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.
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.
IDA grew out of the typical practice of scaling accelerograms by multiplying with a constant factor to represent more or less severe ground motions than the ones that were recorded at a site.
In the wake of the damage wrought by the 1994 Northridge earthquake, the SAC/FEMA project[3] was launched to resolve the issue of poor performance of steel moment-resisting frames due to the fracturing beam-column connections.
A substantial debate has been raised regarding the potential bias in the IDA results due to using the scaled ground motions records that do not appropriately characterize the seismic hazard of the considered site over different earthquake intensity levels.