Fatigue behavior of composite dowels due to the interacting damage processes of steel and concrete

钢-混凝土组合梁的组合销钉是垂直焊接到钢梁顶部法兰上的钢带，或用于桥梁建设的具有向上开放凹槽的单法兰钢型材腹板。在这里，钢、混凝土或两者结合的疲劳过程可能导致复合销钉的过早疲劳失效。混凝土的损伤过程是由裂缝处的多轴应力状态引起的，导致周期性的非弹性滑移增加。非弹性滑移在加载周期中积累，并且在连接中保持恒定，即使在释放外部加载之后也是如此。裂纹在钢带中的萌生和扩展显著增强了钢带的非弹性滑移。非弹性滑移导致组合作用的减小，导致钢梁和混凝土板局部弯矩的增加，以及沿组合连接处内力的重新排列。因此，桥梁设计中假定的钢与混凝土之间初始刚性连接的假设就失效了。多轴混凝土疲劳与钢疲劳之间复杂的相互作用以及内力的重排问题尚未得到研究。本项目通过试验和理论研究，分析了钢和混凝土的相互作用损伤过程，以阐明和模拟复合钉的疲劳行为。

Composite dowels for steel-concrete-composite beams are either steel strips welded vertically to the top flange of steel beams or webs of single-flange-steel profiles that have upward open recesses for use in bridge construction. Here, fatigue processes of the steel, the concrete or a combination of both can lead to a premature fatigue failure of the composite dowel. The damage processes of the concrete result from a multiaxial stress state in the recesses, leading to a cyclical inelastic slip increase. The inelastic slip accumulates over the load cycles and remains constant in the connection, even after release of external loading. Crack initiation and crack propagation in the steel strip enhance the inelastic slip, significantly. The inelastic slip causes a reduction of composite action yielding an increase of local bending moments in the steel beam and the concrete slab as well as rearrangements of internal forces along the composite connection. In consequence, the hypothesis of an initially rigid connection between steel and concrete, which is assumed in bridge design, becomes invalid. The complex interactions between multiaxial concrete fatigue and steel fatigue as well as the rearrangement of internal forces were not yet the subject of research. In this project, the interacting damage processes of steel and concrete are analyzed by experimental and theoretical investigations in order to clarify and model the fatigue behavior of composite dowels.