Nonlinear Performance Evaluation of Reinforced Concrete Frames with Off-axis Steel Braces

Abstract: In recent years, the use of steel bracing in reinforced concrete structures has been proposed for the purpose of strengthening existing weak buildings and also in the seismic design of new buildings as a shear-resistant element against earthquakes. The use of steel bracing with direct connection has been considered for several reasons, including economic issues, easy implementation, and the possibility of securing and strengthening weak reinforced concrete structures against earthquakes. One of the metal bracings used is the Sherwin divergent bracing, which, due to its very suitable and balanced performance, both increases the stiffness and reduces the maximum displacements of the structure, and by absorbing more energy in nonlinear ranges, increases the ductility and, as a result, increases the behavior coefficient of the structure and improves its performance when entering the inelastic range. In this study, the performance behavior of a reinforced concrete structure in two cases, first: a code-accepted design and second: a weakness in the code design, which is strengthened by an off-axis steel bracing, is investigated using nonlinear Pushover analysis and the results of different forms of changing the bracing bond length and its effect on the performance of the strengthened structure are compared. The results show an improvement in performance in the field of linear behavior by increasing stiffness and reducing P-∆ effects, which is one of the main weaknesses in reinforced concrete structures due to the formation of cracks, and in the field of nonlinear behavior against severe earthquakes, a significant increase in capacity and a reduction in ductility requirements in the reinforced concrete flexural frame structure strengthened with a divergent steel bracing. Keywords: Reinforced concrete frame, steel divergent brace, strengthening, nonlinear performance, pushover, ductility