Advances in the Definition of Fragility Models for the Development of Risk-Targeted Hazard Maps

Abstract eng:
Current seismic design codes require buildings to be designed for a given ground motion intensity level that is determined from a prescribed return period. The implicit assumption is that this design criterion ensures that the probability of collapse of buildings, although unknown, is at least uniform. This is unfortunately not the case. Uncertainties in the fragility of the structure and on the shape of the local hazard curve often lead to an associated seismic risk level that is not only sitespecific but also structure-specific, thus invalidating the previous hypothesis. A new approach for the definition of the design ground shaking, commonly called risk-targeted hazard mapping, aims at estimating the ground motion intensity that leads to a uniform distribution of risk or collapse probability. An essential aspect of this methodology is that for the collapse probability at the design ground motion intensity must be known. This parameter, and the associated dispersion, can be constrained by analysing sets of structures designed according to the same criteria. In this study, a large number of structures designed according to the most up-to-date seismic regulation in Europe has been analyzed. The structures were designed for increasing levels of ground motion intensity (PGA ranging from 0.05g to 0.4g). Tridimentional finite element models have been created and nonlinear dynamic analyses have been performed in order to assess the buildings’ seismic performance. Several statistical analyses were performed to estimate boundaries for the collapse probability at the design ground motion, as well as its dispersion. A comprehensive study on the influence of these parameters on the final risk metrics (e.g. annual average loss) was also included. Finally, using the derived fragility parameters we present a suggestion for risk-targeted hazard mapping in Europe.

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