Minimum Spacing of Bolt Holes in Cluster

[LOTE]

I have referenced AASHTO and AISC for the minimum edge distance and bolt hole spacing, but these seem to only pertain to all the bolt holes receiving a loaded bolt.

What are the spacing requirements if you are placing a single bolt in the closest fitting bolt hole in a cluster of say 8 holes? I am thinking of having two parallel rows of holes that are offset from each other like this image and trying to figure out the minimum spacing. This would be in a hot rolled angle loaded parallel to the two rows of holes.

 

[driftLimiter]

(8) Holes for just 1 bolt? Perhaps want to consider bearing deformation at the bolt hole. There is a clearance to nearest opening. If I've understood this correctly I'm not a big fan of a bunch of empty holes nearby 1 loaded bolt.

 

[LOTE]

Correct. This is for a mass produced part that needs to accommodate various configurations in the field. It's not an ideal hole configuration, but I haven't thought of a better one that allows for vertical tolerance without much horizontal torquing on the bolt/rod.

I'll check bolt bearing using the clear spacing as the edge distance. Anything else I am missing here?

 

[driftLimiter]

I would also worry about stress concentrations due to all the discontinuities. Not to mention eccentricity due to just have 1 bolt. For a lightly loaded bolt maybe not so much of concerns. For a heavy load or fatigue, I would be worried about those details more.

So to confirm your load is a shear load that goes 'up-down' on your drawing.

Have you considered just providing slotted holes? that is a way more common approach.

 

[LOTE]

I should clarify, there is one bolt per cluster, and each cluster is spaced roughly every 24" along the angle.

It will be a one-time load for a concrete pour, and will stay in place after curing with no permanent load.

Correct, it is shear load up-down in the drawing.

I don't believe we be able get the required tension in the bolt to allow for a slip critical connection for a slotted hole, but I'll have to verify that with the manufacturer and contractor. The bolt is tightened into a round dowel bar splicer, not a standard nut.

 

[ProgrammingPE]

"The edge distances in Table J3.4 of AISC 360-16 are minimum edge distances based on standard fabrication practices and workmanship tolerances."

"If necessary, lesser edge distances are permitted provided the applicable provisions from Sections J3.10 and J4 are satisfied, but edge distances less than one bolt diameter are not permitted without approval from the engineer of record."

The minimum edge distances given by AISC are dimensions that shops typically use and are recommended, but you are permitted to use lesser values as long as the bolt tearout capacity (Section J3.10) and the rupture capacities (Section J4) are still acceptable.

Having bolt holes with no bolts in them (unloaded bolt holes) would not allow you to space the bolt holes any closer since having empty bolt holes does nothing to increase the bolt tearout capacity of the bolt you are using. (If anything, larger spacing and edge distances may be required because that one bolt must carry all of the load.)

The minimum spacing are given in AISC Section J3.3 (2-2/3*db and a clear distance of db), and it doesn't say that you can use values less than what they prescribe (unlike what is done for the minimum edge distance sections). It does seem like an argument could be made that as long as the tearout and rupture limitations are satisfied that a lesser spacing would still technically work, but this should be avoided if possible.

If you're going to do the offset parallel rows configuration, be sure to remember to check a zigzag line that passes through all of the bolt holes for your net area since that may control. (See Section B4.3b.)

Structural Engineering Software:

http://www.structuralcentral.com/tools/steel-connection

Structural Engineering Videos:

http://www.youtube.com/structuralcentral

 

[JLNJ]

I think I’d start with the 2 2/3 bolt diameter in an equilateral triangle pattern and check for your largest load. I’d be hesitant to put them any closer than that.

 

[BridgeSmith]

If I was doing this per AASHTO LRFD, I would check the bearing resistance at bolt holes per 6.13.2.9 (Factored by the resistance factors in 6.13.2.2). I would ignore the block shear provisions since only one bolt is to be used.

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