Research on the Distributive Relationship between Bond Force and Bearing Pressure for Anchorage Force by Headed Bars

Anchorage force comprises bond force and bearing pressure when headed bars are used. Pull-out tests were conducted on 120 concrete specimens to derive a method for calculating the bond force for reinforcement in straight anchor sections at the yield moment. The parameters include the diameter d, embedded length l_ae, and yield strength f_y of the reinforcement, as well as the strength grade of the concrete f_cg. The experimental results indicated that the specimens underwent three failure modes depending primarily on the embedded length l_ae. The nominal average bond stress τ^u concept was proposed and the difference between τ^u and the actual average bond stress τ caused by the headed bars was observed. To reduce the difference between the τ^u and τ values, the correction coefficient γ was proposed. Analysis indicated that γ increased with an increase in the l_ae/d (on average, 146% higher than the initial value) and decreased with an increase in the f_y/f_t (on average, 33% less than the initial value). A formula was developed to calculate γ, and the bond force in the straight anchor sections at the yield moment for the reinforcement was determined. Thus, a distributive relationship was established for the anchorage force, the bond force, and the bearing pressure.