Investigation of high-strength steel CHS X-joints loaded in compression including effect of chord stresses

Abstract

Internationally representative steel design standards imposed restrictions on tubular joints fabricated from high-strength steels, and this is partly due to concerns regarding their unique material characteristics, such as high yield ratio and low deformability. The joint strength equation cannot be fully utilized for steels wherein yield strength exceeds 355 or 360 MPa. However, the mechanical background of the limitations is not adequately understood. The authors recently conducted experimental testing of high-strength steel circular hollow section (CHS) X-joints and clearly indicated that the current limitations are typically unduly conservative. In this study, supplemental test-validated numerical analyses were performed to further investigate the chord plastification behavior of high-strength steel CHS X-joints subjected to brace axial compression, including the effect of chord stress. Three steel grades ranging from ordinary to very high strength steels were considered in the analyses. The results indicated that the high-strength limitations to the tubular joints in current standards can be relaxed. The assumptions underlying current chord plastification strength formula are questioned and a more consistent joint strength equation is newly proposed based on the concept of effective strain-hardening. Based on a numerical and experimental database of high-strength steel joints, the suitability of the widely accepted 3% indentation criterion is evaluated from the perspective of joint flexibility. High-strength steel joints under the effect of chord stress generally outperformed ordinary steel joints, and their strengths were conservatively predicted via current chord stress functions.