EMD-based stochastic subspace identification of structures from operational vibration measurements

Vibration-based structural health monitoring usually needs to extract vibration characteristics from operational vibration measurements. The stochastic subspace identification (SSI) algorithm is an advanced technique for performing such an operational modal analysis. A newly developed signal processing technique, called empirical mode decomposition (EMD), is capable of dealing with non-stationary signals. An EMD-based stochastic subspace identification procedure utilizing operational vibration measurements is presented in this paper. The output-only measurements are first decomposed into modal response functions by means of the EMD technique, on the basis of specified intermittency frequencies. The stochastic subspace identification method is then applied to the decomposed signals to yield the modal parameters. A case study of the operational measurements from a real bridge is presented, in order to illustrate the applicability of the proposed technique. It is demonstrated that the stable pole in the stabilization diagrams becomes unique and the vibration characteristics are easily identified for the decomposed signals, bypassing the influence of other modal components and fake frequencies due to unwanted noise.