Post-Fire Mechanical Properties of Steel S900MC

This paper discusses mechanical properties after one heating and cooling cycle using experimental tests. The material tested was steel S900MC, which has the nominal yield strength of 900 N/mm2. The specimens were tested with being first heated up inside a furnace to a pre-defined temperature, then cooled down to the room temperature. I n order to study the effects of cooling rates on mechanical properties, two different cooling methods were used: cooling inside furnace, and cooling in the air.

The results indicated a clearly reduction of the strength when the steel was cooled from the temperature above 500 °C. The steel reduced 40% of its yield strength after cooled from 700°C, while only 20% remained when cooled from 900°C. The elastic modulus was regained to its original value after the steel was cooled from temperatures below 500°C, whereas about 80% was regained when the steel was cooled from 900°C. Cooling temperatures between 700°C and 900°C produced a large scatter among all the mechanical properties. The cooling rate did not affect the mechanical properteis when the maximum temperature remains below 700 °C before the cooling starts. However, when exposed to an elevated temperature above 700°C the effect is visible. The air-cooled specimens had higher strength and lower ductility than furnace cooled specimens. The results of this study will help to evaluate the load-bearing capacity and reusability of the steel members after fire-exposure.