Localization and veering in the dynamics of cable-stayed bridges

Cable-stayed systems are known to exhibit local modes that mainly involve the transversal cable dynamics. Their fan-shaped cable nets posses a dense spectrum of local frequencies, in which closeness with global ones commonly occurs. In these cases cable-stayed bridges present coupled cable–deck modes, whose interpretation presently remains incomplete. In this paper the solution of the eigenproblem of a simple cable-stayed beam model enables a synthetic description of the spectral properties of stayed-structures. The model shows the ability of a newly introduced localization factor to identify local modes and, especially, to reveal a veering phenomenon that occurs between local and global frequencies for particular parameter combinations. A small variation of the mechanical parameters is proved to produce a flipping between local/global (cable/beam) modal shapes within the veering region. Under these conditions, hybrid modes arise from the combination of the involved eigenfunctions. The occurrence of modal hybridization can be effectively predicted by the coincidence of the mode localization factors. These dynamical properties, which are further validated by a refined finite element model of a cable-stayed bridge, are proved to significantly affect the linear free and forced dynamics of cable-stayed structures.