$\sigma_i = \frac{0.316P}{h'} \left[ 4\log_{10}\left( \frac{l}{b} \right) + 1.069 \right]$

$\sigma_e = \frac{0.572P}{h^2} \left[ 4\log_{10}\left( \frac{l}{b} \right) + 0.359 \right]$

$\sigma_c = \frac{3P}{h^2} \left[ 1 - \left( \frac{a\sqrt{2}}{l} \right)^{0.6} \right]$

$\Delta\sigma = \frac{q_0}{2\pi} \left[ \cot^{-1} \sqrt{\eta^2\left( \frac{1}{m^2} + \frac{1}{n^2} \right) + \eta^4\left( \frac{1}{m^2n^2} \right)} \right]$

where

$m = \frac{B}{z}, \quad n = \frac{L}{z}$