnt. David A .• 1999• ..A Linear Elastic Dynamtc AnalySIS tifa 1imbt'r Framed SlniCiure. ·· Buildtng Standards.lmernauon.al Conference ofBuildang Offic1als. Whmier, Caltfornta Building Setsmac SaJtty Counc.il, 2003. NatiOnal Earthquake Ht:rard Reduclion Program. Recommended Prowsionsfor Seismic Regulations for New Bwldings. Pans I and 2. Building Seismic Safety Council, Washington. DC. Cobeen. K.E., 1996. ••J>erfonnance Based Design ofWood Strucnues... Proceedings: Annual SEAOC Convention. Structural Engineers Associauon of Caltfomia.. Sacramento, California Coal, J., 1999...Setsmtc Reuofit of an E«1sung Multt-Story Wood Frame Structure;• Proceedangs: Annual SEAOC Con\'entiott. Structural Engineers Assocaauon ofC.aJjfotnaa. Sacramemo. CaJitbmla Cornmins, A. and Gregg. R., I996. Effie/ cfHold Downs and SIUd-Frume Sys1ems on the Cycltc Behtn·ior ofWood Shear Walls, Stmpson Strong-Tie Co., Pleasanton, caJi10rnia Commtns, Alfred D., August 2008, Rod Tie-Down Sys1ems. Part 5-/n.rpecuau. Strueture Magazine, Nalioatal Councd of Suuctural Enganeers Associarjons (NCSEA). Cook, J., 2010, "Stmphfied AnalySts of Wood Shear Walls with Muluple Opemngs" Proceedtngs: Annual SEAOC Cooven1ion. Structural Eng.i~n Assoctation of CaJjforma, Sacramenro, Cal1forma Cook. R.A., I999...Suength Oestgn ofAnchorage to Concre.te." Ponland Cement As:soctauon, Skol:ie,llhnoiS. Countryman. D.• and Col Benson, 1954, 1954 Hori=ontal Pl;wood Diaphragm Tesu.laborotory Repon 63, Douglas Fir Plywood Associatjon, Tacoma. Washington. CURE.e. 1999, Proceedings oflhe JJOrk..thopon Setsmic Testing. Analysis. and De.ttgn of Wood Frame Construction. Cahfomta Umversaty tOr Research an Eal'thquake Engtneenng. Dolan, J.D., I996. Ex~nmental Re.tulufivm Cyclic Rackmg Tesu ofJil>cd Shear Walls with O~nmgs. Timber Eng~netonng Repott No. TE- 1996-001 . Varg1nia Polytechntc: Institute and State Unaversity, Blacksburg. Virgania Dolan, J.D. and Heine. C.P.• 1997a. Monownic Ttstt ofJIObd Frome Shear Walls with f'hrious Openmgs and Bast! Re.s1rai111 Co,(tgurotions. Timber Engtneering Repon No. TE-1997-00 I. Vtrgtnia Pol)1echnjc lnsttrute and State Univetsity. Blacksburg. Virgtnia. 2018/BC SEAOC StroctUtai/Sei.smic Design Manual.

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Dolan. J.D. and Heine-, C.P.~

1991b.Seq~Nnlttll Phastd Displaument Cyclic TRstsofWood Frame Shear Walls with VariorLt Openings and Ba'>e Rtstroi11 Co,-ifigw·aJJons. T1mber Engineering

Report No. TE- 1997-002. Virgin.ia Polytechnic lnsmme and State Umvetsny. Blacksburg. Virgtnja. Dolan. J.D., and Heine.• C.P.• 1997c. Sequential PIJtJStd Displacement Ttst ofJJOOd Fran~ Shear JfO.IIs with CornerS. Timber Engineering Repon No. TE- 1997-003. Virginia Polytechnic lnsurute and State Un1vers•ty. Blac-ksburg. Virgin1a. Eartllquake Engineenng Research lnstl!ute, 1996, "NonJu-idge Eartllquake of January 17, 1994;' Reconnai.uanct Report. Earthquake Spectro. Vol. II, Supplement C. Earthquake Engineermg Research lnstuute, Oakland. CaJ1fom~-a. Elli~ Jett: August 2012 ...Designing Cold-Fooned Steel Framed Lateral

Force-Resisung Systems,"

Stntctun magazine. National Council of Strucmtal Engineers Assoctauons (NCSEA).

Faherty, Keith F.. and \Vtlhamson. Thomas G., 1995, WOod Engmeering Construction Handbook. McGraw-Hill, Washington, oc_ FederaJ Emergency Management Agency. 2003, Natitmal Earthqlltl.ke Ha=ard Reduction Program. Rtcommended Pll'Jl•tstons for Mtsmlc Regultwonlfor New Bmldmgs and Other Structures and Commentary. FederaJ Emergency Managemem Agency. Wa-onch-thick DOC PS I· or DOC PS 2-rated wood structlll111panel (WSP) shemhu1g, with a 32/16 span raung and Exposure I adhestve or \\or 24 mches o.c. mnng. with a 48n4 span raung(40/20 span mung with topping is also accepmble) and Exposure I adhesove or waterproof adhesive. DOC PS I and DOC PS 2 are the US Deparunent of Commerce (DOC) presc.roptive and performance-based standards for plywood and onented strand board (OSB), respecuvely. Wall fram tng. 1S a ..anodtfied balloon framing•· where the jotSL(i hang tfom the walls tn JOISt hangers. (See Ftgure 1-7 detail of lhis and an explanation of Olher common framing conditions.)

Franung lumber f()( studs and posts

2

NDST4A

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2018 IBC SEAOC Stroctu.rai!Seismic Design Manual. \lbl. 2

Design Example 1 • Four-Story VKiod Ught Frame Structure 4

Dou.gllls Fir-Lartb-No. I G radt unadj us tt-d dtsigu \'tlut-s: F• = I ,000 pso

Ft = 1,500 psi Fa =625 psi

F,= 675 psi E = 1,700,000 psi Em,.= 620,000 psi C"'= J.Odry ln-servtce condttions assumed C, = 1.0 normal te:mpetature conditions assumed Frammg lumber used for studs and posts is desogned per lhe National Design Specofication"' (NOS") for Wood ConstrucLJon and NOS Supplement: Destg.n 'hllues for Wood Construc.uon.. Only l'-'' end-use adjustment factors are shown here. Others Will be de-fined and ~'1\ Later tn me design example.

Commott wire nails ate used for shear waJJ~ diaphragms. and straps. Whe.n specifymg nails on a proJect. specttication of the penny wetgh~ type. diame-ter, and length (e.xample IOd cotntnon = 0.148 inc.h. x 3 inches) are recommended.

~' t

~'

';..---...,;,

Figw·e I- I. Buildtng el~ l"lltilm

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Design Example 1 • Four-Story~ Light-Frame StTucture

~ NORTH FigwY 1-1. 7jpicalformdarlonplan

4

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Design Example 1 • Four-Story VKiod Ught Frame Structure 4

4

23/32" APA R~TED SH£A1WNO 48/24 SPAN RATING 10d SCREW SHANK HAllS 0 6" ojc EOct'S PANEL EDGES UNBlOCKED SHE"AlHING GI.UED TO

fRAU lNG

----10

HORIZONTAl. TIE METAL STRAP AND

BLOCKING

I~

----10

·~

NORTH Figunt 1-3. TJ.picaljloor frammg plan

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Design Example 1 • Four-Story~ Light-Frame StTucture

'

I

I'

I'

J - ------0 l

I

I

-----0

g

-----® 15/32. APA RATtO

••

SHEAll-!II+G J2/16 SP RAnNG lOG 0 6• o}c EOGES PANEt. EDGES

----®

UN9LOCKt0 ED

' ·-o

2'-0

~~

~ NORTH

----0 -- --0

~

ll

----® -------®

FtgiJTl' /-4. T)p•ca/ roofframing plan

Notes for Ftgures 1-2 through 1-4: I. Nonstructural ..pop.outs" on the exterior '"ails at hnes I. 4 need special detading showmg the YI'OOd structura1 panel sheat.lung ruruung c:onunuous at hnes I. 4 and lhe pop-outs framed after

the shealhing is u\stalled. 2. All walls stack from the foundauon to lhe fourth floor. 3. 6

availabilil)' of both types of lumber (grren and kiln-dried) is largely dependent on the region and a10sociated market C01tditions. Typteally~ wood used ln construction ut the US southwest has both green (S-GRN) and lc1l~tted (KD) \100 may mean a longer lead ume ln some areas lO obtain 11. Wood Shrinkagr Shr~nkage occurs when wood drtes~ chang1ng the structural dlmensJons of the lumber. llus 1s a faelOr in any wood structure, and the compounding (adduive) effect of multiple stories can mc.rease the potenual lO have a shrinkage pmblent. Shrinkage problems can be crac.ktng of finishes~ ptnchmg of door and ·wutdow frame~

or bucldtng of piping and conduits. Both the me and NOS requare cons1derat:Jon be gaven to the etfeels of eross-gratn dunensJonal changes (shnnkage) when lumber IS fabrica[ed in a green conduion. In addJtton, lBC Section 2304.3.3 requires that bearing walls supponmg more than £WO floors and a roof be analyzed for shttnkage of the wood framutg and that possible Od-Framt Wall and Floor/Ceiling Assemblies.

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Design Example 1 • Four-Story VKiod Ught Frame Structure 4

Table n 141(2) of the me ltsts fire raungs for var1ous wall oonst.ruC'tion types.. Many of the wall consU\ICtion types using wood COJ'ISUUc.tion reference Footnote m. Foomote m of the table requlfes the reductton ofF; to be 78 percent of the allowable whe.re the slenderness rotio 1/d > 33. For sruds w1th a slenderness ratio lid< 33, the design stress shall be reduced to 78 peicent of the adjusted stress F; calculated for studs hav1ng a slet~demess ra110 1/d of 33. TheAWC has tesl"ed a nwnber of wood-frame fire.-mred waJI assemblies to 100 percent design load. There is a d1sparity betwee.n the JBC and publ ic~ujons such as AWC"s DCA 3. Fire-R~slstanuRated UOoti-Frame. lf'(J/1 and Floor!Ctllmg A.u~mblie!. wh1ch does not requtre the reducuon tn allovro.ble suess. l1le bUlldtng·s archuect and/or engtneer shoukf check with lhe local JU..flsdtchon to determine the accepted appmach. The AWC procedure is drouled at hnps://w"'"v.awc.otg/faqslfirelfi.rel what-IS-.00-backgrotmd-behind-footnote-m-f-ibc-20 12-table-721.1-{2).

