Floor Slabs on Grade
Floor Slabs on Grade
(OP)
In a previous topic I had questions on how to determine the amount of lineal load a slab on grade could safely handle.
I have recently come across another reference that addresses this subject: Designing Floor Slabs On Grade by Boyd C. Ringo and Robert Anderson (second edition)
Just wondering what others experience is using this reference for slab design.
I have recently come across another reference that addresses this subject: Designing Floor Slabs On Grade by Boyd C. Ringo and Robert Anderson (second edition)
Just wondering what others experience is using this reference for slab design.
A confused student is a good student.






RE: Floor Slabs on Grade
RE: Floor Slabs on Grade
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: Floor Slabs on Grade
Reading the fine print I realized that the Army manual is using a safety factor of 5.625 whereas the other reference is using the author suggested value of 2.5 instead.
Yikes! No wonder I was having such a hard time getting my bearing walls to work on the slab, my highest wall loads were about 900 plf which I could not get to work with a 6" slab.
A confused student is a good student.
RE: Floor Slabs on Grade
RE: Floor Slabs on Grade
This is the one area where I really wish I had a design program. There were situations where it would have helped immensely I just can't recall off the top of my head.
RE: Floor Slabs on Grade
RE: Floor Slabs on Grade
Under a 900 plf line load, a 6" slab will not sink into the ground, but it might crack. But I don't think it would crack, because, again, the FS is so high.
DaveAtkins
RE: Floor Slabs on Grade
RE: Floor Slabs on Grade
I see people installing 7000lb capacity, 2 post car lifts on 4" slabs without incident (not that I would condone this). Not only is there a point load, but a pretty decent OT moment as well.
I would not worry about a 900 plf load on a 6" slab or a 4" slab for that matter.
RE: Floor Slabs on Grade
RE: Floor Slabs on Grade
At least now I can see where this number is coming from: FS = MR/Fb (Modulus of Rupture/Allow Bending Stress).
So who is correct? The Army Corp. of Engineers or Boyd Ringo? How does he arrive at a safety factor of 2.5 versus 5.625. What is everybody out there using in practice when they have to put a wall on top of a pre-existing slab. It seems like there is a lot of latitude in this field when it comes to analyzing certain situations.
A confused student is a good student.
RE: Floor Slabs on Grade
CJC
RE: Floor Slabs on Grade
RE: Floor Slabs on Grade
A confused student is a good student.
RE: Floor Slabs on Grade
The difference is the safety factor.
If your not worried about floor cracking, you can design the wall foundation as thickened (along with plain concrete bending/shear) and based on allowable bearing values assuming a rigid support, say 1500 psf rather than a flexible support such as the subgrade modulus.
The problem you will have is different settlement between completely different elements cast monolithically.
While that might seem like a big deal, interior footings are designed that way fairly often and without issue, especially if you don't have sensitive floor finishes, but say carpet.
Isolating wall foundations completely from slabs is an expensive task.
RE: Floor Slabs on Grade
A confused student is a good student.
RE: Floor Slabs on Grade
RE: Floor Slabs on Grade
RE: Floor Slabs on Grade
A confused student is a good student.