Fire Resistance Rating - Pan Joist Floor

[mrengineer]

I am looking at fire resistance requirements for pan joist floor, using IBC 2000, Type 1A construction. Per Table 601, for Type 1A, structural frame (columns and beams/girders framing into the columns) requires 3 hour, floor construction requires 2 hour. I am assuming that pan joist top slab thickness therefore can be based on 2 hour, which results in 4.6" minimum thickness per Table 719.1(3). The thing that bugs me is that Table 719.1(3) shows required slab thicknesses for fire resistance ratings up to 4 hours. However, Table 601 does not require 4 hour for ANYTHING. This makes me wonder if I am missing something. Do you agree with the 2 hour/4.6" top slab thickness for Type 1A construction?

 

[jike]

You might also be able to get your rating with a thinner top slab and block fillers in the void between the ribs. No metal pans required for this type of construction, just a flat deck.

 

[SperlingPE]

Similar situation - went with 4 3/4" slab thickness. No questions from local codes or fire marshalls.