SEISMIC PERFORMANCE ASSESSMENT OF BUILDINGS WITH COLD-FORMED STEEL SHEAR WALL PANELS

Transcription

1 SEISMIC PERFORMANCE ASSESSMENT OF BUILDINGS WITH COLD-FORMED STEEL SHEAR WALL PANELS J. M. Mrtínez 1, L. Xu 2* nd Y. Liu 3 1 MM Engineers. Av. Lázro Crdens , Monterrey, N.L. México, CP Deprtment of Civil nd Environmentl Engineering, University of Wterloo 200 University Ave. W., Wterloo, Ont., Cnd N2L 3G1, *Emil: lxu@uwterloo.c 3 Highwy School, ChngAn University, Xin, Chin ABSTRACT Presented in this pper is method for seismic performnce ssessment of cold-formed steel buildings built with sher wll pnels s the lterl lod resisting system. In the proposed method, performnce-bsed design philosophy is dopted to ssess the seismic performnce for the cold-formed steel frming system. The structurl responses of cold-formed steel buildings re obtined from simplified finite element bsed on pushover nlysis developed in this study with ccounting for the nonliner behviour of sher wll pnels. A prcticl exmple is presented to illustrte the effectiveness of the proposed method. The results from the proposed method re compred to results obtined from the conventionl nlysis. Issues ssocited with performnce-bsed design of cold-formed steel buildings re discussed. KEYWORDS Performnce-bsed design, seismic performnce ssessment, cold-formed steel, sher wll pnels, nonliner pushover nlysis. INTRODUCTION The ppliction of cold-formed steel frming in residentil building construction hs incresed significntly in pst few decdes. The globl trend of pplying cold-formed steel frming is dvncing to mid-rise buildings. This includes hotels, multi-fmily housing, dormitories, nd mixed-use buildings of 4-9 stories. Cold-formed steel frming provides n efficient nd economicl structurl system which hs numerous dvntges nd benefits with brod pplictions. Among them, the fetures of being lightweight nd hving good ductility hve mde cold-formed steel frming n ttrctive structurl system in seismic regions where mid-rise buildings trditionlly hve relied on hevier construction mterils. Aimed to more relible mens of chieving life sfety nd property protection in seismic events, performncebsed design principles hve been dopted in new genertion of building codes globlly. In contrst with conventionl design prctice tht focuses primrily on life-sfety lod levels, performnce-bsed design lso requires structure to meet severl performnce objectives t lower lod levels, within cceptble rnges of relibility. Such chnge in design philosophy nd the consequent necessity for more complex nlysis nd design techniques to ccurtely evlute structurl performnce t different lod levels, cretes new chllenge for structurl engineers. The ppliction of performnce-bsed design (PBD) ssessment does not follow prescribed procedure; however, nor is it the sme procedure for ll structurl systems since it depends on the building chrcteristics nd designer s preferences. For instnce, severl methods for crrying out the seismic ssessment of buildings for PBD re vilble in current prctice, such s liner, nonliner, sttic, nd dynmic methods, nd combintions of those methods. The complexity of the ppliction of ech method is different nd so re their cpbilities; s result, some of the methods might not be suitble for nlyzing certin types of structures. Previous study hs shown tht results with resonbly ccurcy cn be expected from pplying pushover nlysis (nonliner sttic method) of cold-formed steel (CFS) buildings with medium height (Mrtinez 2007, Mrtinez-Mrtinez nd Xu, 2011). Therefore, the proposed method is limited to low- nd mid-rise buildings tht hve predominnt fundmentl mode of vibrtion in their response, so tht single mode pushover nlysis cn be used. The inelstic behviour of building in seismic event is consequence of the geometric nd mteril 758

