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

Seismic fragility of steelframes subjected to narrow-bandmotions from soft-soils of Mexico City (Mexico) is evaluated by means of a set of vector-valuedgroundmotionintensitymeasures (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 steelframes are employed as engineering demand parameters for structural performance assessment. As a result of the comparison, it is observed that spectral-shape-based vector-valuedIMs have the best explicative power with respect to seismic fragility estimation. Analyses, even if limited to the peculiar groundmotions 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.