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Extended Endplate Shear Connections?
2

Extended Endplate Shear Connections?

Extended Endplate Shear Connections?

(OP)
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.

RE: Extended Endplate Shear Connections?

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!

RE: Extended Endplate Shear Connections?

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.

RE: Extended Endplate Shear Connections?

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?

RE: Extended Endplate Shear Connections?

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

RE: Extended Endplate Shear Connections?

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

RE: Extended Endplate Shear Connections?

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

RE: Extended Endplate Shear Connections?

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.

RE: Extended Endplate Shear Connections?

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.

RE: Extended Endplate Shear Connections?

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.

RE: Extended Endplate Shear Connections?

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.

RE: Extended Endplate Shear Connections?

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.

RE: Extended Endplate Shear Connections?

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

Brad: Me too!

RE: Extended Endplate Shear Connections?

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.

RE: Extended Endplate Shear Connections?

(OP)
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.

RE: Extended Endplate Shear Connections?

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

RE: Extended Endplate Shear Connections?

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.

RE: Extended Endplate Shear Connections?

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?

RE: Extended Endplate Shear Connections?

I think the reason is simpler myself. When I was looking into extended shear tabs I was surprised to read comments like, "we need further study". Simple shear tabs are very easier to create simple tables for load capacities so long as the basic criteria are followed. When we get into cases where the relative stiffness of the different members is more important that is much more complex for our litigious industry. Look at the pre-eng industry. Behind all those sheets we get they have very complex algorithms (most of the time) to calculate all of the connection details.

Out of interest I did a simple study to see the difference in the OP's case. I do not have much time right now to summarize this in more detail, but I thought I would post a few of the images for others and to see if there was any interest in looking at a few others. I know the von mises stress are not the best for the discussion, but they seem easier than a vast number of plots for the scope of this. I think there is merit to this connection detail for a fully automated plant. In addition to the savings in beam length it also seems very probable one will have more bolts than they would have with a shear tab. I would hope the steel companies will not suggest an asymmetric bolt pattern? For a plant that is not automated this detail seems more prone to fit problems.

RE: Extended Endplate Shear Connections?

In concrete, the compatibility torsion release valve is beam cracking & stirrup yielding. In steel, the release valve is connection flexibility. If you sacrifice your connection flexibility, you switch from having compatibility torsion to just... torsion. And trying to address torsion in steel is usually a much more expensive proposition than detailing to eliminate it.

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: Extended Endplate Shear Connections?

KootK,
There are only two types of torsion: compatibility and stability. By "just...torsion" I assume you mean stability torsion. You don't have stability torsion in the OP's situation. The rotation doesn't have to be released by connection flexibility, but rather by supporting beam rotation. That is one of the most wonderful things about steel...it is ductile. Open steel shapes have little resistance to torsion, so they will rotate a lot with little change in stress state.

RE: Extended Endplate Shear Connections?

Yes, I mean stability torsion. Or equilibrium torsion in the nomenclature that I'm used to. Either way, I disagree with your interpretation.

Compatibility torsion is that which can be redistributed through yielding. The rest is equilibrium torsion. Steel is generally only ductile at the material level. At the member level, many members will fail via some form of non-ductile buckling. The primary story of steel is the story of buckling, not yielding.

Many steel section are indeed flexible in torsion. But that just changes the torsion that member will attract. It doesn't mean that redistribution will occur. You're unlikely to ever plastify a wide flange girder in torsion. Rather, you'll induce some complex mode of buckling or simply tear apart your hapless girder end connections.

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: Extended Endplate Shear Connections?

I suppose we will just have to agree to disagree. You think I am wrong, and I think you are wrong. But if you can point to an actual failure as you described, I will listen.

RE: Extended Endplate Shear Connections?

I'm not going on a lord of the rings style quest to dig you up an example Hokie. AISC thinks that connection flexibility is important enough that they recommend it in the bible. Is that not a good enough reason for you to listen?

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: Extended Endplate Shear Connections?

Buckling of the supporting member is a red herring. The rigid connections make buckling less likely, not more.

RE: Extended Endplate Shear Connections?

I think that's a complicated matter Hokie. I'll assume that we're talking about lateral torsional buckling:

1) The distance between LTB brace points remains unchanged as the distance between supported beams.

2) The fixity of the brace points improves due to the increased torsional restraint provided by the supported beams. This benefit is less significant than it might first appear however. You gain some rotational restraint but do not gain true torsional fixity as warping strain is not restrained.

3) To achieve true torsion redistribution, something has to plastify. In this case, I think that's the flanges yielding inwards from the tips under warping. As the flanges yield, Iy and Cw drop fast and the likelihood of LTB buckling between beams increases.

When you add all that up, I'm not really sure what you get.

I'm really not all that concerned about buckling although I always enjoy debating the finer points of theory. The primary point that I've been trying to convey is that there generally is not girder torsion redistribution at work in steel systems as there often is in concrete systems except, perhaps, in the connections when they are made rotationally flexible. You wanted to know why steel folks care so much about connection rotation capacity. That's why.

You do a funny version of agreeing to disagree. I like it.

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: Extended Endplate Shear Connections?

Koot, I am curious if you would reject the proposed detail? I would not.

RE: Extended Endplate Shear Connections?

Nope, at that scale, I'm fine with it. As I mentioned at the top, I've done much worse with steel supported precast. With that, I ran into issues with precast being installed 100% on one side of the girder before the opposing side was installed. Beam rotation on the order of 30 degrees. Of course that truly was equilibrium torsion in the temporary condition.

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: Extended Endplate Shear Connections?

Yes, I agree in a case like that it is much different. With steel beams supporting precast panels it gets much more difficult when one is dealing with longer spans and panel segments up until the welding is complete.

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