huangyhg

fiberglass bolts in sacrificial connections (firewalls)
when anchoring structural elements to load bearing firewalls we have run across a requirement for the joists on one side of the wall to stay intact and allow the joists on the other side of the wall to collapse. i am thinking of a joist angle seat that only attaches to the joist through a fiberglass bolt that degrades when exposed to heat and no longer provides a positive attachment to the wall allowing it to fall away.
has anyone ever run across this requirement? any ideas or references?
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i've been told that adhesive anchors (e.g., hilti hit) are acceptable for this application, because the epoxy melts in a fire.
daveatkins
could the structure reach the collapse stage in an area away from the firewall before the bolts even melt?
typical solutions include: cantilevered firewall, double firewall, tied firewall and weak link firewall.
don't forget that you also have to leave sufficient distance between the structure and the firewall to accomodate expansion of the steel framing (varies between 2 1/2" and 7 1/2" per nfpa and fm). otherwise, the expansion may damage the firewall.
the best references are nfpa, fm, ncma and the canadian code.
does it matter which side falls away? what if the fire is on the side that has a weld or a steel bolt, or did i misunderstand the detail?
my intent is to provide a cantilevered firewall that remains after the adjacent building collapses. i am struggling with a method of allowing the roof system to detach from the firewall.
the design requires that a fire can occur on either side of the wall
if using a cantilevered firewall, don't attach the structure to it. provide a column line near the firewall. the roof structure should be totally independent, not connected to the firewall. this will allow you to provide the required gap so that expansion of the steel will not damage the firewall.
the architectural and other non-structural details should also be done with care so that they do not create large forces trying to pull the firewall over if the structure collapses.
i hope this helps!
get a copy of nfpa 221, standard for fire walls and fire barrier walls. there is some good info in there for the type of walls you want to design. you will get some sticker shock for the price and the thin book you receive, but it was worth the info it contained in my opinion.

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