13 th World Conference on Earthquake Engineering Vancouver, B.C., Canada August 1-6, 2004 Paper No. 3482

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1 13 th World Confrnc on Earthquak Enginring Vancouvr, B.C., Canada August 1-6, 24 Papr No A TUDY ON THE EIMIC ORCE REITING MECHANIM O A MULTI-TORY HEAR WALL YTEM CONIDERING THE INTERACTION BETWEEN WALL, LAB, OUNDATION BEAM, AND PILE ELEMENT Masanobu akashita 1, Hakim Bchtoula 2, usumu Kono 3, Hitoshi Tanaka 4, umio Watanab 5 UMMARY Two 1/5 scal spcimns wr dsignd and constructd as basic structural assmblag modls xtractd from a practical six-story shar wall systm. Thos spcimns consistd of a bottom two-story part of th shar wall systm, a foundation bam, slabs, and two pils. tatic latral load was applid with proportionally varying vrtical load to simulat loading conditions of th prototyp six-story shar wall systm undr arthquaks. Th foundation bam rsistd by itslf and th contribution from th pils and shar wall was lss than xpctd. This causd unxpctd shar cracking to sprad xtnsivly ovr th foundation bam. Howvr, longitudinal bars in slabs workd togthr with th uppr longitudinal rinforcmnt in th foundation bam. Transition of shar transfr mchanisms at th shar wall bas was obsrvd from th strain distribution of longitudinal rinforcmnt in foundation bams and thos strain distributions of diffrnt loading stag wr prdictd accuratly. Th latral load drift rlations obtaind xprimntally was simulatd wll with a simpl suprposition of flxur and shar lmnts. INTRODUCTION In currnt dsign procdurs [1][2], cantilvr structural walls ar normally assumd to stand on a solid foundation, and th foundation bams, slabs and pils ar dsignd sparatly without considring thir intractions. This is bcaus thir intractions hav not bn thoroughly studid for its complxity. Also nglctd in th practical dsign is th fact that shar transfr mchanisms along th wall bas vary dpnding on th crack pattrs and inlastic dformation lvls at th shar wall bas. This study aims to xprimntally clarify th variation of th latral load rsisting mchanisms considring th intraction btwn a shar wall, foundation bams, slabs and pils, and to stablish mor rational dsign procdurs for ach structural componnt. 1 PhD candidat, Dpt.of Architctur, Kyoto Univrsity, Japan. rc.sakashita@archi.kyoto-u.ac.jp 2 PhD candidat, Dpt.of Architctur, Kyoto Univrsity, Japan. 3 Associat Profssor, Dpt.of Architctur, Kyoto Univrsity, Japan. kono@archi.kyoto-u.ac.jp 4 Profssor, Dpt.of Architctur, Kyoto Univrsity, Japan 5 Profssor, Dpt.of Architctur, Kyoto Univrsity, Japan

