State-dependent fragility functions for Italian building classes

Seismic structural reliability is typically quantified in terms of the mean annual number of earthquakes causing the structure of interest to exceed, in a single shock, a performance threshold (threshold exceedance is a conventional failure). This requires the definition of a hazard curve, which probabilistically characterizes the ground motion intensity at the site of interest, and a fragility curve, that provides the failure probability given the ground shaking intensity. Recently, research attempted to account for the possible failure due to subsequent earthquakes, that is, damage accumulation, an issue neglected in the mentioned (classical) approach. To this aim, so-called state-dependent fragility functions are often used. They provide the probability of getting any intermediate damage condition as a function of the intensity of the earthquake and the damage state of the structure. Fragility functions can also be developed for structural typologies (i.e., matching a given taxonomy) rather than individual structures for large-scale seismic risk assessment. The presented study developed, in a reproducible manner, state-dependent fragility functions for Italian building typologies derived via back-to-back incremental dynamic analyses of equivalent-single-degree-of-freedom systems. The latter are taken from the outcomes of the SERA project (Seismology and Earthquake Engineering Research Infrastructure Alliance for Europe) and refer to existing reinforced concrete and masonry residential buildings.