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Fire Protection for Secondary Structural Members

M

Mitch

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Oct 8, 2021
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17
Location
Brooklyn, NY
The NYC BC in Section 704.4 allows one to protect secondary members with the ceiling of a horizontal assembly which accords with section 712. Does this mean that the fire-rating requirements for secondary members set forth in table 601 is waived provided that one complies with 704.4?
 
Not sure NYC BC is the same as the IBC, but I think it means that if a secondary member requires a given protection, then that protection can be provided by the membrane of the horizontal assembly of the same rating. So no need to encase it within the horizontal assembly.
 
Section 704.1 refers to Table 601 for the protection of structural members including secondary members. Thus, logic would dictate that Section 704.4 is applicable to the protection of secondary members as required by Table 601. Thus, 704.4.2 would also apply to secondary members in horizontal assemblies that are required to be protected per Table 601.
 
Take for example item number 6-4.1 in table 720.1(3) which gives an assembly with 1 layer of wallboard a 2 hour rating. Any secondary members can be protected by the wallboard regardless of the protection 1 layer of wallboard actually provides?
 
Mitch said:
Take for example item number 6-4.1 in table 720.1(3) which gives an assembly with 1 layer of wallboard a 2 hour rating. Any secondary members can be protected by the wallboard regardless of the protection 1 layer of wallboard actually provides?
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Yes, provided the actual installation complies with Item No. 6-4.1. The concrete on top of the metal deck must be at least 2-1/2 inches thick. Plus, you have to make sure the joists comply with Footnote 'e.' If the ceiling is suspended below the joists, then the ceiling support system must comply with Footnote 'g.'
 
On a related topic, beams having direct connections to the columns are designated as part of the primary structural frame, yet they are not necessarily included in the structural members that require individual encasement (i.e. if they only support one story). The allowance for membrane/ceiling protection though doesn't include these members either as that allowance is stated in regard to secondary members. What options are left for fireproofing these beams?
 
Individual encasement means that the beam must be specifically fireproofed even if it is enclosed within a fire-resistance-rated assembly. If the beam is enclosed by a fire-resistance-rated assembly (e.g., floor/ceiling assembly) and the building is two stories or less, then the floor/ceiling assembly can provide the required protection for the beam, and individual encasement is not required.
 
I see what you're getting at. But there is some nuance lost in your interpretation. The requirement isn't for buildings fewer than 2 stories, it is for individual members which support more than two stories. That is a rare condition for a secondary member.
 
redeyedfly said:
I see what you're getting at. But there is some nuance lost in your interpretation. The requirement isn't for buildings fewer than 2 stories, it is for individual members which support more than two stories. That is a rare condition for a secondary member.
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You are correct.
 
RLGA said:
Individual encasement means that the beam must be specifically fireproofed even if it is enclosed within a fire-resistance-rated assembly. If the beam is enclosed by a fire-resistance-rated assembly (e.g., floor/ceiling assembly) and the building is two stories or less, then the floor/ceiling assembly can provide the required protection for the beam, and individual encasement is not required.
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So if I am understanding correctly, although section 704.4 only mentions "secondary members", it means to include beams that support only one story even if they are designated as part of the "primary structural frame" per section 202.
 
Mitch said:
So if I am understanding correctly, although section 704.4 only mentions "secondary members", it means to include beams that support only one story even if they are designated as part of the "primary structural frame" per section 202.
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No, sorry my comment was misstated. Primary members supporting more than two floors or one floor and a roof require individual encasement. Primary members supporting less than that may be protected within a listed floor assembly.
Secondary members require individual encasement unless they are within a listed assembly, load does not matter.
Both UL and GA have some general notes about the limits of their listed assemblies when encasing structural members. GA doesn't allow the beam to extend more than 6" below the assy. If less than 6" you can simply wrap the membrane around the beam.
You have to infer that primary beams within a listed assembly are acceptable in low load conditions per 704.3. Since they aren't required to be individually protected, the only other option is within a listed assembly.
 
Bracing members aren't either specified in section 704. Would you assume that this allowance to protect the secondary members within a horizontal assembly applies to bracing members within a wall assembly as well or would you assume that they require individual encasement?
 
4. Bracing members that are essential to the vertical stability of the primary structural frame under gravity loading shall be considered part of the primary structural frame whether or not the bracing member carries gravity loads.

Bracing is required for gravity loading stability of columns. Depending on the interpretation of the AHJ, that may be all the lateral bracing for the building. The only clear exception are seismic lateral systems.
 
I understand that the bracing needs to be fire protected. My question is if they need to be individually encased or if they can be protected by the membrane of a fire-rated wall assembly.
 
Not all members of the primary structural frame require individual encasement. Section 704.2 mentions columns and Section 704.3 mentions other primary structural members that support more than 2 floors, etc. No mention is made of bracing however.
 
Mitch said:
Not all members of the primary structural frame require individual encasement. Section 704.2 mentions columns and Section 704.3 mentions other primary structural members that support more than 2 floors, etc. No mention is made of bracing however.
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Ah, got it.

I would not consider the bracing to be columns. Column bracing is 2-4% of the column load. I don't believe the intent is that column bracing be protected to the same extent as columns... your local AHJ may disagree.
 
This is an interesting topic as I was just presented something similar. A three-story, Type II-B Construction. The horizontal assemblies, where required, need to be 1-hour for multi-use facility A-3, B and S-2. The 1-hour horizontal assembly we realized would not be required to have the main girders or secondary members fireproofed as they only support one-story. I argued the columns would need to be as they support more than one-story. Am I incorrect? I was told 711.4 on continuity would usurp this. (2012 IBC in Indiana). Thoughts?
 
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