Fire behaviour of fire-protected concrete-filled steel tubular columns

Abstract

This study investigates the fire behaviour of fire-protected concrete-filled steel tubular (CFST) columns through experimental, numerical, and analytical approaches. Fire tests were carried out on the circular and square CFST columns, to obtain the temperature distribution, fire resistance and load-bearing capacity. The results revealed that concrete temperatures were much lower than steel tube temperatures. At a depth of 100 mm, the concrete temperature was around 20 % of the steel tube temperature, regardless of fire protection. The steel tube exceeded 600 °C at the fire resistance. Fire protection significantly reduced CFST column temperatures and improved fire resistance. A finite element model was established to accurately simulate the fire behaviour. A parameter analysis based on the numerical model showed that thicker steel tube and larger column diameters effectively reduce the temperatures within the columns, while internal concrete temperature drops rapidly with depth, independent of fire protection. Additionally, a simplified analytical method was developed to predict the temperature field, applicable when the thermal resistance of fire protection ranges from 0 to 0.4. Moreover, a simplified method for determining the load-bearing capacity of fire-protected CFST columns under fire conditions was proposed. Based on the analytical method, the synergistic effect is negligible since the separation between the steel tube and concrete. The proposed methods showed great agreement with experimental results, providing a practical tool for assessing the fire performance of CFST columns.