Structural identification of a steel frame from dynamic test-data

Structural identification via modal analysis in structural mechanics is gaining popularity inrecent years, despite conceptual difficulties connected with its use. This paper is devoted to illustrate boththe capabilities and the indeterminacy characterizing structural identification problems even in quite simpleinstances, as well as the cautions that should be accordingly adopted. In particular, we discuss an applicationof an identification technique of variational type, based on the measurement of eigenfrequencies and modeshapes, to a steel frame with friction joints under various assembling conditions. Experience has suggested,so as to restrict the indeterminacy frequently affecting identification issues, having resort to all the apriori acknowledged information on the system, to the symmetry and presence of structural elements withequal stiffness, to mention one example, and mindfully selecting the parameters to be identified. In addition,considering that the identification techniques have a local character and correspond to the updating of apreliminary model of the structure, it is important that the analytical model on the first attempt should beadequately accurate. Secondly, it has proved determinant to cross the results of the dynamic identificationwith tests of other typology, for instance, static tests, so as to fully understand the structural behavior andavoid the indeterminacy due to the nonuniqueness of the inverse problem.