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Re: Offset Moment Connection

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> From: CanitzCF(--nospam--at)

> A structural steel fabricator/erector has requested advice from me for the
> following issue. The SOR for a contract the erector is working on is
> requiring him to provide a full moment capacity moment connection for a
> W21x57 beam to W12x72 column connection. All steel is 50 ksi. The beam
> frames into the column's flange. The issue is the beam is offset 7 3/4"
> from the column centerline. Is a moment connection possible with this
> amount of offset?

The column flange width is only 12" so the beam CL is completely off the
flange. I'm guessing that the SOR has requested the full moment
connection in lieu of providing actual design reactions. The connection
is achievable.

A) The target is acceptability to the SOR, rather than what is perceived
from the documentation. The SOR needs to provide enough information for
the fabricator to achieve the SOR's requirements. You may not have
enough, yet.
B) Apparent required moment capacity at the end of the beam is not
necessarily the same apparent required moment capacity at the column.
The fabricator's responsibility stops at the outside edge of the weld
fusion face or bolt hole (more or less).

What I would do:
1) confirm with the SOR that there is an intended eccentricity
(watching out for a friend approach),

2) suggest that the SOR accept responsibility to design/detail this
unique connection
(duck the responsibility approach),

3) failing that, request the actual balanced transfer forces from his
design due to the extraordinary nature of the connection
(put the ball back in the opponents court approach),

4) advise the fabricator to make sure that their insurance is paid and
issue a letter to their client
(CYA approach).

>From a design perspective, the conection would only need to be designed
for the maximum forces that could be developed, regardless of the
section sizes. However, steel is cheap, use lots. If it's a one-off,
don't be stingy with the welds or bolts.

Paul Ransom, P. Eng.
Burlington, Ontario, Canada
<mailto:ad026(--nospam--at)> <>

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