Use of strut-and-tie method to predict the capacity of FRP shear-strengthened large-scale RC beams

The objective of this study is to investigate the ability of the STM to analyze large-scale RC beams strengthened in shear with externally bonded (EB) CFRP sheets. The STM approach is validated with 14 test girders with a shear span-to-depth ratio (a/d = 2.0) representative of deep-beam behaviour. The specimens considered were U-wrap CFRP shear-strengthened with single, double, and for some specimens, triple layers of CFRP laminates. They were grouped into four series based on the distribution of the steel stirrups along the shear span. The failure mode controlling the behaviour of the strengthened specimens was debonding of the CFRP sheets. A practical analysis and detailed design for the CFRP shear-strengthened girders using the STM is presented. In the method, externally bonded CFRP strips on a CFRP shear-strengthened RC member can act as additional tension ties. The tensile forces in the steel stirrups and the CFRP laminates are combined according to a proposed equation. The positioning of the horizontal struts is determined on the assumption that increasing the moment arm would increase the load capacity of the model. Structural analysis is conducted, and the applied load is determined based on the strength of each strut, tie, and nodal face. The results obtained using the STM are compared with the experimental results as well as the Canadian Bridge Design code (CSA-S6-06). The STM analysis approach, without considering the safety factor proposed by the ACI, shows its capability to predict the loading capacities of FRP shear-strengthened large-scale beams with good accuracy.