I'm trying to help another engineer in my office determine forces in some footings using Risa 3D. He isn't comfortable with the results and wanted me to do a comparison on a simple dummy model using Ram Elements and spMats to verify that each program has similar outputs.
When comparing the M11 moments in Ram to Mxx in Risa and spMats what I found was Ram had the highest moments while Risa and spMats were a good bit lower but still not agreeing with each other.
The dummy model was a 10x10x1 footing with a 50k load at the center and pinned supports at each corner. The self weight of the concrete was included in the solver with no additional load factors.
Risa's output is Mxx, Myy, and Mxy which I assume is similar to M11, M33, and M13 in Ram.
Risa's help manual states that for footing design you need to add Mxy to Mxx or Myy to get the "true moment".
Does Ram output M11 and M33 with the contribution of M13 by default? If I subtract M13 from M11/M33 the results agree more with the other 2 programs.
If not, what type of plate does Ram use? I haven't been able to find it in the user manual.
Thank you for your time.
Does Ram output M11 and M33 with the contribution of M13 by default? Or should the absolute value of M13 be added to M11 and M33 when determining what moment to use for flexure steel design?
Thank,
Malton
Use M11 and M33 directly, assuming the shell 1 and 3 axes are aligned to the reinforcement (or whatever it is that you are checking)
I am using Ram Elements. My local axis are aligned to the reinforcement and to the M11 and M13 moment.
In Ram Elements, are you saying I don’t need to add the moment from M13 to M11 and M33 (using Wood and Armer method) to calculate my flexure reinforcement?
Thank you for the quick response,
I don't typically and Ram Elements does not either when it reports area of steel required for shells due to out-of-plane bending. I've only ever considered torsion according to Wood-Armer methods in Ram Concept where that program does it automatically. Even in Ram Concept I would only do this for some irregular system where slab torsion was a significant concern. For a bit more information see: https://communities.bentley.com/products/ram-staad/f/ram-staad-forum/103137/ram-concept---beam-torsion?ReplySortBy=CreatedDate&ReplySortOrder=Ascending