Subspace system identification of support-excited structures—part I: theory and black-box system identification

This paper reviews the theoretical principles of subspace system identification as applied to the problem of estimating black-box state-space models of support-excited structures (e.g., structures exposed to earthquakes). The work distinguishes itself from past studies by providing readers with a powerful geometric interpretation of subspace operations that relates directly to theoretical structural dynamics. To validate the performance of subspace system identification, a series of experiments are conducted on a multistory steel frame structure exposed to moderate seismic ground motions; structural response data is used off-line to estimate black-box state-space models. Ground motions and structural response measurements are used by the subspace system identification method to derive a complete input–output state-space model of the steel frame system. The modal parameters of the structure are extracted from the estimated input–output state-space model. With the use of only structural response data, output-only state-space models of the system are also estimated by subspace system identification. The paper concludes with a comparison study of the modal parameters extracted from the input–output and output-only state-space models in order to quantify the uncertainties present in modal parameters extracted from output-only models. Copyright © 2012 John Wiley & Sons, Ltd.