Determination of Modal Parameters from Ambient Vibration Data for Structural Health Monitoring

A computationally efficient methodology is presented for· determination of the modal parameters of a structure from its measured ambient vibrations at several instrumented locations. The method, which is an extension of a well established and very efficient algorithm, MODE-ID constitutes the first step of a proposed two-step methodology for continuously monitoring the health of a structure by utilizing its natural ambient vibrations. During this first step, changes in the values of the modal parameters identified. The second step involves the determination of the corresponding loss of stiffness within the structure. The advantage in performing the two steps separately is that the computationally intensive second step need only be performed when the identified changes in modal parameters exceed certain thresholds indicating that structural damage is likely to have occurred. Results of testing the proposed methodology on simulated data and from an ambient vibration survey of Caltech's Millikan Library are presented