A thin circular ring of radius r and uniform flexural stiffness carries two radial loads W applied along a diameter. Estimate the maximum bending moment in the ring.
By symmetry the loading actions on a half-ring are \frac{1}{2}W and M_0 . The bending moment at any angular position θ is
M = M_0 – \frac{1}{2}Wr \sin \thetaThen
C = \int_{0}^{\pi}{\left(M_0 – \frac{1}{2} Wr \sin \theta\right)^2\frac{r d\theta}{2EI}}But ∂C/∂M_0 = 0, so that
\int_{0}^{\pi}{M_0 d\theta } = \frac{1}{2} Wr \int_{0}^{\pi}{\sin \theta d\theta}Then
M_0 = \frac{Wr}{\pi}