【摘要】 时-频反应谱是地震动幅值、频谱和持时三要素构成的空间三维谱.基于此,本文提出归一化时-频反应谱定义与计算方法,计算三条典型地震波的归一化时-频反应谱,对比分析表明:不同地震记录的时-频反应谱的幅值在时间和周期两个轴上的分布差别很大,具有不同时-频反应谱的地震波可能对结构地震响应产生不同影响;对12层钢筋混凝土框架结构模型进行弹塑性时程分析,通过结构地震反应、结构损伤曲线与输入地震动的归一化时-频反应谱对比,发现结构最大反应并不一定是造成结构倒塌的直接原因,用结构弹性阶段反应最大值进行抗震设计存在一定局限性,从而证明归一化时-频反应谱可有效用来分析地震动特性和结构破坏机理.更多还原

【Abstract】 Seismic design by the theory of response spectra equivalents to simplifying dynamic design to static design.The maximum value of complex construction under input ground motion can be determined by the superposition principle. Except for amplitude and frequency characteristics,the duration characteristic of ground motion is not taken into account in the response spectrum theory.However,damage to structure caused by duration should not be ignored.Elastoplastic properties and stiffness change of structural elements are taken into account in elastic-plastic time-history analysis.Under input ground motion,the displacement,velocity and acceleration time-history response of each mass point can be obtained through computation step by step.Although the duration characteristic of ground motion is taken into account in this method,it takes a lot of time and the calculations are very complex.In addition,the accuracy of results depends on finite element division,material constitutive relationship and seismic waves.Elastic-plastic time-history analysis has high requirement to hardware for processing a large amount of data.Even though seismic design to a structure by elastic-plastic time-history analysis under certain input ground motion is safe,it may not quite safe under other input ground motion.In order to sole this problem,Normalized Time-Frequency ResponseSpectrum(NTFRS)was proposed and studied.Fist,the time-frequency response spectrum was introduced.Then,such spectra of the Tianjin record in NS direction(Tianjin people’s hospital recording station),ChiChi record in NS direction(Nantou Hsinjie middle school recording station)and Wenchuan record in EW direction(Wolong recording station)were analyzed.After that,the conception of Normalized NTFRS was proposed.The NTFRS of the above three records were calculated.The potential destructiveness and the spectral patterns of them were analyzed and the predict results were verified by elasticplastic time-history analysis.Taking the ChiChi record in NS direction for example(peak acceleration were adjusted to 500 gal which equivalents to the level of 8 degree severe earthquake),the earthquake response of a 12-storey reinforced concrete frame structure was analyzed by using the elastic-plastic time-history analysis method.The earthquake response results of the structure and the performances of structural damage curves on normalized timefrequency response spectrums of the ChiChi record in NS direction were compared.The spectral patterns of NTFRS of the Tianjin record in NS direction,ChiChi record in NS direction and Wenchuan record in EW direction are clearly different.Their spectrum amplitudes distributed along the period axis and duration axis are different from each other.The elasticplastic response results of the 12-storey reinforced concrete frame accord with analysis results of NTFRS of the ChiChi record in NS direction.Earthquake waves with different NTFRS may cause different effects on structures.Therefore,seismic design should take suitable ground motions for certain structures,or the seismic design results may be less reliable.Under strong motions,the natural vibration period of structures would increase step by step.The maximum seismic response of structure might not be the cause of its collapse.It implies that the traditional response spectrum theory has limitation because in the theory the maximum elastic response of structures is used to make seismic design.It can be concluded that the Normalized Time-Frequency Response Spectrum is better for analyzing the characteristics of ground motions and the structural failure mechanism in earthquakes.更多还原