双向地震下RC框架柱端弯矩增强措施的合理取值
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摘要
双向水平地震动的耦合作用将使塑性变形更多集中于柱端,框架结构在双向地震下的塑性铰分布明显较单向地震作用下更差。严格按中国规范设计了8度0.2g区二级抗震规则空间框架结构,并采用上部各层柱端"强柱弱梁"措施与底层柱下端弯矩增大系数不同取值的多种组合,形成了共7个算例框架。在OpenSees平台上,采用基于柔度法的纤维模型从而更加真实地模拟柱在双向弯曲和变化轴力作用下的非线性反应,对各空间框架进行了罕遇地震下的非线性反应分析。结果表明,在双向水平地震作用下,抗震规范给出的8度二级抗震的"强柱弱梁"措施取值明显偏低,框架部分楼层形成了层侧移柱铰屈服机制。基于梁端实际配筋∑Mbua对上部各柱端进行"强柱弱梁"调整的塑性铰控制效果较好,但底层柱下端非线性损伤过大。将底层柱下端的弯矩增大系数提高为1.8,上部各柱端按∑Mc=1.25∑Mb进行增强可形成较为优化的塑性铰控制效果。
More plastic deformation will concentrate on the column ends due to the coupling effects of bi-directional horizontal seismic action,and the plastic hinges distributions of spatial frame under bi-directional horizontal seismic action is obviously worse than that of the corresponding plane frame.Regular reinforced concrete 3D spatial frame of the second seismic grade at 8-earthquake intensity 0.2g-region was designed strictly according to the Chinese code,and seven spatial frame examples were obtained by the combination of varying strong column-weak beam measure in the upper stories with moment amplification factor at bottom sections of ground floor column.Based on the OpenSees framework,the flexibility method based fiber model was adopted to simulate the nonlinear responses of columns under biaxial bending and varying axial force effectively.The nonlinear response analyses of the seven frames under rare earthquake excitation were carried out.The results showed that under bi-directional horizontal seismic action,the strong column-weak beam measure of the second seismic grade at 8-earthquake intensity of Chinese code is evidently weak;the spatial frame develops column hinges mechanism with story side-sway mechanism occurs at some floors.When strong column-weak beam measure in the upper stories is based on the actual reinforcement area of beam ends,namely ∑Mbua,the controlling effects on plastic hinge mechanism are acceptable,but excessive nonlinear damage focuses on the bottom sections of ground floor columns.When the moment amplification factor at bottom sections of ground floor columns increase to 1.8,and strong column-weak beam measure in the upper stories remains to be ∑Mc=1.25∑Mb,a relatively optimal controlling effect on plastic hinge mechanism could be obtained.
More plastic deformation will concentrate on the column ends due to the coupling effects of bi-directional horizontal seismic action,and the plastic hinges distributions of spatial frame under bi-directional horizontal seismic action is obviously worse than that of the corresponding plane frame.Regular reinforced concrete 3D spatial frame of the second seismic grade at 8-earthquake intensity 0.2g-region was designed strictly according to the Chinese code,and seven spatial frame examples were obtained by the combination of varying strong column-weak beam measure in the upper stories with moment amplification factor at bottom sections of ground floor column.Based on the OpenSees framework,the flexibility method based fiber model was adopted to simulate the nonlinear responses of columns under biaxial bending and varying axial force effectively.The nonlinear response analyses of the seven frames under rare earthquake excitation were carried out.The results showed that under bi-directional horizontal seismic action,the strong column-weak beam measure of the second seismic grade at 8-earthquake intensity of Chinese code is evidently weak;the spatial frame develops column hinges mechanism with story side-sway mechanism occurs at some floors.When strong column-weak beam measure in the upper stories is based on the actual reinforcement area of beam ends,namely ∑Mbua,the controlling effects on plastic hinge mechanism are acceptable,but excessive nonlinear damage focuses on the bottom sections of ground floor columns.When the moment amplification factor at bottom sections of ground floor columns increase to 1.8,and strong column-weak beam measure in the upper stories remains to be ∑Mc=1.25∑Mb,a relatively optimal controlling effect on plastic hinge mechanism could be obtained.
引文
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[13]Mazzoni S,McKenna F,Scott M H,et al.OpenSees usersmanual[R].Berkeley:University of California,Berkeley,2006.
[14]Wu Yong,Lei Jichuan,Yang Hong,et al.Discussion onnegative flexural strength of beams including slabs[J].Jour-nal of Chongqing Jianzhu University,200,224(3):33-37.[吴勇,雷汲川,杨红,等.板筋参与梁端负弯矩承载力问题的探讨[J].重庆建筑大学学报,200,224(3):33-37.]
[15]Scott M H,Fenves G L,McKenna Fe,t al.Software patternsfor nonlinear beam-column models[J].Journal of StructuralEngineering,2008,134(4):562-571.
[16]Martinelli P,Filippou F C.Simulation of the shaking tabletest of a seven-story shear wall building[J].Earthquake En-gng Struct Dyn,20093,8(5):587-607.
