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Payloader Slab Design

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Ed,

Remember that the AASHTO slab moment formulas are based on a slab supported 
on beams which deflect during loading of either the slab or the beam, which 
affects moments in the slab, which is accounted for in the moment formulas.

If your slab is a one-way slab supported on pit walls, which do not deflect 
during loading, then I would design the slab as a simply supported slab and 
treat the wheel load(s) as concentrated loads placed anywhere on the slab.  
For the length over which the wheel load is distributed, I would use the 
provisions of AASHTO's distribution for cantilever slabs (3.24.5).  For 
shear, with the wheel load placed adjacent to the support, there would be no 
distribution of the load beyond the footprint.  Like any other one-way slab, 
it is usually not worth the time, effort or material to reinforce it for 
shear, so the minimum thickness of the slab would be determined by the 
minimum thickness required for the concrete to carry all the shear.

Hope this helps.

A. Roger Turk, P.E.(Structural)
Tucson, Arizona

Ed Fasula wrote:

>>How would one appropriately design for heavy equipment loads on a concrete
slab? 

We have a grain storage building with a 4' reclaim pit over which a reinforced
concrete slab will span.  Is using AASHTO moment formulas (sections 3.24.3.1 &
2) and scaling for a 86 kip Payloader (with impact), appropriate?  It seems
the Payloader wheel distribution would be significantly different from a HS 20
truck.  Using 3.30, Tire Contact Area, assuming 40 kip on each wheel, A =
.01*40,000lb = 400 in^2, which gives length = 31.6" and width = 12.7"  which
seems in the ballpark...


Also, AASHTO 3.24.4, which states that shear would not need to be checked,
seems to be a clearly inappropriate assumption to make in this particular
situation.  But what would the assumed shear distribution be, 12.7"?

Thanks in advance for any help.<<