Study Of Soil-base-isolation Interaction System's Seismic Response Under Near-fault Ground Motions

Base-isolation technique is an effective passive control technique. It can decrease structural seismic response by installing isolator between superstructure and foundation that can prolong structural natural period. Existing code and theory of base-isolation don't consider the soil-structure interaction taking a fixed-base assuming, but in practice soil-structure interaction will prolong structural natural period, change structural damping and have an influence on structural seismic response, so we should see soil-base-isolation as a whole when we are studying. In recent years, people find that the near-fault ground motions usually include long period velocity and displacement pulse through the research for near-fault ground motion recordings, this will make structure suffer strong shock at first and cause strong internal force and deformation. Compared with far-field, damage of the near-fault is more astonishing. Based on these reasons, in this paper soil-base-isolation interaction system's seismic response under near-fault ground motion is analyzed and studied.Structure's finite element model is established by finite element software ANSYS. Firstly, soil-base-isolation interaction system's dynamics is knowed by modal analysing and comparing between base-isolation structure based on rigid foundation assumption and soil-base-isolation interaction system located on site classificationâ…¡. Secondly, in order to make the anlysis results to be universally applicable, two near-fault seismic waves are used as the input, and two structures's seismic responses considering and no considering soil-structure interaction are analysed and compared through time history analysis. Finally soil stiffness and ground motion characteristics'influence on structure's seismic responses is studied.The results got from the analysis shows that: compared with the structure no considering soil-structure interaction, natural period of vibration of the soil-base-isolation structure will prolong, superstructure and isolation layer's maximum seismic response of interaction system will increase, superstructure's story drift changes little, isolation layer drift changes remarkably, soil stiffness's variation will change structure's dynamic characteristics and seismic response, extent of the change is relative to soil stiffness; ground motion characteristics will have a significant influence on structure's seismic response, The main reason causing the significant difference is seismic wave energy's different distribution in frequency domain; Isolation layer also have a good isolation effect to soil-base-isolation interaction system.