Towards a Better Estimation of Inspection Intervals for Cracking Steel Railroad Bridges

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American Railway Engineering and Maintenance-of-Way Association

In order to best prioritize limited funds for railroad bridge capital and maintenance, it is important for the bridge engineer to have an accurate estimate of service life for existing steel bridges. In the context of the paper, “service life” is affected by several damage modes such as corrosion, fatigue and fracture as well as other factures such as redundancy. Use of conservative bridge design loads and conservative computation methods can result in an estimated steel bridge life that is inappropriately short, resulting in less-than- optimal allocation of limited funds. Methods recommended to achieve more appropriate life estimates are based on recent research on riveted steel bridge members, as well as inspection and life estimation procedures used in the aircraft and pipeline industries. Collectively these practices are sometimes referred to as Fitness-for-service (FFS). Implementation of FFS allows consideration of inspection policies and trending of inspection, redundancy, material toughness, and statistical variability of loads and member performance. Considerable efforts underway for highway bridges are providing valuable input to the process. Testing of steel bridges at FAST and in revenue service, as well as laboratory testing at Purdue University, is providing additional data for development of new recommendations for better life assessment of steel railway bridges. The recommended procedures utilize an implementable FFS approach that links inspection, fatigue, and material fracture toughness to perform a risk-based assessment of an individual bridge or an entire inventory.