2-hr fire wall stability

[Sifu]

I have a 2-hr fire wall, GA WP4135. It is being used to separate an R2 into 2 different buildings for allowable area reasons. It is coupled with an unrated wall. Both walls bear floor trusses. On the left side, no worries as the floor could pull down the wall and not affect the fire wall. On the right side, the floor joists are hung on the wall with a Simpson DHUTF fire wall hanger, made to be installed over the 2 layers of gyp. If that floor were to collapse, and pull the wall down it becomes a problem. I have asked for an explanation from the architect and engineer and am not getting one. So I am digging. I have requested information from Simpson, but figured I would put this out there while I wait. The hanger has a robust attachment to the wall, using both nails and SDS screws at the face and top flange. It has a very weak connection to the joist, with only 2 10d, 1 1/2" nails. This makes wonder if the intent is for the joist to detach from the hanger in the event of collapse, but the hanger will remain, thereby maintaining the structural integrity of the wall.

Anybody encountered this or have any info?

 

[classicT]

Encountered similar - clarification came from the structural engineer though. The engineer had to notify the architect that the floor (roof in my case) was not structurally detached in a manner that would allow for collapse. The architect then came back with a 2-hr area separation wall using shaft-liner panels.

What I would suggest is that you notify/ask the structural engineer of the requirement from IBC Section 706.2. After review, the structural engineer can then clarify the design to the architect, and they will need to coordinate further for a solution.

 

[Sifu]

Encountered similar - clarification came from the structural engineer though. The engineer had to notify the architect that the floor (roof in my case) was not structurally detached in a manner that would allow for collapse. The architect then came back with a 2-hr area separation wall using shaft-liner panels.

What I would suggest is that you notify/ask the structural engineer of the requirement from IBC Section 706.2. After review, the structural engineer can then clarify the design to the architect, and they will need to coordinate further for a solution.

Yes, I will be asking again, I am just trying to anticipate the answer and increase my own understanding. The response from the first comment was to provide more details of the fire wall, but not how the fire wall will remain in place. The engineer from Simpson is looking into my theory as well.

 

[steveray]

I have a 2-hr fire wall, GA WP4135. It is being used to separate an R2 into 2 different buildings for allowable area reasons. It is coupled with an unrated wall. Both walls bear floor trusses. On the left side, no worries as the floor could pull down the wall and not affect the fire wall. On the right side, the floor joists are hung on the wall with a Simpson DHUTF fire wall hanger, made to be installed over the 2 layers of gyp. If that floor were to collapse, and pull the wall down it becomes a problem. I have asked for an explanation from the architect and engineer and am not getting one. So I am digging. I have requested information from Simpson, but figured I would put this out there while I wait. The hanger has a robust attachment to the wall, using both nails and SDS screws at the face and top flange. It has a very weak connection to the joist, with only 2 10d, 1 1/2" nails. This makes wonder if the intent is for the joist to detach from the hanger in the event of collapse, but the hanger will remain, thereby maintaining the structural integrity of the wall.

Anybody encountered this or have any info?

Like an old "firecut" in a masonry wall bearing wood framing....

 

[classicT]

Yes, I will be asking again, I am just trying to anticipate the answer and increase my own understanding. The response from the first comment was to provide more details of the fire wall, but not how the fire wall will remain in place. The engineer from Simpson is looking into my theory as well.

I would not rely solely upon the answer from Simpson. They will likely provide an opinion on the collapse of the floor and how their hanger would perform in that condition.

What is missing from that opinion is how the wall will remain standing. The structural engineer is likely depending on that floor or roof to support the wall and keep it from falling over. Framed walls are seldom truly self-supporting. Concrete and masonry are rigid and heavy enough that they often do not require horizontal support, but wood and steel walls typically have hinge joints (i.e. plate lines, rim joists, etc.) given the practice of platform framing. These hinge joints must be supported to prevent the overturning moment on the wall.

 

[Sifu]

I am asking Simpson's opinion on whether the hanger is designed to remain in place if/when the joist fails (or if that was even a consideration for a "fire wall hanger"), not whether the actual wall will remain in place. The plan detail they provided in response to my first query seems to be reinforcing the wall, making me "think" this is their intent. I will still be asking them to respond in writing to tell me their actual intent and how they will accomplish this.

My first comment was to demonstrate the structural stability of the fire wall. Both the architectural and structural detail showed the floor sheathing lapping the wall top plate, tying the wall to the floor, and the hanger as I specified. This was an example of how I thought they were not considering the stability of the wall.

The response was to show more on the structural detail, which now provides a note to transfer the diaphragm shear to the wall with A23 clips and terminate the sheathing at the face of the wall, eliminating the tie from the wall via the floor sheathing. So what is left is the Simpson hanger and A23 clips as the only method of connecting the wall to the floor system. I think they are intending that these connections will not pull the wall down. But I am not comfortable with "I think", so I am going to ask them again to specify the intent of the design.