Refined Frequency Domain Decomposition modal dynamic identification from earthquake-induced structural responses

In the present work, earthquake-induced structural responses at heavy damping are considered towards the assessment of current strong-motion output-only modal parameters via a novel refined Frequency Domain Decomposition (rFDD) approach. Classical FDD assumptions of stationary white noise input and light damping no longer hold in such a case, leading to extreme operational conditions for this Frequency-Domain modal dynamic identification technique. The present non-parametric output-only rFDD procedure effectively tackles such issues, through dedicated algorithmic and computational strategies, resulting in a robust identification tool within this challenging identification context. Synthetic earthquake-induced responses are generated from a set of shear-type frames, which are taken as target structural models for the purposes of validation and comparison. Twenty-two "Far-Field" multi-component (NS, WE) seismic base excitations are taken into account from the FEMA P695 strong motion database. In particular, heavy-damped structures (in terms of output-only identification challenge) are considered, raising the modal damping ratios up to 10%. Natural frequencies, mode shapes and modal damping ratios are effectively estimated through the implemented rFDD procedure. The achieved estimates are statistically compared to the target values, by proving the effectiveness of the developed rFDD approach in working with synthetic earthquake-induced responses at concurrent heavy damping. This shall demonstrate a necessary condition for the feasibility of the developed rFDD approach towards Earthquake Engineering and Structural Health Monitoring purposes.