Is that possible to provide only beams for load bearing structure?

Which Beams ?

Lintel Beam !

Yes ! you can provide lintel beam in load bearing structure, actually we do provide them in load bearing structure.

Regular/Conventional Beam !

Why ?? It will serve no purpose..

Why do we provide a slab+beam+column structure ?

To have load transfer a in particular way (slab>beam>column>footing) so as we can have larger carpet area by avoiding large width walls instead we use partition walls.

Thats why we prefer RCC Structure for heavy loading or multistorey building as the load bearing structure will result in uneconomical wall width which will decrease the carpet area to great extent.

In load bearing structure the wall serves as a member (rather than a partition wall) which transfers the load from slab to footing.

So what you are doing by providing a beam is you are just adding a concrete block/section to wall. Thus section will behave same as a brick wall.

Even in case you provide r/f in that beam, it will be more(to great extent)harmful to structure , as the load will be concentrated at wall ends.

So Final Remark, you can provide a beam in load bearing structure, but it will function same as brick wall(which will be uneconomical & also will increase dead load). Still, we do provide beam, well rather call it a block (a small section not extending to full wall length) in some cases at a perticular sections where there stress concentration might occur.