Modal parameter identification using non-stationary ambient vibration data

Identification of system characteristics is usually accomplished using both input and output data from the structural system. In many cases, however, only output measurements are available for structures under ambient vibration conditions. It can be shown that if the input signals can be modeled as non-stationary white noise, which is a product of white noise and a deterministic time-varying function, the theoretical correlation functions and random decrement signatures of structural response will have the same mathematical form as free vibration of the structure. The Ibrahim time domain method is employed to extract modal parameters from vibration data that have been processed by the correlation function method or the random decrement method. Through numerical simulation, the applicability of the modal parameter identification method proposed is confirmed.