Mechanical Performance of Welded-Bolted Hybrid Connection Joints Between Fire-Resistant Steel Columns and Beams Under Fire

The mechanical properties of connection joints and the fire protection design of steel structures are crucial for ensuring structural safety. The utilization of fire-resistant steel in steel structure joints represents a novel approach to enhance fire resistance. In this study, a test on two welded-bolted hybrid connection joints between fire-resistant steel columns and beams was conducted considering both ambient and elevated temperatures. Through an analysis of the failure modes, load-vertical displacement curves, moment-rotation curves, and load-strain curves of the joints, key parameters such as the ultimate bearing capacity, ductility, and deformation capacity were determined. The test results showed that the ultimate bearing capacity of specimen Joint-2-ET at an elevated temperature is 81.14% that of specimen Joint-1-AT at an ambient temperature. While the temperature increases during fire had little effect on the initial stiffness of the joint, it significantly reduced the rotation capacity and ductility of the joint. A finite element model of the joints was developed using ABAQUS software, and its accuracy was validated by comparing the results with the experimental findings. Additionally, a parametric analysis was conducted to explore the effects of temperature and heating region on the mechanical performance of these welded-bolted hybrid connection joints. The outcomes of this research provide valuable insights for engineering applications involving welded-bolted hybrid connection joints between fire-resistant steel columns and beams.