Steel-Concrete Composite Floor Systems Subject to Fire, Phase 1

This study deals with compartment fire experiments on 12.8 m long composite floor beams with various end support conditions. Each specimen was constructed as a partially-composite beam, consisting of a lightweight concrete slab cast on 76 mm (3 in.) deep ribbed steel decking and a W18 x 35 steel beam acting compositely via 19 mm (3/4 in.) diameter steel headed stud anchors welded on the top flange. Test variables included two types of simple shear connections (shear-tab and welded-bolted double-angle connections) and the presence or absence of slab continuity over girders. Hydraulic actuators were used to apply gravity loads to the specimen under fire conditions. The natural gas-fueled burners were used to create a compartment fire with the maximum heat release rate of 4000 kW. This study evaluated the characteristics of the fire loading and thermal and structural responses of the specimens. The test results indicated that the thermal restraint conditions significantly affected the behavior and failure modes of the specimens with simple shear connections. The specimens resisted gravity loads at large vertical displacements near midspan (approximately a ratio of the span length over 20) without collapse under fire loading. Various limit states and vulnerabilities to fires were observed, including local buckling of the steel beams near supports, flexural failure (yielding of steel beams and concrete fracture near restrained end supports), and connection failure (weld shear or bolt shear) during heating and cooling which could lead to partial or total collapse of the floor system.