2 In th xprimntal program, th spcimn configuration was dtrmind from typical six story rsidntial buildings in Japan. Thy normally hav multipl spans of a RC momnt rsisting fram in th longitudinal dirction and a singl span of shar wall systm in th transvrs dirction. In this study, th assmblag consisting of th lowst two floors of shar wall with a foundation bam, th first floor slab, and two pils in th transvrs dirction was scald to 1/5 to mak modl spcimns. Th shar wall was dsignd to fail in flxur and th shar span ratio of th pils was fixd as 2.2 although th shar span ratio is supposd to vary dpnding on th soil, axial forc, and latral forc undr arthquaks. EXPERIMENTAL ETUP pcimns and tst stup igur 1(a) shows spcimn configuration. Th first floor slab xtndd 6 mm on ithr sid of th wall and th total width was 12mm. Th shar wall and th slabs had th sam thicknss of 6mm. Th pils wr dsignd to b lastic and xtndd to th top surfac of th foundation bam so that th sufficint latral forc can b transfrrd to th foundation bam. Th cntr-to-cntr distanc of th pils was 18mm. Th distanc btwn th supporting pins and th top dg of th slab was st 124mm. Two spcimns wr idntical xcpt that thy had diffrnt amount of longitudinal bars in th foundation bam. As shown in Tabl 2(b), th yilding of th foundation bam was dsignd to prcd th yilding of th shar wall for LB16 and vic vrs for LB13. Th foundation bam of LB16 had ight D16 longitudinal rinforcing bars as shown in igur 1(b) whil that of LB13 had ight D13 bars instad. Both spcimns had ight D1 bars splicd to ths longitudinal bars for 4mm long at th midspan as shown in igur 1(b) to simulat th bar cutoff in practic. Matrial proprtis ar shown in Tabl 1. Tabl 1: Matrial proprtis of concrt and bars (a) Concrt Comprssiv strngth (MPa) Tnsil strngth (MPa) Young's modulus (GPa) oundation bam, Pil Wall, Column, Bam (b) tl rinforcmnt Yild strngth (MPa) Young's modulus (GPa) Tnsil strngth (MPa) φ D D D Tabl 2: Typs of rinforcmnt and tst valus Mmbr Column (16 16mm) Bam (12 16mm) har Wall (Thicknss 6mm) Pil (35 35mm) (a) Typ of rinforcmnt Typ of bars tl ratio (%) Longitudinal 4-D1 1.4 Transvrs 2-φ4@8.21 Longitudinal 4-D Transvrs 2-φ4@5.42 Vrtical φ4@8.26 Horizontal φ4@8.26 Longitudinal 8-D Transvrs 4-D1@1.9 Mmbr oundation bam (LB16) (15 48mm) oundation bam (LB13) (15 48mm) (b) Tst Variabls Bars tl ratio (%) Longitudinal 4-D Transvrs 2-D1@1 1.5 lxural yild strngth 64MPa Longitudinal 4-D Transvrs 2-D1@1 1.5 lxural yild strngth 11MPa 66MPa is th momnt acting on th foundation bam whn th shar wall yilds in flxur.

3 27 5 har wall thicknss 6 lab width 12mm oundation bam Th hight of a p oint of c ontraflxur 124mm Loading bam Pil har wall Bam har wa ll 1st floor slab Latral column lab thicknss 6 Th cntr distan c btwn pils 18mm D1 1 4D16 for LB16 4D1 (a) pcimn configuration (b) Rinforcmnt for LB16 igur 1: pcimn configuration and rinforcmnt arrangmnt As shown in igur 2, latral load,, was applid statically through a 1kN horizontal jack to th loading bam. our vrtical jacks wr adjustd to crat appropriat column axial forcs, N1 and N2, which ar a linr function of latral load,, to simulat loading conditions of th prototyp six-story shar wall systm undr arthquaks. N and N = 72 ±.63 ( kn) (1) 1 2 At th rollr support, /2 was applid horizontally to th pil by a 5kN jack in th opposit dirction to th 1kN jack. This causs th possibl maximum axial forc in th foundation bams at th ultimat stag assuming th mchanism in igur 11 whr larg rotation of th shar wall maks th shar forc transfr through th limitd ara undr comprssion. Th load was applid two cycls at ach prscribd load stag until th shar wall yildd, thn th displacmnt control was usd with two cycls at ach prscribd displacmnt. As shown in igur 2, th story drift angl of th first floor was masurd with a displacmnt gaug on a masurmnt fram that was fixd to th transvrs foundation bams. 5KN jack 5KN jack (Comprssion) Loading fram /2 outh North ix Rollr Pin 1KN jack 5KN jack (Tnsion) Displacmnt gaug for 1 story Transvrs bam + - igur 2: Loading systm

