3 hour CMU Firewall as shear wall

[msdengineer]

I am working on a school project and have a 3 hour firewall (CMU) that I cannot use as load bearing. I have provided steel columns inside of the wall to support joist girders that support steel joists. In the attached image, the higher red walls parallel to the joists are the 3 hour firewalls. The lower joists over the corridors are supported by a lower CMU wall.

My question is: Can the 3 hour firewall be used as a shear wall for the high roof diaphragm even though it cannot be used as a load bearing wall?

My understanding is that one side of the structure on either side of the firewall should be able to burn and collapse without affecting the other side.

Has anyone used a specific connection to attach the roof deck to a firewall that would allow shear transfer while still allowing the collapse in the case of a fire?

 

[msquared48]

Sure. Why not? Just detail it to transfer the lateral shear without imparting vertical load. No problem.

Mike McCann
MMC Engineering

 

[BAretired]

There are several options given in the Canadian code for the structural integrity of firewalls. They are:

1. Double Firewall
2. Cantilever Firewall
3. Tied Firewall
4. Weak-link Connections

The double firewall is easy to understand as each wall is tied into the structure on each side, so the walls can be used for bearing or as shearwalls.

The cantilever firewall is not tied into the building on either side so it is neither a bearing wall nor a shearwall.

The tied firewall can be used as a bearing wall and a shearwall but the structure on each side must be capable of resisting the lateral forces resulting from a fire on the opposite side.

The weak-link connections are expected to fail on the fire side of the wall so that the structure on each side supports the firewall but after the fire, one side falls away, presumably leaving the wall supported on the other. The firewall in this case is neither a bearing wall nor a shearwall.

My preference has always been for the tied firewall. The double firewall is excellent too, but I have never found a client willing to pay for the extra wall.

BA