Double Angle vs Shear Tab Connections 1

[HDStructural]

Hello,

At my new company (heavy industrial industry), I have been tasked with updating our general notes. Our steel general notes require that all shear connections be made with double angles and that shear plates and single angles must not be done. I understand the logic of not wanting a single angle but I don't see the issue with a shear tab. To clarify, I am not referring to any connections with crane runway beams or girders, just a standard shear connection for a typical beam, which may support equipment and live loads up to 500 psf.

I haven't found anything in AISC DG 7 or AISE Tech Report 13 forbidding shear tab connections.

Does anyone know why this would be required or if it is a code requirement somewhere?

Thanks

 

[phamENG]

My guess is that they want the flexibility to weld to the column and the beam. In a shear tab, the beam must be bolted or you do not have a ductile failure mode that adequately simulates the assumed pin.

In a double angle connection, you can weld both legs of the angles and the ductility comes from deforming the angle as it pries off the column. (Just have to make sure the welds can handle the prying, of course, which the tables account for, I believe.)

 

[HDStructural]

I understand that, but AISC has limits/requirements on shear tab designs that ensure that the plate will yield (ductile) prior to the bolts or the welds failing. So there would still be the ductile failure mode, it's just unknown where the true pin location occurs. I see that the double angle could have a more well defined zero moment location.

 

[DrZoidberWoop]

That note could definitely be updated to give yourself, or your delegated connection designer, more flexibility. You could spec an "order of preference" for the shear connections in different scenarios, like having the detailer try a DA conx first, then a shear tab, or something else, if that won't work.

As a conx designer for a fabricator, I've seen a similar note while working on a "vibration-sensitive" hospital job in Pennsylvania. The EOR was convinced that double angles were preferable to reduce vibrations that may affect laboratory and operation areas. In the end, we were able to compromise and use a combination of shear tabs and DA's (some of the copes req'd for using DA's were just silly), but they rejected the use of single angles.

 

[CDLD]

HDSturctural, I work in heavy industrial (often corrosive environments) as well and we also require double angle connections.
I think this is fairly common note.

Right or wrong, I believe the reasoning is to provide more redundancy in the structure.

We usually allow shear tabs or single angles for miscellaneous steel/ platforms.

 

[phamENG]

AISC has limits/requirements on shear tab designs that ensure that the plate will yield (ductile) prior to the bolts or the welds failing.

What limits are provided for welded-welded shear tabs in the steel manual to ensure pin-like behavior at ultimate loads?

 

[AskTooMuch]

Double angle is preferred even required by some companies but that is ignored specially for fire proofed structures because that won't work. You need shear tab for fire proofed structures.

 

[271828]

Shear tabs, especially extended ones, are iffy at grating. Maybe that's part of it.

Double angle connections are multiples stronger also, so the 500 psf loads might be part of it also.

 

[HDStructural]

Thanks all,

PhamENG, I am referring to welded-bolted shear tabs, which have maximum plate thicknesses based on bolt group moment capacity, to ensure the plate will yield prior to the bolt group, and minimum weld sizes to ensure the plate will yield prior to the welds failing.

 

[phamENG]

That's exactly what I said in my first post...."the beam must be bolted." In a lot of industrial settings, welds are preferred. So if the preference is to have all welded connections, you need to go with angles to get a shear connection. If you don't care about using bolts and you aren't worried about something not fitting up correctly and necessitating welding the tab to the beam, then there's no reason not to if it is considered carefully.

More than likely, somebody made a broad decision a long time ago to avoid in the future some headache that they experienced. It can possibly be undone as long as each situation is considered carefully.

 

[dik]

First, I don't know what the standard name for a shear tab connection is. Is there a specific name? I consider it as a bar welded to a web or a column to be used for a shear connection. With my clients, I don't know which is the least costly. In addition, some of them have preferences. On a recent project, my eMail to my employer was:

There are only a dozen or so of these connections. With my work, even if not my responsibility, I do a quick check to see that things work, in general... I just don't tell them.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[lexpatrie]

I'd say shear tabs are less expensive, generally.

They may want double angles due to old archaic design practice nobody ever updated, or the guy who knew why they wanted double angles left the company twenty years ago and nobody changed it. I would imagine it's less expensive to erect particularly when it's to the flange, but obviously the beam needs to be coped for the double angle and you have to drop it in from above versus swing it into place for the flange connection.

Call a local fabricator/erector and ask them. Fabricator and erector preference varies, and requiring a specific connection type arbitrarily isn't the best, particularly for simple connections, usually the recommendation is to allow multiple types of simple shear connections so the fabricator/erector can select the one they prefer (particularly if the connection design is delegated).

If you can detail for a shear tab, that's going to have lower capacity, generally speaking, but there's nothing inherently wrong with it, and capacity may not matter, or it may not matter for the typical structure. There are no provisions I know of that forbid them.

Simple Shear Connections, Hewitt, Modern Steel Construction, October 2006.

Some of these practices are just that, practices, like the way older structures tended to require connections that were good for 50% of the beam shear capacity and other non-optimal ways of specifying connection strength requirements.

Say, offhand, does anyone know where that article about the 50% shear strength requirement showing that massive connection depth to a W10? I know it was in Modern Steel Construction, circa, say, 2000? Perhaps in Steel Interchange? I remember pretty low-res graphics being involved in the picture.

 

[sandman21]

What limits are provided for welded-welded shear tabs in the steel manual to ensure pin-like behavior at ultimate loads?

It's the same as the bolted connections

Behaviour of single and double row shear tab connections and weld retrofits

 

[phamENG]

Thanks, sandman21. I look forward to reading that. Dealing with those retrofits has always been a headache for me, especially since the steel manual doesn't address it directly.

 

[haynewp]

I prefer shear tabs at least at column lines to transfer beam axial loads. I would give an option to use double angles or shear tabs for the other connections if I was delegating conn design.

 

[canwesteng]

Double angles are standard in industrial, they give you a lot more flexibility for future expansion or moving equipment around, and the additional cost is pretty negligible. This isn't just your company, it's virtually all of them.

 

[JoshPlumSE]

I always thought that double angles were easier / cheaper for the contractor / erector. This was also for heavy industrial construction. Also, it was mostly pre-2001 when the new OSHA restrictions were adopted.

Post 2001, I feel like there is some bias against DA's because of the extra OSHA restrictions. Regardless, DAs can still be used efficiently. Just with a little more planning (and offsets) so you aren't hanging a beam on either side of the same girder when attaching them.

 

[271828]

For double angles, there's the erection safety issue mentioned above. This only applies at columns, so that problem isn't as bad as I once thought.

https://www.osha.gov/laws-regs/standardinterpretations/2006-05-09

 

[lexpatrie]

That only applies at the double beam connections to a column web, as far as I know.

For most beam connections of this type, this is a detailing hiccup that doesn't change the strength of the connection. Particularly if you are connecting for the actual shear force in the beam versus 50-55% of the maximum shear capacity of a short steel beam.

You can also provide a temp seated angle on the one side if you'd rather, especially if the flange is narrow enough to fit inside the column flanges.

 

[dik]

Different clients of my employer have their own choice. I think a single shear tab is the least costly. I think a single angle may the the easiest because you don't have to hold it at 90 degrees to the web (the angle leg does that)... each has their preference.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik