Structural Behavior of CHS T-Joints Subjected to Static In-Plane Bending in Fire Conditions

Abstract

Fire resistance of steel joints is always a major concern in the design of steel structures under extremely hazardous conditions. However, for circular hollow section (CHS) joints in fire conditions, little information is available, especially for T-joints. To gain more insight into the static behavior of CHS T-joints in elevated temperatures, experimental and numerical studies were conducted on selected T-joints subjected to in-plane bending. The failure modes and ultimate strength of the joints subjected to different temperatures were investigated and compared to the corresponding joints at ambient conditions. Within the range of investigated parameters, at 700°C, the joint strength was reduced to 22.1% compared to the corresponding joint at ambient temperature. Furthermore, it is observed that at high temperatures, a change occurred in the failure mode of the joints. Cracks formed around the center weld toes before the joints reached excessive deformation, which subsequently affected the joint postyield hardening performance. To understand the initiation of the cracks, a material test was performed. The fracture strains of the heat-affected zone of the chord material beneath the center weld at corresponding temperatures were determined. The fracture strains were included in subsequent finite-element (FE) validation models. The verified finite element analysis models were used to analyze the structural behavior of CHS T-joints at elevated temperatures, such as strain, stress, load path, and effect of fracture strains, to gain insight into the failure mechanism of the joints.