STUDY ON THE BOND STRENGTH OF CONCRETE FILLED SQUARE STEEL TUBES UNDER FREEZE-THAW CYCLES ENVIORONMENT

In order to study the bond performance of concrete-filled steel tubes under freeze-thaw cycling environment, 19 groups of 57 concrete-filled square steel tubular short column specimens were designed and manufactured, and the push out tests were carried out on these specimens after freeze-thaw cycle. The load slip curves of the specimens were obtained. The composition of the bond force of concrete-filled square steel tubes and the effects of the number of freeze-thaw cycles, the slenderness ratio of members and the width thickness ratio of steel tube on the bond strength were analyzed. The test results show that the load slip curve of CFST after freeze-thaw cycle is generally similar to that at room temperature, including non-slip section, rising section, falling section and residual section. The bonding action in the non-slip stage is provided by the chemical bonding force, and the bonding action after slip is provided by the friction and mechanical biting force. Under the condition of test parameters, the bond strength of concrete-filled square steel tubes decreases in a power function with the increase of the number of freeze-thaw cycles, decreases linearly with the increase of the slenderness ratio of the member, and decreases exponentially with the increase of the width thickness ratio of the steel tube. Based on the test results, the calculation formula of bond strength of concrete-filled steel tubes after freeze-thaw cycle is proposed, with the calculation results generally consistent with the test results.