Behaviour of restrained high strength steel columns at elevated temperature

High strength steel has been widely used in various types of structures due to its merits of high strength and good ductility. However, high strength steel structures are vulnerable to fire hazards as the strength and stiffness of the steel deteriorate rapidly at elevated temperature. Presented in this paper are the investigations on the behaviour of restrained high strength steel columns at elevated temperature obtained from full-scale fire tests and finite element analyses. In the fire tests, applied load and restraint stiffness are two key factors to be examined. Column responses such as the axial displacement, deflection at column middle height and axial force induced by thermal expansion associated with temperature evolution were reported. Column buckling and failure temperatures were determined based on the criteria of the axial displacemen t and lateral deflection of the specimens at elevated temperatures. The test results show that both the applied load and restraint stiffness have considerable influences on fire resistances of high strength steel columns. It was observed that the columns with only axial restraints failed by flexure buckling about the weak axis whereas the columns with both axial and rotational restraints and subjected to large magnitude of the applied load failed by flexural torsional buckling. Finite element analyses were conducted to simulate the fire responses of the test specimens and the obtained numerical results are found to be reasonably agree with the test data. Parametric studies via finite element analysis were carried out to quantitatively determine the effect of applied load, restraint stiffness and slenderness ratio on fire resistance of high strength steel columns.