Shear Rupture vs Block Shear 2

[HeavyCivil]

Regarding Equations j4-3 and j4-5 in AISC Manual (13th edition, spec), it is clear that Anv in each is a different area, or else one would not need to check j4-5.


My understanding is that Anv for Shear Rupture is based on the Whitmore section, and that Anv for Block Shear is based on the addition of the area of steel subject to Tension PLUS the net area of steel subject to shear.

However, I see the Whitmore section referenced in multiple locations (albeit online) as a factor of block shear. It seems to me Block Shear is unrelated to the Whitmore section.

Please see attached. Is this consistent with your understanding? The application is a double-angle truss web which sandwiches gusset plates.

 

[ToadJones]

I do not think you are properly showing "lv" or "lt" on your sketch.
"lv" should continue to the end of your angle, parallel to the direction of the force.
"lt" should only be the length from the center of the bolt hole out to the nearest edge, perpendicular to the line of force.

I also think you are talking about equation J4-4, NOT J4-3.

Block Shear and Shear rupture different failure mechanisms.
Block shear should be checked on the angle.
Your gusset will not have a block shear failure mode IMO.

 

[HeavyCivil]

Toad -

True - Lt shown wrong, see shaded region for intent.
You're also correct in that j4-4 is the equation.

Since this is a compression member, I don't see why the distance of the angle past the last bolt is relevant, or why it would be included in Lv. On that note though, I think I WOULD include the rest of the angle in LV, and therefore it would be a very high number and probably not control anything...

I understand that these are different failure modes, that's why they have different equations, that's why I drew an example for each. The question is really in regard to using the Whitmore section for Shear Rupture. It would appear that calculating Anv as shown in my example produces Gusset Plate design strengths that are very low and control for every truss connection. It would also seem that since the Length value used in the Anv calculation is that from the Whitmore section, and is perpendicular to the load, the sum of all bolt hole areas would not need to be be subtracted, but rather the area of one bolt hole..

 

[ToadJones]

I believe you will use your Whitmore length in a compression buckling analysis of the plate.
I do not think shear rupture will apply to a compression member as is the case here apparently.
Also, I do not think that Block shear will apply to the angle member if it is in compression only.
If the angle was a tension member, then you will have to check tensile yielding of the gusset using the whitmore section.
I believe this should all be laid out in the Uniform Force Method in the steel manual.

 

[ToadJones]

see steel interchange article as well...

http://www.modernsteel.com/steelinterchange_details.php?id=393

 

[ToadJones]

Read up on the references I give you here....I think you are barking up the wrong tree as far as what limit states you are checking.
In other words, I think you are misapplying equations.

 

[HeavyCivil]

Okay - thanks. I agree with you that block shear should only apply to tension members.

I am not sure I agree that shear rupture would not apply to the gusset plate simply because the member is in compression. I don't think the gusset plate "cares" about the vector.

I am checking all code prescribed limit states, but I think we have identified that at least one (block shear) is indeed inapplicable here. The numbers I'm getting do imply that I am misapplying the Shear Rupture equation: I'm getting big over-stress ratios in a system that has stood up for over a century. I am not, however, convinced that Shear rupture of the plate can be neglected. The shear yield of the plate is simply calculated using the gross area (in this case ~=Lv as shown in previously attached drawing *t-plate.) Could Anv simply be that same area with the total area of holes subtracted?

 

[ToadJones]

Its like checking shear in a column in the direction that axial load is applied.
I must be misunderstanding you

 

[nutte]

The check you're thinking of is bolt bearing. Check that on the gusset.

For a tension case, it would be analagous to a block shear check with the tension area set to zero.

 

[ToadJones]

Yes, indeed, check bolt bearing...

 

[ToadJones]

http://www.bgstructuralengineering.com/BGSCM/BGSCM003/BGSCM00306.htm

 

[ToadJones]

nice analogy nutte, I like that way of explaining it.