SOG Shear Reinforcing Under Wall
SOG Shear Reinforcing Under Wall
(OP)
I am hoping someone can point me in the right direcion. I am looking for recommended shear reinforcing details for a slab-on-grade with a heavily loaded wall. Going thicker with the slab is not a practical option at this point and was wondering if there are any references out there that specifically address this situation. I can find lot with suspended slabs but nothing that seems specific to a slab on grade. Is this not a recommended practice? Particularly if the slab needs to remain water tight? I am currntly entertaining the idea of a "U" or "Z" sirrup but the spacing is going to need to be pretty tight.
I appreciate any thoughts you may have.
Thanks,
waytsh
I appreciate any thoughts you may have.
Thanks,
waytsh






RE: SOG Shear Reinforcing Under Wall
Refer to "Designing Floor Slabs on Grade" by Ringo and Anderson.
RE: SOG Shear Reinforcing Under Wall
A more desirable solution would be to install a thicker footing designed for the wall, but it sounds like the slab base, reinforcing, and wall forms are already in place (?).
RE: SOG Shear Reinforcing Under Wall
So with 3" cover you have about a 10" slab minimum.
RE: SOG Shear Reinforcing Under Wall
RE: SOG Shear Reinforcing Under Wall
Can the wall width be increased? a small pedestal? Is the problem beam shear? or punching shear? Can you use shear friction? with large bars? a recent project has 35M@6"
RE: SOG Shear Reinforcing Under Wall
I assume it already has top and bottom reinforcing. How much reinforcing? Are you sure you need shear reinforcing?
What is the soil modulus?
RE: SOG Shear Reinforcing Under Wall
Maybe I better mention my analysis approach as well in case that is flawed. I have analyzed the slab on STAADPro because of the complexity of the loading and the wall system. For my worst case load combination I am getting a shear stress under my wall of 108.2 psi. Which translates to about 19.5 k/ft. which I am then checking against ACI 318 Eq. 11-3 or 11-5. For my model I used a uniform thickness of 15” but in reality the slab is only 12” thick under the wall because of the keyway. So my d is approximately 8.5. My concrete is 4,000 psi so I am getting an allowable shear strength of 9.68 k/ft for a one foot wide section.
Is this a rational approach or am I oversimplifying?
Thanks,
waytsh
RE: SOG Shear Reinforcing Under Wall
RE: SOG Shear Reinforcing Under Wall
RE: SOG Shear Reinforcing Under Wall
Is there any way to increase the concrete strength?
or
Is there any way to eliminate the keyway?
RE: SOG Shear Reinforcing Under Wall
I need to keep the keyway since it is integral to locking the base of the precast panel in place and the grout and sealent help make it a nice watertight connection. Any connection that would sit above the slab I do not think would perform as well.
Thank you for the suggestions.
RE: SOG Shear Reinforcing Under Wall
RE: SOG Shear Reinforcing Under Wall
Provide enough reinforcement in the bottom to resist the triangulated forces. Then, like a truss, there is no shear only axial forces.
PS: a 15" slab! are they wheeling the titanic around on this?
RE: SOG Shear Reinforcing Under Wall
miecz:
If the load is from the top, then top bars are proper for shear friction... it's a matter of tearing the top bars through the slab for failure to occur.
Dik
RE: SOG Shear Reinforcing Under Wall
The reasoning being that the slab will flex under load and if you had dowels in the middle portion of the wall, they would likely be in tension. Your FE model likely reflects this...
Depending on your lateral load at the base of the wall, a 2x4 key should be sufficient and will have little effect on the shear or flexural capacity... you may be able to use the full slab depth for calculating d.
Dik
RE: SOG Shear Reinforcing Under Wall
You're right, the top reinforcing is proper for shear friction, in this case.
RE: SOG Shear Reinforcing Under Wall
My top bars in this location are only serving to meet the temp. and shrink. requirements of ACI 350 and are not flexural resisting steel. So if I am understanding everyones opinion correctlty it sounds like I could use the top bars as my shear friction bars since they are not providing flexural strength.
Would you be of the opinion that this is as good as thickening the slab? If so I could save the owner some time and money since they will need to bring excavating equipment back out to the site to trench out the thickened area under the wall.
I am also curious what you think about the way I evaluated the STAAD data. Does this seem reasonable? Is there a better approach?
RE: SOG Shear Reinforcing Under Wall
RE: SOG Shear Reinforcing Under Wall
RE: SOG Shear Reinforcing Under Wall
Also, strike that remark I made about reinforcing for the shear in excess of the slab capacity (What was I thinking?). Shear friction reinforcing would need to need to provide for the total design shear at the failure plane.
RE: SOG Shear Reinforcing Under Wall
Dik
RE: SOG Shear Reinforcing Under Wall