Analysis, testing, and load rating of historic steel truss bridge decks

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Bowen, Charles Merrill

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Currently, there are several hundred older metal truss bridges that remain in vehicular service in the state of Texas, many in the range of 70 to over 100 years in age. A number of these bridges are of historical interest due to their age or other unique features. Maintaining a historic truss bridge in service poses significant challenges due to structural or functional deficiencies frequently found in these bridges, very often in the bridge decks. Structural deficiencies can often be addressed by structural modifications or strengthening measures. However, such modifications can sometimes be costly and can affect the aesthetics and historical integrity of the bridge. An alternative approach for addressing inadequate structural capacity of a historic bridge is to apply more refined methods of structural analysis combined with field load testing to develop an improved load rating for the bridge. The use of improved analysis techniques and field load testing can sometimes be effectively used to demonstrate a significantly higher load rating than determined by current standard load rating techniques. This higher load rating may preclude the need for major structural modifications, resulting in cost savings and avoiding disturbance to the historical fabric of the bridge. Two case study bridges are examined, and a full-scale laboratory experimental investigation was performed. The lab work consisted of both “as is” and retrofitted testing. This dissertation focuses on the evaluation and retrofit of structurally deficient bridges due to under design, overly conservative evaluations, and unknown material properties.