Near-fault Ground Motion Simulation And Seismic Response Analysis Of Frame Structure

Due to the complex formation mechanism,the ground motions in the near-fault area has obvious pulse effects compared with the far-field ground motions,which often cause serious damage to the engineering structure.Especially in recent years,with the development of the world economy and population expansion,coupled with the growing scarcity of land resources,a large number of engineering structures have been built in the vicinity of faults,which has attracted the attention of experts and scholars in the field of earthquake engineering to the earthquake-resistant problems of such engineering structures.However,due to the limitation of the current near-fault ground motion records,especially the number of pulse-like ground motion records,taking the simulation of near-fault ground motion as the main inputs,the performance-based seismic analysis of near-fault engineering structures has become the main research trend.In particular,it is of great significance to in-depth study the pulse characteristics of near-fault ground motion and the important influence of mainshock-aftershock seismic sequence on engineering structure and the emergency measures of mainshock-damaged structure to improve the seismic performance of structures.Therefore,this thesis systematically analyzes and studies the near-fault ground motion simulation methods,the important influence of near-fault pulse characteristic and near-fault pulse-like mainshock-aftershock on engineering structures,and the emergency measures for damaged frame structures.The detailed research contents in this thesis are presented as follows:(1)Aiming at the shortcomings of the ground motion simulation method based on the wavelet packet on the simulation of near-fault pulse-like ground motion,an improved near-fault broadband pulse-like ground motion simulation method is proposed by introducing equivalent velocity pulse model to improve the wavelet packet method according to the idea of the hybrid model.Furthermore,the engineering application range of the ground motion simulation method based on the wavelet packet is extended.The artificial bee colony(ABC)algorithm is used to analyze and identify the pulse model parameters of the actual seismic records in the near-fault pulse-like ground motion database.Combined with the regression analysis method,the prediction equation for pulse model parameters based on the source,path,and site characteristics parameters are established.Based on the improved algorithm and model,the comprehensive ground motion simulation software SimGM(Simulation Ground Motion)is developed.The effectiveness and applicability of the improved near-fault ground motion simulation method are verified by simulating the actual seismic records,response spectrum error analysis and comparison with the existing near-fault ground motion simulation method.(2)Aiming at the influence of pulse characteristics of the near-fault ground motion on the seismic response of frame structures,an evaluation method for studying the influence of the pulse characteristic parameters of the near-fault ground motion on the seismic performance of frame structure under consideration of broadband ground motion is proposed.The evaluation method uses the improved near-fault ground motion simulation method to simulate the high and low-frequency components of broadband ground motion respectively,the low-frequency pulse characteristic parameters are adjusted by the control variable method to synthesize the broadband time history with different pulse characteristics,and used as the ground motion inputs for the pulse parameters sensitivity analysis of the frame structure.The feasibility and effectiveness of the evaluation process and the synthesis method are verified by response spectrum analysis and structural drift response analysis.Finally,the evaluation method is used to study the characteristic parameters of pulse-like ground motion,such as pulse amplitude,pulse period,pulse half-cycle number,phase angle and the influence of different frequency components on the seismic response of the frame structure.The results show that the pulse amplitude,pulse period and pulse half-cycle number are important parameters which affecting the seismic response of the frame structure.(3)The seismic response analysis of the mainshock-damaged frame structures under the action of near-fault mainshock-aftershock is carried out,and the influence of the near-fault aftershock on the cumulative damage of the mainshock-damaged frame structure with different mainshock.damaged state is qualitatively and quantitatively studied.The damage degree is classified and as the initial damage states before the aftershock analysis,and then the influence of the aftershock type and initial damage state on the aftershocks' seismic response and collapse rate of the frame structure are studied.Meanwhile,based on the ground motion parameters which can characterize the spectrum(period)characteristics of the ground motion,an index of the relative spectral characteristics of the mainshock-aftershock is proposed,and influence of the proposed index on the structural cumulative damage are studied.The results show that compared with the near-fault non-pulse-like aftershocks,the influence of pulse-like aftershocks on the mainshock-damaged frame structure is significant,and the structural mainshock damage state plays an important role in the seismic response and collapse rate under the aftershock.Also,the proposed relative index can better describe the evolution process of cumulative damage for the mainshock-damage frame structure under the aftershocks action.(4)Aiming at the damaged frame structures after the near-fault mainshock excitation,a fast and effective mainshock-damaged frame structure emergency reinforcement device is proposed,and the reinforcement effects of the emergency reinforcement device on the damaged frame structure under different layout schemes are evaluated from both qualitative and quantitative aspects.The finite element numerical technique is used to establish the mainshock-damaged frame structure model with two kinds of damage states and the structural model after the reinforcement.Through the elasto-plastic time history analysis of the damaged frame structure model before and after reinforcement,the reinforcement effects of the emergency reinforcement device under three layout schemes are quantitatively evaluated.The research results show that the emergency reinforcement device can effectively reduce the seismic response of the damaged frame structure.The position of the emergency reinforcement device has an important influence on the reinforcement effect of the damaged frame structure.In some cases,only the reinforcement of the bottom story of the damaged frame structure is insufficient,which may increase the seismic response of the damaged frame structure.