Choice of an optimal Intensity Measure for the characterization of the damaging power of the ground motion

In Performance-Based Seismic Design, the uncertainty in the estimation of the structural response is strongly dependent on the specific intensity measure, IM, that is adopted to synthesise the characteristics of the seismic action. This uncertainty is a function of the “efficiency” of the adopted IM: in other words, the choice of an efficient IM may reduce the number of nonlinear dynamic analyses that is needed to estimate the seismic demand with a given confidence level. In this paper, the incremental dynamic analysis is used as a tool to compare some alternative IM’s in terms of their efficiency. The choice of the most efficient IM is case-specific, depending on the structural typology and the demand level the structure will experience, as well as on the parameter that is chosen in order to represent the damage to the structure. Therefore, the comparison is performed on two (a rigid and a slender) reinforced concrete frame structures, built in Italy and designed for gravity loads without any seismic provision. Four damage measures are considered, and five intensity measures compared