Residual performance of compression stiffened welded hollow spherical joints after exposure to elevated temperatures

The post-fire residual behavior of the joints and their accurate identification are critical issues for the assessment of the fire damage in the commonly used grid structures. Accordingly, it will be determined, whether the structure is directly used, disassembled, or used after repair. In this paper, the residual performance of compression stiffened welded hollow spherical joints after a fire is studied using the methods of air cooling and water cooling. The failure mode, load-displacement curves, and residual mechanical properties of the joints are analyzed. The results show that the residual performance of the joints after a fire is mainly related to the exposure temperature and the cooling mode. In air-cooled joints, the initial axial stiffness and bearing capacity decrease with the increase of exposure temperature, while the ductility increases significantly. In water-cooled joints, the initial axial stiffness and ductility decrease with the increase of exposure temperature, and the bearing capacity shows a decreasing trend before 500 °C and gradually increases after 500 °C. When conducting the FEM simulation of the experimental specimens, three-dimensional hexahedral elements were adopted with the relationship of the steel material after elevated temperature consisting of a combination of straight lines. The validity of the FEM model was verified by comparison with the experimental results. Based on the results of the parametric analyses, a calculation formula is proposed for predicting the residual bearing capacity and initial axial stiffness of compression stiffened welded hollow spherical joints after a fire.