Prescriptive fire-resistance ratings for structural components provide limited insight into the system-level performance of steel-concrete composite structures in fire. Specifically, long- span composite beam assemblies exposed to fire have vulnerabilities resulting from thermal restraint conditions that can be vastly different from those in short-span assemblies. This paper presents an overview of recent experiments on 12.8 m composite beams with various end support conditions, exposed to combined structural and fire loading. This paper focuses on the results for the specimens with double-angle beam-to-column connections, with and without slab continuity. The experiments showed that the specimens experienced similar thermal and displacement behaviour during the first 40 minutes after ignition. The specimens exhibited local buckling of the beam near the connection, at the average bottom flange temperature of 400 °C. Forces in the continuity bars increased when this local buckling occurred but decreased due to concrete fracture as the vertical displacement of the specimen increased. A thermal gradient in the specimen was observed during the heating and cooling phase. This specimen did not collapse during the fire until its vertical displacement exceeded 1/20 span length. The collapse failure was observed during the cooling phase, which was resulted from weld fracture of the beam end connection due to contraction of the heated beam as it cooled down.
SiF18 - The 10th International Conference on Structures in Fire
June 6-8, 2018
Composite beams, double-angle connections, compartment fires, fire tests