Analysis, Design & Performance
Full Session with Abstracts
342793-4 - Performance of Long-Span Composite Beams under Combined Structural and Fire Loads: An Experimental Evaluation
Saturday, April 21
10:00 AM - 11:30 AM
The National Institute of Standards and Technology (NIST) recently commissioned the newly expanded National Fire Research Laboratory (NFRL) for advancing its large-scale structural-fire testing capabilities through a suite of built-in fire and structural measurement systems. The first test series at the NFRL is being conducted on a series of long-span steel-concrete composite floor beams, with an aim to provide technical information necessary to advance performance-based design of composite floor systems in steel-framed buildings subject to fire. A total of five 12.8-m span specimens are designed following the US design codes and standards. One specimen is tested at ambient temperature to measure the flexural moment capacity of the specimen. The other four specimens are subjected to 50 % of the ambient-temperature bending moment capacity and the maximum 4 MW compartment fire using natural gas fuel delivery system. Each composite beam specimen consists of a W18 x 35 steel beam and a 1.83-m wide concrete slab cast on top of an all fluted steel decking. The concrete slab was lightly reinforced with 6 x 6 − W1.4 x W1.4 wire mesh. The concrete slab was composite with the steel beam via 19-mm headed shear studs welded at 305-mm spacing along the beam length. Two different types of shear connections are considered: (a) bolted/welded double-angle connections and (b) single-plate shear connections. The effects of slab continuity on the fire performance of the composite specimens were also experimentally evaluated. The slab continuity was provided by rotationally restraining the steel reinforcements, including four no. 4 rebars and wire mesh extended beyond the slab ends, at the location of support columns. Test results include a wide range of data sets including the characteristics of a test fire and structural loads as well as thermal and structural responses to fire. Structural loads are applied and measured by a set of hydraulic actuators with integrated load cells. The heat release rate and gas temperature measurements within the compartment are used to characterize a test fire. Thermocouples and thermal imaging cameras installed at various locations, including concrete slab, metal deck, shear connectors, and steel beam, are used to measure the temperature distribution throughout the specimen. Water-cooled camera systems and displacement sensors are deployed at various locations for both qualitative and quantitative measurements for the local and global deformations of the beam specimen and connections. The test results will be essential to assess the fire performance of shear connections and composite beam specimens subject to a structurally significant fire. The test data and the estimated uncertainty in structural-fire measurements can be used for validation of computational models, which will be eventually developed as design tools to advance performance-based design and engineering of steel-framed buildings for fire conditions.