HSS Rect. Column w/ Single Plate & 2L Brace

[sshields]

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

 

[jike]

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.

 

[COEngineeer]

Just use table C-K1.1 page 16.1-368?

Never, but never question engineer's judgement

 

[sshields]

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

 

[kslee1000]

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.

 

[sshields]

http://files.engineering.com/getfile.aspx?folder=4e09a1b3-f36f-4dbb-995d-58be920cf153&file=model.pdf

http://files.engineering.com/getfil...c-b61f-4ef67ecc7a7f&file=plan_-_elevation.pdf

I attached a snapshot of our model, and I patched together some of my ACAD on this already.



Scott Shields
Ghafari Associates, LLC

 

[kslee1000]

You can do as planned to provide diagonal braces in two directions. I may want to provide braces in direction of the climber facing (column L), since it is where the ladder swings the most. For the other direction, I might provide small trianglar brickets to minimize the lateral movement.

The lower brace point sould be made as low as possible. Its angle with respect to the vertical should be around 45-60 degrees.

The design is straight forward. I would assume 50% body weight as horizontal load. From there one, solve the axial load in the brace by simple geometric method. Try to keep the compressive low (say a margin of safety in the ball park of 1.5-2) to make the system more sturdy. For long, slender bracing member to be the choice, you may consider to make it a Y brace (secondary brace from top of ladder to the mid point of the long brace).

If the ladder has tube edge bars, use tube a size smiller, so can be welded the two together.

Just suggestion, hope helps.