Shear Lag in Moment Connection

[amendale]

I have cantilever beam to column moment connection. The column is square HSS, the beam is MC. The channel is welded to the side face of the column by two longitudional welds at the edges of the web. I was wondering how to check if shear lag would be a concern for this connection, since the ends of the beam flanges are hanging and therefore do not have any compression/tension. I know if the welded length is long enough then stress flow would make it into the flanges at the critical moment section but how do I get this length?

I have attached a sketch

 

[JAE]

Your weld symbols are shown incorrectly in that they point to an intersection between upper corners of the channel and the tube back wall.
This is a point, not an intersecting plane.

Are the welds intended to run along the top and bottom channel flanges? Or down the vertical length of the channel web adjacent to the tube corners?

Thanks

 

[amendale]

Its just a quick sketch I made. The welds run along the top and bottom flanges of the channel, as well as down the web. Its welded all around. My concern is that the end of the flange are not connected to anything and would therefore result is shear lag under bending. How would I check the extend of shear lag? I believe there should be some calculation for the length of the weld that is required to develop the stress into the flanges.

 

[KootK]

I never would have thought to check shear lag in this situation but I see your point.

I'd imagine that each flange was an isolated element and then do the typical shear lag calculation for the expected flange forces. Similar to what you might do of the flanges were isolated angles.

 

[JAE]

Not sure that AISC Table D3.1 really covers this. It is very similar to case 4 but you only have half of this condition.

This would be if you assume all the bending tension is in the flange (conservative) and the other end of the flange "plate" is free - not welded as in the Case 4 figure.

I think you do have some shear lag issues in that the bending is taken through the flanges mostly but then is transferred to the channel web.

 

[BAretired]

I don't think shear lag is a problem but there may be a problem with welding procedure, because the channel must be welded to the corner radius of the HSS requiring a special weld.

If the channel had been supported by the two vertical welds alone, the reaction at the right side of the HSS would be M/250 where M is the moment at the left side of the HSS. The top and bottom flanges of the channel would have zero stress at the end, but would pick up fiber stress at approximately a 45 degree angle in plan, which means the channel section would be fully effective at about 30 or 40mm away from the end of the channel, i.e. at a point where the moment is only about M/6 or M/8.

An all round weld, by inspection, is going to be no worse than two vertical welds.

BA

 

[hokie66]

Agree with BA, and shear lag is not a concern, as the shear centre of a channel is outside the web. As long as the weld group is adequate for the moment and shear, I see no issue.