Assessment of an optimal intensity measure for isolated bridges based on the geometric mean of the response spectrum

Abstract The ground motion intensity measure (IM) is an important part of probabilistic seismic demand analysis and is used to predict the seismic response of structures. In this study, two typical seismic isolation bridges were selected as cases, and 80 far-fault records and 40 near-fault records are used as inputs for the time-history analysis. By performing a comparison with 19 common IMs, it is proved that the IM based on the geometric mean of the response spectrum is an optimal IM for isolated bridges in terms of efficiency, practicality, proficiency, and sufficiency. The effects of response spectrum type and period range on this form of IM are investigated. The results show that the response spectrum type has a slight effect on the IM based on the geometric mean of the response spectrum, and the period range has a greater impact on the IM. Finally, the applicability of the IM to the far-fault ground motions and the near-fault ground motions is discussed. The research results show that when only near-fault ground motions are considered, the period range of the IM should be appropriately increased.