Bonding properties of UHPC-high strength rebar based on beam test

To study the bonding properties of high-strength steel bars and ultra-high-performance concrete (UHPC), nine groups of lap beams were designed and fabricated. The influences of specific variables on the bonding properties were analyzed, including lap length, steel fiber volume content, and mechanical anchoring measures. The experimental results show that the tensile steel bars in the lap section of the lap beams connected with UHPC have better performance on the bonding properties with concrete. Increasing the lap length promotes peak load but the average bonding strength of the lap beams on the contrary. With the increase of steel fiber volume content, the peak load and bond strength of the lap beams increase. Mechanical anchoring adopted lap beams show a higher peak load and bonding strength, where bent hooks treated lap beam shows the highest enhancement, with peak load and bond strength improved by 212.4% and 199.4%, respectively, and it is worth mentioning that the hooked lap steel bars yielded. Based on the equilibrium condition of axial force and bending moment at the peak point, the maximum tensile stress of the steel bar in the lap beam was calculated. A calculation method of the average bonding strength between the steel bar and UHPC was then established. The proposed method calculation results were compared with the centre pull-out test and brace lap test results subsequently.