Post-fire ultra-low cycle fatigue properties of high-strength steel via different cooling methods

Abstract

To accurately evaluate the effect of cooling methods on the residual seismic capacity of Q690 high-strength steel (HSS) after fire, an experimental study was undertaken to investigate the post-fire ultra-low cycle fatigue properties of Q690 HSS. Accordingly, Q690 HSS was heated to 600, 700, 800, and 900 °C and cooled using three methods: air, water, and firefighting foam. Fatigue tests on Q690 HSS subjected to heating and cooling treatments were performed, and cyclic stress–strain curves of Q690 HSS were obtained for different temperatures and cooling methods. Based on the test results, the effects of the exposure temperature and cooling method on the ultra-low cycle fatigue properties of Q690 HSS were analysed. Moreover, the microstructure and fracture morphology of Q690 HSS were recorded and analysed. Finally, a method to predict the fatigue life of Q690 HSS subjected to different elevated temperatures and cooling methods was proposed.