Extended Endplate Shear Connections? 2

[JLNJ]

I have searched Google to no avail, so now I’m turning to the even more powerful eng-tips forum members.

We have been seeing a type of shear connection where the web of a tee is fitted perpendicular to a girder web and the connecting beam is bolted through the flange of the tee using an endplate. I guess the advantage to this is that the beam can be cut square and cut short. Additionally, no bolts are shared, so OSHA should be happy. Has AISC commented on these? The mechanism which provides end rotation flexibility is not intuitively obvious to me, and the apparent eccentricity hurts my eyes to look at.

I have used connections similar to these when have a column continuous through a girder (with their respective webs @ 90 degrees). I fit a tee to the girder web to provide a direct load path for the column flange load above into the column flange below through the outstanding tee flange. If a beam intersects at the same point, then it frames into the tee flange with standard clips.

These other connections I’m asking about are one-sided and are not at a column. The tee is simply to shorten the beam and to make the connection outside of the limits of the girder flanges. Has there been any discussion of these types of connections? I presume there has been. They seem to be somewhat common in parts of Europe.

 

[CELinOttawa]

One sided? There may be eccentricity on the line of action which is being neglected as "minor", but a similar condition in NZ in cross bracing and knee braces led to a number of collapses in the mid 2000s.

Sketch, please!

 

[KootK]

I've used a similar detail to support hollowcore plank from steel girders. Imagine a continuous shelf angle welded to the tee flanges with plank on top. Talk about eccentity hurting the eyes...

I don't know of any specific AISC guidance but here are some contradictory thoughts:

1) You might get some rotational flexibility out of the tee flange in ending at the top.

2) If you could call the end plate connection a rigid-ish moment connection, perhaps the connection could be treated like an extended shear tab connection. I very much doubt this is what has been done however.

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.

 

[Brad805]

This paper is not exactly what you describe, but the research/design philosophy seems relevant. Is the WT fitted to the top flange only?

http://www.larrymuir.com/Documents/Design of Unstiffened Extended Single Plate Shear Connections.pdf

 

[nutte]

The connection you describe will apply the beam shear eccentrically to the supporting beam. Has the supporting beam been checked for this? Possibly, but I would think not likely. Common practice is to provide a shear connection capable of developing enogh end rotation to qualify as a pinned support, while putting no meaningful moment into the supporting member. This connection does not do this. To do that you would have to take the eccentric moment through the bolted end plate connection. This would mean engaging the flanges of the supported beam, not just the web, and a lot of non-standard calculations for the WT flange.

By chance is this connection for a big industrial chemical facility?

 

[JLNJ]

See the attached. It's fitted and welded all the way around. This is a small beam with a few small bolts, but we are seeing the same detail on large beams with many rows of bolts.

 

[hokie66]

The picture is worth 'a thousand words'. I think the concerns expressed above do not apply to this connection.

 

[nutte]

That picture is just what I had in mind from the description. My concerns do apply.

 

[hokie66]

The reaction just causes compatibility torsion, which is resisted by the supported member.

 

[KootK]

At that scale it doesn't bother me much but, technically, I agree with Nutte's point about the lack of rotational flexibility. If there's a supported beam close to a girder support, is the girder going to get torqued like nobody's business? Yup. Is it much worse than your common single plate shear tab? Nope. I'm surprised that anyone considers this detail to be a great innovation from an erection standpoint. Single angle clip connections would seem to be much better/cheaper in my opinion. Swinging the end plated beam into place would cause more fit up issues than you'd see with single angles. And The fitted WT cost would surely outweigh the supported beam coping. I guess there's no arguing economics with the guys that actually price the work.



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.

 

[hokie66]

Minor point...it is not actually a fitted WT as shown, but rather two 8 mm plates. I think the benefit, in some shops, would be in automation. Beam copes are fiddly. I don't see the erection costs being an issue.

 

[CELinOttawa]

I think this is going to turn out to be all a whole lot of nothing... This connection imparts some shear onto the supporting beam, yes, but so do many other connection types. We accept, deal with, or ignore this torsional consequence in those situations!

I am not advocating ignoring a possible problem; I'm just saying we should recognize that we've likely been facing and dealing with a similar issue all along.

 

[nutte]

CEL, that's not quite true. We account for this eccentric shear in the design of the connection, so that the idealized case of just shear and zero moment at the support can be assumed. In the sketch shown, the end plate shear connection would have to be checked as a flush end plate moment connection, and I doubt that is being done.

If the original design engineer (Engineer of Record) and the connection engineer are the same, this can be worked out between the two. If they are different parties, the cooperation often is not there. The Engineer of Record will want just shear applied to the supporting beam, and the eccentric shear resolved through the connection.

 

[Brad805]

I would be more interested in the larger connections rather than these. The eccentricity here is only marginally greater than the typical guage length. With a much wider flange the eccentricity could double.

 

[CELinOttawa]

Nutte: True. Probably a good time for a rocker plate.

Brad: Me too!

 

[hokie66]

I see, I think. You guys just don't like end plate connections, but I do. It isn't the torsion that is the issue, because that is taken out by the supporting beam.

 

[JLNJ]

We go out of our way to limit connection angle thicknesses and welds sizes on shear tabs to keep our flexibility at the beam end in concert with the simply supported assumption/theory/testing. I can visualize the flexibility in a pair of angles or in a shear tab. I have more trouble with a 300 HEB shape framing into a 300 HEB (12" wide x 12" tall) where the flanges are in direct contact. And the connections are detailed with sizable continuous welds, so no skimping there.

If these connections find their equalibrium without torsional checks, I would think any connection no matter how rigid could be deemed a shear connection. Or maybe I'm misunderstanding the deisgn process.

I'm a little surprised I can't find anything out there from AISC or others.

 

[CELinOttawa]

It is the taking out if the torsion that people are worrying about Hokie...

 

[hokie66]

What I can't understand is why you "go out of our way...to keep our flexibility at the beam end in concert with the simply supported assumptions..." in a case like this. As primarily a concrete guy, we don't try to build concrete beam intersections to mimic simply supported conditions, but rather allow the supported beams to account for the compatibility torsion. The exception is connections in precast concrete structures (and those have an unfortunate track record of failing). Why are structures built of steel so different? I understand the need for flexibility with moving and impact loads e.g. crane runways, but in run of the mill commercial structures, I don't see it.

 

[CELinOttawa]

Redistribution is inherently safe in well detailed concrete because it is so stiff and rotationally "stiff". I've heard that you could allow steel to redistribute up to 100% if not for torsional issues (LTB, etc). Perhaps this is what throws us off?