The "BEAM_STRESS" output from Abaqus is great to visualize the stress distribution on the cross-section of a beam. I have found an example using B31 elements and an "I" cross-section where the "BEAM_STRESS" appears to be inconsistent with what I see from looking at the stress "S" field output variable. "BEAM_STRESS" is simply a post processing operation, but is such a large discrepancy to be expected? If so, why?

To double check my results, I have:

1. Extracted the "S" values from the ODB file with a python script and verified the values that can be seen in the image.

2. Requested field output at all section points