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Fire Endurance of Floor Assemblies

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The fire testing conducted by NRC/IRC was part of a three year joint government and industry program. The project participants included representatives from the steel, wood and concrete industries, gypsum board and insulation manufacturers, home builders and related government agencies. Thirty-two fire tests were conducted on full scale floor assemblies framed using dimensional lumber, wood-I joists, concrete and cold-formed steel joists. Testing was done in accordance with fire endurance testing standards CAN/ULC-S101-M89 and ASTM E119.

The test results show that the steel framed floors achieve a higher fire resistance than either of the wooden counterparts. For the same floor assembly construction, and switching only the floor joists, the cold-formed steel joists achieved a fire resistance of 74 minutes while the dimensional wood joist achieved a rating of 69 minutes under the same loading conditions. The wood-I framed floors reached 72 minutes and the fire resistance was found to depend on the type of wood-I joist used. The effect of imposed test load was found to be significant. For the solid wood joist increasing the load from 75-100% decreased the fire resistance by 14%. The failure mode for all the floors in this comparison was structural.

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