11te cakufated suesses for F; used in th1s design example w1JI not use the reducuons for Foomote m. 1.3 WEIGHTS

Roor l\'tig.bts:

Floor wtights:

Roofing+ re-roof

5.0 psf

Flooring

She-athing

2.5

Lt. wt. concrete

Trusses

3.0

Sheathing

2.8

Insulation+ sprinklers

2.5

1-JOlst

4.0

2 layers gyp + m•sc

7.0

2 layers gyp+ m1sc

8.2

1.0 psf 14.0

Dead load

20.0 psf

30.0 psf

Live load

20.0 psf

40.0 psf

lntertor and ex1erior \\-all weigtm; have not been tnduded tn the above l oads~ they have bee.n tncluded tn the diaphragm weights shown in Table 1.2. Typical interior and exter1or paruuon '"~-tg.hts (for determming the building we.ights) can "'at)' between 15 psf to 20 psf (based on the horiZOntal plan dtmensJon). depe-nding on room sizes, number of layers of gypsunt board on wans. S[agge.red studs, etc. Weights of roof d1aphragrns are typically determined by taku1g one-half the he.ght of the 1\~lls from the founh floor le\'eJ to the roof. Weights of floor dtaphragms are typtcally determu'led by taking one-half the walls above and below for the.fOurth. th1rd. and second floor diaphragms. The weighlS of all walls,. indudmg interior nonbearsng panjtions.. are included m the respectl\'e weights of tl1e vartous leve.ls. The:

weigh! of parapets (where they occ:ur) ha..~ been mcluded tn tl1e roof weight.

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Design Example 1 •

Four-Story~ Light-Frame StTucture

Table 1-1. Weigh1s ofrooftmdfloor diapl~ragms Assembly

(psi)

Area (It')

Weight (ktps)

Roof

20

5288

105.7

Ex1 "all

15

1350

20.25

Jnt wall

15

5288

39.66

Floor

30

5288

158.6

Ext wall

15

3 100

46.50

Jnt wall

15

5288

79.32

Floor

30

5288

158.6

Ext wnll

15

3 100

46.50

Jnt wall

15

5288

79.32

Floor

30

5288

158.6

Ext wall

15

3100

46.50

lnl v.-all

15

5288

79. 32

Unit Wt

Level

Roof

4th Aoor

3rd Floor

2nd Aoor

Story\Vt (kips)

165.7

284.5

284.5

284.5

W= 3(284.5 ktps) + 165.7 ktps= 1,019 ktps

2. Calculation of the Design Base Shear

ASCE7

2.1 CLASSIFY THE STRUCTURAL SYSTEM

Frocn ASCE 7 Table 12.2-1 tOr beanng-\'r'all systems ustng hght-frame wood walls sheathed Walh wood strucnual pan~ls mted tor shear resistance:

I R=6.5

!l,=3.0 C,=4.0

2.2 DESIGN SPECTRAL ACCELERATIONS The specual acc:elerauons lObe used 1n design are denved from sod profile and stte locauon:

Ss= 1.540g

s, =0.568g

2.3 RESPONSE SPECTRUM

Determine the app..-oxt.mate fundamental butldmg pertod using Sedion 12.8.2. I: C,=0.02 andx=0.75

T., = C,h; = 0.02 x4J0·" =0.34sec (see the tOIIowtngdtscusston)

I T..=0.34 sec I 18

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2018/SC SEAOC Structura/ISf!;smic Design Manual. Vol. 2

Tl2.8-2 Eq 12.8-7

Design Example 1 • Four-Story VKiod Ught Frame Structure 4

r. =0.2~=0.1

s,

568 °·1.026 =O.II soc

s. =S""(0.4+0.6;.)= 0.4+5.6T forT< T,

Eq 11.4- 5

=~=~=0.55soc

§ 11.4.6

Sm ; 0.568 , T>T . - 10r S ; 1 • T T

Eq 11.4-6

T J

SA~

1.026

§ , a "'~or largeopenmg. and so on). Pranclples or SWlCS also appear to be "' odds wllh reducong me "'en..-n•na h• "'that be""- me nbllon boord (wall hel: ....... 10.0 P>q8.21 ft) = 82.1 plf For the 2nd-flOO< through 41Mloor 1.-els: ..... = 10.0 psl\9.44 ft)= 94.4 plf

44

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2018J8CSEAOC-.-DesignManuaJ.~2

Design Example 1 • Four-Story VKiod Ught Frame Structure 4

Table I -6. Dtltnnin~ £h~ar wa/1 uplift forces u:rmg ASCE 7 lood combinations atlm~ C

Strenglh

ASD Uplift (M0 r X 0. 7)-(0.6- 0 .14S"')MR

Level

Drag Truss

b_,

M• (ft-lb)

(ft)

-

-

Mm (fl-lb)

-

M,(0.6- 0.14S,.)' 11 (ft-lb)

-

Dttlerent•al

bS)= (0.6 -0.14 x 1.026)=0.46

2. Drag truss uplift (tension) tbrce Is determined m Section 4.1 and IS applied at the ooe end oflhe shear wall. For simplicity 1n design and de.tathng. the force will be applied to bothe,n dsofthe shear wall. 3. Ovenurning forces (Af01) are from Table 1-4. 4.4C SHEAR WALL TIE-DOWN SYSTEM COMPONENTS

Tit-Down Rod

Tie-down rc.xls are usually made from A36/A307 steel. This IS called standard rod strength. Unless marked, rods should be constdered standard rod strenglh. H tgb-strenglh rods are ASTM A449 or A 193- 87 and are usually marked on the end w•th an embossed stamp, though some rod manufacturers stamp the rod grade on the side. If the rod is stamped at lheend and 1s cut. it needs to be re-marked. There should be a spec.al tnSpection ofhag.h-streng.th rods to coofirm the rod type since the ends of these rods may be embedded 1nto a c.oupler where the marks cannot be ~,n after installation. High-strength rods are usually not weldable ·withoUl special welding procedures. Pro1>rietary systems have spec:Jal rod colors and marklng.~ oo the stdes~

some rods are propnet.ary, the manufacrured components are proprietary. Rod Uongatlon

The net te.ns•le area. A~· is used tn the rod strength ru'ld elongation calculauons. However, to tacilitate rod suength des1gn. AISC 360 Tab1e J3.2 tabulates the nomtnal tensale strenglh, F"" so the destgner may use the nominal bolt area,A6. TheCommentruy states ..F..,= 0.75F,.- and "The factorof0.75 iocluded in thiS equation accounts fonhe approximate ratio of the effecuve tension area of the threaded portion of the bolt to the area of the shank oflhe bolt for common sizes.'· Somejunsdtctions have ltmttson the amount of rod elongation that can occur betw~n restrauus and/or stone~ and some tequtre that the allowable sues:s area (A~ vs. A ) be used an rod elongatton caJculruions. As suc-h, local butldmg depanment requirements should 1 always be checked. This design example uses A~ for rod elongation and .41 or A" fO! rod capacity.

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45

Design Example 1 •

Four-Story~ Light-Frame StTucture

Many conttnuous rod system manufactuters rry to de.termine lhe rnost C-Ost-effecuve solutton fOr a given ttnston load considering rod strength and dtameter. The use of a htgher-strength rod wdl tncrease lhe drift of the shear \valltf used in place of a standard-strength rod due to tncreased rod elongauon from the smaller rod dtameters.. and the modulus of elast1city of lhe steel. whtch does not change, l~ the same forboth standard- and high-strength rods.

Tie-down rod elongation 1s computed bel'ween bearing plates (restraints). This design example has bearang plates located at each fl()()(. Table 1-7 computes the rod capac1ties and elongat10l'IS (per floor) bem~n t11e bearing plates. Table 1-7.

Derennin~ rod si:~s.

capaCilltS. and e/onga11on.t 01 lint C ASDRod Capacity

ASD

Rod

Elf.

Plate Height

Tension De-m.and

Dia.

Dia.

A,

(fi)

(kops)

d, (in)

A,

Level

d (on)

(in')

(in')

F, (ksi)

F, (kso)

2 (kops)

ASD Rod Elong. (in)

Roof

8.1 1

2.88

0 .625

0.527

0.307

0.216

58

36

6.68

0.043

4th Floor

9.44

6.56

0 .625

0.527

0.307

0.216

58

36

6.68

0.113

3rd Floor

9.44

11.93

0 .875

0.755

o.60 1

0.462

58

36

13.07

0.10 1

2nd Floor

9.44

18.34

1.00

0.865

0.785

0 .606

120

105

35.33

0.118

0.7sxr: xA~

Notes for Table I-7:

I. Tension demand (ASD upli11) values are computed tn Table I.. 1

3.14 • 1'4a)((.!....) = 349x(~) = 1220 lb 1.67

IC• J'Sa"(..!...)=349x(1.1..)=440 lb If) 1.67 Detenmnc hon1'..ontal shear ~Orce at upper left 1'2. poc11on:

, •• l'b- · ~·1220 - 440=558 Jb I' SS8 . ··=- · --=44 pll

Lb

2 10ft

c

b

H)

T1EFORCE

221U

12.75 ft

584ft

-

4o --,

8

12.75

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221

l 3Au

l

1.8H

59ft

Design Example 1 •

Four-Story~ Light-Frame StTucture

Determine hortZOntal ue force from header to v.' 1220

X

0.7 = 8541b ... OK

An allowable stress increase has not been used for the metal strap. 5.3 THE DIEKMANN METHOD

Thts method first appeared an the 2018 SEAOC Convention Pmceedtngs and was presemed at mat convention. The method assumes the tOIIowang:

The unh shear above and below lhe ope.ung L 1ps

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2018/SC SEAOC Structura/ISf!;smic Design Manual. Vol. 2

Design Example 1 • Four-Story VKiod Ught Frame Structure 4

Table I-11. Forees to walls tmd reqwred pamd nailmgfor eaJt-wf!Jt dinCttOJ1 1 '~ 3

