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Thread: Parametric roof truss creation help

  1. #1
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    Parametric roof truss creation help

    So I have tried to create a parametric roof truss where I have defined the overall span, roof pitch, heel height, and mid-span post (as in a king-post truss). I am having trouble when I bring the truss into the project, one side of the truss drops to below the bearing elevation, and is distorted to no-where near what I am trying to create.
    In the family creation, I have the members aligned and locked to the reference planes, but I am not sure if I have the correct parameters in there.

    Would anyone like to take a look and give me some advice on how to correct this problem????
    Parametric King Post Truss.rfa

    (I am not sure if this is actually showing up in my posting- on my screen it shows a simple "x")

    thanks, casey

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    Moderator cellophane's Avatar
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    Instead of using reference planes for the top chord use a reference line. Constrain the line to your RP's and then lock the extrusion to the reference line. Feel free to hack apart the attached file. I'm not a structural guy so no guarantees on technical correctness but it behaves the way I need it to

    You might also look into the Truss family rather than modeling the way you did. They take a little bit to figure out from the family creation side of things but it might help. http://www.youtube.com/watch?v=ge7Su4aD-EI (first video a google search gave me that looked decent)
    Attached Files Attached Files
    Last edited by cellophane; May 7th, 2014 at 06:03 PM.

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    I am running 2014, did you upload it with a newer version? Would you be able to re-post it in 2014? And thanks for your timely response, and letting me steal your work

  4. #4
    Moderator cellophane's Avatar
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    Sorry. 2014 attached

    It's not stealing - it's an educational resource
    Attached Files Attached Files

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    So a little more information....
    As you can see In the family editor, I specified the span at 24'. When I bring the truss family into the project, I adjust the span to 46'-6" (in the properties bar, since I made those dimensions parametric).
    Now after watching the video that cellophane posted, although it does not directly address this, it appears that perhaps I do not want to lock & align the excrusions to the reference planes if I wish for it to update properly???

    Or perhaps its because I am creating this as a beam component???

    Another problem is that when i increase the span of the truss, the "midspan post" does not change its dimension from the specified 11'-7 3/4" in the family creator. Do i need to set up a linked dimension for the midspan that functions somewhere along the lines of
    " midspan post dimension= (0.5x"span")".


    I would like to show how the truss is being distorted, but the screenshot app i tried downloading is not working. Basically when i change the overall span length, one side of the top truss drops well below the bearing height, but the other half of the truss displays correctly.

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    I feel like i am so close to getting this correct...arrggh. So what i was envisioning was to have a single .rfa for each type of truss i could save on the server, and bring the correct type of truss in, adjust the parameters directly in the project and be done with it. Right now, my server is populated with a lot of the same type of truss, but different dimensions to correspond with the particular project i am working on. I could adjust this .rfa in the family editor with the desired dimensions, but than i spend time adjusting extrusion parts and reference planes, etc.

    I feel like this should be possible, but am I just being too demanding?

  7. #7
    Moderator cellophane's Avatar
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    Instead of having a separate parameter (unless you need it for some reason?) just constrain it to the centerline RP.

  8. #8
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    Thanks for your help cellophane, I have created a parametric truss family that is a generic model. Please see my thread that I created "Parametric truss-Free for use" for all looking for basic truss families.
    cellophane likes this.

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