3 hour horizontal assembly

[Prestressed Guy]

I have a project that requires a 3-hour horizontal assembly between the 1st and 2nd level and the 1st level is type IA construction. I have assumed that to meet this requirement I would need to design the floor framing system with the primary framing members as 3 hour rated and the secondary members would be 2-hour rated as listed in IBC Table 601 type IA.

The architect of record is insisting that a "3-hour Horizontal Assembly" must have all elements with a 3 hour rating.

Do I need to provide 3-hour rated concrete joists in addition to the 3-hour girders and columns of the primary framing system and slab in order to meet this requirement?

 

[stookeyfpe]

Which edition of the IBC is adopted by the jurisdiction?

 

[Prestressed Guy]

This project will be designed in conformance with section 510 IBC-12 and required a 3-hour rating due to area limits. The assembly is deigned as a thermally restrained 3-hour assembly as follows.

Primary structural frame is prestressed inverted T beams on precast columns. These members are the primary structural framing and will be designed to 3-hour.
The secondary framing members are Prestressed double T joists with cast-in-place topping. The deck will be 2½" DT flange with 3½" CIP reinforced structural topping. Total depth of deck is 6" for +3-hour rating. My intent is to design the DT stems as un-restrained 2-hour beams in conformance with IBC Table 601 Type IA for secondary framing members per MNL-124 rational analysis. These members meet the requirements to be designed as restrained but I am opting to use an un-restrained design to be conservative.

ASTM E119 allows the test for a restrained assembly to continue for a period up to twice the hourly un-restrained rating of the beams as long as the unexposed surface does not exceed 250º above ambient. This means that the beams in a 3-hour restrained assembly must have 1½ hour un-restrained beams minimum. IBC Table 601 limits this to 2-hour for the secondary members.

 

[stookeyfpe]

Based simply on equivalent thickness, and assuming siliceous concrete, your design complies with 2012 IBC Table 722.2.2.1.