The influence of local stresses on the behavior of concrete beams

Abstract

This thesis reports an analytical investigation into the importance of local stresses in influencing the behavior of concrete beams under combined moment and shear. A method of analysis which has recently become available was used to make calculations predicting the behavior of certain beams which were tested earlier by others and reported in the literature. Results of these calculations were compared with test results and also with computations made earlier which neglected the effect of local stresses. In all of the beams considered, the local stresses were created by the application of loads and reactions through bearing on the top and bottom surfaces of the beams. All of these beams were rectangular beams with longitudinal reinforcement but without web reinforcement. This investigation indicates that local stresses created by bearing tend to stabilize the propagation of tensile cracks as they approach the load points, and to increase predictions of beam ultimate load capacity, but usually the magnitude of the influence is small. One particular beam and crack path were studied for which consideration of local stresses gave rise to a significantly different prediction of failure from that predicted when local stresses were neglected, but in all other cases the predictions of behavior at failure were very similar, both with and without local stresses. As expected from a consideration of Saint-Venant's principle, the quantitative effect of local stresses is negligible at considerable distances from the loads and reactions. In overall effect, the influence of local stresses on beam behavior seems less important than certain other factors, for example, the amount of shearing force transferred across a tensile crack by dowel action of the longitudinal reinforcement.