I noticed that if you model a simple beam (1 element, 2 nodes each pinned) in STAAD then shear deformation is not considered. When I added a node to the center of the beam and left everything else exactly the same it then considered shear deformation. Yes, I know that SET SHEAR causes it to ignore shear deformation and if you leave out shear area it won't consider shear deformation. I did not do either of these.
I noticed this when I was comparing STAAD's results to the theoretical results for benchmark case 1 (Fig. C-C2.2) in AISC 14th ed. I got answers that almost perfectly agreed with the "exclude shear deformations" results.
What's happening under the hood to cause this?