New Table J2.3 Watch Out! 1

[14159]

Check the new Table J2.4 -- minimum size of fillet welds.

For as long as I've been around, the minimum size has been based on the thicker of the parts joined. This table uses the THINNER part. I checked with AISC for this and it is correct.

It would be interesting to know how many people read right over this and don't notice the change.

14159

 

[IFRs]

I think they finally fixed an error !!!

 

[14159]

It depends on how you define an error. It intentionally used the thicker one for years and now they intentionally changed it to thinner. It has something to do with modern welding practices, but was over my head, not being a welding expert.

I do think it's the single goofiest code change that I've ever seen.

14159

 

[IFRs]

I retract my eariler statement. I was thinking of the MAXIMUM fillet size, which was to "not exceed the thickness of the thinner part". Is that still the case?

 

[14159]

The maximum size didn't change. It's the same as the 3rd Edition LRFD which is something like 1/16" thinner than the thickness of material for material 1/4" or over, and equal to the material for material less than 1/4". Note that this is along an edge of material, like at a lap joint, not at a tee-type joint, like a column flange to column base plate. AISC has a bunch of FAQ that address this commonly confused issue. The base metal strength check, which is not really new, helps to avoid unreasonably large fillet welds in tee-type joints. Other than that, I don't know that there is a technical max, although common sense dictates welds that are not huge.

Have a good weekend (what's left of it).

14159

 

[structuresguy]

My understanding was that the minimum size was set by the thicker piece to ensure adequate heat generation to allow for a good weld. Do they address preheat now as part of the minimum weld?

 

[14159]

structuresguy typed: "My understanding was that the minimum size was set by the thicker piece to ensure adequate heat generation to allow for a good weld. Do they address preheat now as part of the minimum weld?"

That's always been my understanding also, but apparently times change. The following is from the new Commentary:

"Table J2.4 provides the minimum size of a fillet weld for a given thickness of the thinner part joined. The requirements are not based on strength considerations, but on the quench effect of thick material on small welds. Very rapid cooling of weld metal may result in a loss of ductility. Further-more, the restraint to weld metal shrinkage provided by thick material may result in weld cracking. The use of the thinner part to determine the minimum size weld is based on the prevalence of the use of filler metal considered to be ‘low hydrogen’. Because a 5/16 in. (8 mm) fillet weld is the largest that can be deposited in a single pass by the SMAW process and still be considered prequalified under AWS D1.1, 5/16 in. (8mm) applies to all material ¾ in. (19 mm) and greater in thickness, but minimum preheat and interpass temperatures are required by AWS D1.1. Both the engineer of record and the shop welder must be governed by the requirements."

It's definitely intentional, but I still think it's the goofiest code change I've ever witnessed!!

14159

 

[ajh1]

AWS D1.1 has basically been operating with the "thinner" material for years. They have had the same table as AISC except there was a footnote that basically said, "if you have a low-hydrogen electrode then use the table based on the thinner material." As noted in the AISC Commentary most electrodes are now low-hydrogen. AISC is just catching up to where AWS has been for 15 years.

 

[dik]

Typically for HSS connections, I often go 10% greater than the thinnest wall thickness. Research has show this is appropriate and many European standards reflect this.

Dik