INVESTIGATION OF EXPERIMENTAL BEHAVIOR OF FIXED-ENDED REINFORCED CONCRETE DEEP BEAMS UNDER CYCLIC AND MONOTONIC LOADS

Reinforced Concrete (RC) deep beams are a special type of beams due to their geometry, boundary conditions, and behavior compared to ordinary shallow beams. For example, the assumption of a linear strain-stress distribution in the cross section is not valid. In the past decades, considerable research works have studied simply supported concrete deep beams; however, fixed-ended support conditions have scarcely been investigated. Two reasons may be given for this situation: first, fixed-ended conditions are extremely difficult to create in a laboratory; second, fixed-ended conditions introduce additional parameters that add more complexity to the structural model of RC deep beams.Following the recent tendency for the application of deep beams, the possibility of using fixed-ended deep beams in structures has widely increased. Deep beams are likely to be used as support for upper level columns due to architectural requirements; moreover, the fixed-end connectivity condition will result in experiencing cyclic loads during an earthquake due to the formation of plastic hinges. Therefore, it is necessary to investigate the behavior of this structural element in detail. In this paper, two fixed-ended reinforced concrete deep beams were tested, and their behavior was investigated under monotonic and cyclic loads. The results of these experiments showed that both beams' failures were in shear mode; in addition, the final capacity of fixed-ended deep beam under cyclic load was not significantly reduced compared to `` the final capacity'' under monotonic loading. The Load-Displacement curvature of this beam under cyclic load showed a hysteretic behavior with low energy dissipation (narrow hysteretic loops), low cyclic degradation (a small increase in displacements under consecutive cycles with constant load amplitude), small residual displacements, and low ductility (the steep drop of resistance after peak load). The crack patterns of the cyclically loaded specimen in the last positive recorded load stage prior to failure were essentially the same as those of the monotonically loaded test.