The change of natural frequency according to seismically damaged reicforced concrete (RC) frames was evaluated by using shaking table test results of full-scale one-span RC frame. As the damages of cracks and yields of reinforcing bars were occurred, the frequency decreased. The frequency got decreased to about a half of the initial frequency when the RC frame specimen collapsed.

In this study, the optimal performance based seismic retrofit method for fiber-reinforced polymer (FRP) jackets in existing reinforced concrete (RC) frames is presented. This optimal method minimizes the amount of FRP material while satisfying the constraints on the maximum inter-story drift, maximum strain of concrete, and shear failure prevention of columns. Both of shear reinforcement for preventing shear failure of columns and flexural reinforcement for improving the flexural capacity of columns are simultaneously considered. This method is applied to 3-story RC frame and the reinforced locations and the numbers of FRP reinforcement plies are obtained.