Prediction of elastic-plastic generalized force-displacement responses of tubular joints for three different loading modes

In this paper the method of complementary energy is employed to predict the elastic-plastic force-displacement and moment-rotation responses of the T- and Y-brace ends of a simply-supported tubular YT-joint, for arbitrary radial load paths (i.e. proportional loads, no unloading) in the load space of the structure. The prediction procedure is applied to three combined loading modes, as follows: i) combined T- and Y-brace axial force loading mode, ii) combined T- and Y-brace in-plane bending moment loading mode, and iii) combined T-brace in-plane bending moment and Y-brace axial force loading mode. The prediction procedure is based on normality of the `vector' of generalized displacement components to the level curves of total (i.e. elastic and plastic) complementary work in the load space, taking the generalized displacement axes as parallel to the corresponding load axes. In the present case the results of a series of non-linear, elastic-plastic FE analyses, corresponding to a sample of radial load paths ranging over the load space, are employed to calculate the complementary work level curves and the predictions; alternatively experimentally measured force-displacement and moment-rotation data for the sample of radial load paths could be used.