IDA involves performing multiple
nonlinear dynamic analyses of a structural model under a suite of
ground motion records, each scaled to several levels of seismic intensity. The scaling levels are appropriately selected to force the structure through the entire range of behavior, from elastic to inelastic and finally to global dynamic instability, where the structure essentially experiences collapse. Appropriate postprocessing can present the results in terms of IDA curves, one for each ground motion record, of the seismic intensity, typically represented by a scalar Intensity Measure (IM), versus the structural response, as measured by an engineering demand parameter (EDP). Possible choices for the IM are scalar (or rarely vector) quantities that relate to the severity of the recorded ground motion and scale linearly or nonlinearly with its amplitude. The IM is properly chosen well so that appropriate hazard maps (hazard curves) can be produced for them by probabilistic seismic hazard analysis. In addition, the IM should be correlated with the structural response of interest to decrease the number of required response history analyses. Possible choices are the
peak ground acceleration,
peak ground velocity or
Arias intensity, but the most widely used is the 5%-damped
spectral acceleration at the first-mode period of the structure. The results of the recent studies show that spectrum intensity (SI) is an appropriate IM. The EDP can be any structural response quantity that relates to structural, non-structural or contents' damage. Typical choices are the maximum (over all stories and time) interstory drift, the individual peak story drifts and the peak floor accelerations. ==Development history==