Seismic safety assessment of base isolated buildings using lead-rubber bearings

Base isolation using lead-rubber bearing (LRB) has been well-developed and widely-implemented in high seismic zones worldwide. During strong earthquake shaking, LRB is designed to move horizontally and meanwhile carry large axial load. One of the main design challenges is to prevent the LRB from buckling. Although detailed component behavior of LRB under combined axial and shear loads has been well investigated, the seismic performance of base isolated building with LRB has not been systematically examined. In this study, the seismic performances of two prototype buildings, each with different LRB geometric properties, structural periods, and axial loads, were systematically examined. To properly account for the buckling response of the LRB under combined axial and shear loads, robust finite element models of the prototype buildings were developed using the state-of-the-art LRB buckling model implemented in OpenSees. Nonlinear time history analyses were conducted using ground motions selected and scaled based on the 2015 National Building Code of Canada. As shown by the result, when the LRB is designed without accounting the axial and shear interaction, this leads to high probability of failure of the LRB, which can be difficult and expansive to fix. In some situations, this might lead to the collapse of the base isolated building. To mitigate the failed probability of the LRB during strong earthquake shaking, a simple amplification factor of 2.5 is proposed to amplify the design axial load calculated from the combined gravity and earthquake loads when the coupled axial and shear interaction of LRB is not explicitly modeled.Applied Science, Faculty ofCivil Engineering, Department ofGraduat