Strength design of the built-up radially battened composite column under combined axial compression and any directional bending moment

This paper explores the behavior and design of Built-Up Radially Battened Composite Columns (BRBCC) under axial compression and bending moments in any direction. The BRBCC is constructed by connecting several Concrete-Filled Steel Tubes (CFSTs) with radially and longitudinally arranged battens, leveraging the synergistic effects between materials and multi-component combinations. This design shows significant potential for civil engineering applications, such as in airports and other public buildings, due to its aesthetically pleasing form and high load-bearing capacity. Two finite element models (FEM) are developed for analyzing the sectional strength and buckling strength of BRBCCs. The FEM for sectional strength analysis (FEM-sec) models a short column, ignoring geometric nonlinearity, while the FEM for buckling strength analysis (FEM-buc) models a full column, taking geometric nonlinearity into account. The FEM-sec is used to study the sectional strength of BRBCCs under axial compression, pure bending, and combined compression and bending. The results show that the sectional strength of BRBCCs is closely related to the number of chords, bending direction, and the CFST’s confining factor. Based on extensive FEM calculations, the compression-bending sectional strength is predicted using a quadratic function, which incorporates these factors and reflects the convex nature of the sectional M - N curve of BRBCCs. The buckling behavior of BRBCCs under combined compression and bending moments in any direction is then analyzed using the FEM-buc. The results indicate that the buckling strength of BRBCCs is significantly lower than their sectional strength due to the second-order effects of axial load. The design equation for the compression-bending buckling strength of BRBCCs is derived from their sectional strength, incorporating parameters such as normalized slenderness and stability coefficients based on FEM-buc calculations. Finally, design methods for the batten plate and individual chord are proposed to ensure that the BRBCC does not experience local failure prior to reaching its global load-bearing capacity. A design case is then presented to illustrate the proposed design process.