Upward Pressure for Footing Flexure and Shear 2

[BadgerPE]

Hey all,

If I have a continuous footing which has 14' of overburden cover on one side and only 3' on the other, can the weight of the soil itself be neglected to determine the upward pressure used for flexure and 1-way shear calcs?

 

[BAretired]

I think so.

BA

 

[ron9876]

Unbalanced loading will generate a moment. So it looks like to me that you can't ignore it. For me the real question is what is the allowable net bearing pressure?

 

[trainguy]

I would tend to agree with BAretired, sounds like a conservative assumption.

Having said that, I haven't done one of these in about 13 yrs.

Don't forget to check your vertical wall for bending and shear from the lateral earth pressure, and axial load from gravity (wall weight and/or column loads).

tg

 

[sonofamsquared48]

You bet you can(but...). You should be working the statics twice. Once for service level loads to check the maximum soil bearing loads then run it again with factored loads to check the ultimate shear and moment in the footing. If you are counting on the overburdern to determine you soil bearing pressure profile, you may want to again count on it to reduce your ultimate design forces for the footing. If you do not count on the overburder to determine your soil bearing pressure profile, then of course you would not reduce your soil pressure profile accordingly, since this would not be conservative. Cheers. Just a couple of other pointers in designing footings. Shear calculated d from support. Minimum flexure steel requirements do not apply in footings although you do need to have min tempurature steel. Min shear reinforcement is not required at 1/2(phi)(Vc)... Rambling. cheers.

 

[BAretired]

Crackerjack,

Is the wall laterally braced by a slab at the 3' and 14' levels?

BA

 

[BadgerPE]

It will be braced at the 14' level once the floor slab is installed. Exterior grade is at 3' so it will not be braced by a slab.

I had to design for 2 different conditions with this wall. The first was a cantilever condition where the wall would be backfilled prior to being connected to a tension floor slab. The second condition was for once the wall was tied into the tension slab. I did end up running the statics twice. Once with service loads to determine bearing capacity. The second was with factored loads to determine upward pressure. I kept the overburen on the footing because I feel as though it causes bending in the footing and therefore should be accounted for. It didn't kill my design either. All I had to do was extend the bars in the toe to the back of the heel and that covered my flexure concerns.

 

[BAretired]

I misinterpreted the problem. I thought the 14' fill was on the outside and 3' fill on the inside, so I anticipated a slab at each level prior to backfilling.

You are now talking about a cantilevered retaining wall required only until the floor slab is installed. You could use temporary supports, i.e. diagonal struts to deadmen to hold the wall until the floor slab is placed.

Alternatively, you might consider removing fill on the inside of the wall, using a structural slab where required.

BA