How to check a weld for applied moment?

[awa5114]

I have a single angle connected to a double angle via a 3/16" weld

I know there is a factored, applied moment at that connection. I would like to ask how I can go about checking the capacity of this connection for moment? There is a lot of stuff in AISC for welds in Chapter J, partially and fully restrained moment connections but I am not sure where to start. What chapter/section of AISC codifies this kind of problem?

 

[JAE]

It's not codified - it is simply using proper analysis and statics. My college steel textbook had examples of weld configurations with out-of-plane (or in plane) forces and moments.

Also look at AISC's steel manual - (page 8-9 in the 14th Edition) where they talk about eccentrically loaded weld groups.



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[KootK]

It basically comes down to this:

1) Figure out the shear on the weld assuming that it's uniform (k/in).
2) Figure out the tension and compression stresses that generate the resisting moment at the connection (k/in).
3) Take the vector sum of #1 and #2 (shear + tension) and design the welds for that.
4) If it were me, multiply the answer by 1.25 to compensate for the difficulty inherent in determining the bending stresses accurately.

It's really #2 that will cause you problems in a situation like this. The supporting angle isn't likely to provide a very rigid support so figuring out the tension stresses will be a bit of a crap shoot.

Is your detail a drag strut tying into a steel joist? If so, that isn't a connection where your average engineer would worry about them moments in the weld.

I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.

 

[MrHershey]

Second JAE. Look at that section and especially the associated tables in the Steel Construction Manual. You can do it by hand but if your situation matches any of the tables (and looks like it probably does), you can save a lot of time and headache by using them instead.

 

[chicopee]

If the drawing is true, there is an excessive amount of coping at that welded end of the 3X3X1/4 angle iron. Not only should you refer to the AISC steel manual as indicated by JAE, also check the fabricating practices in that same manual on how to cope. With less metal removed, you 'll have more welding area. With regard to figuring out the stresses from moment, you should give us some sketch showing external loads and external moments imposed on that system.

 

[CANPRO]

Taking a step back from determining the moment capacity of the weld - I think you need to address your original statement "I know there is a factored, applied moment at that connection". I don't think there should be an applied moment at that connection - and if there is, I think you need to re-visit your analysis. Scaling your sketch (I know, only given dimensions to be used) there is less than 1" of connected material there. Without looking through codes and references to determine the moment capacity of that weld, I would call it effectively zero. Think of it this way - how confident would be if the 3x3 angle was a cantilever and only supported by the connection shown in your sketch?

For determining the moment capacity of a weld group, in the past I have taken the section modulus of the line of weld (in^2, mm^2) and used that to determine a linear load on the weld (k/in, kN/mm).

 

[Stenbrook]

When I check the moment capacity of a weld group I usually use the section modulus as mentioned by CANPRO. The total stress would then be P/A + V/A + M/S. Then divide that stress by your weld capacity to determine the thickness of the weld required. If you go to the page below, you can see the equations for the section modulus of common weld groups.

https://valuablemechanisms.files.wordpress.com/2010/04/weld-line-geometries.jpg