4 ANALYTICAL PROGRAM Prdiction of load-displacmnt rlationship Th latral load-drift angl rlations of shar walls wr simulatd using a simpl modl. Th modl mploys a suprposition of flxur and shar actions. Th flxural action was modld with an ordinary flxural lmnt basd on a bam thory and th shar action was modld using Hirata t al. s modl [3]. As shown in igur 8, th nvlop curvs of th flxural lmnt and th shar lmnt wr assumd trilinar. igur 4 compars th calculatd curvs and xprimntal rsults. Th charactristic points ar summarizd in Tabl 3. Th computd flxural cracking strngths wr smallr than th xprimntal rsults and computd flxural strngths agrd wll with th xprimntal rsults. c y K ( K 5 2 Th point of th Th scond point of ( flxural yild strngth 5 K th shar forc 1 K ( ( E K (a) lxural lmnt Th point of th flxural crack strngth K 5 5 (b) har lmnt Th first point of th shar forc igur 8: har forc drift rlations for th flxural lmnt and shar lmnt 5 Tabl 3: Cracking and yilding strngths in flxur analysis LB16 LB13 positiv ngativ positiv ngativ lxural crack strngth,cr (kn) tory drift at cr (%) lxural yild strngth, y (kn) tory drift at y (%) imulation of strain distributions of th foundation bam bfor and aftr th shar wall yildd igur 9 shows a modl to analyz th foundation bam. Th foundation bam is subjctd to momnt from th pils (Mp), and momnt (Mq) and axial forc du to latral forc,, acting on th uppr dg of th foundation bam. Th distributions of Mq and N vary as th shar wall rotats and th contacting ara btwn th shar wall and th foundation bam dcrass. igur 1 shows a schmatic figur of contact and dtachmnt of th foundation bas. Numbrs bsid ach figur indicat th dgr of dtachmnt. If distributd uniformly across th whol shar wall bas, Mp and N can b computd as shown in igur 9. It is assumd that th shar wall rotats and applid is transfrrd through a rgion undr comprssion as shown in igur 11. igur 11 shows th modls of th distributions of Mq and N corrsponding to th dgr of dtachmnt in igur 1. Using th modls in igur 9 and igur 11, th strain distributions of th longitudinal rinforcmnt in th foundation bam wr computd at th thr loading stags in igur 4. It should b notd that D1 bars wr splicd to D13 or D16 bars at 4 mm of midspan and th strain distribution is discontinuous in this rgion.

5 har forc (KN) Yilding of th foundation bam Yilding of th shar wall irst story drift (%) har forc (KN) Yilding of th foundation bam Yilding of th shar wall irst story drift (%) (b) LB13 (a) LB16 igur 4: Latral load - first story drift rlations train distributions of longitudinal rinforcmnt in th foundation bam and in th slabs igur 5 and igur 6 show th strain distribution of longitudinal bars in th foundation bams. Thr lins in ach numbrs in igur 5 and igur 6 show th distribution for thr stags shown in igur 4. Outsid of D1 rgion, strains for LB13 in igur 6(a) tndd to b highr than that for LB16 in igur 5(a) sinc th flxural yilding of th foundation bam prcdd th flxural yilding of th shar wall in LB13. Th ngativ (south) sid location, strains of LB13 incrasd from tag 2 to tag 3 probably bcaus th shar cracking caus th dbonding and th tnsion shift pntratd to th south sid. It is also notd that at th nd rgion nar +6mm in igur 5(a) and igur 6(a), th strains ar lowr than th xpctd linar distribution xtrapolatd from strains of innr rgion. On th othr hand, nar - 6mm in igur 5(b) and igur 6(b), th strains ar linarly distributd as xpctd from th xtrapolation. Thn th rstraind strains of uppr longitudinal rinforcmnt can b attributd to th constraint from th slabs and th shar wall but not to th tnsion shift from shar cracking. Uppr rinforcmnt sms to hav mor influnc on th chang of latral load rsisting mchanism than th lowr rinforcmnt sinc distributions of strain at thr stags ar distinctivly diffrnt. This phnomnon is xprssd latr in igur 11. igur 5(c) and igur 6(c) show th avrag strain distribution of longitudinal bars in slabs and igur 7 shows th cross sction of th foundation bam and th slabs. Each strain distribution in thos figurs agrd wll with th strain distribution at th sam stag in igur 5(a) and igur 6(a). inc longitudinal bars in th slabs at a crtain sction showd narly idntical strain radings, th whol width of th slabs can b considrd ffctiv.

