Post-fire mechanical properties of low-alloyed YSt-355-FR (126 % Mo) fire-resistant steel

Growing demand for fire-resistant steel (YSt-355-FR) in structural engineering applications has been reported by virtue of its superior high-temperature strength properties over conventional structural steel at the material and structural levels. The exposure of structural steel members to high temperatures experienced during the fire event led to the alteration in the mechanical properties of structural steel. However, the extent of alteration in the mechanical properties of the fire-exposed structural steel depends on the exposure temperature and cooling conditions. Therefore, the post-fire investigation of fire-resistant steel is necessary for the assessment of the residual capacity and reusability of the structural steel members. In the present study, the post-fire mechanical properties of fire-resistant steel were extracted by conducting the tension test (steady-state) on the 132 heatexposed steel specimens, which were cooled under following conditions: (a) furnace, (b) air, (c) water-jet, and (d) water. The steel specimens were heated between 100 degrees C and 1000 degrees C at 100 degrees C temperature intervals. The test results were discussed in terms of residual strength-, strain-, and stiffness- properties. It was found that the exposure temperature and cooling conditions markedly influence the post-fire strength-, strain-, and stiffnessproperties of fire-resistant steel beyond 700 degrees C, 600 degrees C, and 800 degrees C, respectively. The water-cooled fire-resistant steel exhibits the highest retention of mechanical properties, followed by water-jet-, air-, and furnace-cooled ones. Fire-resistant steel outperforms the majority of structural steels in terms of strength retention in post-fire conditions. The constitutive equations were proposed to predict the post-fire strength and stiffness properties, which is supported by a sound reliability analysis.