Slab on grade for rigid frame buildings
Slab on grade for rigid frame buildings
(OP)
When using hairpins to transfer frame lateral loads into the slab, how do you handle slab shrinkage? I'm guessing there cannot be any control joints in the slab, and the hairpins tie the slab to the foundation walls.






RE: Slab on grade for rigid frame buildings
I like to use tie beams that span the width of the building and put control joints between and directly on each side of the tie beams.
RE: Slab on grade for rigid frame buildings
Thanks for the respone. Sounds like the joints you describe are running parallel to the tie beam. I'm really interested in the joints running perpendicular to the tie beam, and I'm REALLY interested in how the slab handles both the thrust and the shrinkage when there is no tie beam.
RE: Slab on grade for rigid frame buildings
If you are set on using hairpins instead of tie beams, then you have to check there is enough slab between the first joint and the edge of slab to resist the thrust. I have done this before when I had a small amount of thrust to resist. I had to balance this requirement with the maximum jointed area of slab for shrinkage.
I am not sure how else to handle this, I always show the mesh cut at the control joints (though this likely doesn't happen) so I can't count on that to grab the remainder of the slab past the first joint.
RE: Slab on grade for rigid frame buildings
RE: Slab on grade for rigid frame buildings
Dik
RE: Slab on grade for rigid frame buildings
But then, you may ask, how does the control joint function? I have been told that there has been research done that shows wire mesh, still intact across a control joint, can elongate enough to allow the control joint to crack and open up.
DaveAtkins
RE: Slab on grade for rigid frame buildings
RE: Slab on grade for rigid frame buildings
RE: Slab on grade for rigid frame buildings
I am interested if you can find that research. It wouldn't surprise me if that is the case.
I am pretty sure the control joints don't actually line up with the cuts in the mesh, but I always see it shown this way. The mesh on my projects normally ends up sitting on ground (they try to pull it during pouring) even when I specify it as chaired so I don't know how effective it is one way or the other.
RE: Slab on grade for rigid frame buildings
They used U shaped hairpins with a flat section placed against the side of the column. After the slabs were tensioned they put steel spacers in the gap between the hairpin and the column and welded it to both.
Normally we would put joints in a slab even though it had hairpins.
csd
RE: Slab on grade for rigid frame buildings
Dik
RE: Slab on grade for rigid frame buildings
I am sorry, but I don't have an actual article. Another engineer told me about the research.
DaveAtkins
RE: Slab on grade for rigid frame buildings
Of course it still gives some restraint.
csd
RE: Slab on grade for rigid frame buildings
RE: Slab on grade for rigid frame buildings
Dik
RE: Slab on grade for rigid frame buildings
Larger bars spaced farther apart are less effective at preventing cracking. Personally, I would think this is a bigger issue than having the WWF say 1" too low.
csd
RE: Slab on grade for rigid frame buildings