heavily loaded slab on grade

huangyhg

heavily loaded slab on grade
hello,
i'm working on a manufacturing facility that has quite a few large storage tanks.  these storage tanks are spaced very closely together and are producing a loading of around 2500 psf on the floor slab.  i'm not very familiar with handling loads of this magnitude for a slab on grade.  could someone please offer some general advice or point me in the direction of a good reference to research this topic so that i can get a little more comfortable with this loading.  as it is, the facility has an 8" slab on grade but i'm thinking that this loading may require a thickened mat at the storage tanks.  due to the close spacing, i'm not sure if it's accurate to analyze the punching shear for the tanks individually.  thanks for the help
the quality and uniformity of the soil directly under the slab are probably more important that the slab itself. i recommend that you take steps to find out. if the soil is "good" and the 8" slab has rebar you should be ok.
in this type situation i have always preferred to go with a minimum slab thickness of 12 inches. then you have "room" inside the concrete for identical top and bottom reinforcing steel mats. the twin mats are cheap insurance for unexpected loading conditions.
agree....and also....
depending on where you are located, there could be significant seismic forces that would be applied to the tank and you should have a competent load path for these seismic demands.
either the tanks are braced by some external frame or system, or the base of the tank must be significant enough to resist overturning.
be sure to check.
bevo98...your loading is comparable to relatively high pavement loads, so you might do a quick check on the radius of relative stiffness and compare that to proximity to joints and other tank supports.  if the stress zones impinge or overlap, then you might consider thickening.  assuming a reasonable footprint, shear should not be an issue provided the subgrade (subbase) is appropriately compacted.
i agree with all of the above responses. i have done slabs on grade for fork lifts, airplanes, semi tractors and storage areas as well. the most important item in the design is the sub grade and the compaction requirements. the second is the slab thickness for a given load. third is the joint layout and placement (construction joints and contraction joints). fourth is the shear transfer between the joints (provide dowels). fifth is steel reinforcement.
portland cement association publishes a great booklet that deals with slabs on grade design and construction. you can visit their web site at   
i agree with what has been said above regarding the subgrade under a slab-on-grade.  two other aspects in industrial floor construction that are very important is point loads from rack storage and fork truck traffic loads. both conditions induce moments into the slab, which a much different condition than a uniform loading of 2,500 psf.  
the best reference for floor slab design is "designing floor slabs on grade", 2nd edition, by ringo and anderson, published by the aberdeen group, 1996. there are numberous charts and graphs for both rack storage design and fork truck traffic.
the pca and aci both have very good publications for floor slab construction details.