Influence of directionality of spectral‐compatible Bi‐directional ground motions on critical seismic performance assessment of base‐isolation structures

Abstract

AbstractIn this study, the effects of the degree of directionality on critical seismic performance assessment are investigated from two aspects: the bidirectional seismic demand represented by maximum‐direction spectrum and the performance indices obtained from nonlinear time‐history analysis. Firstly, typical representations of the bidirectional demand of ground motions are reviewed and compared, in seismic design practices (e.g., ASCE 7‐16, Eurocode8, and JRA). Statistical analysis using 83 ground motions underlines the implication of the spectrum‐compatible condition that has not been fully considered in past studies investigating the bidirectional effects. In the second part, a series of spectrum‐compatible bidirectional ground motions with various degrees of directionality are generated as inputs. The corresponding seismic performance assessment results of a base isolation building with the friction pendulum system are investigated. According to the simulation results, the current design practices could introduce unconservative assessment on the maximum bearing displacement due to the omission of the directionality effect included in the design ground motions, particularly, when the directionality parameter is at a large value (less directionality). The cases with nondirectionality always tend to result in a nearly constant envelope of the maximum interstory drift and the maximum floor acceleration assessment for the full directionality case, over all incident directions. For the critical seismic performance assessment, the two extreme cases, namely the full directionality and nondirectionality cases, are recommended to be considered.