钢支撑设计方法对多层框架实际抗震性能的影响
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摘要
钢结构支撑设计分人为放大支撑内力设计的强剪型支撑架和不放大内力设计的弱剪型支撑架,该文对4条地震波作用下的强剪型和弱剪型支撑架的地震响应进行了非线性弹塑性时程响应分析,结果表明:1)强剪型支撑架,不仅增大了地震力,且柱先于支撑屈服发生无侧移失稳,导致结构水平和竖向位移快速增加;而弱剪型支撑框架在地震下发生有侧移变形;2)强剪型支撑架的层间剪力-位移时程响应曲线和支撑的应力应变响应曲线、柱子应力应变响应曲线封闭面积较小,表明结构即使具有耗能能力,也难以发挥作用。并且耗能只是依靠柱的无侧移屈曲,对抗震结构比较危险,而且是一种单一的抗侧力体系;3)弱剪型支撑框架中,支撑能够更早发生屈服,然后支撑和框架继续发生侧移变形,组成支撑架一部分的框架能够起到第二道防线的作用,支撑和梁柱的延性及耗能能力能够充分发挥作用。根据上述分析结果,该文认为不宜人为放大支撑内力,并增加支撑先于柱子屈服的机构验算,保证最薄弱层支撑屈服后属于支撑架一部分的柱子仍基本在弹性阶段工作。
Braced frames are designed in two different philosophies: one is to amplify design force of braces to achieve a strong-shear frame, the other does not. This paper analyzed the nonlinear elastic-plastic time-history responses of these two types of frames under 4 earthquake records. It was found that: 1) columns in strong-shear braced frames buckle in a non-sway mode before yielding of braces, and then horizontal and vertical displacements of the frames increase rapidly. The deformation of a weak-shear braced frame is in a sway mode. 2) curves of inter-story shear force-lateral displacement and the stress-strain response of the brace and columns do not form a hysteretic loop in a strong-shear braced frame, energy-dissipating capacity is unable to be developed to reduce the earthquake response. 3) In weak-shear braced frames, braces yield first, then the brace and the frame may hysteretically deform laterally and continually to develop their ductility and energy-dissipating capacity to reduce earthquake responses, the frame comprising part of the bracing system functions as a secondary structural system against earthquake. Based on these findings, it is suggested that check be carried out to make sure that the brace in the weakest story yields before the connecting columns buckle in a non-sway mode, i.e. to ensure a strong-column weak-brace system.
Braced frames are designed in two different philosophies: one is to amplify design force of braces to achieve a strong-shear frame, the other does not. This paper analyzed the nonlinear elastic-plastic time-history responses of these two types of frames under 4 earthquake records. It was found that: 1) columns in strong-shear braced frames buckle in a non-sway mode before yielding of braces, and then horizontal and vertical displacements of the frames increase rapidly. The deformation of a weak-shear braced frame is in a sway mode. 2) curves of inter-story shear force-lateral displacement and the stress-strain response of the brace and columns do not form a hysteretic loop in a strong-shear braced frame, energy-dissipating capacity is unable to be developed to reduce the earthquake response. 3) In weak-shear braced frames, braces yield first, then the brace and the frame may hysteretically deform laterally and continually to develop their ductility and energy-dissipating capacity to reduce earthquake responses, the frame comprising part of the bracing system functions as a secondary structural system against earthquake. Based on these findings, it is suggested that check be carried out to make sure that the brace in the weakest story yields before the connecting columns buckle in a non-sway mode, i.e. to ensure a strong-column weak-brace system.
引文
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[2]GB50011-2001,建筑抗震设计规范[S].2001.GB50011-2001,Code for seismic design of buildings[S].2001.(in Chinese)
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[4]EC8D,esign of structures for earthquake resistance.Part1:General rules,seismic actions and rules for buildings[S].2003.
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[8]Moghaddam H,Hajirasouliha I.An investigation on the accuracy of pushover analysis for estimating the seismic deformation of braced steel frames[J].Journal of Constructional Steel Research,2006,62(4):343―351.
[9]连尉安,张耀春.钢支撑及双重抗侧力体系研究现状、不足及改进[J].地震工程与工程震动,2005,25(3):67―76.Lian Weian,Zhang Yaochun.Present research problems and improvements on steel braces and dual systems of concentrically braced frames[J].Earthquake Engineering and Engineering Vibration,2005,25(3):67―76.(in Chinese)
[10]蔡益燕.《高层民用建筑钢结构技术规程》修订雏议[J].建筑钢结构进展,2003,5(4):1―4.Cai Yiyan.An envisage on revision of“technical specification for steel structure of tall buildings”[J].Progress in Steel Building Structures,2003,5(4):1―4.(in Chinese)
[2]GB50011-2001,建筑抗震设计规范[S].2001.GB50011-2001,Code for seismic design of buildings[S].2001.(in Chinese)
[3]SPSSB-2005,Seismic provisions for structural steel buildings[S].AISC,Chicago,U.S.A.,2005.
[4]EC8D,esign of structures for earthquake resistance.Part1:General rules,seismic actions and rules for buildings[S].2003.
[5]Rai D C,Goel S C.Seismic evaluation and updating of chevron braced frames[J].Journal of Constructional Steel Research,2003,59(10):971―994.
[6]Roeder C W.Seismic behavior of concentrically braced frame[J].Journal of Structural Engineering,1989,115(8):1837―1856.
[7]Marion E M,Nakashima M.Seismic performance and new design procedure for chevron-braced frames[J].Earthquake Engineering and Structural Dynamics,2006,35(4):433―452.
[8]Moghaddam H,Hajirasouliha I.An investigation on the accuracy of pushover analysis for estimating the seismic deformation of braced steel frames[J].Journal of Constructional Steel Research,2006,62(4):343―351.
[9]连尉安,张耀春.钢支撑及双重抗侧力体系研究现状、不足及改进[J].地震工程与工程震动,2005,25(3):67―76.Lian Weian,Zhang Yaochun.Present research problems and improvements on steel braces and dual systems of concentrically braced frames[J].Earthquake Engineering and Engineering Vibration,2005,25(3):67―76.(in Chinese)
[10]蔡益燕.《高层民用建筑钢结构技术规程》修订雏议[J].建筑钢结构进展,2003,5(4):1―4.Cai Yiyan.An envisage on revision of“technical specification for steel structure of tall buildings”[J].Progress in Steel Building Structures,2003,5(4):1―4.(in Chinese)
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