The critical flange at any point within a segment is assumed to be the compression flange unless either end of the segment is laterally unrestrained in which case it is assumed to be the tension flange.
Because the steel member design module can't detect if the member being
designed is a cantilever or not, it is recommended that for cantilevers
(for which the critical flange may be the tension flange) you check that
the calculated bending effective length is correct and, if not, specify
it manually.
SPACE
GASS is not able to determine whether a loading condition is predominantly
due to gravity or wind and you should therefore check that the above rule
is valid for your situation.
For more information refer to AS1250 clause 3.3.4.7, AS4100 clause 5.5, SABS0162 clause 7.2.3, BS5950 clause 4.3, NZS3404 clause 5.5, AS3990 clause 3.3.4.7, IS800 clause 8.3 or HK CP2011 clause 8.3.