Mechanical analyses and calculation methods of axially-compressed square concrete-filled steel tubular columns with void defects

This paper clarifies how void imperfections affect the axial compressive response of square concrete-filled steel tubular (SCFT) short columns by establishing the confinement zoning pattern and critical void fractions for the infill concrete under different void arrangements. A finite element (FE) model for axially loaded SCFT short columns is developed, explicitly incorporating the influence of internal voids on the passive restraint provided to the concrete core. The governing mechanisms through which void defects alter the load–shortening curve, failure patterns, and cross-sectional stress field of axially compressed SCFT short columns are systematically examined. Additionally, a predictive method for estimating the axial compressive capacity of SCFT short columns is put forward, which takes into account the confinement morphology of the concrete core in the presence of voids. The findings reveal that both the void ratio and the spatial arrangement of the voids exert a profound impact on the mechanical response of the infill concrete and the square steel tube. As the void ratio increases from 0% to 1.0%, the maximum percentage reduction in axial compressive capacity of SCFT short columns grows up to 41.2%. Notably, the presence of three- and four-sided voids has a significantly more pronounced effect on axial capacity compared with other void patterns.