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1 IOP Confrnc Sris: Matrials Scinc and Enginring PAPER OPEN ACCESS Comparison of Sismic Rsponss for Rinforcd Concrt Buildings with Mass and Stiffnss Irrgularitis Using Pushovr and Nonlinar Tim History Analysis To cit this articl: D R Truna 017 IOP Conf. Sr.: Matr. Sci. Eng Rlatd contnt - A psudodynamic tsting algorithm for obtaining sismic rsponss of structurs Shunn-Yih Chang and Chiu-LI Huang - Study of sismic rspons and vibration control of High voltag lctrical quipmnt dampr basd on TMD Chunchng Liu, Chongyang Wang, Long Mao t al. - Passiv bas isolation with suprlastic nitinol SMA hlical springs Bin Huang, Haiyang Zhang, Han Wang t al. Viw th articl onlin for updats and nhancmnts. This contnt was downloadd from IP addrss on 05/1/017 at 15:36

2 doi: / x/180/1/01145 Intrnational Confrnc on Rcnt Trnds in Physics 016 (ICRTP016) Journal of Physics: Confrnc Sris 755 (016) doi: / /755/1/ Comparison of Sismic Rsponss for Rinforcd Concrt Buildings with Mass and Stiffnss Irrgularitis Using Pushovr and Nonlinar Tim History Analysis D R Truna Lcturr, Dpartmnt of Civil Enginring, Univrsitas Sumatra Utara *daniltruna@usu.ac.id Abstract. Pushovr analysis or also known as nonlinar static procdurs (NSP) hav bn rcognizd in rcnt yars for practical valuation of sismic dmands and for structural dsign by stimating a structural building capacitis and dformation dmands. By comparing ths dmands and capacitis at th prformanc lvl intrst, th sismic prformanc of a building can b valuatd. Howvr, th accuracy of NSP for assssmnt irrgular building is not yt a fully satisfactory solution, sinc irrgularitis of a building influnc th dynamic rsponss of th building. Th objctiv of th study prsntd hrin is to undrstand th nonlinar bhaviour of six story RC building with mass irrgularitis at diffrnt floors and stiffnss irrgularity at first story (soft story) using NSP. For th purpos of comparison on th prformanc lvl obtaind with NSP, nonlinar tim history analysis (THA) wr also prformd undr ground motion xcitation with compatibl to rspons spctra dsign. Finally, formation plastic hings and thir progrssiv dvlopmnt from lastic lvl to collaps prvntion ar prsntd and discussd. 1. Introduction Prformanc basd sismic dsign has bcom popular among structural nginr socity ovr th past twnty yars du to its potntial bnfit in assssmnt, dsign and bttr undrstanding of inlastic structural bhaviour during major arthquaks [1,]. Th ky paramtrs of prformanc basd sismic dsign lis th accurat stimation of sismic dmand and structurs capacity. This goal can b achivd only using ithr nonlinar static procdurs (NSP) or by prforming nonlinar dynamic tim history analysis ([3-13]). Th bst way to invstigat th sismic bhavior of a structur undr ground motion xcitation is th nonlinar dynamic tim history analysis (THA) that rprsnts th most rigorous and accurat approach. Nonthlss, it should b kpt in mind that th rspons is snsitiv to th structural proprtis and input ground motion, thrfor svral analyss ar rquird with incrasd complxity, computational costs and tim consumption. This is th rason why NSP is widly usd instad of THA, rgardlss its limitations for assssmnt sismic prformanc of a building. Iwan [9] dmonstratd th inability of pushovr mthods to prdict dmands for puls-lik nar fault ground motions. Krawinklr and Snviratna [10] dclar that NSP procdurs will provid insight into structural aspcts that control prformanc undr arthquak whn implmntd with caution and good judgmnt. For structur with first mod dominatd, NSP will vry likly provid good stimats of global and local inlastic dformation dmand. Furthrmor, Gol and Chadwll [8] invstigat of currnt NSP for concrt building using rcordd strong motion data. It was confirm that th NSP ithr undrstimat or ovrstimat th pak roof displacmnt for svral buildings undr considration, Contnt from this work may b usd undr th trms of th Crativ Commons Attribution 3.0 licnc. Any furthr distribution of this work must maintain attribution to th author(s) and th titl of th work, journal citation and DOI. Publishd undr licnc by Ltd 1

