INTERFACE BOND BEHAVIOUR BETWEEN CIRCULAR STEEL TUBE AND LIGHTWEIGHT AGGREGATE CONCRETE

To ascertain the nature of the interface bond behaviour of lightweight aggregate concrete-filled steel tubes (LACFSTs), 27 specimens were tested by push-out loading and four of them were subjected to repeated push-out loading.Influence factors such as lightweight aggregate concrete strength, concrete vibration and curing method, steel surface conditions, slenderness ratio, and diameter-to-thickness ratio were considered.The bond slip process and strength were analysed and a formula was proposed to calculate the bond strength of the LACFSTs.The results show that the bond-slip curve can take one of two forms: one with an obvious peak, the other without, and each one manifests three different trends after reaching ultimate load.According to the test results, the bond strength is independent of the lightweight aggregate concrete strength.Higher diameter-to-thickness ratios cause a reduction in the bond strength.A good quality of concrete vibration and curing can improve the bond strength.The bond strength after the first of the repeated push-out tests is the largest.In the same push-out direction, the bond strength decreases as the push-out time increases, and the load-slip curves are similar among all samples tested.The comparisons between test results and calculations show that the proposed formula has a good accuracy.