The economic depth of web plate 'd' in the design (in working stress method) of plate girder is: (where 'M' is the maximum bending moment, 'obc' is the permissible bending strength and 'k' is constant)
1
\(\rm d=k\left(\frac{M}{\sigma_{bc}}\right)^{\frac{1}{2}}\)
2
\(\rm d=k\left(\frac{\sigma_{bc}}{M}\right)^{\frac{1}{2}}\)
3
\(\rm d=k\left(\frac{\sigma_{bc}}{M}\right)^{\frac{1}{3}}\)
4
\(\rm d=k\left(\frac{M}{\sigma_{bc}}\right)^{\frac{1}{3}}\)