From this
point of view, the inclination angle of the inclined struts can be
freely chosen as long as yield conditions are not violated. These
yield conditions are usually taken as the shear strength controlled
by the yielding of shear reinforcement (Vs) and the shear strength
controlled by the crushing of the web concrete (Vc ). Therefore, a
lower bound solution for the shear failure load of concrete webs is
(Nielsen 1984)