Comparing vector-valued intensity measures for fragility analysis of steel frames in the case of narrow-band ground motions

Seismic fragility of steel frames subjected to narrow-band motions from soft-soils of Mexico City (Mexico) is evaluated by means of a set of vector-valued ground motion intensity measures (IMs) comprised of two parameters. All the vectors considered have, as the first component, spectral acceleration at the first mode of the structure. As the second component, compared IMs are chosen among peak and integral parameters, the former represent the spectral shape in a range of periods, while the latter refer to cumulative damage potential of earthquakes. The maximum inter-story drift and an energy-based damage index for steel frames are employed as engineering demand parameters for structural performance assessment. As a result of the comparison, it is observed that spectral-shape-based vector-valued IMs have the best explicative power with respect to seismic fragility estimation. Analyses, even if limited to the peculiar ground motions considered, suggest that a recently proposed parameter (Np) is especially promising as a candidate for the next generation of IMs when combined with spectral acceleration. This appears independent of the type of seismic response measure considered.

► IMs based on spectral shape are the most efficient in estimating structural failure.
► 〈Sa(T1), Np〉 is the most representative IM of peak and cyclic seismic response.
► Vector-valued IMs based on peak ground motion parameters are not appropriate.