Field Fabricated Ordinary Moment Frame (Construction Mistake)

[EngineeringEric]

All,
I am looking for some opinions on field made - post installation moment frames. I have project, where the contract drawings and shop drawings all clearly illustrated a moment frame along a line of a small commercial addition. The steel arrived and was installed and then framing went up. One weekend i drove by and looked at the project (prior to Special inspections call) and noticed the steel in place was not prepped or cut to be a moment frames and the flanges were not welded... I am going to kick this back at the fabricator since the product delivered was not what was specified but we have a good relation with the contractor which means we will probably be the ones detailing a repair down the road.

1) Can the proper beam modifications be made in the field (ie flange bezels and web treatments) in your experience?
2) Most cost effective way to fix, construction wise?

Notes: columns are HSS, beams are W16x26, Ordinary moment frames only resisting wind forces. There are 3 consecutive frames (3 beams, 4 columns, 6 connections) The HSS walls were designed to handle the flange couples and shear.

 

[dcarr82775]

I don't see why not, especially since it doesn't require any special seismic detailing. I will admit I am not familiar with 'bezel'. I wouldn't try to do full pen welds on the flanges, but a W16x26 is easily developed with some flange plates and fillet welds, and the shear shouldn't be too hard to make figure on typical type of connection either.

If the shops showed a moment frame and nothing was fabricated that way I wold be concerned what else is missing/not right

 

[EngineeringEric]

Bezel is the neighbor of bevel, lives just three spaces over. same street and everything!
Thanks for the input.

 

[SteelPE]

I think he meant to say bevel instead of bezel.

Adding bevels in the field may prove to be a problem as there are certain requirements for the root opening of a CJP weld in AWS. As currently fabricated you are probably 1/2" away from the face of the column to the edge of the flange as it is now. You would also probably need to cut a "rat hole" (which is probably a requirement of a OMF anyway) in the web so they can properly do the weld.

Adding flange plates top and bottom may be a better alternative but I'm not up on my OMF requirements so I don't know if they are allowed or not.

 

[TDIengineer]

Watch out for your root opening at each end of the beam as SteelPE has noted. Normally a gravity beam is cut much shorter than a moment frame beam. If you're OK with them "buttering" the flanges to close the gap, then ok.

 

[EngineeringEric]

Just got back from looking at it. The beams are about 1"+ from the face of the column (!), and the area is ready to be sheathed with drywall (outside is sheathed already). I think we are going to weld plates to the insides of the flanges to the column. The outside of the flanges is not an option due to constraints. We are looking at some 15 kips per flange, we can handle that. I am unsure about the root opening... With the 1" gap and the shear tab has short slotted holes so I do not think we will be transferring much moment through the web, and none of the elements are close to capacity so i don't think i need to worry about developing any plastic states... and again this isn't seismic so I am a little more relaxed about ductility issues. Time to see where the numbers take me.

Thanks

 

[SteelPE]

When you say inside flange do you mean the 1/2 of the top and bottom flange on the inside of the building? Not sure if I would accept that.

I'm all for helping the guys out.... but if your plans show a moment frame and the shop drawings show a moment frame and one isn't there I would be breathing fire on everyone around. Why should you have to come up with the fix, you should put the fix on the fabricator to hire and engineer to perform the necessary engineering and for you to review their design. You can be certain if you made the mistake they would be sticking this back on the owner with a hefty markup.

 

[connectegr]

I doubt that the proper weld prep, weld access holes, root opening, etc. can be made with the beams as detailed or erected, as simple beam connections. If the beam setback is detailed with a small enough setback for the root opening, the other requirements would be field torch cut, which can look like a 3 year olds disaster. The simplest solution is to provide flange plates. These can be provide with adequate thickness to use partial penetration welds to the column, thus not requiring backing bars. Then fillet weld the plates to the beam flanges. Some overhead welding will be required, but can be minimized based on the plate widths.

http://www.FerrellEngineering.com

Providing fabrication and erection efficient structural design of connections. Consulting services for structural welding and bolting.

 

[EngineeringEric]

SteelPE, by the inside i meant both sides of the web but inside the flanges: the bottom of the top flange and top of bottom flange. This will probably be altered depending on conditions. i would rather have the bottom plate welded to the bottom of the bottom flange and a little wider to eliminate overhead welds, but these are all details.

We kicked it back to the fabricator and they of course say "Not our issue" which is a load of usual. The GC does a lot of work with us and has hired us to come up with a fix and they will back charge the fabricator or withhold payment.

The proper moment frame prep cannot be completed within any degree of cleanliness so really I think I am not going to even try. I will be welding plates to flanges, then connecting those to the columns. I will be making the moment-couple symmetrical about the column axis. So Flange plates it is, just not your typical Flange Plates. Luckily the columns have excessive attachment capacities than applied moments.

 

[dcarr82775]

I would love to know how a fabricator misses an entire moment frame if the shop drawings show it. I wonder what else was done wrong.