Wall

Tnb. Area

IF....,,

IF,

F~

(I\')

(I b)

(I b)

( Ib)

If'' (ft)

F

,. ;.....!!!..

b

F (1.4)b (plf)'"

~· = --!!!!.-

Sheathed I or2 Sides

Allowable

Edge Nail

Sberu'"

Spacing

(pi I)

(in)

Sht-ar \Vall~ a1 Roof Lt~tro• A

170

0

1587

1587

12.5

127

91

I

340

6

B

746

0

6965

6965

22.0

317

226

I

340

6

c

1344

0

12,548

12,548

43.0

292

208

I

340

6

E

1344

0

12,548

12,548

43.0

292

208

I

340

6

F

960

0

8963

8963

43.0

208

149

I

340

6

G

554

0

Sin

5172

22.0

235

168

I

340

6

12.5

127

91

I

340

6

H

170

0

1587

1587

1:

5288

0

49,372

49,372 Shur \Valls al Fourlh- Ftoor Ltvtl

A

170

1587

1792

3379

12.5

270

193

I

655

3

B

746

6965

7864

14,829

22.0

674

481

510

4

c

1344

12,548

14, 167

26,7 15

43.0

62 1

444

I I

510

4

E

1344

12,548

14,167

26,7 15

43.0

62 1

444

I

510

4

F

960

8963

10,119

19,082

43.0

444

317

I

655

3

G

554

5172

5840

11,012

22.0

501

358

I

510

4

H

170

1587

1792

3379

12.5

270

193

I

655

3

1:

5288

49,372

55,741

105, 112 870

2

665

3

Sbur \Valls al Thlrd- VIbor Ltvtl A

170

3379

1195

4574

12.5

366

261

B

746

14,829

5242

20,071

22.0

912

652

I I

c

1344

26,715

9445

36,160

43.0

841

601

I

665

3

E

1344

26,715

9445

36, 160

43.0

841

601

I

665

3

F

960

19,082

6746

25,829

43.0

601

429

I

655

3

G

554

11,012

3893

14,905

22.0

678

484

I

655

3

H

170

3379

1195

4574

12.5

366

261

I

870

2

1:

5288

105,112

37,161

142,273

A

170

4,574

597

5171

12.5

414

295

I

870

2

B

746

20,071

2621

22,692

22.0

1031

737

I

870

2

c

1344

36,160

4722

40,882

43.0

951

679

I

870

2

E

1344

36,160

4722

40,882

43.0

951

679

I

870

2

Sbur \Valls at S«ond- Floor Lt\•el

F

960

25,829

3373

29.202

43.0

679

485

I

870

2

G

554

14,905

1947

16,852

22.0

766

547

I

870

2

H 1:

170

4,574

5171

12.5

414

295

I

870

2

5288

142,273

597 18,580

160,853

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Design Example 1 • Four-Story~ Light-Frame StTucture

Nores tbr Table 1-13: I. In SOC D, E, or F, SDPWS See1ion 4.3.7.1 requires Jx nominal lhickness Slud framing a1 abumng panels or two 2x members \'ltlere lhe required nomtnal shear exceeds 700 plf. or the nail spactng is 2 tnches on ce-nter or less at adjoining panel edges. or IOct common na1ls havtng penettatjon into framing members and blocking of more than I ~ inches are 3 inches on cenrer or less. 2. Refer to Section 7.3 m this design example for sill-plate anchorage.

me Secuoo 1705. 12 requites spec1al inspection where the nad spactng ts4 tnches onc-emer or closer

3.

wilh SOC C and higher. 4. The shear wall length used for wall shears JS lhe ..out-to-our• wall length. 5. Fotces are suength leve-l and lhe shear lR wall is divided by 1.4 lOcooven to allowable streSs destgn.

6. APA « TECO performaoce-ra!ed SlfUCtllral-1-ra!ed wood ''"""ural panels may be enher plywood or OSB. The allowable shear values are fro1n SDPWS Table 4.3A using IOd common nails Wllh a minjmum I ~inch penetratiot\ and 1-MHnch panel thickness and divided by the ASO reduction factor of 2 .0 . 7. Shear \\ails al hnes c. E. and F extend totlte bonom of the prefabncared wood trusses at the rooflevel. Shear t.tanstfr ts oblalOed by framing chps from the bottom chord oftl1e trusses to the top plates of the shear walls. Projec1 1>lans call tOr trusses at these hnes to be destgned fOr lhese horizontal forces (see also comments in Secuon 1.2). Roof shear forces are also uansttrred to lanes A. n. G. and H.

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Design Example 1 • Four-Story VKiod Ught Frame Structure 4

Table 1-14. Foru.t 10 walli and rtqutred panti iJIJIIIngfor north-south du?Ciion1•2•3 F

Tnb.

If''

F

~· = --!!!!.-

(l.4)b (plf)'"

Edge Sheathed I or2

Allowable Sberu'"

Spacing

Sides

(pll)

(in)

6

Area

IF....,,

IF,

F~

Wall

(I\')

(I b)

(lb)

( Ib)

I

1202

0

11 ,223

11,223

64.5

174

124

I

340

13,463

(ft)

,. ; .....!!!..

b

Nail

Shea r \Valls a1 RoofLn't:l 0

60.0

224

160

I

340

6

3

1442 1442

13,463

0

13,463

13.463

60.0

224

160

I

340

6

4

1202

0

11 ,223

11 ,223

64.5

174

124

I

340

6

49,372 Shu r \Valls a l Fourlh- floor Ltvtl I

510

4

2

1:

5288

0

49,372

I

1202

11,223

12,670

23,893

64.5

370

265

2

1442

13,463

15,200

28,663

60.0

478

34 1

I

340

6

3

1442

13,463

15,200

28,663

60.0

478

341

I

340

6

4

1202

11 ,223

12,670

23,893

64.5

370

265

I

510

4

1:

5288

49,372

55,74 1

105,112

I

1202

23,893

844 7

32,340

64.5

50 1

358

I

510

4

2

1442

28,663

10,133

38,797

60.0

647

462

I

510

4

3

1442

28,663

10,133

38,797

60.0

647

462

I

510

4

64.5

50 1

358

I

510

4

I

655

3

Shur \Valls at Third- Floor Ltvtl

~

1202

23,893

8447

32.340

1:

5288

105, 112

37,16 1

142,273

I

1202

32,340

4223

2

1442

38,797

5067

43,864

60.0

73 1

512

I

665

3

3

1442

38,797

5067

43,864

60.0

73 1

522

I

665

3

64.5

567

405

I

655

3

Shtar \ Valls at Sttond-Fioor Lt-nl 36,563 64.5 567 405

4

1202

31,340

4223

36,563

1:

5288

142,273

18,580

160,853

Notes rorTable 1- 14:

I. In SOC D. E. 01' F, SDPWS Section 4.3.7. 1 requires lx nonunal thickness stud franungat abuntng panels or two 2x members where the requ1red nom mal shear exceeds 700 pit: or lhe nail spacmg ts 2 ioc,h eson center or less at adjommg panel edges. or JOd common nails havtng penetration mto framing members and blocking of more than I ~ inches are 3 indtes 01'1 center or Jess. 2. Refer to Sectton 7.3 tn this Design Example tor sill-plate anchorage. 3. IBC Sec.tton 1705.12 requires special inspeeuon when the nail spacing is 4 tnd'!eS on center ot closer with SOC C and h1gber.

4. 1l1e shear wall length used for wall she-ars lS the ..out-Lo-ouf' wall length4 5. Forces are strength level and shear in y,aJl ts divided by 1.4 to convert to allowable suess desagn.

6. APA or TECO performance-rated StructuraJ-1-rated wood struc.tural panels may be etthc-r plywood or OSB. The allowable shear values are from SDPWS Table 4.3A using IOd common nails wtlh a mtnimum I'15:-mch penetratiOn and 1Y.c-mch panel thidmess and dt\•tded by the ASD reductJOO factor of2.0.

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Design Example 1 • Four-Story~ Light-Frame StTucture

6.3 CALCULATION OF SHEAR WALL RIGIDITIES

In thts example-. shear wall ng_~dtues are calculated ustng the three- or fOur-term code deftecuon equauon. These calculation.. are facilitated by the use of a spreadsheet progra.m., which eltminates posstble amhmelic errors from the many repeuuve compulanons that must be tnade. The first step lS to c-31culate lhe displacement (i.e.• ven1cal elongation and deflecuon) of the ue-down assembly elements and the crus.ltutg effect of the boun.dary elemem. ThHl is lhe term dr The force conside-red w act on lhe ue-down assembly is the net uphft force determined from the fte.xtble diaphragm

analyses. These forces are summarized '"Tables 1-1 5, 1-20, 1-24, and 1-28 fonhe roof, the fourth floor,

the third floor. and the second tloor. respectively. After the tJe-down assembly dtsplacements are determtnOO.. the-four-term defleeuon equation ts u.all. bnck. and stone venee,rs. stifferung effects of walls not COI'IStdered. and areas over doors and wtndows. During an eanhquake, some loo•-stressed walls: may malntajn their sttft"ness while others degrade in suflhess. Some walls and thetr collectors may anract signaficandy mote lateral Jood than anticipated tn semt-fte.x:ible diaphragm analysis. The method of analyzing a struc(ure us:tng inflexible

90

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2018/SC SEAOC Structura/ISf!;smic Design Manual. Vol. 2

Design Example 1 • Four-Story VKiod Ught Frame Structure 4

dtaphragms takes signdicruuly more eng~neering eftOn. However, use of the ngid-djaphragm method uldicates that some lateral-resisung elements can aruact sagntficantly htgher se1smic de-mands than tttbutary are-a (a.e., flexible diaphragm) analysis methods. Yet with the ltmited testjng data on multistory wall performance and the ofteat approxtmate methods available for determuung wood-she.athed wall and flOOI' dtaphragm ddJecnons, engtneers are as.ked to design more complex lateral systems that include mulustory narrO\\' shear Y..alls, cantlle\•ered diaphragms, and/or rigid diaphragms to accommodate open-front desigruL

p

- +I-

I

'•

I I I I

l

i

•'1

I I

I

Tie-down

dis.,laeement d.,

L

I

h

r'.

II

I

''

'

'

•

•••

l ~ Figure /_./.

