Post-fire cyclic behavior of Q460qENH weathering steel under different cooling methods

Monotonic tensile tests and four strain-controlled cyclic protocols were used to examine the post-fire response of Q460qENH weathering steel. The results show that the influence of fire exposure was relatively limited up to 600 °C, whereas the yield plateau, cyclic stiffness and cooling-method sensitivity changed markedly after exposure to 800–1000 °C. Air cooling generally reduced the strength level but improved deformation capacity and produced fuller hysteresis loops, while water cooling enhanced the cyclic strength of high-temperature specimens but reduced ductility and ultimate strain. The calibrated cyclic strength coefficient of the water-cooled specimens was higher than that of the corresponding air-cooled specimens, with the difference becoming more pronounced at higher temperatures. A fixed-modulus Ramberg–Osgood relation was fitted to the L1 skeleton curves for each material condition. The calibrated model achieved R 2 values of 0.921–0.989, with mean MAPE and NRMSE values of 2.00% and 5.00%, respectively. L3 data excluded from calibration were used to assess the transferability of relative skeleton stress levels, yielding a mean absolute relative error of 2.49% and a maximum absolute relative error of 6.39% for the late-cycle stress-amplitude ratio between 1.0% and 2.0% strain amplitudes. These results provide a basis for representing the post-fire cyclic skeleton response of Q460qENH weathering steel.