Performance of concrete-filled RHS columns exposed to fire on 3 sides

The behaviour of concrete-filled steel tubular (CFST) columns subjected to uniform fires has been well studied over the past few decades. However, knowledge of the performance of concrete-filled rectangular hollow section (RHS) columns exposed to fire on 3 sides, which is a common scenario in practice, is limited. Hence, this paper presents an experimental and numerical study into the response of concrete-filled RHS columns subjected to 3-sided fire exposure. Three full-scale concrete-filled RHS columns, two of which were exposed to fire on 3 sides and the other on 4 sides, were tested to failure. The temperature distributions, axial displacements, lateral displacements and failure modes were all recorded and discussed. Following the experiments, a sequentially coupled thermal-stress numerical model was developed, featuring heat transfer analysis and stress analysis. The FE model was validated against the test results, and used to assist in the understanding of the observed failure mechanisms and to extend the investigated range of key parameters. These parameters included load ratio, load eccentricity, cross-sectional dimensions, slenderness ratio, steel ratio and strengths of the constituent materials. It was found that the load ratio, cross-sectional dimensions and load eccentricity have a significant influence on the fire resistance. Based on the results of the parametric studies, a simplified design formula was developed for predicting the fire resistance of concrete-filled RHS columns subjected to 3-sided exposure. Furthermore, a reduction factor method was proposed for the design of concrete-filled RHS columns exposed to 3-sided fire, based on fire safety design methods for concrete-filled RHS columns in uniform fire, which may be more convenient for engineering applications.