COMPARATIVE ANALYSIS ON INTERFACE BOND PERFORMANCE OF HIGH-STRENGTH CONCRETE FILLED SQUARE OR CIRCULAR STEEL TUBE AFTER BEING SUBJECTED TO ELEVATED-TEMPERATURES AND SPRAY COOLING

In order to study the difference of interface bond performance of recycled concrete filled square and circular steel tube (RCFSST, RCFCST) short column after being subjected to elevated temperatures and spray cooling, 22 RCFSST and 22 RCFCST specimens were designed for push-out test, with the variable parameters of maximum temperature, concrete strength, constant temperature time, anchorage length and cooling mode considered. The mechanical failure pattern of specimens was observed, and the mechanical properties such as bond strength, shear bond stiffness and interface energy dissipation of the specimens were compared and analyzed. The results showed that with the increase of the maximum temperature, the difference of the interface bond performance between the two sections of steel tube subjected to elevated temperatures and spray cooling was large, and the performance indexes of circular specimen were better than those of square specimen. The increase of concrete strength could improve the bond strength between steel tube and concrete. The influence of constant temperature time on the bond strength of square specimen was greater, with the increase of constant temperature time, the change rule of shear bond stiffness of specimens with two cross-section was opposite. With the increase of anchorage length, the interface bond strength would be reduced, which had a greater impact on the shear bond stiffness and energy dissipation capacity of the circular specimens. Compared with the natural cooling specimens, the spray-cooled specimens had lower bond strength and shear bond stiffness, and higher energy dissipation capacity.