Analysis of a steel gravity frame with composite floor system subjected to compartment fire (test #2)

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This report describes the development and validation of a computational modeling approach for steel gravity frames with composite floor systems subjected to fire exposure. A full-scale compartment fire test conducted on a two-story steel gravity frame structure with a composite concrete floor slab on steel decking was used in the validation process. The experiment was conducted under combined mechanical and fire loading in the National Fire Research Laboratory (NRFL) at the National Institute of Standard and Technology (NIST). The intent of the experiment was to evaluate the influence of the slab reinforcement on the structural performance of the composite floor assembly, which incorporated deformed steel reinforcing bars in contrast with the welded wire reinforcement used in the previous test in the series. The objective of the computational investigation, summarized in this report, was to validate the adequacy of the computational modeling approach to capture the primary structural behaviors and failure modes observed during the fire test conducted in the NIST NFRL and to provide additional insights into the structural performance through detailed modeling of the system response. The computational model of the composite floor system was developed using the LS-DYNA finite element software and incorporated detailed modeling of the system components, including the lightweight reinforced concrete floor slab on profiled steel decking, primary and secondary steel beams and supporting columns, shear stud connectors, and bolted steel shear connections. The model adequately predicted the large deformations observed in the fire test of the composite floor assembly and captured their predominant deformation mechanisms, including lateral distortional buckling of the steel beams supporting the composite floor. Results from this study can further implementation of the performance-based design approaches for structural-fire safety in the U.S. and worldwide.