Thank you very much for your reply😛. I look for analytic solutions. I'm aware that analysis is only valid for a range of width to length or depth to length ratios. But analytic solutions for torsion isn't aspect ratio sensitive. Yes, I refer to torsion. When you twist a bar and if the bar is not of round cross section, there is longitudinal (z) displacement and this is where the warping function psi(x,y) comes from. When the cross section is round, psi=0.
I don't have the book Formulas for Stress, Strain, and Structural Matrices. Don't know if I can find it online.