Concrete Walls
Concrete Walls
(OP)
Does anyone know how to determine the maximum allowable eccentricity for a uniformaly distributed load on a 10" wide, 8 foot high foundation wall?
The walls were poured 3" off square and the result is a parallelogram shaped foundation wall.
The walls were poured 3" off square and the result is a parallelogram shaped foundation wall.






RE: Concrete Walls
Mike McCann
MMC Engineering
RE: Concrete Walls
RE: Concrete Walls
Mike McCann
MMC Engineering
RE: Concrete Walls
RE: Concrete Walls
Is this a free standing retaining wall, or a basement wall?
In general, for a basement wall condition, with reference to the soil face, any eccentricity toward the soil will add to the bending moment and away from the wall will decrease it.
For a free standing retaining wall, eccentricity towaed the soil will decrease the bending in the wall, whereas the opposote will add to it.
Sounds to me that you may not have an easy solution here.
Mike McCann
MMC Engineering
RE: Concrete Walls
RE: Concrete Walls
Outside of the eccentricity, which I consider a minor problem, I have one major concern here:
The fact that it is detailed as a yielding wall, but the footing appears too small and wall improperly reinforced for the soil load. With a 6'+ soil retention depth, this should be an engineered wall. Is the dead load from the structure above sufficient that the soil side of the wall does not go into tension? The footing needs to be large enough with any overturning so as not to overstress the soil at the toe.
I have no feel for the load or rebar values you have mentioned. I am in the states.
Mike McCann
MMC Engineering
RE: Concrete Walls
Thank you for your reply.
A little background into this case.
In Ontario, Canada, designers are permitted to specify wall sizes if they follow the values given in the Ontario Building Code, table 9.15.4.1. This table shows that a 20 MPa (2900 psi) strength wall, 9 7/8" thick can support ground cover to a maximum height of 7'7", provided the top of the wall is laterally supported (which this one will be).
The code futher shows that the minimum footing width for 2 storeys, exterior wall is 17 3/4" (table 9.15.3.3).
So, had the contractor made all the angles square, this wall would be considered acceptable under the Ontario Building Code.
As far as rebar and concrete strength, 15M bar is no. 5 bar and 25 MPa is approximately 3500 psi.
I'm trying to calculate the moment capacity at the top of the wall where there is no reinforcing and to determine if the wall will have sufficient capacity for the eccentricity.
RE: Concrete Walls
I have an ACI publication "Notes on ACI 318-83" put out by the Portland Cement Association. It has guidance for doing the calcs for this situation. There should be a similar publication for the most recent ACI code that you might be able to get and use.
Mike McCann
MMC Engineering
RE: Concrete Walls
RE: Concrete Walls
However, the contractor will provide lateral support at the top with joists.
What is complicating the project is we need to backfill asap since proper shoring was not provided.
I would like to tear down and rebuild as well, but that would significantly delay the project.
RE: Concrete Walls
Mike McCann
MMC Engineering
RE: Concrete Walls
RE: Concrete Walls
RE: Concrete Walls
Before you do the above, check with the code official to see if you can get hold on the background materials/assumptions used in developing the code recommendations. (It might have included certain amount of eccentricity from the structure.)
RE: Concrete Walls
You have concluded that the wall is adequate to resist the lateral pressure of the earth, provided the top is braced. While some of us may disagree, that is not your question.
Building the wall above on top of the floor framing (platform construction) should remove any concern about eccentricity of loading on the concrete wall.
RE: Concrete Walls
I would still like to calculate the moment at the top of the wall and compare to the moment capacity of the wall at the top. I'm thinking of treating as a simply supported beam, with a gradually increasing udl for the soil and a point moment at the top where the eccentricity is.
The problem is an assumption for percentage steel in the calcs.
RE: Concrete Walls
RE: Concrete Walls
RE: Concrete Walls
RE: Concrete Walls
Why do you have to make everything so complicated? He asked one question, you have asked a lot more, and answered your own questions. Do you want us to comment on your questions and anwswers? If so, start a new post.
RE: Concrete Walls
RE: Concrete Walls
Sorry for the distraction. Please continue the discussion if you feel need for better/more ideas. Good luck.
RE: Concrete Walls
Best regards,
BA
RE: Concrete Walls
Did you intend to use platform framing? The sketch didn't indicate that to me, and I can't find it in your posts.
RE: Concrete Walls
How many more problems are you going to have?
Might want to accept a delayed project and insist the contractor redo it. After that, I'm sure he will be paying attention, if you don't insist on him taking it out, the rest of this project may (will) go the same way.
Let us know how it ends up.
Regards.
RE: Concrete Walls
While all my talking above was from a conventional view on a "single wall" that was curving in plane (S-shape), you may want to look the problem globally. I believe the wall forms an enclosure (wall all around) to support the structure above, from this bigger picture, the localized imperfection may not be a big deal, however, attention needs to be put on the local effects. Your decision to do a cal is correct call. The steps and focus points could be tedious, but the cal itsself is rather straight forward. I agree with BAretired' suggestions in case the plain concrete section does not work.