Two approaches for modeling CFST columns under fire conditions

The paper presents a study on the advanced nonlinear analysis of concrete-filled steel tube (CFST) columns at elevated temperatures. Two computationally efficient approaches are analyzed: modeling CFST columns using the concentrated plasticity element based on the generalized plasticity material model (GP model) and using the fiber-based distributed plasticity beam–column element based on the displacement formulation. The GP element is for the first time used for fire analysis of columns with rectangular and circular cross-sections and the formulation is extended to consider additional reinforcement bars. The applied modeling with both elements follows, where possible, the recommendations of the second generation of the Eurocode 4 standard. The applicability of the optimized cross-section discretization schemes in nonlinear fire analysis with fiber element is also investigated. Through extensive validation studies, the results of the two approaches are compared with the available experimental and numerical results. This comparison includes not only the determination of the critical fire exposure time but also the quality of the whole force–displacement response, deformed shape and aspects of computational efficiency. Finally, the benefits and limitations of one approach and the other are discussed and summarized.