Point load on slab

[jeffhed]

I have a tenant improvement with a mezzanine I am working on. The mezzanine is for light storage, so I have some pretty high point loads on the existing 4" slab on grade reinforced with #4 bars @ 18" o.c. What is the effective area of the slab to use for 'footing' calculations. I have been taught to find the area required for bearing (say 24" sq. so as not to exceed the allowable bearing capacity) and then check the existing steel in that 24" sq. area for flexure and the existing slab thickness for punching shear. However, I cannot find any books in our office that show the correct design calculations. Is this the correct mehtod or should I purchase the PCA book for 'Concrete floors on ground'.

 

[dougantholz]

PCA or WRI are much better methods. Essentially treat it as - unreinforced and could find its capacity at 2-3,000 psf of load.

 

[jike]

The slab-on-grade functions like a plate supported by compression only springs. The concentrated load creates both positive and negative bending which will generally limit how much load can be placed on the slab. There are PCA design charts that can help you determine how much load can be placed on the slab.

 

[jeffhed]

Thanks, for the input. It sounds like my method may be too conservative and it would definitely be a good idea to buy the PCA book. I am assuming the design charts will also be contained in this book.