Retention Factors of High-Strength and Stainless-Steel Bolts during and after Furnace Fire

Stainless steel bolts are increasingly used in the semirigid connections due to their superior behavior to high-strength bolts in terms of durability, ductility, and fire resistance. Their thermomechanical properties have been implemented using a number of steady- and transient-state tests. However, their retention factors at a given temperature present a significantly scattered distribution between different previous tests, so their fully fire-induced behavior needs to be investigated considering the effects of multiple factors at a statistical level. Accordingly, their residual properties characterized by reduction factors are first compared in combination with fire-resistant bolts during or after fire according to the previously published studies. Consequently, stainless steel bolts, featuring the pronounced ductility at ambient temperature, have more significant retention of material stiffness and strength than high-strength and fire-resistant bolts beyond 600°C. Finally, the codified strength retention factors of high-strength bolts during fire, confined to an extremely specific test without response to a consistent database, are not always conservative when used for interpolation on bolts with other property classes, and the standardized reduction factors of stainless steels are hardly accurate enough for those of stainless steel bolts exposed to furnace fire. Thus, the temperature-dependent reduction models with a guaranteed rate of 95%, the prediction accuracy of which is strikingly improved compared with the commonly codified elevated temperature reduction factors in EN 1993-1-2 and AISC 360, are statistically proposed for high-strength or stainless steel bolts during and after fire. This factor contributes to the safety of structural fire resistance without highly conservative prediction.