Shear Capacity of Reinforced High-Strength Concrete Beams
Shuaib H. Ahmad, A. R. Khaloo, and A. Poveda
Appears on pages(s):
beams (supports); cracking (fracturing); diagonal tension;reinforced concrete; shear strength; shear tests; span-depth ratio;structural design.
Thirty-six reinforced concrete beams using high-strength concrete (uniaxial compressive strength, fc’ greater than 6000 psi [42 Mpa]) were tested to determine their diagonal cracking and ultimate shear capacities. All the beams were singly reinforced and were without shear (web) reinforcement. The concrete strength was not a prime variable and varied from 9,000 to 10,000 psi (63 to 70 MPa). The beams were tested for six shear span-to-depth a/d ratios and six percentages of longitudinal steel content p. Test results indicate that for slender beams of high-strength concrete and low amount of main reinforcement, the ratio of measured to predicted shear capacity of beams using the current A CI design Eq. (11-16) reduces to about 1.0. Furthermore, Eq. (11-16) of the ACI Building Code underestimates the effect of steel content p. For short beams (1 < a/d < 2.5) the code provisions are overly conservative. On the basis of experimental results of this and other studies, an empirical equation to estimate the ultimate shear capacity is proposed. The proposed equation for predicting the ultimate shear stress also includes the depth factor n to account for the observed decreased shear capacity with increased depth of the beam for a constant shear span-depth a/d ratio.