Modeling thermo-mechanical behavior of concrete-filled steel tube columns with solid steel core subjected to fire

Concrete-filled steel tube columns with solid steel core are increasingly used in high-rise building practice due to their high load-bearing capacity and exceptional structural fire behavior. Simulating the structural fire behavior of these innovative composite columns by means of advanced numerical models is a promising tool to achieve an enhanced understanding of the basic thermo-mechanical behavior observed in costly full-scale fire tests, and eventually, to partially replace them. Moreover, the data necessary for the development of a simplified fire design method can be compiled from a parametric study with such models. This paper presents an advanced nonlinear Finite-Element-Method model that incorporates complex experimental calibration data and therefore can robustly simulate various full-scale fire tests of this type of composite columns. Furthermore, tracking in the model the load share redistribution processes between the different components, confirms the innovative design concept of the structural fire behavior of this type of composite column. Finally, a simplified model version that qualifies for partial replacement of full-scale fire tests or use in both a parametric study and advanced structural design is presented and conditionally validated.