rectangular underground concrete vault built with single rebar mats in walls

[ktcastro]

I have a question, what are the possible fails for a rectangular underground concrete vault built with single rebar mats in walls without connecting the Rebar mats with "L" bars at corners 12" o.c. vertical spaced as typical. In other words none continuous reinforcement at corners.

 

[jayrod12]

If you have no corner bars, what's stopping the walls from creating cracks there?

Also, where I practice at least, any wall 8" and thicker need 2 layers of reinforcing, one on each face.

Lastly, if the vault is intended on being fluid retaining, you may want to look into the codes regarding water retaining concrete structures, it usually limits the spacing of reinforcing to 8" or less.

 

[ktcastro]

Correct, and deformation once the structure is backfilled if poured that way. Thanks for the comment, just trying to complete more training information.

 

[JAE]

I thought ACI only required double mats in walls thicker than 10".

Single mats in thinner walled vaults are used all the time but usually with L bars in the corners as jayrod12 suggests.
But if you have a very small vault (i.e. maybe 3 ft. in size or smaller) then corner bars might not be the end of the world.

 

[ktcastro]

Do I need to concern about the corner bars at the bottom 40 inches (or 1 meter) of the concrete vault walls just before the floor slab? I know in that area the bending is in the Vertical plane and that portion usually designed as cantilever, so the vertical bars will resist the moment?

 

[DaveAtkins]

Normally the walls in a below grade vault are two way slabs -- they span horizontally and vertically. Without corner bars, I think your walls have to span vertically, from base slab to top slab. Are there no dowels between the wall and the base slab?

 

[ktcastro]

Thanks Dave, sure there are, the floor is usually poured first (when made in Symons o no form available) leaving the rebar to connect or sometimes the complete Vertical bar for the walls. The walls are a secondary pour or next day pour (if Symons panels are used), if the form is used the floor and walls as poured monolithically. When I said "Corner bars" I mean the horizontal bars in the walls, at the bottom 40 in. of the walls.

 

[DaveAtkins]

If you can justify the load path, you are OK from a strength and stability point of view. However, the corners could open up and allow ground water to seep into the vault. This in turn could lead to sink holes forming at the ground surface.