Sensitivity of Seismic Response and Fragility to Parameter Uncertainty

As the use for regional seismic risk assessment increases, the need for reliable fragility curves for portfolios (or classes) of structures becomes more important. Fragility curves for portfolios of structures have the added complexity of having to deal with the uncertainty in geometric properties, along with the typical uncertainties such as material or component response parameters. Analysts are challenged with selecting a prudent level of uncertainty treatment while balancing the simulation and computational effort. In order to address this question, this study first evaluates the modeling parameters which significantly affect the seismic response of an example class of retrofitted bridges. Further, the relative importance of the uncertainty in these modeling parameters, gross geometries, and ground motions is assessed. The study reveals that savings in simulation and computational effort in fragility estimation may be achieved through a preliminary screening of modeling parameters. However, the propagation of these potentially variable parameters tends to be overshadowed by the uncertainty in the ground motion and base geometry of the structural class.