3 doi: / x/180/1/01145 poor stimat of drifts in uppr storis du to highr mod ffct, and unrliabl stimat of story shar and ovrturning momnts. Lignos and Gants [1] prformd improvmnt pushovr calld modal pushovr analysis (MPA) and THA for structur with irrgular mass distribution. Th rsults rvald that story drift is significant diffrnc if th structur is lastic, dmands ar undr stimatd at th uppr storis. For inlastic stat, MPA shows adquatly rsults in th uppr storis. Bas shar is ovrstimat and tndncy incrasing if mass discontinuity is locatd at lowr storis. Morovr, Lu t al.[14] studid applicability of NSP to valuat sismic prformanc of stl arch bridg, and it was notd that NSP accptabl accurat in prdiction displacmnt capacitis compar to THA. Currntly, th applicability of NSP as a tool for valuat sismic bhavior of structural building is still pros and cons among of structural nginring community. Th main objctiv of this papr to study comparison of sismic prformanc of six story rinforcd concrt structur with mass irrgularity and stiffnss or strngth irrgularity using NSP and THA. In ordr to vrify th applicability of pushovr procdurs for stimating th ovrall sismic dmands, th pushovr rsults from th frams ar compard with th dynamic analysis. In addition, to provid a ralistic basis for this comparison, th slction and scaling of th ground motions usd ar carfully assssd with rgard to th dsign spctrum. Mass irrgularity is th prsnc of havy mass on crtain floor of a building. In this cas, additional mass qual to 50% of uniform mass ach story ar imposd to scond, fourth, and sixth story, whras for stiffnss irrgularity is dsignd at th first story by incrasing th hight of first story columns. Th comparison btwn both nonlinar analysis in trm of rspons quantitis, i.., story displacmnt, intr-story drift, and bas shar ar prsntd and compard. Additionally, formation plastic hing at th first yild to collaps prvntion ar also dscribd.. Nonlinar static procdurs (NSP) Although THA is th most accurat analysis to valuat sismic dmand, th application NSP is gnrally considrd to b mor appropriat for sismic dsign du to its simplicity and as to us. This mthod is basd on assumption that th rspons of th MDOF structur can b rlatd to th rspons of an quivalnt SDOF. This is th rason why th NSP is known as th most us tool in th nginring practic for assssmnt of sismic bhaviour of structurs, and currntly has rsultd in guidlins such as ATC-40 [], FEMA-356 [4], and FEMA-440 [5] and standards such as ASCE [1]. NSP is conductd by applying th gravity loads followd by latral load is gradually incrasd along a dirction undr considration. Th invstigatd building is pushd according to prdfind latral load pattrn to obtain th targt displacmnt. At ach load stp, th bas shar and th roof displacmnt can b plottd to cratd capacity curv or pushovr curv. It rsults is assumption of maximum bas shar that th structur is capabl to withstand during arthquak vnt. Th distribution of latral load pattrn along th hight of th structur and nonlinar modlling assumption ld to diffrnt pushovr curvs..1. Latral load pattrn Thr ar thr latral load pattrn proposd in FEMA-356, namly (a) invrtd triangular distribution, (b) uniform distribution, (c) distribution of forcs proportional to fundamntal mod (mod 1). Ghaffarzadh t al.[7] studid rspons sismic dmand of RC frams using NSP. Th rsults show that push (a) pattrn and push (c) pattrn yildd similar rsults and rasonably accurat stimats of th maximum displacmnt. Although, slightly ovrstimat in th uppr storis, whil push (b) pattrn ovrstimat dmands at th lowr storis. Morovr, th applicability latral load pattrn on valuation of sismic dformation dmands using NSP wr invstigatd by Kunnath and Kalkan [11]. It was found that in all cass, push (a) pattrn providd closst rsults to th man tim history analysis, and othr two load pattrns tnd to ovrstimat dmands at th lowr storis.

