Numerical study and design of skewed X-type branch plate-to-circular hollow section connections

Structural systems, including space-frames, cable stayed roof systems and bridges, with elements that intersect at non-orthogonal angles necessitating rotated and complex connection geometries, have become commonplace. Non-orthogonal plate-to-circular hollow section (CHS) connections with branch members rotated about their own axis (skewed) have been absent in international literature and design guidelines. A numerical finite element parametric study is presented on the behaviour of skewed X-type plate-to-CHS connections loaded under branch plate tension. A total of 91 connections with wide-ranging values of geometric properties were modelled and analysed using commercially available finite element software. The numerical finite element analysis indicated a smooth sigmoidal (S-shaped) transition between longitudinal and transverse orthogonal extremes. A non-linear interpolation function was developed, for application between longitudinal and transverse design recommendations, that adequately predicts skewed connection behaviour over a wide range of geometric connection configurations. A partial design strength function for skewed X-type plate-to-CHS, which builds on existing design recommendations for non-skewed plate connections, is hence proposed with lower bound reduction (resistance) factors.

Research highlights
► Welded branch plate-to-tube connections updated.
► Plate skew angles (between longitudinal and transverse) considered.
► Design recommendations from FE analysis.