6 D LB16 Bfor yilding 1 LB16 Aftr yilding 2 LB16 Ultimat LB16 Bfor yilding LB16 Aftr yilding 2 LB16 Ultimat D LB16 Bfor yilding LB16 Aftr yilding 2 LB16 Ultimat Location in th slabs (mm) (a) Uppr longitudinal bar (b) Lowr longitudinal bar (c) longitudinal bars (oundation bam) (oundation bam) (labs) igur 5: train distributions of rinforcmnt for LB D1 LB13 Bfor yilding LB13 Aftr yilding 2 LB13 Ultimat LB13 Bfor yilding 1 LB13 Aftr yilding 2 LB13 Ultimat D LB13 Bfor yilding LB13 Aftr yilding 2 LB13 Ultimat Location in th slabs (mm) (a) Uppr longitudinal bar (b) Lowr longitudinal bar (c) longitudinal bars (oundation bam) (oundation bam) (labs) igur 6: train distributions of rinforcmnt for LB13 12 Bars in th slabs(φ 4) Uppr longitudinal bars Lowr longitudinal bars 15 igur 7: Th cross sction of th foundation bam and th slabs

7 ANALYTICAL PROGRAM Prdiction of load-displacmnt rlationship Th latral load-drift angl rlations of shar walls wr simulatd using a simpl modl. Th modl mploys a suprposition of flxur and shar actions. Th flxural action was modld with an ordinary flxural lmnt basd on a bam thory and th shar action was modld using Hirata t al. s modl [3]. As shown in igur 8, th nvlop curvs of th flxural lmnt and th shar lmnt wr assumd trilinar. igur 4 compars th calculatd curvs and xprimntal rsults. Th charactristic points ar summarizd in Tabl 3. Th computd flxural cracking strngths wr smallr than th xprimntal rsults and computd flxural strngths agrd wll with th xprimntal rsults. c y K α K 3 Th point of th α 2 K α K flxural yild strngth Th point of th flxural crack strngth 2 1 K 2 α K 3 Th scond point of th shar forc Th first point of th shar forc δc (a) lxural lmnt δ δ1 δ 2 (b) har lmnt igur 8: har forc drift rlations for th flxural lmnt and shar lmnt δ Tabl 3: Cracking and yilding strngths in flxur analysis LB16 LB13 positiv ngativ positiv ngativ lxural crack strngth,cr (kn) tory drift at cr (%) lxural yild strngth, y (kn) tory drift at y (%) imulation of strain distributions of th foundation bam bfor and aftr th shar wall yildd igur 9 shows a modl to analyz th foundation bam. Th foundation bam is subjctd to momnt from th pils (Mp), and momnt (Mq) and axial forc du to latral forc,, acting on th uppr dg of th foundation bam. Th distributions of Mq and N vary as th shar wall rotats and th contacting ara btwn th shar wall and th foundation bam dcrass. igur 1 shows a schmatic figur of contact and dtachmnt of th foundation bas. Numbrs bsid ach figur indicat th dgr of dtachmnt. If distributd uniformly across th whol shar wall bas, Mp and N can b computd as shown in igur 9. It is assumd that th shar wall rotats and applid is transfrrd through a rgion undr comprssion as shown in igur 11. igur 11 shows th modls of th distributions of Mq and N corrsponding to th dgr of dtachmnt in igur 1. Using th modls in igur 9 and igur 11, th strain distributions of th longitudinal rinforcmnt in th foundation bam wr computd at th thr loading stags in igur 4. It should b notd that D1 bars wr splicd to D13 or D16 bars at 4 mm of midspan and th strain distribution is discontinuous in this rgion.