4 doi: / x/180/1/ Structural prformanc lvl Th sismic prformanc of a building structur is masurd by th stag of damag undr a crtain sismic hazard in which is quantifid by roof displacmnt and dformation of th structural mmbrs. Figur 1 shows forc-dformation rlation for plastic hing in pushovr analysis. This guidlins and standards prviously mntiond dfin forc-dformation critria for potntial locations of plastic hing. Thr ar fiv points lablld A, B, C, D, and E ar usd to dfin th forc-dformation bhaviour of th plastic hing, and thr points lablld IO (immdiat occupancy), LS (lif safty), and CP (collaps prvntion) ar usd to dfin accptanc critria for th hing. Thr ar six lvls of structural prformanc in ASCE 41-13, i.., Immdiat occupancy (S-1), Damag control rang (S-), Lif safty (S-3), Limitd safty rang (S-4), Collaps prvntion (S-5), and Not considrd (S-6). Two lvls of sismic hazard ar commonly dfind for buildings, namly (a) dsign basic arthquak (DBE): an arthquak with a 10% probability in 50 yars of bing xcdd. This is an arthquak with a 500 yars roccurrnc priod, and (b) maximum considrd arthquak (MCE): an arthquak with a % probability in 50 yars of bing xcdd. This is an arthquak with a 500 yars roccurrnc priod. Th cas study building wr dsignd basd on dsign spctrum that constructd for DBE sismic hazard lvl according to Indonsian sismic dsign. Targt displacmnt in this study is dtrmind basd on th displacmnt cofficint mthod dfind in ASCE Procdurs to dtrmin targt displacmnt Th displacmnt cofficint mthod currntly documntd in FEMA-440 and adoptd in th ASCE standard is th improvmnt of th basic displacmnt procdurs in FEMA-356. This mthod is accomplishd by modifying th lastic rspons of quivalnt SDOF systm with cofficint C 0, C1, and C is xprssd as: T t C0C1C Sa g (1) 4 whr, S a is rspons spctrum acclration at th ffctiv fundamntal priod and damping ratio of th building, g and is gravity acclration, T is ffctiv fundamntal priod computd from K K 0. 5 T Ti i / () in which K i, K is th lastic stiffnss and th ffctiv stiffnss of th building in th dirction undr considration, rspctivly, obtaind by idalizing th pushovr curv as a bilinar rlationship, C 0 is modification factor to rlat spctral displacmnt of an quivalnt SDOF systm to th roof displacmnt of th building MDOF systm obtaind from tabl 7-5 in ASCE 41-13, C 1 is modification factor to rlat xpctd maximum inlastic displacmnt to displacmnt calculatd for linar lastic rspons computd from C 1 1.0; R 1 1 ; at 1 R 1 1 ; 800 T T 1.0s, 0.s T T 1.0s, 0.s (3) whr a is qual to 130 for soil sit class A and B, 90 for soil sit class C, and 60 for soil sit classs. D, E, and F, and R is th ratio of lastic and yild strngths is givn as follows: 3

5 doi: / x/180/1/01145 Sa R C V / W y in which V y is th yild strngth stimatd from pushovr curv, W is th ffctiv sismic wight, and Cm is th ffctiv modal mass factor at th fundamntal mod of th building, C is modification factor to rprsnt th ffct of pinchd hystrtic shap, stiffnss dgradation, and strngth dtrioration on maximum displacmnt rspons computd from 1.0; T 0.7s C R 1 ; T m T 0.7s (5) (4) To avoid dynamic instability, ASCE limit th R as R R max d y 4 h ; h ln( T ) in which d is th dformation corrsponding to pak strngth, th ffctiv ngativ post yild slop givn by P P y is th yild dformation, and is whr is th ngativ post yild slop ratio and p is th ngativ slop ratio causd by P-Δ ffcts dfind in Figur, and λ is th nar-fild ffct factor givn as 0.8 for S and 0. for S ( S 1 is dfind