Dynamics of masonry walls connected by a vibrating cable in a historic structure

An original parametric model is presented to describe the modal interactions characterizing the linearized free dynamics of a cable–beam system. The structural system is composed by two vertical cantilever beams, connected by a suspended nonlinear cable. A closed form solution is achieved for the linear eigenproblem governing the undamped small-amplitude vibrations. The eigensolution shows a rich scenario of frequency crossing and veering phenomena between global modes, dominated by the beam dynamics, and local modes, dominated by the cable vibrations. Veering phenomena are accompanied by modal hybridization processes. The role played by different parameters is discussed, with focus on the resonance regions. The discussion allows the identification of an updated set of parameters, which offers a satisfying explanation of some unexpected dynamic interactions, observed in the experimental behavior of the masonry walls of the Basilica of Collemaggio, a historic structure heavily damaged by the 2009 L’Aquila earthquake.