Long-term Deformations in Prestressed Concrete Box Girder Bridges

Abstract

Long-span prestressed concrete box girder bridges are very sensitive to creep and shrinkage which may induce large deflection effects. Designers tend to rely on the simplified procedures contained in codes of practice for the estimation of service load behaviour. Such procedures usually oversimplify a complex problem and are often unreliable and conceptually misleading. This thesis presents a computer-based step by step numerical modelling procedure incorporating the programming language Matlab5 and the finite element package Strand7. The procedure is used to predict the long-term behaviour of the prestressed concrete box girder bridges built by the balanced cantilever construction over the Nepean River at Pheasants Nest, South of Sydney. Nine of the most common mathematical models for creep and shrinkage are used. The results are compared with survey measurements of the bridges since 1982 to present. It is found that only two prediction models give results which are in close agreement with measured deflections of the bridges. Sensitivity analyses are carried out and the results can be improved by varying model parameters such as concrete strength, humidity and concrete age at first loading. A number of recommendations for future research is presented. A simplified creep and shrinkage analysis procedure is also suggested for use in routine design of prestressed concrete structures.