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Ram Elements vs Risa 3D vs spMats

Max Karr
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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.

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  • 0
    This is in the main Ram Elements analysis using plate elements, not the footing module I assume.

    One factor could be the meshing of the plate or the addition of extra supports. For more on this see: communities.bentley.com/.../ram-elements-shells-faq

    Besides M11 and M33 moments, Ram Elements can also plot Mmax or Mmin moments (or Von Mises stresses) to capture the absolute worst case. For more on those check the program help pdf (search for Von Mises).



  • 0 Offline in reply to Seth Guthrie
    Thank you for your reply Seth.

    To my knowledge, yes this is the plate elements and not the footing module. I don't believe we have a license for the footing module.

    Unfortunately I do not know Ram Elements enough to argue the difference in the meshing or the additional supports, other than I know the other engineer set the model up with the same mesh distribution and I can verify that the corners are pinned.

    I've been checking the other contours, and while the values are off the contours themselves are similar in appearance as they should be.

    I think it may come down to what type of plates the programs use. A link was shared with me on eng-tips.com that compared Risa with a thick plate modeler against two thin plate modelers (Risa being a thick plate modeler). The FEM stresses in the thin plate models were higher, and from skimming the results the differences were along the lines of what I am seeing between Risa and Elements.

    So the question then is, what type of plate does Ram Elements use?
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  • 0 Offline in reply to Seth Guthrie
    Thank you for your reply Seth.

    To my knowledge, yes this is the plate elements and not the footing module. I don't believe we have a license for the footing module.

    Unfortunately I do not know Ram Elements enough to argue the difference in the meshing or the additional supports, other than I know the other engineer set the model up with the same mesh distribution and I can verify that the corners are pinned.

    I've been checking the other contours, and while the values are off the contours themselves are similar in appearance as they should be.

    I think it may come down to what type of plates the programs use. A link was shared with me on eng-tips.com that compared Risa with a thick plate modeler against two thin plate modelers (Risa being a thick plate modeler). The FEM stresses in the thin plate models were higher, and from skimming the results the differences were along the lines of what I am seeing between Risa and Elements.

    So the question then is, what type of plate does Ram Elements use?
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