Estimating Camber, Deflection, and Prestress Losses in Precast, Prestressed Bridge Girders
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2019-08-01
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Edition:Final Report
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Abstract:Many medium and long precast prestressed concrete girders have camber less than the design values. This discrepancy between the design and the actual camber creates construction problems during installing the cast-in-place concrete deck. The objective of this project is to improve the accuracy of estimating long-term camber, deflection, and prestressed losses of precast, prestressed concrete girders. The experimental program consisted of measuring the concrete properties and performing field measurements for camber, deflection, and prestress losses for girders in AR. The investigation involved testing nine full-scale girders from two prestressed concrete plants that regularly supply concrete girders to bridge projects in Arkansas. In the project, nine full scale prestressed concrete girders including AASHTO Type II, III, IV, and VI girders were instrumented. Camber and deflection were measured for several girders from each type. Field measurements and the laboratory testing shows that the current method that the ARDOT uses overestimates camber, specifically in the AASHTO Type II and III girders. The measured camber at erection for all girders was less than the design camber by 93%, 128%, and 25% for AASHTO Type II, III, and VI girders, respectively. The over estimation in camber is mainly attributed to the actual concrete compressive strength at release being greater than the specified compressive strength which was as high as 73% for some girders. It was also determined that the 2014 AASHTO LRFD Refined Method of estimating prestress losses overestimates the total prestress losses at the time of deck placement for the AASHTO Type II and III girders.
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