The original post was regarding D1.3. My response has nothing to do with D1.3, and I'm sure that Henry, Milton, Brent, and Al already know these things, but since D1.1 was mentioned, I just wanted to add a couple thoughts. In my experience, when D1.1 criteria is a requirement on a project, AISC criteria is also invoked.
As we know, the limitations in D1.1 and AISC are stated that "the minimum size fillet weld cannot be less than the size required to transmit calculated forces". With regard to AISC Table J2.4, Minimum Size Fillet Welds, the AISC further states, "the minimum size fillet weld cannot be less than the size required to transmit calculated forces" NOR the size shown in Table J2.4", which is based on the material thickness of the thinner part joined. D1.1 and AISC both indicate that the minimum fillet weld size doesn't apply to fillet welds used for groove weld reinforcement, and the corresponding Table 5.8 Minimum Fillet Weld Sizes of D1.1 further requires that for base metal thicknesses of 1/4 or less, the minimum fillet weld size for cyclically loaded structures must be 3/16", whereas otherwise, it would be 1/8".
Table J2.4 (D1.1 Table 5.8) provides the minimum size of a fillet weld for a given thickness of the thinner part joined. These requirements are not based on strength considerations, but on the quench effect of thick material on small welds. This means that the weld needs to be big enough to heat the base material sufficient to create a good bond between the base metal and the weld metal. That being said, as the base metal thickness increases, so does the minimum fillet weld size.
With regard to the maximum fillet weld size, a fillet weld size whose strength equals the base metal strength is basically the largest effective fillet weld. It is, in essence, another practical limit on the fillet weld size. The strength of a welded connection is controlled by the weaker of the base metal or the weld. The strength of the base metal and the weld are based on their effective areas. As the fillet weld size is increased, the weld strength may, at some point, exceed the strength of the base metal. Increasing the weld size to the point that the weld strength exceeds the strength of the connected parts will be a waste of resources since it will no longer increase the strength of the connection. Also, the very rapid cooling of weld metal can result in a loss of ductility, and the restraint to weld metal shrinkage being provided by thick material can result in weld cracking.
Scott,
All very well and true...BUT, it still does not give the fabricator nor inspector any clue as to some magical number or formula for saying 'in the joining of this 1/4" stiffener to this 1/2" plate the fillet weld WILL BE 1/4" on each side or 5/16" on one side'. People say that you use a 1/4" weld on 1/4" material. Prove it. Chapter and verse. Which code supports that? Fillet weld or groove weld? We don't know how to calculate the particular stresses on a particular joint for a particular application. Way above my pay grade.
Sure, it is based on the thickness of the materials in use but there is nothing in the codes we can look at and say 'that weld is too small'. And there especially is nothing in the code that says we can say 'that weld is too large, you'll have to grind it down'.
And, in your last paragraph, there is no way to use the items mentioned to declare "It is, in essence, another practical limit on the fillet weld size." It may be a method used by engineering to determine minimum size. BUT, show me where that is ever used for limiting the size of a fillet weld. I have never seen an engineer call out maximum size. And the code sure does not make such a case for determining maximum size that would let the inspector or fabricator look at the project and say 'that weld must be at least this big and not over this big'. It does not exist.
There is a big difference between common sense application for some piece of equipment that needs repaired and a code specified weld size for public safety with sound basis originating from the applicable code.
Even you don't actually state a maximum weld size, only the results. I have seen fillet welds designed for both sides of a part with each one being larger than the thickness of the material. Seems like overkill, but I'm not the engineer. Stresses are strange.
Back to the OP, the statement is correct that "The minimum is defined by the stress calculation and material thickness." But 'defined' and able to be 'determined' by us are two different things.
Not being able to find the upper end limit is because it isn't there. I get a kick out of inspectors who pull some magical application out of the codes just to be a pain because the fabricator ticked them off and tell the fabricator they must grind down the welds because they are too large. Go right ahead. It will come back around some day to grab you by the tail and cast you into the pit. Somebody will challenge that and you will be the one with egg on your face when the engineer is called into it and says, 'where do you get that?' Especially since, our job is to observe and report. We can't make them do anything.
I still stand by the 'fact' that the codes do not give us any indication of how large a fillet weld can be. Not in design nor in final application. Called for a 1/4". Ends up as a 3/4". Nothing that I can do about it.
Scott, my main point is that we must be careful how we express certain applications when a poster asks a question that was simply a matter of 'how large can the weld be?' The code doesn't give us a definitive. But your points are true and should be considered by respectable fabricators and their welders.
He Is In Control, Have a Great Day, Brent
That’s right. We don’t have a clue. Only the EOR knows. The referenced tables are minimums. There is no maximum. Design criteria may require more or they may require less. As you know, the EOR has the authority to add to, delete, or otherwise modify the requirements of the structural code. There have been many times that I’ve RFI’d EOR’s about what’s shown on design drawings vs structural code criteria. There have been times that they’ve mistakenly stipulated something outside D1.1 criteria. When I questioned it, they thanked me. Other times, they took the time to explain why it was necessary. I’ve always appreciated them taking time to explain it because I learn something new.
My last paragraph is simply a common sense statement in an attempt to explain that when the fillet weld is increased to the point that it exceeds the strength of the connected parts, it does not increase the strength of the connected parts. I’m not suggesting that this is the size limit, because there is no size limit. It’s simply common sense, but again, the size is determined by the EOR. Any time I see a deviation on design or detail drawings from the structural code, I question it.
And in that, yes, first is minimum strength required for the applicable load. Then, the maximum that will ever be reached because of the materials being used calculated by both size and physical properties. Beyond that maximum is total waste as to time and materials/consumables. But, the codes don't give us any way of determining either maximum state. Which is what I want to be careful to make sure people working to codes understand. We don't have a way of finding that size and especially saying, STOP, that weld is TOO large, you MUST grind it down (or even remove it and start over).
I think you and I are on the same page. We are just looking at different aspects of the question.
I also know my mind is still in slow as I just got up. Nights!
He Is In Control, Have a Great Day, Brent
I think so as well.
The only time I've ever had a problem with a fillet weld being too large wasn't when it was shown on a drawing. It was when the fillet weld exceeded the prequalified maximum size for a single pass, but that's another story.
Any time I see a deviation on design or detail drawings from the structural code, I question it.
I question everything
except for what Brent says
and anything Al or Henry says, I question twice
we still have that 6010 debate on moisture
hope this helps
sincerely,
Kent
Then start a new thread Ken.
Henry,
done
Kent
