Experimental study and design of bond behavior in concrete-filled steel tubes (CFST)

Abstract

Steel plate-concrete (SPC) and concrete filled steel tube (CFST) push out test specimens are conducted to study the nature of the bond behavior between the steel tube and concrete and the according contribution of each component (chemical adhesion, micro-interlocking and friction). A total of 10 SPC specimens considering lateral normal pressure applied on the concrete and 18 circular CFST specimens with reversed loading have been carried out, where the surface roughness of the steel tube and the length of the specimens have been considered as variables. The chemical adhesion contributions are obtained through the SPC specimens without normal pressures. The micro-interlocking and friction can be calculated through both the SPC and CFST specimens. The micro-interlocking coefficient concept has been proposed and determined together with the friction coefficient through SPC test specimens with normal pressures. Both the micro-interlocking and friction component contribution to the bond behavior can be determined through the steel tube hoop strain from the CFST specimens and the obtained coefficient accordingly. The bond mechanism of CFST specimen has been systematically and quantitively explained by analyzing the full-history developments of the chemical adhesion, micro-interlocking and friction components. A bond-slip constitutive model considering both the physical significance and prediction accuracy has been proposed and verified, which may promote refined numerical analysis.