I assume that you are talking about 2 angles with their heals together or nearly so. They usually have alternating batten plates holding them together.
I have delt with these in the past, but do not ever recalling seeing any design tables. You may have to analyze them on your own.
Warning: These columns can easily fail in torsion since they have no significant torsional resistance!
I have an old section book from the 1970's. This gives safe working loads for starred angles based on BS 449. The angle sizes vary from 50x50 angles up to 200x200 angles. It covers both mild steel and high yield steel. If you wish I could send you a copy.
