Collar Tie Truss

[cyrankam]

In Short: How one would go around creating collar tie truss, so it could be attached to sloped roofs easily. The requirement is the possibility to change the collar height accurately by the user.

Desired truss

Explanation: We do design a lot of very similar roofs, that differ only in span and slope. Usually all are constructed with collar tie. Right now we model rafter, and collar ties as separate beams, but as the design process continues it becomes more and more cumbersome to handle any changes. Idea is to create truss family, where user can draw a roof, drop truss family, attach it to the roof and then just copy the family desired amount of times. After that you could forget it, changing slope, to the roof would drag the truss with it. I have made some tries but to no avail, changing the height of the collar tie makes the truss to behave funky. Additionally, making the top cord to meet the roof (same slope) is quite difficult - changing truss height requires changing its length as well. Please see the attached family.

One of the try

Bonus question: is there a way to create truss with double beam as below so it would be scheduled as two separate beams?

Additional question

[barthbradley]

Can you use a different compression utility? Many of us don't have WINZip. 

...Trusses??? Not Beams?  I would use Beam Systems throughout.  Maybe I'll change my mind when I see your RVT. 

[cyrankam]

Sure, see attached.

Beam systems are nice idea, but have some limitations. First, joining beams doesn't seem to work in some cases. Secondly, trusses usually are not spread evenly.

[barthbradley]

It tests pretty well in the Project -- after I labeled the Dimension to the Collar Tie.  I'm not readily seeing the issue.  What am I looking for? 

Regarding "Bonus Question": Create a "Collar Truss" Structural Framing Family as a Shared Family, and Nest and place two instances of it a Host Family (e.g. "Double Collar Truss").  

[barthbradley]

[barthbradley · Accepted solution]

Regarding Bonus Question: Why not overlap 2 Web Lines to host 2 Collar Tie Structural Framing Members - using 2 different Justifications in the Project (e.g. Right and Left - not Center)?  

[ToanDN]

Attached is the revised truss family loaded in a project.  It attached to the roof correctly.  The Collar Beam Height can be adjusted for each truss.  The Truss Height is automatic per the roof it attached to, no need to mess with it.

To create the double chord tie, just duplicate the member profile and make it a double, load in your project to create a new structural framing type and assign it to the tie beam.

[barthbradley]

[cyrankam]

Thank you all for your replies. Regarding double tie, what @barthbradley  is proposing looks promising and exactly what I wanted to achieve. I will give it a try.

Before that - the truss. I am not getting it, I think that I am doing something wrong and cant get it to work. The top chord beams are going into the roof a little bit. I have set up a parameter to control tie height (distance from bottom chord to the tie), and it doesn't seem to work. Please see attached.

[barthbradley · Accepted solution]

Your family isn't constrained properly. Check the apex.  Align and lock the TIPS of the Chord linework to intersecting Ref. Planes.  

[cyrankam]

You are right, I must've break down the constrains when I was meddling with the family. All is good now. Except for the tie height. The parameter works perfectly when the truss is not attached to the roof, I think it has something to do with the Truss Height parameter, that is not reporting correct value while the truss is attached. It almost seems that it sets the value proportionately to what Revit thinks the truss height is, and not to what it actually is. Please see the fallowing.Not attached - correct height

Attached 1 - values do not match

Attached 2 - when the value is set close to what Truss Height parameter report tie is close to real height of the truss

[barthbradley]

Try inputting my formula for the Collar Height.  I posted it above. Worked for me.  

[cyrankam]

It does work, but it sets the height at constant level of 1/3 truss height, right? While I would like to control it independent of truss height. For instance 1000 mm of the bottom chord. 

[ToanDN]

Did you look at the file attached in my post? You can move the collar up or down in project without breaking anything.

[cyrankam]

I believe it has the same issue, the value set do not match value measured when truss is attached.

[cyrankam]

Ok, so eventually I have figured, that way easier way to achieve the goal would be to  use bottom chord as tie, and then extend the rafters to desired level. The downside is that structurally it is not a valid model, and length of the rafter is reported incorrectly. Scheduling Cut Length provides required information so for me it is acceptable.

[ToanDN]

The collar beam height reflect the dimension when the truss profile is not modified.  If the truss height is different from the roof height and you use Attach Top to match the roof then the collar height appears to be incorrect.  So the easy way to fix it is set the truss height to match the roof height then attach it to the roof.

[barthbradley]

Why not use the formula I posted in Message #5?  2*(Truss Height/3). The Collars will maintain the ratio then.  

[ToanDN]

Thought he wanted the distance to be flexible, not tied to a ratio (see #13).

[barthbradley]

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@ToanDN wrote:
Thought he wanted the distance to be flexible, not tied to a ratio.

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Maybe I read it wrong.