Safety Margin Evaluation and Proposal of Design Method of Seismically Isolated Buildings Considering Redundancy for Earthquake Ground Motion Levels

Abstract

It has been pointed out that seismically isolated buildings (SIBs) have low redundancy, which causes damage to develop rapidly when the response of the superstructure reaches a certain limit, and the importance of safety margin evaluation and assurance is increasing with the recent increase in earthquake ground motion levels. In this paper, the safety margin of SIBs is probabilistically evaluated by incremental dynamic analysis. The poor redundancy of the SIBs' superstructure is also considered the relationship between the D_s value and the ductility factor, and a formulation is attempted. Using this relationship, a simplified evaluation of the safety margin of SIBs is performed and compared with the probabilistic evaluation. Furthermore, based on the comparison with seismic resistant structures, we present a new concept of safety margin evaluation for SIBs and propose a design Method to secure the safety margin.