Concrete Basement Wall Design 2

[skbeng]

Case 1: I am trying to design a concrete basement wall and I have columns offset from the wall 10" all the way down to the footing/base of wall. I thought that I could use the column load x the "e=10" to get a point load moment and add it to the lateral load moment to design the wall. Would this be the correct way to go? Or could I just assume that the lateral load moment would couteract column load moment hence making it neglegible? Does anyone have a reference for good examples for basement wall design with a point load?

Case 2: Can I just sum the column loads along the wall divided by the wall length (eg: 1200k/60'=20klf) and use this uniform loading along with the lateral earth pressure an design the wall as a cantilever retaining wall to take the column load rather than using individual footings under each column?

 

[Lion06]

I am confused. Do your columns sit on the wall or not? It seems from your post (Case 1) that the columns go to the base of the wall, and I can only assume that means they do not sit on the wall. If that is the case, why would you have to design the wall for the column loads?

 

[youngstructural]

I am with StructuralEIT in being a bit confused, but I think I get your question... I've done alot of basement and foundation walls, and would be pleased to help you out; I just need to be sure I'm right about your situation.

Please clarify and I know someone will be able to help you (if they beat me to the reply, otherwise I will). It's a really good idea to post a clear sketch of your situation and then post the address for our review prior to helping you out.

Good luck,
I'll check back later,

YS

B.Eng (Carleton)
Working in New Zealand, thinking of my snow covered home...

 

[civilperson]

I assume from the question 2 that the foundation design is what is under discussion. If so, then a combined footing is the correct way to go and the wall should be a simple beam between the first floor and the base,(not a cantilever which requires much more foundation and reinforcement).

 

[skbeng]

Sorry about the confusion. Let me try to clarify this is a bit.

The columns do not sit on the wall, they go to the base of the wall and sit on the foundation. StructuralEIT your question is a good one so I shouldn't have to worry about the column load in the wall design. On the other hand if I opted to sit the column on pier in the wall then I would need to consider that load for the wall. If this is the way I go then would my previous post be the accurate way?

Now in the case 2 below, whether or not the column is sitting on the wall or at the base of the wall wouldn;t the load have to be included in the retaining wall design, and if so, would this be a correct procedure?

Case 2: Can I just sum the column loads along the wall divided by the wall length (eg: 1200k/60'=20klf) and use this uniform loading along with the lateral earth pressure an design the wall as a cantilever retaining wall to take the column load rather than using individual footings under each column?

Civilperson are you saying "a combine footing" meaning spread footings for the column load and strip footing underneath the walls?

Thank you all for the input.

 

[Lion06]

skbeng-
I would be careful about turning your column load into a uniform klf load unless they are spaced relatively close together. The foundation will really only behave that way if it is very stiff (thick). Also, if your column loads are significant, you would have to check for punching shear (you should anyway, but is usually not a problem with small loads. On second thought, I definitely would not do it that way, design for the column loads and apply them over a width you feel is reasonable, then design for a 1 ft width based on that loading.
If the column goes to the footing, it should have no part in the design of the wall - only the footing. It will increase your max bearing pressure, but help with the stability analysis. Although, for the stability analysis, you might want to neglect the column loads since most of the wall footing won't see it. But I would definitely include it (worst case) in the footing design.

 

[skbeng]

StructuralEIT,

Thanks again for the advice. I'll be sure to consider this in my analysis.

 

[civilperson]

A combined footing is one footing for multiple loads, i.e. the wall and the columns. The size of the footing when designed as a cantilever will be 300% -400% of the same wall designed as a simple beam spanning between the first floor and the basemwnt slab. The savings require that the wall is left unbackfilled until the first floor is completed.

 

[skbeng]

civilperson,

Thanks for the claification. I will surely look at using the basement wall rather than the retaining wall.

 

[COEngineeer]

I think you are thinking too hard on this skbeng. Just design your foundation wall and footing. Then for the column right next to your wall, just figure out the size of pad you need (Load/bearing)^.5. Just draw that pad right on the center of the column and combine it with your footing. Just use your engineering judgement sometimes I feel comfortable letting the column sit on the footing if it is closer to the wall (rather than the edge of the footing) and has a small load.