Replicate Fire Endurance Tests of an Unprotected Wood Joist Floor Assembly
Keywords:
Fire resistance, fire endurance, floorAbstract
To encourage new developments in building technology, a solid basis for building code requirements is needed. Fire endurance is a code requirement, yet no objective procedure exists for computing a structure's chances of failing (degree of risk) in a fire. However, a model for predicting the fire endurance of part of a structure, a conventional unprotected wood joist floor, is available. The aim of this study was to determine the fire endurance performance of an unprotected wood joist floor for use in the model.
Eleven ASTM Standard E 119 floor tests were conducted. All the floors were 2 by 10 Douglas-fir wood joists, sixteen inches on center with 23/32-inch-thick plywood as the floor sheathing. In addition to one trial test, five tests were conducted using a live load of 11.35 lb/ft2. For the other five tests, the live load was 79.2 lb/ft2. Twenty joists were tested for modulus of elasticity and modulus of rupture.
The joist population had a mean modulus of rupture of 5.280 lb/in.2 and a mean modulus of elasticity of 1,530,000 lb/in.2. For the five floors loaded to 11.35 lb/ft2, the mean time for initial joist failure was 17.9 min with a coefficient of variation (COV) of 3.7%. For the five floors loaded to 79.2 lb/ft2, the mean time was 6.5 min with a COV of 11.6%. Based on linear interpolation of these results, first joist failure would have occurred in 13.1 min if a 40 lb/ft2 live load had been used, which is the typical live loading specified in the building codes for residential one- and two-family dwellings.
As a result of this study, fire-resistance performance of a wood floor is known for a specific population of wood joists with known structural properties. These results can be used to verify and revise the model for predicting fire endurance.
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