Effective area for fillet weld for tubular structures

[RmzK]

Hi,

Effective area of the fillet weld, according to AWS standard, is effective length x throat size and so for tubes, effective length should be pi x diameter. Can anyone confirm if I have to take only half of this area for shear stress calculation according to API RP 2A standard.

Thanks

 

[Ron]

The throat of a fillet weld is its cross section through the center of the weld.
In your case, the shear area would be the leg height of the fillet (take the lower if different) x 0.707 (to account for the geometry of the throat) x the circumference of the outside diameter of the pipe. (slightly conservative since the length of weld is actually the circumference of the weld centerline around the pipe)

 

[RmzK]

Ron,

Appreciate it! I know how to calculate weld area. I dont know if you are aware, according to API, shear area for tubular cross section is half of the cross section area, so my question is if we have to consider this for weld and consider only half of the calculated area like below:

Shear area of weld = pi x pipe OD x .707 x leg size / 2

 

[Ron]

Are you using WSD or LRFD version of the standard? Check the fatigue requirements...could be a safety factor for fatigue under LRFD...but not sure. It would be best if you got a copy of the standard to which you have to design or meet. Yes, API standards are expensive, but it is the cost of doing business correctly....and if you are designing something significant, the cost of the standard would be considerably less than the cost of a design mistake because you didn't have the right information.

 

[JStephen]

Rmzk,
Your best bet is to refer to the document itself, as Ron noted.

If the document itself is not clear, you may be able to get an official interpretation through API. That is available for some API standards, but I don't know if it applies to every API document. It may take a couple of months. And the "Recommended Practice" documents may work differently than the regular standards.

In general, when asking questions here, if your question is something fairly mainstream, you will find quite a few knowledgeable people willing and able to help you. If it is something more obscure, you may or may not find anybody familiar with the topic. But being rude to people that attempt to help certainly won't encourage anyone else to contribute.

There is also a subforum here for "API Code Issues", but you may or may not find anyone there familiar with the document in question.

 

[nutte]

If you were welding a wide flange, you would use just the welds at the web to resist the shear. You wouldn't include the flange welds in the area resisting the shear, because you know the shear is primarily in the web.

If you were welding a square HSS, you could make a similar case that the welds at the two "webs" should be the ones used in resisting the shear in the member.

For the round HSS, they're implying that only half of the section is useful for resisting shear. The AISC specification does the same thing. It would be reasonable to use only half of the fillet weld to resist shear.

 

[corus]

The average stress across a hollow cylinder is V/A but the maximum shear stress is 2V/A, or in other words V/(A/2). That's why you take half the area. You can check this by googling 'shear stress distribution across a cylinder' and refer to Table 13.1 in the google book shown - 'Practical Stress Analyis in Engineering'