Optimal intensity measures for the characterization of the ground motion in performance-based seismic design

In Performance-Based Seismic Design, the uncertainty in the estimation of the structural damage is related to the "efficiency" of the intensity measure, IM, adopted to describe the site-specific seismic hazard. Moreover, the choice of an efficient IM may reduce the number of nonlinear dynamic analyses that are needed to estimate the seismic demand with a given confidence level, and taking into account the record-to-record variability. In this paper, the incremental dynamic analysis is used as a tool to compare the efficiency of five IM's. The choice of the most efficient IM depends on the structural typology, the damage level the structure will experience, and the damage measure, DM, that is adopted to describe the damage state of the structure. Thus, the comparison is performed on two reinforced concrete frame structures, built in Italy and designed for gravity loads without any seismic provision; four damage measures are considered.