Optimal Retrofit Strategy Design for Highway Bridges Under Seismic Hazards

A significant number of US Highway bridges are inadequate for seismic loads and could be seriously damaged or collapsed in a relatively small earthquake. On the most recent infrastructure report card from the American Society of Civil Engineers (ASCE), one-third of the bridges in this country are structurally deficient. To improve this situation, at-risk bridges must be identified and evaluated and effective retrofitting programs should be in place to reduce their seismic vulnerabilities. In practice, the Federal Highway Administration uses the expected damage method, which compares the severity of expected damage for each at-risk bridge and the bridges with the highest expected damage will receive the highest priority for retrofitting. However, this method ignores the crucial effects of traffic networks on the highway bridges. The bridge failures or even capacity reductions may redistribute the traffic to the entire network. In this study, the authors develop a new retrofit strategy decision scheme for highway bridges under seismic hazards and seamlessly integrate the scenario-based seismic analysis of bridges and the traffic network into the proposed optimization modeling framework. A full spectrum of bridge retrofit strategies is considered based on explicit structural assessment for each seismic damage state. The authors use a simplified four-bridge network in the Charleston area, South Carolina to validate and illustrate the applicability of the model. The results of the case study justify the importance of taking a system viewpoint in retrofit strategy decision process.