hss rect. column w single plate 2l brace

huangyhg

hss rect. column w/ single plate & 2l brace
hello,
i'm designing a pretty straight forward connection, a hss 6x3 with a gusset plate (welded longitudinaly, (sp)).  i'll have double angles bolted to the gusset.  
reference aisc 13th, commentary, section j, page 16.1-366-368 --  my question, is a vertical brace w/ single plate gusset connection a, "concentrated foce distributed longitudinally at the center of the hss width and acting perp to the axis or a concentrated force distributed longitudinally at the center of the hss width acting parallel?
up to this point in my career (1 yr), i haven't had to design a connection using a hss column before and i'm trying to piece together a plan.  i typically like to start in commentary sections and work back into the spec.  can anyone point me in the right direction please?
scott
  
scott shields
ghafari associates, llc

i assume this is a knee brace connection on a tube that you are asking about and how to reinforce the tube wall to take the axially force....is this correct?
if so, i usually design a face plate on the tube wall to carry the force over to the side walls.
just use table c-k1.1 page 16.1-368?   
never, but never question engineer's judgement
the situation is a suspended platform at bottom chord level (approx 20' from finish floor elev.).  the plat form has one of those industrial type ladders at the end of it, the problem is that the last eight feet of the ladder are retractable, such that the tube that supports the ladder doesn't attach to the ground.  what you basically have is a cantilever ladder & tube assembly hanging off the side of the platform, except for when the bottom 8' feet are deployed.
now, i was speaking with the arch. on this job, and he can't change the ladder configuration, so we're stuck with this.  i told him that strength wise it'll be fine, but what i'm worried about are lateral loads & serviceability (i know i hate it when i'm on a ladder that sways).  basically when a person is climbing a 20' ladder that is unbraced its going to sway, so i want to put kickers in both directions that frame into the tube and back up to the platform framing (w8's).  make sense?
so my question is that these kickers will have reasonably small axial loads, but what is a good rule of thumb for knee brace length?  say a 20' foot column, should i connect the brace 3,5,7,10 feet down?  does it matter?  further, the table on page 16.1-368 of aisc 13th gives nominal connection strength, but i' not entirely sure how to work this table, b/c my connection is longitudinal plate, do i only use the one equation next to it?  that's how it appears to me, but sometimes, it's not always that simple.
  
scott shields
ghafari associates, llc

sshields:
it took too much space to describe the situation. can you post a simple plan & elevation view, so everyone would be on the same page.