Deep Walls 1

[rendevouspoo]

Hello all,
I'm having a go at designing a deep wall and am having problems finding a starting point. Inside the walls, it will be filled with soil up to slab therefore it won't be a basement area. Are there any useful guides or resources that can help me in the design of the deep wall? I have my spread footings designed already. It is a PEMB. Any help would be greatly appreciated.

 

[charliealphabravo]

Can you provide a sketch? Why is it a wall instead of a pier or pedestal? Is it exposed on the outside if not on the inside?

 

[rendevouspoo]

The grade drops about 12' in 50 and we aren't filling the area.

 

[rendevouspoo]

bump

 

[jayrod12]

Honestly try posting a sketch because I think most people here don't understand quite what the situation is.

 

[rendevouspoo]

Sorry, I've provided a simple sketch. The building as you can see ia 60' x 40'. We're not filling to finish floor. We will pour our footings and then have a wall (acts like a basement but will be filled in, therefore no access) that meets fin. flr.

 

[jayrod12]

If it is on a strip footing and there is no backfill differential between inside of wall and outside of wall then put in minimum steel and be done with it.

If there is backfill differential causing out of plane bending then you'd either have to laterally restrain the top of the wall and then design as a normal wall for bending or leave the top of the wall free and design it as a cantilevered wall which requires special attention at the connection to the footing. And in the second case you'd also need to appropriately design the footing for the overturning moment.

 

[rendevouspoo]

Thanks for the quick response! It will, in fact, be backfilled inside the walls. I'm planning to laterally restrain the top of the wall. What process would you go about designing the wall? Would you analyze it as a continuous footing?

 

[gagne73]

Have you ever designed a concrete beam or any other typical foundation wall? its the same thing. apply the lateral earth pressure load from the inside, if it is slab-on-grade dont forget to add in the surcharge loading for whatever the usage is. get your moment, and put your reinforcing in. The vertical reinforcing should be on the outside of the wall if I am understanding your problem correctly, you havent made it very clear tho. Your sketch didnt help at all, should have drawn a section of teh wall to show grade on each side.

 

[jayrod12]

If it were me, I would start with minimum reinforcing steel requirements for your area and see if that is enough to work for strength (and deflection however I've never seen that govern a standard height concrete wall yet) when the backfill differential is it's largest.

As for the surcharge load you could assume that you have 100% stress transfer (which would be conservative), i.e. if you have a 100 psf live load on a 6" slab floor you would apply a 150 psf load against the whole wall.

You would use passive pressures for the soil on the exterior as resisting forces. So to clarify on the inside of the wall you would have the surcharge loading due to the floor and the active pressure from the backfill on the interior. On the exterior side you would have passive pressures resisting the applied loads. Then do a stress distribution to determine the max moment on the wall and then design it as a beam of set width (let's say 3' wide by the wall thickness deep) determine the steel you need for that width and ensure you provide that required steel.

If that makes any sense,

maybe another member has a better design method or can clarify what I'm trying to say here.

 

[gagne73]

agree with jayrod,

I just re-read my post, Sorry I didnt mean to sound condescending, which I realise I definitely did in my quick response, my bad. what i basically meant is that most on here have designed a simple beam, and this isnt much different. just weanted to point it out because sometimes that brainfart happens when you forget that they are the same.

but good call by jayrod for checking your minimum reinforcing first for the highest grade differential, then just use it throughout.

what is the max grade differential on each side of the wall, and what is the total wall heighet?