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Thread: Truss Top and Bottom Chords

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    Default Truss Top and Bottom Chords

    I am trying to make a truss that has a different length bottom chord from the top chord. I put reference planes in the family lock the bottom chord to these reference planes, and import the truss into the project. When I initially place the truss everything looks fine, but if I make any adjustments to the properties of the truss the bottom chord will extend to the length of the truss. Attached is a couple of pictures of a Warren truss that comes with Revit. In that family the bottom chord is shorter than the top, similar to what I want. When I initially place the Warren truss everything looks fine (see attached), but if I change the height the same thing happens in that the bottom chord defaults back to the truss length (see attached). Anybody else experienced this?
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    All AUGI, all the time kathy71046's Avatar
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    Default Re: Truss Top and Bottom Chords

    I haven't figured out how to lock a chord difference into a truss family yet, but you can adjust the length of the framing members individually.

    Is your bearing set to the top chord? (if it's changed to bottom then it will push itself out rather than hang on skyhooks)
    Kathy Taylor
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    Default Re: Truss Top and Bottom Chords

    The bearing chord is set to the top chord. I just find it odd that it would come in correct but then revert back to the overall length when ever any modifications were made.

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    Default Re: Truss Top and Bottom Chords

    The whole joist family confuses me.

    The insert reference plane should be joist bearing, not top of steel.
    Bearing shoe depth should be independently controlled at start and end.
    Bearing shoes should always be aligned with the slope of what they bear upon (horizontal 99% of the time) while the joist itself can slope.
    When joists are placed on beams, sometimes they bear correctly (bottom of shoe on top of beam), other times the top of joist is the same as top of beam (?).

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    All AUGI, all the time kathy71046's Avatar
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    Default Re: Truss Top and Bottom Chords

    Quote Originally Posted by djn View Post
    The bearing chord is set to the top chord. I just find it odd that it would come in correct but then revert back to the overall length when ever any modifications were made.
    I hade the opposite problem, where I wanted the bottom chord to reach the walls/steel and it wouldn't.

    Not sure if it will help, but you could try to reset the truss.

    Sorry sthedens, I don't get what you mean by shoe, and afaik, a beam will insert according to where you set the z-direction justification (at least in all my loaded members)
    Kathy Taylor
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    Default Re: Truss Top and Bottom Chords

    Perhaps the three attached images explain what I'm talking about.

    3D.jpg shows two aligned joists bearing on a beam.

    Section.jpg shows bearing shoes sloping at same angle as joists as opposed aligning with the beam they are bearing on.

    Plan.jpg shows the same two joists' symbolic lines behaving differently.
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    All AUGI, all the time kathy71046's Avatar
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    Default Re: Truss Top and Bottom Chords

    Not sure how your shoe works model wise, (we don't really use that type of connection) if it's considered a web, setting it vertical rather than orthogonal might straighten it, but it will also affect any other webs in your truss.

    I believe the software is designed to create an analytical model, not actual connections, so you may be best just to leave it and use a drafting view to show how it should sit, since any section should be at a scale where you can't see a small kink like that.

    As for the stick lines, if they are the default stick figures, they are controlled by start and end extension, see the pic attatched.

    Hope that helps some.
    Attached Images Attached Images
    Kathy Taylor
    Senior Structural Draftsperson & Proprietor
    TaylorCAD
    www.taylorcad.com.au

    I don't suffer from insanity - I enjoy it!
    Revit User Phase 3, 4, 5, 4, 3, 5, 4.....

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    Default Re: Truss Top and Bottom Chords

    hi how do you design top and bottom chords?

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