Shear Rupture of Uncoped Beam 1

[ChrisNYCEng]

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.

 

[MacGruber22]

jayrod12: Are you talking about a non-top flange coped beam end? Or, categorically you don't understand the whole block shear failure mode?

The moment at the end of the beam is zero

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).

 

[MacGruber22]

Ugh...my grammar. *the plane between the holes*

 

[jayrod12]

I mean in this specific example where the beams are uncoped

 

[MacGruber22]

Well, there will be tension there, no doubt. The question is of what magnitude? It seems like not enough to make a difference before another limit state controls, hence no block shear for non-coped beams.

 

[ChrisNYCEng]

The questions is specifically about shear rupture. Not a block shear failure. If we can, let's stay on topic. In calculating the gross shear capacity of the beam we strictly use the area of the web. So I'd like to pin-point where AISC may say that we specifically do not need to check rupture of the beam web across the shear plane through the bolt holes if the beam is uncoped. To this point, I do not see where it states we do not check it.

 

[nutte]

Like I mentioned above, AISC provides several documents with example connection problems. This is not a limit state they check (in anything that has come out in the last 20 years). That ought to be good enough.

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.

 

[KootK]

@Chris: I thought that shear rupture was block shear rupture? As Nutte has pointed out, we've pretty solidly established that AISC doesn't think it should be checked.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

 

[WinelandV]

@KootK,

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).

 

[MacGruber22]

You are speaking about row tear-out, I believe.

 

[KootK]

Point taken Winelandv. However, the two provisions are mathematically identical. It's just a matter of the what geometry one assume's for the failure plain. Certainly, in the context of a basic shear connection, I think that it makes sense to be considering shear rupture and block shear rupture under one umbrella.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

 

[MacGruber22]

It makes no difference. If the tension rupture is not a possibility, how are the rows going to rupture? If there is no block shear tension+shear rupture, there is no row tear-out (shear rupture), right?

 

[ChrisNYCEng]

AISC Steel Solutions has answered that this is not a limit state they consider for coped beams because:

"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...

 

[MacGruber22]

If the flange prevents block (shear+tension) rupture, it prevents row tear-out (shear rupture). You would have to have some unconventional mixture of over-sized and standard holes, with some in bearing and others in slip-critical condition to allow a local row shear rupture, right?

 

[KootK]

What do you know, we do rely on the flange strength. I shall now scour the internet for test data...

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

 

[MacGruber22]

Ha! Good luck, KootK. By the sounds of the Steel Solutions' answer, it might have been a subjective decision without empirical validation.

 

[MacGruber22]

KootK: Did you find anything?

 

[KootK]

Nope. Thirty minutes of intense Googling yielded nothing. Oh well, knowing what's to be done, even if I don't fully understand why, is a step in the right direction.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.