LAUSR

Abstract To solve the problem of insufficient interface bond strength of concrete-filled square steel tubes (CFSSTs), 16 large CFSST specimens with eight different types of connectors (no additional connectors, built-in studs, built-in circular ribs, built-in vertical ribs, built-in reinforcement cage, and various combinations of the above) were designed for push-out testing. Specimens were constructed using high-strength concrete or high-strength recycled aggregate concrete (RAC). The bond behavior and slip failure mechanism were analyzed by comparing the force-slip curves, slip displacements, and steel tube strains. The bond strength calculation method and bond-slip constitutive relationship of the interface under multiple parameters were obtained. Experiments revealed the following: bond-slip curves for CFSST without additional connectors were composed of an ascending section and a residual section; for tubes with different connectors, the peak values of the curves were higher; the performance-price ratio of studs and circular ribs for improving bond strength was high, and the combined use of studs and circular ribs can work well; the combination of circular ribs and vertical ribs can significantly improve bond strength and energy dissipation capacity; RAC had better bond behavior than normal concrete in HSCFSST without additional connectors or built-in vertical ribs. The predicted force-slip curves agreed well with the test curves, providing a theoretical basis for CFSST applications.