With the increasing demand for structural resilience under extreme fire scenarios, iron-based shape memory alloys (Fe-SMAs) have attracted growing attention as a potential fire-resistant material. However, their mechanical degradation during fire exposure and structural applications remain insufficiently understood. In this study, transient-state tensile and thermal expansion tests were firstly conducted to characterize the stress-dependent strain-temperature evolution and thermal expansion behavior of Fe-SMA. Based on these results, transient-state stress-strain relationships and reduction models for strength and stiffness were established. Although Fe-SMA exhibits more pronounced degradation under transient-state heating than under steady-state conditions, it maintains superior performance at elevated temperatures compared with high-strength steels. Furthermore, transient-state fire tests were performed on five Fe-SMA-bolted T-stub specimens, with grade 8.8 bolted joints as references. The influences of flange thickness, bolt-to-web distance, and bolt diameter were examined. High-strength bolted joints exhibited only 67% of the failure displacement of Fe-SMA-bolted joints. Reducing flange thickness from 12 mm to 8 mm and increasing bolt-to-web distance from 40 mm to 50 mm enhanced fire-induced ductility by up to 84% and 68%, respectively, and increased critical temperature by approximately 12% and 9%. The findings provide experimental evidence and a feasibility assessment for the engineering application of Fe-SMA as a novel fire-resistant material.