Minimum Bolt Spacing Code Compliance (AISC)
Minimum Bolt Spacing Code Compliance (AISC)
(OP)
This may seem like a silly question but it's something that I have been thinking about for years and I'd prefer to ask those more experienced with this subject.
As we all know, AISC explicitly states that a minimum bolt spacing requirement of 2-2/3(d) is required -> 3d preferred.
As far as I know, they have omitted any reference to load orientation as it relates to the minimum spacing. In addition, they have chosen to use the general word spacing as opposed to gage or pitch.
We know that this minimum spacing is intended for constructability and to add some inherent bearing/tearout strength although the latter is not guaranteed to be adequate.
My question, although it may seem silly, am I not in compliance with AISC360 if I choose to space (perpendicular to the load path) my bolts at a smaller distance than required? Especially knowing that workable angle gages do not always comply with this requirement.
If I am in compliance, can someone reference me to text in the AISC360 that would protect me, as an engineer, from building code violation.
As we all know, AISC explicitly states that a minimum bolt spacing requirement of 2-2/3(d) is required -> 3d preferred.
As far as I know, they have omitted any reference to load orientation as it relates to the minimum spacing. In addition, they have chosen to use the general word spacing as opposed to gage or pitch.
We know that this minimum spacing is intended for constructability and to add some inherent bearing/tearout strength although the latter is not guaranteed to be adequate.
My question, although it may seem silly, am I not in compliance with AISC360 if I choose to space (perpendicular to the load path) my bolts at a smaller distance than required? Especially knowing that workable angle gages do not always comply with this requirement.
If I am in compliance, can someone reference me to text in the AISC360 that would protect me, as an engineer, from building code violation.






RE: Minimum Bolt Spacing Code Compliance (AISC)
RE: Minimum Bolt Spacing Code Compliance (AISC)
RE: Minimum Bolt Spacing Code Compliance (AISC)
RE: Minimum Bolt Spacing Code Compliance (AISC)
Archie264, I am trying to restrict bolt spacing perpendicular to the load path.
nutte, No, I'm just using it as supporting evidence that smaller bolt spacings are ok in addition to the commentary.
RE: Minimum Bolt Spacing Code Compliance (AISC)
RE: Minimum Bolt Spacing Code Compliance (AISC)
Dik
RE: Minimum Bolt Spacing Code Compliance (AISC)
In the right circumstances (loading), I could buy off on that.
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The name is a long story -- just call me Lo.
RE: Minimum Bolt Spacing Code Compliance (AISC)
RE: Minimum Bolt Spacing Code Compliance (AISC)
Anecdotally, when we pull rivets out of bridges, they occasionally show a shear plane between the plies they were connecting -- but you don't see a significant flattening at the bearing point between the rivet and the base material hole. So I (similarly) suspect bolt shear strength doesn't require too much assistance from "confinement" around the periphery of the base material hole, and it happens mostly in local hertzian stresses.
(Yes, those ones are a bugger to get out).
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The name is a long story -- just call me Lo.
RE: Minimum Bolt Spacing Code Compliance (AISC)
The minimum bolt spacing for standard, oversized, short-slotted and long-slotted holes is the same. Let's keep this discussion without the bounds of bearing and say I have 2 columns of 3/4" bolts with short-slots perpendicular to the load path. My minimum spacing, as per AISC is 2". My short-slots are 1" long leaving me with 1" of steel between my bolts with absolutely no effect on the strength of my connection besides reducing my tensile rupture plane. Therefore, by deduction we can assume that a spacing of less than 2" with standard sized holes is in line with the AISC but yet we are still given this minimum requirement in Chapter J of the Specifications.
Archie264, how about this for another example: For an L5 angle, a workable gage of 1.75 is provided between bolt columns. As per AISC, the minimum for a 3/4" bolt would be 2". Therefore is this workable gage even compliant with AISC360 specifications? I know that structurally it would be ok, I'm just wondering if there anything in the AISC that would allow me to bypass that minimum requirement.
dik, your adjacent net shear plane is still smaller, there is enough net tension area to resist block shear and there's no direct bearing pressures. Still confused?
JoshPlum, in my case I'm not trying to eliminate the material completely from between the bolts but you're on the same page as I am as far as the question goes. If the connection and reduced member passes all strength checks, the only concern I would imagine is moving closer to a theoretical roller with snug-tightened bolts and possible stability issues if the opposite connection was the same.
Lomarandil, exactly! That's why I'm wondering if there's anything in the text to protect me from confused special inspectors or the buildings department. I have zero concern with this from a structural engineering perspective... only legal.
RE: Minimum Bolt Spacing Code Compliance (AISC)
Not yet, but, thanks...
Dik
RE: Minimum Bolt Spacing Code Compliance (AISC)
RE: Minimum Bolt Spacing Code Compliance (AISC)
Josh, yes, but surely only due to the material at the edges, right?
ahypek,
I should have prefaced all of this by saying that I'm not any form of steel expert while there are plenty here who are. As such I perhaps shouldn't have weighed in. But I am interested in learning and will at least be following this discussion. Perhaps what's throwing me is the "perpendicular to load path" portion of it. To me that implies tension, where the fracture plane is a critical component of the analysis per Sections D3 and B4.3b. It seems to me that reducing the spacing would reduce the net area, An, which is what resists the tension. Maybe not by enough to matter and I suppose that's really the question at hand. I will try to dig a bit more deeply into it on my end, as time permits, but that's perspective I'm coming from.
RE: Minimum Bolt Spacing Code Compliance (AISC)
Just anecdotally, it would be interesting to know if the minimum spacing was based on in-depth research or simply established practices. I.e., are the any interferences among the stress fields, or something like that? I almost hope for the latter, given what the in-depth research has done to concrete anchorage requirements. (Tongue-in-cheek intended.)
RE: Minimum Bolt Spacing Code Compliance (AISC)
RE: Minimum Bolt Spacing Code Compliance (AISC)
RE: Minimum Bolt Spacing Code Compliance (AISC)
Without being entirely explicit, they seem to be in agreement with my train of thought and it could be done provided constructability demands are met. They reference Chapter A1 of the Specifications as reference text to protect myself.
As far as the 1.75" gage goes for the 5" angle leg, the 15th Edition of AISC360 has already corrected this with 2".
Hope this information is as valuable to you folks as it is for me.