How to define correctly lateral buckling length for steel beam divided in several segments in Robot Structural Analysis

Solution:

Define "super member" consisting of all beam segments. Define lateral buckling parameters for "super member".

1. Open Design >Steel Members design -Options >Member/Groups -Definition.
2. Click New.
3. Activate Member list.
4. Select beam components to be defined as "super member".
5. Define "Super member" name.
6. Check "Super Member " number.
7. Save. 

8. Define lateral buckling length for defined "Super Member" (refer to the following  procedure).

Replace bar defined by small segments with one continuous beam. Define lateral buckling parameters for this beam.

1. Select beam components,
2. Delete from keyboard
3. Open Geometry >Members.
4. Select required section.
5. Define continuous beam using remaining end nodes.
6. If necessary update load definition for new continuous beam. 
7. Define lateral buckling length for defined "Super Member" (refer to the following  procedure).