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?

 

[CELinOttawa]

Probably not... Even drywall is good for 30mins, so it is likely that the rest of your assembly will provide the first hour, and then the remaininig two hours can come from the two hour rating of the joists themselves.

BUT, in such matters I *NEVER* argue with the Architect. Presumably you are already on record as trying to spend less of the Owner's money (makes me wonder if the Architect is on one of their famous costs plus percentage of total cost of work contracts), and thus you have already tried to defend the client's pockets.

When there is a difference of professional opinion such as this, the tie should always go to increasing safety.

 

[Prestressed Guy]

This floor assembly consists of a bare prestressed double tee with cast in place topping. The flange + topping is 6" with a rating of 3+ hours. The question is for a 3-hour rated horizontal assembly, do the secondary framing members need to be 3 hour rated or are they 2-hour rated per table 601. The primary framing is all 3-hour rated PC girders and PC columns. The DT's will be thermally restrained and there are multiple bays in both directions. The cast in place topping is 3½" minimum with reinforcement and structurally tied to the perimeter walls.

This horizontal assembly is a building separation between a parking garage and a retail store per IBC 510. Both are fully sprinkled.

 

[Prestressed Guy]

One additional piece pertinent info is that the DT's are restrained from thermal expansion by a structural CIP topping slab and by end restraint of perimeter walls and girders.