2 nonliner behviour of its structurl components. Where, the mteril nonlinerity is ccounted for by incorporting the nonliner lod-to-displcement curve of the lterl-lod resisting system of the building. PBD ssessment involves trnsforming ech selected performnce objective to be stisfied by the structure into tngible prmeter tht cn be mesured in seismic nlysis. This study dopts spectrum-bsed pushover nlysis pproch, lso known s the force-bsed pproch, in which the performnce objectives re trnsformed into corresponding trget bse shers. When the lterl lods pplied on the building rech to the trget bse sher ssocited with one of the governing performnce objectives, the sher wll pnels (SWP) re checked to determine if they comply with the cceptnce criteri corresponding to the performnce level. In this study the cceptnce criteri (limit dmge stte) for CFS buildings re estblished s function of the lterl drift nd lterl strength of the SWP. FEMA 273 (1997) provides limit drift rtios for severl types of structures, including steel moment frmes, concrete wlls, msonry infill wlls, nd wood stud wlls. The four performnce levels shown in Tble 1 re ssocited with limit drift rtios to determine if structure design is dequte. It is common to use the drift rtios to compute trget displcements for the displcement-bsed PBD ssessment of buildings. FEMA 273 provides such limit drift rtios for wood frmed pnels only nd no informtion is vilble for CFS sher wll pnels. Therefore, in this study, the drift rtios for CFS buildings re determined from experimentl test results. Tble 1 Performnce objectives (SEAOC, 1995) SPECTRUM-BASED PBD ASSESMENT OF CFS BUILDINGS In this study, the spectrum-bsed pproch is preferred over the displcement-bsed pproch for the PBD ssessment of CFS buildings. Typiclly, building design is crried out using design spectr from pertined seismic design stndrds, which re used to compute the trget bse shers nd the mgnitude of the pplied lterl lods of the building. Conversely, if the displcement-bsed pproch is chosen for the PBD ssessment of building, lterl displcement is used s trget prmeter. Arbitrry lterl lod increments or lterl displcements re pplied to the building until the trget displcement is reched or until the structurl collpse occurs. Then, with the totl lterl lod pplied on the building in the nlysis, the bse sher cn be computed nd consequently the ccelertion is then compred to the site design spectr to determine if the building stisfies the site requirements. Thus, in the displcement bsed pproch, designers do not know if the building stisfies the site requirements until the nlysis is complete. This my require more unnecessry displcement or lod increments. The spectrum-bsed pproch, however, is consistent with the seismic design stndrds. A discussion on the dvntges nd disdvntges of both pproches ws presented by Grierson et l (2005). For spectrum-bsed PBD ssessment, ech performnce objective is ssocited with prticulr erthquke hzrd. The corresponding bse sher is dopted s the dmge trget prmeter, which represents the mximum bse sher tht building cn undergo during n erthquke. The trget bse sher for building is computed s function of the spectrl ccelertion (S ), structurl seismic weight (W), nd grvity ccelertion (g) for ech selected performnce objective s follows: for ech of multiple performnce objectives (PO) possible for building (see Tble 1), the bse sher is computed s: V PO S PO W g b (1) 759

3 PO Where S is the spectrl ccelertion t the selected performnce objective (PO), W is the seismic weight of the building nd g is the grvity ccelertion. SPECTRUM-BASED PUSHOVER ANALYSIS FOR CFS BUILDINGS In the spectrum-bsed pushover nlysis dopted in this study, the building is subjected to incrementlly pplied lterl lods until the trget bse sher is reched or the structure collpses (the lterl force resisting elements hve lost their strength nd stiffness). Throughout this nlysis process, the grvity lods re mintined constnt on the building. Upon pplying lterl lod increment on the structure, the structurl nlysis cn be crried out by the finite element nlysis. In this study, however, the nlysis is crried out using simplified finite element method discussed below with ccounting for both geometric nd mteril nonlinerities of the CFS sher wll pnels (SWP) (Mrtinez-Mrtinez nd Xu, 2011). From the structurl