Erection Problem Requires Fix? 2

[SteelPE]

I have a job that has concentric brace frames. During erection, the erector decided that it would be a good idea to cut the gusset plates in order to fit the bracing into the proper location (see attached picture). They cut these holes into all the gusset plates around the building.

I would like to have this fixed but am not sure about how to go about doing it. I believe new gusset plates should be installed but this would require a lot of field work. I’m also not sure if this is realistic or not.

The erector would like to CJP a new section of plate that he removed in order to set the brace. I’m not convinced that this can be done properly in the field.

Has anyone run into this problem before? If so, how did you go about fixing the problem?

 

[ishvaaag]

It seems some logical reinforcement would ask for some "flange" welded to the gusset plate but all will depend on checking the codes and if permissible behaviour. The triangle cut may be infilled, or not.

More clean solution might ask tu cut the braces etc with temporary substitute bracing, also cumbersome task. I more likely if permissible from codes and behaviour would go for the other.

 

[InDepth]

This looks like an ordinary brace frame connection. An infill piece would probably work. I guess the concern would be in the welding procedures and quality (and details) in order to minimize potential crack initiation points and stress concentrators.

0) Submit an addservice to owner for repair & possibly include a fee for hiring a welding specialist & or FEM analyst.
1) Develop a detail with high fracture toughness (removal of backing bars, angle of cuts, edge prep).
2) Ask for a WPS submittal of proposed welds. I would also specify AWS D1.8 requirements for this weld. Review the submittal for heat input (evaluate HAZ), electrode toughness, etc.... You may even what to specify a mock-up (make that contractor work for his mistake). I would look into a double bevel to reduce heta input.

Worst case..sharpen that pencil or perform FEM to prove that notch is acceptable as is (with some grinding).

 

[Stillerz]

in depth:
Do you mean Ordinary Concentric Braced Frame (OCBF)?
How is that any different than waht Steel PE called it?

How can you look at a snapshot of one connection and tell what type of braced frame it is?

I am confused here?

 

[SteelPE]

The system LFRS is technically a “Steel System Not Specifically Designed for Seismic Resistance” (R=3) concentrically braced frame.

The building is actually relatively small. this problem happens at all brace locations… 4 in all.

 

[Stillerz]

would the braces not fit without cutting the gusset?
Did the contractor HAVE to cut the gusset like that?

 

[SteelPE]

Stillerz

This is a bit of a debate. I contend that the erector didn't try hardest to try and fit the brace. It wasn’t going to be easy. Making these connections never is. I believe (by looking at the shop drawings) that it could have fit without cutting the gusset plate.

Of course the erector says it’s impossible to make the connection.

However, all of this finger pointing doesn’t solve the problem.

 

[InDepth]

Ordinary is very different from special concentric brace frames. "Special" triggers various code requirements including protection of hinge zones, special detailing, weld requirements, and more substantial calculations (See AISC). The design is substantially different (gussets larger with yield lines, etc...) If this is a system that is not specially detailed, I say go for the welded triangle, you aren't going to expect substantial inelastic yielding in this system.

You can quickly tell a special from an ordinary brace frame because the offset requirements and assumed yield lines make SCBF gussets larger (whitmore requirements). With OCBF you can essentially place the brace right up against the beam/column. Google SCBF pics and look at AISC design guides.

looks like the contractor didn't sequence the construction properly.

 

[Stillerz]

In depth:
I understand the diffence between OCBF, SCBF, EBF etc, it just sounded like you were saying the same thing as SteelPE. There is an Ordinary Concentric Braced Frame.

SteelPE:
I would say this is the WHOLE debate. If the contractor couldn't erect the braces, the detailer is most likely at fault. When we detail, we make it very clear that the erector must clear any problem with us prior to say, cutting a huge notch in a brace gusset.
I have designed & detailed braces exactly like this before and I always make sure that they can be fit up in the field by making the slots long enough in the HSS and making sure there are no other interferences.
If these braces would have fit w/o cutting, i'd make the contractor replace all of the gussets.

 

[corus]

In the present situation FEM would be useless as you have a sharp cut-out corner which would give an infinite stress.
The cut-out also effectively reduces the length of weld along the brace, and the sharp corner is close to the toe of an adjacent weld, for which both are stress raisers. A patch plate over the cut-out (in my view) would cause problems with welds upon or close to other welds, and frankly would look messy. I'd just simply infill the cut-out so that the gusset has its original load bearing capacity.

corus

 

[nutte]

Stillerz, there is usually little benefit to the pissing match you propose.

 

[Stillerz]

nutte, I know, but it pisses me off when somebody hacks the hell out of one of my structures & he said there were only 4 connections.

 

[nutte]

Yes, it is irritating, but the question here now is how to fix it. That doesn't mean accepting a substandard fix, or doing the additional work for free. But rubbing the contractor's nose in it isn't going to help you or the situation.

 

[Stillerz]

nutte, i know it all too well. I work for a design-build & demo company. The good part for me is, when i screw up the erectors help me out and vice versa becasue we are all on the same team.
I guess my point is, the contractor should have contact the engr's and detailers prior to getting out the hot wrench.

 

[Stillerz]

Getting back on point here, I do think a good qualified welder using proper prepping techniques could CJP a new piece of plate back in place. I'd get it inspected (ultrasonic or radiograph type. All said and done, you'd never know it was cut. I have had some welders really save my ass on a few jobs.

 

[SteelPE]

I agree that while I would love to make a point of this problem, it probably isn’t in my best interest to do so. At first I was reluctant to accept an infill patch. The more I think about it the better off I think we will be with the patch.

The only way I can see the erector replacing the gusset is by removing the brace itself. By the time they are done they are probably going to need a new brace and gusset. Overhead welding of the new gusset to the existing beam isn’t going to be easy.

If I go with the infill patch, I can have the erector grind the existing cuts smooth and square. I could then have the fabricator make a site visit to trace the infill pieces for fabrication. Have the fabricator prep the CJP weld, using a Double-Bevel-Groove weld. The erector can then install the new pieces and the have them UltraSonic test the new welds.

This seems more feasible.

 

[InDepth]

You may want to specify a radius in the corner of the cut (1-1/2"). Look at AWS D1.8 and AISC for maximum surface roughness of repairs and prep, I believe it is 500 microinches. At the ends of the CJP there will be weld tabs /baking bar extensions. Remember to have them grind the backing bars and weld tabs off to the 500 microinch spec (no need to have additional stress risers left from the repair).

In addition to UT you may want to also specify dye penetrant or mag testing to locate surface flaws.

 

[jike]

If you are going to have him full pen the welds then make sure you have a "runoff tab" so that he carries the weld beyond the plate and then grind off flush. Otherwise you will get a weld terminated prematurely which would be a stress riser where tearing could begin.

 

[Ron]

Since this is not a seismic issue, I would look at grinding the existing flame cut area, and providing a fillet welded cover plate over the cutout. Do it on both sides (if accessible) and weld to the column, brace, and gusset.

An out of position CJP weld in the field is a challenge. You'll then have to radiograph the completed weld.

Perhaps a stupid move on the erector's part, but "it is what it is"...

 

[JLNJ]

This is a guess of course, but it looks to me like a stout brace for a "small" building. There's a chance you don't need that part of the plate at all.

Maybe this is an opportunity to build some capital which you might be able to spend elsewhere...