Shear Rupture of Uncoped Beam
Shear Rupture of Uncoped Beam
(OP)
I am trying to find an answer while reviewing calculations of shear connections. In my connections with bolts at webs of supported beams, the flanges in some cases are not coped. Do we need to check shear rupture for the net section of the web even though there are flanges present? I have always said yes, but am being told otherwise by the connection designer. Some other input, or a documented reference would help, I do not see anywhere that AISC specifically says where/where no to perform this check, so I interpret that as check anywhere you shear section is reduced.
Thanks.
Thanks.






RE: Shear Rupture of Uncoped Beam
Obviously check block shear though.
Maine EIT, Civil/Structural.
RE: Shear Rupture of Uncoped Beam
1) There would be considerable deformation before you fully mobilized the flange in shear and;
2) The deformation mentioned in #1 might even be enough to initiate and unzipping kind of failure.
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.
RE: Shear Rupture of Uncoped Beam
BA
RE: Shear Rupture of Uncoped Beam
RE: Shear Rupture of Uncoped Beam
RE: Shear Rupture of Uncoped Beam
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.
RE: Shear Rupture of Uncoped Beam
As for documentation, the AISC design examples that accompany the 14th edition Steel Construction Manual don’t check it. Neither do the 13th edition examples. Neither do the examples in the silver Volume II companion to the 2nd edition LRFD manual. The one exception is the Volume II companion to the 9th edition ASD and 1st edition LRFD manuals (the green and blue book). There is one example there where they check shear rupture on the web of an uncoped beam. But I’ve spoken with people involved with the creation of these manuals, and I believe this check is there because it was easy to calculate and include, not because it should have been checked. Regardless, we have several years’ worth of documents that have come out since the green and blue book that indicate it is not a valid limit state.
If you insist on checking it, you would have to include the flange area in your area calculation. If you were going to tear out the web, you’d have to take the flanges with you.
RE: Shear Rupture of Uncoped Beam
If you did try and check it what would you use for the Anv? Do you assume the whole flange, none of the flange, or just the k portion of the flange? In reading the commentary they suggest other examples of where block shear strength limit states apply, other than the coped beam end case (CJ4.3 paragraph 2) but none of those examples ever cross an out of plane element.
For further support Table 10-1 does not consider block shear of uncoped beams. The beam web available strength only considers bolt bearing for uncoped beams. If AISC intended this to be checked I would think they would have gone through the calculation like they did for coped beams. It is not explicit but the weight of evidence is toward not checking in my mind.
RE: Shear Rupture of Uncoped Beam
You guys have convinced me. I change my answer and no longer believe that shear rupture needs to be checked in this situation. Thanks for the education. Still, I would very much like to understand why shear rupture doesn't need to be checked. The arguments presented above to the contrary are pretty attractive.
I'm not at all convinced that the flange participates in providing shear resistance. Before the flange tips would be fully mobilized in shear, I feel that one of two things -- maybe both -- would occur:
1) You'd have to develop a ton of shear deformation in the web, perhaps enough to cause rupture and;
2) You'd have to yield the flanges locally in bending.
Check out the attached sketch for an illustration. At the very least, I would think that this would be a lousy serviceability condition. Maybe serviceability isn't pertinent here.
I did think of one significant benefit that would be provided by having the flange present above the tear out block. Without the flange, the tear out block requires bending stress on one or both of the failure planes in order for equilibrium to be satisfied. With the flange, the tear out block doesn't require these bending stresses. Rather, equilibrium can be satisfied purely through shear stresses. This is analogous to a building with bracing on three sides. Again, check out the attached sketch.
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.
RE: Shear Rupture of Uncoped Beam
Another item to consider: Have you ever heard of a beam failing in this way? If not, that might be a reason not to worry about this proposed limit state.
RE: Shear Rupture of Uncoped Beam
If a logical hierarchy of failure modes precludes shear rupture for an un-coped beam, that should able to be demonstrated by calculation somehow.
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.
RE: Shear Rupture of Uncoped Beam
RE: Shear Rupture of Uncoped Beam
So try it. Figure your net shear area, including the flanges, and see what you get.
RE: Shear Rupture of Uncoped Beam
RE: Shear Rupture of Uncoped Beam
BA
RE: Shear Rupture of Uncoped Beam
RE: Shear Rupture of Uncoped Beam
@Nutte: You'll have to hold on to your gauntlet. Since I don't buy the flange participation bit yet, my numbers would be the same as for the coped case and the exercise would bear no fruit. That, and I'm way too lazy for a homework assignment
@Jayrod: if I understand correctly, the tension is an internal stress rather than an external loading.
@MacGrubber: your point ties in with what I was trying to get at with regard to the moment -- or lack off -- on the rupture block. The Ubs factor in J4.3 penalizes the capacity due to non-uniform stress on the tension rupture plane, at least for multiple row connections. I speculate that the presence of the flange minimizes that non-uniformity and might contribute to a higher capacity. I'll read the paper over the weekend. Thanks for digging it up.
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.
RE: Shear Rupture of Uncoped Beam
RE: Shear Rupture of Uncoped Beam
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.
RE: Shear Rupture of Uncoped Beam
No, it is not exactly zero. It is "zero" when considering transfer of moment to adjacent members. In coped connections, there is a moment that needs to be considered that is the reaction times the distance from the cope length. That moment can induce non-uniform stresses on the web in the locale of the bolts. But, regardless of a moment forming, there the group of bolts pull upward, creating a tension force in the plan(s) between the holes. The assertion is that when the top flange of the beam is intact, those tension forces cannot develop to a failure limit state before some other limit state occurs (bolt bearing, faying surface slip for SC bolts, bolt shear, etc).
RE: Shear Rupture of Uncoped Beam
RE: Shear Rupture of Uncoped Beam
RE: Shear Rupture of Uncoped Beam
RE: Shear Rupture of Uncoped Beam
RE: Shear Rupture of Uncoped Beam
For yielding of the beam web, we all agree the flanges don't contribute to the capacity. For rupture, you have to actually tear through the section. The flanges would have to go as well.
RE: Shear Rupture of Uncoped Beam
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.
RE: Shear Rupture of Uncoped Beam
No, shear rupture is not the same as block shear (though block shear does have a shear rupture component). If you have a copy of the AISC 13th or 14th edition, you can check out the difference in J4.2 (Strength of elements in shear - yielding and rupture) and J4.3 (block shear strength).
RE: Shear Rupture of Uncoped Beam
RE: Shear Rupture of Uncoped Beam
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.
RE: Shear Rupture of Uncoped Beam
RE: Shear Rupture of Uncoped Beam
"It is felt that the flange will provide enough strength to preclude these failure modes..... This issue has been discussed by the Manual Committee. and at this point we have not chosen to include these checks for uncoped beams. If we ever do choose to include the checks, they will take into account the strength of the flange in some manner."
A bit elusive in response but, in writing, they state the checks are not required...
RE: Shear Rupture of Uncoped Beam
RE: Shear Rupture of Uncoped Beam
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.
RE: Shear Rupture of Uncoped Beam
RE: Shear Rupture of Uncoped Beam
RE: Shear Rupture of Uncoped Beam
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.