Evaluation of Long-Term Prestress Losses in Post-Tensioned Box-Girder Bridges

Evaluation of Long-Term Prestress Losses in Post-Tensioned Box-Girder Bridges - Printable Version

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Evaluation of Long-Term Prestress Losses in Post-Tensioned Box-Girder Bridges - mahyarov - 10-30-2012

This study assessed the accuracy of the long-term prestress-loss estimation methods given in the current AASHTO LRFD Specifications for post-tensioned bridge girders, and developed more suitable analysis methods for these members. A refined analysis method and a simplified method were proven to be accurate using field data collected from two bridge structures that were monitored for prestress losses over a period of more than four years. Formulas for calculating the creep and shrinkage of concrete have been evaluated with the material data obtained from concrete cylinders cast with the same batches of concrete used for the monitored bridge girders, and have been used for the loss calculations. The formulas in AASHTO 2004 provide a much better correlation with the creep and shrinkage data obtained from the concrete cylinders than AASHTO 2007. In general, the AASHTO 2007 formulas significantly under-estimate the creep and shrinkage of the concrete cylinders, and result in calculated long-term losses that are much lower than the measured values. The creep and shrinkage formulas provided in AASHTO 2004 therefore are recommended for the prestress-loss calculations using the proposed refined analysis method. Suggestions are provided for possible implementation of the proposed analysis methods in the AASHTO LRFD Specifications for calculating long-term prestress losses in post-tensioned bridge girders. Both methods are expressed in forms that can be readily implemented in the AASHTO LRFD Specifications.

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