Simplified Procedure for Evaluating the Effects of Creep and Shrinkage on Prestressed Concrete Girder Bridges and the Application of European and North American Prediction Models

Abstract

The effects of time-dependent phenomena on concrete prestressed girder bridges are investigated. The study concerns the case of bridges built directly in their final configuration and that of bridges built by a sequence of stages in which geometry, restraints, and loads vary until the final configuration is achieved. An analytical approach based on the principles of aging linear viscoelasticity and the age-adjusted effective modulus method is followed. The paper has two aims: the first is to provide an efficient and simplified tool for the evaluation of the structural response in the early stages of design; the second is to compare the results of the analyses on actual cases of bridges when different shrinkage and creep prediction models are used. Numerical applications show that the influence of stress redistribution on bending moments, attributable to the change in static schemes, is reduced by the load-balancing effect of the dead load and prestressing and that bending moment diagrams for bridges in service do not change significantly with the different prediction models. Opposite results are found on deflections, which differ significantly in reference to the model used. Differences between predictions models are underlined, suggesting that designers should manage them with prudence to predict the long-term performance of concrete. Finally, Eurocode predictions always underestimate final deflections and stress redistribution because of the static scheme variation.