Theoretical and Experimental Study on the Bond-Slip Relationship in Prestressed CFST Beams

Concrete-filled steel tube (CFST) beams are widely used in civil engineering, especially for bridges and tall buildings, because of their strength, stiffness and durability. Good bonding at their interface is essential for ensuring that steel and concrete can work well together. However, if interfacial slippage does occur it not only hinders the plasticity of a beam's performance in full section but also weakens its strength and stiffness. To study the mechanism of slip occurrence and its impact, eight prestressed CFST rectangular beams were tested under monotonic loading. Slippage was measured during the entire loading procedure. Based on the elasto-plastic theory, a nonlinear finite element model, considering slippage is developed in this paper. The results show that slippage occurred when the concrete began to crack. This plays an important role in the overall performance of a beam after the steel has yielded. The maximum slip occurred near the section of quarter-span. To some extent, the slip curves generated by this model agreed with the test results, and it could be used to predict the bending capacity of prestressed CFST beams.