Book Description

Historic bridges are an important part of the nation's infrastructure. However, many historic bridges are not being maintained to a level that will ensure their continued use. In 2007, the I-35 W Mississippi River Bridge collapsed demonstrating significant issues with the safety of older bridges in service. Currently there are so many bridges that are considered structurally deficient that transportation authorities are continuously faced with the dilemma of distributing limited bridge funds. This situation underscores a need for cost effective and reliable maintenance and rehabilitation strategies. This thesis promotes historic preservation in two main tasks: (1) rehabilitation and repair methods are determined to guide engineers, preservationists, and other stakeholders and (2) an assessment is performed for a prototype historic bridge. More specifically, the assessment is performed in three tasks: (1) modeling of the historic bridge, (2) evaluation of the bridge using load rating procedures, and (3) rehabilitation strategies are recommended based on the results of the assessment. The prototype bridge is a 1930s variable depth T-beam bridge. The bridge did not meet requirements for flexural capacity at the mid-sections of the approach and main span interior girders. Three rehabilitation methods considered were support modification at the cantilever ends, external fiber reinforced polymer (FRP) plies, and external post-tensioning. The support modification raised the bridge to a 75-year exposure period, the highest level of evaluation, without disrupting the historical integrity of the bridge. The FRP plies raised the positive moment capacity of the bridge to legal load standards, a 5-year exposure period. The FRP retrofit was limited by de-bonding issues. The external post-tensioning raised the positive capacity to design load standards at the inventory level, a 75-year exposure period. The external post-tensioning was limited by the use of a straight tendon, but is less visible than a draped tendon. From the information in the assessment, support modification is more effective than the other methods and will not negatively affect the bridge's historic integrity. Other factors such as the projected effects on other bridge elements including the substructure, cost, installation procedures, and durability should be considered and might lower the benefits of the considered methods. The electronic version of this dissertation is accessible from http://hdl.handle.net/1969.1/149606