One hour steel beam with wood?

[mtlogcabin]

I have a steel beam supporting a one hour occupancy seperation between a merchantile and 2 floors of R-2 above. 2009 IBC full nfpa 13 system V-B construction. The beams are below the floor ceiling assembly. The architect wrapped 2x4 around the sides and bottom of the beam at 24" OC and wants to attach 2 layers of 5/8 type X and is calling this a one-hour assembly under Section 721. I have never seen a steel beam listed assembly that included wood for attaching the gypsum board to. I understand the assembly is to limit the tempature rise of the steel beam. I am wondering if the gypsum board will provide enough thermal protection to keep the wood from igniting. Any thoughts, do I have legitimate concerns or am I being over cautious here.

 

[Mark K]

Would the two layers of gyp board provide a one hour rating for wood construction?

 

[RLGA]

If Section 721.6 is referenced, then no way is that considered 1-hour protection for steel--that section is strictly for wood assemblies. If Section 721.5 (specifically, Section 721.5.2 for steel beams) is used, then there is no mention of gypsum board for protection of steel beams--only sprayed fire-resistnat material is mentioned.

Therefore, I say that it does not comply with Section 721, and an approved, tested assembly be submitted. A sprayed fire-resistant material applied over the beam at the requisite thickness and then covered by wood framing and gypsum board is acceptable.

 

[AegisFPE]

Gypsum board could be used per 721.5.1.2, but is shown to be attached with noncombustible material.

 

[RLGA]

Section 721.5.1.2 is for columns, not beams.

 

[AegisFPE]

To assist the applicant in moving forward where there design does not satisfy 721, you could offer to consider an alternative approach as described in 703.3(4).

In this case, it may be possible to consider GA BM1137 as a reference together with another assembly that uses wood framing in a similar orientation with similar gypsum membrane to achieve the prescribed fire-resistance rating, thereby demonstrating wood as an acceptable material within the BM1137 assembly.

However, if individual encasing is required, wrapping the beam in 2x4 may make embedding utilities very tempting to the contractor, which could be problematic during construction per 704.8.

 

[mtlogcabin]

In this case, it may be possible to consider GA BM1137 as a reference together with another assembly that uses wood framing in a similar orientation with similar gypsum membrane to achieve the prescribed fire-resistance rating, thereby demonstrating wood as an acceptable material within the BM1137 assembly

This is exactly what he has done. His notes reference GA BM 1137 that 2 layers of Proprietary Gypsum Board is sufficient and then notes IBC 721.6.2(1) That 2 layers of 5/8 Type X with the 2x4 installed flat will work. I agree the Type X should provide 40 minutes each on a wood framed wall I am reluctant to aprove it for steel beams without some documentation. I have suggested he contact an FPE to review his proposal but that has not happened yet.

 

[Paul Sweet]

Gypsum Association FC 5406, 5407 & 5408 use 2 layers of 5/8" type X gyp. board to provide one hour protection for wood framing. This might also work for the steel if it doesn't require individual encasement.

http://www.gypsum.org/download.html

 

[AegisFPE]

I have suggested he contact an FPE

Good call!You're not saying "no," you're just pointing out that the code requires the applicant to present an engineering analysis since they're beyond a prescriptive assembly per 721. This is a great example of how Item 4 of 703.3 could be applied.

They're probably weighing the cost and schedule implications associated with changing the detail to meet BM 1137 versus an FPE analysis seeking to maintain the wood blocking.