Behavior of Reinforced Concrete Frames Braced with a Combination of X and knee Bracing

In this study, 4 and 8 story reinforced concrete frames retrofitted with X and Knee bracing systems using SAP2000 V14 software and nonlinear static analysis. Then the behavior of these two systems are compared with each other and according to standard 2800 requirements, X-bracing system are located on the lower stories. Static analysis is performed using a uniform and triangular load patterns. Nonlinear plastic hinges have been assigned to the each seismic elements (beams and columns of moment resisting frame, steel bracing and knee elements). Models are chosen such that the participation of moment frame columns and steel bracing in different models have varied. The results indicate that in the X-braced reinforced concrete frames, large tensile forces are applied to the adjacent columns of steel bracing, especially in the lower stories. This problem cause forming plastic hinges in the columns. Also, reinforced concrete frames with knee bracing have the low strength and stiffness, while it is not always more ductile than X bracing. In this research combination of two systems, X and knee bracing, at the height indicate a bracing system that has desirable features of two bracing systems simultaneously and disadvantages of each system can be modified by the other.