Performance of belly-shaped concrete filled steel tubular (CFST) columns: Finite element analysis and design methods

Belly-shaped concrete-filled steel tubular (CFST) columns have been extensively used in main load-carrying structures of long-span public buildings owing to their superior mechanical performance and distinctive architectural esthetics. The accurate and simplified method for predicting the axial stability load-carrying capacity is fundamental to the static analysis and design of such composite members. However, for existing design methods, the minimum cross-section of the belly-shaped columns is regarded as the governing cross-section and the design formulas intended for the straight CFST columns with the governing cross-section are usually adopted to calculate the axial stability load-carrying capacity, resulting in overly conservative predictions deviated from actual behavior. Set against the above backgrounds, a finite element analysis (FEA) model was firstly developed to investigate the performance of belly-shaped CFST columns, with its accuracy validated against relevant experimental data. Based on the validated FEA model, the axial load-carrying mechanism of the belly-shaped CFST columns was comparatively analyzed against that of the straight CFST columns and then followed by a comprehensive parametric analysis. Based on the results of the parametric analysis, two calculation methods for the axial stability load-carrying capacity of belly-shaped CFST columns were proposed, i.e., one is based on the Euler buckling equation and another is based on the equivalent straight column method. The proposed methodologies can provide a theoretical reference for the design and practical application of the belly-shaped CFST columns.