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Up Topic Welding Industry / Technical Discussions / Steel Joist Inspection
- - By Wildturkey (**) Date 06-13-2002 13:30
I was recently on a job inspecting field welds when I noticed that some of the joist welds looked really bad (Porosity, Undercut, Cold Lap). I brought this to my client’s attention even though joist welds were not in my scope of work. To cut the story short the manufacturer agreed that the welds did not meet the Steel Joist Institute Technical Digest #8 Recommended Practice visual acceptance criteria but the welds would meet the design load. The manufacturer called in an independent structural engineer to inspect the welds. The structural engineer measured the length of these welds and found that the welds would meet the design load. He also agreed that the welds looked bad but was not a requirement of SJI. He said the only requirement of SJI is that the welds are strong enough to carry the load and digest #8 was just a recommended practice. I watched the engineer while he was measuring the welds and I noticed that he never took a throat or face dimension. Also if there was two inches of weld and the first inch was full if porosity and the last inch showed none at the surface he counted one inch of weld. My questions are:
1) Is the only requirement of the Steel Joist Institute is that the welds must be strong enough for the design load? If so then does a manufacturer have to qualify welders and have a WPS?
2) If you have a weld and only part of it is acceptable do you not reject the whole weld? Does a start and stop (Tie-in) count as a separate weld?
Sorry for such a long post....and thanks in advance for the replies
Parent - By GRoberts (***) Date 06-13-2002 14:59
I can't really answer your specific questions, but I do know that many, many joist come into the job site with terrible looking welds, that would never pass muster on any other part of the structure.
Parent - By tiweld Date 06-13-2002 19:28
To over simplify the laws of physics the strength of the weld is proportional to the volume (area) weld material deposited. Gross Porosity is a volume reduction of material. Hence a “stress riser” because the load is concentrated unevenly over the rest of the weld area. The same goes for cold lap and other discontinuities. By considering the least volume, meaning only the “good” weld, an additional built in safety margin is achieved for simple “ dead weight” loads. Most fillets are way oversized for the designed safe load factor and also because standard practice is to call a weld out to the next largest standard size 1 /4” or 3/8” or what ever. My only concern is that to know the actual volume it is kind of nice to know the face and throat to calculate the weld area.

The conditions of loading have a CONSIDERABLE effect on how the member performs in service. A few pinholes has little effect on a load in static compression but the same porosity in stagnant water might lead to accelerated corrosion if the weldment were a tank for instance. Flex or bend the weldment and now the thing might rip apart if undercut or coldlap was present.
So it is a judgment call on the part of the engineer as to what ALL the factors are. The engineer is responsible to define what the acceptable criteria pertains to that weldment. It would be even better if he shared that info with you prior to the start of the job. I do not know the Steel Joist Institute requirement’s, only general welding engineering information.
Sorry for the oversimplified yet long winded reply.
Parent - - By CHGuilford (****) Date 06-13-2002 20:48
As GRoberts said, it isn't unusual to see bad looking welds in steel joists. But since the owner was aware of the concerns you had and a structural engineer was hired to look at the conditions, I would assume the engineer was qualified to do the inspection. If he was satisfied, there isn't much else you can do. I wouldn't worry about how he determined weld sizes unless you know the welds are definitely undersized for the design requirements. Possibly he could see the welds were much larger than they needed to be.
Of course, with porosity in most of the weld, who knows what is underneath the surface of the "good" weld. But in this case, I would regard the welds the same as one of the plastic weld replicas used in the CWI practical exam in 1991. The "weld" looked like someone trowelled manure on a tee plate, with obvious slag inclusions, lack of fusion, overlap, porosity, "ropey" beads... you name it, it was in there. However the only criteria that was to be inspected was the undercut and that was right at the limit but acceptable.
CHGuilford
Parent - By RonG (****) Date 06-13-2002 22:44
"DESIGN OF WELDED STRUCTURES"
by THE JAMES LINCOLN ARC WELDING FOUNDATION
"Test specimens exhibiting undercut, undersize, lack of fusion and porosity. In spit of those adverse conditions considered individually, the weld under steady tensile load was found to be stronger than the plate. This is not meant to lower quality of welds. How ever they are striking evidense of how easy it is to make full-strength welds."
Parent - - By bmaas1 (***) Date 06-15-2002 11:20
If the engineer accepted it in the "as is " condition then it becomes their responsibility. Make sure you note your findings and all documentation you can get. Have the engineer submit something in writing for you.
As far as your first question I don't know.
Second question it is a single weld. If it a fillet weld and the termination is outside of the effective length than no it is not rejectable(at least for being undersize).



Brian Maas
Parent - - By DGXL (***) Date 06-15-2002 16:46
Hey again WildT:
I have a copy of that technical doc at work and will retreive it on Monday. I have been told the very same thing while inspecting pre-engineered structures. I also rejected most of the truss welds.

My response to the manufacture was "You can say it complies with the joist-guide requirements, but you can't say you perform your work in accordance with the D1.1 (or any other codes) unless your going to comply with them all." The manufacture actually revised there data sheet on these to note compliance only with the truss-guide.

What's wrong with this picture Building Inspectors?
Parent - - By Wildturkey (**) Date 06-17-2002 11:43
Hello DGXL,
I hope life has been treating you well. I this particular case the job specifications only required that the joist be manufactured to SJI Specifications. One of the questions that I have asked is "Does manufactured to SJI Specifications include Technical Digest #8?" I have'nt got a straight answer on this yet.
Parent - By DGXL (***) Date 06-19-2002 01:50
WildT:
Someone at our office has checked out the truss digest you referenced at the office library. There is more concern regarding this subject than meets the eye (ours). Will try to get an "unofficial interpretation" from one of the senior staff engineers on this as you are not the first to make this observation.

I'll be traveling again, so don't hold your breath for a response (from me)until sometime next week. May try to contact you one on one.
Good luck.
Up Topic Welding Industry / Technical Discussions / Steel Joist Inspection

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