Shell modeling in ANSYS

JeppeMM

I have been modeling a sandwich box in ANSYS using layered SHELL281-elements, which is somewhat new to me. The box is modeled with rounded edges, and it is affected by a positive pressure on one side and suction on the opposite side. This way the force is in the negative x-direction on both sides.

My question is related to the xy-shear strains, which vary from positive to negative though the thickness of my shell. I am guessing that this should not be the case, but I cannot get my head around, why this is the result I am getting.

Similarly I have tried to model a slender beam using the same element in order to investigate, what I am doing wrong and to compare with a solid model. In this case, however, my xy-shear strains are zero. This makes me think, if it is a good idea to model a slender beam with shell elements, and if the shear strain results from the shell-element are trustworthy? When observing the first-order-shear deformation theory they should at least make some sense.

Of course my first priority is to get a good estimate for the shear strains in the box, but I would also like to understand, what I am doing wrong with the beam. I hope someone with a little more experience in layered shell-modeling can help me.
Best regards