Analytical Strength Prediction Model for Full-Width Circular Hollow Section X-Joints

Abstract

Full-width tubular joints, consisting of chord and brace members of the same width (or diameter), have been frequently used in architectural, civil, and offshore structures owing to their higher load resistance compared with partial-width joints. In design standards, the full-width circular hollow section (CHS) joints have been treated as exhibiting chord plastification behavior similar to those of joints with lower brace-to-chord diameter ratios. However, in this study, it is found that for full-width CHS X-joints, the bearing or buckling behavior of the chord sidewall should also be considered for more accurate and consistent prediction of the joint strength. A new analytical model based on the column buckling approach, which accounts for both chord sidewall failure and chord plastification, is proposed. Further, it is shown that the proposed model could be regarded as more generic than the classical ring model that formed the analytical basis of current design standards. The proposed model is employed to derive a new design formula for CHS X-joints subjected to brace axial compression including high-strength steel. The application of the proposed design formula is limited to laterally restrained joints because the reduction in joint strength due to sidesway instability can be significant.