Fillet Weld Leg size bigger than thickness of plate to be connected

[KKaabbaa]

Hi guys,

First of all I want to thank this forum and people contributing to it in advance.

I do have a question about fillet welds that is bothering me quite a lot lately. If 2 plates are to be welded with each other in a T section form, assuming that both plates are 10mm thick, with 2 fillet welds, how would be the maximum leg-throat thickness of the fillet welds be determined. I am aware of the common rule that the throat thickness of the fillet weld should be roughly 0,707*minimum plate thickness. I am just in a position where the throat thickness of the fillet weld needs to be bigger than plate thickness due to fatigue reason. The American code states what the maximum throat should be, but in the newest version of the Eurocode it has been removed. It surely doesn't mmean that could use 100mm thick throat thickness. Right? Obviously this is related to heating temperature, heated zone and etc etc, but from a designer point of view, how could we determine the absolute maximum fillet weld size?

Thanks in advance

 

[canwesteng]

Not sure there should be any maximum fillet thickness here. Obviously at some point the weld is stronger than the plate and adding more weld doesn't do anything though. Make the welds as thick as they need to be to limit stress amplitude for fatigue and make sure you've checked the plate as well.

 

[WARose]

The max size I always use is thickness minus 1/16" inch. If (for example) you had a 1/4" thick plate, the max weld size you would call out is 3/16".

 

[KKaabbaa]

My concern refers to the heating of the plate to be welded. Obviously the weld, if it is very thick, it will not be done in one run. It makes sense that if the weld become too big it is stronger than the plates to be welded. But assuming we don't care about that, does it mean that we are not restricted at all, in terms of maximum size of fillet weld?

 

[MotorCity]

If your plates are arranged in a T, the maximum weld size does not apply. You could theoretically build out the weld without limitation. The maximum size weld applies when you are welding on the edge of plates. The weld size of 1/16" smaller than the plate thickness is because you want to be able to see the top edge of the plate to make sure it was not melted away during welding. That said, if your weld needs to be larger than your plate thickness, then your plate is probably not thick enough to begin with as it will never develop the strength of the weld.

 

[JAE]

Agree with MotorCity.

At some point there is no reason to increase the weld beyond what you need for strength.

The T- 1/16" rule is only for welds on the edge of plates, not on the sides.



Check out Eng-Tips Forum's Policies here:
faq731-376

 

[WARose]

[blue](JAE)[/blue]

The T- 1/16" rule is only for welds on the edge of plates, not on the sides.

Good point. Although......I've never been 100% certain what constitutes being close to a "edge"......so I've always observed the T- 1/16" rule.

 

[JStephen]

I thought the 1/16" rule was just so you could see where the weld ended. IE, so you didn't put a small weld and then grind off the lip on the plate where you couldn't tell the actual weld size.

 

[WARose]

I thought the 1/16" rule was just so you could see where the weld ended. IE, so you didn't put a small weld and then grind off the lip on the plate where you couldn't tell the actual weld size.

I always thought it was to avoid "burn through" on the base material.

 

[JAE]

If you look in the commentary for AISC Specification section J2.2b - Limitations, they provide some good insight.



Check out Eng-Tips Forum's Policies here:
faq731-376

 

[wannabeSE]

For lap joint, see the commentary in AISC's Steel Construction Manual. 14th edition page 16.1-390, section comm. J2.2b and figure CJ2.1

 

[JAE]

beat you to it!!!

Check out Eng-Tips Forum's Policies here:
faq731-376

 

[canwesteng]

Don't think you'd be able to burn through structural plate... bigger welds are also made in multiple passes, I think the largest single pass fillet is aroung 5/16", so if you can place one weld without burning through why not multiple?

 

[KKaabbaa]

That was very helpful, thanks a lot guys!

 

[Ron]

From a code standpoint, only welds up to a certain size are likely "prequalified". The other issue is distortion from overheating or inconsistent heating/cooling.

If you exceed the prequalified joint conditions, you will usually need to do a qualification procedure to comply with code provisions.