Analysis, Design & Performance
Full Session with Abstracts
342793-5 - Comparison of Computational and Experimental Results for Composite Beams under Combined Structural and Fire Loads
Saturday, April 21
10:00 AM - 11:30 AM
Joseph Main, PhD
Research Structural Engineer
National Institute of Standards and Technology
This paper presents a comparison of computational modeling results with experimental measurements for composite beams under combined structural and fire loads. These results correspond to a series of five tests conducted at the National Fire Research Laboratory at NIST on W18 x 35 beams with a span length of 12.8 m and a slab width of 1.83 m. The first specimen was tested under gravity loading only, to determine its ultimate capacity at ambient temperature, while the remaining four specimens were subjected to compartment fires under structural loading corresponding to 50 % of the ambient-temperature capacity. Two of the specimens tested in fire had double-angle shear connections, as did the ambient-temperature specimen, while the other two specimens tested in fire had single-plate shear connections. For each connection type tested in fire, one specimen had free slab edges while the other specimen had restrained slab edges. The computational analyses used a reduced-order shell-element-based modeling approach, and the same finite-element model was used for both thermal and structural analyses. Thermal loads were applied using convection and radiation boundary conditions, with gas temperatures obtained from fire dynamics simulations. Pre-test analyses were used to support the test planning and instrumentation layout, and uncertainties in the model parameters were considered in the pre-test analyses to evaluate the range of expected responses and failure modes of the test specimens. Post-test comparisons enable evaluation of the adequacy of the modeling approaches for the various components of the composite beam specimens and reveal aspects of the modeling where refinements are needed. In evaluation of the thermal analysis results, comparisons focus on temperature histories at various locations through the depth of the steel beam and the composite slab. In evaluation of the structural analysis results, comparisons focus on the load versus midspan deflection curve from the ambient-temperature test and the midspan deflection versus time curves from the fire tests. Observed failure modes are also of interest, with a focus on the behavior of the shear connections at the beam ends and the shear studs connectors between the beams and the slabs.
The target audience for this presentation includes (1) researchers and practitioners interested in the actual response of composite beams under fire loading, and (2) engineers engaged in design of engineered fire protection and performance-based design for fire. This presentation will provide the audience with validated guidance on modeling composite beams, and more broadly composite floor systems, subjected to structurally-significant fires.