Minimum weld 4

[precast78]

I understand the reason of maximum weld. You do not want to burn through the thinner member being weld. But what is the reason for the minimum weld? Can someone give me a reason why I cant use 1/8 weld on each side of a 5/8 plate connected to another 5/8 plate. I need smaller weld to gain some flat spot next to the plate (product development for structural application). Design wise the weld will be way over designed.

Cheers!

 

[racookpe1978]

No. Or "Yes." 8<) We can't give you a reson why you can't use the smaller weld.

Minimum weld weld is that necessary to do the function intended. Almost always, that function is carrying a load, so as long as your 2x 1/8 fillets are strong enough to carry the load you expect (plus a margin for unknowns!) that is all that is required.

Be careful: a one-sided fillet weld will shrink as it cools and pull the two plates towards one another. Two fillet welds will even out that pulling force.

 

[StructuralEddie]

Easy. AISC specification 2005 commentary: table J2.4 provides min. size of fillet ... Not based on strength considerations, but on the quench effect of thick metal on small welds. Very rapid cooling of weld metal may result in a loss of ductility.

 

[SteelPE]

The answer to your question can be found on page 16.1-331 of the AISC 13th edition manual and has to do with the cooling indicated above.

 

[precast78]

Thank's StructuralEddie, I forgot there was the gray commentary section. Have not used this manual for a long time. That makes sense.

 

[dhengr]

Precast78:
I would want to know more about the details and the loading conditions, but AISC and AWS admonitions to the contrary, you can probably still do what you want to do. As others have mentioned, the codes and commentaries give the reasoning for the min. limitation in daily production: potential weld cracking due to quick cooling, loss of ductility, lack of penetration; all due to the quick quenching affect of the heavier plates w.r.t. the very small weld. You just don’t/can’t input enough heat energy with that small weld to allow a good weld to be made consistently. That small weld is almost like a tack weld, and they tend to crack and cause hard spots too, again, for lack of heat input and the quenching affect. The solution is to apply a little preheat to the 5/8" plates so the quick quenching can’t happen. Also, you’ll find that a welder really has to work hard to hold a weld to a 1/8" fillet, with many processes. You will more than likely get a larger weld, welders hate to be called on too small a weld profile. Make a few sample welds on your detail and have them tested, you will probably be o.k. on a lightly loaded detail.

 

[TehMightyEngineer]

What dhengr said, unless you give them a good reason to be held to 1/8 they would probably be happier just putting down 3/16 and grinding it down to 1/8 rather than doing preheat and fighting with getting a proper weld that small.

Maine EIT, Civil/Structural.