Hi,
it's a rather simple issue but I'm not sure what actually happens here. Consider a rectangular plate meshed with 3D solid elements. The plate is placed between two rigid planes and I model it by simply constraining two opposite faces in all directions. The plate is subjected to uniform compressive force on all 4 side walls. Now what I don't understand is why strain in the direction normal to constrained faces is not zero. Analytical solution for this problem assumes zero strain in this direction. What's more, the resultant reaction force in this direction is different than it should be according to analytical solution.

Do you know what can be wrong here and what causes this non-zero strain in Z direction?