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Re: "The weakest link"

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Kevin:

I believe that for wood floor/roof joists to a masonry firewall, it is
common to use what is referred to as a "fire cut" (at least that is the
term that I have heard).  A "fire cut" (as I understand it) is basically a
diagonal cut from the top of the joist at about 4 to 6 inches from the
end to about the mid height of the joist at end of the joist.  In other
words, you "clip the corner" of the joist.  In theory this allows the
joist to rotate out of the beam seat in the masonry wall and fall to the
ground/floor with out pulling on the wall.

As pointed out by James Kester in response to Paul Feather's similar post,
the other way is to do a double firewall with appropriate distance between
the two walls to allow for things like seismic movement, etc.

Regards,

Scott
Adrian, MI

On Wed, 26 Apr 2006, Kevin Below wrote:

> In wood structures separated by a masonry firewall, the attachments of
> the wood to the masonry wall should be designed so as not to cause
> collapse of the wall if the wood structure on one side burns and
> collapses.
> In the Canadian Commentary M to the NBC 1995, they show a system using a
> "liaison faible" which I guess is translated from "weak link".  The idea
> is to provide lateral support to the masonry wall at each floor level,
> and to resist certain lateral loads such as seismic and wind, as well as
> loads which may occur during the fire, such as the force of the water
> jet.  But in the case of fire, to be weak enough to break under the
> force of the falling structure.
>
> There is not much detail as to how to implement this.
>
> Does anyone have any examples ?
>
> Kevin
>
>
>

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