Abstract
Operational Modal Analysis also known as Output Only Modal Analysis has in the recent years been used for extracting modal parameters of civil engineering structures and is now becoming popular for mechanical structures. The advantage of the method is that no artificial excitation need to be applied to the structure or force signals to be measured. All the parameter estimation is based upon the response signals, thereby minimising the work of preparation for the test. Two estimation techniques are used: a non-parametric Frequency Domain Decomposition (FDD) technique, and a parametric data driven Stochastic Subspace Identification (SSI) algorithm. Operational Modal Analysis is compared to the traditional input-output Modal Analysis.