8 Mp=/2 h D/2 Mq Tnsion Comprssion Lh N /2 /2 /2 /2 (a) Momnt from pils (b) Momnt du to latral forc (c) axial forc du to latral forc igur 9: Momnt and axial forc acting on th foundation bam Dgr of dtachmnt Column(Tnsion sid) hadd rgion is th ara of contact. har strss is assumd to distribut uniformly. har wall Whit rgion has no contact. No strss transfr is assumd Column(Comprssion sid) igur 1: Th rgions whr th shar wall lifts up D/2 Mq D/2 D/2 D/2 D/2 Mq Mq Mq Mq Dgr of dtachmnt Tnsion Tnsion Tnsion Tnsion Tnsion Comprssion Comprssion Comprssion Comprssion N N N N N /2 /2 /2 /2 /2 /2 /2 /2 /2 / (a) DD= (b) DD=.25 (c) DD=.5 (d) DD=.75 () DD=1. igur 11: Distributions of Mq and N corrsponding to th dgr of dtachmnt (DD)

9 igur 12 shows th comparison btwn th computd and xprimntal strain distributions of LB16. Contribution of rinforcing bars in th slabs is considrd in th computd. Lins,.25,.5,.75 and 1. indicat th strain distributions corrsponding to th dgr of dtachmnt in igur 1 and igur 11. Whn th shar wall yildd, th strains of th uppr longitudinal bars rapidly incrasd at midspan. This is bcaus th distribution of momnt shifts from igur 11(a) to igur 11(b) or (c). Without th rgion nar 1mm in lowr longitudinal bars, th computd strain distributions agrd wll with xprimntal rsults Bfor wall yilding Dgr of Dtachmnt= Dgr of Dtachmnt= Bfor wall yilding 1 Dgr of Dtachmnt= Dgr of Dtachmnt= (a) Uppr longitudinal bar (b) Lowr longitudinal bar ( i ) Bfor th shar wall yilding Aftr wall yilding Dgr of Dtachmnt=.25 Dgr of Dtachmnt= Aftr wall yilding 2 Dgr of Dtachmnt=.25 Dgr of Dtachmnt= (a) Uppr longitudinal bar (b) Lowr longitudinal bar ( ii ) Aftr th shar wall yilding Ultimat Dgr of Dtachmnt=.5 Dgr of Dtachmnt= Ultimat 3 Dgr of Dtachmnt=.5 Dgr of Dtachmnt= (a) Uppr longitudinal bar (b) Lowr longitudinal bar ( iii ) Ultimat 3 igur 12: train distributions of longitudinal rinforcmnt of LB16

10 CONCLUION Two 1/5-scal cantilvr structural wall systms wr tstd to clarify th variation of th latral load rsisting mchanisms considring th intraction btwn a shar wall, foundation bams, slabs and pils. Th main conclusions can b summarizd as follows. Monolithic action btwn foundation bam and priphral mmbrs, such as shar wall and pils, was much lss than xpctd and unxpctd shar cracking sprad xtnsivly ovr th foundation bam. Howvr, longitudinal bars in slabs workd togthr with th uppr longitudinal rinforcmnt in th foundation bam. As dsignd a priori, th shar wall of LB16 had mor damag than that of LB13. train distributions of longitudinal rinforcmnt in foundation bams from xprimnt and analysis show th shar transfr mchanism clarly. In th analysis, it is assumd that th foundation bam is subjctd to momnt from th pils (Mp), and momnt (Mq) and axial forc du to latral forc,, acting on th uppr dg of th foundation bam. Latral load drift rlations can b simulatd wll with a simpl suprposition of flxural and shar lmnts. REERENCE [1] Architctur Institut of Japan, AIJ tandard for tructural Calculation of Rinforcd Concrt tructurs Basd on Allowabl trss Concpt, 1999, pp [2] Paulay, T. and Pristly, M.J.N., ismic Dsign of Rinforcd Concrt and Mansonry Buildings, John Wily & ons, 1992, pp [3] Hirata, M., Naraoka,., Kim, Y., anada, Y., Matsumoto, K., Kabyazawa, T., Kuramoto, H., Hukuda, T., Kato, A., Ogawa, M., Dynamic Tst of Rinforcmnt Concrt Wall-ram ystm with oft irst tory Part 1-Part 4 ummaris of tchnical paprs of annual mting architctural institut of Japan, 21,pp (in Japans).