I am analysing a slab of about 14.5'x14' with 5" thickness. When i use RC floor (bending only analysis) as calculation option, it gives me a reinforcement of about 4.5" center to center at the bottom (-ve reinforcement). but if i select shell as (bending, compression and tension) analysis, i am getting a reinforcement of about 8" center to center at bottom. In both of these analysis, cracking and deflection option was turned on. The load is about 20psf live and 37-40psf dead load on the panel. The parameter beams have dimensions of 9x18" and concrete is 3ksi.
The deflection is same in both the cases.

Should not the bending only analysis have less reinforcement as compared to second one?
(The reinforcement should be about 11" spacing.)
In reinforcement required, the spacing is shown to be about 12"-14" which is correct upto some limit but when i click reinforcement provided and generate the drawing it gives me 8" spacing. Any idea, why?


I am more interested in bending only since it is a roof of a building.