In llus example, shear wall ng.tdities, ~are computed ustng the baste st.iffness equatiOn

Of

F k =;;

Estimation of Roor-Lt\'tl Rigiditits To estimate roof-level wall ngtdities, roof-le\•el dtsplacemems must first be detemllned. The followtng are a series of calculauons m table form to esumate the roof:tevel drifts, 6, 1n eac.h shear \\o'all. Ftrst, the shear wall tie-down assembly displacements are determined (Table 1- 15). lbese and the parameters gwen m Table 1- 15 are used to arnve at the drifts.~ for each s:hear \1/all at the root level (Tables 1- 16 and 1- 17). Rigtdities are estirnated 10 Table 1-18 tOr waJis in both dtrections. Once the drifts are known, a drift check ts performed. Thts ts summanzed 1n Table 1-19.

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91

Design Example 1 •

Four-Story~ Light-Frame StTucture

Table I -I 5. !Htermine tit-down anembly displaumtnts at the IT)()f/en!/1 S[(et~gth

ASD

Design

T1e-Down Assernbly D1splaceme-m

Dovm Devtce(6•

Uphftm (lb)

Uphft"' (I b)

Elo1\gation (1n)

(1n)

(1n)

(in)

Bear.ng Plille Crush (1n)

0

0

0.000

0.030

0.03 1

0.003

0.000

0.064

1922

2691

0.040

0.030

0.03 1

0.009

0.008

0.118

H

Rod Rod Rod Rod Rod Rod Rod Rod Rod Rod Rod Rod

I

2a

Takeup Tie-Down( 2; ) ;1]2 = 1174 plr w, = 0.208(14 psf)(320 ft)+ [ 0.208(90.6 psf)(23>(~) ;I}= 1407 plf In lhts example-. the effect of any wall openings reduc-tng the wall weight has been neglected. Thts is considered 3.1' acceptable stmplificatton because the opemngs usually occur tn lhe bottom half of the wall. In addmort, sagnificant changes in parapet hetght should also be cons1dered tf lhey occur due to stgntfic:ant roof slope.

Diaphragm shear at lane A and on tl1e north stde of lane B lS 23,500 lb _ . If 97 9 240ft p

Diaphragm she.ar at the south side of line Band at ltne E is S4,400 lb - 264 If 320ft p

Nortb-soulb dlrtction

Diaphragm forces for lhe nonh-soulh dtreclion are computed usmg the same procedure and assumptions as the ea( ~3 ) ;I}

W,= 824 plf w, =0.208(14 psf)(l60 ft)+[0.208(90.6 psf)(2J)(~) ;I} W,=941 plf

Diaphragm unit shearal lu\e I and lhe west side ofhne 3 is 33,000 lb ,r r 120ft - - >pf

138

20 18 lBC SEAOC Slructurai/Seismic Design@Seismicisolation Manual, 1.01. 2 @Seismicisolation

Design Example 2 • Aexible Diaphragm Design

I~-~ I1.--_-. ".-_- ,I 1----'

t•t• t tit t t t t t titt ~=a24,.tf

W,r• ~11)(1

"''"""

, ,,. k

..

, ,

Figure 2-5. North-JOJith dlaphrogm loading

Diaphragm untt shear at lhe east s1de of line 3 and at line 9 is 113,000 lb _ If 706 160ft p

3. Shear Nailing of the Roof Diaphragm (North-South)

SDPWS

The du:tph.ragm loaded 1n the north-south direction has been selected to Illustrate the design of a wood struc.tural panel roof dtaphragm. A similar design ts requtred in the other onhogorlal dtrec.tton, ea(it-west.., but IS not iUusuated here~ Allowable sues:s destgn (ASO) wall be used. The baste loadmg eombtnauons are gwen in IBC Secuon 1605.3.1, and those tn\'olvtng eanhquake loading have been simpltDed 1n ASCE 7 Section 2.4.:5.

The govenung seismic load combi.natJoo ror allowable stress design is (8)

i.OD+ 0.7£, +0.7£,

§2.4.5

where£,= pQ,

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139

Design Example 2 • F/Wble ()japhragm Dt!sign

When destgntng lhe st.ru&::tural diaphragm. the engineer need nm coosider the venicalloading in conjunction with the lattral diaphragm shear stresses. Therefor~ the dead load D = 0 and the vemcal earthquake effec-t E, = 0 tn this load rombmation. For diaphragms of buildings tn Setsmtc Destgn Category D~ E, or F~ the redundancy factor p is requtred withtn lhe seismtc-foad combination, but is typical f)• set top= I .0 for diaphragm loads per Section 12. 10.3 Item 3. In untque mulustocy sttu.auons where the diaphragm tS acung 10 transfer forces hort20f'ltally due to ventcal syste.m offsets or due 10 changes in venteal element stiffnesses, the redundancy factor p Will conform to Sections 12.3.4 and 12.1 0.3.3. In thtsexample, p = 1.0 for the diaphragm destgn. Thus, the applicable basic lood oomblnatton reduces to stmply 0.1Qt· IS to be constructed wnh ·~!-inch $t.fU('tural-l OSB sheathing (wood struc-tural panels) with all edges supported (blocked). Referto the 2015AWC SDPWS Table 4.2A for nailing requirements. The sheathing arrangement (sh0\\1\ tn Figure 2-2) for north-south seismic forces is Ca'ie 3

Assume the dtaphragm

with the long pane.l direction parallel to the supports. Because open-web stte-1joist purl ins tn a hybnd roof structure have full-wtdth wood nail er~ the conunuous sheath1ng edges loaded tn this nonh-south direction are supponed by framing_ greater tJ"IaJt a 3-tneh nominal width, allowing nail S1Jac1ngs of2% inches or less at adjouung panel edges (AWC SDPWS Sectjon 4.2.7.1.1 ). HO\vever, in the east-west direcliOJ\ the sheathtng edge.~ are supported by only 2x subpurlin franung. and the strength IS there tOre Iunited by the nad spac tngs as.:soc rated with 2-tnch oom uta! franung width. Although not applicable 1n lhis example, 3x framing ts required \\'here adjoin1ng panel edges are fastened wnh IOd common nails at 3-tnch spacang tfthe nail peneuauon is greater than I% tnches. In these large panelized roof systems. the nailtng contrac-tor lS often instructed to order custom 2-tnch length n.atls to obtam the I %-tnch penetrauon. allowtng 2x franung m ce-rta.tn loc:auons. Various nail spactngs al sheathtng panel edges and their respective seismtc shear capac:iues for Case 3 (nonh-soulh seismic loadtn_g) are given in Table 2- I. Mtn1mum tntetmedtate (field) nailing is 10d common rwls at 12-inch spacing. and IOd common nails require 1Y:-tnch member penetration. A stmtlar calcularjon (nOl shown) mUSt be done for east-west setsnuc fOrces. Tab/~

1- 1. Allolt'a.ble diaphragm !ltea.r c.a.pacillts

Edge Nailingl'· 11

Eas!-WeSl Edge Nrultng''- 31

Nominal Unu Shear

Zone

Capacity (pi f)

ASD Allowable Shear {plf)

Boundaty and North-South A

10d @2Y.ttno.c.

10d @ 4 '"o.c.

1280

640

B

IOd @ 4 1n o.c.

IOd @ 61n o.c.

850

425

c

IOd @ 6

10d @ 6 '"o.c.

640

320

10 o.c.

Notes for Table 2- I:

I. The nonh-south runntng sheel edges are lhe ..conttnuous paneJ edges paralle1 to load" men[toned 1n SDPWS Table 4.2A

2. The east-weSt sheet edges are the "other panel edges" tn SOP\VS Table 4.2A. The naJitng for east-west runntng dtaphragm boundaftes 1S per the ughter boundary spacing. 3. Natls are common smooth-shank n.atls ( IOd = 0.148-tnch dtam.e-ter). Screw-shank nails (deformed shank) are ofte-n used tn some regton."i of the counuy where spec tal concerns e:-ft or 32.4 k1p-ft 8

As shown 1rt Part 4, thi~ building contams a Type 2 horizontal sm~c.tutal irregularity, and the reqUirements ofSecuoo 12.3.3.4 apply. Th1s result..~ 1n a 25 percent tncrea~e Ln selsnuc fotces fot coUectors and the1r oon.nections. The collectOr's aJoal seismic force becomes Qs:= 1.25 x 11 8 kaps= 148 kips. Additionally, collectors m SOC C through F requlre a 1.5 muluplier per Section 12. 10.3.4 because ofthe1r criucal role.

ThUS, Q,= 1.5 X 148 kips :2221ups.

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Design Example 2 • Aexible Diaphragm Design

AISC 360 Sect100 HI contains the equauons tbr combined a.xiaJ compression and bending. Because the bc!.ndlng ts not biaxial. it is ad\'antageoos tbr lhe e:ngtneer to use Sectton H1.3 by checking failure about each axis independently. In this example. the collector's top flange JS continuously supponed with closely spaced dlaphtagm nailing. thus pt'e,·enllng lateral-torsional buckhng. The colleclOr·s bouotn flange will be larerally braced at the member's equal third pcHnL~ Y.'lth use of an angle brace (destgn not sho,vn). resuJtmg in an unbraced lenglh of L., = 40/3 = I 3.33 1\. The strong axis unbraced length is Simply lhe span L, = 40 fl As a condition of AJSC 360 Section H 1.3. the efttcuve lateral-totSJonal buckhng length Le: must be less than the effecuve out-of-plane weak-axis bockhng length LC? and thts 1s confirmed.

Le S: L9'

o n,; 13.33 n Frulure will be checked sepatately about each axis per Secuon H1.3. X-a:ds limit statt ( in-plant instability)

AISC 360 Secuon H J.J(a) provides lhe approach to check tn-plane stability oflhe loaded Wl8 x 50 collector. F1rst. the designer must compute the available tn-plane stre-ngths Pex and M0 for use in Equarjon H 1-1 . PaIS the available axial strength and is a funcuon of the collector's strong-axis w1braced length. La = KL, = 1.0(40.0)12 _ . 65 0 r:r r.7.38

§E3

Eq E3-4

r, Bocau~

FJF, s 2.25. Equatton EJ-2 is applicable.

