Influence of Cross-Section Type and Boundary Conditions on Structural Behavior of Concrete-Filled Steel Tubular Columns Subjected to Fire

Composite columns consisting of steel hollow sections filled with concrete offer numerous advantages including high fire resistance. However, there are limited provisions for fire design of these columns, and current European code provisions yield unconservative fire resistance in cases of composite columns having relative slenderness greater than 0.5. To overcome the current knowledge gaps, a set of fire-resistance experiments was carried out on a large number of concrete-filled steel tubular columns (CFST). The test variables in the experiments included cross-section type and size, column slenderness, and the support conditions of the CFST columns. From these tests, detailed response parameters, including the evolution of cross-sectional temperatures, axial displacements, lateral deflections, fire-induced axial forces, and failure times, were evaluated. Results from the analysis clearly indicate that cross-sectional shape, support conditions, and column slenderness have significant influence on the fire behavior of CFST columns. Specifically, the axial stiffness reduces the fire resistance of CFST columns, whereas the rotational stiffness increases their fire resistance. Furthermore, CFST columns with an elliptical cross section provide higher fire resistance than equivalent square-shaped or rectangular-shaped columns under certain boundary conditions.