How does the 2nd floor bearing wall load be transfered to wall below?
How does the 2nd floor bearing wall load be transfered to wall below?
(OP)
It is hard to understand some common details on residential construction. Here is one. Most roofs are built with roof trusses, which can have long span like over 20 or even 30 feet. The bearing wall take quite a big load. But when the floor joist underneath is parallel to the bearing wall, the wall only rest on rim joist which is just 1.25" wide. Although there usually has blocking at 32" or 48", that means the bottom plate will span that long. Unless you consider the wall work as a composite beam, I do not see how it works. Does anybody ever worry about this before?






RE: How does the 2nd floor bearing wall load be transfered to wall below?
RE: How does the 2nd floor bearing wall load be transfered to wall below?
RE: How does the 2nd floor bearing wall load be transfered to wall below?
Basically you will get a small couple from the vertical load eccentricity that will be counteracted by a couple in lateral loads at the top and bottom of the wall.
RE: How does the 2nd floor bearing wall load be transfered to wall below?
I have been contacted by another engineer trying to figure out why in a four story wood framed building the first floor walls are bowing out up to 3/4" in only the parallel conditions.
I haven't been out to the job site but suspect a combination of inadequate nailing, blocking, eccentricity, etc. has created this anomaly.
RE: How does the 2nd floor bearing wall load be transfered to wall below?
RE: How does the 2nd floor bearing wall load be transfered to wall below?
DaveAtkins
RE: How does the 2nd floor bearing wall load be transfered to wall below?
RE: How does the 2nd floor bearing wall load be transfered to wall below?
I cannot see how the walls would bow inward if the rim joist is on the outside, it must bow outward surely?
RE: How does the 2nd floor bearing wall load be transfered to wall below?
If the load is too large for the bearing area of the stud overlapping the rim joist, the designer is at liberty to add a second rim joist or some squash blocks under the studs.
Assuming that no such additional compression filler is added, the studs between the floor and roof will bow inward as a result of the eccentricity.
Best regards,
BA
RE: How does the 2nd floor bearing wall load be transfered to wall below?
With a two story wall, and the rim joist on the outside, the upper joist has a reaction which is inside the rim joist and hence wants to rotate the top inwards and the bottom outwards with the reactions opposing these forces. The bottom wall is the opposite of this with the top tending to rotate outward.
Hence with no reaction at the first floor the wall would tend to bow outward on this. Do your own freebody diagrams and you will se I am right.
RE: How does the 2nd floor bearing wall load be transfered to wall below?
I don't think you're talking about the same thing here. This post is referring to the walls that are parallel to the joist, not the walls supporting the joists.
RE: How does the 2nd floor bearing wall load be transfered to wall below?
The lower stud is loaded eccentrically top and bottom. No horizontal reactions are required for equilibrium but a constant moment occurs through the lower stud.
Both upper and lower studs bow inward as a result of the eccentricity.
Best regards,
BA
RE: How does the 2nd floor bearing wall load be transfered to wall below?
Never, but never question engineer's judgement
RE: How does the 2nd floor bearing wall load be transfered to wall below?
RE: How does the 2nd floor bearing wall load be transfered to wall below?
The eccentricity of the load would induce a clockwise rotation in the topwall and a counterclockwise rotation in the bottom wall.
If correctly fixed then the floor diaphragm would resist this.
RE: How does the 2nd floor bearing wall load be transfered to wall below?
I think we are talking about different things. I am talking about the studs bowing inward between second floor and roof and also between main and second floor. Please see the cross section in my previous post.
You are talking about the second floor bowing outward. I would agree with you if this is the only lateral force acting on the second floor. If the joists are aligned throughout the floor, the detail on the opposite wall is presumably the same. In that case, the floor experiences a slight tension but no bowing.
Best regards,
BA
RE: How does the 2nd floor bearing wall load be transfered to wall below?
This is why engineers talk better in sketches.
RE: How does the 2nd floor bearing wall load be transfered to wall below?
The first floor walls at top plate have moved outwards up to 3/4". T.O. second floor is at zero, T.O. of first floor double top plate at 3/4".
This is a 4 story wood framed building, S.O.G., and only happening on the 1st floor.
RE: How does the 2nd floor bearing wall load be transfered to wall below?
I tend to agree with your earlier assessment that the problem likely stems from inadequate nailing and blocking. It is a serious deficiency which must be corrected.
Best regards,
BA
RE: How does the 2nd floor bearing wall load be transfered to wall below?