What is this weld doing?

[JStructsteel]

The top weld, is it a bevel weld with a slot weld over it?

 

[Deadblow]

It looks to me like this is a moment connection between the beam and the column. The weld at the top flange of the beam is a complete joint penetration bevel weld with a backing plate.

EIT

 

[JStructsteel]

Yes, a moment connection. So I get the bevel weld. What is the slot weld called out for?

 

[SJBombero]

No slot weld. That is the symbol for a backing bar.

 

[JStructsteel]

Ah, ok. How is that differentiated from a slot weld, or is it supposed to be known with a bevel weld, it would be a backing bar?

The detail shows the backing bar, so why do I need it on the weld?

 

[JLNJ]

The symbol under the horizontal line is the weld on the joint side the arrow points to. In this case, you have a single-bevel groove weld in a butt joint.

AWS says that to be prequalified as a complete joint penetration weld you need the backer bar (the backer symbol is above the line, so it is on the away side of the joint). Without the backer bar, the root might be too wide to make a good one-sided CJP weld.

 

[JStructsteel]

Ok, thanks. Its just confusing to have the same symbol for different things.

 

[271828]

Like others typed, that is a CJP field weld with backing.

There needs to be a weld access hole at the top weld to make room for the backing. See the AISC Spec and Commentary to J2 for the required geometry.

 

[JStephen]

The backing symbol always has a weld symbol on the other side of the arrow.
The plug weld symbol never has a weld symbol on the other side of the arrow.
The plug weld symbol is a little larger as well.

 

[JLNJ]

On a separate note, be careful about welding to the face of an HSS to create a moment connection. HSS columns tend to be rather thin walled.