Applying Hilbert-Huang Transform to Identifying Structural Modal Parameters

The application of Hilbert-Huang Transform (HHT) for identification of structural modal parameters is investigated in this paper. The theory of HHT is briefly reviewed and it is proposed to identify the modal parameters of structure using measured free vibration time histories. For a multiple-degree-offreedom (MDOF) system under free vibration, the structural response is first decomposed into modal responses using the empirical mode decomposition (EMD) approach. Then, the Hilbert transform is applied to identify the natural frequency and damping ratio of each mode. Finally, this method is applied to identify the modal parameters of a free steel beam in laboratory. Responses of the beam are recorded by nine accelerometers. The free vibration response is obtained from the measured response using random decrement technique (RDT). Results indicate that the natural frequencies and damping ratios of structure can be identified by HHT, based on a single measurement at one appropriate location. These results are also compared with those obtained using Fourier analysis and DHMA modal analysis software. The HHT method is effective and suitable for structural modal parameter identification.