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Re: UMB Wall Anchors & Fires

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I think you've raised a good point here Bob.

The old fire cut joist ends may indeed be defeated with certain fixed
plate connections. I would see this possibly being more detrimental at
beam/wall connections, but certainly closely spaced wall anchors could
produce a problem also.  Typically spacing ties at 5+ ft. may even be
sufficient to crank moment into the wall if the whole platform looses
interior support.

Perhaps the plate end of the fastener could be purposefully spaced out
from the wall to allow some movement.

I have a habit of using a continuous ledger like angle under the joists
to act as supplemental vertical support but can see when I fasten the
tie plates to this it may be creating a continuous moment in the wall
under these circumstances.

It's a damned if you do and damned if you don't proposition when it
comes to thinking through these things.

Any others??

Barry H. Welliver

"Robert J Bossi, PE" wrote:

> Last night there was a 6 alarm fire in a vacant one story
> brick warehouse in San Jose, CA (1st & Julian Sts.)  The
> wood roof collapsed and one exterior wall fell outward
> injuring two fire fighters.  Luckily they were able to dive
> behind a fire truck and the injuries were minor.  The truck
> did no fair as well.
>
> The failure was unusual from the news photos I saw in that
> the wall failed some what below mid height and the middle
> section of the wall ended up in the street.  The building
> appeared to have been retrofitted as the were closely spaced
> wall anchor plates showing on the portion of the wall left
> standing.  Some of the plates ended up pushed outward but
> still hanging from the anchor rods.
>
> My concern is that the type of retrofit wall anchor that are
> currently being used are capable of inducing some level of
> fixity in the wall to framing connection.  When interior
> support is lost, as in a fire, this can crank a moment in to
> the wall, causing tensile force in the outer wythe of
> brick.  Compare this detail with old government or "dog"
> anchors: a single pin in the joist loosely held in place
> with clinched nails.
>
> In our desire to achieve seismic safety have we missed
> something?   Should we be assuring that wall anchors create
> a "pinned" condition so as not to induce this type of
> failure?  Any comments would be welcomed.
>
> Bob Bossi
>