Multi-objective seismic retrofit method for using FRP jackets in shear-critical reinforced concrete frames

Many research studies have been conducted on seismic retrofits of existing reinforced concrete (RC) frames with fiber-reinforced polymer (FRP) jackets. Although existing RC columns are vulnerable to shear failure because of insufficient transverse reinforcement and deficient seismic details, little research exists on the reinforcement locations and FRP reinforcement level required to prevent column shear failure. In this paper, the optimal seismic retrofit method that uses FRP jackets for shear-critical RC frames is presented. This optimal method uses non-dominated sorting genetic algorithm-II (NSGA-II) to optimize the two conflicting objective functions of the retrofit cost as well as the seismic performance, simultaneously. To minimize the retrofit cost and maximize the seismic performance of a structure, this optimal method minimizes the amount of FRP required and the coefficient of variation of inter-story drift ratios while satisfying the constraint conditions on the shear failure prevention, maximum inter-story drift ratio, and maximum compressive strain of concrete. Both the flexural reinforcement method and shear reinforcement method of FRP jackets are adopted to strengthen the flexural capacity and shear strength of columns, respectively. The two reinforcement methods are applied sequentially to minimize the total amount of FRP material required. The proposed method is applied to 3-story RC frame and the optimal retrofit schemes that suggest the reinforcement locations and the number of FRP reinforcement plies are obtained.