huangyhg

beam supporting slab design
it's common while designing joist slab. however, for solid slab design, i don't think it's very common. since the inertia of the beam is almost same as that of slab, the whole system tends to behave like flat plate rather than beam/slab system. deflection control will govern large slab depth and by specifying width of the embedded beam actually dictates reinforcement as a means to curb deflection rather than inertia.
i agree in that is less common for solid slabs. maybe short cantilevers made that way 1 side of the beam.
respect the justification, proper assignment of the beam rebar to some width resulting in satisfactory calculated stresses and deformation may validate one such design, whilst the issues of behavior 2 way as named by benishak will still be present.
don't forget that the loads of the notional slab need be passed to the beam axis, i.e, bending along the direction orthogonal to the beam encompasses the full extent of the floor along such line, the width of the notional beams included.
zap,
this is sometimes done around voids in slabs to provide a support or strong band to support the load for the area of slab that is not continuous to the supports. the design width is then the width that you logically think will be supporting that load. it should not normally be more than about .1 to .15 of the span length. there was a post on strong bands" which discussed this a couple of weeks ago.

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