Structural fire resistance of partially restrained, partially composite floor beams, II: Modeling

This paper is Part 2 of a two-part investigation of the structural fire resistance of a partially composite, one-way spanning steel floor beam assembly with partial translational and rotational end restraint provided by shear tab connections to a supporting frame. A preceding paper (Part 1) described a pair of experimental tests on structurally identical composite floor specimens (one protected and the other unprotected) that are subjected to fire via a large modular furnace. In this paper, those experimental results are used to validate numerical models that conservatively capture the thermo-mechanical response of the specimen assemblies to fire. Models are developed to maximize simplicity toward implementing performance-based design of these assemblies in practice. Thermal analysis of the steel is performed using a multiple lumped mass approach, which can be implemented via spreadsheet or a simple, non-iterative programmed solution. Thermal analysis of the slab via a simple one-dimensional heat flow model is compared against a more detailed computational solution. Two types of structural finite element analyses were performed: one composed of shell elements (more complex) and another composed of fiber-beam elements (simpler). The results of all models show conservative agreement with the experimental data. These models are used to analyze the tested assemblies for variations in applied load and fire protection thickness to demonstrate the utility of the ASTM E119 standard fire test as a validation baseline for performance-based structural fire engineering evaluation. •2 structurally identical composite floor beams are modeled for fire exposure.•Passive fire protection was applied to one specimen, and the other was unprotected.•Simple calculations conservatively predicted experimental temperature measurements.•Complex & simple predictions of structural behavior are validated with test results.•Models are used to examine variations in flexural loading and protection thickness.