Bond and development of deformed square reinforcing bars

Square deformed reinforcing bars were widely used prior to and during the transition to circular deformed reinforcing steel upon adoption of ASTM A 305-50, which standardized geometry, weight, deformation height, and spacing requirements. Bond stress and development lengths for deformed square bars have traditionally been computed as equivalent round bars of equal cross-sectional area and weight, although this approach has not been validated. Data is presented from archival research on deformed square and circular reinforcing bars both prior and subsequent to adoption and implementation of ASTM A 305-50 that provides information for assessment of bond and development of deformed square reinforcing bars in vintage and historic structures. Pullout test results show that deformed square bars exhibited average bond stress similar to those of round deformed bars. Based on the archival test results and the comparisons presented, treatment of deformed square bars as equivalent round bars for calculation of development length appears reasonable and conservative.