Retaining wall as One Way Horizontal Slab
Retaining wall as One Way Horizontal Slab
(OP)
I have a tall basement retaining wall (18ft) that I wish to design as a horizontal one way slab system (not a typical vertical one way slab/beam)because my horizontal dimension is much less than my vertical dimension. I have perpindicular walls at the ends of the subject wall that can restrain the horizontal one way slab. I assume I can design the wall as 12" wide horizontal strips and in accordance with ACI 318 one way slab provisions. I'll verify I have enough mass/friction on the perpindicular walls to resist the end reaction and develop the horizontal steel into the perpindicular walls.
My questions are: Do you see any problems with this? Do I really even need to worry about much of a footing on this wall (other than self weight of course)? Do I have shear concerns at the ends of my wall? Reading ACI I don't get the impression I have to worry about shear at the ends for this case. I plan to install #4 vertical at 12" o.c. for temp, shrink, and force distribution.
My questions are: Do you see any problems with this? Do I really even need to worry about much of a footing on this wall (other than self weight of course)? Do I have shear concerns at the ends of my wall? Reading ACI I don't get the impression I have to worry about shear at the ends for this case. I plan to install #4 vertical at 12" o.c. for temp, shrink, and force distribution.






RE: Retaining wall as One Way Horizontal Slab
For shear, you shouldn't have any problems. You can use full phiVc.
Regarding the footing, you'll have to evaluate if there are any other loads acting on the wall. Is it supporting any framing?
If you're retaining on both sides you shouldn't have to worry about having enough mass on the perpendicular walls to resist any sliding.
#4 @ 12" only works for T&S steel if you're less than 10" thick.
RE: Retaining wall as One Way Horizontal Slab
Check φVc
RE: Retaining wall as One Way Horizontal Slab
RE: Retaining wall as One Way Horizontal Slab
If the panel between supports is 18' (vertical) * 12' (horizontal) then it is a two way slab supported on 4 sides!
Also, make sure you do not use active pressure for the soil pressure calculation! You need to design this for full passive pressure.
RE: Retaining wall as One Way Horizontal Slab
RE: Retaining wall as One Way Horizontal Slab
The φVc/2 limit is only for beams as rapt suggests.
With this basement wall & horizontal spanning concept, you would use at-rest pressure not active.
RE: Retaining wall as One Way Horizontal Slab
I used active pressure, not at rest, so I should be conservative.
RE: Retaining wall as One Way Horizontal Slab
RE: Retaining wall as One Way Horizontal Slab
I don't think you get a moment at the footing just because you have bars there (well, ok, some small nominal moment, but certainly not a fixed condition). We design footings for vertical load only all the time and there are always bars from the wall into the footing. It's about the amount of bars. If you provide enough bars for shear friction to work and these bars can't develop a significant moment, I would ignore it.
RE: Retaining wall as One Way Horizontal Slab
As for two way action, if you rely on such to reduce the horizontal steel, then you are saying that there is yielding wall action in the vertical direction, and you will correspondingly have to perform another analysis for the wall acting vertically. This will affect the size and positioning of the wall footing.
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Retaining wall as One Way Horizontal Slab
RE: Retaining wall as One Way Horizontal Slab
RE: Retaining wall as One Way Horizontal Slab
RE: Retaining wall as One Way Horizontal Slab
In a basement wall design, which is simply supported, the wall is considered "non-yielding". However, a cantilever wall design is a yielding condition in that the top of the wall will move or deflect laterally. In that regard the pressure is reduced by the movement. Such is not the case for non-yielding walls such as the scenario you have. Use 50 psf minimum.
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Retaining wall as One Way Horizontal Slab
Right?
RE: Retaining wall as One Way Horizontal Slab
RE: Retaining wall as One Way Horizontal Slab
RE: Retaining wall as One Way Horizontal Slab
RE: Retaining wall as One Way Horizontal Slab
If the foundation is well drained, there should be no water table above the basement floor. Otherwise, the design requires special attention.
BA
RE: Retaining wall as One Way Horizontal Slab
Not sure that is always true BAretired. You can have a naturally high water table condition (such as that found in Grand Forks, North Dakota - 2 feet deep always). A foundation drain won't do you any good in that condition unless it is pumped out - and only then it works if the pump can draw down the water table - depending on soil porosity, etc.
RE: Retaining wall as One Way Horizontal Slab
BA
RE: Retaining wall as One Way Horizontal Slab
RE: Retaining wall as One Way Horizontal Slab
Correct, 50 psf/ft. Glad you clarified that.
Hokie:
And bottles run dry too (as in fail), right?
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Retaining wall as One Way Horizontal Slab
BA
RE: Retaining wall as One Way Horizontal Slab
What is typical for a normal basement wall restrained at the top and bottom? I can't remember what ASCE says. I thought for basement walls ASCE allowed you to use active? Thanks.
RE: Retaining wall as One Way Horizontal Slab
RE: Retaining wall as One Way Horizontal Slab
Active pressure is used for cantilever retaining walls, but it requires a certain amount of movement in the wall to justify it. If the wall is very stiff, the pressure will be greater than active, but if the wall can't take it, it will simply yield until active pressure is achieved.
Passive pressure occurs when you push a wall or a foundation against the soil so as to fail the soil. It requires lateral movement into the soil mass.
BA
RE: Retaining wall as One Way Horizontal Slab