Fire Resistance of Seismic Bracing

James Mutrie · **Joined:** 2008 **Posts:** 19

There has been much discussion of this topic over the years. APEGBC Building Code committee has recently become involved. SEABC would like to develop a standard approach. The attached document is a draft suggestion. There are three possible paragraph 3's included that have been added/or modified by suggestions received to date. Please review and submit your comments to the forum to help us decide what approach is the best.

Quote:

SEABC Technical Committee
Fire Rating of Seismic Bracing
Draft Proposal
March 7, 2010 (Revision 2)

The APEGBC Building Code Committee asked SEABC to review the question of whether or not seismic bracing is required to be fireproofed. The following is a suggested standard approach.

1. The following requirements apply only in the case where columns are required to be fireproofed.

2. Bracing that is a part of the gravity load carrying system must be fireproofed.

3. Sufficient fireproofed bracing must be provided to resist the factored effects of sway, including the notional loading in accordance with CSA-S16-01 Clause 8.7.2, plus the factored effects of wind loading using Load Combination Case 2 from Table 4.1.3.2 of NBCC.
or
3. Sufficient fireproofed bracing must be provided to resist the factored effects of sway, including the notional loading in accordance with CSA-S16-01 Clause 8.7.2, plus the factored effects of a 1/10 wind loading using Load Combination Case 4 from Table 4.1.3.2 of NBCC.
or
3. Sufficient fireproofed bracing must be provided to resist the factored effects of sway, including the notional loading in accordance with CSA-S16-01 Clause 8.7.2, plus the factored effects of the Load Combination in NBCC Commentary A paragraph 25 plus a companion one in 10 year (q10) wind loading with a load factor of 1.0.

4. Seismic bracing added to a building as part of a seismic upgrade need not be fireproofed provided all elements that contributed to the building’s original lateral stability remain intact.

Discussion

Sufficient bracing must always be provided for stability of the structure under gravity loading and this bracing must function under fire conditions. The probability of a fire at the same time as the design earthquake is extremely low. Fires are often triggered as a result of an earthquake but normally occur after the event. The probability of a fire at the same time as the design wind is also very low but the probability of a lower level wind at the same time as a fire may be significant. There is no clear guidance that we have found to indicate how to handle the fire plus wind case. We are suggesting, until better information is available, that we take what we believe is a reasonable approach to this problem.

James Mutrie · **Joined:** 2008 **Posts:** 19

We were having a few tething problems with the forum yesterday and I could not attach the original document but it now is possible.

Tejas Goshalia · **Joined:** 2009 **Posts:** 16 **Location:** Vancouver

Does this (or How does) this discussion apply to seismic bracing of non-structural components that may pose to be a falling hazard critically compromising the building's functioning?

James Mutrie · **Joined:** 2008 **Posts:** 19

I believe there is currently no requirement to fire-proof bracing for non-structural components and the proposal will not change that, in fact it likely reinforces the idea that fire-proofing is not required for elements required only for seismic forces.

Peter Kiddie · **Joined:** 2009 **Posts:** 2 **Location:** Vancouver

In general I feel this is a reasonable approach however i feel that the situation of a fire and an aftershock probably needs some consideration. I am not sure what the probability of this is but expect that it could be significant. I expect that a suitable force level would be very much lower than the normal seismic design force but it might be signficant especially in already damaged buildings.

Vincent Liu · **Joined:** 1970 **Posts:** 2

Any concern about the heat-transfer between un-protected steel bracing members and fireproofed structural steel elements in the event of fire? If the temperature in un-protected bracing members rises, the temperature in connecting structural members (beams or columns) will likely increase as well. Do we need to consider its effect to make sure that the stability of the main framing members will not be affected?

James Mutrie · **Joined:** 2008 **Posts:** 19

Vincent

And interesting question and one I don't have any answer for. The fire testing is on individual assemblies of components so there generally is no influence of heat conduction being tested except between the assembly components. I expect the conduction effect, while real, will not have a big influence on the overall fire resistance but I have to say that is a guess not based on special knowledge. Perhaps code consultants might have some more educated thoughts, I will try to see if I can get one of them to add any insights to the question.

Jim Mutrie

Fire Resistance of Seismic Bracing

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