Size Effect in FRP RC Beams with and without Shear Reinforcement

This paper discusses the effects of member geometry (size effect) on shear behaviour of glass fibre reinforced polymer reinforced concrete (GFRP RC) beams with and without FRP shear reinforcement. The experimental programme comprised 6 beams with no shear reinforcement and 6 beams reinforced with closed external FRP shear links providing a minimum amount of shear reinforcement (calculated according to ACI440.1R-15). The beams were similar in mechanical properties, albeit varied in overall depth from 260mm [10.24 in] to 460mm [18.12 in]. All of the beams were tested in 3-point bending keeping the shear span-to-depth-ratio typical as for the beams failing in diagonal shear (about 2.65). Along with conventional instrumentation, a three dimensional digital image correlation system was employed in this study to gain an additional insight into the shear cracks development and their influence on shear strength. The experimental results showed that shear strength of GFRP RC beams is size-dependent, notably for beams without shear reinforcement. It was found that size effect is related to the shear crack opening and relative stiffness of the members. In addition, DIC measurements yielded meaningful information on diagonal cracks initiation and development along the shear span, and helped to better understand how shear cracking affects the shear resisting mechanisms in FRP RC beams.