Redundancy and Fracture Resilience of Built-Up Steel Girders

A significant percentage of the steel bridge inventory is approaching or has surpassed its intended design life. Due to limited replacement funds, methods for increasing the service life, while maintaining safety, are of increasing importance. Most large steel bridges constructed prior to the mid-1960s are composed of riveted built-up members which, based largely on anecdotal evidence, have demonstrated resilience to failure through member-level redundancy. This internally redundant behavior of built-up steel girders provides a member with the ability to resist collapse in the event of a failure of an individual component. However, due to the lack of experimental data, built-up steel girders are currently required to be inspected as fracture-critical members when deemed non-redundant in a bridge system, and therefore do not take advantage of the redundant behavior of the members. A full-scale experimental research program was carried out to evaluate the fracture resilience of built-up steel girders. Parameters affecting the remaining load capacity of partially failed sections were also investigated. Specimens were then cycled in fatigue to determine their fatigue life in the partially damaged state. Results from this study were used to develop recommended assessment procedures for built-up members containing a failed component. Additionally, proposed specification language has been developed for inclusion in the AASHTO evaluation specifications. These provisions will permit the removal of the fracture critical classification for existing and new bridges in which built-up members meeting specific criteria are utilized. In cases where sufficient capacity exists and the fracture critical designation can be removed, guidance on setting a rational in-service inspection interval as well as inspection level of detail have been developed.