Effects of Near-Fault Ground Motions on Seismic Isolated buildings and Corresponding Design Strategies

Effects of Near-Fault Ground Motions on Seismic Isolated buildings and Corresponding Design Strategies

The concept of seismic isolation design is an accepted and effective method for the seismic mitigation of urban structures. However, in Taiwan, an earthquake prone island, many sites are located in near-fault zones. The recorded seismic waves show near-fault characteristics, such as velocity pulses and displacement pulses. These seismic waves may cause excessive displacement demands on the isolation system and transmit significant acceleration to the superstructure. Consequently, the design of seismically isolated structures located in near-fault areas is challenging. In this study, the superstructure is modeled as a single degree of freedom system such that the entire structure, including the isolation system, is modeled as a two degree of freedom system. The isolation system is composed of bilinear hysteretic bearings and viscous dampers. The superstructure is assumed to remain elastic during ground shaking. The system is designed using the response spectra of measured near-fault ground motions. Inelastic dynamic analysis is used to investigate the effectiveness of the isolation design. Both the maximum displacement and transmitted force of the isolation system subject to near-fault and far-field ground motions are examined. Further, the responses of the superstructure are discussed. It is concluded that isolation design considering only near-fault ground motions will dramatically reduce isolation effectiveness against far-field earthquakes. Nevertheless, incorporating linear viscous dampers is recommended for future research to meet design goals.