Analysis Of Modal Response Contribution Of Building Structures Under Near-fault Strong Earthquake Ground Motions

At present,the frequently happened earthquakes in the world have caused serious damage to the engineering structure,and brought heavy casualties and economic losses to human society.Therefore,in order to reduce the damage and disaster losses caused by the earthquakes,it is necessary to strengthen the seismic response analysis and seismic shock absorption design of building structures.The near-fault ground motions are paid close attention by the community of earthquake engineering because of their distinct large amplitude,long-period pulse motion and the great structural damage under them.The primary task of the seismic design of the building structures is to analyze the structural seismic response.The commonly used mode decomposition method for seismic analysis of structure usually determines the number of vibration modes based on the Mode Contribution Factor(MCF),while the error of the velocity response is high for the high-rise buildings.Moreover,the applicability for near-fault ground motion also needs in-depth study.In this thesis,the concept of the Seismic Mode Contribution Factor(SMCF)is introduced to overcome the shortcomings of the MCF to determine the mode number.Analysis of modal response contribution of the shear-type frame structure,shearing type and bending type cantilever beam under near-fault strong earthquake ground motions are carried out.The main research contents are presented as follows:First of all,taking the shear-type frame structure as an example,this paper studies the advantages and rationality of structural seismic response analysis based on SMCF.The SMCF of displacement and velocity of near-fault strong earthquake ground motions are obtained under 30 real impulsive near-fault ground motion records with forward directivity effect,impulsive near-fault ground motion records with fling-step effect and non-pulse near-fault ground motion records.SMCF,MCF and the SMCF of near-fault strong earthquake ground motions are analyzed and compared.It is shown that SMCF reflects the dynamic effect of earthquake ground motion on structural modal response.The SMCF of displacement is different from that of velocity.The SMCF is more accurate than the MCF to represent the modal contribution to the structural response.When the ground motion records with pulse are considered,the SMCF can still accurately reflect the contribution of the mode to the displacement and velocity.The MCF can also get the accurate contribution of the mode to the displacement.It is very inaccurate to use the MCF to solve the contribution of the mode to the velocity when non-pulse near-fault ground motion records are considered.Then,both SMCF and MCF are utilized to calculate the required vibration modal numbers.The mode decomposition method is used to obtain the displacement and velocity seismic responses of the shear-type frame structure.Comparison of numerical results illustrates that,SMCF can achieve more reasonably the required modal numbers than MCF,by which the dynamic response of structure has high computational accuracy.Secondly,the analysis of modal response contribution of shearing and bending cantilever building structure is carried out respectively.The results show that for the shearing cantilever building structure,the number of modes which is obtained by SMCF can be used to solve the seismic response accurately.When the number of stories is few,the number of modes which is obtained by MCF is reasonable.However,when the number of stories increases,the accuracy of the seismic response calculated using the MCF is getting lower and lower,especially for the velocity response.For the bending cantilever building structure,the seismic response obtained by MCF is not accurate,and the seismic response by SMCF is accurate,regardless of the number of stories.