Civil Engineering Association

Approximate incremental dynamic analysis using the modal pushover analysis procedure

Incremental dynamic analysis (IDA)—a procedure developed for accurate estimation of seismic demand
and capacity of structures—requires non-linear response history analysis of the structure for an ensemble
of ground motions, each scaled to many intensity levels, selected to cover the entire range of structural
response—all the way from elastic behaviour to global dynamic instability. Recognizing that IDA of
practical structures is computationally extremely demanding, an approximate procedure based on the modal
pushover analysis procedure is developed. Presented are the IDA curves and limit state capacities for the
SAC-Los Angeles 3-, 9-, and 20-storey buildings computed by the exact and approximate procedures for
an ensemble of 20 ground motions. These results demonstrate that the MPA-based approximate procedure
reduces the computational effort by a factor of 30 (for the 9-storey building), at the same time providing
results to a useful degree of accuracy over the entire range of responses—all the way from elastic behaviour
to global dynamic instability—provided a proper hysteretic model is selected for modal SDF systems. The
accuracy of the approximate procedure does not deteriorate for 9- and 20-storey buildings, although their
dynamics is more complex, involving several ‘modes’ of vibration. For all three buildings, the accuracy
of the MPA-based approximate procedure is also satisfactory for estimating the structural capacities for
the limit states of immediate occupancy, collapse prevention, and global dynamic instability.