Response of Base-Isolated Building with Secondary System under Earthquakes and Pulse-Type Ground Motions

Abstract

Important secondary structures such as pipes may experience damage and become cracked during earthquakes. This not only may cause the piping to lose its functionality, but also may lead to secondary hazard such as fire if the piping carries flammable fluid supplies. This study investigated the effectiveness of base isolation for the safety of buildings with secondary structures when subjected to real earthquakes and pulse-type ground motions. The coupled equations of motion for multiple-degree of freedom (MDOF) secondary systems supported on MDOF fixed-base and base-isolated structures are developed and solved using Newmark’s integration method. A lead–rubber bearing called the N-Z system is used as an isolation system to improve the performance of the coupled system subjected to ground motions. The variation in moment and shear at the base, the top floor absolute acceleration and bearing displacement, and the interstory drift ratio (IDR) for these structures under different ground motions is computed. The effect of the shape of the force–deformation loop of the N-Z system on the response of the base-isolated structure is studied under the variation of important system parameters such as isolator yield displacement and yielding strength of the N-Z system. It is found that the base-isolation technique is effective for response control of structures under both type of ground motions. It is concluded that the N-Z system with lower yield strength can effectively control the dynamic response of both primary and secondary structures. In addition, maintaining a lower yield displacement is a suitable design choice for the isolator. Therefore, designing the N-Z system with a yield displacement of 30 mm is recommended.