nlysis results t ech incrementl lod level, the corresponding incrementl displcements re obtined, nd then the ccumulted totl displcements up to the current stge of the loding process re found. In the PBD ssessment of CFS building, the cceptnce criteri for the SWP re checked when the bse sher of the building is equl to the trget bse sher for ny selected performnce objective, V b PO. Thus, if the structurl elements stisfy both the deformtion nd strength requirements, the cceptnce criteri for the specified performnce objective re stisfied. Simplified Finite Element Anlysis The simplified method cn be used with ny finite element nlysis softwre with orthotropic shell elements. For tht purpose, SWP in CFS building needs to be trnsformed into flt shell with equivlent properties in both x nd y directions s shown Figure 1. s F s F E, E, G Sx 1 Sy 1 1 ts 1 c 1 c 2 z E, A, I t F F F s C Screw s 2 Sx 2 Sy 2 2 y x () l t eq E xeq, E xeq, G eq (b) Figure 1 ) SWP cross section; b) equivlent shell Figure 1 shows the cross section of CFS SWP nd its equivlent shell cross section, where: s F is the spcing between CFS C-shpe studs, s C is the distnce between screws on the edge of the pnel, nd c 1 nd c 2 re the distnces from the centre of the studs to the mid-plne of Oriented Structurl Bord (OSB) shething on side 1 nd 2, respectively. The prmeters E F, A F, nd I F denote the modulus of elsticity, cross sectionl re, nd moment of inerti bout the strong bending xis of the studs, respectively; while l is the length of the pnel nd equivlent shell element; nd t S1 nd t S2 re thicknesses of the shething on side 1 nd side 2, respectively. E sx, nd E sy re the modulus of elstic of the shething for the x nd y directions for ech side, nd the G s is the shething sher modulus of elsticity. Troitsky (1976) developed equtions to determine the equivlent rigidity of orthotropic ribbed pltes in bending. Mrtinez-Mrtinez nd Xu (2011) extended Troitsky equtions to ccount for the xil rigidity of the pnel in the direction long the longitudinl xis of the studs (i.e., y direction). The equivlent thickness nd modulus of elsticity in the y direction of shell element re determined by equting nd solving the xil nd flexurl rigidities of pnel nd n orthotropic element. Afterwrds, the equivlent modulus of elsticity in x direction is determined by equting nd solving the bending rigidity of pnel nd n orthotropic shell. The equtions for computing the equivlent properties for the SWP re provided by Mrtinez-Mrtinez nd Xu (2011). 760

4 Nonliner finite element nlysis The shell element used in this study to model SWP in CFS building is n isoprmetric element, which typiclly hs between four nd sixteen nodes. It is recommended tht sixteen-node shell element to be used becuse of its ccurcy of modeling typicl 4 8 (1200mm 2400mm) CFS SWB with one shell element. Ech node of the sixteen-node shell element hs five degrees of freedom (i.e., three trnsltions long the x, y, nd z xes, nd two rottions bout the x nd y xes), which is dequte to simulte CFS pnels used in construction prctice. An updted Lgrngin formultion is dopted to develop the element stiffness mtrix of the sixteen-node shell element, where the vlues of ll prmeters, sttic nd kinemtic, re computed in ccordnce with the ltest deformed configurtion of the element. The procedure to chieve the elstic nd geometric stiffness mtrices for the sixteen-node shell element is presented in Bthe nd Bolourchi (1982). PERFORMANCE ACCEPTANCE CRITERIA FOR CFS BUILDINGS The cceptnce criteri determine if building is properly designed to stisfy the performnce levels (demnds) imposed by the seismic hzrds. In PBD ssessment, the cceptnce criteri re ssocited with the performnce levels. If FEMA 273 (1997) criteri re dopted, s tht in this study, the intensities of building dmge increse from low to high for the Opertionl (OP), Immedite Occupncy (IO), Life Sfety (LS) nd Collpse Prevention (CP) performnce levels. In CFS buildings, the SWP s re the primry structurl elements in resisting lterl lods; consequently, cceptnce criteri bsed on SWP lterl