firewall seismic R value

[peal724]

I've designed cantilevered CMU firewalls before, but it's always been where the seismic wasn't that bad. Got one now in a pretty bad seismic area and I'd like to stop and examine my methods to make sure the way I've always done it is still correct.

What R value do you others use for seismic? R=1.0 for ordinary concrete moment frame is about the closest system in my opinion.

 

[peal724]

Using the IBC as the design code, the language for structural stability states ".....for the duration of time required by the required fire-resistant rating."

If it's a 3-hour fire wall then why am I designing it for 500 year occurrence seismic forces?

 

[PicoStruc]

A] Answer for your second post.

1) The earthquake that happen 1 time in 500 year cause a fire.
2) The fire last longer that 3 hours.
3) Then you have 3 hours to evacuate people from the building in fire

For (3) to be possible, you must design you building to sustain earthquake load of level (1 time in 500 years)

B] Answer for your first post.

If your concrete block wall IS NOT structural, they must be considered as ELEMENT NOT PART OF SEISMIC RESISTANCE SYSTEM, Check you local building code (ASCE 7-10).

If your concrete block wall IS structural, they must be considered as PART OF SEISMIC RESISTANCE SYSTEM, Check you local MATERIAL code.

 

[DaveAtkins]

I assume your firewall is only a cantilever after a fire collapses the structure on one side of the wall.

This situation has been discussed in many threads in Eng-Tips Forums, with no real consensus among engineers (because the code is unclear).

What I have done is design the wall for the appropriate wind load or seismic load for the permanent condition (when it is not a cantilever), and for internal pressure (5 psf) for the short term condition during a fire (when it is a cantilever). I feel this assures the wall is stable during a fire, and can take some level of wind load or seismic load.

But, as I mentioned above, some engineers will think this is not conservative enough.

DaveAtkins