Output-only Modal Identification

Abstract

This chapter is focused on the methods for modal parameter estimation from previously acquired and pretreated time histories of the structural response to ambient vibrations. The fundamental assumptions of OMA methods and the basic concepts of structural dynamics models in time and frequency domain are illustrated, pointing out the common mathematical background behind different and apparently unrelated procedures. Then, criteria for the classification of OMA methods are summarized and fundamental theoretical aspects of well-established and popular OMA techniques are illustrated, providing relevant details for their software implementation. Finally, additional aspects concerning post-processing of modal parameter estimates, validation of layout and modal identification results, and correlation with numerical models are discussed. The ultimate objective of this chapter is to provide the reader all relevant information for implementation and practical application of a number of OMA methods and post-processing tools for validation and correlation. In this sense the implementation details and the basic software provided with the book are intended to fit the needs of both the modal analysts on one hand and undergraduate/graduate students, researchers, and developers on the other. The latter, in fact, are usually interested in writing their own code for further developments or business opportunities, and the accompanying software serves as a reference. On the other hand, modal analysts can find here the tools and the fundamental information to promptly start the modal tests and properly interpret the results. Using the basic software accompanying the book they can take confidence with different OMA procedures and choose their favorite ones. Thus, the chapter can be also intended as a guide supporting the choice among the different commercial software packages available on the market and relying on different OMA methods.