Fa=

(o.658~ ~,. = (o.6586~1 ~o = 36.7 hi

P~= F,A,= 36.7(14.7) =539 kips

Eq EJ-2 Eq E3- l

P0 = ~' Pm = 0.90(539) = 485 kips

§EI

Mn is lhe avaJlable fte.xural strength for tn-plane bendtrtg. Ma = 0,M. = 0,F,Z,= 0.90(50 kstX IOI) =4545 ki(>-tn Ma = 379 kl(>-ft

Second, the destgner mus[ de[ermme the reqUJred axiaJ and flexural strengths P, and M, usang tlte baste LRFD load cmbtnaiiOn (6) 1.4D + Q,: P, = Q£= 222 k1ps (mcludes the 1.25 tncre-ase for plan irregularity ru'ld the 1.5 increase tbr oollecror) M, = 1.4M0 = 1.4(32.4) = 45.4 lip-ft

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Design Example 2 • F/Wble ()japhragm Dt!sign

Per Section Ji 1.3(a). the in-plane stability check uses Equation H1-1. Pa tS the appropriate m-plane buc.ldtng strength.

~

P0

=

222 = 0.46• 0.20 485

The.refore, E7!> 1.0 ... OK \'-axis linlil st.att (out-of-plant butkll.ng a.11:d lattral-torsional budding) AlSC 360 Section lll .3(b) provides the approach to check out-of-plane buckhng and late.ral-torsiOilal

buc.ldang oflhe loaded collector. First. the destg.nc-r must oompute the available out-of-plane strength P9 and Lateral-torsional budding strength Ma For use 10 Equation H 1-3. Pq tS theavadablea-xtal strength and is a funcuon of the collector's weak-a.·os unbmc.ed length. §E3 Eq E3-4

Because F/F,,; 2.25,AISC E, = o.680g

§ 11.4-2 and § 11.4-4

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Design Example 3 • Thre&-Story Ught-Frame Mulifamily Bu;lding Design Using Cold-Formed-Steel 'WaN Framing andv.bod Floor and Roof Framing

Sitt-Sptcitic Ground Motion Prottdurt:s

§11.4.8

Per Item 3 ofthis sect.iOI\ a ground motion hazard analysis shall be performed m accordanc.c with Secuon 21.2 for structures located on etlher Sotl Site Class 0 orE where S1 as greater than or equal to 0 .2. Tile ground motton hazard analysls l~ not required for struCtures 1ocated on Soli Site Class 0 when the followang are satisfied: I. C,(per equation I2.8-2): Use 1.0 x C, (when T,; 1.5T,) where T, = S0 ,1S.o l.5T,) 3.

(.~(per equation

12.8.4): Use 1.5 x C, (when T> T,)

A response spectrum analysis ts not required tOr this butldtng structure. Tile eqUJvalent lateral force procedure shall be used fOr thiS analysts.

T 12.6· 1

3.3 BUILDINGS A AND B-SEISMIC DESIGN REQUIREMENTS

Structural system: l1ght- ftame CFS walls sheathed Wtth wood structuml panels Number offtoors: 3 Buildtng hetgllt (above tl\e podium level)= 11, = 31 ft Risk Category: II

IBC T 1604.5 aod T 1.5· I

Sod Site Class: 0-sutT sotl Seismac Design Category (SOC): 0 lmponance. factor: 1, = 1.0 Bu1ldU''I;g response modification coefficient: R = 6.5

From Solis Repon T I 1.6- I and T I 1.6· 2 Tl 1.5· 2 T 12.2· 1

Building period detemunat.ion: Approximate period parametet, C~ = 0 .02 Approxunate period parameter. x = 0.75 Approxamate fundamental period~ =C,H'.= 0.263 sec Coefficient C.= 1.4 Butldtng period (1) used= CJT.,) = 1.4 x 0.263 =0.37 see< 1.5T, = 1.5(0.609)

T T T T

12.8· 2 12.8·2 12.8· 7 12.8· 1

ASCE 7 §I I .4.8 (Exeepuon 2)

Nme-: Seismic Design category E is not re-quare thlS bu.ildtng wooJd be cons1deJed a(i being four stories (one level of podium and three levels ofhght-frame construction), \\-hich is Jess than the five-story limit.

3.4 BUILDING MASS Ctntrit- Building Footprinlfl.ayour or Building§

The schematic OUI.lines oflhe tw"O three-story buildings on the first floor podium are shown tn Ftgure 3-7. As noted prevtously. only the seasnuc fOrces tOr Budding B are betng calculated.

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Design Example 3 • Thre&-Story Ught-Frame Mulifamily Bu;lding Design Using Cold-Formed-Steel 'WaN Framing andv.bod Floor and Roof Framing

,.----------- ... .-------1 Zooe 82 Zone 81

: Bldg. B

"'-----------..1 Figure 3-7. Layout of Building$ A and 8 on larger podf11m deck

Building 8

The ftoor area tOr each floor level will be determined utiltZ.ing a sumJnation. of rectangular ateas that are slightly la~ger than the actual ftoot footptin.t. Floor open1ngs,. such a~ stairs or duct/pipe c.hao;es, wlll not be subuaeted out and will be considered as being solid. Recesses and notches along the penme-ter of the butldtng wiU be considered as nonexlstent 8UJid1ng B is d1v1ded uuo two rectangles for calculating the building weaght. Zones B I and B2. This t.s to account fat' add1Uonal point loads/masses atlhe floor and roof levels and the fact tha[ Roof Zones B 1and 82 are almost essentially detached from each other. as can be seen in. Figure 3-5...Roof plan."" Though there ts some conservatisrn 1n this approach. using a more accurate floor area cah:::ulauon does oot usually lead to a Significant decrea~ in the seismic mass at each ftoor level of the buildtng. If the opemngs are signtficantJy large in the ftoor or roof. then the designer may warn to account for these openings in reducang the mass assoc1ated wath that ftoor level The other reason to use a slightly target footprint IS to account fof pmenual adjustme-nts 1n the build1ng footprmt by the architect as the construeuon documents are developed. It is always benef for the designer to be conservative on the \'-'eight of the building than to discover larer that the bujlding weight/mass has been Wlderestimared. Two SurfaceArtu (81. 82) and Unreal Fttt or Exttrior \Vall As noted above. the actual bu1kling dimensions have been tncreased shghtJy for calculating the 8001' and roof areas.

Seool'ld- and thtrd-ftoor are.as:

Bl =45 X 135 =6075 fl' B2 =45 x96 =4320 t\'

Roofatea:

Bl =40 X 135 = 5400 fl' B2 =40x 96 = 3840 t\'

The calculated budding aiea is larger at the flootS than the-roof to account tor the e:aerior canulever walkways. Perome1er \\rul lengills (second and llurd):

B I = 40 + 135 + 40 + 135 = 350 lineal fe IS% 81: 1341V(I34 ft + S ft + J9 ft) = 7S.J% > IS%

82: 5 IV(J9 ft + 5 ft)= 11.4% < IS% B2: 6 IV9S ft = 6.3% < IS%

Floors: liave Type 2 trregulanty (reentrant corner)

Roof: Cons•derc..-e b!Jildtng. It tsalso recomme.nded mat p = 1.3 If a mjnimum of two light-frame shear waHsare not being provtded along or near each perimete-r race of the buiJdtng.

9. Selected Analytical Procedure ASCE 7 Table 12.6- 1 hsts the permmed analytteal procedures that can be used to e,·aluate the bu1lding.. The tquwalent latera.J force procedure per A.SCE 7 Sect10n 12. 8 is permmed to be u.-.;ed since the suuctural

characteristk of the btuldmg superstructure is ltght-fiam.e construction.

10. Distribution of Seismic Forces to Shear Walls Seismic des1gn forces are dasltlbuted to lhe individual shear walls ba~ on their tributary area s1nce lhe floor and roofdtaphragms are constdered to be flexible. ln th•s desagn example. stnce p = 1.0. the calculated seismac design forces do not have to be adjusted re1ated to redundancy issues.. I. Redundancy factor, p = 1.0.

2. Inherent tors1on consKJerattons are omitted per flextble dulphragm assumptaons.. so the designer does not have to co11sider building lOtsion.

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Design Example 3 • Thre&-Siory Ught-Frame Mulifamity Buildng Design Using CokJ.Forrned.Ste/Wall Framing

and IMlod Floor and RoofFraming

Table 3 -13. Buildmg B ~·~rtlcal !tiJnuc-foru-t?sislmg sys1em !eismic !IOry/or= Z5fut)

LRFD

Level 3rd Floor

2nd Floor 1st Floor

r Shear Wall ForceM-

qM.>M**-

Z reqwred = MQIF1

Z requ1red = (Miq)IF1

= 3750(1.67)136,000

= (437410.9)136,000 =0.135 inl

=0.174 in 1

Z= !xi'/4 b = 3.0- (1.125 + ~>~•)

Z= lxi'/4 b= 3.0- (1.125 + Y,,)

b= 1.813 in

b= 1.813 on

r=J4Zib

r=J4Zib

= J(4)(0.174)/(1.8 13)

= JI4XO. JJS)/(1.813)

= 0.620 tn

=0.546 In

Use 0.625-mch-t.htclc plate minamum.

Use 0.625-mch-tJuck plate mmlmum. 1

1.6M1 = 1.6Fy5,

1

S, = blr 16 = 3(0.625) /6 = 0.1953 on'

= 1.6(36)(0.1953) = 11.25 1n-kop M, =F,Z= (36)(3)(0.625)'14 = 10.55 in-ktp < 11.25 in-k1p ... OK

2. Plate lhickne~Sher

AISC 360 §G I and G2

Shear is typically not a problem for the beatmg plate, butu is checked for completeness of the

bearang-plate desagn. ASD (H = 1.67) LRFD (~ = 0.9)

v, = 0.6F_,A..C.

