Circular concrete-filled double-skin steel tubular short columns under axial compression: An improved theoretical model and design

Abstract

Existing theoretical analysis methods for concrete-filled double-skin steel tubular (CFDST) short columns generally ignore the reduction of concrete strength due to brittleness. As a result, these methods cannot accurately capture full range behavior for CFDST columns containing high-strength concrete. By focusing on the reduction effect of concrete strength in CFDST columns due to concrete brittleness, this paper proposes a reduction factor for use in design, for the first time. Based on this reduction factor, a theoretical model for axially compressed circular CFDST short columns considering non-uniform confinement effect of the sandwiched concrete is established. A substantial experimental database of 168 CFDST columns with carbon circular steel tubes is then compiled. By comparing with this database, the proposed theoretical model is shown to achieve greater accuracy than existing approaches. Utilizing this model, the influence of column parameters on the performance of the studied CFDST members are investigated and the results are discussed. It is shown that concrete strength, hollow ratio, yield strength of the outer tube, and the diameter-to-thickness ratio of the outer and inner tubes are influential to the ultimate strength and ductility of CFDST columns. However, the yield strength of the inner tube only affects the ultimate strength of CFDST columns but has a negligible influence on the ductility. Finally, utilizing the experimental and theoretical data presented, the accuracy of existing design codes for concrete-filled steel tubes for the design of CFDST members with or without considering the reduction effect of concrete strength is assessed. The results indicate that Eurocode 4 provides a more reasonable prediction result.