drift is estblished. In ddition, the strength of ech SWP lso needs to be checked to prevent premture structurl filure prior to rech the limit drift. In some cses, the lterl drift of SWP might be less thn the limit vlue but the pplied lterl lods my exceed the strength of SWP, or vice vers. Therefore, both the lterl drift nd strength of the SWP need to be checked to determine if the pnel hs been designed ppropritely. For CFS SWP, FEMA 273 (1997) does not provide ny informtion bout the limit drift rtios nd cceptnce criteri for estimting trget displcements. Although wood nd CFS sher wll pnels re built in similr mnner, their force-displcement curves re not similr. Thus, the limit drift rtios for wood-frmed SWP cnnot be used for CFS-frmed SWP. In this study, the limit drift rtios for CFS sher wlls re estimted from experimentl dt by Brnston et l. (2006). FEMA 273 (1997) provides the equtions for determining the normlized deformtion ssocited with the three performnce levels CP, LS nd IO. The equtions re expressed s function of the ductility d of the SWP, which is the normlized lterl deformtion of the SWP t the CP performnce level. The eqution for the normlized deformtion corresponding to the OP performnce level is not provided by FEMA 273 (1997). For SWP, it hs been reported tht 40% of the yield displcement represents the service lod level (Brnston et l, 2006). The limit drift rtios for SWP t ny performnce level re given by the following eqution: y LDR(%) PL y 100 (2) h where LDR is the limit drift rtio for the selected performnce level (PL); h is the height of the SWP; nd rtio is the normlized deformtion. PL y The limit drifts for the performnce objectives need to be computed before the pushover nlysis is initited. The limit drifts (Drift PO ) for SWP re evluted by multiplying the SWP height by the corresponding performnce level LDR (i.e., 2.5%, 2.1%, 1.0% nd 0.20% for the CP, LS, IO nd OP performnce levels, respectively). If the SWP lterl drifts obtined from the pushover nlysis re less thn the corresponding limit drifts, the displcement performnce criterion is stisfied nd otherwise the design must be improved. In ddition to checking the limit drifts of the SWP, the dequcy of lterl strength lso needs to be stisfied to ensure the lterl strength of SWP, P R, is greter thn the pplied lterl force, P. The lterl strength of the SWP, P R, cn be obtined from the published codified dt (AISI, 2012) which is determined by testing. In the bsence of pplicble dte, rtionl nlysis such s the method proposed by Xu nd Mrtinez (2006) cn be considered to determine the corresponding strength. While design CFS SWP, the following design considertions hve significnt impct on the lterl strength of the SWP: incresing the shething thickness, ttching shething on the both sides of the SWP (vs. shething being used only on one side), reducing the spcing of the screws for the shething-to-frming connections t the perimeter of the SWP, nd incresing the dimeter of the screws; while modifictions below re considered to hve minor influences on the lterl 761

5 strength of SWP: incresing the thickness nd depth of the CFS wll studs, reducing the spcing between the studs, nd reducing the spcing of the screws for the shething-to-frming connections in the field of the SWP. The effects of the foregoing design considertions on the lterl strength of SWP hve been observed from experimentl tests by Serrette et l. (2002) nd Brnston et l. (2006); nd confirmed by the numericl nlysis conducted by Xu nd Mrtinez (2006). STIFFNESS DEGRADATION MODEL FOR THE SWP Experimentl investigtions, such s those reported by COLA-UCI (2001), Fulop nd Dubin (2004), nd Brnston et l. (2006), hve shown tht the lod-displcement reltionship for CFS SWP is nonliner. In ddition, it is observed in the forementioned experimentl investigtions tht the loss of stiffness nd the filure of SWP re primrily due to the filure of shething-to-frming connections. Therefore, the nonliner reltionship between lod nd displcement of SWP needs to be ccounted for in the finite element model of the