Rebar on retaining and basement walls

[engr567]

ACI section 14.3.4 states that "for walls thicker than 10", except for basement walls, reinf. in each direction shall be placed in two layers." What happens in case of retaining walls and basement walls? Which section of ACI talks about this? I would appreciate your help.

 

[DaveAtkins]

I have always interpreted this to mean that basement walls thicker than 10" can have rebar in only one layer (presumably at the tension face).

DaveAtkins

 

[rapt]

DaveAtkins,

The problem with badly written code rules like this is designers accept them without thinking and be mislead about the intent.

Often, retaining and basement walls will have tension on both faces, either at the same time depending on support conditions or under different load conditions. Then they need reinforcement on both faces too. And this type of wall <10" thick needs reinforcement on both faces also.

Maybe the clause should talk about walls under direct axial effects (compression / tension) only and walls in flexure!

 

[concretemasonry]

The classic question -

Is the basement wall a cantilever, a "propped cantilever" or a wall with simple supports/restraints at the top and bottom?

It is easy to make it a complicated engineering analysis.

For a basement most of the walls are lightly loaded with uncontrolled/unknown soils/backfill and little or no vertical load.

Dick

 

[msquared48]

The answer to the classic question is that it depends on how it was designed and detailed as to how it functions.

Mike McCann
MMC Engineering

 

[hokie66]

Unless it functions differently to how it was designed and detailed.

 

[paddingtongreen]

Clearly, the rule is for simple basements, propped by the basement slab and the ground floor. Any other arrangement would need to be reinforced according to the design needs. These code rules are to provide limits, not to replace thoughtful examination by the designers and engineers.

Timing has a lot to do with the outcome of a rain dance.

 

[BAretired]

The Canadian code has a similar provision which says "Walls greater than 250mm shall have the reinforcement placed in two layers parallel with the faces of the wall".

Walls 250mm or less can have reinforcement placed in one layer. If there is moment reversal, one layer of reinforcement in the middle of the wall serves both, although cracking could be a problem if the moments are large.

Residential contractors in this area build basement walls without engineering input because it is typically not required by the authority having jurisdiction. For eight foot high, eight inch thick walls, many place 2-15M bars top, bottom and mid-height and use no vertical bars at all. Some extend this to nine and even ten foot high walls, which is a bit much if the backfill extends to the top of wall.

BA