Answer:
The partial safety factor γM for reducing the modulus of elasticity is very likely activated in RFEM 5 / RSTAB 8, but is not considered in the manual calculation.
γM can be displayed and adjusted, if necessary, in the "Edit Material" dialog box.
Furthermore, the "Activate stiffness modifications from RFEM/RSTAB" option must be considered in the General Data in the RF‑STABILITY or RSBUCK add-on module.
For the effective length of 35.405 m, the second moment of area of 8,356 cm4, the modulus of elasticity of 21,000 kN/cm², and the partial safety factor of 1.1 as a divisor, the following buckling load results (see also Image 03) according to the following formula:
