Comparison of parametric excitation and excitation of an elastic stay cable

In cable-stayed bridge applications, the vertical vibrations of a bridge deck induce vertical motions of the cable anchors that may cause large amplitudes oscillations of the cables. This vertical motion is not collinear with the cable chord and can be split into a transverse and an axial component. The latter one is responsible for a parametric excitation. Since this phenomenon leads to serious dynamic instability, whereas the transverse component provides simple resonances only, the transverse anchor motion is often disregarded or considered in a separate analysis. However, because of the cable’s non linear behaviour, the response of the cable under both components cannot simply be added. It is thus important to consider at once this actual “cable excitation”, rather than approaching it by an axial excitation, as often reported in the study of parametric excitations. In this paper, the difference between the two modes of excitation is illustrated with a finite element model. The simplicity of the model allows an efficient parametric study of the vibrations of a cable under both excitations, for various cable inclinations and anchor frequencies.