UNT and UNB is the unbraced length of TOP and BOTTOM flange regardless if they are under compression or tension.
- UNB should be L if the bottom flange is not constraint anywhere at the intermediate location.
- UNT and UNB are the unbraced length of the top and the bottom flange. The program figures out which flange is in compression and accordingly uses either of UNT or UNB.
- By default STAAD.Pro uses the member length as UNT and UNB.
