Another Collar tie/rafter tie question
Another Collar tie/rafter tie question
(OP)
Is there any remedy for a roof framed with a "rafter tie at 46% instead of 33% above rafter bearing? The obvious fixes are move it down or ridge beam but the vaulted ceiling has already been installed. The building width is 25'-7,4/12 slope 2x6 at 16 with 2x6 ties on both sides of eaxh rafter. Tried to run it in RISA but the deflection is like 2" and the load from it being a reaction I'm sure is too high for a wall to take. Problem is I can't even get a span table rafter to run as a pass in RISA (with rafter ties at bearing), so I think something wonky is going on in the program or with me. Thanks for any input.






RE: Another Collar tie/rafter tie question
Could you install cable ties every so often, at the top of wall level? You would see them inside the space, of course.
DaveAtkins
RE: Another Collar tie/rafter tie question
Mike McCann, PE, SE (WA)
RE: Another Collar tie/rafter tie question
RE: Another Collar tie/rafter tie question
Mike McCann, PE, SE (WA)
RE: Another Collar tie/rafter tie question
RE: Another Collar tie/rafter tie question
Are you sure that this is a problem? The drywall along the collar tie ought not be an issue as there's going to be little deformation there. And you're going to have a natural crack controlling joint at the ceiling pitch breaks. All that you really have to worry about is the curvature along the rafter tail extensions.
The wall should be treated as roller supports. Consequently, there should be no horizontal reactions to cause you grief at the top of the walls.
If the 2" deflection is a major concern, you could get into the attic and truss the system by adding a king post with a diagonal web on either side. This would stiffen the back span of the cantilevered rafters and thus stiffen the entire system. This would not, however, affect the bending moment or curvature in the rafter tails. As such, I'd be inclined not to bother.
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.
RE: Another Collar tie/rafter tie question
Any chance of adding in a structural ridge under the existing ridge.
I would ignore RISA if you are checking it with the collar tie at plate bearing. Use the code span tables for that situation.
RE: Another Collar tie/rafter tie question
Mike McCann, PE, SE (WA)
RE: Another Collar tie/rafter tie question
XR250 I won't be able to get them to put a ridge beam in, it'll be a tall one and 3 1/2" wide to it. It would be a 28' long one too, I mean if they came to me first we could have gotten that done but you know engineers aren't needed I've been building for 30 years I got this.
RE: Another Collar tie/rafter tie question
RE: Another Collar tie/rafter tie question
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.
RE: Another Collar tie/rafter tie question
DaveAtkins
RE: Another Collar tie/rafter tie question
RE: Another Collar tie/rafter tie question
DaveAtkins
RE: Another Collar tie/rafter tie question
Might want to check it out. Lots or working structural elements to consider here.
Mike McCann, PE, SE (WA)