walterbrennan
Structural
- May 21, 2005
- 50
Continuing Wood Panel Diaphragms Through Fire Walls
NOTE: Questions at the end... any thoughts would be greatly appreciated...
PERTINENT CODE PROVISIONS:
IBC 2018, 706.2 Structural Stability
Fire walls shall be designed and constructed to allow collapse of the structure on either side without collapse of the wall under fire conditions. Fire walls designed and constructed in accordance with NFPA 221 shall be deemed to comply with this section.
EXCEPTION: In Seismic Design Categories D through F, where double fire walls are used in accordance with NFPA 221, floor and roof sheathing not exceeding 3/4 inch (19.05 mm) thickness shall be permitted to be continuous through the wall assemblies of light frame construction.
NFPA 221-15 (2021 Edition), Chapter 6: Fire Walls
6.2.1 – Fire walls shall be designed and constructed to remain stable after collapse of the structure due to fire on either side of the wall.
6.2.2 – Fire walls constructed in compliance with the requirements of 6.3, 6.4 and 6.5 shall be deemed to provide the required stability.
6.3.2 (Cantilevered Fire Walls) – Such walls shall be erected where there is a complete break in the structural framework.
6.4.2.3 (Tied Fire Walls) – The framework on each side shall be designed so that it resists the maximum lateral pull that can be developed due to framework collapse in a fire on opposite sides.
6.5.3 (Double Fire Walls) – Each fire wall shall be supported laterally by the building frame on its respective side and shall be independent of the fire wall and framing on the opposite side.
ALTERNATIVE PATHWAYS TO CODE CONFORMANCE:
1. The project location is such that the SDC is D, E or F, and the diaphragm sheathing does not exceed 3/4" in thickness.
2. The wall is a “Tied Fire Wall”, as described by NFPA 221.
DISCUSSION:
The (new, as of 2018) IBC 706.2 exception allows the use of NFPA 221 “Double Fire Walls” without burdening the engineer with meeting the NFPA “Tied Fire Walls” requirements.
By the explicit nature of the exception, any building designated as SDC A, B or C must (by extension of the original code requirement) strictly comply with the NFPA 221 requirements for the type of fire wall constructed.
For an SDC A, B, or C project, constructed of light wood-framed construction, for which the structural wood diaphragm continues through the fire wall, the only applicable NFAP 221 configuration which seem to apply is a “Tied Fire Wall.”
“Tied Fire Walls” must be designed to “resist the maximum lateral pull that can be developed due to the framework collapse in a fire on the opposite side.”
QUESTIONS:
- For an SDC A, B, or C project, constructed of light wood-framed construction, for which the structural wood diaphragm continues through the fire wall, is there any other pathway to code conformance besides that suggested, above...?
- If the wall configuration is considered to be a “Tied Fire Wall,” what is the basis of derivation for the “maximum lateral pull” for a collapsing, multi-story, wood-framed construction...?
- What is the basis of derivation for the failure load of a collapsing wood panel diaphragm in a multi-story, wood-framed building; such that the diaphragm behaves as a “fuse” at the fire wall, rather than imposing a collapse-level load on the structure at the other side of the fire wall.
NOTE: Questions at the end... any thoughts would be greatly appreciated...
PERTINENT CODE PROVISIONS:
IBC 2018, 706.2 Structural Stability
Fire walls shall be designed and constructed to allow collapse of the structure on either side without collapse of the wall under fire conditions. Fire walls designed and constructed in accordance with NFPA 221 shall be deemed to comply with this section.
EXCEPTION: In Seismic Design Categories D through F, where double fire walls are used in accordance with NFPA 221, floor and roof sheathing not exceeding 3/4 inch (19.05 mm) thickness shall be permitted to be continuous through the wall assemblies of light frame construction.
NFPA 221-15 (2021 Edition), Chapter 6: Fire Walls
6.2.1 – Fire walls shall be designed and constructed to remain stable after collapse of the structure due to fire on either side of the wall.
6.2.2 – Fire walls constructed in compliance with the requirements of 6.3, 6.4 and 6.5 shall be deemed to provide the required stability.
6.3.2 (Cantilevered Fire Walls) – Such walls shall be erected where there is a complete break in the structural framework.
6.4.2.3 (Tied Fire Walls) – The framework on each side shall be designed so that it resists the maximum lateral pull that can be developed due to framework collapse in a fire on opposite sides.
6.5.3 (Double Fire Walls) – Each fire wall shall be supported laterally by the building frame on its respective side and shall be independent of the fire wall and framing on the opposite side.
ALTERNATIVE PATHWAYS TO CODE CONFORMANCE:
1. The project location is such that the SDC is D, E or F, and the diaphragm sheathing does not exceed 3/4" in thickness.
2. The wall is a “Tied Fire Wall”, as described by NFPA 221.
DISCUSSION:
The (new, as of 2018) IBC 706.2 exception allows the use of NFPA 221 “Double Fire Walls” without burdening the engineer with meeting the NFPA “Tied Fire Walls” requirements.
By the explicit nature of the exception, any building designated as SDC A, B or C must (by extension of the original code requirement) strictly comply with the NFPA 221 requirements for the type of fire wall constructed.
For an SDC A, B, or C project, constructed of light wood-framed construction, for which the structural wood diaphragm continues through the fire wall, the only applicable NFAP 221 configuration which seem to apply is a “Tied Fire Wall.”
“Tied Fire Walls” must be designed to “resist the maximum lateral pull that can be developed due to the framework collapse in a fire on the opposite side.”
QUESTIONS:
- For an SDC A, B, or C project, constructed of light wood-framed construction, for which the structural wood diaphragm continues through the fire wall, is there any other pathway to code conformance besides that suggested, above...?
- If the wall configuration is considered to be a “Tied Fire Wall,” what is the basis of derivation for the “maximum lateral pull” for a collapsing, multi-story, wood-framed construction...?
- What is the basis of derivation for the failure load of a collapsing wood panel diaphragm in a multi-story, wood-framed building; such that the diaphragm behaves as a “fuse” at the fire wall, rather than imposing a collapse-level load on the structure at the other side of the fire wall.
