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Thread: Truss Issues

  1. #1
    Member doni49's Avatar
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    Truss Issues

    Hi all!

    I'm trying to work with the Truss tools in Revit and it's just not working out right.

    The first image shows what I'm trying to duplicate (another user in the office drew each member manually on a previous project per the architect's requirements).
    Truss Issues-truss-desired.png

    This image shows what my family looks like (I've attached the RFA file).
    Truss Issues-truss-familysketch.png

    This image shows what I get when I attempt to use the truss in a project (RVT file is also attached in the zip file). Notice how the top chords don't meet the bottom chords? The bottom appears to be offset towards the background for some reason.

    Truss Issues-truss-inproject.png

    This image shows the plan view of what the truss looks like in the test project.
    Truss Issues-truss-planview.png
    Attached Files Attached Files

  2. #2
    Forum Co-Founder Alfredo Medina's Avatar
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    This should work (see attached truss family). I opened a "Pratt Gabled Truss-4 Panel" family, and I modified it to be a "Pratt Gabled-2 Panel plus Overhang" family.
    Attached Thumbnails Attached Thumbnails Truss Issues-pratt-gable-truss-2-panels-plus-overhang%5B1%5D.jpg  
    Attached Files Attached Files
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    Member doni49's Avatar
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    Quote Originally Posted by Alfredo Medina View Post
    This should work (see attached truss family). I opened a "Pratt Gabled Truss-4 Panel" family, and I modified it to be a "Pratt Gabled-2 Panel plus Overhang" family.
    Thanks Alfredo. That looks like it should work. But my real goal was to learn how to do this myself. I'm not finding the help very helpful. I'll try to reverse engineer this and hopefully I can figure it out.

    But in the meantime, I've been trying to figure out how to tell it what the members are (they'll all be wood beams -- I still need to find out from the engineer what size members). But as you can see from this image, the List under Structural Framing Type doesn't include any options for wood beams. I looked through the help and all I can find is "Defines the structural framing type of the top chords".
    Truss Issues-truss-frametype.png

    And then there's the issue of telling it how the members should be joined together.
    Truss Issues-truss-elevationviewofprattgabledtruss.png

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    Member TRWhitehead's Avatar
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    Don,

    Do you have any wood members (as structural framing) loaded? That pick list shows any structural framing member that is loaded in the project. If it isn't loaded, it isn't available for a truss.

    As for joining, I think you can use the "Coping" tool under the modify|Structural Trusses tab. You have to unpin the elements first, apply coping appropriately, then pin them back to allow them to update. Trusses are great to a degree but can get really tedious in some conditions.
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    Member doni49's Avatar
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    Quote Originally Posted by TRWhitehead View Post
    Don,

    Do you have any wood members (as structural framing) loaded? That pick list shows any structural framing member that is loaded in the project. If it isn't loaded, it isn't available for a truss.
    That explains it thanks. I thought I needed to enter this in the family definition somewhere but I wasn't finding a place to do so.

    Quote Originally Posted by TRWhitehead View Post
    As for joining, I think you can use the "Coping" tool under the modify|Structural Trusses tab. You have to unpin the elements first, apply coping appropriately, then pin them back to allow them to update. Trusses are great to a degree but can get really tedious in some conditions.
    I'll look in to that.

  6. #6
    Forum Co-Founder Alfredo Medina's Avatar
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    Don, what I did was this:

    • Open the most similar truss family, the Pratt Gable 4 Panel
    • Save as Pratt Gable 2 Panel plus Overhang
    • Remove one vertical reference plane from each side of the truss, which deletes the 3 equal constraints for 3 panels.
    • Restore the equal-equal constraint to create 2 panels on each side.
    • Add 3 parameters, "Overhang_X", "Overhang_Y", and "Slope", to calculate, by trigonometry, the extension (overhang).
    • Delete the top chords, and do them again from the top intersection to the intersection of the ref. planes of the overhang.
    • Delete the web members and do them again, constrained to the new top chords.
    • Flex and test.


    What I didn't do, and needs to be done:

    • Load the wood framing families into the truss family.
    • Specify those wood framing families as the default members for chords and web members.


    After that, you need to:
    • load the family into the project
    • Use the coping tool on each member to get the final result.

  7. #7
    Member doni49's Avatar
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    Quote Originally Posted by Alfredo Medina View Post
    Don, what I did was this:

    • Open the most similar truss family, the Pratt Gable 4 Panel
    • Save as Pratt Gable 2 Panel plus Overhang
    • Remove one vertical reference plane from each side of the truss, which deletes the 3 equal constraints for 3 panels.
    • Restore the equal-equal constraint to create 2 panels on each side.
    • Add 3 parameters, "Overhang_X", "Overhang_Y", and "Slope", to calculate, by trigonometry, the extension (overhang).
    • Delete the top chords, and do them again from the top intersection to the intersection of the ref. planes of the overhang.
    • Delete the web members and do them again, constrained to the new top chords.
    • Flex and test.


    What I didn't do, and needs to be done:

    • Load the wood framing families into the truss family.
    • Specify those wood framing families as the default members for chords and web members.


    After that, you need to:
    • load the family into the project
    • Use the coping tool on each member to get the final result.
    Wow! Thanks for the detailed response. It's greatly appreciated.

    I do have another Q though. How can I go about getting the ridge beam to show up? Or am I getting ahead of myself and that's later in the process?

    EDIT: I guess maybe I'm confusing the two here. If using ridge beam and rafters, the trusses wouldn't be used. I guess I was looking for a simpler way to show the framing than placing each and every framing member.
    Last edited by doni49; July 10th, 2015 at 06:12 PM.

  8. #8
    Forum Co-Founder Alfredo Medina's Avatar
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    The ridge beam needs to be modeled in the project. This family just takes care of the trusses but does not have anything to do with the ridge beam. Locate the trusses, then model the ridge beam and the rafters. The rafters can be modeled as a parametric beam system.

    EDIT: oh, after reading your Edit note, it seems that you didn't need a truss at all.
    All you need is beam systems and some individual beams.
    Last edited by Alfredo Medina; July 10th, 2015 at 07:44 PM.

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