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Field Problem

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I had a contractor call this morning with a problem.  A beam (W18x86) for a
project I worked on was fabricated ~2.25" too short (or perhaps the concrete
pilaster it is supposed to frame into was built in the wrong place).  It is
currently held in place with some rigged up system so they can proceed with
joist placement.

The original connection was like this: A plate w/ headed studs was embedded
in the pilaster.  A pair of angles (LL4x3x3/8) were field welded to the
plate (toe and 1" return only to allow for rotation).  The angles had
standard holes, and the beam had SSL holes to allow for standard concrete
tolerances.  The end of the beam was supposed to be 1" from the face of the
plate.

The edge of the beam is now 3.25" away from the plate, and the bolts will
not fit up.

The forces on the embedded plate are ok.  I can specify slightly thicker
angles and beef up the weld to the plate, so that will work.  The problem is
that the load on the bolts is slightly too high.  Or is it?  From Table XI
(page 4-62 of the green book), with n = 5, b = 3, and l = 4.75", I get a C
of 3.08.  With 3/4" A325 bolts in double shear (threads included) I get rv =
18.6, for a connection capacity of 57.3 kips.  The calculated load is 60
kips, or 4.7% over stressed.

My potential justification for allowing this is: Table XI (AISC green book
pg. 4-62) is for standard holes.  Since the actual holes are SSL, the beam
can rotate freely, and the resultant force on the bolts is still vertical.

Another option is to ream the existing holes in the beams to allow 7/8" A325
bolts.

Any comments?

-----
Jason Kilgore
Leigh & O'Kane, L.L.C.
(816) 444-3144
jkilgore(--nospam--at)leok.com



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