Predicting Camber, Deflection, and Prestress Losses in Prestressed Concrete Members

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Predicting Camber, Deflection, and Prestress Losses in Prestressed Concrete Members

Author: Rizkalla, Sami Zia, Paul Storm, Tyler | Size: 2.97 MB | Format: PDF | Quality: Original preprint | Publisher: North Carolina State University | Year: 2011 | pages: 174

Accurate predictions of camber and prestress losses for prestressed concrete bridge girders are essential to minimizing the frequency and cost of construction problems. The time-dependent nature of prestress losses, variable concrete properties, and problems related to production variables make it difficult to predict camber accurately. The recent problems experienced by NCDOT during construction are mainly related to inaccurate prediction of camber. In this report, several factors related to girder production are shown to have a significant impact on the prediction of camber. A detailed method and an approximate method for predicting camber that both utilize adjustments to account for the production factors are proposed. The detailed method uses time-dependent losses calculations and creep factors to predict camber, while the approximate method uses multipliers. The current NCDOT method and the proposed methods are analyzed and compared using an extensive database of field measurements. The proposed methods are shown to provide significant improvements to the camber predictions in comparison to the current NCDOT method. Recommendations for design and production practices are provided.

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