Grain Storage Structures and Silos

A silo has hopper bottom inclined at angle $\alpha = 45^\circ$ with horizontal. The static coefficient of friction between grain and hopper steel sheet is $\mu = 0.40$ (friction angle $\theta = \arctan(0.40) \approx 21.8^\circ$). The safety margin angle $(\alpha - \theta) = 45.0^\circ - 21.8^\circ$ for gravity discharge in degrees is (rounded off to one decimal place):