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.
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.
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