building. Shown in Figure 2 is the proposed nonliner model to chrcterize the stiffness degrdtion of SWP subjected to q lterl forces: K i is the initil stiffness of the SWP s the tngent t P r = 0; K is the secnt stiffness corresponding to the lod increment, q; P R is the lterl strength of the SWP; P is the mgnitude of the totl lterl force pplied on the top of the pnel t lod increment q; (q) is the stiffness degrdtion coefficient tht chrcterizes the nonliner behviour of the SWP under the pplied lterl forces until filure nd is defined by, q q P 1 (3) PR where β=(38mm/s C) is stiffness degrdtion nonlinerity exponent, clibrted in ccordnce with experimentl results from Brnston et l. (2006) nd COLA-UCI (2001). It is observed from the results of the experimentl investigtions tht the nonliner lod-displcement reltionship for SWP is primrily influenced by the shething mteril nd edge screw spcing. For resons of simplicity, β ws clibrted considering the screw spcing on the SWP perimeter (s C) only in this study s described by Mrtinez (2007). (q) shown in Eq. (3) is equl to unity t the initil lod increment, indicting tht the SWP lterl stiffness hs not yet been ffected. When the pplied lod P is equl or greter thn the mximum strength P R, (q) becomes zero, which indictes tht the SWP hs completely lost its stiffness to resist lterl deformtion. However, the modulus of elsticity of the CFS studs remins unchnged in the y direction of the shell element, which mens the equivlent shell my still hve sufficient stiffness contributed by the studs to llow the SWP to continue crrying grvity lods. Figure 2. Chrcteriztion of the SWP loss in strength PROCEDURE OF PBD ASSESSMENT FOR CFS BUILDINGS A flowchrt shown Figure 3 summrizes the procedure of the proposed method for PBD ssessment of CFS buildings. 762

6 2 1 CFS building informtion: preliminry design, building loction prmeters, nd performnce objectives (PO) Determine the pplicble grvity lods, W g 12 3 Apply lterl lod increment: F x 0. 01F, i xi i = Story 3 Evlute lterl strength of the SWP, P R 13 Solve the structurl stiffness mtrix eqution to obtin nodl displcements 4 5 Determine the fundmentl period of the structure, T Clculte the seismic bse PO PO W shers: V b S g PO = OP, IO, LS, CP. 14 Clculte the building bse sher t lod increment q: V ( q) 15 q Stories i1 F xi 6 V PO b mxv b mx No V (q) V b PO 7 Determine verticl lod coefficients, Cvx, nd lterl forces: F C V, i = story xi vxi b mx 16 Yes Determine Drift SWP, nd compre it to Drift PO 8 Clculte the SWP limit drifts rtios for ech PO, Drift PO 17 Determine P, nd compre it to P R 9 10 Initite the lterl strength reduction coefficient nd lod increment =1.0 nd q = 1 Form structurl stiffness mtrix, K = K L + K NL 11 q =1 No 19 Yes Updte q nd the stiffness mtrix K (q) =K (q-1) Apply the totlity of the verticl lod, W g No 18 V ( q) Yes V PO b mx End: Building PBD ssessment completed Figure 3 Proposed PBD ssessment procedure EXAMPLE Shown in Figure 4 is three-storey CFS building, for which the lterl displcements re to be computed for four performnce levels using the pushover nlysis, nd the results obtined from the pushover nlysis will lso be compred to tht of conventionl liner elstic nlysis. The typicl floor pln of the building is shown in Figure 5. All the SWP in the building re built with cold-formed steel C-shpe studs 152S mm (600S mils), shethed on both sides with 12.5 mm (1/2 in) Dougls Fir Plywood (DFP). The studs in 763

7 SWP 2 re spced 610 mm on centre. In ll the SWPs, single end-stud is used. No. 8 screws re used to ttch the shething to the frming t 102 mm nd 305 mm spcing on the edge nd in the field of the SWP, respectively. The size nd spcing of the screws re included to evlute the lterl strength of the SWP in ccordnce with the procedure described in Xu nd Mrtinez (2006). All the SWP on the first storey hve pin supports. The floor pnels consist of concrete slb of 127 mm thickness, supported by 254 mm (10 in) deep CFS joist, designted 254S mm (1000S mils). The height for ll the storeys is 2850 mm, nd the pitched roof hs 17% slope. For