Shear deformations based on variable angle truss model for concrete beams reinforced with FRP bars

The contribution of shear deformations to total deflections in slender concrete beams is often ignored in design practices. The negligence of shear deformations could lead to the underestimation of total deflections in slender concrete beams, which will result in unsafe designs of slender concrete beams at service conditions. The shear deformations could be more critical in concrete beams reinforced with FRP bars than reinforced concrete beams because of the lower elastic modulus of FRP bars as comparing to steel ones. To address this problem, this paper attempts to determine shear deformations of slender concrete beams reinforced with FRP bars based on the variable angle truss model. The shear span of the slender concrete beams is divided into the truss units. The inclinations of struts in these truss units are first calculated by using the principle of virtual work. The shear deformations of the beams are then evaluated by summing all the shear deformations in the truss units. The calculated shear deformations are incorporated into ACI 440.1R-15's deflection approach (2015). Comparisons are made between the analytical and available experimental results of slender concrete beams reinforced with FRP bars with respect to the deflections at 50% and 75% of the failure loads. Better results as comparing to the existing design guidelines in calculating the deflections of the slender concrete beams reinforced with FRP bars are obtained by incorporating the proposed shear deformations.