[17]Hashemi A,Mosalam K M.Shake-table experiment on rein-forced concrete structure containing masonry infill wall[J].Earthquake Engng Struct Dyn,2006,35(14):1827-1852.
[2]Ministry of Construction of the Peoples’Republic of China.GB50011—2001 Code for seismic design of buildings[S].Beijing:China Architecture and Building Press,2001.[中华人民共和国建设部.GB50011—2001建筑抗震设计规范[S].北京:中国建筑工业出版社,2001.]
[3]Ministry of Construction of the Peoples’Republic of China.GBJ11—89 Code for seismic design of buildings[S].Bei-jing:China Architecture and Building Press,1990.[中华人民共和国建设部.GBJ11—89建筑抗震设计规范[S].北京:中国建筑工业出版社,1990.]
[4]Ministry of Housing and Urban-Rural Development of thePeople’s Republic of China.GB50011—2010 Code for seis-mic design of buildings[S].Beijing:China Architecture andBuilding Press,2010.[中华人民共和国住房和城乡建设部.GB50011—2010建筑抗震设计规范[S].北京:中国建筑工业出版社,2010.]
[5]Yang Hong,Wang Jianhui,Bai Shaoliang.The effect of bi-di-rectional horizontal seismic excitation on the moment ampli-fication factor of columns[J].China Civil Engineering Jour-nal,2008,41(9):40-47.[杨红,王建辉,白绍良.双向地震作用对柱端弯矩增大系数的影响分析[J].土木工程学报,20084,1(9):40-47.]
[6]Yang Hong,Gao Wensheng,Wang Zhijun.An evaluation onthe rationality of plane model simplifying three-dimensionframe in seismic responses analysis[J].Journal ofChongqing University,2008,31(11):1267-1272.[杨红,高文生,王志军.空间框架简化为平面模型的抗震分析[J].重庆大学学报,2008,31(11):1267-1272.]
[7]Wei Feng,Yang Hong,Bai Shaoliang.Calibration of seismicprovisions for RC frames in different earthquake-intensity re-gions in China[J].Journal of Chongqing Jianzhu University,200,123(6):1-9.[韦锋,杨红,白绍良.对我国不同烈度区钢筋混凝土框架现行抗震规定的初步验证[J].重庆建筑大学学报,2001,23(6):1-9.]
[8]Yang Hong,Wei Feng,Bai Shaoliange,t al.Effect of momentamplification factors of columns on controlling plastic hingemechanism of RC frames[J].Engineering Mechanics,2005,22(2):155-161.[杨红,韦锋,白绍良,等.柱增强系数取值对钢筋混凝土抗震框架塑性铰机构的控制效果[J].工程力学,2005,22(2):155-161.]
[9]Comite Euro-international du Beton(CEB)Task GroupⅢ/2.Seismic design of reinforced concrete structures for con-trolled inelastic response(design concepts)[R].London,UK:Thomas Telford Ltd,1998.
[10]Yang Hong,Zhu Zhenhua,Bai Shaoliang.An evaluation onthe effectiveness of Chinese strong column weak beam meas-ure under bi-directional horizontal seismic excitation[J].China Civil Engineering Journal,20114,4(1):58-64.[杨红,朱振华,白绍良.双向地震作用下我国“强柱弱梁”措施的有效性评估[J].土木工程学报,201,144(1):58-64.]
[11]Yang Hong,Wang Zhen,Wei Fenge,t al.Effect of amplifi-cation of moments at the bottom section of columns on seis-mic behavior of RC frames[J].World Earthquake Engineer-ing,200,218(4):66-72.[杨红,王珍,韦锋,等.柱底抗弯能力增强措施对钢筋混凝土框架抗震性能的影响[J].世界地震工程,200,218(4):66-72.]
[12]Ministry of Construction of the People’s Republic of Chi-na.GB50010—2002 Code for design of concrete structures[S].Beijing:China Architecture and Building Press,2002.[中华人民共和国建设部.GB50010—2002混凝土结构设计规范[S].北京:中国建筑工业出版社,2002.]
[13]Mazzoni S,McKenna F,Scott M H,et al.OpenSees usersmanual[R].Berkeley:University of California,Berkeley,2006.
[14]Wu Yong,Lei Jichuan,Yang Hong,et al.Discussion onnegative flexural strength of beams including slabs[J].Jour-nal of Chongqing Jianzhu University,200,224(3):33-37.[吴勇,雷汲川,杨红,等.板筋参与梁端负弯矩承载力问题的探讨[J].重庆建筑大学学报,200,224(3):33-37.]
[15]Scott M H,Fenves G L,McKenna Fe,t al.Software patternsfor nonlinear beam-column models[J].Journal of StructuralEngineering,2008,134(4):562-571.
[16]Martinelli P,Filippou F C.Simulation of the shaking tabletest of a seven-story shear wall building[J].Earthquake En-gng Struct Dyn,20093,8(5):587-607.
[17]Hashemi A,Mosalam K M.Shake-table experiment on rein-forced concrete structure containing masonry infill wall[J].Earthquake Engng Struct Dyn,2006,35(14):1827-1852.
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