Research on residual behavior of tensile stiffened welded hollow spherical joints after exposure to fire

Abstract

Space grid structures are subject to fire like other building structures, but they rarely collapse as a whole after exposure to fire. The welded hollow spherical joints are the main joint types of space grid structures. It is particularly critical to accurately identify the mechanical behavior of welded hollow spherical joints after exposure to fire to confirm whether the grid structure needs reinforcement or demolition for reconstruction. Therefore, the mechanical behavior of tensile stiffened welded hollow spherical joints after exposure to fire without load was studied by experiment. The failure modes of stiffened welded hollow spherical joints after exposure to fire are pull-out failures and oblique splitting pull failures. The initial axial stiffness of stiffened welded hollow spherical joints declines with the increase of exposure temperature, and the cooling method has little effect on it. When the exposure temperature is low, the cooling method has no impact on the load-bearing capacity of the joint. The load-bearing capacity of the air-cooling joints decreases linearly with the progress of exposure temperature, while the water-cooling joints present an opposite trend. The ductility of the air-cooling joints increases rapidly with the growth of exposure temperature, while the water-cooling joints fluctuate up and down. The strain of the tensile stiffened welded hollow spherical joints closely relates to its location. The numerical model of the joint after exposure to fire without load and with load was established, and the model was verified against experimental results. Through the numerical simulation, a method for calculating the residual mechanical behavior of stiffened welded hollow spherical joints after exposure to fire without load and with load was presented.