Bond-slip response of ultrahigh-strength steel bars with spiral grooves embedded in reinforced concrete

This paper examines the results of bond-slip experiments on reinforced concrete with embedded ultrahigh-strength steel bars with spiral grooves (UHSSBs). It includes the analysis of twenty-seven pullout specimens with different concrete compressive grades and embedment lengths to evaluate the bond responses. The rotations of UHSSBs are recorded during pullout tests to describe the theory behind the bonding mechanism of UHSSBs embedded in reinforced concrete. According to the test results, the specimens with higher concrete compressive strengths exhibited higher bond strengths. Moreover, all the specimens with different embedment lengths exhibited similar trends i.e., the bond strength decreased to different degrees with increasing embedment length. After the mechanisms of the bond behavior were described, a new analytical model was proposed to analyze the bond strengths of UHSSBs embedded in reinforced concrete under monotonically increasing tensile loads, taking into account the spiral characteristics of UHSSBs. Based on the model introduced, the parameters (i.e., the concrete strength and embedment length) affecting the analytical model were discussed, and the calculated bond strengths agreed well with the measured values, which indicated that the values could be obtained quickly and offered a reference for further practical structural design.