as th 1-scond spctral acclration for th Maximum Considrd Earthquak). Forc B A IO LS CP C D Dformation Figur 1. Forc-dformation for pushovr hing E V d V y 0.6V y Bas shar K 1 K P K Displacmnt Figur. Idaliz forc-dformation curvs 3. Dscription of buildings usd in valuation Th building slctd for this study is six story of thr bay rinforcd concrt (RC) frams as shown in Figur 3. Four cass of building with diffrnt mass, i.., building having uniform mass is dsignatd as M 0, building having irrgular mass is introducd at scond, fourth, and sixth story dsignatd as M, M 4, and M 6, rspctivly. Mass irrgularity at an individual floor is considrd by a 45 kn/m dsign load, with rspct to 30 kn/m of th othr floors, whil liv load for all building ar qual to 15 kn/m, and th corrsponding first mod vibration priods ar 1.57s, 1.59s, 1.68s, and 1.76s, rspctivly. For building with stiffnss irrgularity at first story is similar to M 0 but th first story hight is dfind 5m, and dnotd as S T, with fundamntal priod of 1.67s. Th rinforcmnt of th bams and columns ar listd in tabl 1 and tabl. All concrt columns ar spcifid to 40 MPa, all concrt bams ar dsignd 350x700mm of 30MPa, whil yild strss for all rinforcmnt is 400 MPa. Th puls typ ground motion rcords of Northridg arthquak compatibl to rspons spctrum dsign as shown in Figur 4 wr applid in THA. K (6) (7) K 4

6 doi: / x/180/1/ Analytical modl Th computr program SAP 000 Vr.10.1 was usd to prform finit lmnt analysis of th RC fram using ithr NSP or THA. Th structur is modld as a D assmblag of lmnts connctd at nods. Lumpd mass is applid at nods and nod has 3 DOF. On dimnsional lmnt is usd in th finit lmnt mshing, and foundation wr modld as fixd support at ground lvl. To account th inlastic bhavior of bams and columns componnt, both nd of ach lmnt ar modld as concntratd plastic hing as dscribd in FEMA-356. Non-linir gomtry option was also turn on to considr ffct P-dlta. For THA, Rayligh damping was constructd through th first and th third mod of vibration wr spcifid 5% of critical damping. Dirct intgration mthod using Nwmark-Bta was slctd for numrical solution. In addition, for NSP procdurs, latral load pattrn is slctd as invrtd triangular. M 6 M 4 M 6x4m=4 m 5x4m=0m 8m 8m 8m (a) M 0 8m 8m 8m (b) M 0, M, M 4,and M 6 Figur 3. Schmatic of lvation for th 6 story RC frams (c) S T 5m Acclration (g) 1,5 1, 0,9 0,6 0,3 0 DBE Spctrum Targt Northridg 0 0,5 1 1,5,5 3 3,5 4 Priod (T) Figur 4. Scal ground motion to spctrum dsign 5

7 doi: / x/180/1/01145 Frams typ M 0, S T 5D/ M M 4 M 6 Tabl 1. Dtail of bam rinforcmnt Story 1 Story Story 3 Story 4 Story 5 Story 6 4D +D19/ 4D +D19/ 4D +D19/ 4D +D19/ 6D5/ 3D5 6D/ 6D/ 4D +D19/ 4D +D19/ 6D/ 6D/ 4D +1D19/ 5D/ 4D5 +D/ 3D35 4D +D19/ D +3D19/ 6D19/ 3D19 6D19/ 3D19 D +4D19/ D +3D19/ 6D19/ 3D19 6D19/ 3D19 6D/ 5. Discussion of rsults 5.1 Pushovr curvs and global prformanc lvl Figur 5 prsnt pushovr curvs obtaind from NSP. Ths curvs provid global bhavior of th fram. Th slop of curvs is gradually rducd with incras th latral displacmnt. It dmonstrats that all th pushovr curvs show rasonabl similar trnd, in which yilding and prformanc point occur at th almost th sam displacmnt xcpt for irrgular mass fram in sixth story (M 6). For M 6 fram yilding and prformanc point occur at th displacmnt largr than othr frams. Furthrmor, th smallst and th largst displacmnt at th prformanc point occurrd for uniform mass fram (M 0) and for irrgular mass fram in sixth floor, rspctivly. A comparison of NSP