Field Welded Clip-Angle Shear Connections - Embed Plate

[SteveGregory]

We typically show the outstanding legs of the clip angles welded to the embed plate along the outer vertical edge with a 2X (or 1/2") return on the top at the corner. It is my understanding that this provides some flexibility for a simple shear connection.

Well, the contractor welded the entire length of the top edges of the angles to the embed plates. Should I have these welds "cut" off? Or what?

 

[TehMightyEngineer]

I've seen this happen a lot in industrial applications where the mentality is the more weld the better. Welds on the top will make it a stiffer connection but also add a moment into the connection.

If it's a light load sometimes the angles and welds can take it. However, this will put a torque into the supporting member and change the moment distribution in the supported member.

If it were me I'd reanalyze the beam as having a moment connection and check the members and connections for these new forces. However, that's more than likely more expensive than just grinding those extra welds off (assuming there's not a hundred of these connections).

As a final note, having those welded like that will cause a possible loss of ductility where it could cause the weld or angles to fail in a sudden, brittle fashion.

EIT with BS in Civil/Structural engineering.

 

[TehMightyEngineer]

I guess the short answer is, unless you check the new connection forces, I would grind them off.

EIT with BS in Civil/Structural engineering.

 

[ToadJones]

How are the clips connected to the beam?

 

[SteveGregory]

Thanks Mighty!

Toad, the clips are bolted to the beam with horiz. slotted holes.

The connection is to an embed plate that uses headed studs. This places extra moment into the connection which in turn loads up the studs embedded in the concrete.

More App D pain than I want to endure again.

 

[ToadJones]

I think your bolted connection at the beam-to-clip location will have sufficient rotation.
You'll still have a moment from P*e, "e" being the distance from the bolt centerline to the embedded plate.

In other words, you'll have nothing even remotely close to a moment connection as has been suggested.

 

[nutte]

Are the slotted holes short-slots or long-slots? If they're long-slots, you'd want to have slip critical bolts if you expected the original connection to behave like a pinned connection.

 

[SteveGregory]

Toad,
I did use the 'e' in my design as you noted. However, if they were as eager to crank down on those bolts as they were to weld the angles then I could still get a good moment out of the connection. There is no paint on the steel.

I think the slots only serve to help with erection fit. The slots are 1.5" long.

 

[TehMightyEngineer]

Yeah, I assumed that it was standard size holes with bolts or welded but the slotted holes will definitely reduce the moment. I'd still take another look at the connection and make sure that it will perform as expected but with slotted holes I would expect that they will prevent large moments from being transferred to the embedded plate.

I wouldn't worry about them cranking down on the bolts too much but you are correct that it could increase the moment in the embedded plate. I'd say that, unless you're right on limit of the capacity of the plate, you may get away with the connection as is.

1" long is a short-slotted hole.

EIT with BS in Civil/Structural engineering.

 

[TehMightyEngineer]

Actually, I should have said that 1" long is "typically" short-slotted for 3/4" bolts. You can have longer short slots for larger diameter bolts. 1.5" long is a long-slot for 5/8" dia. bolts.

Since you do have such a long slot you will likely (depending on bolt size) have to have a slip-critical connection.

Note that, per AISC, slip-critical connections have reduced capacity unless you use finger shims (section J3.2).

EIT with BS in Civil/Structural engineering.

 

[a2mfk]

I'd have them grind it off.

You can look up commentary in AISC (9-13 and Spec J1.2 in 13th edition), but significant research and case history is at work with these pre-qualified simple shear connections in order to allow them to rotate enough to allow you to treat them as shear only connections. As already stated you will have P*e moment, plus an unknown moment from this lack of rotational ductility caused by the full welding around the connections.

Depending on field fit-up, your slots may or may not provide the additional rotational ductility lost by the welding. My gut feeling is this connection is probably OK, but I would feel better if this were connected to a beam or column which would provide additional ductility. An embed plate will offer no ductility that I am aware of, and as has already been addressed, the embed plate will now have to resist additional unknown moment that you did not intend in your design.

So... Grind it off, not your bust, why take the responsibility.

 

[Brad805]

The wall is not infinitely stiff, so a little rotation on its part will relieve some of the moment. This connection would be at best something between fixed and pinned. I am with Toad. Its all good, move on.

Brad

 

[ToadJones]

I'd say let it go.
There is slop in the bolt holes as is, even is they were std. holes. Slotted will provide for more rotation.
Make your self a little sketch and you'll see the beam can rotate at the end before the bolts engage the sides of their holes (in a perfectly fab'd world). The beam end rotation will be tiny anyway.
This isn't much different than worrying about moments in any simple shear connection aside from the relatively stiff embedded plate.
You were going to have some moment in that plate anyway....no you are essentially talking about secondary effects.