Test and analysis of the interfacial bond behaviour of circular concrete-filled wire-arc additively manufactured steel tubes

Interfacial bond behaviour of the circular concrete-filled wire-arc directed energy deposition (DED) steel tubes was investigated experimentally, in which wire-arc DED, commonly referred to as wire-arc additive manufacturing (WAAM), represents a metal 3D printing method. Firstly, a 3D laser scanning was employed to generate the 3D models of the WAAM steel components to obtain the geometric features. A parameter relating to the surface undulation was proposed to evaluate the roughness of the WAAM steel tubes. The results of tensile testing undertaken to obtain the mechanical properties of the WAAM material were summarised. Twelve push-out specimens were tested to obtain the load-slip response and bond strength, while the influence of surface undulation, diameter-to-thickness ratio and interface length was also assessed, respectively. The test results demonstrated that: 1) after reaching the peak load, a slowly descending region appeared until a relatively stable residual load was achieved; 2) the average bond stresses of the push-out specimens were greater than those of the push-out specimens fabricated by conventional steel tubes and even checkered steel tube. Comparisons of the bond strength of the push-out specimens against existing structural design standards indicated the design guidelines of various codes were quite conservative. There needs to consider the influence of the surface undulation of the WAAM steel tube. Finally, based on the nonlinear regression of the test data generated in the present study, an empirical equation was proposed for the prediction of the average bond strength for concrete-filled WAAM steel tubes.