Experimental study on mechanical properties of high strength steel S900MC at elevated temperatures and after a heating-cooling cycle

The increased use of high strength steel (HSS) in building construction and other civil engineering applications imposed the need for studying its material mechanical properties, and properties at elevated temperatures and after a heating-cooling cycle. Currently, the mechanical properties at elevated temperatures provided in design codes such as EN 1993-1-2 are based on the results tested on mild steel. No rules are provided on the post-fire mechanical properties of HSS. In addition, few studies on the mechanical properties of this particular steel at elevated temperatures and after a heating-cooling cycle. The test specimens are manufactured using water cutting technique from a hot-rolled plate. For the determination of the mechanical properties at elevated temperatures, transient-state and steady-state testing methods were used. Whereas for the post-fire mechanical properties, the specimens were first heated up inside a furnace to the preselected target temperature, then cooled down to room temperature either inside a furnace or in the air to simulate the different cooling rate. In all cases, the specimens were tested on the universal testing machine at elevated temperatures or after a heating-cooling cycle. The mechanical properties are derived from the stress-strain curves measured in the test. In addition reduction factors and reserve (retention) factors of mechanical properties are calculated at elevated temperature and after exposure to fire, respectively. The results are compared with those presented in the EN 1993-1-2 and literature studies on other grades of HSS. Besides, based on the mechanical properties determined from this experimental study, new equations are proposed to predict degradation of mechanical properties at the elevated temperatures and after a heating-cooling cycle. The results of material mechanical properties obtained in this study will help to evaluate the loading-bearing capacity of steel members made of HSS at the elevated temperatures and reusability of the steel members after exposure to fire