Behavior of welded hollow spherical joints after exposure to ISO-834 standard fire

Welded hollow spherical joints are extensively used as a connection pattern in space lattice structures. Provided that structural collapse does not occur after a fire, a reliable evaluation of the residual performances of the structures is necessary to decide whether the structures should be dismantled, repaired, or directly reused. Thus, understanding the post-fire residual behavior of welded hollow spherical joints, which act as key connection elements, is crucial for fire damage assessment of the space lattice structures. In this paper, experimental and numerical studies were conducted to reveal the residual structural behavior of welded hollow spherical joints after fire exposure. Axial compressive tests were performed on eight joint specimens after exposure to the ISO-834 standard fire (including both heating and cooling phases), and three highest fire temperatures, i.e., 600 °C, 800 °C, and 1000 °C, were considered. The temperature distributions in the specimens during the heating and cooling process and the related mechanical behavior of the specimens, such as axial load-displacement curves, initial axial stiffness, yield loads, load-bearing capacities, ductility level, and strain distributions, were obtained and analyzed. Finite element analysis (FEA), including both heat transfer and stress analysis, were also developed using the ABAQUS software. Having validated the FE models against the experimental results, a design method was proposed on the basis of parametric studies to predict both the residual load-bearing capacity and initial axial stiffness of welded hollow spherical joints after fire exposure.