Seismic fragility and risk management of highway bridges in New York State

Although New York State lies in a region of moderate seismic activity, earthquakes pose a significant hazard to the State's highway infrastructure because of the risk of extensive damage to its existing aging bridge network. The object of this dissertation is to develop an improved method for the seismic fragility analysis of typical New York State highway bridge components and systems, and obtain objective measures to assess their seismic risk.; To meet the stated objectives, typical bridge structural types along with their topological layouts and structural details are identified through a statistical analysis of the National Bridge Inventory (NBI) files. An in-depth parametric study is carried out to evaluate the sensitivity of a bridge's seismic response to variations in its structural parameters. Probabilistic models are developed to describe the structural properties of the critical parameters using experimental data collected from the published literature. Statistical samples of typical New York State bridges are matched with earthquake samples of various intensities for the nonlinear seismic demand analysis. Nonlinear and multivariate regression fits of the seismic analysis results serve to develop probabilistic models of the demand to capacity ratios for different damage limit states. These models are used to construct seismic fragility curves and fragility surfaces to study the probability of damage for individual components and complete bridge systems as a function of peak ground accelerations or as a function of moment magnitudes and epicentral distances. A second-order reliability method provides narrow bounds on the probability of failure accounting for seismic risk from multiple failure modes.; The effectiveness of several retrofit measures, such as the use of elastomeric bearings, lead rubber bearings, viscous dampers and carbon fiber jackets, are compared by studying the changes that these measures would introduce to the original fragility curves and fragility surfaces. The results of the fragility analysis developed in this research for both as-built and retrofitted bridges would help state engineers develop effective strategies for seismic retrofit prioritization, loss estimation, and network seismic vulnerability assessment.