Camber Estimates for Precast, Pre-tensioned Concrete Bridge
Girders
PIs: J.F. Stanton and M.O. Eberhard
Research Assistant: Michael Rosa (Win 2006)
Field and analytical 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. The
program 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 latertime. The
programs' 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 the2006 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.
WSDOT report