This issue comes up repeatedly in my analyses so I have built a small model to isolate the problem and try to find solutions.
This is a model of a storage bin outlet with a normal pressure applied on the shell. The outlet is stiffened with beam elements. I am using a mixed mesh with shell/beam elements with manually defined contacts. I am doing a simple static analysis. The stresses in the beams are not symmetrical while the problem is perfectly symmetrical. The stiffness of the beams seem correct because the deformed shape is symmetrical.
File is attached if anybody wishes to have a look. I feel like I am missing something obvious but haven't been able to find it.
Any help appreciated,