boiler on slab on grade or an individual footing for i

huangyhg

boiler on slab on grade or an individual footing for it
hi,
i have two boilers that have to be housed in a cmu building.
they weight about 83110 lbs each. i am wondering if i can simply and directly seat them on a 6" slab -on - grade?
or i have to design those heavy/thick isolated footing for each of them separately.
next question is since the building is a heated place do i need to sink the footings of boilers (in case you prescribe me to have individual footing rather than having them seated on slab on grade)to the frost depth or there is no need for going to the depth frost?
the boilers are hot water boilers inside a cmu building.
is there any code requirement that requires me to have individual footing for boilers or is just based on crunching numbers?
i appreciate any information. if you also know a source that talks about the boiler footings please mention it.
any thermal effects that i have to consider in my footing design?
thanks,
bfstr  
whatever your local code says, i would think twice before subjecting a typical floor slab to a permanent 80+kip load.  my reference for allowable slab live loads:
tm 5-809-12/afm 88-3, chap. 15
if it were my call, i would recommend an isolated footing for boiler support.  a six-inch slab seems a bit thin for an 82 kip load, unless you have a very good subgrade, strong concrete, and can spread the load out to 1ksf or so-- equivalent to a stiff 9x9 foot (2.77x2.77 meter) square pad.  
thermal effects depend on soil type and moisture content, frost depth is a local consideration but is generally ignored in climate-controlled spaces.  
try a search for other threads on this forum regarding tank foundations and thermal effects.  
mikeroweworks.com

a uniform pad is easier to construct. if the boiler is supported on a base frame and the load is distributed uniformly, a grade slab is a better option.
to design, first check the  bearing pressure . a rough estimate would be the boiler load/ foundation area. if the bearing pressure is less than the soil bearing capacity , you are okay.
also check the punching shear at the supporting points.
normally, punching shear governs the thickness of the slab.
you may arrive at a thicker slab than 6 inches, but it would be easier to construct than individual footings. you may also save time in constructing and removing formwork.
rebar placement is simpler in slab than isolated footings.