Fire wall loading

[rrmiv]

Does anyone know of a Code reference to the load required for a fire wall to withstand after collapse of one side of the building? IBC section 705.2 says the wall must not collapse after "collapse of construction on either side" - but my question is, under what load?. If it is now an exterior wall, does it need to withstand Code required wind and seismic loading? This seems very conservative. I have arbitrarily used 10 psf in the past, but would like some verification. Any help?

 

[JAE]

I think the theory is two-fold:

1. If there's a fire, the collapse of the adjacent portion of building should not instigate the collapse of the other. - talking about connectivity here.

2. Once the other building has collapsed, then you now have a mess on one side (fire damaged building) and a structurally safe building on the other which has been protected by the firewall and can continue to be occupied.

The logical process would be that the damaged portion could be subsequently cleaned up while the other serves as a code-safe structure, not requiring any heroic stabilization efforts. If you design for only 10 psf, then you now have a clean-up on one side and a stabilization project on the other, which may be OK with the code, but may not be OK with the owner to have to deal with.

I don't think the code specifically addresses this, but it seems that you could more simply design for the higher component wind load and make life simpler if indeed a fire did occur.

 

[rrmiv]

JAE,

Thanks for your thoughts. However, if I were called to evaluate the condition of a building adjacent to a fire wall which remains after a fire burned the other side down, I would first stabilize this fire wall. The Code says the fire wall must be stable "for the duration of time indicated by the required fire-resistance rating." This implies that it need not be designed as a permanent exterior wall - or in my opinion, even a wall to remain during clean-up without evaluation. Any thoughts?

 

[JAE]

rrmiv - yes, I agree with you that the code doesn't absolutely require the exterior wind load capacity. I was just suggesting that there is some wiggle room here for you and your client to discuss as to designing this wall so you don't have to stabilize it after a fire.

I know the probability of a fire is probably small, but you could very easily offer your client a comparitve cost estimate for the two concepts and let he/she decide which way to go.

Just be clear to them that they aren't obligated to have more than a 5 or 10 psf interior wall capacity, but should a fire happen, they could spend X amount of money to avoid the potential later expense of stabilizing the wall...as the re-build time would be long enough to require a full code wind capacity.