Research On Standard Seismic Action Based On Multi-stage Modal Load Combination

The dynamic nonlinear analysis method has the shortcomings of large influence of seismic wave selcection and time-consuming calculation,so the static nonlinear analysis method has become one of the mainstream methods for seismic performance evaluation.In this paper,a standard seismic action based on multi-stage modal load combination is proposed based on three characteristics of seismic action,spectrum,duration and amplitude.Based on the theoretical research of multi-stage updating mode of combined modal load,the multi-stage cyclic loading mode is established,and the seismic performance evaluation of structure under different performance requirements is extended to realize the standardization of static seismic action simulation.In this paper,the seismic input problem is solved,and a standard seismic action is provided instead of dynamic nonlinear analysis method,which can effectively and accurately simulate the nonlinear stage response requirements of structure.The main research contents are listed as follows:A unidirectional loading mode based on multi-stage modal load combination.Based on the spectrum characteristics of ground motion,considering the contribution of higher-modes and the redistribution of internal forces in nonlinear stage,a unidirectional loading mode based on multi-stage modal load combination is proposed.On the basis of modal load combination,a multi-stage updating unidirectional loading mode is established by simplifying the redistribution characteristics of internal forces in nonlinear stages.Based on the comparison of the response results of the two frame models,the rationality of the multi-stage updating mode and the method of determining the performance point is clarified,and the accuracy and superiority of the multi-stage unidirectional loading mode structural response simulation are verified.Cyclic loading mode based on multi-stage modal load combination.Based on the duration characteristics of ground motion,a cyclic loading mode based on multi-stage modal load combination is proposed,considering the cyclic action of earthquake.The multi-stage cyclic loading mode is established by using the multi-stage mode load combination mode,the concept of equivalent broken line of multi-stage loading mode,and the statistical law of displacement history of single degree of freedom system.Based on the comparison of the response results of the two frame models,the rationality differences between the unidirectional and cyclic loading modes are discussed,and the accuracy and superiority of the cyclic loading mode response simulation based on multi-stage modal load combination are verified.Research on standardization of static seismic action based on different performance requirements.Based on the amplitude characteristics of ground motion,the standardization of seismic action based on multi-stage mode load combination is realized.The accuracy and applicability of the improved method are verified by selecting the earthquake action corresponding to different performance requirements,and the standardization of static seismic action simulation is realized.In order to facilitate the development and application of the research theory,the application of seismic design based on standard seismic action is proposed to replace the nonlinear dynamic time history analysis to check the elastic-plastic performance of the structure.