Shear Strength of Lightly Reinforced T-Beams

Abstract

Fifteen lightly reinforced concrete T-beams, 11 with stirrups and four without stirrups, were tested to failure. The major variables rit the study were the amounts of flexural and shear reinforcement. The flexural steel varied from 0.5 to 1 percent, and the shear reinforcement varied from 0 to 110 psi (0.75 MPa). The test results are analyzed and compared with the shear design provisions of "Building Code Requirements for Reinforced Concrete (AC1 318-77)" and the recommendations of AC1 Committee 426, Shear and Diagonal Tension. The test results confirmed the findings of other investigators, that the present AC1 equations for the shear cracking load are unconservative for beams without stirrups, having a longitudinal reinforcing ratio less than 1 percent. However, for beams with stirrups the web reinforcement was 1.5 times as effective as predicted by AC1 318-77 and compensated for the lower shear strength of the concrete. It is recommended that the shear design provisions of AC1 318-77 be retained in their current form.