Behaviour of double-sleeve TubeBolt moment connections in CFT columns under cyclic loading

This research proposes a connection utilising a new blind bolt called TubeBolt to connect I-beams to concrete-filled tubular (CFT) columns. The aim of this study is to resolve the common problems of bolted connections in CFT columns such as column face deformation, bolt elongation, bolt sliding, and low flexural capacity. Tests were carried out on six half-scale specimens exposed to cyclic loading. The experiments were carried out on specimens with TubeBolts or EHB bolts. Different parameters such as hysteretic response, energy dissipation and ductility, failure modes, rotation and stiffness were extensively examined in this paper. Also, the effects of bolt types, bolt grades, and twin stiffener plates were studied on the structural response of the new connections. Test results demonstrated that the connections significantly reduce the above-mentioned problems, exhibit higher energy dissipation and ductility, and lead to a sizable hysteretic loop area. The connection with TubeBolt has higher capacity and stiffness and can avoid severe column face deformations compared to EHB bolts. It was found that using the TubeBolt with a higher bolt grade and twin stiffener plates can prevent brittle failure in the welded zone of the beam-extended endplate. Most importantly, connections with the TubeBolt meet the ductility and seismic design requirements for moment-resisting frames.