Collapse Analysis Of The Serial Isolation Structure Subjected To Multi-dimensional Earthquake

Base isolation technique provides an effective way of protecting structures andprotecting the equipments inside the buildings. Some isolated structures experienced therecent major earthquakes occurred in different part of the world, and the effectiveness ofisolation technique in mitigating structural damage are widely recognized. Successivelyoccurred earthquakes in recent years have enhanced people’s desire of using such newtechnology as isolation for protection of structures in near fault area. However, theapplication of isolation technique in near fault area should be carried out carefully dueto lack of experience of precedent application of isolation structure in near fault area atpresent and the knowledge on the dynamic response characteristics and failure mode ofisolation structure in the near-fault earthquake is still very limited, further theoreticalanalysis and experimental study are needed.Isolation design is based on one-dimensional seismic input, multi-dimension is afeature of near–fault earthquake, it have an adverse effect on the isolated structure. Thispaper presents an investigation of collapse pattern of seismic isolated structure subjectto multi-dimensional earthquake using the method of incremental dynamic analysis(IDA) with the help of FEM software MARC. With different parameters assigned, fourmajor patterns of isolated structure collapse occurred, i.e., isolator collapse, first storycollapse, basement column collapse. The result shows that the collapse in an isolatedstructure might occur more easily when subjected to multi-dimensional earthquake thansingle directional earthquake input. Through adjusting the bearings and other structureelements’ lateral stiffness, discovered that the collapse mode of isolation structures isrelated to lateral stiffness of each floor. This can provide a theoretical basis for revealingthe failure mechanism of isolation structures.Under near-fault pulse-type seismic motion, the isolation story will have agreater deformation, potential pounding may occur at the isolation level between thebuilding and its surrounding retaining walls. In this paper, non-linear springs wereemployed to simulate the impact of the boundary, elastic-plastic deformation of theupper structure was also considered. Used the collision model based on nonlinearsprings, pounding response of the isolation structure under near-fault and far-faultseismic were analyzed, impacts of the pounding under different tectonic space werestudied. Through “birth-death” element defined in the user’s subroutine, collapseleaded by pounding was simulated. Based on IDA analysis shows that：Compared with far-fault seismic, structures under near-fault seismic were more likely to crash, and it ismore relevant with overturning of isolation structure. Simulation results show thatpounding lead to isolation bearing damage and subsequent overturning collapsed.