The topic of this paper lies in the field of non-destructive parametric identification. Its objective is to evaluate the mechanical characteristics of constituent bars in existing truss structures. In particular, it locates bars with reduced mechanical properties and quantifies the loss of stiffness. The suggested algorithm takes into account plane and three-dimensional structures, both statically determinate and indeterminate. In the case where it is possible to measure strains only on some bars, the procedure uses Genetic Algorithms to overcome the lack of information.