DESIGN AND ANALYSIS OF A CASE-STUDY LOW- RISE BUILDING WITH MOMENT-RESISTING COMPOSITE FRAMES. Abstract

Transcription

1 Australan Earthquake Engneerng Soety 009 Conferene, Newastle, NSW DESIGN AND ANALYSIS OF A CASE-STUDY LOW- RISE BUILDING WITH MOMENT-RESISTING COMPOSITE FRAMES Huang Yao 1, Helen M.Goldsworthy, Emad F. Gad 3 1. Researh Fellow, Department of Cvl and Envronmental Engneerng, The Unversty of Melourne, V 3010, Australa. Emal: jayao@unmel.edu.au. Senor Leturer, Department of Cvl and Envronmental Engneerng, The Unversty of Melourne, V 3010, Australa. Emal: helenmg@unmel.edu.au 3. Assoate Professor, Department of Cvl and Envronmental Engneerng, The Unversty of Melourne, V 3010, Australa and Faulty of Engneerng & Industral Senes, Swnurne Unversty of Tehnology, Hawthorn, V 31, Australa. Emal: EGad@swn.edu.au Astrat Although omposte frames wth moment-resstng onnetons are an exellent hoe for mult-storey uldng strutures, they are not wdely used n prate n Australa due to lak of approprate pratal desgn methods. Ths paper presents a pratal desgn method for a prototype fve-storey uldng omposed of omposte olumns, eams and moment resstng onnetons. The ojetve of ths study s to nvestgate the valty of momentresstng frames wth omposte olumns under lateral loadng (wnd and earthquake atons as well as gravty load. The paper overs oth the strength and drft demands on low-rse uldngs n regons of low to medum sesmty. The effets of ste sol type, olumn ase fxty, rgdty of eam-to-olumn onneton, and loadng of external façade system on the frame ehavour are examned. The proposed method enales the desgn of the onnetons, eams and olumns for rgd and sem-rgd omposte frames that are to e used n engneerng prate. Keywords: Composte frame, moment-resstng onneton, lateral load, drft, sem-rgd onneton

2 1. Introduton Moment-resstng omposte frames have not reeved wdespread applaton n prate due to the pereved omplexty of analyss requred and the lak of relale nformaton on the moment-rotaton haratersts of the onnetons as requred y desgn spefatons. Lak of moment olted onnetons n the past has also hampered the use of suh omposte systems. The reent development of lnd olts wth extensons has overome ths shortomng (Yao et al In 004, a new verson of the Australan rdge desgn standard AS5100 was ssued for rdge desgn (Standards Australa 004. It nluded desgn gudane for omposte olumns and eams. Although the ojetve of AS5100 was to provde natonally aeptale requrements for the desgn of road and ral, rdges, the spef ontent of Part 6 on steel and omposte onstruton s also applale for uldng onstruton. Extensve researh has een arred out to nvestgate the atual ehavour of sem-rgd onneton and to assess the performane of strutural frames wth sem-rgd onnetons (Leon 1990, Xao et al. 1996, Rodrgues et al. 1998, Lew et al. 000, Hensman and Netherot 001, de S Vellaso 006. A lttle effort was devoted to develop smplfed pratal methods to desgn sem-rgd and rgd omposte frames (Leon and Ammerman 1990, Carero and Bayo 005, Wong et al Ths paper ams to nvestgate the performane of moment-resstng frames wth omposte olumns under lateral loadng (wnd and earthquake atons as well as gravty load.. Prototype uldng A prototype uldng wth 5-storey, four-ay y four ay s desgnated as an offe uldng loated on a ste wth sol type of lass D n Melourne or Sydney. The uldng struture s lassfed as an ordnary moment-resstng frame wth lmted dutlty. Resstane to the lateral fores s provded prmarly y rgd frame aton n the oth dretons. The moment-resstng frames are omposed of onrete-flled steel tuular olumns, steel eams wth omposte slas and lnd-olted T-stu rgd onnetons (see Fgure 1. The desgn of lnd-olted moment onnetons for the omposte frame s part of a separate study. The floor plan of the prototype uldng s 33.6m x 33.6m n area wth four ays of 8.4 m n eah dreton as shown n Fgures and 3. The longer ay spang makes t more representatve of Australa prate. The frst floor of the uldng has a heght of 4 m, whle the rest of the stores have a heght of 3.5 m. All nteror and exteror frames are moment-resstng frames n oth dretons. The prototype uldng had a omposte floor system usng profled metal sheetng. The sheetng has suffent strength to support the wet onrete durng onstruton, and no proppng of the floor system s requred.

3 Fgure 1 Blnd-olted moment onneton Fgure Buld plan Fgure 3 Buldng elevaton 3. Desgn proedure

4 3.1 Loadng ondtons Desgn loads are estmated ased on urrent Australan loadng spefatons AS/NZS 1170 (Standards Australa/Standards New Zealand 00. Dead loads nlude self weght of strutural omponents, elng, serves, parttons, et. Lve load of 3 kpa s adopted for the offe floor areas. Wnd loads are appled to the uldng assumng ths offe uldng s loated n Regon A1 (non-ylon. The uldng s lassfed as mportane level wth return perods of 500 years for the strength lmt state of wnd and earthquake atons. For servealty lmt state, 0 years return perod of wnd speed s assumed. For the uldng ste n regon A1, regonal wnd speed s 45 m/s for ultmate lmt state and 37 m/s for servealty lmt state. By applyng relevant fator of wnd dreton, terran/heght, sheldng, and topograph, the desgn wnd speed s desgnated to e m/s. Therefore, the desgn wnd pressure s 1.05 kpa on the wndward sde and 0.56 kpa on the leeward sde. The wnd aton on the edge frames and nteror frames an e otaned aordngly. For ths prototype uldng, the earthquake load effets are determned usng the equvalent lateral fore proedure outlned n AS (Standards Australa 007 wth ase shear alulated usng Equaton 1. The earthquake loads and load effets are ased on equvalent stat lateral fores atng at eah floor, dstruted over the heght of the uldng as shown n Equaton. The sum of these fores s equal to the desgn ase shear of the struture, wth ther dstruton depends on the fundamental perod of the struture. p h p W t V K ZC ( T S / (1 where K p = 1.0 (for p=1/500 year earthquake Z = 0.08 (Melourne/Sydney T 1. s (moment-resstng steel frame (T = 1.65 (lass D sol or 0.9 (lass B sol C h S p = 0.77 (OMF, lmted dutle (OMF, lmted dutle F n t n t k 1.35 Wh Wh j1 W h k V j1 W h 1.35 V ( where F = horzontal stat desgn fore at the th level W = sesm weght of the struture at the th level h = heght of level aove the ase of the struture

5 The earthquake loadng on the same uldng wth heavy façade and lght façade are alulated respetvely. The lateral loads an e dstruted to the edge frames and nteror frames. All loads are fatored and omned to provde desgn lmt state loads. The non-strutural omponents suh as nfll walls, parapet walls, façade et. are norporated n sesm weght of the struture to otan the equvalent lateral fore under sesm atons. The srutny on detaled examnaton of the effet of non-strutural omponents on the uldng struture s not wthn the sope of ths study. 3. Frame analyss The three dmensonal uldng struture an e smplfed as two dmensonal omposte moment frames ased on the assumpton that omposte floors ehave as rgd daphragms and the permeter omposte moment frames work together wth the nteror frames n resstng the lateral load. The nteror frames along grd lnes B, C, and D are seleted for frame analyss. Frames sujeted to gravty, wnd, and earthquake loads must e desgned to provde the neessary strength requrements and must satsfy the drft lmts under varous load omnatons. Frames desgned to sustan earthquake loadng should also e desgned and detaled to provde adequate dutlty. 3.3 Desgn for strength Strutural analyss program SPACE GASS (Integrated Tehnal Software 007 s used to otan the prelmnary moments and axal fores n the eams and olumns due to oth gravty and lateral loads. The moments and axal fores are then fatored and omned for a prelmnary seleton of the eams and olumns. An elast seond order analyss of the frame s performed and the memer desgns are heked for the varous load omnatons. The analyss s refned untl fnal memer szes are seleted. The detaled alulatons of seton and memer apates for the omposte olumns and omposte eams, axal fore and moment nteraton for the onrete-flled steel tue and strength & stffness of the omposte eams at the saggng and hoggng moment areas an e otaned n AS5100 Part 6. The strutural stffness s formulated ased on entre lne dmensons and rgd onnetons etween eams and olumns. It s found that the omnatons of 1.G + 1.5Q and G + 0.4Q +E govern the desgn of the olumns and the eams. 3.4 Drft lmts Inter-storey drft s one of the sgnfant parameters n assessng the performane of a struture under wnd and earthquake loads. The ontrol of drft s to ensure satsfatory

