Hi

If I understand correctly your problem; I think this YouTube link can help you.

https://www.youtube.com/watch?v=J0cCA1PAINU

Dear Mr. Amani!

Many thanks for the prompt reply. I saw the video. It is very useful, but my problem is that I have no beam to use beam tools. All part of my model  was made with surface body. and all elements are shell 181.

Thank you

It seems that some researchers in Researchgate had the same problem.

Please have a look:

https://www.researchgate.net/post/Does_anyone_have_knowledge_on_decomposition_of_stresses_in_shell_elements-membrane_and_bending_stresses

Hello Dear Amini!

Thank you for reply again. I saw the link and it was useful, but finding bending moment is my problem, not bending stress.

Thank you again for your answers.

With the bending stress you can find the bending moment value using basic strengh of materials.