Side-Face Blowout Failure of Large-Diameter High-Strength Headed Bars in Beam-Column Joints

Abstract

The provisions of ACI 318 on headed bars have several limitations on the bar yield strength, cover, and effects of transverse reinforcement. Anchorage strengths significantly depend on failure modes and geometric conditions where headed bars are anchored. Twenty- seven simulated beam-column joints were tested using 550 MPa (80 ksi) headed bars of 43 and 57 mm (No. 14 and 18) diameter. Intentional side-face blowout failure occurred by preventing the other failure modes. As the embedment length and side cover increase, the anchorage strength also increases. Hairpin-type transverse reinforcement enhanced the strength. The 550 MPa (80 ksi) yield strength of large-diameter headed bars could be developed even with a 1db side cover by providing hairpin-type transverse reinforcement, increasing the embedment length, or increasing the compressive strength of concrete. From regression analyses of 59 sets of data, a model is proposed for predicting the anchorage strength of headed bars terminated within exterior beam-column joints.