Post-fire performance of thin-plated stiffened T-stubs after controlled heating and natural cooling

This study experimentally investigates the post-fire residual behavior of thin-plated, stiffened T-stub connections subjected to controlled uniform heating up to 1200 °C, followed by gradual natural cooling to ambient temperature. The influence of temperature, bolt diameter, and the distance between the stem and bolt row (p f ) on strength, deformation capacity, and failure mechanisms is systematically evaluated. The results indicate that plastic resistance (P jRd ) is highly sensitive to temperature, with a pronounced reduction beyond 600 °C, whereas ultimate resistance (P u ) decreases at a significantly lower rate. As a result, the P u /P jRd ratio increases with temperature, indicating a change in structural response at elevated temperatures. The parameter p f has a limited effect on ultimate strength but strongly influences deformation behavior. Increasing pf from 40 mm to 80 mm substantially increases ultimate displacement and ductility. A comparison with existing design approaches shows that AISC and Eurocode formulations provide reasonable predictions but with varying levels of accuracy. The AISC-based model yields an R 2 value of 0.755, while Eurocode Method 1 and Method 2 achieve R 2 values of 0.801 and 0.848, respectively. The proposed formulation demonstrates improved predictive performance, with an R 2 value of 0.961, indicating a higher level of agreement with experimental results. In addition, the proposed reduction factors due to elevated temperature show a strong correlation with experimental data; R 2 values are 0.976 for ξₚ and 0.945 for ξᵤ. Overall, the results confirm that the proposed formulation provides a more accurate prediction of the post-fire behavior of stiffened T-stub connections. • Post-fire behavior of thin-plated stiffened T-stubs was experimentally investigated up to 1200 °C. • Plastic resistance degraded more rapidly than ultimate resistance with increasing temperature. • Stiffeners provided substantially greater resistance gains for specimens with larger p f values. • Proposed temperature-dependent models showed strong agreement with the present experimental dataset.