Effect of concrete triaxial confinement on the nodal-zone efficiency of concrete deep beams reinforced with GFRP bars

This study examined the effect of concrete triaxial confinement on the nodal-zone efficiency of concrete deep beams reinforced with glass fiber-reinforced polymer (GFRP) bars. Eight large-scale GFRP-reinforced concrete deep beams and one steel-reinforced concrete deep beam (reference)—all with web reinforcement—were tested to failure under two-point loading. The only variation in the specimens was the dimensions of the loading and/or supporting plates relative to the concrete beam width. All other factors—such as the shear-span depth ratio, main reinforcement ratio, and specimen geometry—were kept constant. The failure mode of the tested specimens was identified as diagonal strut compression failure, except for the fully confined specimens that experienced diagonal shear failure. In addition, the results confirm the formation of arch action in the tested specimens, as evidenced by the cracking pattern and measured strain along the longitudinal reinforcement. On the other hand, the results reveal that both the flexural and diagonal crack widths remained below the limits specified in CSA and ACI standards governing GFRP-reinforced concrete structures. Additionally, the results confirm that triaxial concrete confinement is effective in GFRP-reinforced concrete deep beams, with the confinement efficiency increasing from 81% for the non-confined specimen to 119% for the fully confined specimen.