Best load distribution on beams from loaded slab can be achieved by defining the
slab as a membrane without meshing (one way or two way slabs), take care when
using non mesh membrane slab (two or one way) in complicated roofs, because
Etabs will give the beams incorrect load distribution at some points and these
points not always can be controlled. the results (in the attached etabs model)
from the S300SHCON (where the material is normal concrete) is lower not higher
than the other 2 types (note that the S300SH is the same as S300SHCON but using
a different material to reduce the inertia of the slab section (by reducing the
modulus of elasticity). Also note that all of them give higher results than the
S300MEM2way which gives results similar to the manual calculations.