Ten 54 in. (1372 mm) deep U-beam test specimens were fabricated and load-tested in shear. The first five specimens were built following existing standard designs, with variables including reinforcement type and number of prestressing strands.
All of these test specimens failed near the support, along the interface between the bottom flange and the web of the beam, at shear loads significantly below the calculated shear capacity. The shear force at failure did not vary with reinforcement or prestressing levels. The second five test specimens were designed to increase the capacity of the bottom flange-to-web interface.
Three of the specimens contained significantly more reinforcement crossing the bottom flange-to-web interface near beam end and/or a longer end block than the first group of beams. These specimens failed in typical web-shear failure modes at loads well in excess of the calculated shear capacity, with no signs of distress at the bottom flange-to-web interface.