One of the common methods used as an alternative to shear walls in the retrofit of reinforced concrete (RC) structures is steel braces. The use of steel braces is preferred because of its rapid application as well as the increase in stiffness and strength. By using different types of braces in reinforced concrete frames, displacements can be reduced and properties such as structural performance, shear capacity, ductility, stiffness and strength can be increased. If the behavior characteristics of the hybrid system are known, the structural performance of the reinforced building can be predicted after the retrofit. In this study, the effect of different types of steel braces recommended in the Turkey Building Earthquake Code 2018 (TBEC-2018) on reinforced concrete building retrofit, was investigated. For this purpose, a 9-storey RC frame system was retrofitted using diagonal, X, inverted V, V and K type bracings. Considering the strength and stiffness results, an answer was searched for the question of which brace type had the best result in retrofit. The results obtained from the analyzes show that the X and K type bracings stand out in terms of strength and stiffness.

In this study, the effect of the friction damper location on the earthquake behavior of a building was investigated. Diagonal braced friction dampers were placed on different floors, and the changes in building behavior were examined. For this purpose, a scaled experimental building model with five floors, with a single span in the x and y directions, was used. Numerical model validation was carried out by taking into account the experimental and numerical period values obtained via the effect of free vibration. The period, peak displacement, and maximum shear force of the friction dampers, arranged in various configurations, were compared using the numerical model in conjunction with three different earthquake acceleration records. According to the investigations, the damper performance of the design changes depending on the earthquake acceleration that is affecting the building. Friction dampers located on the lower floors are more effective at reducing period, peak displacement, and floor shear forces than those located on the upper floors.

The contribution of GFRP (glass fiber reinforced polymer) fabric to the bending behavior of steel RHS (rectangular hollow section) beams was investigated by experimental and numerical studies. In the first part of the study, small-scale RHS profiles were strengthened with GFRP fabrics in ten different configurations in the experimental study. The bending behavior of the profiles was determined by three-point bending tests, and the best strengthening configuration was decided. The numerical models were verified with the experimental results. In the second part, real-size RHS beams were strengthened with the optimum strengthening configuration. In the results of the study, it was determined that the U-shaped strengthening provided the maximum contribution to the RHS beams bending behavior. The minimum GFRP size to be used in strengthening is important, as an insufficient GFRP length leads to GFRP failure, and the number of layers should be increased for more load capacity. A total of 25% of the net beam span was determined to be the minimum GRFP length. In full-size beams, a double-layer GFRP increased the maximum load-bearing capacity by 7%. Formulas were obtained to determine the contribution of single and double-layered U-shaped GFRP to the shape factors of the RHS. With the formulations, the plastic moment capacity can be determined.