Development Length of High-Strength Steel Rebar in Ultrahigh Performance Concrete

Ultrahigh performance concrete (UHPC) is increasingly making its way into the construction field. Characterization of UHPC has therefore received much-needed attention in the research arena. One effective application of UHPC is in combination with high-strength steel (HSS) reinforcing rebar in shallow beams or slabs. However, bond and development characteristics of HSS rebar in UHPC have not yet been investigated. This paper presents the experimental results of the pullout and flexure tests conducted with HSS rebar in UHPC. This work was a part of a larger project to develop a new light-weight UHPC-HSS bridge deck system for a moveable bridge. Because the bridge deck was designed with #10 and #22 rebar as the main reinforcement, only these two rebar sizes were used in the experiments. First, pullout specimens were tested with three different embedment lengths of 8, 10, and 12 times the rebar diameter. Then, from the results of pullout specimens, beam specimens were tested with embedment lengths of 10, 12, 14, and 48 times the rebar diameter for #10 rebar and 14, 16, 18, and 21 times the rebar diameter for #22 rebar. The size of the T-section beam specimens was derived from the size of the rib in the proposed deck system to simulate the actual conditions. The study showed that #10 and #22 rebar develop at embedment lengths of 12 and 18 times the rebar diameter, respectively. The paper also presents a comparison between experimental results and the development length recommendations of ACI 318-08, ACI 408R-03, and AASHTO, demonstrating that the ACI 408R-03 compares more favorably with the test data.