Expert: Arshad Khan - 9/8/2007

Question
Mr. Khan,

   I am planning to build a 1000 sqft wood framed mezzanine in our warehouse we have recently acquired. I have obtained the structural drawings from my local municipality and and trying to decipher how much weight the 6" reinforced concrete slab can take for a column point load. I have come up with a viable design for the mezzanine structure using my past engineering training I acquired years ago at my local tech school, but to my dismay, have not retained all the information I had so desperately studied to learn from years gone by. My question is a simple one, but I just want to reassure myself that what I am reading from the structural plans is what I interpret it to be.
The plans state the following:
Uniform design load of reinforced slab on grade = 500 PSF
& the design load for rack post = 6000 lbs.

I am assuming that the rack post load is referring to a single column or post weight of 6000 lbs. maximum and am wondering is this the maximum for any column I place on the slab to support the mezzanine?
the mezzanine is 32.5' x 32.5' (1060sqft area) I am only providing (4) 5.5" x 5.5" support columns down the center to support a built up beam. they are spaced @ approx. 11' o.c.
Please let me know if 6000lbs is the maximum and if so can a distribution plate of some kind provide for a greater point load? Thank you very much for your time and consideration.  
Scott


Answer
Hi Scott,

This is a bit difficult to answer without knowing the foundation conditons. If the slab can take 500 psf, then the post should be spread over say 6000/500= 8 SF, or around 2.75 by 2.75 square. You could then put the post anywhere- this could be reduced to say 2 ft by 2 ft, and spread the load by using a reinforced concrete pedestal, say 1 ft high?

Hope that helps!

Kind regards,

Arshad