Research on the Axial Compression Performance of Double C-Section Partially Encased Composite Columns

To investigate the axial compressive behavior of double C-section partially encased composite (DCPEC) columns, 10 DCPEC specimens and two back-to-back bare steel C-section specimens were designed and tested under axial compression. The effects of key parameters, including steel wall thickness, member slenderness ratio, connection type of the built-up double C-sections and connection density, on the failure mode, load–displacement response and ultimate load-carrying capacity were examined. The test results showed that, under otherwise identical conditions, the ultimate load of the bolted stub column was 8.4% higher than that of the welded stub column. When the steel wall thickness increased from 2.0 mm to 3.0 mm, the ultimate load increased by approximately 16%. In contrast, when the slenderness ratio increased from 25.98 to 41.57, the ultimate load decreased by approximately 30%. A finite element model was then established in ABAQUS and validated against the experimental results. The numerical analysis further confirmed that increasing the slenderness ratio reduced the axial load-carrying capacity, whereas increasing the steel wall thickness improved the resistance of the member. The results indicate that the proposed DCPEC column can effectively develop the composite action between cold-formed thin-walled steel and lightweight aggregate concrete, thereby improving axial resistance and showing promising potential for engineering applications.