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

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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.