Recommended Provisions and Commentary on Development Length for High-Strength Reinforcement in Tension

Abstract

Design provisions on development length for straight reinforcing bars in tension are presented in code format and compared with those in ACI 318-14 (Building Code Requirements for Structural Concrete) and fib MC2010 (fib Model Code for Concrete Structures). The proposed provisions are based on a simplified version of the design equation in ACI 408R-03 (Bond and Development of Straight Reinforcing Bars in Tension) extended to apply to high-strength concrete up to 110 MPa (16,000 psi) and high-strength reinforcement up to 1070 MPa (155,000 psi). Compared with those in ACI 318-14 and fib MC2010, the recommended provisions produce designs with improved reliability and longer development lengths for conditions of low confinement or low concrete cover, but generally shorter development lengths for bars with higher degrees of confinement and wider spacing between bars. The recommended development length design equation gives values within 10% of those obtained from the design equation in ACI 408R-03.