ETABS 2013 meshing fro slab systems

[Shoja91]

Hi all;

Let's say we have a simple structure and we want to have one-way and two-way slab system. Should I use membrane for one-way system due to its in-plane stresses and shell elements for two-way system for out-of-plane stiffness? The matter herewith is distribution of loads from slab system to adjacent beams (in case surrounded by beams). I seen somewhere that if ratio of span/thickness of slab is more than 40 choose membrane otherwise go for shell.

I appreciate expert's view on this matter as in my office we're about to eliminate the hand calculation for simple and small projects and I need to know the exact behavior of load's distribution from slab to beam.

Thanks a ton