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

中文翻译：

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钢-混凝土连续组合箱梁负弯矩疲劳性能试验研究

实验结果表明了复合梁在负弯矩区域的疲劳性能以及在反复荷载下复合梁的刚度和变形的变化。在两个双层复合梁上进行了疲劳测试。得到了在完全剪力连接下具有不同配筋率的复合梁的疲劳性能，以及在疲劳载荷下挠度，钢筋的应变，钢梁的应变以及裂纹扩展的变化。结果表明，低配筋率的混凝土板的抗疲劳性能远低于高配筋率的混凝土板，而在疲劳载荷下，负弯矩区域焊钉的应力较小，滑移率较大。几乎可以忽略不计。刚度的下降和裂纹的发展主要是由于混凝土和钢筋之间的粘结滑移的下降。疲劳破坏模式是在负弯矩区域上筋的断裂。这项研究获得的结果有助于复合梁的设计。