AISC Reduction in Load Capacity for Long Bolted Joints

[dik]

Does the AISC reduce the capacity of a tension member with bolted connections based on the length of the bolted part. For example if the tension member bolted part is 20" long compared to one that is 10" long. This might reflect the 'flow' of the load from the loaded end to the 'dead' end.

Thanks, Dik

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[271828]

The short answer is the "length" is the length of bolt group, not a member length.

I suspect you knew that, though, so I'd have to see a picture to provide a better answer.

 

[dik]

Correct... my error. Something like the flange splice plates on the attached, where the length of the bolted part is about 14".

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[lexpatrie]

I think it's more like 30" length, but yes, in the line of force for long lengths, there's a reduction. Some of the tables have that note, maybe for the W36 beam connections?

What they think happens is the lowest bolts don't see much load and the top bolt can get plastified in shear before the others see much load. If I recall Ray Tide had a good seminar on the subject when the bolt provisions were tweaked maybe 8-10 years ago. It's not the same thing as the so-called poison bolt.

OKAY, looks like it was 38 inches and it's perhaps been eliminated as of 2017 or so. I don't see the note in the W44 beam connections in the 14th edition manual.

Refer to:
Raymond H.R. Tide (2017). "Shear Capacity of High-Strength Bolts in Long Connections," Engineering Journal, American Institute of Steel Construction, Vol. 54, pp. 61-68.

Let us know what you find out.

You can also search for that 38 in the specification for structural joints (which AISC kind of modifies, by the way) -
Specification for Structural Joints Using High-Strength Bolts, June 11, 2020

 

[canwesteng]

Not for that connection, but table D3.1 for shear lag applies when only some of the element is connected.

 

[271828]

This is described in Design Guide 17 Section 5.1. In this case, the length would be 4x the bolt spacing or a little shorter than Nb/2. According to the AISC Specification (16th ed.) Table J3.2 footnote c, a reduction applies if this length exceeds 38 in.

I don't think it has anything to do with the member or plate lengths.

 

[dik]

Thanks... 14" each end. Is there a means of calculating the reduction?

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[271828]

It only gives one factor: 0.833.

Footnote c: "For end-loaded connections with a fastener pattern length greater than 38 in., Fnv shall be reduced to 83.3% of the tabulated values. Fastener pattern length is the maximum distance parallel to the line of force between the centerline of the bolts connecting two parts with one faying surface."

 

[dik]

Thanks... for greater than 38"... I would have thought it would have been greater for a shorter length...

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[271828]

Thanks... for greater than 38"... I would have thought it would have been greater for a shorter length...

What would've been greater for a shorter length? The reduction?

The Fnv values have a 0.9 reduction built into the derivation for shorter connections. Theoretically, that would apply to only end-loaded connections, but it is applied to all bolted connections. For single plate shear connection ductility checks (not a "Spec." check), you can see the 0.90 getting divided out. There's a little discussion in Part 10 about this.

When the connection gets over 38 in., slap another 0.833 reduction on there.

 

[dik]

Thanks, gentlemen (binary term for those that need one).

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[lexpatrie]

Alright I got the scanner working.

Here's a nice photo of bolt deformation, Design in Structural Steel, Lothers, 1953.

 

[dik]

Thanks...

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[lexpatrie]

If I didn't already mention, there was a Ray Tide Seminar I watched not too long ago that covered a lot of the same "long connection" material and showed test results.

This might be it. The year doesn't feel right, but if there's a slide at the beginning with Tide laundry detergent on it, then it's probably the one, unless Ray does that in all his seminars. It was after some revision to the bolt provisions. I remember "as simple as possible, but no simpler," too.

Developments in the Design of Bolted Connections: Bolt Shear Strength and Slip Resistance, Ray Tide, 2009 North American Steel Construction Conference

I'd look at it, but this one is I guess so old you need to log in to watch it, and I blew my two attempts at remembering my password.

 

[dik]

Will take a gander... I know my AISC password . I entered a survey by Atlas Tube and won a hard copy of the AISC Steel Construction Manual, 16 Edition. It arrived on Friday... it's a lovely text, and much appreciated. The AISC has many design examples that the Canadian CISC doesn't have.

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[lexpatrie]

Man. Foot stop. You ain't even gonna use it like. Congrats though.

 

[dik]

I already have...

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[lexpatrie]

Sorry guys I can't edit my previous post, the reference is wrong. This is from Structural Steel Design, Lambert Tall, chief editor, Lynn Beedle, and Ted Galambos, Fritz Engineering Laboratory, Ronald Press Company, New York, 1964. Page 50. I scanned it downstairs then decided what book it came from upstairs, because I kind of wasn't expecting to correctly guess the scanner buttons correctly in the dark.

In my glee to upload the images, I got the references wrong on two posts in the forum.

Again, sorry.

 

[dik]

Thanks...

-----*****-----
So strange to see the singularity approaching while the entire planet is rapidly turning into a hellscape. -John Coates

-Dik

 

[PersonalProfile]

The following also states background information regarding joint length, if I have understood the enquiry:

Figures 5.51 and 5.52 show that a 40 ksi allowable shear stress for A490 bolts would provide the needed margin for joint lengths up to about 50 in. For joints with a length exceeding 50 in., the allowable shear stress in the bolts must be reduced to ensure a minimum factor of safety of 2.0. A 20% reduction in the allowable shear stress provides this margin for joint lengths between 50 and 90 in., as illustrated in Figs. 5.49 to 5.52.

Ex:
Guide to Design Criteria for Bolted and Riveted Joints

https://www.boltcouncil.org/files/2ndEditionGuide.pdf

Regards.