AISC table J3.2 foot notes 2

[BAGW]

Hi,

In AISC table J3.2, there is a foot note regarding fastener pattern length. I am having hard time understanding fastener pattern length definition. Is there a figure or something which they refer to, which shows the 38'' dimension.

Thanks

 

[JAE]

This is the distance between your bolts in a connection where that distance is parallel to the force.

What they are worried about here is that with very long bolted connections, with many bolts, you could get an irregular distribution of shear on individual bolts and the 0.833 factor accounts for this.

Read the commentary on Section J3.6 where they discuss this a bit. In my 14th Edition Manual it is on page 16.1-403.

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[JAE]

So to further clarify - say you had a very deep beam (48" plate girder) and you had a clip angle at the end of it with 14 bolts spaced at 3 inches on center.

This would require a clip angle of about 42 inches in length. The distance between your top and bottom bolts is (14-1) x 3" = 39" which is greater than the 38". Thus, the 0.833 factor would be required.

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[nutte]

JAE, your example is incorrect. The 38" length applies to 'end-loaded" connections. In the example you describe, the load along the bolted connection is applied incrementally, along the depth of the beam web, and it leaves the angle and goes to the support incrementally, at each bolt row.

An example of an end-loaded connection would be a flange plate axial connection on this girder. The flange force is in the plate all at once, but has to distribute to the beam along the length of the connection. If the bolt pattern exceeds 38" in length, you need the 0.833 factor.

I've heard this described in seminars, but I don't recall seeing a sketch that shows it.

 

[nutte]

This Steel Quiz discusses the 38" limit and what an end-loaded connection is.

https://www.aisc.org/globalassets/modern-steel/archives/2014/03/2014v03_quiz.pdf

 

[JAE]

Nutte you may be right. I’ll check it out further.

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[BAGW]

38'' in length is the confusing part. Is this length of the bolts on one side of the splice plate? So the total length of the connection has to be like 76'' for this reduction to apply?

 

[wannabeSE]

I agree with Nutte. Figure C-J3.1 in the 14th edition clearly show an end loaded connection and the fastener pattern length.

 

[JAE]

Nutte - looked at your link and it makes sense. The "end loaded" term means exactly that - a load applied to the end of a steel connection part that is connected by a parallel length of bolts....not a shear condition like what I mentioned as that load is imparted along the side length of the part, not its end.



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[nutte]

BAGW, correct, the 38" length applies to one side of your splice plate example.