Hysteretic performance of structural steels after exposure to elevated temperatures

This paper presents both experimental and analytical investigations on the hysteretic behaviour of normal strength and high strength structural steels after being exposed to elevated temperatures. The test parameters include the highest temperature experienced, the cooling method and the loading protocol. The metallographic analysis is conducted to study the change of micro structure after elevated temperature exposure. The test results show that the yield strength of Q355 and Q620 steels cooled in the air decreases up to 21% and 45%, respectively; while the energy consumption capacity decreases up to 25% and 42%, respectively. For specimens cooled in water, the energy consumption capacity of Q355 increased by 39% when the strain level was 0.6%, while that of Q620 decreased by 21% at the same strain level. A hysteretic model for steels after being exposed to elevated temperatures is proposed by regression analysis, where the key coefficients are calibrated from the experimental data. The proposed model captures well the hysteretic behaviour of both normal and high strength steels after exposure to elevated temperatures, which provides the basis for the post-fire seismic performance assessment of steel structures.