Behavior of thick-walled CHS X-joints under cyclic out-of-plane bending

This paper deals with experimental investigations to study the seismic behavior of thick-walled circular hollow section (CHS) X-joints subjected to out-of-plane bending (OPB). Important geometric parameters were varied in designing three full-scale joint specimens in order to evaluate their effect on connection behavior. Test results indicated that the failure modes and the connection efficiency of these joints significantly depended on the brace-to-chord thickness ratio τ and the brace-to-chord diameter ratio β. The tension fracture was identified as a critical failure mode for thick-walled X-joints with large β. CHS X-joints with larger β ratio were found to demonstrate better connection ductility and more satisfactory energy dissipating capacity than those joints with smaller β ratio under cyclic OPB loading. This observation was further verified by the proposed simplified analytical model results. Finite element (FE) analyses were performed to simulate the experimental behavior and facilitate the interpretation of the important test observations.