Optimal intensity measures for probabilistic seismic demand models of steel moment frames

Selecting an optimal ground motion intensity measure (IM) is a vital step in the earthquake fragility analysis of building structures using probabilistic seismic demand models (PSDMs). This study proposes optimal IMs among 20 considered for seismic fragility analysis of structural steel moment frames in PSDMs. Five steel frames of different heights were selected to propose optimal IMs for steel frames between 2 and 20 stories. The IMs were evaluated using two engineering demand parameters (maximum interstory and roof drifts). Two characteristics of ground motions were investigated (pulse and non-pulse). The results revealed that velocity-related parameters (Housner intensity (HI) and peak ground velocity (PGV)) and spectral pseudo-acceleration at the first natural period (PS_a(T₁)) tend to be optimal IMs for steel moment frames. For maximum interstory drift, HI is suggested as the optimal IM for steel frames of 2–12 stories for both types of ground motions, while PGV is suggested for steel frames from 12 to 20 stories. Under maximum roof drift, PS_a(T₁) is the optimal IM for steel frames of all investigated stories subjected to either ground motion type. Peak ground acceleration, which is widely used as a ground motion IM, was observed to be unsuitable for all steel moment frames investigated in this study.