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The evaluation of Cooper ratings for in-service timber railroad bridge stringers independent of the timber specie
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The objective of this thesis is to determine a method for assigning a rating to in-service timber railroad bridges. The standard method of rating a railroad bridge is to assign a Cooper E rating which corresponds to the largest Cooper E train that can safely traverse the structure. Furthermore, a method to determine the strength of stringers, previously subjected to fatigue loading, is sought. Consequently, this study includes 1) the analysis of 14 bridge models to determine shear and bending stress envelopes and histories, 2) the calculation of a method to estimate stringer shear strength, and 3) the detailing of a method to assign a Cooper rating to in-service bridge stringers. To better understand the behavior of a timber railroad bridge, two bridge models were created, a single-span and a two-span continuous. Typical demands on each of these bridges were calculated by simulating the passage of six known train models and one Cooper E72 train over the bridges. Shear and bending stress envelopes and histories were developed for each of the 14 models. Moreover, the analysis technique used for these bridge models may also be used as a method by which railroad engineers can determine the forces in a bridge caused by typical train traffic. Furthermore, data obtained from three timber fatigue testing programs conducted at Texas A&M University was used to develop a relationship between the modulus of elasticity and ultimate shear strength of a stringer, independent of the timber specie. This method, which estimates the shear strength of a stringer previously subjected to fatigue cycles, was essential to establishing a rating system for in-service bridges. The bridge analyses and the stringer shear strength estimation techniques were used to create a method for determining a Cooper E rating for in-service timber railroad bridges. The rating technique can be employed to estimate the fatigue degradation of the bridge as well as to determine if increasing the axle loads on the bridge is feasible. The rating method is straight-forward and should prove beneficial to railway engineers as well as helping to prolong the life of the aging timber infrastructure.
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Includes bibliographical references (leaves 57-58).
Issued also on microfiche from Lange Micrographics.
Bartell, Brent Cameron (2003). The evaluation of Cooper ratings for in-service timber railroad bridge stringers independent of the timber specie. Master's thesis, Texas A&M University. Available electronically from
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