Unified Analytical Model for Circular Confined Concrete Stub Columns with Solid, Hollow, and Double-Skin Tubular Column Sections under Axial Compression

Abstract The design of circular concrete columns confined by steel or fiber-reinforced polymer (FRP) tubes critically depends on the accurate estimation of the stress state within both the concrete core and the confining materials (steel and FRP). A precise understanding of these stress states enables the development of reliable stress–strain relationships and their ultimate conditions. Although numerous design equations and analytical models exist for various types of confined concrete columns, a unified framework is not available in the literature. This study addresses this gap by proposing a unified analytical model applicable to six distinct types of circular confined concrete columns: double-skin steel tubular columns, hollow steel tubular columns, solid steel tubular columns, double-skin steel-FRP tubular columns, hollow FRP tubular columns, and solid FRP tubular columns. The proposed model incorporates the nonuniform distribution of lateral stresses in the confined concrete core, a biaxial stress state, the local buckling effects of steel tubes, and the inherent nonlinear behavior of filament-wound FRPs with arbitrary fiber orientations. To validate the proposed model, full-range axial stress (load)–strain predictions are compared with 43 experimental results across all six column types. Furthermore, an experimental database comprising 203 specimens is compiled and used to compare the peak load predictions of the proposed model with those from 17 existing studies (6 design codes and 11 analytical models), and the comparisons reveal that the predictions of the present model are in close agreement with the test results.