The most common assumption adopted in relation to chord support conditions for individual tubular joint testing and analyses is that of simple supports. In studying the force-displacement characteristics of tubular joints the effects of alternative support conditions should be investigated, since it is known that brace loading paths do not typically remain radial. This paper presents an investigation of the effects of encastre chord support conditions (versus simply-supported) on both the force-displacement response and the failure locus of a representative tubular YT-joint. The work is relevant to the simplification of framework collapse techniques via localised representation of non-linear joint behaviour.
The development of a single elastic-plastic tubular joint element would represent a significant step forward in tubular framework analysis capability since it would permit inclusion of the local detailed nonlinear joint behaviour in the global response of the structure, e.g. see Billington et al. (1993) and Lalani (1993). This is important for the accurate estimation of the reserve strength ratio and other platform integrity measures (Banon et al., 1994 and Bea, 1996) of the large numbers of aging platforms in operation throughout the world, and also from the perspective of potential use of jacket structures for deep water applications. At present it is not generally possible to include elasticplastic joint behaviour in framework analyses due to the inordinately large numbers of degrees of freedom required for typical threedimensional shell or brick element models of complete frameworks. Consequently such analyses are typically carried out using beam element models (e.g. see Broughton and Silva, 1996). An important consideration in the development of a single tubular joint element is the effect of chord support conditions on the non-linear force-displacement characteristics of the joints.