Rotational stiffness of a blind-bolted connection to concrete-filled tubes using modified Hollo-bolt

Moment resisting connections to hollow sections tend to utilise welding and reinforcements to achieve the stiffness required to resist moment. Blind-bolted connections to hollow sections offer a simpler, more economical and construction-friendly means of connecting to hollow sections. Such connections have been used in nominally pinned connections and in non-primary structural connections. Exploratory research work has been done by a number of researchers to improve the stiffness of such bolted connections through the use of concrete filling. Concrete filling tends to improve the stiffness of the connection. However, the improvement is not sufficient to attain significant moment resistance allowing such connections to be classified as rigid connections. This is because they address only half of the problem. That is the flexibility of the tube face. This paper reports on a blind-bolted connection to concrete-filled square hollow sections using a modified blind-bolt that addresses the issue of the flexibility of the blind-bolt connector as well as that of the tube face. The paper reports on this novel connection type and on an experimental programme aimed at measuring the resulting connection stiffness. The programme tested eight full size connections, principally varying the connection endplate type, column thickness and concrete strength. The data was cross validated with a finite element model. The paper assesses the performance of this connection using connection stiffness classification methods. It concludes that the connection is able to develop the required stiffness for it to be used as a rigid connection in braced frames.

► Reports on a blind-bolted joint for moment connections to concrete-filled tubes.
► The proposed connection enhances the flexibility of the fastener and tube face.
► The proposed fastener exhibits strength comparable to that of standard bolts.
► The proposed connection is classified to exhibit at least semi-rigid behaviour.