punching shear
punching shear
(OP)
We have 9" flat cast-in-place concrete slab with concrete columns. Because the parking garage in the first floor and the basement, the column spacing has to go 29' apart. According to ACI, the minimum slab thickness should be l/30, which is about 12", but client doesn't want to use that much thickness slab, how I we solve the problem without failed punching shear?






RE: punching shear
To reduce the depth, you could add drop panels and edge beams. Or possibly a prestressed system might reduce the depth. But I would strongly advise not to violate the code provision on minimum thickness. You're likely to have problems and the client will conveniently forget what he requested.
RE: punching shear
RE: punching shear
Acturally the deflection is fine but the puching shear around the column fail after we considered the unbanlance moment.
RE: punching shear
RE: punching shear
RE: punching shear
And you could post-tension the slabs to get them as thin as possible without having deflection problems.
RE: punching shear
RE: punching shear
thanks
RE: punching shear
I have done a lot of similar projects with 30' spans where 8" post-tensioned slabs with studrail reinforcing turned out to be the most economical solution.
RE: punching shear
If you have problems with punching shear, there are several products like Decon Studrails or Lenton Steel Fortress that can really help you out. Need to watch out for penetrations within 10 times the slab thickness IIRC- it reduces your punching shear perimeter and can cause a great deal of problems if you have an MEP engineer or architect that doesn't understand punching shear.
http://www.erico.com/products/steelfortress.asp
h
RE: punching shear
ACI 421.1R-99 Shear Reinforcement for Slabs
http://www.normas.com/ACI/PAGES/421.1R-99.html
RE: punching shear
On what basis did you calculate that the deflections are ok for an RC slab with a L/D ratio of nearly 40. It is a good depth for a PROPERLY DESIGNED PT slab. It will not work for RC slabs unless your end spans do not control.
As others have said, capitals or shear heads, but get the deflections right first.
RE: punching shear
The alternative to caps/drops is to opt for a thicker slab (if normal reinforced) and pay the hit for additional shear and concrete. Post tensioning is an option, just a matter of care for joints and corrosion. You also take a bit of a hit due to the increased concrete cover.
Dik
RE: punching shear
RE: punching shear