Experimental study of shear behavior of CFRP strengthened ultra-high-performance fiber-reinforced concrete deep beams

This experimental study aims to examine the effectiveness of shear stirrups and carbon fiber-reinforced polymer (CFRP) strengthening scheme in enhancing the deep beams’ shear strength. For this purpose, a total of six deep beam specimens of 150 mm × 300 mm (depth) × 1000 mm with an effective span of 750 mm, classified into three groups of two specimens each, were prepared. The beams of the first group were of normal concrete (NC). The beams of the second group were prepared using ultra-high-performance fiber-reinforced concrete (UHPFRC). In the third group, the UHPFRC deep beams were strengthened using CFRP strips. Each group had two beams – one with no shear stirrups and another with shear stirrups. All deep beams were tested under four-point loading until failure. According to the experimental results, shear stirrups effectively contributed to enhancing shear strength, ultimate load, and deformation capacity for NC deep beam. By utilizing the UHPFRC mix, the deep beams’ shear strength was upgraded significantly compared with the NC deep beams, but the deformation capacity was reduced. The implemented strengthening scheme was effective in the enhancement of deep beams’ shear strength and deformation capacity. The improvement in the shear strength of strengthened UHPFRC deep beams was moderate (16%); however, a considerable increase was observed in the deformation capacity as the displacement and energy ductility indices were enhanced by 49% and 185%, respectively.