and THA in trm of roof displacmnt, bas shar and global prformanc lvl ar listd in tabl 3. It was notd that NSP poor stimat in roof displacmnt and bas shar (at th prformanc point) compar to THA. Additionally, th roof displacmnt at nar collaps obtaind from NSP clos to th rsults of THA. Also, th rsults indicats th displacmnt ratio is mor inaccurat than bas shar ratio. Morovr, NSP provids global prformanc of all frams fall into damag control (S-), whras THA xhibit global prformanc lvl of all frams is within th Limitd safty rang (S-4). Furthrmor, th capacity curv (bas shar) of fram M 6 and fram S T obtaind from both mthods ar smallr than othrs frams. This dmonstratd that havy mass in placd on th top story and fram that having soft story provid poor sismic prformanc Figur 5. Pushovr curvs (capacity curvs) 6

8 doi: / x/180/1/01145 Tabl. Dtail of column rinforcmnt Frams typ Columns siz & rinforcmnt Storis 1& 600x600mm Storis 3&4 500x600mm Storis 5&6 450x600mm M 0, M, M 4, M 6, and S T 0D-mm 16D-mm 1D-mm Frams typ NSP ( at th prformanc point) BS Disp. (kn) mm (%) Tabl 3. Comparison of NSP to THA NSP (at THA nar collaps) Disp. mm (%) BS (kn) Disp. mm (%) M (.4) (1.37) (.08) M (1.40) 50 (.) (.14) M (1.38) 476 (.0) (.54) M (1.61) 518 (.) (.39) ST (1.43) 575 (.4) (.3) NSP (prformanc point) / THA Global Prformanc lvl NSP THA BS Disp. ratio ratio S- S S- S S- S S- S S- S-4 5. Story displacmnt and intr-story drift dmand Figur 6 and Figur 7 show comparison of story displacmnt and intr-story drift obtaind from NSP and THA. In gnral, th Figur indicats that story displacmnt and intr-story drift xhibit idntical shaps rgardlss of analysis mthod utilizd, and th maximum intr-story drift location clos to middl story. Furthrmor, in trm of intr-story drift and corrsponding to local prformanc lvl in third story, NSP procdurs rval that fram M 6 produc limitd safty rang (S-4) prformanc lvl, whil fram M and M 0 xhibit lif safty (S-3) prformanc lvl. Th rmaining frams xhibit damag control (S-) prformanc lvl. Morovr, th story displacmnt and intr-story obtaind from NSP ar always smallr than th rsults of THA. NSP (M0) THA (M0) NSP (M) THA (M) NSP (M4) THA (M4) NSP (M6) THA (M6) NSP (ST) THA (ST) Bas shar dmand Formation 0 of plastic hing Story displacmnt (mm) Story lvl Figur 6. NSP vs. THA for story displacmnt Story lvl NSP (M0) NSP (M) NSP (M4) NSP (M6) NSP (ST) THA (M0) THA (M) THA (M4) THA (M6) THA (ST) 0 0,5 1 1,5,5 3 3,5 4 4,5 Intr-story drift (%) Figur 7. NSP vs. THA for intr-story drift 7

9 doi: / x/180/1/ Formation and status of plastic hings Th formation and status plastic hing and dformd shap for M and M 6 frams obtaind from NSP and THA displayd in Figur 8. Th fram M was slctd as rprsntation of M 0, M 4, and S T frams, sinc thos frams dmonstrat accptabl similar bhavior, and du to spac limitation. Th hing formation shows th strong column-wak bam failur pattrn as xpctd. Th plastic hings at th first yild formd on scond floor for M fram, whil for M 6 fram occurs on th scond and third floors simultanously. Additionally, local prformanc in lmnt or story lvl can b obsrvd through plastic hing status. NSP shows all bams in fram M ar within th IO (S-1) lvl, whil in fram M 6 vary, i.., IO (S-1), LS (S-3), and CP (S-5) lvls. Furthrmor, THA prsnt th local prformanc lvl for both frams fall into IO to CP lvls. Morovr, M 6 fram xprinc mor damags compar to M fram using both mthods. Furthrmor, th status and formation of th hings formd on th frams indicat that svr damags concntratd at bams on th lowr to th middl floors. M M M NSP NSP NSP NSP M 6 (a)at first yild (b) At targt disp. (c)at maximum disp. (d)at first yild M 6 M 6 NSP NSP M THA M 6 THA () At targt disp. (f) At maximum disp. (g)at xpctd disp. (h)at xpctd disp. Figur 8. Formation and status of plastic hings at diffrnc stags of th displacmnt. 