Developing a Parametric Seismic Fragility Model Based on Pushover Performance

Focusing on typical highway structures, this study introduces a novel approach to developing structure-specific parametric seismic fragility curves. Combining the capacity spectrum method (CSM) with a structural reliability framework, the proposed method differs significantly from existing methods for fragility analysis by relying solely on cyclic or backbone pushover performance. In particular, a fragility model is shown to be generally governed by seismic capacity and spectral modification factors. These two high-level parameters are then related to geometry, material, and spectral characteristics following common seismic design and evaluation procedures. As a result, the new approach aligns naturally with deterministic or semiprobabilistic seismic analyses of structures. Additionally, it can reduce to the HAZUS fragility curves (a popular class fragility model) based on assumptions clearly laid out in this study. When the HAZUS assumptions are refined or loosened, the proposed method yields structure-specific fragility models comparable to those obtained from more sophisticated techniques for fragility curve development. The new method also enables rapid development of fragility curves for retrofitted or deteriorated structures. Finally, the approach is used to demonstrate that (1) the widely used HAZUS fragility curves may introduce considerable model uncertainty for a specific in-class structure, and (2) due to this high in-class variation, it can be challenging to use class-level baseline models to incorporate deterioration or retrofitting effects. In contrast, the proposed method is capable of capturing these effects and distinguishing between structures of the same class, supporting more targeted and effective retrofit decision-making.