This paper presents results of an experimental investigation into the effect of flange geometry on the shear strength of point-loaded, reinforced concrete T-beams. A procedure to normalise the ultimate strength and calculate a concrete contribution is implemented. This is used to discuss the effect of varying the ratio of flange width to web width and the ratio of flange depth to effective depth on the shear strength of a reinforced concrete T-beam. An increase in the ratio of flange width to web width is shown to produce an accompanying increase in the ultimate strength of a reinforced concrete T-beam, providing the ratio of flange depth to effective depth is above a certain minimum value. This increase in shear resistance with an increase in the ratio of flange width to web width continues until the flange is wide enough to allow formation of a failure mechanism whereby the load point punches through the flange.Key words: shear, T-beams, flange, reinforcing, strength, failure mechanisms.
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.
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