A number of recent studies employing realistic, deteriorating structural models have been able to observe and quantify the influence of ground motion duration on cumulative damage indices and structural collapse capacity. These studies have, however, not attempted to study the underlying physical mechanisms that cause the observed effects of ground motion duration on structural response. This research project will study the influence of various model parameters on the sensitivity of structures to duration by conducting incremental dynamic analyses (IDA) using sets of spectrally equivalent long and short duration ground motions. Special attention will be given to the relation between ground motion duration and the ratcheting collapse mechanism aided by destabilising P-Δ effects. This study will serve as the starting point to understand the influence of ground motion duration on structural response, and to consider its effects in structural design and assessment.