Effect of shear span-to-effective depth ratio and FRP material type on the behaviour of RC T-beams strengthened in shear with embedded FRP bars

Shear strengthening of existing reinforced concrete (RC) structures with embedded fibre reinforced polymer (FRP) bars has received significant attention during the last decade. Yet, little consideration has been given to the effect of shear span-to-effective depth ratio (a/d) on the structural performance of shear-strengthened RC beams. This paper presents the results of a synergistic experimental, numerical and analytical investigation on the effect of a/d and FRP material type on the behaviour of shear-strengthened RC beams. Seven RC T-beams with an a/d ratio of 1.9 or 3.0 were tested. Two beams were unstrengthened (control) beams while the remaining five beams were strengthened with carbon FRP (CFRP) or glass FRP (GFRP) bars. A nonlinear finite element (NLFE) model was developed, validated using the experimental findings and utilised to interpolate the experimental results. Finally, the NLFE predictions and experimental findings were utilised to examine the predictions of existing design models. The results showed that beams with an a/d ratio less than 2.5 failed due to shear compression while beams with an a/d ratio greater than 2.5 failed due to diagonal tension. The total shear force capacity and the concrete contribution to shear strength decreased while the FRP contribution to shear strength increased with increasing a/d from 1.9 to 3.0. CFRP-strengthened beams exhibited a greater increase in shear strength compared to GFRP-strengthened beams. The investigated design models underestimated the total shear force capacity of the tested and modelled beams. However, the design model for deep beams gave better predictions than the corresponding model for slender beams.