The experimental work presents results on the fatigue performance of composite beams in the negative moment region and the\nchanges of stiffness and deformation of composite beams under repeated loads; fatigue tests were carried out on two double-layer\ncomposite beams. The fatigue performance of composite beams with different reinforcement ratios under complete shear\nconnection and the variation of deflection, strain of the reinforcement, strain of steel beam, and crack growth under fatigue load\nwere obtained. The results showed that the fatigue resistance performance of concrete slab with low reinforcement ratio was much\nlower than that of concrete slab with high reinforcement ratio whereas, under the fatigue load, the stress of the welding nail in the\nnegative moment region was small and the slip was almost negligible. The degradation of stiffness and the development of cracks\nwere mainly due to the degradation of bond-slip between the concrete and reinforcement. The fatigue failure mode was the\nfracture of the upper reinforcement in negative moment region. The results obtained in this study are helpful in the design of\ncomposite beam.
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