Post-fire mechanical properties of Q620 high-strength steel with different cooling methods

Abstract

To evaluate the residual resistance of steel structures after fire, it is important to clarify post-fire mechanical properties of structural steels. Considering that high-strength steel (HSS) is increasingly used in steel structures, it is meaningful and necessary to investigate its post-fire mechanical properties. Therefore, mechanical properties of Q620 HSS exposed to elevated temperatures and cooled with different methods were investigated through experiment. Q620 HSS specimens were heated to pre-determined temperatures, later cooled to ambient temperature. Considering possible cooling environments in actual fire event, three different cooling methods were selected, namely, cooling in air (CIA), cooling in water (CIW) and cooling in fire-fighting foam (CIF). Then, tensile tests were performed to obtain post-fire mechanical properties of Q620 HSS. Test results indicated that exposed temperature and cooling method had significant effects on post-fire mechanical properties. Post-fire mechanical properties of Q620 HSS with CIF were close to those of Q620 HSS with CIA, which were different with those of Q620 HSS with CIW. Moreover, effects of exposed temperature and cooling method on elastic modulus of Q620 HSS could be ignored. Necking at failure of Q620 HSS exposed to elevated temperatures and cooled with different methods was discussed. Post-fire mechanical properties of Q620 HSS were compared with those of HSSs in other strength grades, the mild steels and the stainless steel. Predictive equations were proposed to quantify the effects of exposed temperature and cooling method on post-fire mechanical properties of Q620 HSS.