Seismic Performance of Reinforced Concrete Beams with Proposed Lap-Spliced Intermediate Hoops

Two types of lap-spliced intermediate hoops were proposed to address the construction difficulty encountered for conventional intermediate hoops or stirrups used in the plastic hinge regions of beams of special moment-resisting frames. In the proposed type one hoops, a set of U-bars was lap-spliced to the other set of U-bars. The U-bar set was formed by multiple U-bars welded together by the longitudinal holding wires. Weldable steel wire reinforcement was used. In the proposed type two hoops, two three-dimensional stirrups were lap-spliced to form two intermediate hoops. The lap-splice length was based on the Class B tension lap splice of ACI 318. Three full-scale beam specimens, including two specimens with the proposed lap-spliced intermediate hoops and one control specimen with conventional intermediate stirrups, were tested using lateral cyclic loading. Test results showed that the specimens with the proposed lap-spliced intermediate hoops exhibited better drift capacities, energy dissipation ability, and moment strength than the control specimen. The proposed lap-spliced intermediate hoops were more effective in restraining the buckling of longitudinal bars than the conventional closed stirrups.