BEHAVIOR OF BOTTOM LOADED CONTINUOUS DEEP BEAMS

Abstract

Reinforced concrete deep beams are widely used as main elements in concrete structures such as water tanks, bridges and high rise buildings. Loading direction affects the behavior of deep beams. The behavior of top loaded deep beams is completely different from that of bottom loaded ones. The purpose of this research effort is to experimentally investigate the behavior of bottom loaded continuous deep beams and to identify the major differences between top and bottom loaded deep beams. Six large-scale continuous deep beams were tested up to failure in a test set-up that was especially constructed for this investigation. The variables considered in the experimental program were the shear span to depth ratio, vertical and horizontal web reinforcement ratios. A formula for predicting the ultimate capacity of bottom loaded continuous deep beams has been derived based on a shear friction truss model for the behavior of such beams. The formula makes use of the previous research on the subject of shear friction of reinforced concrete together with the familiar truss model for reinforced concrete beams. The proposed model is checked against the experimental results and a reasonably good agreement has been obtained. In order to get insight to the flow of forces in bottom loaded continuous deep beams, a modified plasticity truss model has been proposed and checked against test results. Taking into account the contribution of the yielded horizontal web reinforcement, the model has successfully predicted the ultimate capacity of the beam .