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Forums >> Revit Structure >> Technical Support >> Arched LH series bar joist

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Fri, Sep 18, 2009 at 7:00:57 AM | Arched LH series bar joist

#1

arusso5


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Hello all, I posted this under Revit Building, but it's really a structural question.  I have been challenged to build a model of a Fieldhouse, that we designed a number of years ago, in Revit.  The structural framing calls for LH series bar joist, that have an arched top chord.  The roof is a barrel vault.  The bearing walls have different bearing heights on the front and rear walls.  Most of this is no problem, I have the bearing wall heights set, I've applied the roof to a mass that fits the profile, added my overhangs, I can import bar joists and set them to 2 different bearing heights, but how do I modify the joist to have the curved top chord?

I need the top chord to have 3' extensions as well.  I can't find anything even remotely close to this anywhere and I'm not comfortable enough with the family editor to create this.

Anybody help with this, or give me an idea how to modify the existing LH series bar joists to accomplish this?

Thanks in advance.  I love this forum.


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Mon, Sep 21, 2009 at 12:42:49 PM | Sloped Bowstring joist...

#2

arusso5


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Okay, so I got a little education and what I'm looKing for is a sloped bowstring joist.  I did find one that Tim0thyj posted in 2007, but there are a lot of variables that need to be tweaked.  Starting offset, ending offset, extensions, changing the angle of the seat, etc.

 Can anyone help me with the family editing?


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Fri, Oct 9, 2009 at 2:09:21 PM | Arched LH series bar joist

#3

emgeeo


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Joined: Wed, Mar 12, 2008
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Is this an existing structure, or just something that has been previously designed and unbuilt?

 

The second question is:  Do you need the family to be parametric?  Families do not need to be parametric in order to be effective.  If you have only one or two types of truss, you can model each one as a stand-alone, non-parametric truss.  Families don't need to be parametric/flexible in order to be effective.

 

I looked at the truss by Timothy.  It looks good and seems to flex well.  I'd be willing to help you modify the family, but you'll have to provide specific information.



Edited on: Fri, Oct 9, 2009 at 2:17:44 PM

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Mon, Oct 12, 2009 at 1:24:39 PM | Arched LH series bar joist

#4

arusso5


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emgeeo-

 Thanks for the offer to help.  The truss is part of a completed set of drawings for a high school that we designed and was built.  As a training exercise we are attempting to build the project in Revit for the client to use in the future.  The sloped bowstring joist that I need has two different bearing points, the front side is at 12' aff, the back side is 16'-8" aff.  That is the part I can't make work (at least it's one of them).  The bearing plates on Tim0thyj's bowstring truss are not flexible from a rotation standpoint and I have no idea how to fix that.  The radius portion of the truss needs to extend 3' past the masonry bearing wall.

See the attached image for a little more clarity.  While I don't think this type of truss will be used often in the future, I'd like to know how to modify it, and I can't figure it out.

Any help would be much appreciated.

Thanks in advance.



Attached Images

67441_truss_image.jpg

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Mon, Oct 12, 2009 at 6:07:38 PM | Arched LH series bar joist

#5

emgeeo


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3.5 Stars: 7 Votes


Since it's an existing structure, you really don't need to have a parametric truss.  I'm assuming that the majority of trusses are identical.  I would just use static, non-parametric geometry.

Do you have a CAD file you can import to Revit and use to trace?  This would be the easiest thing to do.  Then you can just pick lines.

Step by step if you have a CAD background.

1.  Start with a new family file - structural framing - trusses and complex.

2.  Under Settings -> Family Categories and Parameters -> [Check: Work Plane Based, Uncheck: Always Vertical]

3.  Insert your CAD background into a default Left or Right view.  Position the CAD sketch so that the middle a bearing point - it can be the high or low bearing point - is at the predefined crosshair.

3A.  In regards to step 3:  You may also be able to, and this would be the preferred method, position the crosshairs on the CAD drawing.  For the preferred method you will want to insert the CAD drawing at origin to origin, and move the crosshairs in the Left/Right views as necesary.

4.  Use your CAD background to pick lines - Symbolic Lines -> Structural Projection.  I would pick the top of the top chord, the bottom of the bottom chord, and the bottom of the extensions.  You'll also need to pick the centerline of the webs.  This is easiest to accomplish using the offset command in AutoCAD prior to building the truss.

5.  Trace your masonry walls with Reference Planes.  It doesn't need to be detailed - just the top of wall, inside and outside faces.  You'll need these to create your bearing plates while in plan view.

6.  Load the families you need to use.  There are two ways of accomplishing this.  You can load actual 3D modeling elements such as the W-Beam family, or you can load the individual 2D profiles.  Revit will still try and snap certain framing members together, so it may be easiest to just load the 2D profiles and create sweeps with them.

7.  Begin creating sweeps, but turn your CAD background off first, and cut a section at the midpoint of your sweep paths.  This section will allow you to adjust the position of your 2D profiles relative to the path centerline.  Use the 'Pick Path' option and select the symbolic lines you just created.  For editing the sketch, choose the 2D profiles you just loaded into the project.

8.  Use a single sweep for the webs.  They appear to be bar-joists.

9.  Depending on how your bearing plates are constructed, you can either use a double angle profile for a sweep, or you can create extrusions in plan. This is where you'll be using the reference planes you traced the masonry walls with.

10.  Visibility - Everything in your family has a visibility setting, I believe that includes the CAD drawing as well (which you should erase when you are done using it).  See step 3 and 3A.  If you insert the CAD drawing at origin to origin, it will be easier to modify the family if you left something out.  You can always insert at origin to origin and know that the drawing is placed in the same location as the first time you created the family.

But, back to visibility.  Everything in your family has a visibility setting- including lines and geometry.  You'll want your lines to be visible in course views, and your geometry to be visible in medium and fine views.  You can adjust the visibility of each element through the 'Visibility' button on the editing bar.  You can edit visibility of elements on an individual basis, or with multiple elements selected.

11.  After you've adjusted visibility paramaters, load the truss in your project.

12.  In your project, you'll want to create a reference plane or datum plane you can associate your truss to.  You'll have to rename the reference plane if you decide to use a reference plane.  Also, I pin any reference planes I rename, since they're easy to unkowingly erase.  Now, if you erase a pinned reference plane, Revit will warn you that pinned objects are being deleted. 

13.  Choose to create a beam, and select your new truss from the type selector- which by default should be the truss you just loaded into the project.  When you are placing the reference plane, you will receive a 'not allowed' icon for your cursor.  From the editing bar choose to place by work plane, and select the reference or datum plane you just created in step 12.

 

 

That's pretty much all there is to it.  You'll of course want to save the family, but you won't need family types.  If you need to make a modification to the truss, I would just copy the one you've just created, do a save as, and modify as needed.

Was that clear?  How did you do?


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Mon, Nov 2, 2009 at 7:44:38 AM | Arched LH series bar joist

#6

arusso5


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Joined: Mon, Aug 10, 2009
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emgeeo-

 Your directions worked perfectly.  I drew the bowstring truss and used it on the project and it looks spectacular (if I do say so myself).  I was getting hung up on the truss being parametric and not focusing on this being a one time thing.  Thank you for setting me straight. 

Everyone repeat after me... Not everything has to be parametric to function the way you want.

Thanks again.


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