Fracture Resilience of Steel Built-Up Members Subjected to Flexure

Built-up steel girders were a primary fabrication method used for bridges until the early 1960s. Many bridges in the transportation inventory from this era consisted of built-up two-girder systems. Because built-up members are mechanically fastened instead of welded, there are discontinuities between individual components, preventing fracture propagation among components. There is ample evidence that suggests that these members have significant ability to resist crack propagation from one component to another and therefore are able to resist complete member fracture in the event that a single component suddenly fractures. However, because of the lack of experimental and analytical evidence, current regulations require that built-up members be conservatively considered susceptible to complete catastrophic failure in the event of a single component failure and prohibit member-level redundancy from being explicitly exploited in design or evaluation. Recent experimental testing on large-scale bridge girders showed that for members with typical proportioned components, failures of a single component do not propagate into adjacent components. Furthermore, guidance has been developed on how to evaluate built-up members to ensure appropriate application of member-level redundancy.