Experimental Study on Residual Mechanical Properties of Bolt-Sphere Joints After a Fire

Through tensile testing of 15 steel bolt-sphere joints and 15 aluminum alloy bolt-sphere joints, influencing rules of material type, high temperature and cooling mode on tensile properties of post-fire bolt-sphere joints were studied, and then failure modes of the joints were determined. According to experimental data, the calculation formula of residual tension capacity of post-fire bolt-sphere joints was presented. Experimental data indicated that (1) decreased extension on the mechanical properties of aluminum alloy bolt-sphere joints after high temperature in the fire was significantly higher than that of the steel bolt-sphere joints; (2) when fire temperature was lower than 800 °C, the tension capacity of steel bolt-sphere joints could be restored by more than 90% after cooling; (3) when fire temperature was lower than 500 °C, the tension capacity of aluminum alloy bolt-sphere joints could be restored by more than 50% after cooling; (4) bolt-sphere joints could still satisfy the requirement of “strong node and weak member” after a fire; and (5) material type and fire temperature were the main factors that influenced post-fire mechanical properties of bolt-sphere joints.