design of simply supported tank cover

[fyaure]

Hi,
Can someone tell me where I can find design procedure for single span slab, simply supported (on beams) on all four sides? The condition is like a simply supported cover for a concerete tank.
Also, how do I calaculate momemnt coefficient? My length to breadth ratio is 1.

 

[JedClampett]

Roark and Young, "Formulas for Stress and Strain" 5th Edition, Table 26, sheet 386 among other places.