Proof in concept - New Roof Truss Family Idea

[erikbjur]

Let me state right off the bat that this is just to prove the concept that with some minor tweaking by the factory, we could have a easy method to lay out a truss roof of any shape and complexity. The problem with the current implementation for roof trusses is that you manually have to define their shape. If a roof is complicated, you have to create many different types of roof trusses to complete the roof. If the roof ever changes (which it will) during design, you have to manually modify each and every truss that changed and possibly create more truss families that match the shape you want. If you throw vaulted ceilings in there or other coffered or raised elements of the ceiling into the mix, you will have a mess. This is very un-revit like. With the exception of architectural trusses (ones that wouldn't be covered up), the truss will fill the space between the ceiling and the bottom of the roof. It would make sense then to have trusses that are defined by those elements.
What I have done in this example is use wall elements to fill the space between the roof and ceiling. I attached the top of the wall to the roof, and the bottom of the wall to the ceiling. The best part of this (besides the fact that it only took about 4 minutes to layout the whole roof), is that if the roof ever changes, so do the "trusses". You can change the roof pitch, shape, sloped edges...etc and the trusses will automatically adjust. What do you guys think? This won't work for a real project because there is no way to have truss tails or to create the analytical model for those that use it. It just seams that the current method of adding trusses to a project is backwards. The bounding elements should define the shape of the truss. Of course, we could still use the current method for defining those trusses that the engineer would layout, but sense most roof trusses are designed by a truss manufacturer the engineer of record needs only to define their shape and location. I couldn't care less where they put the webs. I just want to make sure it all fits.

[kmarsh]

Hi Erik,
This proof of concept is great and an idea that I hope we can see in a future release. In the meantime, have you tried the "attach to roof/floor" and/or the "profile edit" features of the new truss element? I've attached pictures of your example where i've used the truss tool with a "Howe Flatt Truss" which has been attached or profile edited to match the requirements of the roof/ceiling.

If you have a complicated roof, you can select any of the "flat" trusses (those families with horizontal top/bottom chords), place the trusses as though they were beams, then select all the trusses and select the "attach" button on the options bar, select your desired roof and all the trusses will attempt to conform their top chords to the shape of the roof you've selected. This should give you most of the functionality you are looking for. (though only the top chord can be attached to a roof/floor though so read on to see how to effect the bottom chord requirements)

In cases like you've mentioned (coffered, vaulted ceilings etc) you might be interested in the "profile edit" functionality. First you must "unattach" the trusses which need custom bottom chords from the roof. Then select each truss in turn and enter "profile edit mode" by clicking the button in the options bar and then sketch the exact profile of the top and bottom chords. (In my example, I selected your ceiling lines in the section view as a quick way to define these lines).

I've left most of the webs out of the picture but you should be able to get the idea. The intent of the truss element was not that you should create individual truss families for each truss but rather that you would use flat trusses with attached or profile edited shapes. The additional truss types provided with the Revit content are for situations where you know exactly what truss type you need and don't want to deal with attaching or profile editing.

I hope this helps. However, I can see where your suggested method would have a lot of benefits.

Thanks,

[dbaldacchino]

Hmmmm now why would an Architect/Designer need to have this tool and functionality in Revit Architecture? ;)

Seriously, a while ago I was asked if we had a double pitched joist/girder and I sweated for hours trying to figure if this could be done parameterically with formulas etc in a framing family (using Revit Architecture), only to find out later that there is a family type in Revit Structure that can do a paramertic truss in seconds! You can imagine that I was not a happy lad....

This tool seems to work quite similar to walls. The only difference is that walls let you attach their tops and bottoms but at the same time, you can edit the wall's profile. From your description of the tool, it seems that in this case, it's either one or the other. It would surely be a great enhancement to be even able to attach the bottom chord to other surfaces, just like requested in the original thread. Thanks for posting!

