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How to calculate the centre of gravitation for a pre-cast concrete panel?

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    #1

    How to calculate the centre of gravitation for a pre-cast concrete panel?

    Hi All,

    I've been aproached by a person who (incorrectly) thinks me to be a "Revit-know-all" person.

    I promised that I'll at least try to find an answer.

    Question: Is it possible and if yes how to calculate in Revit the centre of gravitation for a pre-cast concrete panel modelled in Revit?
    Tags: center, centre, gravitation, panel, pre-cast
    #2
    Well, you could do this by implementing some major mathmetic formulas. In principal the centre of gravitation depends solely on the geometric appearance of a form, and in the case of concrete the combined form of concrete and rebar (assuming that the material is known). Since this is known in Revit, you could build in the Formulas which calculate that.
    Now as for the actual implementation: if you could provide the needed calculations, it would be a nice challenge...
    Martijn de Riet
    Professional Revit Consultant | Revit API Developer
    MdR Advies
    Planta1 Revit Online Consulting

    Comment

      #3
      Hi Jerry,

      we discussed this in the French section here some days ago. One of my fellow countryman had an answer from Autodesk, telling him that it was not possible.
      I wonder if it's possible with API, but AFAIK it should be possible, but not easy.
      I've explained in the same post the workaround I personaly use:
      export 3d dwg > set the object at the 0,0,0 point > use massprop command in Autocad > put a sphere at the location indicated > link to Revit if needed.

      I guess this feature is really missing in RST to achieve a real precast workflow (I wont talk here about detailing...... )
      Julien
      "Au royaume des aveugles, les borgnes sont mal vus!"
      P. DAC
      Follow me on Twitter @Jbenoit44 - Blog: http://aecuandme.wordpress.com/

      Comment

        #4
        My french isn't all that good, and apparently my english isn't either. Julien, what's the centre of gravitation exactly? I'm confused because I thought it's the point in which the force of an elements own weight is supposed to "grab" on to that element. For instance, if you have a beam 400x400mm, the centre of gravitation would be 200mm up and 200mm to both sides of that beam. Am I correct?
        Martijn de Riet
        Professional Revit Consultant | Revit API Developer
        MdR Advies
        Planta1 Revit Online Consulting

        Comment

          #5
          absolutly right. the correct word seems to be center of gravity in English.
          for calculation, you'll need integra and other stuff that is not allowed yet in Revit, at least outside the API. That's why the Factory answered it's not possible in Revit.
          Julien
          "Au royaume des aveugles, les borgnes sont mal vus!"
          P. DAC
          Follow me on Twitter @Jbenoit44 - Blog: http://aecuandme.wordpress.com/

          Comment

            #6
            If it´s "just" a matter of getting the center of gravity for an object of uniform composition, it should most definitely be possible to calculate it in Revit, as Martijn suggested. The formulas are pretty basic for these kind of shapes. More info here on composite shapes (eg. panels with openings)

            I guess the real question is: How are the pre-cast concrete panels modeled in Revit? Families, system families, in-place, or is it something build into RST? And how complicated is the geometry?

            On the other hand... just because we CAN do it in Revit dosn´t mean that we should... there´s probably better software for this, and would like to know if anyone have first hand experience with the workflow (What software to use, and how to export from Revit)
            Klaus Munkholm
            "Do. Or do not. There is no try."

            Comment

              #7
              Originally posted by Munkholm View Post
              If it´s "just" a matter of getting the center of gravity for an object of uniform composition, it should most definitely be possible to calculate it in Revit, as Martijn suggested. The formulas are pretty basic for these kind of shapes. More info here on composite shapes (eg. panels with openings)

              I guess the real question is: How are the pre-cast concrete panels modeled in Revit? Families, system families, in-place, or is it something build into RST? And how complicated is the geometry?

              On the other hand... just because we CAN do it in Revit dosn´t mean that we should... there´s probably better software for this, and would like to know if anyone have first hand experience with the workflow (What software to use, and how to export from Revit)
              Well, I think that it IS crucial to be able to do this in Revit. If memory from school serves me well, the center of gravity is also the place where the analytical model system line should be. And this IS used by Revit to make the analytical model.

              Btw: Integra and other more advanced mathmethics ARE useable in Revit, but you'll need to be able to rewrite the original formulas. For instance, I once got this to work without the use of any API... Only a few days work of hard labor, lot's of headaches, etc.
              Martijn de Riet
              Professional Revit Consultant | Revit API Developer
              MdR Advies
              Planta1 Revit Online Consulting

              Comment

                #8
                Originally posted by mdradvies View Post
                the center of gravity is also the place where the analytical model system line should be. And this IS used by Revit to make the analytical model.
                This is correct. Revits analytical model line is at the "centroid" of the object for OOTB content. However you are able to change where that line is, so I would venture to guess that its not mathmaticaly driven location.

                Also the structural families do not behave as they should when you have a non symetric object. Its a known issue with those families and Autodesk keeps telling us that it will be corrected in the next version.
                Last edited by Alex Cunningham; May 24, 2011, 03:14 PM. Reason: added stuff
                -Alex Cunningham

                Comment

                  #9
                  Originally posted by Alex Cunningham View Post
                  This is correct. Revits analytical model line is at the "centroid" of the object for OOTB content. However you are able to change where that line is, so I would venture to guess that its not mathmaticaly driven location.

                  Also the structural families do not behave as they should when you have a non symetric object. Its a known issue with those families and Autodesk keeps telling us that it will be corrected in the next version.
                  How do you mean this? They behave wrong because the centroid is off or is it just not supported at this time.
                  Can you dimension the centroid? If so, it would theoratically be possible to make it mathematical driven. All the info is there isn't it?
                  Martijn de Riet
                  Professional Revit Consultant | Revit API Developer
                  MdR Advies
                  Planta1 Revit Online Consulting

                  Comment

                    #10
                    I mean that. However the OOTB families are built that they do not really take into account the actual geometry. Play around with the C-Channel beams. Flip the Justification on them . They flip off the centroid... but they do it as if the beam was symertical. Completly useless when it only take into account for beams that are symetric. This gives you incorrect dimentions if you are change the justification. Lame. Try it out.
                    -Alex Cunningham

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