Identification of modal parameters from output-only data is studied in this work. The proposed methodology uses transmissibility functions obtained under different loading conditions to identify resonances and mode shapes. The technique is demonstrated with numerical simulations on a 2-DOF system and a cantilever beam. To underpin the simulations, a real test was done on a beam to show the efficiency of the method. A practical application of the method can be to identify structures subjected to moving loads. This is demonstrated by using FEM-model of a cantilever beam with a moving load.

Operational Modal Analysis (OMA) is being increasingly used as an experimental technique to identify the dynamic properties of many types of large-scale constructed systems. For industrial structures in real operation condition, it is sometimes hard or impossible to measure excitation forces so some identification techniques have been developed to work on response data only. In Operational Modal Analysis (OMA), there is no need to make any assumption about the nature of force and consequently resonance frequencies are recognised. In this thesis, one application of Operational Modal Analysis which is called transmissibility measurement is supposed to be engaged to find resonance frequencies. Operational Modal Analysis has become a valid alternative for structures where a classic forced-vibration test would be difficult to conduct. The use of in-operation modal analysis is particularly interesting because the structure remains in its normal in-operating condition during the test. This is an important advantage because the conditions during a laboratory forced-vibration test are often considerably different from the real working conditions regardless of constraints and limitations. Therefore, this method enables us to find system parameters without any assumption about the nature of the forces.