On the identification of the axial force in stay cables with unknown boundary conditions

Identification of tensile force in axially-loaded structural elements is of paramount importance for health monitoring and safety assessment purposes. Dynamic testing techniques provide the ground for quick and cheap identification strategies, based on the knowledge of: (a) a set of identified natural frequencies, and (b) a structural model that relates natural frequencies to the axial force value. Reliability of results, hence, is inherently related to the predictive capabilities of the underlying structural model. Errors may arise, in particular, from the modeling of boundary conditions. The present paper analytically investigates the effect of unknown boundary conditions on the modal properties of a shallow cable with small bending stiffness. Starting from theoretical results obtained on this archetypal structural model, a simple but effective numerical procedure to identify the axial force in stay cables is then presented.