Local buckling castellated beam

[reyhanmailoa]

I've been doing my final project about ultimate design of castellated beam. I use "Design of Castellated Beams" by Knowless as my reffference. Later I found that most of castellated beams profile (Tee's stem) do not meet the local buckling requirement (BS 5950-1:2000). I've searched many literatures but i couldn't find any guidance for adjusting the slenderness ratio for the Tee's stem.
Has anybody got any suggestions where information might be found to help in the solution?
Help would be appreciated.