Detection of seismic damage on a RC building using the proportional flexibility-resembling matrix

When an existing civil structure experiences a significant seismic event, permanent reductions of stiffness may be induced, thus resulting in changes in its dynamic behavior. Ambient vibration surveys performed before and after a seismic event are thus useful tools for the inspection and management process of the structure. A vibration-based approach for damage detection and localization has been developed by the authors in previous research. This approach is based on estimating a matrix that approximates a proportional flexibility matrix, termed proportional flexibility-resembling (PFR) matrix. This matrix is computed through signal processing operations to be executed after applying the first steps of the Frequency-Domain Decomposition technique. The main feature of the PFR matrix, compared to the traditional modal flexibility matrix, is that it can be assembled without the need of an explicit identification of the modal parameters. The matrix is in fact obtained by processing all first singular vectors and also all first singular values in a selected frequency range. In previous research by the authors the approach has been validated through numerical simulations and using the experimental data of laboratory tests performed on a small-scale frame structure. The objective of this contribution is to test the approach based on the PFR matrix on a full-scale reinforced concrete (RC) building structure that has experienced seismic damage. This structure was tested on the large-scale Network for Earthquake Engineering Simulation (NEES) shaking table of the University of California, San Diego (UCSD). During the experimental tests, some historical earthquake records were applied at the base of the building structure, and this induced progressively increasing levels of damage. After each strong motion test, low-amplitude vibration tests were performed for damage characterization purposes.