System identification of a three-story infilled RC frame tested on the UCSD-NEES shake table

A 2/3-scale, three-story, two-bay, infilled RC frame was dynamically tested on a shake-table. The test objectives were to assess the seismic performance of existing, non-ductile, infilled RC frames and provide data for the evaluation of newly developed analytical methods predicting the behavior of such structures. The shake-table tests were designed to induce damage on the structure progressively through scaled earthquake records of increasing intensity. Between the earthquake records, the response of the frame to low-amplitude ambient vibration and white-noise base excitation tests was measured. At these low levels of excitations, the structure can be considered as a quasi-linear system with parameters depending on the damage state. The deterministic-stochastic subspace identification method based on system input and output signals has been used to estimate the modal parameters of the test structure at its various damage states. The identification is conducted considering the white-noise base excitation and the resulting structural response measured by accelerometers. The study has quantified the decrease of natural frequencies and the increase of structural damping at progressive damage states. The identified modal parameters have been used for damage identification of the infilled frame in a companion paper.