Fire resistance of locally produced 500W structural steel bars

Steel has been used for many decades in structural applications because of its good combination of mechanical properties. In recent years in Bangladesh the demand for TMT 500W steel bars has increased profoundly, for its higher strength and good ductility. But fire remains one of the serious potential risks to most buildings and structures. To understand the effect of fire on mechanical properties of steel bars at elevated temperature a locally produced 500W TMT bar of 8 mm diameter has been investigated. Both macroscopy and microscopy were carried out to reveal different zones such as hardened case, soft core and transition zone in the cross-section and microstructure respectively of the steel bars in the as received condition. Finally, high temperature tensile tests were conducted at 500°C, 600°C, 650°C in steady state method at a strain rate of 0.5mm/min and the results at these 3 temperatures were noted. Data generated from the room temperature and high temperature tensile tests were compared. The test results demonstrated that the high temperature severely degrades the tensile strength of the 500W TMT steel bars and they can hardly bear any load at temperature above 600°C. (paper)