this exmple, for the reson of simplicity, the roof pnels re ssumed to be identicl to the floor pnels. Figure 4 Exmple: three-storey CFS building Figure 5 Typicl floor pln nd element illustrtion of the three-storey CFS building The three-storey building is considered to be ordinry ccording to the ctegories estblished by SEAOC (1995), so tht the building must stisfy the four performnce objectives described in Tble 1. The building is ssumed to be locted in Cliforni t ltitude 41.0 N nd longitude W on site clss B. The four performnce objectives re the following: OP for 50%/50 yer erthquke, IO for 25%/50 yer erthquke, LS for 10%/50 yer erthquke, nd CP for 2%/50 yer erthquke. The seismic weight of the building is W=405 kn. The nturl period of the building is T=0.324 second in the x direction, which is computed ccording to the procedure dpted by Mrtinez (2007) for CFS buildings. 764

8 Shown in Tble 2 re the trget bse shers corresponding to the specified four performnce objectives, which re computed s functions of the zone seismic prmeters nd nturl period of the building. After the bse shers re computed, the lterl lod for the pushover nlysis is defined by the mximum trget bse sher V b mx= kn. The lterl lods re pplied on the building in 1% increments of kn, until the mximum trget bse sher is reched or the structurl collpse occurs. PO Tble 2 Trget bse shers (kn) S S S 1 S MS S M1 S DS S D1 T o T s S V b (g) (sec) (g) (kn) OP IO LS CP Presented in Tble 3 re the inter-storey drifts nd limit drifts for the SWP relted to ech performnce objective, which re computed by the limit drift rtios 0.2%, 1.0%, 2.1% nd 2.5% for the OP, IO, LS nd CP performnce level, respectively. The limit inter-storey drifts re obtined by multiplying the lterl drift rtios to the height of the SWP. SWP 1 nd 3 exhibit the lrgest lterl drifts, becuse the seismic lods re pplied on these pnels. It is found tht both the lterl drifts nd the lterl strengths of SWP 1 nd 3 stisfy the specified performnce objectives. Tble 3 SWP inter-storey drift (mm) Performnce objective SWP OP (limit=4.8) IO (limit=24.0) LS (limit=50.4) CP (limit=60.0) Storey Storey Storey Storey Indicted in Tble 4 re the lterl strengths P R nd lterl forces P for the SWP t different performnce objectives. The lterl strengths re computed in ccordnce with method proposed by Xu nd Mrtinez (2006), nd the lterl forces re obtined from the pushover nlysis. Since the lterl forces in the SWP re less thn the corresponding strengths, the performnce objectives re deemed to be stisfied. The lrgest forces re obtined for the CP performnce objective, since it is ssocited with the mximum trget bse sher. It is observed from the tble tht the summtion of lterl forces in the SWP is different from the lterl lods pplied on the building, i.e., for the CP performnce objective the summtion of forces is 677 kn while the lterl force pplied on the building is 730 kn. The reson for the difference is tht the pnels in the y direction (i.e., perpendiculr to the SWP 1, 3, 7 nd 9) re resisting smll proportion of the lterl lods. The lods tht re resisting by SWP 2, SWP4 nd SWP5 re kn, kn nd kn, respectively. Listed in Tble 5 is the stiffness degrdtion coefficient, represented by λ, for ech SWP. It cn be observed tht none of the pnels hs filed, lthough severl pnels on the first storey re very close to filure for the CP performnce objective due to the loss of lterl lod resisting cpbility (λ 0.1). From the results of the spectrum-bsed pushover nlysis, it is observed tht the building stisfies ll seismic requirements. The four performnce objectives re deemed to be stisfied since the inter-storey drifts nd lterl strengths for the SWP re less thn the limit vlues. Therefore, the PBD ssessment for seismic forces is completed, nd the lterl design of the building does not require modifiction. 765

