Fragility analysis of existing precast industrial frames using CFRP reinforcement

Transcription

1 Internatonal Conference on Appled Scence and Engneerng Innovaton (ASEI 2015) Fraglty analyss of exstng precast ndustral frames usng CFRP renforcement Jan Zhu 1,3, a, Pn Tan 2, b and Janmn Jn 2, c 1 Department of Cvl and Hydraulc Engneerng, Nng Xa Unversty, Ynchuan , Chna. 2 Earthquake Engneerng Research Center, Guang Zhou Unversty, Guangzhou , Chna. 1 Department of Cvl Engneerng, Chang An Unversty, Xan , Chna. a arrow66@163.com, b tanpng@gzu.edu.cn, c jnjm@gzu.edu.cn Keywords: CFRP renforced, Exstng ndustral frames, Sesmc fraglty, Random ground motons, Nonlnear analyss. Abstract. Ths study focus on dervaton of such fraglty curves usng Carbon Fber Renforced Polymers (CFRP) technologes retroftted conventonal renfored concrete (RC) factory buldngs. A set of random earthquake waves whch compatble wth the response spectrum of major hstory earthquake waves n Chna are created. Dynamc analyss s used to compute the random sample of frames. Dfference of stochastc damage scatter dagrams n two drectons of buldngs s consdered. Sesmc fraglty of CFRP-renforced ndustral frames s lower than unrenforced buldngs obvously, and sesmc capablty of frames usng CFRP technologes s enhanced especally under major earthquake. Introducton In the last several decades, dramatc ncrease n the losses caused by natural catastrophes has been observed n the whole Asa-Pacfc rng. Peoples are remnded once agan that happen at last three major earthquakes n Eastern Asan regon n the new century ncludng Nepal Earthquake (Ms8.1) just happened n Aprl 25, Not only the dsappearng of thousands of lves but also destructon of amount of ndustral and resdental buldngs. Especally large number of ndustral buldngs bult between the 1990s and 2000s n Western Chna wth economy rapd development. But many of the constructon bult wthout specfc sesmc provsons because of undeveloped sesmc code of Chna n that perod and later enlargement of sesmc zones after Wenchuan Earthquake (Ms8.0) n So how to evaluate fraglty of the ndustral frames and strengthen these frames wth CFRP retroft technology for future earthquake n Western Chna s urgent msson. Carbon Fber renforced polymers (CFRP) have a varety of advantages over other materal, such as low densty, hgh stffness and strength, adjustable mechancal propertes, resstance to corroson, solvents and chemcals, flexble manufacturng and fast applcaton. They have wdely been used n structural reparng and sesmc resstance[1-6]. In ths framework, the renforce effect of confnement ntroduced by the CFRP wrappng the RC columns are modeled and calculated. Dynamc nonlnear analyss method been used n the framework. Sesmc fraglty analyss also ntroduced n the work, whch s the condtonal probablty of a buldng reach or exceedng a certan performance level for a gven ground moton parameter, allowng methods whch correlate the damage of the buldng stock to these nput parameters to be proposed, as shown n Eq.1. 1 S k P( D ds S Sk) Ln( ) (1) ds M ds Where P s the probablty that the damage state ds wll be acheved or exceeded for a ground moton severty S k, D and S are the varables representng the damage and the severty of the nput moton respectvely. s standard normal dstrbuton, M ds and ds are the mean and standard devaton of the damage states The authors - Publshed by Atlants Press 1869

