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RE: Firewall Connection

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As promised, an answer from my colleague Farid Alfawakhiri.
 
Rick Burch asked about doorways through double-wall systems. I have seen these detailed as a penetration through both walls with a single door inside it.
 
Charlie
 
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According to “Firewalls: A Design Guide” by the Canadian Concrete and Masonry Codes Council (1992), there are basically 3 types of single firewalls (there are also double firewalls – i.e. two walls each attached to their respective building or separated part of the building)

1)   Cantilever firewall is a freestanding wall that is not structurally connected to the building frame. Precast concrete cantilever walls will usually employ stiffening ribs in their design to provide the required stiffness for stability.

2)   Tied firewalls derive their stability from the building framework. The wall encapsulates a single row of columns, or flexible links and ties are used where the wall is located between two rows of columns.

3)   Weak link tied firewalls, where the structural components (joists, beams) are supported by the firewall in such a way that the failing structure may collapse (break away) without damaging the integrity of fire-wall.

The above publication contains some detailed structural considerations and several relevant figures, but none of them are seismic-related.

In US the weak links are also called sometimes the breakaway connections - these are proprietary connection designs mostly based on aluminum parts that are supposed to melt in fire. Unfortunately, I don’t have information on those at this time. Because these designs are proprietary, they are not included in the NFPA 221 “Standard on Fire Walls and Fire Barrier Walls”. Some info on firewalls is available on the Factory Mutual website. There is also general information on firewalls in Section 7/Chapter 5 of the NFPA Fire Protection Handbook.

In your seismic case, you might choose to go with a freestanding single firewall or with a double firewall, but in both cases sufficient spacing should be provided to avoid adjacent structures impacting each other in an EQ event. A freestanding firewall is probably not very feasible if it is too high. Types 2 and 3 (above) for single firewalls are also valid options, if the details are worked out.

Farid

 

-----Original Message-----
From: Derek [mailto:derekh(--nospam--at)krahn.com]
Sent: Wednesday, July 14, 2004 1:40 PM
To: seaint(--nospam--at)seaint.org
Subject: Firewall Connection

 

Hi Folks,

 

I had a brief search of the archives for this topic but had no luck in finding any assistance.

 

I have a situation where I need to design a firewall (not fire separation) between an existing freezer building (steel frame clad with insulation panels) and a new processing facility. the firewall will be constructed in between the insulation panels of the existing building and the steel framing of the new building.

 

The building is in Vancouver BC which most of you know is a high seismic zone. The dilemma is how to connect the fire wall to the new steel frame such that collapse of the building doesn't cause collapse of the firewall and yet still support the wall by the frame and roof diaphragm under seismic loads. Any magical connection out there that can achieve this? My brief search of the archives returned some mention of melt-away anchors, however, the possibility remains that the fire is remote from the wall (say on the next row of columns parallel to the wall). This could still cause the building to collapse without the opportunity for these melt-away anchors to weaken.

 

My other question relates to the existing building. For those familiar with the NBCC or BCBC. Does the existing building need to be tied to the firewall? My understanding is that the intent of the code is simply to supply a wall that remains standing in the event that either building collapses. In essence, for the pure purpose of a firewall, it does not have to be tied to either building, it can be free standing.

 

any assistance is greatly appreciated.

 

Derek