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RE: allen bolts

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?Allen? bolts, as I understand them, are simply any type of bolt ? but
instead of a hex cap head or an opening for a screwdriver bit, then have a
hexagon shaped hole.  Then a 6-sided rod (Allen wrench) is inserted in the
hole and turned.

If this is the case, then you design the connection like normal, and you
would spec whatever strength you need.  The wood connection can be straight
out of NDS.
Ultimate Tensile Strengths of bolt grades and equivalent "construction"
Grade 2 = ASTM A307 =  60,000 psi
Grade 5 = ASTM A325 = 120,000 psi
Grade 8 = ASTM A449 = 150,000 psi
This just compares ultimate tensile strengths - not thread pitch, toughness,
head size, etc.  A Grade 5 bolt is NOT identical to an ASTM A325.

As for the bolt-to steel connection... 
You'll have a greatly reduced area for direct bearing, unless you count the
sloped head portion.  You'll have to add tension to the bolt from the sloped
portion of the head.

On the plus side, if the structure becomes an architectural "feature", then
they usually want it to look "strong" (I did a bank once where the 3.5" HSS
columns buried in the walls were carrying more load than the 12" HSS columns
under the drive-canopy).  Therefore you can probably get away with
specifying lots of bolts.


Jason Kilgore
Leigh & O'Kane, LLC
Kansas City, Missouri
From: Dan Morrow [] 
Sent: Wednesday, March 31, 2004 6:20 PM
Subject: allen bolts

I?m working on a residential steel stair with channel stringers and bolted
connections at floor levels and landings.  The architect wants to use allen
bolts ? the type with a beveled head (like a bugle screw) that flushes with
the surface when tightened.  Does anyone know of a source for design
information on this type of bolt?  Seems to me that it?s not your typical
bolt bearing condition.
Dan Morrow, P.E.

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