Fragility Assessment of Coastal Bridges under Hurricane Events Using Enhanced Probabilistic Capacity Models

The susceptibility of the transportation network, in particular coastal bridge, along the US Gulf Coast to hurricane damage has been demonstrated in previous hurricane events. Accordingly, it is vital to have an approach for reliability assessment of coastal bridges to evaluate the vulnerability of existing bridges, prospective retrofit measures, or even new designs. Probabilistic assessments are required in order to capture the uncertainties in the performance of bridges stemming from variability in the loading and the natural hazard itself, which include surge and wave parameters, as well as structural design and construction. The conditional probability of failure of a structure under a given hazard condition, known as the fragility, has become a well accepted tool in risk assessment of structures; yet an approach for derivation of the fragility of coastal bridges is required to support risk assessment in these regions. This paper reports on a methodology for construction of fragility surfaces for bridges with high strength connections between super- and substructure subjected to coastal storms. Although these configurations are less common than typical simple supports with minimal connectivity, they do exist among coastal bridge inventories and moreover, such provision for enhanced connectivity has been suggested for retrofit or new design techniques. Construction of these fragility surfaces requires probabilistic estimates of structural capacity and demand. This research provides a consistent methodology for capacity limit state appraisal based on the numerical simulations of bridges under hurricane induced wave and surge loads, and global performance objectives for bridges related to post event loss of stiffness or load carrying capacity. Predictive probabilistic models are developed for the demand parameters identified as primary indicators of capacity loss (e.g. columns axial strain) and the bridge fragility is constructed for each damage state to demonstrate the application of the proposed method.