Residual behavior of welded hollow spherical joints after exposure to elevated temperatures

Welded hollow spherical joints are widely applied as main connection pattern in space lattice structures. During fire events, structures are inevitably exposed to elevated temperatures. Provided the general appearance of the structure remains satisfactory after a fire, the residual behavior of welded hollow spherical joints in these structures should be accurately estimated to ensure safety. However, the post-fire behavior of welded hollow spherical joints has not been explored in existing studies. Hence, experimental and numerical studies were conducted to reveal the post-fire residual mechanical behavior of welded hollow spherical joints. Seventeen specimens were initially heated to six various preselected temperatures up to 1000 °C and were subsequently cooled down to ambient temperature via two different methods: air cooling and water cooling. Axial compressive tests were then performed, and related mechanical properties, such as axial load-displacement curves, initial axial stiffness, yield loads, load-bearing capacities, ductility level, and strain distribution, were obtained and analyzed. The mechanical behavior of welded hollow spherical joints significantly changed after exposure to temperatures exceeding 600 °C, with phenomena of reductions in stiffness and strength but an increase in ductility level. Furthermore, the influences of different cooling methods were remarkable. A 3D finite element (FE) model was also developed using the ABAQUS software and validated against experimental results. Simplified design methods, based on parametric studies, were proposed to predict the post-fire residual load-bearing capacity and initial axial stiffness of welded hollow spherical joints.