Fragility of California bridges - development of modification factors

Abstract

This research study concentrates on the effects of geometric irregularities on the seismic response and fragility analysis of bridges. The experiences of past earthquakes have affirmed that bridges with geometric irregularities or inconsistencies in configuration have a higher probability of damage than the regular, straight bridges. Although previous studies have explored the fragility analysis of different types of bridges, there is a lack of research that focuses on the effects of various types of geometric irregularities on the development of fragility curves. The current work aims to address this deficiency by focusing on the impacts of (i) skew angle, (ii) unbalanced stiffness of frames, and (iii) tall column bents on the seismic performance of concrete box-girder bridges in California. This research first identifies the analytical modeling considerations associated with the design and construction of bridges in California. In the next step, bridge plans are extensively reviewed to determine the appropriate distribution of parameters needed to set up the various bridge components required for finite element modeling. Following the analytical modeling of bridges, a sensitivity analysis is performed on different bridge attributes to classify all of the categories of bridges existing in California. This classification helps keep the number of simulations and computational efforts within a reasonable range. The impacts of each type of irregularity on the probabilistic seismic demand model and the fragility of bridges are investigated in the later phases of this project. Finally, implementing statistical techniques, the results are compared to the responses of bridges with regular configurations. This results in the development of modification factors that allow the fragility curves of regular bridges to be modified, taking irregularities into account. Eventually, the proposed modification factors for each type of irregularity are tested and finalized.