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Tension load normal to a fillet weld

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dcmiles

Structural
Jun 30, 2022
8
Hi y'all,

I'm not very well versed on welding and I have a question about appropriate welds for resisting tension in a direction orthogonal to the weld axis.

I am in the process of designing some brackets which will attach to a clevis and tension rod to hold up a canopy. I attached a picture for clarity -- the tension rods span from the upper lintel on the building frame to the outer end of some steel HSS members.

When I look in the Canadian steel code, there is no mention of fillet welds in tension (unless combined with partial penetration groove welds). I was hoping to create a simple design where the bottom bracket was a simple plate bent up on both ends with the 'base' welded onto the HSS. At the upper side, I would like to simply weld the brackets onto the HSS lintel. Using a plate like this would be easiest to do a fillet weld along, but as discussed I'm not sure how appropriate they are for tension (the upper bracket will be experiencing quite a lot of tension directed directly outwards from the HSS).

Does anyone with more experience have any guidance on how this could work, or a better way to approach this?

Thanks!

Screenshot_2023-01-20_161911_gctfrl.png
 
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Some more understanding of fillet welds is needed.

Your connection may be in tension because its a tension rod, but the weld itself is a fillet, meaning its a triangular profile on the edge of your connector plate.
Long store short, the weld has to be in shear to transmit your tension load from one plate back to the HSS.

There is a strength adjustment to fillet welds depending on the orientation of the loading yes.

The tension load of the road is resolved into a down load and outward load at the connection. The effects of both of these loads including eccentricity from the weld group need to be considered to properly design this weld.

Blodgett's Design of Welded Structures is a good resource to learn more about this.
Also BGStructural engineering has some great resources for learning more as well.


BGS
 
The lower brackets might work, but
The upper bracket design looks bad. Welds should be in shear, not tension. Make the base of the upper brackets larger around all edges of the lugs, and then bolt it to the beam with multiple fasteners. If you must weld it, then make the base of the bracket into a U shape that wraps around the top and bottom of the beam and weld all edges.
 
With HSS, I generally don't distinguish between the angle of loading. Packer suggests that because the welds are eccentric that that offsets the increase in strength for the angle of loading. Fillet welds are not often loaded in tension... just shear at a different angle.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik
 
How exactly are you guys are saying the weld in tension? The weld stress is shear. The weld group is taking a normal load, a downward shear, and an out of plane bending. All of those forces resolve into simply shear in the weld. Some of it is oriented in the longitudinal direction and some of it oriented in a direction transverse to the longitudinal axis.

I don't see any reason why this cant work if properly designed. As dik points out, Packer and the strength of the HSS wall with this weld profile needs to be looked at as well.

Here would be my take on checking the weld stress.


[URL unfurl="true"]https://res.cloudinary.com/engineering-com/image/upload/v1674262379/tips/weld_shear_wr3hkz.pdf[/url]

I've made some simplifications and maybe dont have the same setups as the OP but the principle is the same.

There is nothing magic about a load normal to the weld. Yes there is a weld strength increase if the load is transverse to the longitudinal axis of the weld, AISC notes that weld ductility is decreased for this condition.
 
I didn't realise the comments were only for the clips... Packer, the AISC and CIDECT all have recommendations about loading HSS transverse to the tube...The loading condition of the clips can use the added strength from loading at 90deg, but I normally don't accommodate the increase.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik
 
@dik @driftLimiter @SWCompotites Thanks so much! I'm a first-year EIT building up my arsenal and I've only just started getting into this topic.

Over the weekend I had a big read up on fillet welding and I understand it much better now -- and it was really helpful to have your input here.
 
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