Study On Simulation Method And Seismic Response Of Underground Structures

With large scale construction of the subway and other underground structures,the problem of security reliability has received worldwide attention,especially reliability analysis of subway structure under seismic effect. The response of underground structure under earthquake is different from the structure on the ground, as well as the seismic analysis methods. Therefore,it is of great significance to study seismic response characteristics of underground structures and its analysis methods both in theory and in practical design.The selection of the artificial boundary and the ground motion input method is directly related to the validity of the calculation results. So, this paper has demonstrated that the principle of non-reflection boundary in dynamic analysis software LS-DYNA is consistent with viscous boundary firstly. Put forward four kinds of common boundaries and the ground motion input afterwards, which verified the validity of the no reflection boundary and the interplay of artificial boundary and the ground motion input method. To illustrate that the artificial boundary and the ground motion input method has great coupling effects on seismic simulation results of underground structure.Secondly, the paper has derived calculation formulas of equivalent earthquake load corresponding to non-reflection boundary. Then compile procedure with FORTRAN program language in the secondary development environment provided by LS-DYNA for user on base of formulas. Through application programming interface(USER_LOADING_ SET) to deal with the motion input. Not only the correctness of calculation formulas and the related program but also the compatibility of the non-reflection boundary and the motion input by program presented in the paper has been demonstrated through numerical experiments.Finally, based on non-reflection boundary and the ground motion input method put forward and verified in the paper,a numerical model is established by LS-DYNA to analyze different vibration characteristics between the underground and ground structure, the influence of stiffness,the thickness of the overburden soil layer upon seismic responses of the structures. Then this paper established a numerical model through the prototype of subway station structures, which selected four different seismic waves to investigate the seismic behavior of subway structure and ground soil around it. This study indicates that distance from the ground and structure is immediately related to the motion of ground soil. The closer to the ground it is, the larger change the seismic response is. The closer to the structure it is, the greater the impact on motion of ground soil is. Besides, it illustrated damage mechanism of underground structure.