Title: Main Tension Steel in High Strength Concrete Deep and Short Beams

Author(s): Kang-Hai Tan, Susanto Teng, Fung-Kew Kong, and Hai-Yun Lu

Publication: Structural Journal

Volume: 94

Issue: 6

Appears on pages(s): 752-768

Keywords: building codes; cracks; deep beams; deflections; diagonal crack; high strength concrete; main steel; shear span; shear strength; ten-sion steel; ultimate strength.

DOI: 10.14359/9735

Date: 11/1/1997

Abstract:
Twenty-two reinforced concrete deep beams with cylinder compressive strengths f’, generally exceeding 5.5 MPa (8000 psi) were tested under two-point symmetric top loading. Based on the main steel ratio pw the beams were organized into four groups with pw = 2.00, 2.58, 4.08, and 5.80 percent. Web reinforcement comprising 10 mm (0.4 in.) diameter plain mild steel stirrups at 300 mm (11.7 in.) centers was provided for all specimens, giving a vertical web steel ratio pV of 0.48 percent. The beams were tested for different shear span-to-overall-height ratios a/h, ranging from 0.25 to 2.50 (equivalent to a/d from 0.28 to 3.14). The comparisons among the series serve to highlight the influence of pw and a/h ratio on the shear behavior of high strength concrete deep and short beams. It is shown that the a/h ratio (or equivalent a/d) dominates the failure modes while the beneficial effect of pw is more significant at the low end of a/d, say for a/d ,< 1.50. With a/d > 1 SO, the influence of the main steel ratio declines, except for the particularly high value of 5.80 percent, where the relative increase in shear strength due to main steel remains constantly high, regardless of a/d. The test results are then compared with predictions based on the cur-rent ACI Code, the Canadian Code, and the UK CIRIA Guide-2. It is shown that the ACI predictions are generally conservative, with the smallest standard deviation, though with a/d > 1.50, a few cases are overestimated. The predictions from the Canadian Code are comparatively good, but the UK CIRIA Guide-2 estimations are generally unconservative, with the greatest scatter. The study shows that the CIRIA Guide-2 predictions may be unconservative for specimens with f’, 2.55 MPa (8000 psi) and with pw 2 2.58 percent.