HSS Truss Connection Configuration

[Spencer10]

In a K connection of a structural truss, all of the books are telling me that an overlap connection or a gap connection is acceptable. It is unacceptable, however, to provide a K connection where the two brace members are cut and have a vertical weld between them.

There is very little explanation as to why this is unacceptable. Can anyone shed some light on this subject??

 

[Lion06]

Why is it unacceptable and where does it say it's unacceptable. What I'm picturing is an overlapped K-connection which is dealt with in AISC 360-05 K3d (page 16.1-134).

Am I misunderstanding your condition?

 

[connectegr]

I don't think it is unacceptable. It might be inefficient. Why double cut both diagonals? And welding the flush matching vertical walls would require a CJP with backing bar.

http://www.FerrellEngineering.com

 

[BAretired]

Here's what Packer and Henderson say in their book "Hollow Structural Section Connections and Trusses" published by CISC.

BA

 

[Spencer10]

BAretired:

That's exactly the situation I'm referring to, and actual have that text book open in front of me. The assembly shown in figure c - WHY is this unacceptable? If there is still sufficient weld metal, penetration, etc. in the configuration to allow for the forces to be transferred, is it still not acceptable?

Packer simply states that it is unacceptable because it does not develop the required strength and the vertical weld is difficult. Is there some other inherent failure in this type of configuration that he is leaving out and that I should consider?

A steel manufacturer has gone ahead and fabricated a truss using this connection that Packer deems unacceptable. If the member sizes, welds, and geometry show that the loads can be safely carried, is it still unacceptable, but only because Packer says so??

 

[connectegr]

I looked at Design Guide 24 - HSS Connections. Dr's Packer, Sherman, and Lecce simply make no reference to the detail requiring the vertical weld.

http://www.FerrellEngineering.com

 

[BAretired]

Spencer10,

One web member is in compression and the other is in tension. Taken together, their resultant is a horizontal force which goes into the chord (unless there is an applied load at the point of intersection).

The top wall and part of each sidewall carries a portion of the load, but does not come in contact with the chord. The load must be carried by shear in the sidewalls immediately above the chord.

That and the difficulty of making a decent weld, I believe is why the connection is deemed unacceptable. It does not mean the connection is incapable of carrying load, but it is not a full strength connection.

Connections (a) and (b) from my earlier post are capable of developing the full strength. So is the overlapping detail attached.

BA