slab on grade restraint
slab on grade restraint
(OP)
Good day.
I don't have that much experience with slabs on grade.
What I am facing is the following
The design drawings are indicating a slab on grade for a residential house with ground beams to tie the columns. The slab on grade is separated from the ground beams and the columns by a separation joint of 20mm. the thing is that the client doesn't want that much joint and would like to remove them.
Removing joints will result in restraining the slab from contracting due to drying shrinkage which will increase the stresses due to shrinkage / temperature.
I was reading the ACI360R which deals with the design of slabs on grade. There is the formula of subgrade drag which depends on the joint spacing. A joint is defined as the length between the free ends of the slab. In my case, I have no free joint since it will be connected to the ground beams.
In my case, I doubt that I can use the subgrade drag procedure since no free joint is in this structure. What is an alternate solution ?
I have already sent the request to the design office but I would like to hear your thoughts about the above. Thank u
I don't have that much experience with slabs on grade.
What I am facing is the following
The design drawings are indicating a slab on grade for a residential house with ground beams to tie the columns. The slab on grade is separated from the ground beams and the columns by a separation joint of 20mm. the thing is that the client doesn't want that much joint and would like to remove them.
Removing joints will result in restraining the slab from contracting due to drying shrinkage which will increase the stresses due to shrinkage / temperature.
I was reading the ACI360R which deals with the design of slabs on grade. There is the formula of subgrade drag which depends on the joint spacing. A joint is defined as the length between the free ends of the slab. In my case, I have no free joint since it will be connected to the ground beams.
In my case, I doubt that I can use the subgrade drag procedure since no free joint is in this structure. What is an alternate solution ?
I have already sent the request to the design office but I would like to hear your thoughts about the above. Thank u






RE: slab on grade restraint
RE: slab on grade restraint
So for residential slab on grade, u are saying that the presence of the joints isn't that critical. therefore, it can be deleted
RE: slab on grade restraint
However, put on your attorney hat for a minute. In the US, claims and lawsuits regarding slab cracking are in the top 3 of all construction claims.
The uploaded image does not quite have the clarity needed.
Regarding your question, can you minimize the joint thickness without eliminating it? Say, 10mm?
For concrete, I prefer to either tie two members together, or separate them. If you kind of connect them, you get unpredictable results.
If you butt two relatively brittle members together that contract and expand occasionally, you risk spalling at the interface edges in the long term.
RE: slab on grade restraint
RE: slab on grade restraint
Assuming the perimeter beams are an exterior wall, you should isolate the slab for shrinkage and thermal reasons. As Ron said, a 20mm joist is quite large. I've typically seen 3/8" (10mm) joints, which are filled with either a backer rod and sealant or a true flexible isolation material with sealant.
On the other hand, I have very often seen house foundations where the slab was poured on top of the perimeter footings (separate placement) all the way to the edge of the building line. (similar to my suggestion for the middle grade beam above)
Side note: Are you planning on cutting control joints in this slab? Control joints will minimize random shrinkage cracking, which is not a huge concern unless there is an exposed slab (like a garage). I would still suggest it.
RE: slab on grade restraint
RE: slab on grade restraint
I wanted to ask if when a sawcut is introduced to the grade slab, will it be ok to covet this sawcut by floor finish ?
Thank u
RE: slab on grade restraint