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Re: Field Problem

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Jason,

For a case like this, I would suggest first looking into relatively easy
things.  First I check my load assumptions to see if I have a little fat in
there which I can cut.  You've assumed (conservatively) that you have bolts with
threads included (A325-N).  Is that the actual condition of the field bolts that
they have or are they really A325-X?  Even if they are -N, make them get -X (if
possible) and your problem with the bolts goes away.
Next choice for me in these situations is to use LRFD to check the connection.
This often works if the ratio of live to dead loads is not too high.

Eric Ober
Cagley & Associates
Rockville, MD

Jason Kilgore wrote:

> 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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