Alignment of Welded Column connection 1

[gvot]

Total of (29) heavily loaded W12x65 columns land on (29) independent existing steel baseplates. It was understood that existing conditions were not perfect and the design documents stated that the contractor shall trim the bottom of individual columns so that the tops are aligned. The contractor choose to not trim the columns and instead erected a majority of the superstructure “hoping” the problem would resolve itself. This didn’t happen and we now a condition where gaps exists between the bottom of the column and the baseplates. Most of the gaps are not uniform and vary from 0” to ½” across the width or depth of the wide flange. The contractor has proposed following AWS specification which permits up to a 3/16” root opening on fillet welds. The issue is the designed connection has a 1/2” fillet on one side of the flange with a 5/16” fillet on the opposite side. The flange is 0.605” think and if a 3/16” root is permitted the fillet weld sizes need to increase by the depth of the root opening meaning the 0.605” flange will have a 11/16” & 1/2” fillet weld…this brings concerns for laminar tearing or cracking in the welds. Any other obvious concerns?

 

[dvd]

A picture/sketch would go a long way in understanding your issue. Why didn't you grout these columns? Shoot the baseplates in and grout underneath?

 

[gvot]

Baseplates are existing and part of an existing barge so traditional grouting and anchor bolts not possible. Also traditional surveying no longer possible as the barge is free floating. Welding is the only option Photo link... [URL unfurl="true"]https://res.cloudinary.com/engineering-com/image/upload/v1642652106/tips/DSC08772_rwocl4.pdf[/url]

 

[TugboatEng]

You need to trim the bottom of the column even and either insert the deck with thick enough plate to fill the gap or add a doubler.

 

[gvot]

Thank you...TubboatEng as that is exactly the resolution we required but the contractor is resisting.

 

[TugboatEng]

Brackets are commonly used to attach stiffeners and such. They allow for loose fit up. I don't know that I have seen brackets on a column, though.

 

[dhengr]

Gvot:
The fillet welds btwn. a stl. col. and a base pl. are really not intended to be the primary vert./col. load transfer mechanism. They do take moments, shears, and of course, some of the compressive load too. Within the fab. and erection tolerances columns are intended to transfer their primary compressive loads in end bearing. They certainly don’t do that in the photo you showed. Although, I must confess, I don’t see a WF12x col. in that photo either (well, maybe). If the col. is in the right position in plan, and plumb, I would make them scribe the base of the col. to the base pl., add a length adjustment to get the top elev. right, and cut the bot. of the col. off. This cut should be finished, on up to the scribe line by grinding off the cutting crap. A 3/16” root opening on fillet welds is pretty extreme for most fillet welds. I’d like to see the AWS sections immediately around that 3/16” allowance statement, to see how the GC is stretching his interpretation of that. I’ll bet that 3/16” gap is not intended to apply to col., end to end, or base pl. bearing fit-up. Alternatively, they could gouge bevels on the bot. of the standing col., in prep. for CJP welds to the base pl. and then apply the prescribed fillet reinforcements. Then, they have to go up-top and bring the col. tops into elev. and alignment, into plane. They shot the bull, you didn’t. And, you shouldn’t have to accept a half-assed job because of their slopy efforts and workmanship.

 

[dvd]

Expecting anyone to scribe and trim those columns seems bizarre. Engineering laziness resulting in huge amount of field effort. I would have tried to work this one out in advance with the trades superintendent.

 

[TugboatEng]

For those complaining about the gaps, there is an entire trade around ship fitting which involves making things fit irregular structures. Ship repair is a tedious and expensive process. That is a fact. The structures aren't uniform and that needs to be taken in to consideration. In ship fitting butt and fillet welding of beams isn't common. The beams usually get fit to be short and a bracket is lapped on to the side to make up the difference.

 

[gvot]

Appreciate everyone comments and thoughts! This an elevated platform being constructed on a deck barge and is for private industry. The contractor was fully aware of the challenges during the bidding phase but more importantly during the planning phase. Conditions in a marine environment are challenging as there is no way to grout columns as everything needs to welded at the interface of the structure and the barge deck. Again no surprise and the contractor was aware of the challenges. The overall superstructure is traditional structural steel with bolted connections and steel erection has gone smooth. Lastly although full bearing of columns would be great the reality of achieving "full" is not realistic. Because of this the stated goal was to trim columns to match the varying base plate elevations but the welded connection is designed to carry the full axial load. The preferred resolution allows for the column bases to be trimmed and a doubler (another word for a thick shim) plate installed between the column and existing base plate. The gap between the bottom of the column should be between 0" and 1/16" to prevent increasing the size of the fillet welds.

This brings us to the original question...the contractor is pushing hard to use 3/16" root per AWS at fillet weld locations. They actually don't recognize the fact that the welds need to also increase in size to maintain the required effective throat. Our documented concerns are when the fillet weld sizes are increased the result would be 11/16" fillet on one side and 1/2" fillet on the opposite size of a 0.605" think column flange. Are there procedures and QC processes that can be implemented to verify the integrity of the welds and base metal?

 

[EdStainless]

Was there a weld procedure and qualification for the original configuration?
If so them require them to fully requalify the proposed new procedure, with all destructive testing and such.

Sounds like someone needs to take the contractor by the nuts and enforce the original rules.

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P.E. Metallurgy, consulting work welcomed

 

[dvd]

You can't survey it because that is too difficult (3-D scan?), but expect the erector to establish top connection elevation and then scribe the bottom of the columns? I side squarely with the erector on this. I can envision multiple ways to do a better job on this than to try and weasel out of it with a drawing note. AISC Code of Standard Practice.

 

[TugboatEng]

Also, depending on the rigidity of the structure, there is a good chance your ship fitters can use dogs, wedges, and hoists to bring everything together.

 

[gtaw]

Considering the size of the fillet welds required to compensate for the rather large root openings, would a CJP groove weld with a backing bar be easier to accomplish? It is a matter of what is more cost effective and yet provide the structural integrity required.


Best regards - Al

 

[gvot]

GTAW:

I believe a CJP with backing bar would have been a good choice. Contractor actually offered as a possible solution and we concurred. However, the plan stopped when we asked about their level of confidence with "accurately" beveling the flanges. Some tough work positions and we have been bitten in the past with poor weld preps leading to poor welds...not expecting shop level preparations but wanted some level of confidence. The topic just went away after that and they seem insistent on the 3/16" root opening.