Fragility Curves for Risk-Targeted Seismic Hazard Maps

Abstract eng:
In the past decade the philosophy often known as risk-targeting has started to be used to develop maps of design accelerations for use with seismic building codes (e.g. Luco et al, 2007). The aim of this method is to estimate seismic accelerations that when used for design purposes lead to a chosen level of risk (e.g. annual probability of collapse of 10e-5), which is uniform nationally. This procedure relies on convolving hazard curves from a standard probabilistic seismic hazard assessment with fragility curves that are a function of the design acceleration (e.g. buildings designed against a higher acceleration have fragility curves shifted to the right). This approach has recently been tested for mainland France by Douglas et al. (2012) with respect to the recent French seismic zonation to be used in conjunction with Eurocode 8 (EC8). Amongst other conclusions, they emphasized the lack of studies on how fragility curves change as a function of the design acceleration. This deficiency of knowledge is a current block on the adoption of risk-targeting for the next generation of seismic design codes. The purpose of this article is to investigate the impact of the design acceleration on fragility curves by deriving fragility curves for several reinforced-concrete buildings designed using EC8 for different levels of earthquake loading. For that purpose, a few characteristic structures that are representative of new European structures have been designed so that they fulfill the requirements of EC8. Then numerical models of the structures have been made by using the software Opensees (McKenna, 1997), so that their vulnerability to earthquake loading can be studied. Hundreds of dynamic nonlinear analyses have been carried out to predict the damage induced by earthquake shaking. Fragility curves were then derived from the results of these numerical simulations, so that the influence of the design acceleration on the structure’s fragility can be assessed. Finally, the impact of the results of this study on application of the risk-targeting approach in conjunction with EC8 is discussed.

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