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Thread: Help with custom truss

  1. #1
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    Help with custom truss

    I'm trying to create a custom truss and could use some pointers. I've attached a sketch of the truss that shows makeup of the top & bottom chords and webs, including architectural trim. You can see that the bottom chord is made up of two 2x6s joined with a 2x4 to make a "U" shape, the top chord is two 2x6s with 1/2" plywood sandwiched between, and the webs are like the top chord except using 2x4s. This truss is consistent throughout the building, so it shouldn't need to be adjustable, but I'd still like to do it the "right" way.

    I've been able to create the custom truss family, but I haven't yet figured out how to accurately show the composition of the chords. I'm guessing I need to create a custom structural framing family, but haven't gotten that far. I'm wondering if I should nest 2x4/6s into the structural framing or just model them. I understand nesting families is tricky (it didn't work correctly when I tried with a custom structural column), and I don't understand the downside to just modeling them directly in the truss family (but please let me know if it shouldn't be done this way).

    Also, I'm guessing I should just add the trim later as an architectural component.

    Any pointers folks can provide would be greatly appreciated. I'm brand new to Revit, so my apologies if these are "stupid" questions. Also, I'm using Revit 2014.

    Thanks!
    Attached Files Attached Files

  2. #2
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    I forgot to ask one more thing: when I place a truss the middle of the bottom chord is aligned with the top of my column and the top and bottom chords are "coped" to the column. I'd like for the bottom chord to rest on top of the column instead, without "coping" (actually the truss slips over the column, but I'm not sure if that can be modeled). If this just a matter of changing the offsets, or can/should I set up the structural framing family somehow to align it the way I want?

    By the way, if anyone can provide a link to a good structural framing family tutorial with nested dimensional lumber that would be great.

    Thanks again.

  3. #3
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    So its been a while since I created a truss, luckily Something I don't have to do often.
    The Tools may have been upgraded since I did this, but as I recall, you can set the profile type for each chord of the truss.
    Careful though, I mean you can set an individual extrusion/profile type for each of the following chords;
    Top Chord
    Bottom Chord
    Verticals (including any inclined chords)

    Meaning that all of the verticals will be the same profile.
    You can either change this after placement, or set it in the family itself.

    Having looked at your profiles there, I would be including all of the pièces in one extrusion family. (for your U shape for example you also have some other lumber on the sides, include these in the one same family.)
    You will need to create some specialised families (beams) to make those extrusions and then you can simply assign them to each chord as appropriate.

    The problem you may have is on creation the trusses need a fair bit of cleanup done for the connections.
    You will have to then go around and trim/cut geometry so its looking tidy. As I recall I had to unpin chords to be able to cut their geomeotry, and then I had to leave them unpinned. I suggest you create one truss only, unpin the elements you want to tidy up, create a GROUP of that truss once it is cleaned up and then copy that GROUP around for duplicates. That way you are only having to edit one truss to clean up all of the others.
    Last edited by Karalon10; May 30th, 2017 at 06:59 AM.

  4. #4
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    Thank you Karalon10. I have gotten to the point of creating the extrusions, which I believe should be Structural Framing, but that is where I am stuck...

    Also, where the various profiles come together different pieces of lumber/trim extend or overlap other pieces by different amounts...is it possible to do this with a truss? I'm beginning to wonder if a generic model would be better.

  5. #5
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    Some images from old old projects.
    You can see the truss in the image of the metal chords is in some places not nicely cleaned up and probably I missed these or chose not to do them at the time because it served no real purpose for my documentation..

    The cleaner looking joins have been manually cleaned up to look right.

    Your structural framing (yep you chose correctly) doesnt need to be anything more complex than an extrusion with an adjustable length.

    I might have a copy of the old truss family laying around for you so you can see how it was done, it was a specialised truss with specific formula to calculate vertical placements. This is more than you need I am willing to bet, but you will be able to see how I constrained it and how I set the chords by the profile types.

    With revit there are many ways to skin a cat, you could also model a generic family thats more of a block than a truss family. You can also just model each piece individually but basically that is what the truss family is already just sort of automated for you.

    The truss family creation did my head in back in the day and it is throwing yourself in the deeper end of family creation but once it clicks you will get it, stick at it.
    Attached Thumbnails Attached Thumbnails Help with custom truss-ext.jpeg   Help with custom truss-05-10-2016-09-47-45.png  
    Last edited by Karalon10; May 30th, 2017 at 06:29 PM.

  6. #6
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    Thanks Karalon10. When you say "manually cleaned up" do you mean stuff done in the model (like coping) or detail annotations? Were those steel connections done with any extensions, or just plain Revit?

    EDIT: By the way, if you do have the truss family handy I would appreciate it. Otherwise I'll just keep at it.
    Last edited by sleeknub; May 31st, 2017 at 06:13 AM.

  7. #7
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    they were done with coping. as i said you have to unpin the elements before they will cope. if you then repin them, it will lose the coping. its a PITA to be honest.
    Thats why I said make 1 truss, unpin everything and cope the objects, then make a group of the truss and use that group to make duplicates.
    Coping was just done in native revit with the coping tool, easy peasy just time consuming.

    a couple of old truss families for you to take a look at
    Attached Files Attached Files
    Last edited by Karalon10; May 31st, 2017 at 12:02 PM.

  8. #8
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    Thanks for the files, but I'm using Revit 2014 so I can't open them. Is it possible to save them as an older file type? If not, no worries.

    As far as I know the coping tool is essentially automatic (other than choosing the chords and setting the coping distance). I need to be more detailed with the junctions and ends of my structural framing members. Is that something I can do with the coping tool, or is there some other way to do it? Otherwise I guess I could just use a generic model for my truss...but I'm not sure if I'll loose some functionality.

    I'm also having another problem with my truss. I want the truss to have a specific angle that matches the roof slope (6:12), so on my truss family I dimensioned the angle of the top and bottom chords and locked it. Ideally when I place a truss it would scale/adjust it to fit whatever length I draw out, then calculate the truss height based on the angle and the length. However, when I place the truss it keeps defaulting to a truss height of 3' 8" (even though may truss family was created with a height of 3'), and it keeps the angle constraints, so it ends up drawing a truss that is longer than it should be (the end of the truss is well past the end point I specified). Anyone know how to fix this to get the behavior I want?

    Thanks.

  9. #9
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    Here is an image of a sketch to help explain what I am looking for as far as coping is concerned. Sorry it is so light...

    The top chord/rafter part of the truss needs to be squared off at the end, and the bottom truss needs to be angled at the end even though it overlaps the top chord.

    Attached Thumbnails Attached Thumbnails Help with custom truss-2017-05-31-23.16.47.jpg   Help with custom truss-2017-05-31-23.16.47.jpg  
    Last edited by sleeknub; June 1st, 2017 at 06:26 AM.

  10. #10
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    Unfortunately, I can not save them in previous versions. I don't have previous versions available, and even if I did, revit is not backwards compatible (unlike autocad where I can save in format DWG 2007, I can not do this for Revit).

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