Response of Base-Isolated Structures during Impact to Near-fault Motions

Impact response of base-isolated structures under near-fault earthquakes is presented. A five-storey base-isolated building is considered with lateral-degrees-of-freedom at each floor subjected to faultnormal component of near-fault motions. The adjacent structure is modeled using a spring-dashpot oscillator. The top floor acceleration and bearing displacement for different isolation systems during impact on the adjacent structures is computed. A parametric study is also conducted to investigate the effects of isolation gap distance, stiffness of the adjacent structure and isolation time period on the impact response. It is observed that the superstructure acceleration increases significantly when impact occurs reducing the effectiveness of isolation. The superstructure acceleration increases with the increase in isolation gap initially and with further increase of isolation gap those are found to decrease. However, the superstructure acceleration during impact decreases with increasing isolation time period and decreasing stiffness of the adjacent structure. A sine-pulse is also generated to observe the nature of near-fault ground motion and it is found that the near-fault ground motions cannot be modeled as short duration pulses for impact response of isolated structures.