Seismic Fragility Analysis for Highway Bridges with Consideration of Soil-Structure Interaction and Deterioration

Bridges are critical elements within the highway transportation network. It is very important for the owner or designer to perform the risk assessment of the highway bridges during extreme events, such as earthquakes, due to their importance to the network, commerce, economic vitality and mobility. Recent studies show that seismic fragility curves are useful tools for the seismic risk assessment of highway bridges. Although general seismic fragility approach has been well established in the last two decades and numerous retrofit methods have been applied to highway bridges in New York City (NYC) metropolitan area, which has been classified as moderate seismic zone as per American Association of State Highway and Transportation Officials (AASHTO), there is a need to carry out detailed and further work on seismic fragility by considering soil-structure interaction (SSI) and deterioration effects because of the differences in ground motion characteristics, construction practices and inevitable deterioration of construction materials. The main objective of this research work is to refine existing methods for the development of analytical seismic fragility curves for bridges in NYC metropolitan area by introducing detailed consideration and modeling of the SSI and deterioration of critical bridge elements. To meet above objective, several sets of typical synthetic bedrock and ground surface motions in NYC metropolitan region are developed in this thesis. A detailed soil material modeling along with the sensitivity analysis of the soil properties has been investigated, followed by the development of more reliable SSI model. General deterioration models, for both elastomeric bearings and reinforcement steel deterioration have been constructed. With these investigated and developed models, more realistic structural model for the typical multi-span continuous (MSC) bridges in NYC metropolitan area has been constructed. Nonlinear structural analysis as well as corresponding limit states and probabilistic analysis, have been carried out using this detailed bridge model. Based on analysis results, more realistic and reliable seismic fragility curves, which is the function of peak ground acceleration, for bridge and its components have been developed. The evaluation of seismic fragility curves constructed in this research work shows that typical MSC bridges in NYC metropolitan area would benefit from the consideration of the detailed SSI model and the risk of these bridges experiencing different extents of damage under earthquake disaster decreases because of modeling of SSI effects. However, when these bridges have been in service and have undergone deterioration for 20 years, the risk increases by the same level as the decrease because of inclusion of SSI modeling