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Type IIB Construction - Primary Structure Frame Protection

jar546

jar546

CBO
Joined
Oct 16, 2009
Messages
12,725
Location
Not where I really want to be
If a building is Type IIB construction, per Table 601 of the FBC, there is no protection required for the primary frame. (note C is for heavy timber)
1698238508137.png
The building is CMU with tie beams, bond beams, and a structural steel frame to support the 2nd floor of this 2-story fire-sprinklered building.

Why would the engineer choose to fire-protect the columns, I-beams and underside of the decking to the second floor? I don't believe it is required under 601 or 704.1, 2 or 3.
Is the first floor frame required to be protected? If yes, then why isn't the 2nd floor required to be too? After all, it supports a concrete roof.
IMG_4038.JPG
 
Well... not much to go on there Jar. Surely there is a horizontal assembly providing separation for some reason. Could only think of like a couple dozen reasons that may be the case, so... need more info.
 
Occupancy separation?

Maybe the second floor supports rated fire barriers? If so, everything that supports rated construction must also be rated.

Why not ask the designer?
 
classicT said:
Well... not much to go on there Jar. Surely there is a horizontal assembly providing separation for some reason. Could only think of like a couple dozen reasons that may be the case, so... need more info.
Click to expand...
The first floor is an open area, a kitchen for the FD and some bunk rooms. The second floor is all offices. Does this help?
 
jar546 said:
They are separated by 2" pan decking with 6" of concrete. So why the column if it is a 2B? If it was 2A, I could understand.
Click to expand...
Doesn't meet an exception to 711.2.3.

2020 FBC - 711.2.3 Supporting Construction​

The supporting construction shall be protected to afford the required fire-resistance rating of the horizontal assembly supported.
Exception: In buildings of Type IIB, IIIB or VB construction, the construction supporting the horizontal assembly is not required to be fire-resistance rated at the following:
  1. Horizontal assemblies at the separations of incidental uses as specified by Table 509 provided the required fire-resistance rating does not exceed 1 hour.
  2. Horizontal assemblies at the separations of dwelling units and sleeping units as required by Section 420.3.
  3. Horizontal assemblies at smoke barriers constructed in accordance with Section 709.
 
Don't overlook the possibility that the designer (or their lackey) may have grabbed some standard details / notes from a different Type IIA project and pasted them in there, without checking to see if this was overkill. It happens more often than you know.

I've seen a number of single family residences where the plans called for a full NFPA 13 sprinkler system, and you know that someone just copy/pasted standard fire protection notes from a commercial project.
 
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