Post load on SOG
Post load on SOG
(OP)
Need design procedure for a post load on an existing SOG with WWF. Load is in 20k range and slab thickness is in 9"-10" range.
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RE: Post load on SOG
I can send you the sheet or a rendering of the calculation if you so want.
RE: Post load on SOG
RE: Post load on SOG
RE: Post load on SOG
So if I have a 8x8 base plate and 10" slab (reinforcing at 7"). Is it simply 4*(8"+2*(7"=d))*(v~70psi wsd)*10"= 61k?
Then I have 61k/(22"*22")=18ksf on the soil! If the soil yields, I engage more slab area and then do I need to consider flexural cracking of the slab?? If the platform is used for temporary storage and fully loaded (post load may be 40k if we can accommodate) and unloaded, does this
affect the design?? I suppose it becomes a fatigue problem.
RE: Post load on SOG
ACI SJ Vol. 93 Nº 5 September-October 1996
p. 503
Analytical Computation of the Punching Strength of Reinforced Concrete
Philippe Menétrey
For the yield lines capacity I used a look-up table of formulas in a Jiménez Montoya's "bible" RC text.
Of course after verification of the punching and bending capacity soil comes... punching however extends -you see in practice twice the depth form the plate (if rigid) and then a 20 kip in a 40x40" inches gives a plastified solicitation more than acceptable by almost any competent soils. Not that I was thinking on this when I answered but should neither be a problem. Of course if you can't find a suitably reinforced area around the point the soil will control and you would need additional work.
RE: Post load on SOG
According to "Concrete Floors on Ground" - PCA:
Assuming: Load=20000lbs
fc=3000psi
Slab Thickness = 10in
CENTER OF SLAB LOADING
MOR=7.5(fc)^1/2=410psi (ACI-318)
8x8 Base plate (64sqin)
Allowable Bearing Stress:
4.2(MOR)=1725psi
Computed Bearing Stress:
20000/(8*8)=312.5psi
Bearing Stress is OK
Allowable Shear Stress:
0.27(MOR)=111psi
Load Periphery(LP)=4(64)^1/2=32in
Computed Shear Stress:
Post Load/(Slab Depth*(LP+(4*slab thickness))
20000/(10*(32+(4*10))=28psi
Shear stress is OK
The above values neglet the structural effects from any reinforcing in the slab. Not knowing the spacings of your frame...
Assuming: 8ft spacing in each direction
k=100pci
FS=2
Joint Factor=1.6
The PCA suggested slab thickness is nearly 10" exactly. Looks like a 20k load will work according to PCA standards.
While a 40k load is acceptable concrete "stress-wise" you could have problems with the soil. PCA suggests using experimental data and deflections to determine if the soil is acceptable (although they don't list a reference to do this?).
P.S. You used the wrong load (61k) in calculating your soil stress above. Plus a larger soil area would resist the load than a 22"x22" area (as ishvaaag mentioned).
HTH!!
---
Andrew