For simplified shear design of slender RC beams (a=d > 2.5) with stirrups, a modified variable-angle truss model is developed in this paper. The conclusions can be drawn as follows:
. An analytical solution of the inclination of struts (θu) in the truss model is derived by combining the theory of plasticity and the concrete softening of the MCFT. As indicated in Eq. (8), there is a decreasing linear relationship between cotθu and lnω, where lnω is the natural logarithm of the mechanical shear-reinforcement ratio (ω). The proposed limit for strut angles is 18° ≤ θu ≤ 40° derived from the limits on ω.