What is the sign convention for slab or strip moments in S-Foundation?

Todd Taylor
Todd Taylor New Altair Community Member
edited August 2023 in Community Q&A

What is the sign convention for slab or strip moments in S-Foundation?

Correct me if I'm wrong, it appears that positive moments require top reinforcing, and negative moments require bottom reinforcing? 

Is there a way to reverse this sign convention in S-Foundation settings, so that a "positive moment results in a smile"?

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Answers

  • Tayen Aguilar_20350
    Tayen Aguilar_20350 New Altair Community Member
    edited August 2023

    Hello Todd, I think I might be able to help you.

    The sign convention for S-FOUNDATION is the same as S-FRAME's, as seen below:

    image

    image

    Fx acts on the ‘X-Face’ in a direction parallel to the X-axis. Mx is the moment that
    works on this same face and thus is the moment resulting from spanning parallel to the X-axis.

    Another way to think of this in the context of modeling slabs is that rebar parallel to the X-axis resists Mx. Fxz is
    the out-of-plane shear force acting on the X-face. All these forces have their Y-axis equivalents.

    With that said, regarding your second question, you are correct, positive bending moments Mx and My will cause tension on the positive z-surface of the element.

    In S-FOUNDATION these results can be with respect to different coordinate systems at the user's choosing (Global or Panel) so you can invert the positive direction of the Z-axis so the positive moments act "downward", thus, requiring reinforcement on the bottom.

    I hope that you find this information useful, please let me know if you have any additional questions.

    Best regards,

    Tayen Aguilar

    Altair Support

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