Concentrated Force on HSS

[ToadJones]

I have a connection I am analyzing for a fixture or sorts (NOT a building connection)where a 2.375" dia. round HSS is slid through holes of the same diameter drilled thru both walls of a 6" HSS rectangular tube.

The 2.375" round is loaded as a cantilever so it will have concentrated forces resulting from the moment where it bears on the rectangular HSS.
I am trying to check this condition using Chap K in AISC 360-05 and in particular equation K1-1.
K1-1 refers you to K2-1 for determining the factor Qf.
I am getting an extremely low value for Qf killing my connection capacity.

Is Qf even applicable here?

ConnectEgr - you out there?

 

[SteelPE]

Have you checked the commentary with reference to the calculation of Qf. They do have some helpful diagrams.

Wouldn't this be similar to a "thru" plate?

 

[ToadJones]

Yes I read the commentary but it's not much help.

What are your thoughts SteelPE?

 

[SteelPE]

Is this connection acting as a "through" plate (see attached)?

 

[ToadJones]

Essentially yes

 

[SteelPE]

Then I am not sure you are using the correct equations. I would design the example as if it was a through plate using the method described in HSS connection manual.

 

[ToadJones]

I dont think I agree...all this is is a 6x6 tube with a hole drilled in it with 2.375" HSS round slid through the hole.

The 6x6 is a column and the 2.375" round is loaded as a cantilever.

The reactions where the round HSS passes through the walls of the 6x6 tube are essentially concentrated forces transverse to the longitudinal axis on the 2.375" round HSS.

NO?

 

[SteelPE]

If you look in the design example they give you an example of a longitudinal plate and a transverse loaded plate. Both of those examples are different how your "outrigger" tube is loaded.

In the HSS connection manual they end up with a resultant shear in each face of the tube. This shear is what you design your weld for.

I may be wrong but more diagrams should be given in the AISC manual to make this a little more clear.

 

[ToadJones]

this "outrigger" is not welded.

 

[SteelPE]

The outrigger is not even welded a little? What stops it from falling out?

If that was the case, I would use the same equation and then use a modified bolt bearing equation to resist Vf and Vr. How much force are we talking about?

 

[hokie66]

It's just a propped cantilever. If the pipe is good in bending, the tube is good in bearing, and the tube is still structurally adequate with the hole, what's the problem?

 

[ToadJones]

Checking the tube bearing is the problem. I was trying to check it is if it were a concentrated force according to AISC chap. K.

I will also need to check the bearing on the hole itself.
Also not sure what to apply here.


The tube is held in place with a collar and a set screw

 

[SteelPE]

I think you are using the wrong equations. I always thought the equations in Chapter K were for tubes/plates welded to the face of a HSS. Your connection is different.

Bearing on the hole would be the same as bearing for a bolt. What's the difference? Bearing on the tube would be the same as well.

 

[RFreund]

Toad -
Are you concerned with crushing of the round HSS or with bearing on the wall of the HSS 6x6 column?

As far as crushing of the round HSS I would need to look at DG24 more or I would look at roark's rings section.

For bearing on the HSS square column unless there is something more specific in DG24 I think checking bearing as is done with bolts (as SteelPE suggested) should be a reasonable solution

EIT

 

[ToadJones]

Yes.
I am concerned with the round HSS wall crushing as it bears on the Rectangular HSS wall.
I am also concerned with bearing on the thin wall of the Rectangular HSS

 

[ToadJones]

So are you suggesting that I simply use Chapter J.8?

Seems to simplistic

 

[ToadJones]

Actually, how does concentrated forces on HSS not apply here?

The reactions of the pipe on the tube walls are concentrated forces on the pipe, no?

 

[hokie66]

The pipe is fully restrained. It can fail in bending, but arching action will prevent any other mode of failure.

 

[SteelPE]

OOOOHHHH, you are concerned about the concentrated force acting transverse to the 2.375" dia pipe. For some reason I was thinking you were concerned about the HSS6x6 square tube.

Kind of an odd duck here. If you are having problems, why can't you just increase the size of your 2.375" dia pipe?

 

[ToadJones]

yes- I was wondering why no one agreed.

The connection is existing.