AISC 360 Eq G2- l

Cr= 1.0 for flat plates 1

A,. = 3.0 in x 0.625 in=- I .88 in

v. = 0.6(36)( 1.5)(1.0) = 32.4 kips ~~~=

0.9(32.4)= 29.2 kipS> 3969~. 7 = 5674Jb

V,/0=29.2/1.67= 17.5klps>39691b It is acceptable to use.: ASD: a 3.0- incll x 5.0-inch x 0.625-inch-thick bearing plate LRFD: a 3.0-tnch x 4.0-tnch x 0.625-inch-lhick bearing plate

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Design Example 3 • Thre&-Siory Ught-Frame Mulifamity Buildng Design Using CokJ.Forrned.Ste/Wall Framing

and IMlod Floor and RoofFraming

A smaller 3-inc.h x 3-tnch plate could be used if the c. increase

Jn allo\~o'able beanng \WS considered. The piare would have been the same thickness and the deformation of the wood would be a linle more than 0.nUnUOUS element), Stnee ~: 3.0 is gre.uer than evaluating the podium deck uslng the 1.3 force ampJdication associated v.IJ.th the ratlO of the uppe.r and lower late-ral-restsung system R-mlues.

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Design Example 3 • Thre&-Story Ught-Frame Mulifamily Bu;lding Design Using Cold-Formed-Steel 'WaN Framing andv.bod Floor and Roof Framing

The des1gn ofthe oommuous rod -t~podium eonnecnon is not pan ofthtS design example. and n is assumed the engineer tS famd1arwnh ACI318 Chapter 17. The desagn of the pod1um slab is also not panoflhis design e=ple. Autbor•s Discussion

MultlstOI')' residential buildings cypicaUy have many shear walls. and typically a symbol mark IS shown on the framing plans representing the locations of the connnoous rod tie-downs {hold-downs) for each of the shear \'l'alls. These marks then refer back to a conunuous rod (hold-down) schedule that 1denufies all oflhe c.omponents of the commuous rod ue-down sySiem. usuaJiy wnh a gene-r1c detatl show1.ng how the conunuous rod ue-down system is assembled. Projects 1nay use a combanation of differe-nt hold-down types such as CFS strap hold--downs, enlbedded CFS strap hold-d0\1/1\S, conve-ntional CFS hold-downs. and eontinuouo; rod tie-down systems. As the budd1ngs become taller. conunuous rod tie-down systems are used. as they typteaHy have more sueng.th than com'enuonal hold-downs. When destgning multistory bulldmgs.lhe framing contmctor should be requjred 10 pr0\11de the engtneer of record 1nstallauon drawmgs showing all the dillerent types ofoonunuous rod ue-down runs. along wnh framtng plans that shO\v wheJ'e these conunuous rod tie-downs octur in plan. Some bu1lding departments, or the junsdicuons havtng responsabll ny. Will reqUJte these conttnuou.s rod ue-down installatton drawtngs be submiued for pemumng ao; a deterred submmal. There are conunuous rod tie-dov•.-n component manufactuters that will produce these shear wall continuous rod ue-down installauon drawtngs as part of their setvice ro the fram1ng contractor who purchases lhe oomponems t:i'om them. The conu.nuous ue-down component manufacturer may also c.ons1der and su_ggeSI ahernative materials (steel-rod material. CFS stud material, beartng-plate sizes. etc.) for substitution based on what JS cUJTe!ltly avaiJable 1n the construction marketplace. Ar'r]r substitutioos by the conttnuous rod tjedown component manufacturer are to be submitted to the engineer of record as well as to the jurisdiCLion for rev1ew and approval if the subsutuuon IS proposed durtng or after plan check. 12.6 SHEAR WALL CHORD STUDS

Chotd studs (verucal boWldary members, eJtd studs) are at each end ofa shear wall and prunarily res1st the shear wall o-venumtng and gravny-oompressJon loads. The chord studs are placed symmetrtcaHy on either side of the shear waH continuous rod tte-down use ro resist the uplift forces. In thls destgn example. there are two oven:uming-restrrunt (tie-down) system configurations used. I. The thtrd-ftoor shear wall conunuous rod rermmates at the bf1dge block several teet below the lOp of the waJI. As the \\'3.11 hfts up from ove.nurntng. the faslener connection of the CFS chord studs to CFS cripple stud~ located under the v.'Ood bridge block, uansfers the upld't force to the CFS cripple sruds, which then uansfe.-s the force to the unders1de of the bridge block through beanng. lne.n the sreel bearing plate on top of the \\'Ood bndge block resist.(i the uphft fotce through beattng and JS supported by the co.umuous rod. 2. The second- and firsl-ftoor shear wall conunuous rods e.~tend through the floor above. and as the wall lifts up from ovenumjng. tJ'le CFS chord studs resist the uplift force through bearmg in the CFS top track. which in tum bears on the w'ldersade of the Vt'OOd floor rim jotst. The conunuous rod steel bearing plate tS p1aced tn the CFS bonom uack of the wall at the floor level above. and it holds dO\m the v.'Ood rim floor joiSt.

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Design Example 3 • Thre&-Siory Ught-Frame Mulifamity Buildng Design Using CokJ.Forrned.Ste/Wall Framing

and IMlod Floor and RoofFraming

The chord studs are checked fOr ruu different compressive axial load1ng cooditjoJ'ts: 1. Chord studs used for uansferr1ng the overturnmg uplift load are located on each side of the conHnuousrod and under the steel bearing plate m the bottom r.rac.k of the wall above and any

wood filler block or nm joist under the steel beanng plate. 2. Chord studs resistutg downward ovenumjng and gnwny compression forces are located on each stde oflhe ~I beanng plate 1n t11e wall bouom track or posstbly bearoo top of the

beanng plate. When R IS other than 3.0. the CFS chord studs are requtred to have the available strength to restst the compresstve ax.LaJ force equal to lhe lesser of ( I) the setStniC load combtnauons wuh lhe overstrength fac10r ot (2) !he expeal

shear strength. • ·,.. muJuplied by the expected su-e:ngth filctOt'", n£. The expected suength factor ts I .8 for shear walls with wood structural panels pe.r AJSI S400 Secnon E 1.3.3. Thjs l)'pically governs the destg.n of the CFS chord studs rather than lhe dtfferential load. as the overturnmg and gravity loads are cumulati\·e downward. Only the ovenurrung uplift load m each floor le"Vel (dift'C-rent:ial load) should be considered tOr the compression destgn of the uplift. studs at lhat floor le"Vel. The difrerenual upltft loo.ds were derived earlier using the amplified loads subt.ractutg out the resisung dead loads. In tltis desig,n e.~ple~ the CFS chord Sluds resisung uplift bear on tl'le top Lmck., which bears on a wood top plate. \\ohich bears on a wood run JOiSt, whtch is held down by the stee.l beart.ng plate tn the wall above. AJSI 0 110..1 6 Co/d-FOI"med Sttel Fl"tJmmg Design Guidt AppendiX F has a destgn example for desagn1ng an axtally load steel stud-to track-to concrete bearmg coodtuon, whtch may provide gutdance for a steel stud-to steel track-to wood beanng condition. In additton, lhere will be crushing or bearang deformatiOn at lhe steel chord stud to wood top plate, lhe wood top plate to the wood nm joist, and the wood nm jo1st to the steel beanng plate. AWC NOS Comme.ntary Section C4.2.6 states the amount of deformatiOn IS approximately two and one-ha1ftimes a metal plate to VI'OOd bearing joint when a JOint contatns two wood members loaded perpendicular to yam. nus beartng detbrtnation should be added to the vertJcal ovenurnang-restra.int-system diSplacement ponion of the shear wall deflectioo equation. AJSI 0 II().. I 6 Co/d-FOI"med Sttel Fl"tJmmg Design Guidt AppendiX F provides an example of one methodology for calcuJating the approximate bearmg area when destgning CFS compt""esston studs in a bottom track bearutg on concrete. Chord-Stud Assrmbly Compre:ss ion

Load~

The des1gn forces shown are for 1lle Optton 3 shear wall (LRFD).

Roof-Ltvtl Otsig.o Lo1ds (Third-Floor Sbur W•lls) Wall ya\•tty-cmnpressJon Joads: Dead load= 153 plf

Ltve load =0 plf(roof live load not used in load combinations) Load onmbtnation = ( 1.2 + 0_2(S"'))D + 0.5L = [ 1.2 + 0_2( 1.117)]( 153) + 0.5(0) = 2 18 plf Chord srud boundary gravtl)' load= (25-ft-long wai112X2 18 pll) = 27251b Assumed chord stud boundary \\1dlh = 2 ft

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ASCE 7 Eq 6 §2.3.6

Design Example 3 • Thre&-Story Ught-Frame Mulifamily Bu;lding Design Using Cold-Formed-Steel 'WaN Framing andv.bod Floor and Roof Framing

Wall seismic forces (amplified seismic loads - compression loads): OTM (Including the seisrntc overstrength factor 0.0) = 270.848 ft-lb Lever arm= centelitne ofhold-dO\\n to centerline of hold-down =25 ft- 2(1 ft) =- 23 ft C= T=270,848123 =I 1,776 Jb

Expected shear waJI strenglh - compression loads: Wall length= 25ft, #8 screws a! 61n o.c., V......,= v. = 890 plf,fl,= 1.8 OTM = (25 ft)(890)( I .8)( I I ftYIOOO = 440.55 kop-ft Lever arm= cemeritne ofhold-do""ll to centerline of hold-down=- 25- 2( I ft) = 23 ft C=440,550/23 = 19, 154 Jb >I 1,776 Jb; therefore,use I 1,776 Jb

Conunuous rod te.ftsile capacity (for up1ift comparison}: C.onlinuous rod= .Yt-tnch diameter (0.442 in2) R, = 1.2 (ASTM A36 matenal)

AISC 34 I TA3. I

Continuous rod nom anal tension strength= (0.442)(0.75 x 58 ksi)( 1.2) = 23.07 ktps AISC 360 §J3.6

Summary of chord-stud assembly axlaJ loads: 23.07 kips (rod uplift capaci!y)

> 19.154(expected-compression) > I 1.776 kops(amplified - compression) > 10.371 kops(rod amplified dift"eren!ial uplift)

Third-floor O..igo Loads (Setood-Fioor Sh.. r Wills)

Wall gmvity-compc-ession loads: Dead load= 153 + ~64 = 617 plf Live load =(I 1.8 ft x 40 pst) =472 plf

