Considering Vertical Pressure of House Structure on Foundation Wall
Considering Vertical Pressure of House Structure on Foundation Wall
(OP)
I apologize if this is the wrong forum for this question. I am not a civil or geo engineer.
We have a 9' foundation wall which is 33' feet long, 7' below grade and is bowing about 1" to 2" horizontally in the middle. We have gotten various foundation repair folks to look at it and they have recommended either steel columns or carbon fiber to reinforce the wall to prevent further inward movement.
I was discussing the solutions with a friend who has a physics - but not engineering - background and he is curious why none of these solutions consider the weight and pressure of the house, and focus entirely on the lateral soil pressure. I looked at both commercial and engineering resources on the web, and almost all them fail to even mention the weight of the house as a consideration. Why is that so?
We have a 9' foundation wall which is 33' feet long, 7' below grade and is bowing about 1" to 2" horizontally in the middle. We have gotten various foundation repair folks to look at it and they have recommended either steel columns or carbon fiber to reinforce the wall to prevent further inward movement.
I was discussing the solutions with a friend who has a physics - but not engineering - background and he is curious why none of these solutions consider the weight and pressure of the house, and focus entirely on the lateral soil pressure. I looked at both commercial and engineering resources on the web, and almost all them fail to even mention the weight of the house as a consideration. Why is that so?






RE: Considering Vertical Pressure of House Structure on Foundation Wall
RE: Considering Vertical Pressure of House Structure on Foundation Wall
The downward pressure of the house would help explain a part of why the top is restrained. Simply speaking... Walls prefer to freely topple over than bow in the middle and only bow when something is pushing the opposite way from above (and below at the slab or footing restraint point)
There is a debate about whether you pin the top of wall with the floor diaphragm or get to count down-pressure/friction on the sill plate.... but that is a different thing all together. most egrs i know design the top of wall to be restrained by the joists/blocking of the floor and then enjoy the downpressure as additional uncomputated safety factor.
i don't see how "steel columns" you mention would help unless they are actually being used as Buttresses, while looking like steel columns. i'm skeptical about the carbon fiber you mentioned too, but give it the benefit of the doubt, and i can't trash the idea without understanding how it would be used here.
There are probably a bunch more things that could be done, but the real answers require site observations to pick an optimal & functional approach that satisfies Owner needs in exchange for money.
RE: Considering Vertical Pressure of House Structure on Foundation Wall
RE: Considering Vertical Pressure of House Structure on Foundation Wall
Mike McCann, PE, SE (WA)
RE: Considering Vertical Pressure of House Structure on Foundation Wall
RE: Considering Vertical Pressure of House Structure on Foundation Wall
RE: Considering Vertical Pressure of House Structure on Foundation Wall
RE: Considering Vertical Pressure of House Structure on Foundation Wall
FWIW, I recently was on a job where the contractor installed the carbon strips over a painted CMU wall. Needless to say, they did not stick.
RE: Considering Vertical Pressure of House Structure on Foundation Wall
I have been leaning towards Carbon Fiber myself because of it's disappearing profile. And yes,any reputable provider should be grinding the entire height of the wall before epoxy'ing the carbon fiber strips (or so I've learned). The provider that I am likely to go with does actually bolted at the top to the rim joist.
And the floor joists run perpendicular to this wall.
Do you prefer the steel columns because they support the house up in addition to supporting the wall against lateral pressure? While the carbon fibers only add support to the wall?
RE: Considering Vertical Pressure of House Structure on Foundation Wall
RE: Considering Vertical Pressure of House Structure on Foundation Wall
Perpendicular is ideal. Generally how it works is they break out a portion of the slab adjacent to the wall directly below a floor joist. The steel column (I generally use either HSS tubes or angles, prefer tubes but some contractors fight for angles) is then placed in this hole on top of the existing footing and is bolted to the floor joist above. The hole in the slab is then filled with concrete. Any gaps between the wall and the steel should be grouted with some form of "non-shrink" cementitious grout.
The size of the steel columns and connection to the floor joists should be sized by an engineer.
I have never attempted to removed the bowing from the wall but rather just stop any further movement. If the movement is so bad that they feel they need to attempt to push the wall back out then in my mind it's usually time for replacement.