AISC J3.10 Member Bearing - Bolt Hole Dia. & LC Dist.

[Howlyn2]

Hello All. When computing member block shear I've often seen the Net Shear Area & Net Tensile Area take into account the diameter of the bolt + 1/8" to find the area of the bolt hole that shall be taken away from the area calculations. The 1/8" in addition to the bolt dia. is a derivation of 1/16" additional area for the use of standard bolt holes (when bolts are less than 1" dia. via Table J3.3 Nominal Hole Dimensions) plus an additional 1/16" per B4.3b when calculating net area for tension and shear for a total of 1/8" + bolt dia.

Member Block Shear is classified as an Affected Elements of Members and Connecting Elements check in J4 of the AISC Manual (15th Edition). This section clearly states to use Effect Net Area per D3 which references back to B4.3b. Member Bearing & Tearout back in J3.10 indirectly uses the bolt hole diameter when checking tearout of a connection with multiple holes. The bolt hole diameter comes into play when calculating Lc - clear distance in the direction of the force, between the edge of the hole and the edge of the adjacent hole or edge of material. When calculating Lc for tearout in a direct line of holes what additional increase in bolt dia. should we be using (if any) 1/16" or 1/8"? Thank you.

 

[271828]

For tear-out, use the nominal hole dimension. Don't add the extra 1/16 in.

The AISC Manual Companion Volume 1, 15th ed., Example II.A-1A shows this.

The following starts a download of this document.

https://www.aisc.org/globalassets/aisc/manual/v15.1-companion/v15.1_vol-1_design-examples.pdf

 

[Howlyn2]

Thank you 271828. I have no reasoning to question the AISC Design Examples. I can move forward accordingly. Out of curiosity though do you know why AISC chooses to use the bolt dia. + 1/16" instead of the 1/8" for member block shear? Tear out is a bolt to bolt block shear rupture so it just seems counterintuitive that different value would be used.

 

[271828]

I think you meant "Why does AISC use the nominal hole dimension instead of adding 1/16 in. for tearout?"

I couldn't find a clear statement on this. (I'd love to have one! One certainly exists.) The following is the best I have at the moment. LOL.

According to Muir (2017), tearout first showed up in the 1999 AISC Specification. He says the shear model does not reflect the actual behavior for tearout. The 1999 Commentary talks a little about tearout, but mostly kicks the reader to the 1994 RCSC Specification, which talks more about tearout but still doesn't give a solid statement for the question at hand. They mention the ultimate shear stress is 0.62Fu, not 0.60Fu. Kim and Yura's 1999 Journal of Constructional Steel Research paper is on the subject. That paper is based on Kim's 1996 thesis. Near the bottom of Page 57, Kim says "The equations based on the clear distance approach underestimate the strength at 1/4 in. displacements."

Reading between the lines, I think the tearout equation is conservative and approximate enough so that the extra 1/16 in. isn't needed. Don't quote me on that, however.

References:

Muir (2017):

https://www.aisc.org/globalassets/modern-steel/archives/2017/05/ataleoftearouts.pdf

1999 AISC Specification and 1994 RCSC Specification free downloads for AISC members:

https://www.aisc.org/publications/historic-standards/specification-for-structural-steel-buildings/

Kim and Yura (1999):

https://www.sciencedirect.com/science/article/abs/pii/S0143974X9800220X

Kim (1996):

https://fsel.engr.utexas.edu/pdfs/96-11.pdf