classification of lipped section - bs 5950-12000

huangyhg

classification of lipped section - bs 5950-1:2000
with reference to cl. 3.5.1 of bs 5950-1:2000, an "internal" elements are attached to other elements on both longitudinal edges whereas "outstand" elements are attached to an adjacent element at one edge only, the other edge being free. i reckon that both the top and bottom flanges of a lipped section are classified as "outstand" elements though they are attached to other elements on both longitudinal edges but one of them is "free".  do you think that the top and bottom flanges of a lipped section be classfied as "outstand" elements or "internal" elements?
the classification is all to do with the local buckling capacity of the element.  if the element is attached on both sides such as a web it stronger and then more likely to reach its plastic state before buckling than only attached on one side.  hence the higher b/t ratio.
i would be inclined to class them as outstands as one of the sides is free and that is a more conservative approach.