Influence of Stiffeners on Bond Behavior of Recycled Aggregate Concrete-filled Square Steel Tubes

To solve the problem of insufficient interfacial behavior of recycled concrete-filled square steel tubes (RCFSST), the pull-out test was carried out on 30 RCFSSTs with stiffeners or studs. The core concrete was prepared by using 2 kinds of water-binder ratios and 3 recycled coarse aggregate (RCA) replacement ratios. Through failure modes, load-slip curves, and steel tube strains, the influence of different inner constructions and concrete types on the interface bond behavior were analyzed, and shear strength of specimens with horizontal stiffeners was calculated. Results show that the vertical stiffener and horizontal stiffener can effectively improve the bond strength, residual bond strength, and energy dissipation capacity of RCFSSTs. The composite construction of vertical and horizontal stiffeners has the best improvement effect. The bond strength is 5.4% higher than that of the sum of the 2 constructions. The studs construction only increases the initial bond strength, however, has little effect on the residual bond strength. With the construction reinforced the bond strength of specimens with low water-binder ratio increases more than that of specimens with high water-binder ratio. The bond behavior of RCFSST with 100% RCA replacement ratio is unstable. Compared to the test results, the shear strength calculation of horizontal stiffener specimens in this paper is safer.