Optimal retrofit strategy design for highway bridges under seismic hazards: A case study of Charleston, SC

A significant number of US highway bridges are inadequate for seismic loads and could be seriously damaged or collapse during 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 the United States are deemed to be structurally deficient. To improve this situation, at-risk bridges must be identified, evaluated, and effective retrofitting programs implemented to reduce their seismic vulnerabilities. In practice, the Federal Highway Administration uses the expected damage method and indices method to assess the condition of bridges. These methods compare 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, these methods ignore the crucial effects of traffic networks on the highway bridge's importance. Bridge failures or even capacity reductions may redistribute the traffic of the entire network. This research develops a new retrofit strategy decision scheme for highway bridges under seismic hazards and seamlessly integrates the scenario-based seismic analysis of bridges and the traffic network into the proposed optimization modeling framework. A full spectrum of bridge retrofit strategies are considered based on explicit structural assessment for each seismic damage state. A simplified four-bridge network is used to validate the model, and then a modified version of the validated model is applied to the bridge network in Charleston, SC to illustrate the applicability of the model. The results of the case study justify the importance of taking a system viewpoint in the retrofit strategy decision process and the benefit of using the developed model in the retrofit decision making process.