Choice of an optimal intensity measure for the characterization of the damaging power of the ground motion

In the framework of Performance-Based Seismic Design, the uncertainty in the estimation of the structural response is strongly related to the specific intensity measure, IM, that is adopted to synthesise the characteristics of the seismic action. In fact, the uncertainty is dependent on 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, and depends on the parameter that describes the damage state of the structure, that is, the damage measure, DM. 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.