I actually implemented the shell elements and to test it I modelled just the spar fixed at one end and having a point load at the other. the deformation i got at the free end was much underestimated compared to analytic solution (PL^3/3EI). However, when I did the same with solid elements, I got the same deformation and stress as in analytic solution despite horrible mesh. The mesh generated for shell model had high element quality, so its unclear to me why is it modelled incorrectly.
I attach a picture of my mesh with solid elements. the ribs appear to have high quality mesh while spar who is arguably simpler geometry is severely distorted. maybe you have some advice on how to
resolve that? 
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