Quick Fillet Weld Calculation 2

[struggle67]

Hi,

If my fillet weld cross-sectional area at throat x (connecting member strength/weld shear strength) is equal to the connection member cross-sectional area, then logically can I say that my fillet weld is as good as full penetration butt weld and connection calculation is not required?

Thanks

 

[KootK]

In AISC (US) there is a provision wherein a pair of fillet welds may be considered to "develop" a plate if those filled welds are each [5/8 x plate thickness].

 

[desertfox]

Hi struggle67

I don’t think you can say that because fillet welds fail usually in shear, you don’t say how the joint is loaded and whether it’s under fatigue conditions or not, any chance you can provide further details of your situation?

“Do not worry about your problems with mathematics, I assure you mine are far greater.” Albert Einstein

 

[slickdeals]

Please don't ever consider putting so much weld that it needs multiple passes in the field.

 

[struggle67]

Thanks KootK,
You always know what is in my mind. Answer straight to the point.

Thanks desertfox,

fillet welds fail usually in shear, you don’t say how the joint is loaded and whether it’s under fatigue conditions or not, any chance you can provide further details of your situation?

To account for the different strength I will have this factor (connecting member strength/weld shear strength). It is a general question but for example, lets say it is an I beam moment connection to a steel column so I will have fillet welds at flanges equal to the respective flanges X-area. And at web, a pair fillet weld X-area will be equivalent to the member web X-area.

Thanks slickdeals,
I won't. It is for last minute resort.

 

[Agent666]

As "good as" in what way, strength, ductility, fatigue. All quite different scenarios when comparing relative performance between FW's and CPBW's.

In AISC (US) there is a provision wherein a pair of fillet welds may be considered to "develop" a plate if those filled welds are each [5/8 x plate thickness].

Interestingly, here in NZ it comes out at 1.0 x plate thickness for each FW being required to develop the lower 5% characteristic strength of the plate. EDIT - based on leg lengths, not sure after re-reading if thats what you were referring to or throat thickness!


I also wouldn't be using one sided FW's if thats what you were implying. Always use same size weld each side, otherwise you're asking for issues as the weld root of a FW is a nice crack initiator when the loaidng isn't symmetric....

 

[struggle67]

Agent666,

In term of strength.

 

[kingnero]

@ slickdeals, I'm not a big fan of the advice you're showing there, if it comes without any more explanation.
While there is some truth behind it, single pass fillet welds are also most prone to failure.
Mind - I'm not advocating overdoing it, but that adivce should be used with caution - not as a rule of thumb.

 

[slickdeals]

@Kingnero
I wasn't making any mention of strengths. All I was pointing out is that multiple pass fillet welds tend to get very expensive. The OP may have a very specific situation leading to this question. But as you can see from the chart, the cost increase vs strength gain is not proportional.

 

[gtaw]

AWS and AISC limit the unit stress of the fillet weld to 0.3 X Tensile Strength of the filler metal for carbon and high strength low alloy steels. You need to consider the strength of the weld and compare it to the strength of the base metal in both shear and tension. Ideally, they should all match.

For a simple T-joint where the butting member is being loaded; if the base metal is an ASTM A36 and the filler metal is 70ksi, double fillet welds will match the strength of the base metal in both shear and tension when the fillet size is 3/4 x the thickness of the base metal.

That's about the simplest approach to sizing fillet welds. There are other considerations that can be found in AWS D1.1 Structural Welding Code / Steel assuming that is the base metal you are working with.

I do agree that the cost of the fillet weld increases quickly as the weld size increases, but there is an offset when one considers the cost of preparing a groove for welding and the added cost of labor due to limited access for depositing weld and cleaning between weld passes, etc. Partial joint penetration groove welds are on par with fillet welds with regards to the allowable stress. CJP groove welds lose some advantage when one considers they must be welded with backing or the second side must be back gouged before welding from the second side. The cost of the extra labor for including a back gouge can be considerable.

Best regards - Al

 

[Tmoose]

With the meager info provided I do not feel I have a clear picture of either the OP's question or situation.

The loading, and the especially the geometry of the components being welded is VERY important.
Plates intersecting plates or I-beam flanges at 90° can have MISERABLE load paths, unless stiffeners or continuity plates are provided. The is result a tiny bit of the weld is providing pretty much ALL the stiffness and resistance, and will fail soon and leave the rest of the weld to unzip.

https://weldtalk.hobartwelders.com/forum/equipment-talk/general-welding-questions/50248-i-get-a-call