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Modeling straight purlins on a curved roof

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    Modeling straight purlins on a curved roof

    So I have a curved roof I want to model some purlins on. They will be 2x4's laid flat. I don't want them to curve in plan - these will be straight members laid directly on top of the roof - they are not curved. The result will be a slight bend in elevation of the members as they attach to the roof.

    Does anyone have any suggestions on how to go about modeling these? The beam family doesn't seem to be able to work in such a fashion. Can I make a face-based family that will attach to the curved surface?


    I was really trying to picture what you are thinking about here. Would it be something like in the video below?

    If yes, I just modeled this by creating a Mass that was curved in elevation but would be straight as requested in your post. Then created a Curtain Wall System on top of that Mass. The purlins would then be Mullions.

    Or I could be way off from what you are after. Some images would help if that wasn't it.


      This looks like a good workaround solution. I've actually never modeled a curtain wall -- I'm a structural guy. Can the curtain wall system attach to a roof or do I need a mass?


        You would need a face to attach, so a Mass would probably be the easiest to work with. I guess I haven't tried a Model-In-Place component. I usually just start out with a mass. See image below for that.

        The second option I can think of is using Dynamo, but thought you would really not want to touch all of that. Marcello has some classes on creating curved beams with Dynamo. That would inevitably lead you to your tessellated beams / purlins.
        Attached Files


          So I tried many things unsuccessfully. Curtain wall mullions would not conform to the freeform curve shape.I tried modeling a truss and attaching the top, profile was invalid error. I could not select a line of the roof as there wasn't one... the roof is sloped in one direction and curved in the other.

          In the end I had success by modeling a solid roof for the depth of the purlins (actually skip sheathing), and the using extrusions to cut out the roof to form 2x4's.

          I think the only other way to do it is using adaptive components and/or Dynamo.


            In the past when I did this, it was simply a matter of calculating the angle of rotation - so triangulation of the Z coordinate, and then a rotation on the member. Then you place the element on a reference plane, you can either create multiple planes at each purlin level or just calculate it from a single reference plane. Then in the properties of each member you can set the rotation. No need for any fancy methods here really.

            I used to set this up in autocad for ease of arraying it and modifying and measuring then just set the model up


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