Post-Fracture Redundancy Evaluation of a Twin Box-Girder Shinkansen Bridge in Japan

As the national bridge inventory ages and traffic volumes increase, the government is spending more on maintaining their existing structures to extend the service life of the current bridge inventory. This includes two-girder bridges that are classified as fracture critical and non-redundant. Owing to the increased inspection costs associated with these fracture-critical bridges, there is a need to evaluate alternate load paths and to implement retrofit methods on existing bridge structures to avoid bridge replacement. In this paper, after-fracture redundancy of two-girder bridges is investigated through a case study for a four-span continuous steel-concrete composite twin box- girder bridge. The finite element analysis was carried out to evaluate the load-carrying capacity after failure of one girder of the two-girder bridge. Two types of the main-girder damage, including fracture of the bottom flange only, and fracture of both bottom flange and the web were considered respectively in this study. Typical damage locations including mid-span section of the main girder and the sections near the intermediate support were also considered in the numerical analyses. On the basis of the numerical results, the present continuous steel-concrete composite box-girder bridge was classified as a redundant bridge, and the concrete deck was considered as the key member for ensuring the bridge redundancy after severe damages occurred on the main girders.