Damping identification using weighted fitting of Frequency-response-function (WFF) method

Modal identification is usually a necessity for structural damage identification and health evaluation. However, the modal damping is difficult to be accurately identified. Even though some new damping identification methods arise in recent years, it is difficult to apply these methods in engineering practice due to their complexity in theory and computation. This paper presents a frequency-domain modal identification method-Weighted Fitting of Frequency-response-function (WFF) Method. The principle and methodology of this method is first addressed. The target functions are defined as the differences between the measured and computed frequency-response-functions (FRFs) multiplied by appropriate weightings for different excitation frequencies. The modal parameters, modal frequency and damping, are obtained by the FRF fitting that leads to the minimum value of the target functions. The modal identifications for single- and multi-degree-of-freedom structure responses exited by band-limited white-noises with measurement noises are conducted to verify the effectiveness of this method. Then this method is applied to modal identification of a box-gird railway bridge with a passing train. Compared with half-power-bandwidth method, this method is shown to be simple and reliable for the accurate identification of the modal damping.