You need to use the following function to extract the member length of any member--
Geometry.GetBeamLength <BeamNo>
If you use the same function, then provide me your code and mention the exact error message that you have received. For axial force, as it remains same throughout the length of the member, program calculates the axial force value at the start and end node of the member. For any intermediate section, same value is reported. You can upload your STAAD.Pro model and mention the member number so that I can check the same in my machine.
Geometry.GetBeamLength <BeamNo>
If you use the same function, then provide me your code and mention the exact error message that you have received. For axial force, as it remains same throughout the length of the member, program calculates the axial force value at the start and end node of the member. For any intermediate section, same value is reported. You can upload your STAAD.Pro model and mention the member number so that I can check the same in my machine.