2 System defnton n ndustral frames There are a lot of exstng ndustral buldngs bult between the 1990s and 2000s based old Chna sesmc code n many ndustral dstrcts. The reasons whch led to such large scale use are strctly related to the socal and economcal scenaro of that tme: Chna came nto economy reform age and expand ndustry process. House, ndustral structures were largely requred and workers and constructon materals were nsuffcency. On the other hand, t was necessary to buld rapdly and keep the cost as low as possble. Some ndvdual buldngs among those bult even wthout any consderaton of horzontal sesmc loads. So nowadays they are often exposed to hgh levels of sesmc rsk. Smlar structures are also occuped n other developng countres. A regular, sngle-storey ndustral frame confguraton s chosen to represent the system after wdely ste survey and collectng many and accurate data on the buldngs characterstcs n Western Chna. The frames are desgned accordng to the prescrptons for loadng, materal, member dmensonng and detalng of the sesmc desgn and gravty load desgn codes n place n former Chna code [7]. Based on a revew of avalable nformaton, a frst rough classfcaton can be done dependng on the layout of man horzontal members and roof arrangement: full retcular trussed beam, so span lower than 30 m generally. The structural system adopted for the precast ndustral buldngs could be made by straght elements, frame parts n ste could be easy to manage. The sample structures conssts wth general confguraton of bent wdths and bay wdths between 4-6 m and m respectvely, the whole buldng have meters long wth 6-12 columns and m wdth, It s symmetrcal n plan and elevaton, and rectangular renforced concrete rng beam ( m) on the bracket of two sde longtudnal columns of the buldng. At the same tme RC column ( m) whch connected rng beam as confned frame element array along the exteror sde of the buldng at the ntersect wth nner confned brck wall between columns. The roof of buldng whch heght s 8-10 m consst n steel fbre truss, the truss depth s changed from 2.4 m n centre to 1.5m of two sdes, there are four knd of crcular hollow rod beng defned to usng wth dameter from 0.03 m to 0.05 m, and thckness of bar secton s also verfy from 2 to 3 mm. The buldng s wall between columns generally consst of load-bearng nfll masonry walls commonly made of clay brcks n Chna, confned by renforced concrete vertcal columns and wdth and thckness of wall are changed from 0.24m to 0.37m accordng Chna masonry code. Columns must have four 24mm and 28mm dameter longtudnal renforcements, 8mm dameter strrups must be spaced 200mm n the elements. Category of avalable retrofttng ndustral buldngs s external bonded CFRP platng around each RC rectangular column.. column secton. beam secton Fg.1 Fnte element sample of the ndustral frame Fg.2 Detaled drawngs of frame secton The ndustral frame was desgned accordng to the Chna code for both gravty and sesmc loads. The gravty load scenaro conssts of dead load and lve load. When calculatng the dead load, the weght of the structural members and the masonry nfll walls was ncluded. The roof lve load used was 0.5 kn/m 2, whch s typcal for an ndustral buldng. Other types of loadng, such as wnd and snow were not consdered [8]. Materal and member property As regards the materals, the clay brck strength must at least MU15 and the mortar strength must at least M10 accordng to Chna masonry code, so typcal masonry shear strength s Mpa. Steel and concrete used for precast members were characterzed by the actual performance avalable at that 1870

3 tme. Blnear stress-stran relatonshps wth stran hardenng were used for renforced members whch typcal yeld strength for common applcatons were 220Mpa, concrete compressve strength s 25 Mpa n consderng of that many ndustral frames n Western Chna regons have been bult two decades ago. And coeffcent wth varaton of 0.3 has been consdered for steel and concrete respectvely. Unaxal nonlnear constant confnement concrete model that constant confnng pressure s assumed throughout the entre stress-stran range s proposed by Madas to apply to element of concrete n ths calculaton [9-10]. A smplfed unaxal tr-lnear CFRP model that assumes no resstance n compresson s used n the research. Four model calbratng parameters are defned n order to fully descrbe the mechancal characterstcs of the materal. They are tensle strength, ntal stffness, post peak stffness and specfc weght, and the default values are 3000 Mpa, 300Gpa, -500Gpa and 18kN/m respectvely n consderaton wth smplfcaton [11]. Numercal analyss The am of numercal analyss s the evaluaton of the sesmc capacty of the reference buldngs presented n the prevous secton, n order to determne, ther sesmc fraglty n the evaluaton the demand s dentfed assumng that the sample ndustral buldngs are placed n the area of Manzhu regon n Schuan provnce of Western Chna, characterazed by a PGA equal to 0.3g and return perod equal to 475 years accordng to recent Chna sesmc classfcaton, whch are medum sesmc rsk areas, t s assumed that ndustral buldngs are located n ths area affected by ncrease of sesmc rsk classfcaton. Typcal buldngs are studed by nonlnear analyss. Useful nformaton have been obtaned by analyss, made on spatal models by the computer program Sesmostruct, takng nto account beam-column connectons geometrcal eccentrctes: modal shapes wth vbraton frequences and axal forces of columns due to vertcal loads to be combned wth sesmc forces. The frst three perod of sample structure, whch s 66 meter ncludng 12 columns n longtudnal drecton and 24 m n transverse drecton[12], are 1.285s (longtudnal dr.), 1.094s (transverse dr.) and 1.066s (rotatonal), at the same tme, the frst three perod of CFRP renforced structure are 0.805s, 0.696s and 0.693s. Ground moton characterstcs have a sgnfcant effect on the fraglty curves and specal attenton s requred durng the record selecton phase. Consderng ths fact, 15 corrected stochastc artfcal ground motons have been used n dfferent ntensty coverng a wde range of characterstcs wth a magntude range. The motons are generally recorded on soft to medum stes accordng to local crcumstance where bass promnent perod range from 0.35s to 0.45s accordng Chna sesmc code[8]. Fg.3 Random waves accordng response spectrum Four lmt state condtons have been taken nto account: lght damage, moderate damage, extensve damage and complete damage as tab.1 So f a buldng deforms beyond the extensve damage lmt state t mght not be economcally beneft to repar the buldng because many of the ndustral frames of Western Chna regon were be set up wthout carefully thought of structural sesmc codes of Chna n desgn[8]. 1871

4 Lmt state Lght Moderate Table 1 lmt states and correspondng ISD% Inter-story drft Inter-story drft Inter-story drft Lmt state (mm) rato (ISD%) (mm) Extensve Complete 240 Inter-story drft rato (ISD%) Fraglty Curves Dynamc tme-hstory analyss s used to evaluate the sesmc response and to derve the sesmc fraglty curve. Ths approach s the most tedous but t s also the more drect and accurate way to assess the fraglty of ndustral buldngs n Western Chna. The selected frame wth or wthout retrofttng CFRP technology was subject to each group of the stochastc artfcal records. Each group records were conssted of three stochastc ground motons. Fg.4 Stochastc damage scatter for orgnal frames wth Sv-ISD%(:X axs, :Y axs ) Fg.5 Stochastc damage scatter for CFRP renforced frames wth Sv-ISD%(:X axs, :Y axs ) The stochastc damage scatter dagrams were llustrated n Fg.4-Fg.5. The damage ndex (Y-axs) s descrbed n terms of ISD%. X-axs s descrbed as spectral velocty. Scattered data depct the sesmc resstant capablty of each of ndustral frame and corresponds to damage level. We can fnd that sesmc capablty of CFRP retrofttng frames s hgher than orgnal frames, and damage level s also lower than the un-retrofttng frames. For example, when Sv reach 100 cm/s, damage ndex medum value of orgn model n X axs s equal to 0.01, but medum value of retrofttng frame s only 0.005, and the latter value s half of the former value. The results hnt that sesmc fraglty of retrofttng frames s hghly lower than orgnal frames. The best ft curve of the stochastc damage scatter data was expressed n Fg.4-5, whose statstcal relatonshp between nter-story drft rato and ntensty ndcators such as spectral velocty, peak ground accelerator or spectral accelerator as Eq.2: b b a Sv a pga (2) The scatter for each frame and each sesmc ntensty measure was calculated usng the Eq.3: n 1 ˆ 2 COV ( In In ) n 2 1 (3) 1872

5 Detal explanaton n reference [13]. Smlar trends were observed for all frames, as summarzed n Tab.2. Table 2 The effcency comparson wth Sv for two sesmc ntensty measures Frame Perod Nunber of COV (%) wth orgnal COV (%) wth FRP (s) GM records X axs Y axs X axs Y axs Industral frames % 49.08% 43.01% 33.76% Fg.6 revealed the fraglty expected contrastve results of typcal used ndustral frames n Chna wth or wthout CFRP retrofttng n spectral velocty parameters. The two drecton sesmc fraglty of orgnal sample structure was almost same especally n mnor earthquake. The lght and moderate damage results started when spectral velocty values equal to 10cm/s and 20 cm/s. The gap between moderate fraglty curve and extensve fraglty curve was bgger than former curves and started when spectral velocty equal to 50 cm/s. The sesmc capacty of renforced ndustral buldngs rsen dramatcally after the columns of orgnal sample buldngs were strengthen usng CFRP wrappng method and extensve damage state began when spectral velocty values reach 70cm/s. At the same tme, the dfference of sesmc fraglty n two drecton was also been notced. Fg.6 Sesmc fraglty curves of ndustral frames wth spectral velocty ( : x axs; : y axs) Concluson The representatve ndustral buldngs are chosen as researchng sample for fraglty curve. Dynamc nonlnear analyss was performed on the buldngs, whose choce s based on a large nvestgaton on structural typologes, detals and materals. Indcatons as below: (1) Probablty of moderate damage s much seldom when Sv<20cm/s under foundaton stablty pre-condton, n contrary probablty of moderate damage was started to ncreasng when Sv>30 cm/s. (2) The sesmc capablty of longtudnal (X axs) and transversal orentaton (Y axs) of structure s dfferent. Probablty of slght damage s coherent under mnor earthquake; X axs of frames s more sesmc fraglty than Y axs under major earthquake slghtly. (3) The CFRP retrofttng sample buldngs had more excellent sesmc capacty and decreased sesmc fraglty dramatcally n comparson to orgnal buldngs. Acknowledgement Ths work was fnancally supported by the Natural Scence Foundaton of Nngxa (NZ13021) and Natonal Natural Scence Foundaton of Chna (No ). References [1] Cro Del Veccho, Marco D Ludovco, Andrea Prota, Gaetano Manfred, Analytcal model and desgn approach for FRP strengthenng of non-conformng RC corner beam column jonts, Engneerng Structures, 87(2015)

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