Load-Dependent Critical Temperatures for Standard Fire Resistance of W-Shape Floor Beam Assemblies: Experimental Validation and Simplified Analysis

Comprehensive results of ASTM E119 (2019) standard fire tests (performed by AISC/AISI in 2015) are used to validate load-dependent critical temperature relationships that conservatively predict the thermally induced loss of flexural resistance for W-shape floor beam assemblies. The 16 tested assemblies used the same W8×28 section (coated with the same thickness of passive spray-applied fire resistive material), supported 22 in. (64 mm) of lightweight concrete (reinforced with welded wire mesh) on a 2 in. (51 mm) corrugated metal deck, and had a clear span of 154w in. (3.93 m) in one-way bending. Four specimen groups in the following configurations were tested with four specimens each: restrained ends with composite slab, unrestrained ends with composite slab, restrained ends with noncomposite slab, and unrestrained ends with noncomposite slab. The four specimens in each group were each tested with a constant applied flexural load but at a range of magnitudes, inducing maximum bending moment from 23 to 60% of the section’s ambient nominal moment capacity. The results of these tests clearly demonstrate a relationship between the loss of flexural resistance and the increase in steel beam temperature (particularly the bottom flange temperature) as a function of applied loading. The fire-induced temperature increases in the protected steel beams are then used to validate lumped mass thermal calculations per the AISC Specification (2022) and Part 1-2 of Eurocodes 3 and 4 (CEN, 2005, 2008), which are classified as simple analysis methods per Section A-4.2.4d of the AISC Specification. The results of this study demonstrate that simplified thermal analysis methods can be combined with load-dependent critical temperature relationships to conservatively predict the standard fire resistance of W-shape floor beam assemblies at the onset of flexural failure.