High-temperature material degradation of Q345 cold-formed steel during full-range compartment fires

Abstract

High-temperature material properties are the most important input parameters for the study of the fire resistance of steel structures. Meanwhile, the structural failure of steel structures might occur during compartment fires. This paper presents steady-state experiments on Q345 cold-formed steel (CFS) during the rising and falling temperature periods. The results show that whether in the rising or falling temperature periods, the material properties of Q345 CFS decrease as the load testing temperature increases. Meanwhile, the difference between the test results of the rising and falling temperature periods can not be ignored. Under the same load testing temperatures, the differences in the elastic modulus reduction factors of Q345 CFS between the rising and falling temperature periods are within −0.16 to 0.057; meanwhile, the differences in the yield strength reduction factors between the rising and falling temperature periods are within −0.009 to 0.142. For the fire resistance design, if the material properties during the rising temperature period are used to replace those during the falling temperature period, the calculation results of the fire-induced deformation for Q345 CFS members may be conservative, but the corresponding high temperature bearing capacity will be over-predicted. In addition, the differences in the reduction factors of material properties for Q345 CFS caused by the maximum temperature are significantly lower than those for G550 CFS. Finally, a maximum temperature influence coefficient is introduced and unified expressions are put forward, which can be appropriately used to predict the material properties and stress-strain curves of Q345 CFS during full-range compartment fires.