If 'M’ is maximum moment in the plate girder, 'P’ is allowable bending stress and ‘tw, is the thickness of web, Economical depth for a plate girder is given by:-
1
\(\sqrt{(M/P) \times t_w}\)
2
\(1.2 \sqrt{(M/P) \times t_w}\)
3
\(1.1 \sqrt{(M/( P. t_w)}\)
4
\(1.3 \sqrt{(M/P) \times t_w}\)