Fire Behavior of Ultra-High Strength Concrete Filled Steel Tubular Columns Under Non-uniform Heating

This paper presents a numerical study of concrete-filled steel tubular (CFST) columns with square high strength steel tube (HSS) and ultra-high strength concrete (UHSC) under fire. CFST columns with high strength materials allow reducing material quantities and loads on foundations in buildings by reducing member sizes. However, there have been few studies on CFST under non-symmetrical fire loading with normal strength materials and none with ultra-high strength materials. In this paper, the columns are studied under non-uniform thermal exposure conditions simulating a realistic fire scenario in the building. The finite element (FE) models capture the temperature dependent material properties of the high strength materials and the effect of the thermal contact at the interface between the HSS tube and UHSC core. The numerical results are compared with experimental data on specimens exposed to uniform and non-uniform fire, showing good agreement in terms of temperature distribution, axial displacement, and failure time. Parametric analyses are then conducted to investigate the influence of various factors on the fire performance of the CFST columns including the material properties and the fire and loading conditions. Overall, the validated numerical model can be used to simulate axially loaded CFST columns under non-uniform heating and derive fire design methods for these members. The parameters which influence the behavior of the columns are discussed and recommendations are provided for developing design guidelines. Improved understanding of fire behavior of these members can support sustainable and efficient modular construction.