Table VII.3 shows that for Construction Type IB, the IBC requires a 2-hour rating for both the structural frame and floor construction. Steel-framed structures are classified as restrained; therefore a UL assembly supporting a 2-hour restrained rating must be found. In addition, the assembly must support the use of composite beams, lightweight concrete and fluted deck. UL tests D902 and D925, utilizing SFRM materials from Isolatek International and W. R. Grace & Co., respectively, are commonly referenced unprotected deck designs. In this example, UL design D902, shown in Figure VII.3, will be evaluated.
Slab Design: UL D902 supports the use of both normal weight and lightweight concrete. The assembly requires a 34 in. (82.6 mm) lightweight concrete deck for a 2-hour restrained assembly rating. The compressive strength of the concrete shall be 3,000 psi (20.7 MPa). The unit weight of the concrete used in design should fall within the range of 107-116 pcf (1,710-1,860 kg/m3) as specified in the assembly. Differences in the unit weight of the concrete may adversely alter the insulating properties of the slab from those tested. Deck Design: The assembly allows both composite and non-composite fluted decks. Fluted units may be either galvanized or phosphatized/painted. The deck is to have a gauge 22 MSG minimum thickness. SFRM Thickness: Figure VII.4 shows a summary of the SFRM thickness amounts required by UL D902 for a W8x28 beam coated with Isolatek Type D-C/F material. UL D902 lists several unrestrained beam ratings for each restrained assembly rating. For instance, the 2-hour restrained assembly rating used with lightweight concrete systems provides 1-, 2-, and 3-hour unrestrained beam ratings requiring a in. (9.5 mm), 1 in. (25.4 mm), and 1b in. (39.7 mm) of material thickness, respectively. A 2-hour restrained assembly rating with a 1-hour unrestrained beam rating is an acceptable solution for this example and requires the least amount of fireproofing material. Therefore, a a in. (9.5 mm) thickness applied to the W8x28 test beam will be chosen.
Fig. VII.2 Example Floor Plan
Fig. VII.3 UL Design D9025
Fig. VII.4 UL D902 SFRM Thickness Requirements5
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