Deflection of beams

The traditional structural analysis considers beams as practically undeformed. Nowadays, with the accurate analysis using finite elements, it is possible to form structures of remarkably higher stiffness of beams than slabs.
The effect of vertical deformation of beams to the deformation of the slab is insignificant for beams with cross-section 300/1000 (deformations of beams practically zero).

The effect of vertical deformation of beams to the deformation of the slab is moderate for beams with cross-section 300/500 (considerably smaller with respect to those of the slab).

The effect of vertical deformation of beams to the deformation of the slab is significant for beams with cross-section 300/300.

In the two-dimensional finite element method, the secondary bending moments are always sig-nificant, while the moments in the main direction remain relatively constant.
In this case, like the modelling using members, the effect of vertical deformation of beams to the deformation of the slab is insignificant for beams with cross-section 300/1000 (deformations of beams practically zero).

In both cases of modelling, the effect of vertical deformation of beams to the deformation of the slab is moderate for beams with cross-section 300/500.

In both cases of modelling, the effect of vertical deformation of beams to the deformation of the slab is significant for beams with cross-section 300/300. In conclusion, the assumptions of frame elements being modelled with members and slab ele-ments being modelled with two-dimensional finite elements are considered to be both logical and successful. This success is greater the stronger the beams cross-section (mainly their depth), the smaller their span, and also the smaller the thickness of the slabs is.