Learning operational modal analysis in four steps

Operation Modal Analysis (OMA) is the testing procedure yielding experimental estimates of the modal parameters from measurements of the structural response only. Most of the OMA methods have been derived from traditional experimental modal analysis procedures, based on the analysis of the structural response to a known input applied by an appropriate excitation system. However, over the years OMA has evolved as an autonomous discipline. Unfortunately, the documentation about the different OMA methods is traditionally disseminated in a huge number of publications, and the first book entirely devoted to OMA and its applications has been only very recently published. The increasing interest for OMA is motivated by the possibility to carry out cheap and fast tests, which do not interfere with the normal use of the structure. In fact, the idea is to take advantage of vibrations naturally induced in the structure by wind, traffic or microtremors, thus avoiding the application of an artificial input. As a consequence, the identified modal parameters are representative of the actual behavior of the structure in its operational conditions, since they refer to levels of vibration actually present in the structure. The present review paper aims at giving the non-specialist all the necessary elements to have a first insight into OMA, illustrating the main theoretical concepts and practical aspects of output-only testing and data processing. Relevant references are provided at the end of the paper for the reader interested in learning more about specific aspects or methods.