Application of the Random Decrement Technique in Operational Modal Analysis

The random decrement (RD) technique is a time domain procedure, where the structural responses to operational loads are transformed into random decrement functions, which are proportional to the correlation functions of the system operational responses or can, equivalently, be considered as free vibration responses. This paper presents a general review on the application of the RD technique in operational modal analysis. It refers its application in association with time domain modal identification methods, like the Ibrahim time domain method or the stochastic subspace covariance driven method. It also describes the use of the RD technique in association with frequency domain output-only modal identification methods, like the frequency domain decomposition method (FDD). A practical example is given showing the results obtained from ambient vibration tests performed in a civil engineering structure.