Response and component characterisation of semi-rigid connections to tubular columns under axial loads

This paper examines the behaviour of open beam-to-tubular column bolted connections with angles subjected to direct tension and compression. Experimental and numerical studies as well as simplified mechanical assessments are presented. The response of seven tension tests and six compression tests on blind-bolted angle connections and combined channel/angle configurations are described and discussed in detail. Firstly, the experimental set-up, connection details and material properties are introduced followed by a detailed account of the results and observations from the tests. Based on the experimental results, the main behavioural patterns are identified and the salient response characteristics such as stiffness, capacity and failure mechanism are examined. It is shown that, for Hollo-bolted details, the distance between the blind-bolt and beam flange, the angle thickness and the column thickness have significant effects on the initial stiffness and tensile capacity of the connection. In addition, in the case of reverse channel connections, a direct relationship is deduced between the thickness of the channel component and the connection stiffness and capacity. It is also shown that the inelastic axial mechanisms exhibited by these types of connections are largely determined by the relative widths of the column/reverse channel and beam/angle components. Complementary finite element simulations are presented and utilised, together with the experimental findings, to highlight the main inelastic response characteristics for these forms of connections under direct axial action. Finally, the component-based method is extended to deal with angle connections between open beams and tubular columns employing Hollo-bolts or reverse channel components. To this end, expressions for the estimation of connection stiffness and capacity under axial actions are proposed and validated.