Fire resistance of two types of composite beams constrained by rigid joint

Abstract

To study the fire resistance of different types of composite beams in integral structures, transient state tests were performed on two-span composite beams (one span is a monolithic composite beam with a laminated slab and the other span is a composite beam with a cast-in-place slab) with rigid beam-to-column connections. The temperature distribution, displacement changes, and failure modes of the two types of composite beams were evaluated in tests mimicking the entire process of a real fire disaster. The following results were obtained in this study. Under the influence of fire, cracks of different patterns were formed on different types of composite beams. When the heating was stopped, the temperature of the steel beam experienced a sudden and sharp drop, whereas the temperature of the concrete slab rose within a short period of time. These behaviours cause the composite beam to undergo retraction in a reverse arch shape during deformation. Severe buckling occurred in the lower flange under the two ends of the steel beam as well as the web of the steel beam. During the test, the welds at both ends of the laminated-slab composite beam were cracked, whereas those at both ends of the composite beam with a cast-in-place slab remained undamaged. Finally, a method for calculating the axial force of the composite beam that considers the constraints at the beam ends is proposed in this study. The calculation results are in good agreement with the experimental test results.