Showing how green I am.......... again. Welds this time. 1

[Lion06]

Hi all,

This question is on welds. I know the 13th addition manual allows a 50% increase for welds if they are loaded perpendicular to the weld axis. The question I have is where is the line drawn for the capacity of the weld. Does the base metal check constitute the weld capacity such that the you can increase it even if the base metal is controlling the strength of the connection (or would control with the 50% increase in the weld strength)?

Let me say I also just learned that the capacity of the base metal is based on the interface of the fillet weld leg and the base material. I didn't realize that. I thought it was the thickness of the material, not the interface.
With that in mind, for a 36ksi plate and a fillet weld with 70ksi rods, the capacities are virtually identical (assuming the welds are longitudinally loaded and there is no increase allowed). If you take that weld and rotate it such that the load is perpendicular to it, you can clearly take a 50% increase in the weld strength, but can you do the same for the base metal check (the shear plane at the interface of the weld and base material)?

I tend to think not because that would put the base metal at 0.9Fy, which just doesn't make sense to me.

Can anyone please comment?

 

[JAE]

For fillet welds:

The increase in weld strength due to the angle of force relative to the weld line (Equation J2-5 in AISC 13th) is for the welds only...not the base material.

The base material strength is governed by Section J4 (as indicated in table J2.5) which does not include provisions for angle of force.

Also, I would disagree with your statement: [red]"the capacity of the base metal is based on the interface of the fillet weld leg and the base material.:[/red].

If you read the commentary for section J2.4 in AISC's 13th edition specification, page 16.1-339 in the manual, you will see the applicable sections required to check for strength of weld and base metal. These do not include the interface between the leg of the fillet and the base metal.

In fact, the commentary states: [blue]

"The strength of the welded joint is the lowest of the strengths calculated in each plane of shear transfer. Note that planes 1-1 and 3-3 are positioned away from the fusion areas between the weld and base metal. Tests have demonstrated that the stress on this fusion area is not critical in determining the shear strength of fillet welds."[/blue]

 

[nutte]

An important distinction is this increase is just for fillet welds, not groove welds. It makes it a little trickier to find the equivalent PJP weld size with a known fillet weld size, if this increase for the angle was used. And keep in mind, the eccentrically loaded weld tables in the manual do use this angle increase.

I concur that the base metal checks are for the thickness of the connected part, not the interface at the weld.

 

[Lion06]

Is there any check to be done at the interface of the weld?

 

[Lion06]

JAE-

Star for the post! Thanks!

That commentary actually confirms what I learned in school and what made intuitive sense to me. I had a rather lengthy discussion in a little seminar where what was being explained to me didn't make sense and I was the lone dissenter of the group. Everyone else in the room seemed to think it did make sense, but what can I say.

Thanks again.