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Fatigue analysis of single-span and two-span solid-sawn, creosote-treated southern pine railroad bridge stringers
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The purpose of this study is to assess the performance and reliability of existing timber bridges that have been subjected to heavy axle load (HAL) operations. Specifically, the study focuses on the behavior of a single-span versus a two-span stringer subjected to three different configurations of HAL trains. Results from laboratory tests and structural analyses were used to estimate the service life for each of six models. The results indicate that the single-span stringers should be the preferred method of construction and rehabilitation of timber bridges. To properly assess the fatigue resistance of timber bridge stringers, it was necessary to conduct full-scale fatigue tests on stringer specimens. As part of the Timber Bridge Life Extension Program, the Transportation Technology Center, loc. (TTCI), sponsored Texas A&M University to conduct tests on full-sized timber bridge stringers. In 1998-1999, static and fatigue tests were performed on a group of unused, solid-sawn, creosote- treated, southern pine bridge stringers donated by Norfolk Southern Railway. The results from these and other relevant studies were compiled to obtain an empirical relationship between extreme values of pulsating shear stress and number of cycles to failure. The predominant mode of failure seen in the laboratory testing and reported from field inspections was horizontal shear. A straightforward but detailed structural analysis was used to examine stress histories experienced by typical stringers in a timber bridge. Two bridge models were analyzed : single-span and two-span chord systems. The axle loads applied to each model were based on dimensions and weights provided by TTCI. Based on observed horizontal shear failures, attention focused on shear stress results. Shear stress envelopes were used to identify critical shear locations along the stringer span. Shear stress histories were computed at the critical locations. Subsequently, service life estimates were made using the critical shear stress histories, data from the fatigue tests, and Miner's rule for fatigue damage accumulation. The estimated service lives for new, two-span, continuous stringers were found to be significantly less than service lives for the single-span stringers.
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Includes bibliographical references (leaves 30-31).
Issued also on microfiche from Lange Micrographics.
Comardo, Angelique France (2000). Fatigue analysis of single-span and two-span solid-sawn, creosote-treated southern pine railroad bridge stringers. Master's thesis, Texas A&M University. Available electronically from
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