Improving Predictions for Camber in Precast Prestressed Concrete Bridge Girders

This research was conducted to develop improved methods of predicting camber in prestressed concrete girders. A computer program was written to calculate camber as a function of time. It takes into account instantaneous and time-dependent behavior of the concrete and steel and performs the calculations in a series of time steps. It was calibrated by comparing its predictions with the camber from 146 girders, measured in the fabricators yard both after release and at a later time. Its long-term predictions were then compared with the responses of 91 girders that were monitored during construction at the Keys Road Bridge site.
The results showed that the response was sensitive to the predicted prestress losses, and that the 2006 AASHTO values for prestress loss provided much better estimates than did the 2004 provisions. In addition, the camber was found to depend on the elastic modulus of the concrete, its creep coefficient, and the use of the prestress losses in the calculation of the creep camber. To achieve the best match with the measured cambers, the AASHTO-recommended values for the
elastic modulus and the creep coefficient had to be multiplied by adjustment factors and the prestress losses had to be taken into account when computing the creep component of camber.

Publication Date: 
Saturday, March 1, 2008
Publication Number: 
WA-RD 669.1
Last modified: 
10/12/2016 - 15:41
Michael A. Rosa, John F. Stanton, Marc O. Eberhard.
Washington State Transportation Center (TRAC)
Number of Pages: 
Curvature, Modulus of elasticity, Prestressed concrete, Shrinkage, Precast concrete, Mechanical properties by mathematical limits or values, Structural members, Creep properties.