6 oupany requrements under wnd loads and to mnmze non-strutural damage durng earthquakes. The earthquake standard AS reommends that nter-storey drft at the ultmate lmt state shall not exeed 1.5% of the storey heght for eah level under earthquake loads. The desgn storey drft should e fatored n aordane wth Equaton 3. Also, the standard AS/NZS reommends that the nterstorey drft should not exeed h / 500 when the uldng s sujeted to spefed wnd for servealty. x d de (3 S p where d = desgn storey drft at the th level d = storey drft at the th level determned y an elast analyss e The uldng s heked for the drft lmt requrement and the desgn s refned untl t meets the ode requrement. The fnal memer szes for the nteror frames are lsted n Tale 1. Analyss shows that the strutural desgn s ontrolled y drft lmts rather than strength requrement for the lower floors, n partular, the ground floor wth the pn ased olumns. These strutural memers are used n the followng senaros to explore the effets of onneton rgdty, olumn ase ondtons, and façade types. Tale 1 Memer szes for nteror frames Level Composte Column Composte Beam 5 CHS 33.9 x UB CHS 33.9 x UB CHS 406 x UB 67.1 CHS 406 x UB CHS 508 x UB Composte frame wth rgd onneton 4.1 Rgd frame wth pn ase It s assumed that olumns n the frame are pnned at the ase. All the eam-to-olumn onnetons are rgd wthn the omposte frame. The frames wth heavy façade and lght

7 façade are studed under the load omnatons of 1.G+1.5Q, 1.G+0.4Q+W, and G+0.4Q+E. The lateral load of earthquake ndues moment reversals at some of the onnetons at level 1. Under these ondtons, the sla an transfer very large fores to the olumn y earng f the sla ontans renforement around the olumn n the two prnpal dretons. However, rttle falure modes of rushng of the onrete and uklng of the sla renforement should e prevented. The nter-storey drft at levels 1 to 5 are 19.8 mm. 11. mm, 10.3 mm, 15.5 mm, 7.0 mm under the omnaton of G+0.4Q+E and 5.8 mm,.9 mm,.1 mm, 3.3 mm, 1.0 mm for the ase of G+0.4Q+Ws. These nter-storey drfts are wthn the drft lmts requred y the ode AS/NZS1170 whh are lsted n Tale. If the heavy façade of onrete panels are replaed y lght façade of urtan wall and glazng, the lateral drfts of nteror frame wth lght façade under G+0.4Q+E are redued to 17.0 mm, 9.7 mm, 8.9 mm, 1.7 mm, and 6. mm for levels 1 to 5 respetvely. The reduton of frame drft s aout 1% ompared to the struture wth heavy faade. The ground floor s rtal n the desgn for the drft lmts. In the frame analyss, the eams provde aout 49% of storey drft and the olumns provde the remanng 51% of storey drft. At the ground floor, the desgn of olumns and eams are governed y the drft requrement. However n the upper floors, the desgn of the frame s ontrolled y strength. The ontruton of olumn and eam flexure to the storey drft an e estmated y Equaton 4 for the ground level and Equaton 5 for the upper levels for the ases of frames pnned at the ase. Tale Inter-storey drft lmts Level Ultmate lmt state ( d e Wnd servealty ( h x / mm 7 mm 4 0 mm 7 mm 3 0 mm 7 mm 0 mm 7 mm 1 3 mm 8 mm V h (4 1 ( / L ( / h

