Appeal 33628

OSSC 722.7.1(2), based on modifications by the American Wood Council NDS Technical Report No. 10, Section 3.8.2

OSSC 722.7.1(2): Minimum required protection. Where required by Sections 602.4.1 through 602.4.3, noncombustible protection shall be provided for mass timber building elements in accordance with Table 722.7.1(1). The rating, in minutes, contributed by the noncombustible protection of mass timber building elements, components or assemblies, shall be established in accordance with Section 703.6. The protection contributions indicated in Table 722.7.1(2) shall be deemed to comply with this requirement where installed and fastened in accordance with Section 722.7.2.

The intent of this appeal is to prove the equivalence of utilizing (3) layers 5/8” Type ‘X’ gypsum wall board (GWB) to provide the required fire protection of the mass timber column base connection in lieu of (4) layers provided during life safety review.

In response to a life safety checksheet comment, a 4th layer of GWB was added to column base detail 4/A0.16 to provide additional protection of the steel baseplate component of the column connection. This was to address the 50% reduction in fire resistance of the layer of GWB in contact with the steel baseplate per NDS Technical Report No. 10, Section 3.8.2. The proposed design omits the 4th layer of GWB because equivalent fire protection can be provided by (3) layers 5/8” Type ‘X’ GWB when considering the acoustic mat and gypsum concrete on top of CLT.

Refer to attached Exhibit 1 for an engineering analysis with a more detailed description of the Proposed Design. Refer to Exhibit 1 also for sheets A0.16 and A0.17 where details have been revised with the Proposed Design, as well as sheet A0.20, which further clarifies the locations of column connections impacted.

Fire protection of the structural connection is based on the thickness of protection from a worst-case fire location. When considering the 5/16” acoustic mat and 2” of gypsum concrete placed on top of the CLT floor structure, the worst-case fire location would be against the column on top of the gypsum concrete, 2” above the steel baseplate. When measured diagonally from where a fire would occur through (3) layers of GWB to the steel baseplate below, calculated fire resistance of (3) layers of GWB is 145.6 minutes, exceeding the 120 minutes required.

Refer to attached Exhibit 1 for a full engineering analysis justifying the Reason for Alternative.