Dear Ayad,

In general, shell elements can have also through the thickness integration points, so, in principle you can also capture through the thickness stresses.

Regards,

Hunor

Simple shell theory provides bending stresses uniformly varying from top to bottom of the plate, being maximum positive to maximum negative. Added to this the in-plane stresses will give the total stress at any point along the thickness. There are complicated models of layered shell analysis, but are more useful for analysis of composites. For simple solid plates, the single shell model through the thickness is sufficient and analysis is quite fast and accurate too.

I think you should check also the Stacked-Shell theory which is used in composite laminates.

I think for thin-walled plates, shell element gives more accurate results than solid element. Solid element overestimates the stiffness as it doesn't provide rotational degree of freedom. Please correct me if I am wrong. 

Looking again at the original problem, which Ayad Mutafi has stated, he is more interested in press forming thin sheets where there is extensive plastic flow of the sheet material. The sheet being thin the magnitude of bending stresses will be negligibly small compared to membrane (in-plane) stresses. In such a situation investigators have tried visco-plastic stress analysis using membrane shell elements with success.

 Make sure you have enough integration points through thickness.