Performance of Axially Restrained Hollow and Concrete Filled Oval Steel Columns Subjected to Hydrocarbon Fire

This paper represents the outcomes of the first research in the world involving experimental and validated theoretical study to investigate the performance of axially restrained steel columns with hollow and concrete filled elliptical sections subjected to fire. The test programme involved 9 hollow and concrete filled columns with 200 × 100 × 8 mm oval section yielding a slenderness λ=51 and tested under the severe hydrocarbon fire curve. The 1800 mm columns were tested under loading ratios = 0.2, 0.4 and 0.6 of the ultimate strength. The paper presents the obtained experimental results including measured axial and lateral displacements, restraint forces and failure time. A three-dimensional model was built using the finite element method (FEM) and was validated using the obtained tests results. By using variable with temperature thermal expansion coefficient and the EC3 thermal parameters, the finite element model demonstrated an excellent agreement with test results of failure temperatures, failure modes, axial displacements and generated axial forces. The verified finite element model was used to conduct a parametric analysis involving a range of parameters of loading level and slenderness. The study has shown that the concrete filled sections have demonstrated an improved fire resistance when compared to the hollow sections under low loading ratios. The research indicates that imposing axial restraint has reduced the fire resistance of columns by approximately one third on the time domain. The study has also shown a non-linear relationship between the loading ratio and slenderness of elliptical columns and that the load ratio has more effect on fire resistance of columns with high slenderness.