ASCE 7 &j 6 §2.3.6 Load comb1na1ion = ( 1.2 + 02(SJJS)D + O.SL = [1.2 +0.2(1.1 17)](617)+0.5(472) =I 115 plf Chord stod boundary gravo1y load= (25-ft-long wall/2)( I I 15 pi f)= I3,938 Jb Assumed chord-stud assembly houndruy \\idth = 2 ft W3JI seismic forces (amphfied se1smie loads - comp(eSSIOO loads): (Jf)V( = 820,598 fi-Jb

Leve.rarm = 23 ft T=C=35,6791b Expected shear waJI strenglh - c.ompression loads: Wall length = 25 ft, #8 screws at 3 1n o.c., V__, = J~ = I775 plf; o, = 1.8 OTM = (25 ft)( 1775X I .8X 10 ft)IJOOO = 799 kop-l\ OTM 1otal (roof+ !hord floor)= 440.55 + 799 = 1239.55. Use 1240 k1p-ft Leve-r arm= centerhne ofhold-dov..n to centerline-of hold-down= 25- 2( I fi) = 23 ft C= 1,240,000123 = 53.913 lb > 35,679 lb; therefore, use 35,679 lb

Conttnuous rod renstle capacity (for uplitl c.omparison): Continuous rod= ~-inch diameter (area= 0.44 tn2)(F.. =- 125 k.s1)

R, = I. I (assumed for ASTM A I93 !!7 matenal) Conlinuous rod nom1nal lension strength

=(0.44)(0.75 x 125 ksiX I .I)

AISC 360 §J3.6

= 45.375 kips

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227

Design Example 3 • Thre&-Siory Ught-Frame Mulifamity Buildng Design Using CokJ.Forrned.Ste/Wall Framing

and IMlod Floor and RoofFraming

Summary of chord-st\KI assembly axial loads: 45.375 k tps (rod uplift capacuy)

< 53.913 ktps (expected compresston) > 35.679 kips (amplified compression) > 19.640 ktps (rod amplified-differential uplift)

S«ond-floor Drsign Loads (First-floor Shur \Valls): Wall yav&ty-compression 1oads; Dead load= 153 +464 +464 = 1081 plf L""' load= ( 11.8 fl x 40 psf) + 472 plf = 944 ptf Load combination = ( 1.2 + 0.2(S..,))D + 0.5L ASCE 7 Eq 6 §2.3.6 = [1.2 +0.2(1.117)](1081) + 0.5(944) = 1539 plf +472 plf=2011 plf Chord st\KI boundary gravity load= (25-ft-long wall/2)(2011 pit)= 25,138lb Assumed chord-stud assembly boundary width= 2ft

Wall selsmic forces (amplified seism&c loads - compression loads): OTM = 1522.123kip-fl Lever arm = 23 ft T=C=66,180 lb Expected shear wall suength - oompress1on loads:

wau lenglh = 25 ft. #8 screws at 2 in o.c.• f-:._...., = v. = 2190 plf. fit= 1.8 OTM = (25 11)(2190)( 1.8)( 10)/1000 = 986 k1p-ft OTM total (roof+ third floor+ second floor)= 44 1 + 799 + 986 = 2216 ktp-ft Lever arm= cemerl tne of hold-down to centerline of hold-down= 25 - 2( I ft) = 23 ft C=2226/23 = 96,7831b > 66,180 lb; d~erefore, use 66,180 lb Cormnuous rod tensile capacity (for uplift c.ompanson): Conunuous rod= I Ys-inc.h diameter (area= 0.994 in2 ) (F, = 125 ksi) R, = 1.1 (asstuned for ASTM Al93 87 material) Conunuous rod norntnal capacuy

= (0.994)(0.75 x 125 kst)( 1.1 ) = 102.51 ktps

AISC 360 §J3.6

Summary of chord-stud assembly axial loads:

102.51 kips (rod uplift Cl 96.783 kips (expected compression) > 66.18 ktps (amphfied compression) > 26.240 kips (rod amplified dtfterenLial uplift)

GM1trning loads ror Compression CFS Chord Sluds Table 3-38 shows the governing CFS chord stud destg.n loads for both the story-level diffe(enttal uplift and accumulative downward compression loads due to the shear wall ove·rturnmg for each story level of the buddlng. ln a typiCal conunuous rod ue-dov.n system for CFS c.onsuuction,lhe chord studs are requtrtd to I. Have the available strength to resist the comprcsstve axial load due to the cumulative overturning do,~onward compresston design load.' 1.ncludtng the design gravtty lood~i. 2. Have the avrulable strength to res 1st the compress1ve a..;tal load when beanng agautst the ftoor fromtng or wall above on the te.nston (uplift) side of the shear \WI I.

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2018/BC SEAOC Slructurai/Seismic Design Manual, 1.01. 2

Design Example 3 • Thre&-Story Ught-Frame Mulifamily Bu;lding Design Using Cold-Formed-Steel 'WaN Framing andv.bod Floor and Roof Framing

The chord stud des1gn on the compression stde of the shear wall governs the chord stud des1gn. as the compress1ve axlal load 1S cumuJauve wnh each successi,•e SlOI)' and includes the gra\'aty Joods. Table 3 -38. Opuon 3 shear wall: summtlr)t q[CFS dmrd s1ud differenlial uplift and accrumt/(JJh·e dowm•·anl compre.uion dtsign loads

Level

arM DitrerenuaJ Uplift Loads (k1ps)

3rd Floor

10.371

2od Floor

19.640

1st Floor

26.240

Load Type'''

OTM Compression Downward Loads (k1ps)

Lood

Gravuy

Type•lJ

Loads (kips)

11.n6

amplified

2.725

35.679

amplified

13.938

66.180

amplified

25.138

amplified

differential amplified

differential amplified

differenual

I. The uplift loads are lhe amplified ddTerenual SUll')' loads from Table 3-37.

2. The downward comp!ession design loads ate-the smaller of the calculated oversuenglh and expected loads. Chord Stud Resisting Compression Out to 0\•trturning and Gnwity loads

The CFS-chord studs are designed for the governing compression forces uulizmg commercially available CFS design software. The selected CFS StlJd stzes for lhe three floor levels lhat have an avaalable compressive a-< tal stte11gth 10 res1s1 1he lesser of ( I) !he expee1ed streng1h of on the shear wall chord studs. 4 . This destgn example uses a 3-tnch space between the CFS cnpple studs beiYo1 the bridge block on either side of the continuous rod at lhe Llurd ft{)()( and a 9-lnch width betwee.n the CFS chord stud packs at lhe second and lh1rd fi()()(S. The gap needs to be adequate to install the uphft resmunt systenl. which mcludes the cootinoou.~ rod to the coupler nut., the take-up device. etc. 5. The shear wall CFS studs are mechamcally braced by steel sttaps on each side and periodlC tntermitte1n blockmg at midpo.nt at the lhud and second floors and at thtrd po1ms at the first floor. The compressive axial strength of the mdividual CFS studs

JS dependent on lhe presence ofbrac1ng. lf mechan1ca1 steel btactng is used. the axial capacity also depends on lhe spacmg of the bfacmg. As is dtscussed later 1.n Secuon 14. 1 on waJI-stud braci11g. the bracing must be adequately secured to prevent Late-ral twisung and buc.klmg of lhe CFS studs and must have anchorage to resist the cumulath•e bractng

force fo< a"ally loa.'ttngutshers, and othe.r waJI opentngs. The CFS continuous stmp bracing should not be used as badang for objects to be supported off the tace of the shear wall, so the engineer should cons1der the location and elevatton of wall fixtures. wall-hung cab1nets, and the tops offtoor-supported cabt.nets. Stud Slrap Bradng for CFS Stud Axial Capacity (Bradng Forte- and Bntting Syfttm) IBC Section 22 11 states tl1Si----cm AI tCNtf> rAt( TO

AI lj( O.C. Al C~ll"PL( S1'UDS U.N 0.

(NO AnACHMtr...--:s

BtTWEEN

srvos)

/__J

i1"''---el'< CHVRO SiUOS AUCNE.D rACt ·o rAC£ (NO AtTACitMOtr$ BfT\\'(fN S1UCS)

3 " 1/!N

Figure 3- 25. Wood bndge block tJIIhird-/foor chord-swd assembly

Cbord-StudAi.~tmhly

ar Bridgt Block; Shtatbing-Scrtw Uplifl Fortt Tranfftr Exampks

E.xamplt 1: The lhtrd-floor uplift bndge b1ock uses the chord-stud sheathing edge-screw des1gn but without edge screws to the cripple studs. instead using field scte\VS to the crappie smds under the bridg.e block. Uplift= 10,371 lb (LRFD amplified force) Stud heigJu to wall nm joist= II ft- I ft = 10ft Shear per foot of stud height= 10,371/10 = 10371blft Shear per foot ofhe~ght per stud= 1037/4 chord studs= 260 lb

#8 screws 316 inches on c-enter tn plywood sheathing (nominal strength)= 890 lb 890 lb > 260 lb

However. shear wall edge fasteners are divided equally between chotd sruds 10 shear walls using c.ontinuous rod tte-down systems (but they should not exceed 12 tnches on center). The third-floor shear wall uses #8

screws at 6 mches on .::enter. and there are four chord studs. 6-tnches-on-cemer edge-screw spac1ng x 4 chord studs= 24-tnches-o~nter edge-screw spacll'lg at each chord srud. However. the designer nwsr not ex:ceed spactng of 12 tnches on center. 2018 IBC SEAOC Structural/Seismic Design Manual. \lbl. 2

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239

Design Example 3 • Thre&-Siory Ught-Frame Mulifamity Buildng Design Using CokJ.Forrned.Ste/Wall Framing

and IMlod Floor and RoofFraming

Use #8 SCI\."\VS at 6 inc.hes on c-e-nter for general wall-sheathing edge screv.'ing. except use 12 tnches on center to each oflhe chord compression studs on each side of the bridge block. Stagger tlte screws between adjacent chord studs. Attach sheath1ng to cnpple studs ustng field spactng of 12 inches on center. Load Tran.sftr bttwttn lbt C hord Stud and tht Cripple Stud

Use #8 se.rew anachmenL~ bemreen the 54-mtl CJ-""S chotd srud web and the-54-mil CFS cnpple stud web for uplift force transfer to the bndge block: Tronsfertorce = 10,37Jn chord stud packs= 5186 lblchord pack #8 screw capacity (•Pul = 0.5 x I278 = 639 Jb

(from Table 3-40)

(•Pu) fcrbeanng and ttlung See Section 12.8 fOr screw des1gn infonnatton.

