Title: Shear Tests of High- and Low-Strength Concrete Beams Without Stirrups
Author(s): Andrew G. Mphonde and Gregory C. Frantz
Publication: Journal Proceedings
Appears on pages(s): 350-357
Keywords: beams (supports); compressive strength; cracking (fracturing); high-strength concretes; regression analysis; reinforced concrete; research; shear strength; shear tests; statistical analysis; structural design.
Three series of reinforced concrete beams without shear reinforcement were tested to determine their diagonal cracking strengths and ultimate shear capacities. Within each series the shear span-depth ratio was held constant at 3.6, 2.5, or 1.5, while nominal concrete compressive strength was varied from 3000 to 15,000 psi (21 to 103 MPa) in otherwise identical specimens. Test results indicate that for slender beams the ACI beam shear strength equations are conservative, but their accuracy varies greatly with concrete strength. A new regression equation is presented to more accurately predict ultimate shear capacity of slender beams over the entire range of concrete strengths tested. The effect of concrete strength on shear capacity becomes more significant as the beams become shorter. For the shorter beams, the ACI equation underestimates the actual shear strength by 71 percent at high concrete strengths.