Identification of metallic rods by frequency estimation on the historic vhurch tower in S. Vito al Tagliamento

In the present paper a dynamic procedure for the evaluation of the constraining rate between the ends of metallic rods supported between masonry elements is presented. As a first step, an analytical model for flexural free vibrations of Euler- Bernoulli beams subjected to axial forces, is introduced. Accordingly, closed-form natural frequencies associated to first fundamental modes of the rod can be obtained. The reliability of the model is verified through experimental tests performed on some tie-rods subjected to different levels of axial force. Natural frequencies of lower flexural modes can be assessed for each configuration and the corresponding axial force are measured by means of strain gauges. Once the characteristic dimensions and boundary conditions are set, equating the first two experimental frequencies and the corresponding analytical frequencies, permits to evaluate the axial force of the rod. Following this procedure, the axial forces acting in some metallic rods of the church tower in San Vito al Tagliamento near Pordenone, have been determined.