[erikbjur]

Hi Erik,
This proof of concept is great and an idea that I hope we can see in a future release. In the meantime, have you tried the "attach to roof/floor" and/or the "profile edit" features of the new truss element? I've attached pictures of your example where i've used the truss tool with a "Howe Flatt Truss" which has been attached or profile edited to match the requirements of the roof/ceiling.

Thanks for the input. I have tried to use the supplied revit trusses and was able to use the methods you mentioned. Although it works, because you have to manually edit the profile mode to adjust the bottom chord, the bottom chord won't adjust when the ceiling changes. My idea was to eliminate this step and just attach it to the ceiling element (or roof element used to model the ceiling sense Revit Structure won't allow us to create ceiling elements). Once attached to the roof and ceiling, the trusses would draw themselves based on what their surroundings were doing. My whole point is that the factory already knows how to implement the attach to bottom function in walls. Lets just apply it to trusses. Also, allow the truss members to miter together like they do in real life. Give us an option on weather to cut back or miter. In fact make that an option on all structural members. The cut back function is nice 80% of the time. However, when you don't want it, it is a royal pain in the butt.

Could you post your model for us to see how you used the truss elements.

[dbaldacchino]

Have you tried locking the profile sketch for the bottom side of the truss to your ceiling?

[bebrett]

I like the idea....my problem is showing what happens out at the eave. Either way mentioned above does not give you the eave condition which in essence defines the truss....along with the slope and span.

[erikbjur]

I like the idea....my problem is showing what happens out at the eave. Either way mentioned above does not give you the eave condition which in essence defines the truss....along with the slope and span.

The Revit Trusses do let you add eaves. You do this by modifying the extension property of each top chord member in the truss you want to extend. This is hit or miss because you never know which is the right side or left side. 50/50 guess. My original post was just to show how I would like the truss family implemented. I would rather have a generic truss family that will attach to the roof and ceiling it is bound by. Attaching the profile to the shape of the roof or ceiling should be as easy as clicking an "Attach Top Chord" or "Attach Bottom Chord" button. The truss family should have an eve length for each side as well. Any thoughts?

[troberts]

Hi Erik,

If you have a complicated roof, you can select any of the "flat" trusses (those families with horizontal top/bottom chords), place the trusses as though they were beams, then select all the trusses and select the "attach" button on the options bar, select your desired roof and all the trusses will attempt to conform their top chords to the shape of the roof you've selected. This should give you most of the functionality you are looking for. (though only the top chord can be attached to a roof/floor though so read on to see how to effect the bottom chord requirements)

In cases like you've mentioned (coffered, vaulted ceilings etc) you might be interested in the "profile edit" functionality. First you must "unattach" the trusses which need custom bottom chords from the roof. Then select each truss in turn and enter "profile edit mode" by clicking the button in the options bar and then sketch the exact profile of the top and bottom chords. (In my example, I selected your ceiling lines in the section view as a quick way to define these lines).

I hope this helps. However, I can see where your suggested method would have a lot of benefits.

Thanks,

These are some great ideas and they have helped me quite a lot. I see that this post is quite old. Has anyone come up with some better ways. What do you do with complicated roofs with a lot of valleys and overframing? Will 2010 have any truss improvements?

[scowsert]

One basic thing I want is for the truss to actually show up in coarse view, hidden line on the roof plan. Every other beam does. Wouldn't you want to see a truss too? They show up in medium and fine view. I thought it was a 2008 bug but its still in 2009 so I'm assuming it was on purpose.

Oh and no I don't want my roof transparent. Yes I know you 'can' do that with its own side effects.

[david_peterson]

More of a comment for Ken and Eric.
In the ACA world you can set up a roof using a 3d-party add on that allows you to export the roof to Apline Design (Roof Truss design Software), lay out your roof, set up your trusses, design them, add the plates and dump it back into ACA. I'm wondering if you Adesk has looked at trying to get a group like Alpine or Mitek to help produce a link.
Just a thought. There's a nice example of what I'm talking about on the ACA Gallery page.