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Backside web stiffener at steel girder

Backside web stiffener at steel girder

Backside web stiffener at steel girder

(OP)
I have a fairly basic question regarding a typical steel connection. If the connection consists of a wide flange beam framing into the side of a wide flange girder, one side only, top of steel equal, top flange of beam is coped and beam web extended, with a single shear tab and 1 row of bolts, is a backside web stiffener on the girder at the connection required? If so, is this stated in the AISC somewhere? Thank you very much for any response.

RE: Backside web stiffener at steel girder

It's not required but I have seen the scenario you are describing detailed many times. I have also seen the beam itself bolted into a full depth stiffener plate. Depending on the load, it might be a good idea. If its a lightly loaded joist, probably not a big deal. If its at girder/girder connection it's a cheap way to prevent buckling or twisting of the supporting girder web.

RE: Backside web stiffener at steel girder

I agree that it isn't a prescriptive requirement. And, if the shear tab is a full depth stiffener in its own right, it's hard to see what additional benefit would come about as a result of the back side stiffener. With partial height shear tabs, there's sort of a tendency for the lower edge of the tab to attempt to punch through the girder web. Mechanically, the backside stiffener is a slick way to address 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: Backside web stiffener at steel girder

(OP)
Thank you very much for the responses.

KootK - I definitely agree with the punching effect.

I'm going back and forth on 2 different basic beam to girder connections (let's assume equal depth beam and girder): a full depth shear tab or a partial depth shear tab that's held back at the top and bottom by a distance of "k" on the girder (to avoid the extra weld at the top and bottom flange of the girder). It seems like a full depth shear tab wouldn't need a backside stiffener since the shear tab itself would be a stiffener, but a partial depth shear tab would require a backside stiffener due to the punching on the girder web by the shear tab. Would you agree?

RE: Backside web stiffener at steel girder

I'm not sure I would totally agree. The rotation caused by the eccentricity of the bolt group load on the tab plate will certainly, as Kootk mentions, impart some punching force into the beam web.

However, there would need to be some positive resistance to that punching force from the supporting beam itself in torsion. And we all know that wide flange and other open type sections have low torsional stiffness. The actual torsional stiffness might be tough to pin down - based on other attached beams nearby defining a torsional length - as well as slippage in the other shear tabs.

To be conservative, you could assume the supporting wide flange is infinitely rigid - then yes, a full depth stiffener might be required.

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RE: Backside web stiffener at steel girder

You might want to pose this question to the AISC Steel Solutions Center. I suspect they might be able to direct you to relevant papers related to this topic or, failing that, provide a rationale for why it is not a design criterion for the typical beam-to-girder connection.

RE: Backside web stiffener at steel girder

Quote:

(JAE)

However, there would need to be some positive resistance to that punching force from the supporting beam itself in torsion. And we all know that wide flange and other open type sections have low torsional stiffness. The actual torsional stiffness might be tough to pin down - based on other attached beams nearby defining a torsional length - as well as slippage in the other shear tabs.

I think it would rotate before there would be any significant "punching" on the web. (Especially if all the connection involved [for the whole girder] were simple shear.) I've used single shear tabs on a bunch of jobs in the past and it was no issue.

RE: Backside web stiffener at steel girder

I'll add my vote to the "I don't think it's a big deal" chorus.

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: Backside web stiffener at steel girder

(OP)
Hokie93 - I agree, I'm going to contact AISC.

WARose - were your single shear tabs full depth without a backside stiffener at one sided connections?

I know the easiest route is to just detail a backside stiffener, but it seems like there could be some significant cost savings if the backside stiffener was eliminated.

Thanks to all for contributing to the discussion so far!

RE: Backside web stiffener at steel girder

Quote:

WARose - were your single shear tabs full depth without a backside stiffener at one sided connections?

I've had them be full depth and partial depth (one-sided) connections.....no stiffener.....and no issues.

Think of it this way: you don't check bolted/welded angle shear connections for such a failure mode.....and even though the eccentricity is higher for shear tabs....it's not going to control for them either.

RE: Backside web stiffener at steel girder

In my designs I don't worry about backside stiffeners. As far as I understand, they're not at all necessary for conventional single plate shear connections and only sometimes needed for extended plate shear connections.

Here's a paper that sheds some light on extended single plate shear connections.
http://www.larrymuir.com/Documents/Design%20of%20U...

It's my understanding that by following AISC's design procedure, you'll hit the capacity of the plate before causing any issues with the web of the supporting element. So if this is the case with the extended plate connection, I think it's likely fine with conventional configurations even though they can take more load.

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