Fire resistance of floor framing members: development of an intermediate-scale screening test

Abstract

Engineered wood floor framing members, such as I-joists, must pass full-scale fire endurance tests to demonstrate equivalency to unprotected nominal 2 by 10 dimension lumber (actual dimensions 38 by 235 mm (1.5 by 9.25 in.)) if used in fire-rated assemblies. The full-scale test is performed in a furnace with dimensions of at least 3.7 by 3.7 m (12.1 by 12.1 ft) with a floor assembly loaded to 50% of the allowable stress design bending load. The standard fire curve is used during the test. The acceptance criteria of 15.5 min was determined from equivalence to the calculated fire resistance of a solid wood 2 by 10 assuming three-sided fire exposure. However, the full-scale test is expensive and cumbersome, making it difficult to assess potential new fire-protective technologies. The purpose of this study was to examine the suitability of an intermediate-scale test method for floor framing members for the purpose of screening new technologies before the expense, time, and effort of conducting the full-scale test. The intermediate-scale test used two joists spaced 406 mm (16 in.) on center and 3 m (120 in.) long with a 1.8-m (72-in.) heated length. Two hydraulic actuators loaded the assembly creating maximum bending stress equal to 50% of the allowable stress design bending load. Solid wood 2 by 10 dimension lumber and I-joists with various web protection strategies were used to evaluate the suitability of this intermediate-scale test. Failure times and failure modes varied across different protection strategies. Although, in general, the intermediate-scale test had shorter times to failure than did the full-scale test, the intermediate-scale test may still be useful for screening new fire protective technologies for engineered wood.

Citation

Zelinka, Samuel L; Bourne, Keith J.; Beynon, Toby; Schauwecker, Christoph F.; Davis, Daniel. 2024. Fire resistance of floor framing members: development of an intermediate-scale screening test. Research Paper FPL-RP-721. Madison, WI: U.S. Department of Agriculture, Forest Service, Forest Products Laboratory. 8 p. https://doi.org/10.2737/FPL-RP-721