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Existing Double Angle Connection Welded on top and bottom

Existing Double Angle Connection Welded on top and bottom

Existing Double Angle Connection Welded on top and bottom

(OP)
I have been asked to analyze a double angle connection that has been welded on the top, side and bottom. How do I do this? AISC examples only recommend welding on the side and a partial portion at the top to the supporting member. Please provide guidance. This is supposed to be a simple shear connection. Thanks

RE: Existing Double Angle Connection Welded on top and bottom

Do you need the top and bottom weld to achieve your capacity? The 'C' shaped weld provides some additional strength and more rigidiy. Stresses in the top and bottom weld are generally much less.

Dik

RE: Existing Double Angle Connection Welded on top and bottom

For what type of loads are you analyzing this connection?

If it's pure shear, then use the Instantaneous center of rotation method same as any other connection.

Now, I suspect that this connection may have some axial load as well. That being the reason for adding the weld along the bottom. In that case, the instantaneous center of rotation method gets if not impossible to solve, then close to it. Therefore, you would revert back to an elastic solution method for the connection.

RE: Existing Double Angle Connection Welded on top and bottom

(OP)
this is a project where I designed the connections for. It was designed as a bolted connection to the supporting beam, vertical shear load only. However the bolt holes did not align so therefore they field welded the connection. I do not need the top and bottom welds. I just thought if it was welded at the top and bottom it would cause the connection to behave differently?

RE: Existing Double Angle Connection Welded on top and bottom

Capacity wise, you should be able to do the calculation pretty easily. Even if you ignore the lower weld.

The worse thing you have to worry about is the "rotational ductilty" check. Meaning that the connection may be more rigid for rotation than a shear connection would normally be assumed to be. What are the implications of this? Maybe imparting some moment into the girder or column supporting your beam.

RE: Existing Double Angle Connection Welded on top and bottom

As you've correctly identified, the connection can be expected to behave differently with the top welded. You loose some of the rotational ductility that Josh mentioned.

For what it's worth, the Canadian steel manual still shows welds on all three sides for this connection based on some research done at the University of British Columbia some time ago. The connection gets designed and constructed that way here often and, to my knowledge, problems do not result.

Practically, I'd expect unanticipated end moments in the beam to be of little significance. You have them until the upper weld gives way and then I'd expect the moments to redistribute without incident. And, based on past performance, typical beams seem to be designed stiff enough to prevent even the weld damage from occurring.

I do realize that nothing that I've shared here necessarily gets you street legal in terms of US code acceptance. Hopefully some it will help to inform your judgement on the issue should it come to that.



I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

RE: Existing Double Angle Connection Welded on top and bottom

KootK... I believe they determined that because of the rigidity of the beam relative to the connection, that the top and bottom welds had little overall effect on the behaviour of the overall connection.

Dik

RE: Existing Double Angle Connection Welded on top and bottom

Agreed. I'm pretty sure that I've googled that UBC paper and it's "getable" if desired.

The rotational ductility concerns have always bothered me. I feel that research in our field is, of necessity, mostly reactive. Stuff goes wrong and we figure out how to deal with it. Unless there are a bunch of related connection failures in the field that I'm unaware of, the rotational ductility business seems proactive to me. The answer to problems that have not yet organically manifested themselves.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

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