Qua:nuty of#S screYt'S = 5186/639::: 8.1 SCWr\'S; Lheref«e.• use etght #8 scre\li'S mimmum. #8 screw spacong = (3.67 ft x 12)/((8n rows)- I)= 14.68 tn > 12tn Since the required screw spacing IS greater than 12 tnches. it is recommended to nm exceed I2-inch spacing.

Use two tO\\o'S of#8 screy..s at 12 i.oches on center. Load Ttans ftr bttwttn lndh'idual Chord Stud.~ and Jndivid:ual Cripplt Stud.~

ll'!echord studs must be designed to tranSfer 10,371/4 =2593 pounds between lhem ussng weJds, and the pairs of cripple studs at each end of the bndge bloc-k also need to be destgned to transfer 518612 crtpples = 2593 pounds between lhem ustng welds. Instead of screwmg the one chord stud 10 the one ct1pple stud. it may be easier for the fabric:arot to shop we-ld the chord stud 10 the crtpple stud and bring_ it out as one assembly. since the welding between indtvtdual c.h«d studs (face to face) and cripple studs (face to face) wtll likely be done tn the shop.

Ex.amplt 2: At the third-floor uphft bndg_e bloc I; the chord-stud sheathing edge-screw des1gn tncludes lhe edge screws lOthe shoner cnpple studs under the bridge block. Otord and crtpple studs are n01 auached togelher except tbr a sang_le chord stud we.b screwed to a single cripple stud web at each end of the bridge block(see Ftgure 3-25). Uplift= 10,371 Jb (LRFD ampltfied force). The bndge block is assumed to be 10 tnches deep. The stud height to the underSide of the bndge block=4.5 ft - 10 tn=3

n 8 tn=3.67 ft

The uplift above the hotton1 of the bndge block= 10,37 1 x [(10ft- 3.67 ft)/10 1\j =6565 Jb The shear per foot of stud height ahove the hottoro of the bridge bloc.k =65651(10 n- 3.67 fi) = 1037 Jblt\ The shear per foot of chord stud ahove the bottom of the bridge block= 10371(2 chord stud 12-mch-on-center spac:•ng~ therefore. use 12 utches on cente.r. Use #8 screws at6 1nches on center 10 all chOI'd studs s1.n.ce i.nd1v1dual chotds studs are not mterconnec.ted by screws or \\'tlds.and use#8 screws at 12 1nches on center to the uxhvtdual

cripple studs below the bridge block.

load Transftr btt~tt-n tbt Cbord Stud and tbt Cripplt Stud

#8 screw anachment(i between the 54-mil chord stud we-b and the 54-mll cripple stud web for upl1ft fbcce transfe-r: Tran are taken fi'om CFSEI Techn1cal Note F70 1- 12. wh1ch prov•des an average screw shear vaJue based on rev.ew of sever31 manufacturers' test reportS. The nominal scre\\o'S shear values are s.hovm m Table 3-41. H1gher screw shear values are poss1ble based on the designer specify1ng sc.rews that are evaluated 1n an evalwujon repon ln accordance with pubhcally developed and publica11y available acceptance or evaluation criteria. Tab/~ 3-./ I. Nommalscmv shetJr mlrNs (P,) from CFSEI Technical Note Fl0/-11

Sc.rewSize

Nomtn.al

LRFD (~ = 0.5)

ASD(0=3.0)

PM (Ib)

~PM(Ib)

P,/O(Ib)

~

1278

639

426

#10

1644

822

548

#12

2330

1165

777

y.•

3048

1514

1016 AISI S IOO §J 6.1

C. Sbtar R upturt (V..) if Scr ew Pulls tow11rd Limiting Edgt

AISJ SIOO Eq 16.1- 1

For a connection where lhe screw pulls through the steel toward lhe limiung edge: AISI SIOO Eq 16.1-1

A_.=2nte'""

"=number of Scte\\'S along critical cross.-secuon (assume I screw) 1 = ba~ steel thtckness e...,= c.lear distance !rom e·nd of member a~td edge ofscrew hole (assume 3 u1) A.= 1(1)(0.0566)((3X02 16)J =0.07335 1n2 ~~ =

o.6(65,oooxo.o73JS) = 2861 lb

LRFD= =

1i, x (h,lb2 ) + 11,_1 ,._1 = 0.137 tn x ( 120 in/300 on)+ 0.0472 tn = 0.102 in

Amphfy story dnft us:utg ASCE 7 Equauon 12.8-1 5 to ensure n lS Less than the aUO\'I'able story drtft, !!(If. 11. = 0.025/ou = 0.025( 120 in)= 3.0 on (firs! and second floorll segment)

3. 0.90+£=0.70+£• P, = 20.2 ktps; M, = 59.5 ktp-ft; V, = 17.3 kips (at the top of the wall segment) P.= 24.6 ktps; .If.= 120.6 ktp-ft; 1',= 18.7 ktps(at the bouom of !he wall segment}

Check the capac.ny wtlh mdalloads alone rutd no ftexuralloads..

282

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Design example 4 • Mosavy Shear

war Building

ll\e effecuve hetght for compression loads. h. ts equal to the full story hetght, H. slnce Lateral suppon 1n

the out-of':pla.Jle dtrection occuts only at the ground and roof levels. As specified tn TMS 402 Section 9.3.2, retnfOrctng steel IS not used to restst compresston because tt ts not supported by lateral lies. 7.63 tn Jii = -:ti2 = 2.20 m !! =16 11(12) =87.3 < 99

r

=

r

I

2.20

11te nom mal a.x1al strength. P,.. tS therefore equal to:

P,

=08[08J;(A, - A.)+

f,A.][1-c:~r

n

=0.8[0.8(2 ks.)(7.63 '" x96 m - (0)+60

TMS 402 Eq 9- 15

ksi(OJ)[I-(~:: )']= 573 kips

where A, ts the net area of the cross sectton and AM tS the area of latemUy ued long_~tudmal reantbrcement (which P, . . . OK For a gaven runal load (P..). the correspondtng moment (M,) on the mteractton diagram IS dete.nmned by senmg the m.a.:;onry suatrlln the extreme oompresston tiber at r.... (wtuch IS equal to 0.0025 for cooc.rete masonty; see TMS 402 S~lion of9.3.2) and selecting a neuual a-.:is depth (c). The eompresston force in the masonry tS g1"\·e-n by:

c. = 0.64cbf: where b ts wKflh of the compression block, whtch is equal to the wall thk:kness, 1 in this case.

Using Similar tnangl ~ the stram tn each remfbrc1ng steel bar (t..J IS given by: d

-c)

£ • =£.... ( - ·t:- -

where d, IS the distance from the extreme oompression fiber to the reinforcing bat. The force tn each remforc1ng bar ( TJJ) IS then g.l\'en by:

where£, is the steel modulus of elasucity, A,.. is the area of each reinforcing bar. and/y 1s the steel yteld str~s. If the selected ne.utra1 axis locauon does not result in eqmlabrium of fOrces on the cross se1.0

3.0

< 1.0

1.5

-

1.5

All

>1.0

1.5

> 1.5

< 1.0

1.5

M.= 1049 lb-ftlft .. . OK

The above procedllre can be repeated to show the '"'all re1nfbrceme-m IS satJsfactory tor other appl1cable load combinauons. The wall reinforcement needs to be checked against the maximum limits tn TMS 402 Section 9.3.3.2. From Table 4-3. tlte tensile stram in the extreme steel fiber must be at least 1.5 Limes lhe y1eld stratn (a= 1.5) for the followmg load comb1nat1on: P_ = P0 +0.75PL +0.525PQ, = [858+ 255]+0.75(0) +0.525(0)= I I 13 lb

From the commentary ofTMS 402 Section 9.3.3.2, tl1e maximum re-inforcement ratio for a fully grouted member with only conce-ntrated te.nsion reinforcement is:

-0.64J;,(,_•:a.J£i f. 64(

P-=

y

0_

2000

i)(

ps

113

0.0025 )- I lb/11 0.0025+1.5x0.002 1 12 m x 3.8 1tn -0.009 60,000 psl

The wall re1ntbrcement ratio ts: A

p = -'- = bd

292

0 .10 in' - 0.0022 < 0.009 ... OK 12 m(3.8 1m)

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Design example 4 • Mosavy Shear

war Building

ll\e \~tall horizontal deflectton at mtd-hetght under allowable stress design load combu..auoos~ Sp must

satisfy the fOllowing equation: 8Jo s: 0.007/J

TMS 402 Eq 9-32

For the allowable sttess load combu1atioo 0.6D + 0.7£:

"'• = 0.7(31.2) = 21.8 psf P.r= 0.6(255) = I 53 lbltl P, = 0.6(255 + 601)= 514 lblfl And St.llce the dessgner can assume the \'r'allts not cracked because tt was uncrac.ked under suength-leveJ loads. the deflectton at mtd-height l~ equal to: 1 wh Pe -1 - +...L & 8 2 s 48£,.1,

5h2

(

21.8 psf(l6 fix 12)' + 153 lbltl(6.3 1n)) 8(12) 2 48(1,800,000 psi)(444 in') - 514 lblfl 5(16 fiX 12) 2

- (P,)

= 0.04 '"< 0.007/r = 1.34 1n .. . OK As wttll the determi.nauon oflhe strength oflhe wall. the wall can be checked tbr lhe other allowable sttess

design 1oad combinmion to verify that the deftecuon is acceptable. 4.2 DESIGN OF WALL SEGMENT ON LINE A

TMS 402 §9.3.5.4 .3

The 8-foot \WI! segment on line A tS adJacent to openings. TherefOre.• as shown sn Ftgure 4-9, the segment

suppons out-of-plane loods over a trtbutary width larger than its width. A conservative approach ts to ignore the openings and destgn lhe 8-foot segment to resist a w'liformly distributed load mat corresponds to a 28foot tributary widlh over lUi entire height. Wnh this approach, the equations for pinned-pinned boundary condmons and un1fonnJy dtstrtbuted loads. whteh were descnbed in the prevaou:s secuon. can be used.

Tributary Arta ror

·\r

Out-of Plaoe Load