Experimental investigation and analysis on anchorage performance of 635 MPa hot-rolled ribbed high strength rebars

Abstract

Due to the rapidly increasing urbanisation in China, the energy consumption of buildings and infrastructures has increased; this has resulted in environmental problems such as excessive carbon emissions. Increasing the strength of steel rebars enables manufacturers to use less steel and save more energy. The micro-alloyed 635 MPa hot-rolled ribbed high strength rebars (HRHSR) offer the advantages of high strength, good ductility, and low costs, compared to ordinary rebars. Bond anchorage is one of the key problems that limits the promotion and application of 635 MPa HRHSRs in practice. In this study, the bond properties of 635 MPa HRHSRs embedded in concrete subjected to monotonic loads were investigated. A total of 120 specimens, which consisted of 60 simple-anchored and 60 hooked-anchored specimens, were subjected to direct pull-out tests to evaluate the effects of anchorage length, hoop ratio, concrete cover, rebar diameter, concrete strength, and anchorage types on the anchorage feature. Meanwhile, the mechanical properties and failure modes of 635 MPa HRHSRs were also analysed. The results demonstrated that the concrete compressive strength, cover size, anchorage length, and stirrups ratio had a positive influence on the ultimate bond strength, whereas the bar size had a negative influence on the ultimate bond strength. Furthermore, four typical failure modes were analysed, including rebar yielding, concrete splitting, concrete crushing, and rebar rupturing, which occurred during the pull-out tests. Thereafter, a modified equation for calculating the ultimate bond strength of 635 MPa HRHSRs in concrete was derived based on the mechanical model and further verified using the test data. This study is expected to be beneficial in promoting the widespread application of 635 MPa HRHSRs and enabling resource savings in the future.