Thin walled beams with internal unbonded cables: balance conditions and stability

A technique for controlling the stress and strain state of beams consists in introducing stretched slipping cables at their interior. This provides a coupling between the local cable strain and the global rod deformation which makes conventional rod models based on local balance conditions inapplicable. The paper presents a model for this kind of structural system in order to formulate the elastic problem and to analyse the stability of known balanced configurations. A generic cable path crossing the interior of the rod is considered. Both variational formulation and local formulation are reported; in particular the latter leads to integro-differential equations. Some qualitative aspects related to the particular coupling between the system components and the effect on the cable path geometry on the stability are discussed.