Valley Beam Reactions
Valley Beam Reactions
(OP)
I have a structural valley beam coming in at 45 degrees (horizontal projection down) which is bearing on a corner wall at one end and a ridge board/beam on the other. Of course on the other side of the beam is the other valley beam which is the same configuration.
My expertise is roof trusses not rafter framing and I'm trying to wrap my head around conventional framing.
I'm trying to sort out the bearing of the valley beam on that beam/board. I believe that that valley causes a vertical reaction on the ridge beam/board, but someone else is telling me that the valley beams because they come in to the same point from opposite sides act like the peak of a set of rafters tying into a ridge board. I just don't think it is the same. I believe that the valleys cause a vertical reaction at the wall and on that ridge. But the other individual is saying the vertical reactions are all going to the wall cause the valleys oppose each other (at 45 degrees).
So, is there a vertical reaction on that ridge beam/board or does it all go to the wall?
My expertise is roof trusses not rafter framing and I'm trying to wrap my head around conventional framing.
I'm trying to sort out the bearing of the valley beam on that beam/board. I believe that that valley causes a vertical reaction on the ridge beam/board, but someone else is telling me that the valley beams because they come in to the same point from opposite sides act like the peak of a set of rafters tying into a ridge board. I just don't think it is the same. I believe that the valleys cause a vertical reaction at the wall and on that ridge. But the other individual is saying the vertical reactions are all going to the wall cause the valleys oppose each other (at 45 degrees).
So, is there a vertical reaction on that ridge beam/board or does it all go to the wall?





RE: Valley Beam Reactions
RE: Valley Beam Reactions
RE: Valley Beam Reactions
I hate these old conventionally framed homes. I had someone recently tell me that sometimes it's now worth it to try and renovate them structurally, but just tear down and start from scratch.
RE: Valley Beam Reactions
Look at another posting from today: http://www.eng-tips.com/viewthread.cfm?qid=435528
Eric McDonald, PE
McDonald Structural Engineering, PLLC
RE: Valley Beam Reactions
Draw a free-body diagram. Generally there are two mechanisms that may be available to provide support:
Vertical restraint or thrust resistance. It has to be one or the other but sometimes it is a little of both!
For a cone shaped roof, I think there must be thrust resistance.
In your example of (one or two) valley(s) framing into a ridge, IF the ridge can provide vertical support, that will contribute. IF there s some thrust resistance (such as adjacent roof sheathing) that would contribute too but there has to be at least one or the other. If they are both contributing, the contribution will depend on relative stiffnesses of each.
It is possible to support a valley without vertical support at the ridge. Just think of all of the old stick framed ranch roofs with 1x or 2x ridge boards. Plenty of early 1900's roofs have no ridge board/beam at all. Not saying that's a good idea. Most of those that I look at need "help". I generally try to install redundant systems (like ceiling beams) because it is difficult to determine exact stiffnesses in many situations and I want something that is reliable and that I can quantify. (BTW, I'm not a fan of the argument that "it's been standing for 100 years so it must be OK"). Each situation is distinct though.