Welded-Welded Shear Tab

[nutte]

What do you do when bolt holes in a shear tab don't line up? (For those unfamiliar with the term, a shear tab is a plate welded to the supporting member and bolted to the web of the supported member.) Sometimes, due to fabrication or erection issues, the holes in the shear tab don't line up with the holes in the supported beam web. So the easiest thing to do is to weld the shear tab to the supported member, right? See the attached sketch. But then you have a connection that doesn't allow for any end rotation, so your model of a pinned connection is no longer valid. Indeed, AISC doesn't recognize this connection type.

My question is, does anybody know of any research or documentation on these types of connections? This is a common problem, and the common proposed remedy is "weld the shear tab to the supported beam web."

 

[KBVT]

It seems that your concern about end rotation is valid, see AISC's response to the same question.

http://www.modernsteel.com/steelinterchange_details.php?id=211

 

[KBVT]

I've typically gone to a seated connection in this scenario with a small angle close to the beam top flange for erection stability.

 

[slickdeals]

I don't know if that is the specific reason why fabricators I have worked with repeatedly request single plate shear tabs to be replaced by single angle connections.

Obviously an angle can be welded-welded and still flex.

 

[CTSeng]

How far off are the holes? If close, ream and use larger bolts or use slip critical assembly. Otherwise remove shear tab and field weld on a new one.

 

[connectegr]

In the old Astaneh method of calculating single plate connections the flexibility of the connection was determined based on the supporting member, not the connection itself. A single plate has very little flexibility whether welded or bolted. The research that lead to the 13th Ed tables found that beam end rotations were tiny. Also if a beam is composite, the studs and concrete will restrict beam rotation even more regardless of the connection type. By the Astaneh method connections to column flanges (for example) were considered rigid connections. Beam to beam connections were considered flexible based on the flexibility of the girder web. My point is that a single plate connection is a pinned connection, but not the ideal flexible condition whether welded or bolted. We frequently use bolted single plate connections. I would not recommend welding the single plate to the beam web, primarily because very little research is available for this condition. The present single plate design does not consider any eccentricity in the bolts. Is this not similar to a welded/welded plate? The use of short slots is allowed, but not for flexibility, since "bolt plowing" is expected to resist any horizontal force.

In a field repair situation, I suggest that you look at the entire condition. Is this a beam to girder connection? Are the beams composite or otherwise limited from rotation? An alternate connection type may be necessary, but maybe not.

http://www.FerrellEngineering.com

 

[connectegr]

Slickdeals,
Single angles, especially bolted/bolted, are great for a CNC beam line shop. Prior to 13th Edition the connection capacities were greater for single angles. GOL=2 1/2" was less than the eccentricity using in a single plate. The beam and supporting members pass through the beam line for cut and holes. The single angles can be fabricated similarly. No shop welding is required, the angle is bolted to the support or beam web and is ready for paint or delivery. No labor fitting material or welding. CNC for the entire connection. Some beam lines can even provide the copes if necessary.

It is probably an unexpected bonus that a miss-fit can be field welded.

http://www.FerrellEngineering.com

 

[connectegr]

In relation to Dr. Zoruba's Steel Interchange response. AISC does not prohibit the use of slip critical bolts in single plate connections. How would bolt plowing or the thickness limit for ductility (d/2 + 1/16) apply? Also, a slip critical connection would be very similar to welding.

Also note, the ductility check refers to the supporting web or plate. This is also a very conservative limit on the plate thickness. I have attached a sample calculation of how we determine the plate thickness (ref 13th Ed p7-19).

http://www.FerrellEngineering.com

 

[271828]

I'd consider classifying the connection as an extended shear tab and use the ductility check with Mmax. You'll need to figure out an equivalent to C', though. Remember that an "extended shear tab" is any shear tab that does not fit into the conventional configuration category. I'm sure there has never been research on this exact connection and this is stretching the Manual's concept, but it seems worth considering.

KBVT, that response was pre-2005 Manual, so the extended configuration shear tabs didn't exist then.

 

[nutte]

I like that approach, 271828. Find the nominal moment-only strength of the weld at the shear tab to beam web and make sure the moment capacity of the plate itself is less than that. Then the connection does have the capacity for inelastic rotation (yielding of the plate, prior to the ductile failure of the weld) to keep the end of the beam from picking up a lot of moment. Now if only some university guys would test a bunch of these connections to make sure they do behave this way, we'd be set.

 

[ToadJones]

no engineering........plug weld holes and re-drill.

 

[civeng80]

Hi nutte

If the holes dont line up it must be pretty sloppy workmanship from the contractors or steelfabricators.

I wouldn't allow the use of welding of the joint, its sloppy doesn't look good and the joint doesn't do what it supposed to do.

Further I would be investigating why the holes dont fit and closely look at all workmanship in the whole project and I guarantee you will find many more serious issues.

 

[connectegr]

Sometime steel construction has field issues. We are not building a Swiss watch. Steel tolerances are much better than concrete construction. Fabrication and mill tolerances are facts of construction. You should have a feel for whether your fabricator and erector have an adequate quality control system in place.

Plug welding and redrilling can have additional problems. The weld metal can cause the drill to drift and create a no conforming hole.

http://www.FerrellEngineering.com

 

[civeng80]

connectegr

Fair enough !

But I still would not allow a welded joint in Lieu of the bolted joint.

 

[nutte]

Civeng80, we wouldn't scrap a Mercedes because of one bad spring. And ditto on Connectegr's comment. I don't even know how to speak Swiss, much less read their watches.

 

[271828]

Now if only some university guys would test a bunch of these connections to make sure they do behave this way, we'd be set.

Unfortunately, I'm sure nobody would pay for such tests.