This thesis investigates output-only dynamic identification for monitoring damage evolution in full-scale, three-dimensional, single-bay, three-story reinforced-concrete (RC) buildings subjected to shaking table tests and evaluates the effectiveness of seismic retrofitting. Two nominally identical RC frames, one as-built and one retrofitted, were evaluated under controlled laboratory conditions. The frames were subjected to repeated low-level white-noise excitations, alternating with earthquake records of increasing intensity, using dense accelerometer instrumentation on both structures. The data were then reoriented to a common frame, time-aligned, uniformly resampled, and anti-alias filtered to make them suitable for modal analysis. Modal parameters at each stage were estimated using Frequency-Domain Decomposition in combination with covariance-driven Stochastic Subspace Identification as part of the operational modal analysis.