aisc 13th ed-w beam to hss column moment conn

huangyhg

aisc 13th ed-w beam to hss column moment conn.
greetings all,
i preformed a search on this subject and got a few good ideas on connections. however, i am using the 13th ed. asd, and i need to check the sides of my hss column.  part 12 details a few connections but notes "the buckling strength of the hss side wall must be checked."  the only calculations i have found that refer to this is in chapter k of the specifications, under paragraph 4 "concentrated force distributed longitudinally at the center of the hss diameter or width, and acting perpendicular to the hss axis." which i believe are the conditions for a beam-column moment connection. i am using equations k1-9 & k2-12.  the issue i am having is that my calculated u is greater than 1.0, due to the moment. this is having an adverse effect on my qf calculation and subsequently equation k1-9.  this leads me to three questions:
1 & 2. am i on the right track? or is there an alternate (read easier) method?
3. what is the significance of u?  it is not clearly defined in the commentary.
any suggestions would be greatly appreciated. thanks.  

yes i believe you're on the right track, that is what i'd use anyway. since you're putting additional stress on the hss side wall, you need to know how much stress is already there. u gives you that ratio of how much capacity is already being used. if you're u is over one, you should check your   
agostage,
thanks. i appreciate it.