Strut-and-tie model for FRP effectiveness in shear strengthening of RC deep beams

In this article, a strut-and-tie model (STM) is proposed for predicting the ultimate shear capacity of fiber reinforced polymers (FRP)-strengthened reinforced concrete deep beams. The proposed STM accounts for the effect of concrete strength, FRP ratio, ratio of main steel, horizontal and vertical stirrups ratio and shear span-to-depth ratio. The ultimate shear predictions of the proposed model are validated with 55 test results from the literature. The comparison showed that the proposed model performs well in predicting the ultimate shear capacity of FRP-strengthened RC deep beams. The overall average value of the ratio between the experimental capacity to the theoretical capacity of the proposed STM (Pu(EXP)/Pu(STM)) is of value 1.16 with a standard deviation of 0.18. Also, comparative studies between the proposed modified STM and the STM provided by the ACI code and other researchers in the literature are presented. Finally, FRP effectiveness studies are performed to study the effect of many structural parameters on the ratio between the ultimate strength for RC deep beams strengthened with FRP materials and the ultimate strength for ordinary RC deep beams. These parameters are FRP ratio (p(FRP)), the fiber orientation angle to the longitudinal axis of the deep beam, material type of FRP, concrete compressive strength (f'(c)) and the shear span-to-depth (a/d) ratio