Concrete Floor Fire Resistance Rating

[eyanovich]

We have a project where an architect is questioning if a 4 1/2" slab is thick enough to provided with a code perscribe fire rating of 2 hours. I've consulted the simplified design of reinforced concrete buildings of moderate size and height and discovered a table that states thickness requirements based on aggreate size (and notes minimum concrete cover requirements). This table is based on the CRSI reinforced concrete fire resistance manual.

This guide pretty much excludes me from using the 4.5" slab as a 2 hour rating by itself.

Does anyone know of a UL listing of floor slab thicknesses/fire ratings. Or what fire proofing would be required to supplement the concrete flooor? I have looked through the UL catelog but have not found an assembly that includes a one way slab, with precase joists at 8'0" O.C.

Any help would be greatly appreciated!

 

[jike]

4.5" slab thickness is required to achieve a 2 hour rating with normal weight concrete. I do not have UL book handy.

 

[eyanovich]

wow talk about a quick response.

So your saying the 4.5" slab is OK? Just hoping to be able to quote something to the architect that states that explicitly.

Thanks!

 

[jike]

I cannot find a UL assembly but you could use the Prescriptive Fire Resistance Method per IBC 2006 Section 720.

Slab with siliceous aggregate and 3/4" minimum cover requires 5" thickness (oops not 4.5"...sorry) to achieve 2 hour rating. Also see table 721.2.2.1. Also see table 721.2.3(3) for cover for various widths of beams. You might also check with local precaster on the required beam size and cover for load and 2 hour rating.