Research On Modified Response Spectrum Method For Seismic Analysis Of Structures

China boasts a vast territory and is one of the most earthquake-prone countries in the world.The calculation of earthquake action effect is the foundation of seismic design of structures,which is related to the seismic safety of structure.With the development of society and economy,the construction of super high-rise building structures and long-span bridge structures is in full swing,and the structural systems and structural forms are also constantly innovating.At present,the response spectrum method(RSM)is recommended for calculation of the seismic responses of structures in the codes of various countries,and it is used as the basis of seismic design.The RSM which can consider the random effects of seismic excitations to a certain degree is simple for calculation,and meets the seismic analysis requirements of most regular structures.However,there are some assumptions involved in RSM,which may exert different degrees of influence on seismic response calculation of complex high-rise building structures and long-span bridge structures.Therefore,it is of great theoretical and practical significance to explore the influence of the assumptions introduced in the traditional RSM on the calculation of seismic responses,and propose the corresponding modified RSM for seismic analysis of large-scale complex building and bridge structures.The major contributions of this dissertation are described as follows:(1)The influence of the assumptions introduced in the traditional RSM on the calculation of seismic responses is investigated.The precise complete quadratic combination(CQC)rule for the peak value of structural response is analytically derived based on the random vibration theory and the response spectrum theory.Introducing the assumptions that the seismic input is white noise and the modal peak factors equal the total peak factor,the approximate CQC rule for the mean peak value of structural response of the traditional RSM is derived.The influence of the above two assumptions on the calculation of mean peak value of structural response is investigated by taking real building and bridge structures as examples.(2)A modified RSM is proposed for seismic analysis of structures.Employing non-white-noise input to calculate the modal correlation coefficients and modal peak factors,a modified RSM is proposed based on the precise CQC rule for the fractile value of structural response,without introducing the assumptions of white-noise input and equal peak factors.Furthermore,the proposed modified RSM can yield the fractile value of structural response with uniform probability of exceedance.(3)The application of the modifed RSM for seismic analysis of building structures is carried out.The direct iteration method is used to obtain the equivalent earthquake power spectra compatible with the design response spectra of the Guangdong Province standard "technical specification for concrete structures of tall building".Based on the equivalent earthquake power spectra,the corresponding modal cross-correlation coefficient surfaces and modal peak factor curves can be obtained.Combined with the given probability of exceedance of structural response,the fractile value of structural response with uniform probability of exceedance is further obtained,which can be used as the basis for seismic design of building structures.(4)The application of the modifed RSM for seismic analysis of bridge structures is carried out.The direct iteration method is used to obtain the equivalent earthquake power spectra compatible with the design response spectra of the "specifications for seismic design of highway bridges".Based on the equivalent earthquake power spectra,the corresponding modal cross-correlation coefficient surfaces and modal peak factor curves can be obtained.Combined with the given probability of exceedance of structural response,the fractile value of structural response with uniform probability of exceedance is further obtained,which can be used as the basis for seismic design of bridge structures.Engineering applications of building and bridge structures indicate that the assumption of equal peak factors is the main reason for the underestimation of the mean peak values of structural responses when the traditional RSM is adopted,and the mean peak values of structural responses obtained by the traditional RSM can not provide the information of probability of exceedance.The proposed modified RSM which has good computational accuracy compared with the random vibration method can yield the fractile values of structural responses with uniform probability of exceedance,and is of good operationality and applicable to engineering structures.