Frequency domain identification of modal characteristics and loads from output-only measurements

This paper proposes a frequency domain framework for concurrently estimating the modal structural parameters and modal loads from the measured output response. A mathematical load model is theoretically developed and compared to the load determined by force identification. Unlike conventional modal identification schemes, the proposed approach can effectively accommodate the spectral shape of the external load in the frequency domain, enabling the determination of the modal parameters without explicit white noise assumption. The proposed approach is verified by applying it to a single-degree-of-freedom system system representing a modal response, an aeroelastic model in an atmospheric boundary layer wind tunnel, a multi-degree-of-freedom system, and the measured acceleration response of a 40-story building. The simulation results demonstrate that the proposed technique can reliably estimate the modal parameters and load model and is robust against the noise present in the response and the order of the load model. Additionally, the proposed technique can be applied to various loading conditions such as vortex-induced and buffeting effects since the modal parameters and the load model can be identified for any shape of the loading spectrum.