In FEM Application Guide is stated:
Let us suppose:
-composite structure (steel and concrete)
-small element length in steel part of section (element 5 to 6 - bottom drawing) e.g. smaller than 2 cm
What is acceptable longitudinal subdivision of girder if we have in mind this small length of sheel element?
Have you any advice for modeling such geometry?
In our experience there is no need to super subdivide the FEM model due to composite structures as in the longitudinal direction the beam behaves more like a line girder. This FEM observations are concerning shear and it would include the concrete slab where the dimensions are considerably higher. For the steel part local warping will require, as usual, stiffeners, bracings and cross-frames.