Laboratory investigation on the buckling restrained braces with an optimal percentage of microstructure, polypropylene and hybrid fibers under cyclic loads

Normal braces have a high stiffness but are buckling under compressive strength and have very low ductility. To overcome these disadvantages in recent years, a buckling restrained braces system has been used. In this study the optimal percentage of Microstructure, Polypropylene and Hybrid Fibers were determined by using tensile and compressive test, the results exhibited that the highest rate of tensile and compressive strength were occurred in the case of reinforced concrete with polypropylene fibers and the composition of polypropylene and metal fibers as known hybrid fibers compared to the non-fibrous concrete for test specimens containing (0.15-0.3) percent polypropylene fiber and reinforced concrete with the composition of polypropylene and sinusoidal fibers related to test specimens containing (1.5%) metal fibers. Also, the results of scanning electron microscope imaging of concrete core sheaths obtained from fiber concrete in this study showed that fibers play a micro role in concrete. In addition, this research the effect of using optimum amount of fibers in the concrete sheaths in the buckling restrained braces were investigated. For this purpose, 6 samples of buckling restrained braces were made and examined in three modes. Concrete sheaths of buckling restrained braces without fibers, with polypropylene fibers and composition of polypropylene and sinusoidal metal fibers were the three modes. The samples made were then shifted to the intended location and installed in the laboratory under the loading protocol of BD/SAC - 02/97, also by applying the horizontal displacement contained in this protocol, the applied load and the amount of related peripheral displacement were calculated. Backbone, loading cycle-force, horizontal displacement - lateral displacement, push over curve and bilinear behavior model were finally drawn. By examining the results, it is shown that the maximum number of loading cycles, the coefficient of ductility, the energy absorption, and the maximum amount of applied force in the specimen produced by the composition of polypropylene and sinusoidal metal fibers are accrued.