Hybrid steel beam moment connection

[haynewp]

I have a request to use a bolted (pre-tensioned) moment connection for the top flange of a steel beam with a CJP weld at the bottom flange. This is for a splice in an underhung crane that will seldomly be used. The shear plate at the web appears to also require welds based on the crane wheel assembly clearances as the rolling assembly could hit bolts in the web.

I have never used a moment connection that had a bolted flange plate at one flange and welds at the other flange. I have decided I am going to recommend against it since this is only to save in some field welding they didn't want to do and I'm not comfortable doing this. But I am interested if there is anything outside of AISC J1.8 that I can point to that discourages a hybrid connection like this or if anyone else has done it. I can't find any moment connections in AISC that show this type of arrangement either.

 

[KootK]

It makes me nervous for, presumably, the same reason that it does you:

1) Will the welded shear tab take up the moment before the top flange bolts kick in?

2) Will the bottom flange CJP weld suffer from some bending abut its own axis before the flange bolts kick in?

3) Fatigue, although I assume that you mentioned infrequent use specifically to take that off of the table.

I've not done such a hybrid connection and would be hesitant to do it unless somebody else came to the table with relevant, positive experiences with it.

 

[KootK]

All that said, I don't know that the usual prohibitions on mixed bolt/weld connections were really meant to apply to such a case. I see it as a bit of a grey area in that respect.

 

[BridgeSmith]

KootK, whether your points 1 and 2 would be concerning would seem to depend on whether the loading exceeds the slip resistance of the bolted connection. If the beam is loaded to the point where the plates slip, your concern in #1 is definitely valid. If the bolted connection doesn't slip, though, the forces should be distributed no different than a welded connection.

Rod Smith, P.E., The artist formerly known as HotRod10

 

[haynewp]

I couldn't find specific limitations on this type of load sharing assembly between bolts and welds and I agree that the provisions seem more geared towards sharing of an in-line force. My hesitations are the same as KootK listed except for #3.

AISC Design Guide #7 has the attached detail for underhung crane beam splices which I don't like at all.

 

[WinelandV]

First question: does it need to be a moment connection? Or is the crane beam system stable if this is a pinned (i.e., shear only) connection? That, at least, appears to be what the AISC is driving at - with the full pen weld for a uniform bearing over the joint.

 

[haynewp]

It's a single span gantry so my case would be a moment resisting splice.

 

[Teguci]

J1.8 and 10 is enough to prevent an engineer from condoning this.

Constructibility would also be a problem. Can't pretension those bolts until after any welding deformation has been completed.

 

[KootK]

KootK, whether your points 1 and 2 would be concerning would seem to depend on whether the loading exceeds the slip resistance of the bolted connection.

As I understand OP's original post, the bolts here are pretensioned rather than slip critical. I like slip critical much better, of course, but still would be hesitant.

 

[WinelandV]

How long is the span - longer than 50'?

 

[haynewp]

Slip critical would be fine, but still same initial concerns.

 

[haynewp]

No,only 16 ft long. It's going into a small room of an existing facility with very limited access due to hazardous materials.

 

[phamENG]

Seems like you wouldn't save all that much avoiding the field weld, would you? By the time you prep the surfaces and install the bolts for a SC connection, how much have you saved over a single CJP when there's already a welder there doing the bottom flange (presumably for crane travel on the bottom flange)? If you had a 100 of these, may be worth it, but for a one-off I don't see it.

 

[haynewp]

They have to shut down operations to weld in the facility is the reason for their request, but I also don't see that much difference if this area has to be shut down for 1 CJP versus 2. The first request was for an all bolted connection which physically can't work, the next request was for CJP at the bottom only.

 

[BridgeSmith]

For the connection of flanges strictly in compression, without enough cycles of loading for fatigue to be a concern, is a CJP weld necessary, or would simpler (and quicker) type of weld suffice?

Rod Smith, P.E., The artist formerly known as HotRod10

 

[haynewp]

A welded bottom flange plate would be in the way of the underhung rolling assembly. A welded top flange plate could be used.

 

[BridgeSmith]

I was just thinking of PJP or maybe a butt weld to connect the top flanges, since it won't see any tension. As you can probably tell, I'm not well versed in weld types or procedures, but I know we don't specify a CJP unless we need it to get to a higher fatigue category...

Rod Smith, P.E., The artist formerly known as HotRod10

 

[bones206]

Discussion on similar connection from a couple years ago: thread507-402177

 

[MotorCity]

While I have not done this, I would allow it as long as the bolts were slip critical. The concern would be differential move between the top and bottom flange. The splice of the bottom flange certainly will not move since it is CJP welded. The top flange splice "shouldn't" move as long as the SC connection does its job. No amount of engineering can predict whether or not a slip critical connection will ever slip or not.

 

[WinelandV]

I know that space is an issue, but I vote for figuring out how to get the 16' beam in, in one piece.