PI: Ian Hodgson
University: Lehigh University

Welded steel bridges constructed in the 1970's and earlier can be susceptible to fatigue cracking caused by vehicle loading. Despite their age, these bridges remain critical components of the transportation system in Pennsylvania and the United States. Without proper repair, fatigue cracks have the potential to grow, which can lead to brittle failure and bridge collapse. Additionally, repair measures increase in complexity and cost with increasing crack growth. Hole drilling is a common and cost-effective repair procedure employed to address certain types of fatigue cracking. Visual inspection is used to identify the crack geometry and locate the crack-arrest hole, such that the crack tip is captured and removed from the bridge. In practice, the hole drilling repair often does not stop the crack growth. This is either due to the fact that the hole is not properly engineered, leaving local stress concentrations which allow the crack to re-initiate, or the crack tip is not accurately identified, such that the crack-arrest hole does not capture and remove the crack tip.

This multi-year project is proposed to address these two potential deficiencies of the hole-drilling fatigue retrofit. First, the potential for fatigue cracks to reinitiate from stress concentrations at the edge of the hole caused by an intersecting weld toe will be investigated. Recommendations for proper engineering of crack-arrest holes to avoid crack re-initiation will be developed. Second, the reliability of non-destructive evaluation methods to determine the crack geometry will be assessed. This proposal outlines the scope of work and deliverables for the first of these two tasks. For this first task, the project goals will be achieved through a literature review, small- scale fatigue testing and associated FEA, and development of improved crack-arrest hole recommendations, which can be used by bridge owners.