| A strong motion usually is followed by some aftershocks,which means that structure actually suffers from main shock and some aftershocks.Basicly,if structure is damaged after main shock, the damage will grow during the aftershock,and even lead to collapse.The similar disasters can be seen in recently strong earthquake,So it is essentially to consider the effect of aftershock in design.However, two problems need to be solved.Firstly,there are no completed and systematical study on main aftershock character and it still have difficulty in the choice of the index which can directly and accurately reflect the difference of main aftershock character.Secondly,the existing design approaches focus on the force and deformation and can't effectively respect the effect of main aftershock on structure.Considering that,from the view of energy,the difference of main aftershock character and the effect of strong aftershock on structure are studied in this paper.The main contents and conclusions are follow:(1) Based on corrected Japan 311 ground motion, though studying the modal of main shock input energy spectrum,the modal of hysteretic energy rate spectrum of main aftershock and main shock, and the attenuation rules of modal parameters, and modeling the rate spectrum of main shock hysteretic energy and main input energy,a set of completed energy spectrum construction methods of main motion and main aftershock are developed which establish the foundation for subsequent study.(2) Though analyzing existing study based on energy design, a set of completed energy design method of frame structure is proposed. Taking some main aftershock ground motion as input, a six story concrete frame structure is desiged by the besed energy method.The effect of strong aftershock on structure is researched by nonlinear dynamic analysis and Park-Ang damage index.(3) The construction method of main aftershock ground motion is developed and a four story concrete frame structure is designed by taking this ground motion as input.The result shows:Under main aftershock ground motion,the story damage and story drift of structure both have the increase and the scope drop from weak story to the top and the bottom,which means that weak story in main shock is easily to be damaged in aftershock.The amount of stirrups considering the effect of the aftershocks is about 1.1 times of only considering the effect of the main shock in the structure designed by the proposed approach;Under the main afterschok ground motion,the considering aftershock structure have some decrease in story damage and story drift comparing with the structure without considering the aftershock,and the maximum decrease happen in weak story.All of those prove the validation of method in this paper.The paper embodies the main differences of main aftershock ground motion characteristic by the plastic energy spectrum, and seismic design method based on energy is used to reflect the strong aftershock's influence on the structure, solving how to effectively take into account the influence problem of strong aftershock in the current aseismic design. The innovation of the paper can be summarized as:(1) Choosing the plastic energy spectrum to intuitive, accurately reflects difference of main aftershock ground motion characteristic;(2) Through theoretical and statistical analysis, the paper establishes mathematical model of the main aftershock's plastic energy spectrum(input energy, hysteretic energy spectrum and the energy ratio spectrum) and the attenuation rules of modal parameters,a set of completed energy spectrum construction methods of main motion and main aftershock are developed which establish the foundation for subsequent study.(3) The construction method of main aftershock ground motion is developed, by constructing the main aftershock ground motion as input,applying RC frame structures based on energy seismic design reflects the strong aftershock's influence on the structure, which proves the validation of method in this paper. |
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