Load Distribution and Shear Strength Evaluation of an Old Concrete T-Beam Bridge

There are about 330 T-beam bridges in the Australian state of Victoria that were built before 1950. Australia-wide there are nearly 1,000 of these early T-beam bridges. The shear capacity of these bridges, when assessed in accordance with current codes of practice, is in some cases not adequate for the current design loading. In 1996, VicRoads, the Victorian state road authority, initiated a project to enable a more accurate assessment of the shear capacity of these bridges to be made so that decisions on load rating or replacement could be made. An analysis of an existing reinforced concrete T-beam bridge that had been identified for a load test to failure was commissioned. The purpose of the analysis was to predict the load distribution behavior and the ultimate strength and to advise on the testing and monitoring program. After successful load testing of the bridge, a comprehensive analysis of the observed behavior was carried out and compared with the theoretical models. The pre-and posttesting analysis, which was undertaken with linear and nonlinear finite element analysis and with the modified compression field theory, are described and the analysis results are compared with the real behavior of the tested bridge. In particular, the load distribution in the elastic range and the ultimate shear strength of the reinforced concrete T-beams are discussed. The consequences of these findings on the load rating procedures are discussed, and a strategy for rating old reinforced concrete T-beam bridges is outlined.