Negative Moment Region Shear Strength of Lightly Reinforced T-Beams

Abstract

The negative moment region shear strength of lightly reinforced concrete T-beams is studied. Nine restrained T-beams with and without web reinforcement were tested. The primary variables were the longitudinal reinforcement ratio (0.47 and 0.70 percent) and the nominal stirrup strength .(o to 84 psi). The test results are analyzed and compared with the shear design provisions of "Building Code Requirements for Reinforced Concrete (ACI 318-83)" and predictions of other investigators. The tests indicate that both the concrete and stirrup contributions to shear strength are lower in negative moment regions than in positive moment regions. In both positive and negative moment regions, the cracking shear is lower than predicted by ACI 318-83, while the stirrup contribution exceeds that predicted by ACI 318-83. The current AC I shear provisions appear to be conservative for the positive moment regions of beams with l9ngitudi na l reinforcement ratios greater than or equal to 0.5 percent. The ACI shear provsions are also conservative for the negative moment regions of beams in which the factored shear is less than or equal to the design shear strength of the concrete. However, the ACI shear provisions appear to be unconservative for the negative moment regions of beams with longitudinal reinforcement ratios less than 0.85 percent and factored shears greater than the design shear strength of the concrete.