The aim of this paper was to determine the effect of fiber-reinforced polymer (FRP) strengthening on the dynamic characteristics of reinforced concrete (RC) frames using ambient vibration-based automated model updating procedure. Four different structural conditions were examined: undamaged, damaged, "repaired with injections"; and "strengthened with FRP composites". Ambient vibration tests were conducted to extract the experimental dynamic characteristics using enhanced frequency domain decomposition (EFDD) and stochastic subspace identification (SSI) methods. To validate the experimental results, an initial finite element (FE) model was constructed and numerical dynamic characteristics obtained. To eliminate the differences between initial FE and experimental results, global and sensitivity-based automated model updating procedures were applied to account for various uncertain parameters. The maximum differences were reduced from 38.38% to 4.14% and 0.21% with global and automated model updating. The updated FE model was used as the initial model for the damaged condition. This procedure was followed for each structural condition in turn to demonstrate the effect of FRP strengthening.