Prestressed stayed columns are an innovative type of structural system where the compressive load-carrying capacity can be enhanced through prestressed external cable stays. A nonlinear analytical model for prestressed stayed columns with multiple crossarm systems along the column length, based on the Rayleigh Ritz method, is presented that capture modal interactions for perfect geometries explicitly for the first time. It is demonstratedcthat the theoretical compressive strength enhancements under certain configurations canconly be obtained at the expense of triggering a sequence of destabilizing bifurcations. This can give rise to dangerously unstable interactive post-buckling behaviour in
luding so-called "mode jumping" and "snaking" phenomena. Parametric spaces where the system is most susceptible to the modal interactions are identified and it is for those configurations that the system is likely to be highly sensitive to initial imperfections. The model is validated using a nonlinear nite element model formulated within the
commercial code ABAQUS and excellent comparisons are obtained.