"Parametric identification of analytical and finite element models for a three-dimensional frame"

The multi-faceted identification process aiming to assess the structural matrices of a low-order physical model describing the three-dimensional motion of a frame structure, is illustrated. The acceleration data (known-output) from ambient vibration (unknown-input) tests are used to employ an output-only identification procedure of the model inertial and stiffness properties. Applying the EFDD procedure, a modal model, consisting of frequencies and modes, is first estimated. Since the output-only techniques do not furnish orthonormalised modes, and neither the mass nor the stiffness matrix are here assumed known a priori, additional information are needed to identify the structural matrices of the physical model. In order to first assess the structural inertia, an asymptotic method is used to solve the problem of orthonormalising the experimental modes with respect to the unknown mass matrix. Therefore, the frequencies and orthonormalised modal shapes permit to identify the stiffness matrix of the physical model, purposely condensed in order to balance the dimension of the modal information available. The identification results, consisting of both the modal and the physical model, are finally compared with those obtainable from the structure’s experimental response to hammer impacts (known-input), by applying classical identification techniques based on the knowledge of the excitation, together with automated procedure for finite element model updating