Behavior of Hollow Structural Section Branch-to-Casting Node Connections for Free-Form Grid Shell Structures

AbstractCasting nodes are used to connect branch members at joints of freeform grid shell structures. In this study, the structural performance of a rectangular hollow section (RHS) branch-to-casting node connection was investigated. A RHS branch member with an access hole (i.e., opening) for temporary bolting was weld-connected to the T-shaped node fabricated by a conventional casting method. Six RHS branch-to-node connection specimens were tested under tensile and compressive loading. The eccentricity of axial loads was considered as the main test variable. Tests showed that, despite the opening near the weld joint, the RHS branch-to-casting node connections exhibited good performances. For tensile specimens, the ultimate strengths were greater than the yield strengths of the casting nodes, and weld rupture eventually occurred at the stiffener-to-casting node wall joints. On the other hand, for compressive specimens, the ultimate strengths were limited by flexural and torsional buckling modes accompanying local buckling and crippling of the casting node walls. The ultimate strengths degraded by the eccentric loading and openings were evaluated in accordance with current design codes. The failure modes and consequent strengths of compressive specimens were further investigated through finite-element analysis. Based on the investigations, design recommendations of RHS branch-to-casting node connections with openings were given.