Evaluating the Redundancy of Steel Bridges: Full-Scale Destructive Testing of a Fracture Critical Twin Box-Girder Steel Bridge

AASHTO defines a fracture critical member as a “component in tension whose failure is expected to result in the collapse of the bridge or the inability of the bridge to perform its function,” and requires costly bi-annual inspection of all bridges designed with fracture critical members. Failures of fracture critical members on in-service bridges, however, have demonstrated that these structures often possess sufficient capacity through redundant load paths overlooked by the fracture critical provisions of the AASHTO specifications.

The Texas Department of Transportation and the Federal Highway Administration funded a large-scale research project through the Ferguson Structural Engineering Laboratory at the University of Texas to develop methods for evaluating the redundancy of fracture critical steel bridges. Provided with new tools to estimate the redundant capacities and ultimate loads of their structures, transportation authorities will be able to tailor their maintenance and inspection schedules to their bridge inventories, appropriately managing labor and financial resources.

As part of the research project, a full-scale twin box-girder steel bridge representative of fracture critical bridges in Texas was decommissioned from the highway system in Houston, rebuilt at Ferguson Lab, and prepared for testing. Twin box-girder bridges are designed with two tension flanges, and both are designated as fracture critical members.