8 V h 1 1 (5 1 ( / L ( / h where V =storey shear for level h = storey heght for level I, I =moment of nerta of olumns and eams L = ay length 4. Rgd frame wth fxed ase The olumn ase fxty has great nfluene on the frame ehavour, n partular, the storey drft at the frst level. The nter-storey drft for rgd frame wth fxed ase are 4.9 mm, 9.8 mm, 10. mm, 14.4 mm, and 6.9 mm for levels 1 to 5 under the omned load of G+0.4Q+E. The storey drft at the level 1 s only 4.9 mm ompared to 19.8 mm for the frame wth pnned ase. Therefore, the olumn and eam sze of the frame an e adjusted to the smaller dmensons as lsted n Tale 3. The nter-storey drfts for the frame wth redued memer szes are updated to 3.0 mm, 19. mm, 19.8 mm, 14.4 mm, and 7.0 mm for levels 1 to 5. These values meet the requrement of drft lmts. The frst storey drft of the frames wth rgd ase an e estmated y Equaton 6. Tale 3 Memer szes for nteror frames wth fxed ase Level Composte Column Composte Beam 5 CHS 33.9 x UB CHS 33.9 x UB CHS 33.9 x UB 67.1 CHS 33.9 x UB CHS 33.9 x UB 67.1 V h ( h L h 1 6 L

9 5. Composte frame wth sem-rgd onneton From pratal pont of vew, the man dfferene etween the desgn of unraed rgd frame and sem-rgd frame s the ontruton of the eam-to-olumn onneton to the lateral drft and moment dstruton. In order to meet drft lmt requrements, t s neessary to adjust the stffness of the olumns, eams, and onneton to aheve the optmal dstruton of resstane to the drft. Normally, t s reasonale to dstrute aout equally to eams, olumns and onneton. However n low rse frames, t may e advantageous to let olumns provde the majorty of the resstane to drft. For nstane, 40 to 50% assgned to olumns and the rest dvded equally etween the eams and onnetons. In order to lmt the drfts, the use of fxed olumn ase s mperatve n the desgn of sem-rgd frame. Therefore, attenton should e pad to the detalng of the foundatons and the olumn ases. 5.1 Sem-rgd frame wth pn ase The frame models of nteror and exteror frames wth pn ase are altered to nlude the sem-rgd onnetons. The ntal stffness of the eam-to-olumn onneton s hanged to one of four values, 1000 knm/radan, 10,000 knm/radan, 100,000 knm/radan and 100,000 knm/radan n the omposte frame. As expeted, the stffness of the sem-rgd onneton affets the nternal fore dstruton n the frame elements (eams and olumns. The eam endng moments are redued and moments at the md-span are nreased ompared to the ase of rgd onneton. It s favourale to utlze the seton strength apaty of the omposte eams at the md-span and redue the demand at the negatve endng area. However, sem-rgd onnetons nrease the storey drft dramatally as shown n Tale 4 under the omned load of G+0.4Q+E. Susequently large olumn and eam szes for the ground floor need to e used n order to lmt the drft. These sem-rgd omposte frames need to e omned wth onrete ore or raed ore to aheve the requrement of lateral dsplaement. It s oserved that the response of a frame wth sem-rgd onneton wll get loser to that of the frame wth rgd onnetons as the onnetons n the frame eome stffer. The requred rgdty of the onneton that ehaves lke a rgd onneton s related to the stffness rato of the olumn to the eam ( K / K joned y the onneton. A typal range of the stffness of the rgd onneton vares from 400,000 knm/rad to 4500,000 knm/rad. The ontrutons of flexure of olumns, eams and onneton rotatons to the storey drft an e estmated y Equaton 7 for ground level and Equaton 8 for upper levels for the pnased frames wth sem-rgd onnetons. It s worthwhle to note that Equatons 4 to 8 are lose-form solutons for solvng storey defleton ased on assumpton that the nfleton ponts of the eams are at md-span n elast analyss. For the nelast sesm effet, ths s onsdered y the fator of / S n Equaton 3. p

