flatter and varied considerably from 20 to 40° when the mechanical shear-reinforcement ratio decreased from 0.46 to 0.04. From the test results, it can be found that the strut angles remain around 40° when ω > 0. , fitting well with the upper limit for strut angles in the proposed truss model.
The measured angle refers to the principal strains but the calculated one refers to the principal stresses. There is a tendency that the change in principal stress directions lags behind the change in principal strain directions, but it is practical to assume that principal stress and strain directions coincide (Vecchio and Collins 1986).