Creep behavior of Grade 10.9 high-strength bolts under and after fire

As an important component in steel connections, high-strength bolts have a high stress level and may experience creep deformation at high temperatures. This will lead to great deformation and even failure of steel connections, thus affecting progressive collapse resistance of steel structures. This paper experimentally and numerically investigates the creep behavior of 10.9 high-strength bolts under and after fire. The creep strain-time curves at different temperatures and stress levels were obtained using DIC measurement systems. The micromorphology and failure mechanism of high-strength bolts is examined by SEM. The Field & Field creep model is calibrated against test results, and parametric studies are conducted on T-stub connections. The experimental results show that the creep deformation of high-strength bolts is significant at high temperatures, and the creep strain is positively correlated with temperatures and stress ratios. The numerical results show that the Field & Field model is suitable for characterizing the creep behavior of high-strength bolts under fire situation. The fire resistance of T-stub connections is significantly affected by creep-related parameters. It is necessary to consider the effect of creep for predicting the behavior of high-strength bolts and steel connections, ensuring a safe design.</p