Development Length Criteria: Bars Without Transverse Reinforcement

Abstract

An expression that accurately represents development and splice strength as a function of concrete cover and bar spacing is developed and used to establish and evaluate modifications to the bond and development provisions of the ACI Building Code (ACI 318-89) for bars without transverse reinforcement The expression for development and splice strength is similar in form to expressions developed by Orangun, Jirsa, and Breen (1975, 1977), but is obtained using techniques that limit the effects of unintentional bias in the test data. The resulting expression provides a more accurate representation of development and splice strength than do the earlier expressions, and provides better guidance when there is a significant difference between the concrete cover and one-half of the clear spacing between bars. The expression for development and splice strength is used to establish new criteria that follow the format of ACI 318-89 and to evaluate design criteria that are currently under review by ACI Subcommittee 318-B. The new criteria that follow the format of ACI 318-89 are generally conservative and economical. The provisions under study by Subcommittee 318-B are unconservative for No. 6 bars and smaller with minimum covers and close spacings, and are overconservative for most bars with higher covers and wider spacings. Modifications are recommended that increase both the safety and the economy provided by the provisions under study by ACI Subcommittee 318-B.