9 Tble 4 SWP lterl strength P R nd lterl force P (kn) Lterl force, P SWP P R OP IO LS CP Storey Storey Storey Storey Tble 5 SWP stiffness degrdtion coefficient λ OP IO LS CP SWP Storey Storey Storey Storey Illustrted in Figure 6 is comprison of the inter-storey drifts nd lterl displcements for SWP 1, obtined from the pushover nlysis nd the liner elstic nlysis t the level of CP performnce objective. LINEAR (Totl displcement) Inter-storey drift (17.18mm) 5.10mm PUSHOVER Inter-storey drift (Totl displcement) 9.44mm (45.68mm) (12.08mm) 6.07mm 14.84mm (36.24mm) (6.01mm) 6.01mm 21.40mm (21.40mm) CONCLUSIONS Figure 6 Inter-storey drifts nd displcements of SWP 1: pushover vs. liner nlysis One of the primry difficulties to conduct the PBD ssessment of structurl system is to estblish the cceptnce criteri nd levels of dmge ssocited with the performnce levels of the lterl lod resisting components. In this study, the cceptnce criteri of CFS buildings for different performnce levels re estblished ccording to the lterl drift nd strength of the SWP. To ccount for the nonliner behviour of the 766

10 SWP, stiffness degrdtion model ws introduced in proposed push-over nlysis which cptures very well the nonliner behviour of the SWP. In ddition, the model monitors the stress in the SWP during the nlysis nd predicts the filure of the SWP. The results obtined from the proposed PBD ssessment method of the presented exmple were compred to tht of the conventionl liner nlysis. At the CP performnce level, the building ws subjected to the sme loding condition for both types of nlysis. The mximum lterl displcement of the building obtined from the pushover nlysis ws 2.65 times lrger thn tht of the liner nlysis which gretly underestimted the lterl drifts of the building. Therefore, considering the fct there is no pproprite method for ssessing the seismic performnce of CFS buildings in current prctice, the proposed PBD ssessment method is recommended for the seismic ssessment of low- nd mid-rise CFS buildings. ACKNOWLEDGMENTS This project is prtilly funded by discovery reserch grnt from the Nturl Sciences nd Engineering Reserch Council of Cnd. REFERENCES AISI S213 (2007). North Americn Stndrd for Cold-Formed Steel Frming-Lterl Design. Americn Iron nd Steel Institute, Wshington, DC. Bthe, K. J., nd Bolourchi, S. A Geometric nd Mteril Nonliner Plte nd Shell Anlysis. Computers nd Structures; 1982; Vol. 11, pp Brnston, A.E., Chen, C.Y., Boudreult, F.A., nd Rogers, C.A. (2006). Testing of Light-Guge Steel Frme - Wood Structurl Pnel Sher Wlls. Cndin Journl of Civil Engineering, 2006; Vol. 33 No. 5, COLA-UCI (2001). Report of Testing Progrm of Wll-Frmed Wlls with Wood-Shethed Sher Pnels. Structurl Engineers Assocition of Southern Cliforni, COLA-UCI Light Frme Committee, FEMA 273 (1997). NEHRP Guidelines for the Seismic Rehbilittion of Buildings. Federl Emergency Mngement Agency. FEMA 450 (2003). NEHRP Recommended provisions for Seismic Regultions for new Buildings nd other Structures. Federl Emergency Mngement Agency. Fulop, L., nd Dubin, D. (2004). Performnce of wll-stud cold-formed sher pnels under monotic nd cyclic loding Prt I: Experimentl reserch. Thin-Wlled Structures; 2004; Vol. 42, pp Grierson, D.E., Xu, L., nd Liu, Y. (2005). Progressive-Filure Anlysis of Buildings Subjected to Abnorml Loding. Computer-Aided Civil nd Infrstructure Engineering; Vol. 20, pp Mrtinez, M. J. (2007). Seismic Performnce Assessment of Multi-Storey Buildings with Cold-Formed Steel Sher Wll Systems. PhD. Tesis, University of Wterloo. Mrtinez-Mrtinez, J. nd Xu, L. (2011). Simplified Nonliner Finite Element Anlysis of Buildings with CFS Sher Wll Pnels. Journl of Constructionl Steel Reserch; 2011: Vol. 67, pp SEAOC, VISION 2000 (1995). A Frmework for Performnce Bsed Erthquke Engineering. Structurl Engineers Assocition of Cliforni; 1995: Vol. 1. Serrette, R. L., Morgn, K. A., nd Sorhouet, M. A. (2002). Performnce of Cold-Formed Steel-Frmed Sher Wlls: Alterntive Configurtions. Snt Clr University; Finl Report LGSRG Troitsky, M. S. (1976). Stiffened Pltes, Bending, Stbility nd Vibrtions. Elsevier Scientific Publishing Compny; Amsterdm; New York. Xu, L. nd Mrtinez, J. (2006). Strength nd Stiffness Determintion of Sher Wll Pnels in Cold-Formed Steel Frming. Thin Wlled Structures; 2006; 44(10), pp