Jincheng Zhao

Experimental studies of the behaviour of unprotected steel frames in fire

Abstract The deformation behaviour of unprotected steel framed structures exposed to real fire conditions has been studied experimentally and theoretically. A total of three tests on steel frames under different load level and different heating process are conducted, all the tested frames are single span and single story. In order to simulate a real fire condition, heating is attained by a specially built gas furnace. Behaviour of each tested frame in fire is described and comparisons are made between fire test results and results calculated by a 2D finite element computer program—NASFAF developed in the paper. The secant stiffness matrix which relating the total element displacements to the corresponding total element nodal forces is used in developing the program and the effects of geometrical non-linearity, “softening” of material at elevated temperature, gradual penetration of inelastic zone both along and across each member, non-uniform distribution of temperature are all taken into consideration. Creep effect is considered in an approximate way in the temperature-dependent stress–strain curves of the material.

Dynamic mechanical behaviour of Q345 steel at elevated temperatures: experimental study

Abstract The quasi-static compression and impact experiment of Q345 steel by the MTS material testing machine and SHPB (Split-Hopkinson Pressure Bar) testing technique has been carried out. It aims to study the Q345 steel’s mechanical properties at elevated temperatures under different strain rates. The experimental results show that, at normal temperature, the dynamic strength of the Q345 steel is markedly higher than that under the quasi-static state. It displays an obvious strain rate strengthening effect. With the ambient temperature rising, the plastic stress decreases below 400°C but increases between 450 and 600°C, while it displays a strain rate strengthening effect below 400°C and strain rate softening effect between 450 and 600°C. Based on the experimental data, a constitutive model used for structure analysis under impact loading was determined.