(EIT) Welding an HSS beam 2

[onlym112]

Hello everyone,

I have a small HSS beam that only carries shear loads at its support. One end of the HSS beam is connected to the web of a w-section column. Generally, an HSS is welded all around, however I do not want to attract any moment to my column due to welding the HSS all around. As this connection is only a shear connection and my vertical welds on each vertical wall is more than sufficient to resist the shear load. Is there any possible reasons why I may not be allowed to just weld the vertical walls? This area is protected from outside, thus I don't see the need to weld all around to satisfy a seal weld. I also know that a single sided weld is not favorable as any small rotation to the member could easily tear the weld at the root, however I don't think that is possible welding to each vertical HSS wall as it will give me the rigidity. Have you guys ever welded just the vertical wall of an HSS before? If not, is there a reason why it is a common practice to always weld all around? P.S. I am an EIT.

Thank you for you help.

 

[dik]

It's not uncommon just to weld the vertical faces. As a further comment. If the end rotation of the beam is less than the rotation of the column due to the eccentric load, then fully welding the HSS to the column may be beneficial.

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

-Dik

 

[canwesteng]

I don't think there is appreciable rotation of the column, OP is welding to the web not the flange

 

[KootK]

If not, is there a reason why it is a common practice to always weld all around?

I agree, it is uncommon in my experience as well.

I also know that a single sided weld is not favorable as any small rotation to the member could easily tear the weld at the root, however I don't think that is possible welding to each vertical HSS wall as it will give me the rigidity.

That would be precisely my concern as well. That said, I don't know that it's a valid reason to avoid web only welding altogether. I suspect that all around welding is often the default because:

a) It's generally thought to not increase costs significantly, at least for fillet welds,

b) It does minimize the risks associated with the root tearing as well as general, non-uniformity of weld stress.

c) Omitting the flange welds really does not prevent moment transfer at the connection in most cases.

I do not want to attract any moment to my column due to welding the HSS all around.

If there's an error in your reasoning here, I feel that this is it. In most cases, I feel that omitting the flange welds would not appreciably reduce moment transfer at the joint. It would just make moment transfer at the joint weaker and, perhaps, invite a weld failure that would then compromise your shear transfer at the joint.

 

[CANPRO]

I feel that omitting the flange welds would not appreciably reduce moment transfer at the joint. It would just make moment transfer at the joint weaker and, perhaps, invite a weld failure that would then compromise your shear transfer at the joint.

I agree with this statement. Don't confuse strength with stiffness. If you wanted (needed) to transfer moment at this joint, the weld on the horizontal faces of the HSS would be critical, because that is where your primary bending stresses are carried. However, by welding just the vertical faces you're still restricting end rotation of the beam, which creates the potential for moment transfer at the joint.

In general, you either need to detail your connections to suit your design assumptions, or adjust your design to suit restrictions/practical limitations on how your members are connected.

Not welding the horizontals could cause durability or aesthetic issues - water intrusion, accelerated corrosion, rust bleeding out from the un-welded edges, etc...

 

[onlym112]

Wow thank you everyone for you prompt and valuable response!

 

[canwesteng]

The connection should have enough ductility to meet the design assumptions - it doesn't need to be detailed to transmit load exactly as designed, and virtually no connections do that anyway.

 

[TLHS]

Is this a retrofit? This feels like a situation that would come up with an addition, since you'd generally bolt something like this if it were shop fabricated.

There's likely a couple of ways to do this if you want it to rotate a bit more, but I agree that just welding the verticals doesn't really do that. The things that head more towards pins will involve bolts, though.

The conventional way would be to have a knife plate or similar in the HSS, then bolt that to a shear tab on the web (stiffened as appropriate).

You could also potentially do something like an angle on either side of the HSS with a couple of through bolts (or weld the angles to the HSS), and bolt those angles into the web of the column. You'd need a pretty big column depth to make that fit, though.

Seated connections are a possibility, but you have to balance stability and unexpected rotational restraint. It's easy to accidentally make a moment or torsional connection.

That being said, restraining moment at the connection may not really be a problem. It depends. If your HSS is quite small, then the column might laugh off a bit of local moment that will resolve itself where it hits the lateral system. If the column is small, then the column might not have enough weak axis stiffness to stop rotation and the moment might be small.

What's the reason you're using HSS in this application? I ask because HSS is commonly the choice where you have weak axis or torsional loading in addition to the stronger axis bending direction, and either of those situations significantly affects how you might want to connect the beam.