Structures are built on a design and then damaged in time by natural and manmade effects, repaired and strengthened for reusing. Determination of the structural behavior is very important to avoid future disaster. Operational Modal Analysis has been widely used recently to determine the inherent modal parameters of engineering structures and give significant information about the structural condition. Also, this method can be used to further studies such as model updating, damage detection and health monitoring. In this paper, it is aimed to investigate the changes of modal parameters considering undamaged, damaged, repaired and strengthened conditions using ambient vibration tests. For this purpose, a reinforced concrete frame model having two-floor with two spans in the longitudinal direction considering 1/2 geometric scales is built in laboratory. Four different cases are considered to emerge the efficiency of this procedure and the undamaged RC model is measured firstly to determine the initial modal parameters. Secondly, the lateral forces are applied to floor levels to obtain the damages, especially in beam-column joints. Thirdly, the damaged model is repaired using injection material and lastly strengthened with Carbon Fiber Reinforcement Polymer. It is also examined that what rate the dynamic characteristics return to back after repairing and strengthening studies by the comparison with undamaged condition? In addition to this the evaluation of carbon fiber reinforcement polymer effectiveness in strengthening for real applications is presented. It is seen that ambient vibration test is enough to identify the modal parameters of engineering structures for different conditions. The modal parameters are decreased distinctly with damages, and reverted almost initial condition with strengthening.