10 V h Vh (7 1 ( / L ( / h 1 K on V h 1 1 Vh (8 1 ( / L ( / h 1 K on where K on = stffness of eah onneton at level Tale 4 Inter-storey drft of pn-ased frame wth sem-rgd onnetons Inter-storey drft (mm 1000 knm/rad 10,000 knm/rad 100,000 knm/rad 1000,000 knm/rad Level Level Level Level Level Sem-rgd frame wth fxed ase For the ase of sem-rgd frame wth fxed ase, the storey drft demand an e met wth onneton stffness of 10,000 knm/radan or greater. For example, the nter-storey drft for the fxed ase frame wth onneton stffness of 100,000 knm/radan are 8. mm, 16.0 mm, 16.4 mm, 19.4 mm, and 9.7 mm for level 1 to 5 under the omned load of G+0.4Q+E. It shall e noted that although a great effet of the ase fxty on frame drft s oserved; suh degree of fxty of olumn ase may not e aheved easly n prate as most of the footngs are not perfetly rgd. 6. Conlusons A fve storey moment-resstng omposte frame has een desgned and analysed n aordane wth urrent Australan standards. Wthn the present sope of nvestgaton, the followng onlusons an e made. For low-rse uldng struture, drft lmt ontrols the desgn of the ground floor. For the upper floors, the moment at negatve endng regon ontrol the omposte eam desgn.

11 The use of sem-rgd onneton n the omposte frame tends to nrease lateral defletons sustantally, alet the moment at the negatve endng are redued. The fxty of olumn ase has great nfluene on the storey drft and moment dstruton of edge olumns. The omposte moment-resstng frames an provde sustantal reserve apaty, relale fore dstruton mehansms, and ertan degree of dutlty. In addton, they an also provde enefts at the serve load level y redung defleton and vraton ontrol. Aknowledgements The authors would lke to aknowledge the generous support of Ajax Engneered Fasteners, Australan Tue Mlls and ARC through Lnkage Projet No. LP Referenes Carero, J.M. and Bayo, E. (005 Development of prata l desgn methods for steel strutures wth sem-rgd onnetons, Engneerng Strutures, Vol. 7, pp de S Vellaso PCG, de Andrade SAL, da Slva JDS, de Lmo LRO, Brto Jr O (006 A parametr analyss of steel omposte portal frames wth sem-rgd onnetons, Engneerng Strutures, Vol. 8, pp Hensman, J.S. and Netherot, D.A. (001 Numeral study of unraed omposte frames: Generaton of data to valdate the use of the wnd moment method of desgn, Journal of Construtonal Steel Researh, Vol. 57, pp Integrated Tehnal Software (007 SPACE GASS, verson 10.5, Geelong, Vtora. Leon, R.T. (1990 Sem -rgd omposte onstruton, Journal of Construtonal Steel Researh, Vol. 15, pp Leon, R.T. and Ammerman, D.J. (1990 Sem -rgd omposte onnetons for gravty loads, AISC Engneerng Journal, Vol. 1, pp Lew, T.Y.R., Chen, W.F., Chen, H. (000 Advaned nelast analyss of frame strutures, Journal of Construtonal Steel Resaerh, Vol. 55, pp

12 Rodrgues, F.C., Saldanha, A.C., and Pfel, M.S. (1998 Non-lnear analyss of steel plane frames wth sem-rgd onnetons, Journal of Construtonal Steel researh, Vol. 46, No. 1-3, pp Standards Australa (004 AS Brdge desgn, Part 6: Steel and omposte onstruton, Sydney, Australa. Standards Australa/Standards New Zealand (00 AS/NZS 1170 Strutural desgn atons, Part 0, Sydney, Australa and Wellngton, New Zealand. Standards Australa (007 AS Part 4: Earthquake atons n Australa, Sydney, Australa. Wong, Y.L., Yu, T. and Chan, S.L. (007 A smplfed analytal method for unraed omposte frames wth sem-rgd onnetons, Journal of Construtonal Steel Researh, Vol. 63, No.7, pp Xao, Y. Choo, B.S., and Netherot, D.A. (1996 Composte onnetons n steel and onrete part Moment apaty of end plate eam-to-olumn onnetons, Journal of Construtonal Steel Researh, Vol. 37, No.1, pp Yao, H., Goldsworthy, H.M., Gad, E.F., (008 Expermental and numeral nvestgaton of the tensle ehavour of lnd-olted T-stu onnetons to onrete-flled rular olumns, Journal of Strutural Engneerng, Ameran Soety of Cvl Engneers, Vol. 134, No., pp