AISC360-22 design equations for high-strength concrete-filled tubes: From rectangular to circular sections

Abstract

The current AISC Specification lacks clear guidance on the design of circular concrete-filled tube (CCFT) members, while updates to material strength restrictions and the P-M interaction design curve apply exclusively to rectangular shapes. This research is a response to the growing call within the engineering community to update the AISC 360–22 design guidelines for CCFTs. A deterministic and probabilistic approach is presented for assessing the applicability of unifying current AISC 360–22 P-M interaction design equations for use in circular-filled tubes. This assessment is informed by the most up-to-date experimental test results comprising 508 eccentric axially loaded CCFTs with different material strength combinations. Reliability analysis using Monti Carlo simulation demonstrates that the authors' proposed P-M interaction design equations in Appendix II of the AISC 360–22, along with the proposed equation for column, and beam maintain a consistent level of accuracy across different material strengths of circular shapes. An increased safety factor of ϕ_c = 0.85 for columns and ϕ_b = 0.9 for beams is recommended for a more economical design, aligning with AISC 360–22's requirement for achieving a minimum reliability index of 2.6 under commonly used load combinations. The research findings present a compelling proposal for inclusion in design codes, offering practical tools for engineers to enhance structural design and safety optimization.