The behaviour of anchored extended blind bolts in concrete-filled tubes

Extended Hollo-Bolts (EHBs) are blind bolts that have an extended bolt shank ending in an anchor nut. When used with concrete-filled tubes, the extension and the anchor in the concrete serve to enhance significantly the performance of both connection components: bolts in tension and tube face in bending. The enhancements are a result of confining the concrete, preventing local buckling of the steel tube and allowing the blind bolt to achieve a tensile strength equal to that of standard bolt+nut fasteners. Overall, the use of the EHB results in a moment-resisting bolted connection to hollow sections which can achieve rigid behaviour under certain configurations. This paper summarizes research work done to date on such connections at the University of Nottingham. This includes experimental, numerical and analytical modelling. The aim of the work is to provide a fundamental understanding of the behaviour of anchored blind bolt connections to concrete-filled columns, leading to the specification of appropriate design rules that allow the use of such bolted moment-resisting connections in practice. The work has proposed analytical models for: connection stiffness, column face-bending strength considering both single and group behaviour of bolt rows, anchored bolts in tension and anchored bolts under combined tension and shear.