Moment Connection - Steel Beam 3

[Veer007]

Hi All,
I have been working with AISC standards for years and recently I had a suspicion, is the welded-bolted combination structurally acceptable? Especially for the moment connection when I got a detail from the engineer, the flange was welded but the web is bolted. I hope the web bolts should atleast be slip critical, however I am not satisfied with this, please provide your valuable feedback.

Thanks in advance!!

 

[human909]

I agree that the cleat plate should be site welded all around too.

 

[jayrod12]

Why should the web connection be welded? It's for shear only. I don't disagree that it could/should be slip-critical, but I don't see the necessity for welded. In fact, the bolted shear connection would significantly aid in erection as they'd be able to bolt the beam up and release the crane, then the welder can go and do the flange welds.

 

[human909]

Why should the web connection be welded? It's for shear only. I don't disagree that it could/should be slip-critical, but I don't see the necessity for welded. In fact, the bolted shear connection would significantly aid in erection as they'd be able to bolt the beam up and release the crane, then the welder can go and do the flange welds.

Good question, and one that I contemplated before posting my reply.

No arguments about the use of a bolted cleat plate for erection purposes. But achieving slip critical in your bolting seems more difficult that running a site weld down the cleat given you are already site welding.

Either way you need the shear connection to be rigid in shear to avoid the rigid flange welds having to take too much shear. Bolts in bearing are significantly less rigid in shear due to the small bearing area that will compress and yield.

 

[JoshPlumSE]

I'm with Jayrod on this. I don't see any compelling reason for the shear tab to be welded rather than bolted.

If this were high seismic and part of the main lateral force resisting system (SMF or IMF), then this connection wouldn't work (because it's not one of the AISC 358 pre-approved moment connections). But, I don't see a compelling reason to require all welded.

If it were sharing shear load with a weld, then I'd say you should weld it. But, it's taking all the shear load itself. Not a problem.... It might be BETTER if it were welded, but this is the type of thing that engineers get push back on all the time. A fabricator or erector comes back and tells us "the welding makes it a much more expensive connection, so please let us just bolt it".

 

[dauwerda]

As long as it is not a seismic detail, AISC does not require the bolts to be slip critical, as they are not on the same faying surface as the welds. As the bolts are installed prior to any welding, the bolts will be in bearing to start, granted they won't be close to seeing their full load yet and more deformation is likely under full live loads, but this is by no means detrimental to the joint (under static loads). See point 17 from the linked AISC, Modern Steel Construction Article:

https://www.aisc.org/globalassets/modern-steel/archives/2004/05/2004v05_good_rules.pdf

 

[ProgrammingPE]

Modern Steel Article saying that welds are not required and the bolts do not need to be slip-critical.

A common misconception is that slip-critical joints are necessary at the web connection to limit the vertical movement of the beam after the flanges have been welded. This would presumably prevent secondary bending and shear stresses in the beam flange in the area between the column flange and the weld access hole. However, the tests showed no decrease in strength when bearing joints were used. Furthermore, most of the tests with slip-critical joints had slip occur at some point in the testing, effectively rendering the web connection a bearing joint anyway.

...tests have shown that these connections can carry moments greater than the plastic capacity of the beam, even when combined with shear loads approaching the shear yield strength of the beam.

Structural Engineering Software:

http://www.structuralcentral.com

Structural Engineering Videos:

http://www.youtube.com/channel/UCOj2mXXf3ZbZtgxTc6BtkGg

 

[human909]

Thanks for the good info.