LRFD Steel Design (Block Shear in Welded Connections) Question?

[CriticalMass2001]

I have a question regarding block shear in welded connections designed for eccentric loading.

What is the "gross/net shear area" term given in AISC LRFD pg. 16.1-67 (2004 edition)? Is it the longest (largest) length of weld running parallel to loading, or is it the sum of the lengths of the weld running parallel to the loading?

[For example, if a L-angle is welded to a gusset plate (eccentric design) is it the length of the long side of the weld, or the sum of the long and short side (top and bottom)?]

Its hard to explain without being able to post a picture, if you don't understand the question let me know and I'll try and rephrase.

Thanks

 

[Ron]

The shear area is the effective throat of the weld times its length.

 

[CriticalMass2001]

Gusset
-------------------|
B A Tension Member
|------------|---------------------------------
|---------------------------------------------
|
| -------->
|
|
|
|
|---------------------------------------------
C D |E
|
-------------------|

 

[CriticalMass2001]

Thanks for the reply Ron...I forgot to include the throat in my above post, but the question should have been "the shear area is the throat times what length?"

Alright, I figured I needed a picture and couldn't figure out how to post one if its possible, so excuse the crudeness of the above, but:

Given that the weld is from A to B to C to D by design, is the shear area the sum of the length of AB and CD times the throat, or just AB times the throat?

And also, why would the shear length not be ABCDE? In any failure the length DE, or from D vertically down to the edge of the gusset would have to fail, would it not? Is it not included in your gross/net shear area, and if not, why not?

Thanks.

 

[HgTX]

If your failure is through the throat of the weld (AB and CD in shear, BC in tension), then DE doesn't come into play; the throat there is zero (if I read the diagram right). If you unzip your entire weld start to finish, you've separated the two members; no need for any failure in the members themselves for the connection to fail.

The only way you'd have a problem in the gusset in DE would be if you failed in the plate rather than the weld. Not sure how you'd do that unless you had very large (or maybe just very overstrength) welds on very thin gusset. In that case your failure would be around the outside of the weld, in the gusset.

What I'm not sure of is whether both of the above cases would be considered block shear. Both meet the criterion of having both shear and tension paths. Someone else can come along and dope-slap me on this.

Hg

 

[CriticalMass2001]

Thanks HfTX, I understand the situation now. For whatever reason I was only considering the failure of the member and that is what caused the confusion. I suppose I didn't consider a failure of the weld itself because I'm used to analyzing block shear of bolted connections, where the members are failing.

 

[HgTX]

Same here. I poked around and found references that say that block shear is theoretically possible in welded connections and should be considered, but not a whole lot on what form that would take.

Hg