Minimum edge distance for bolt holes 6

[Logan82]

Hi!

The minimum edge distance for bolt holes depend on the bolt diameter, but not the plate thickness.
- Why are these values independent of the plate thickness in this table?
- Were the minimum edge distances calculated for a certain plate thickness?
- How were the minimum edge distances obtained?

Source: CSA S16-09

 

[GC_Hopi]

These are workmanship standards based on the manufacturing process. You still need to check the edge distance to see if it meets your strength considerations. Those design calcs use the plate thickness, edge distance, etc

 

[skeletron]

I agree that they are derived from fabrication tolerances/processes.
You need to check end tear-out based on your plate thickness.

 

[rb1957]

our bearing allowables drop if e/D < 2, 1.5 is minimum.

another day in paradise, or is paradise one day closer ?

 

[BridgeSmith]

Most likely, those limits are set so that bearing capacity of the steel at the side of the hole is critical over tear-out. That's how it is for the edge distance limits in the AASHTO bridge design spec.

Rod Smith, P.E., The artist formerly known as HotRod10

 

[dik]

Thanks, Bridge...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

 

[ProgrammingPE]

At the minimum edge distances and minimum spacings, tearout always controls over bearing.

Tearout Capacity = 1.2*lc*t*Fu​

Bearing Capacity = 2.4*d*t*Fu​

So, Tearout Capacity ≤ Bearing Capacity when lc ≤ 2*d​

To simplify things, we can treat the hole diameter as the same as the bolt diameter which means we will be overestimating the tearout capacity a little bit.

For an edge distance of 1.75*d, lc = 1.75*d - d/2 = 1.25*d which is ≤ 2*d so Tearout Controls​

For a spacing of 2-2/3*d, lc = 2.67*d - d = 1.67*d which is ≤ 2*d so Tearout Controls​

This means that exceeding the code minimums will increase your bolt capacity as long as bolt shear is not controlling.

Structural Engineering Software:

http://www.structuralcentral.com

Structural Engineering Videos:

http://www.youtube.com/channel/UCOj2mXXf3ZbZtgxTc6BtkGg

 

[BridgeSmith]

The AASHTO spec has the same equations posted by ProgrammingPE, but does not identify what failure mechanisms they are supposed to prevent; only that the 2.4*d*t*Fu is used where the clear distance between holes or to the end of the plate is not less than 2.0d, and 1.2*Lc*t*Fu is used if it's less.

Does the AISC indicate that the 1.2*lc*t*Fu is the tearout capacity? The Commentary in the AASHTO LRFD spec (8th Edition) would seem to indicate otherwise (unless I'm misreading it, which is entirely possible):

"Using finger-tight bolts, it has been shown that a connected plate will not fail by tearing through the free edge of the material if the distance L, measured parallel to the line of applied force from a single bolt to the free edge of the member toward which the force is directed, is not less than the diameter of the bolt multiplied by the ratio of the bearing stress to the tensile strength of the connected part (Kulak et al., 1987).

The criterion for nominal bearing strength is:
L / d >= rn / Fu

Where:
rn = nominal bearing pressure (ksi)
Fu = specified minimum tensile strength of the connected part (ksi)"

Rod Smith, P.E., The artist formerly known as HotRod10

 

[dauwerda]

BridgeSmith, AISC does indicate that that equation is used for a tearout check, however it states that it is used when "deformation at the bolt hole at service load is a design consideration". When deformation is not a design consideration it presents the same equation only with a constant of 1.5, not 1.2.

 

[BridgeSmith]

Thank you, dauwerda. I was just curious if I had been misunderstanding the AASHTO commentary. I'm still not sure, but what you posted from the AISC, I think, supports my of the AASHTO commentary, right?

I guess it doesn't really matter what the mode of failure is for design; we just use the equations to calculate the capacity, and move on. It would just be nice to have a clearer understanding of it.

Rod Smith, P.E., The artist formerly known as HotRod10

 

[BridgeSmith]

Upon further reading, specifically this article, it seems ProgrammingPE is probably correct, after all.

Rod Smith, P.E., The artist formerly known as HotRod10