Wood Truss

[JStructsteel]

Got a wood truss spanning about 25', its about a 6:12 pitch. Is there a rule of thumb for the span/pitch and deflection? There is a wall at the center of the truss below, but I would not expect it to be load bearing, especially since over doorways, they didnt put headers in. Just wondering if they would have a wall to limit deflection?

 

[boo1]

For wood roof trusses, the deflection in inches due to live load cannot exceed the span in inches divided by 240 (L/240). For wood floor trusses, the deflection in inches due to live load cannot exceed the span in inches divided by 360 (L/360).

Creep can be up to 1/2 LL deflection

 

[XR250]

Usually, the deflection of moderate pitch roof trusses is not significant and is well above L/240

 

[manstrom]

25' is no problem. Sloped trusses usually don't have big issues. You can run them 60' if you can get them on a truck.

(Very)General rule of thumb is X' span, X" deep. So 25' span needs 25" depth. You should have 6', so rock and roll.

When I am working on a problem, I never think about beauty but when I have finished, if the solution is not beautiful, I know it is wrong.

-R. Buckminster Fuller

 

[KootK]

From my past experience as a wood truss designer, for typical loading scenarios, anything with a flat bottom and a pitch greater than about 4:12 tends to work just fine.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[jayrod12]

If they didn't install a slip joint at the top of the wall, it's likely that the wall is load bearing now to a certain degree, even if it wasn't intended that way.

 

[BSVBD]

If a panel point does not occur at that (intermediate) wall, the bottom chord of truss could experience undesirable stress.

 

[JStructsteel]

Thanks, I was pretty sure it would be ok. I have never come across a truss that is loadbearing in the center. Also especially since the openings below in the wall do not have a header.

Thanks

 

[jayrod12]

I've been in many a building where non-load bearing walls still have a header. Some carpenter's don't know any better and just frame every door opening the same.

 

[DaveAtkins]

My experience with one story wood framed buildings is the contractors build all of the interior walls tight to the underside of the trusses, without slip connections. It just seems to work. Maybe the trusses don't deflect much, maybe the interior walls become load bearing to a certain degree, maybe the bottom chord of the trusses flex upward, relieving the stress.

DaveAtkins

 

[BSVBD]

I have never come across a truss that is loadbearing in the center.

In long-span situations, I've designed many buildings that have had intermediate (center) bearing points. Often, the truss manufacturer prefers it which, reportedly , would keep the cost down since they could avoid what would otherwise require a 2x8 or 2x10 bottom chord.

I've been in many a building where non-load bearing walls still have a header.

I've seen this in smaller-span residential construction where the general contractor told me these are cookie-cutter houses that have previously been estimated and the material bill is constant.

My experience with one story wood framed buildings is the contractors build all of the interior walls tight to the underside of the trusses, without slip connections. It just seems to work. Maybe the trusses don't deflect much, maybe the interior walls become load bearing to a certain degree

I've also seen this in smaller-span construction where i suppose deflection wasn't an issue. I also assume this was common practice in older construction where large spans were not in demand as today.