6. Conclusion Th principal objctiv this papr is to valuat th accuracy NSP procdurs in comparison to THA, in ordr to stimat sismic dmand of six story rinforcd concrt buildings (RC frams) with uniform mass, irrgular mass and first soft story. Thr ar thr gnric frams whr mass irrgularitis is introducd at th scond, fourth, and sixth storis, on frams having uniform mass, and on fram dsignd with th soft first story wr invstigatd. Th gnral rsults confirm that rspons quantitis wr influncd by mass irrgularity in placd at diffrnt story and stiffnss irrgularity at first story. Although, Pushovr procdurs or NSP dmonstrat insufficint to stimat targt displacmnt at th roof and bas shar dmand, howvr, NSP provid bttr undrstanding inlastic frams bhaviour that can b usd to idntify wak lmnts or story through plastic hings status and formation. In this cas study, th diffrncs btwn NSP and THA is mor significant in roof displacmnt rathr than bas shar and th rsults obtaind from NSP ar always smallr than rsults of th THA. Morovr, in trm of global prformanc lvl, NSP produc damag control (S-) prformanc lvl, whil THA xhibit limitd safty rang (S-4) prformanc lvl for th whol fram cass. Evaluation of th frams in local prformanc lvl (plastic hing status) indicat that fram M 6 varis from IO to th CP prformanc lvl, and th rmaining frams ar idntical prformanc lvl (damag control). Furthrmor, both procdurs indicat that frams having mass irrgularity in top story (fram M 6) or having soft first story (fram S T) show th poor prformanc lvl (lowr bas shar capacity and highr displacmnt dmand). Nglcting th highr mods ffct, ignor th potntial rdistribution of inrtia forcs and simplicity in assumption may lad to NSP procdurs significant undrstimation, as 8

10 doi: / x/180/1/01145 yilding and cracking govrn th inlastic structural bhaviour. Although, pros and cons among of structural nginrs in accuracy of NSP for valuat sismic dmand of structural building, th nd of improvmnt NSP procdurs is to discuss th limitations and shortcomings involvd in th us of currnt ons. Rfrncs [1] ASCE/SEI Sismic Evaluation and Rtrofit of Existing Buildings, ASCE Standard, Amrican Socity of Civil Enginrs, Rston, Va, USA [] ATC Sismic Evaluation and Rtrofit of Concrt Building 1 Applid Tchnology Council, Rdwood City, California [3] Bhatt C and Bnto R 01 J. Earthquak Enginring [4] Ests KR and Andrson JC 004 Proc. 13 th World Confrnc on Earthquak Enginring, Vancouvr, Canada papr No. 376 [5] FEMA Prstandard and Commntary for th Sismic Rhabilitation of Buildings, Th [6] Amrican Socity of Civil Enginrs for th Fdral Emrgncy Managmnt Agncy, Washington DC, USA [7] FEMA Improvmnt of Nonlinar Static Sismic Analysis Procdurs, Applid Tchnology Council for Dpartmnt of Homland Scurity, Fdral Emrgncy Managmnt [8] Agncy, Washington DC, USA [9] Ghaffarzadh H, Talbian N, and Kohandl R 013 J. Earthquak Enginring and Enginring [10] Vibration 1(3) [11] Gol R K and Chadwll C 007 Evaluation of currnt nonlinar static procdurs for concrt [1] buildings using rcordd strong-motion data, Data Utilization Rport, California Strong Motion Instrumntation Program, CDMG, Sacramnto, California 9