Study on straight development length of tensile threaded bars in high-strength reinforced concrete members

The main purpose of this study is to investigate fundamental bonding behavior of high-strength reinforced concrete adopting tensile threaded bars and to verify the applicability of the formula of the straight development length as recommended in ACI 318-14 on tensile threaded bars embedded in the high-strength reinforced concrete. Additionally, appropriate surface geometric properties of threaded bars shall be defined for ensuring enough bond strength. This study conducts 42 sets of bonding tests, of which 2 sets adopt plain bars as the control group, and the remaining sets adopt threaded bars. The primary study parameters include the concrete compressive strength, the relative rib area of threaded bars involving the rib height and rib spacing, and splitting index. The test results show that when the concrete strength is limited to 70 MPa by ACI 318-14 recommendations, all sets of threaded bars can provide the expected bond strengths. However, when the concrete strength is not limited to 70 MPa, only the threaded bars with relative rib area exceeding 0.17 can provide the expected bond strengths. In addition, the correlation between relative rib area Rr and the effectiveness of the bonding performance is approximately perfect.