Experimental and finite element study of the non-linear force-displacement characteristics of tubular YT-joints under combined axial loading

This paper describes an experimental and finite element investigation of the non-linear elastic-plastic force-displacement response of a simply supported tubular YT-joint under a range of ratios of the T- to Y-brace applied loads, in order to develop an understanding of the dependence of the joint response on loading path. The experiments consist of the static testing of simply supported tin-lead alloy models of tubular YT-joints under combined, proportionally applied T- and Y-brace-end axial forces. A number of different finite element approaches are presented and discussed via comparison with the test results. An improved version of the energy-based elastic-plastic prediction procedure of the present authors is presented; this is shown to represent a framework for the determination of the non-linear local joint T- and Y-brace force-displacement responses to arbitrary radial loading paths in the load space. The work is considered relevant to the simplification of tubular framework analysis methods for the calculation of accurate collapse loads, incorporating non-linear joint behaviour.