Experimental and Numerical Investigations of CFCST-Gusset K-Joints

Among the various connection forms of tubular joints, tube-gusset joints are used widely in practical engineering because of their simple structure and convenient manufacturing processes. It has been demonstrated that filling the chord with concrete is an effective strengthening method when the bearing capacity of the tube-gusset joints is insufficient. However, few studies have investigated the failure mechanism, force transmission mechanism, and bearing capacity calculation model of concrete-filled circular steel tubular (CFCST)-gusset joints. In this study, four CFCST-gusset K-joints and a circular hollow section (CHS)-gusset K-joint were tested experimentally. The tests were performed considering parameters such as the chordal diameter to thickness ratio (γ), web to chord diameter ratio (β), web to chord wall thickness ratio (τ), and gusset plate to web thickness ratio (tg/ti). The finite-element method (FEM) was employed to analyze the influence of these parameters on the mechanical behavior of the CFCST-gusset K-joints. The results indicated that the CFCST-gusset K-joints exhibited two distinct failure modes: web member and gusset plate failures. However, the CHS-gusset K-joint failed due to excessive plastic deformation of the chord tube. The ratio tg/ti is the most critical factor affecting the failure patterns and bearing capacity of CFCST-gusset K-joints. In practical engineering, tg/ti≥2 is ensured to prevent joint damage. The least-squares method was used to fit the bearing capacity computational model of the CFCST-gusset K-joints. The regression validation verified the high accuracy of the proposed model.