Modified Concrete Confinement Model for Multicell Double-Skin Tubular Columns

Double-skin tubular columns (DSTCs), composed of two concentrically placed hollow steel tubes with sandwiched concrete infill, are efficient composite sections for resisting high axial loads. However, localized buckling failure of the steel tube restricts its structural efficiency. Multicell DSTCs (MCDCs), incorporating stiffeners between the tubes, improve confinement and ductility, but existing confinement models fail to accurately capture stiffener-induced effects and are constrained by limited experimental evidence. This study introduces a modified confinement model that explicitly accounts for the enhanced confinement provided by the stiffeners, representing a significant advancement over previous models. The model is validated through nonlinear finite-element analysis and experimental comparisons, demonstrating an excellent accuracy ( R 2 = 0.99 and average error < 5 % ). A comprehensive parametric study is also conducted, covering the stiffener number, distribution, and hollowness ratio across a wide range. The findings reveal the governing parameters controlling the axial strength and failure modes and highlight the limitations of existing axial strength prediction models. By addressing gaps in the past research and providing a more comprehensive design methodology, this work provides new insights and an analytical framework for optimizing the structural performance of MCDCs in structural engineering applications.