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Firewall:(was)CMU Wall Supported by Plyw

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Scott Maxwell wrote:

. > Now about firewalls...

[snip]

. > The first thing is to realize that there is a difference between a
. > firewall and a fire separation wall.  A fire separation wall is a wall
. > between two spaces that is meant to stop or slow the spread of fire.  A
. > fire wall is essentially a fire separation wall that MUST remain standings
. > AFTER one side of the building has collapsed (or is one of the two
. > buildings has collapsed).

. > If you must have a firewall, then that wall between the two buildings must
. > be designed in a fashion that it would remain standing if either building
. > collapses.  Thus, if the new building falls, then the fire wall MUST
. > remain standing or if the existing building falls, then the fire wall MUST
. > remain standing.

. > This can typically be done one of several ways.  You can:

. > 1) [snip]

. > 2) Do a single wall that is tied to each structure that has "break away"
. > connections so that one side can fall without causing the other to
. > collapse or bringing down the wall.  With a masonry wall with wood joists,
. > this has traditionally been done with a "fire cut".

. > 3) [snip]

It seems to me that a "fire wall" would be virtually impossible in seismic 
country as the code requires that the diaphragm be tied to masonry/concrete 
walls.  "Fire cuts" would be ineffective as the joists are tied to the wall 
with "tension ties" or other anchors.  A "fire cut" would only be effective 
for wood joists resting on or in walls without any other type of connection 
between the joist and the wall.  For a fire cut to be effective with tension 
ties, the tension tie would have to be a fusable link and even then it is 
questionable whether that would work, e.g., a fire destroys the wood joist at 
mid-span, but does not reach releasing temperature at the fusable link at the 
wall.

A. Roger Turk, P.E.(Structural)
Tucson, Arizona