Question:
Why does the deformation of a modeled single-span beam not correspond to the manual calculation?
Answer:
The shear stiffness was probably not considered in the manual calculation, or it was assumed as infinite. In RFEM/RSTAB, this is taken into account by default in accordance with reality, so that the deformation is less favorable than in a manual calculation, which only includes the deformation component from bending.
The shear stiffness can be deactivated under the global calculation parameters (menu "Calculation" → "Calculation Parameters"); see the image.