Fatigue of composite constructions with composite dowels: Fid-Bau Portal

Fatigue of composite constructions with composite dowels

Christou, Georgios / Classen, Martin / Wolters, Kevin / Broschart, Yannick

Composite dowels are being applied increasingly over the past years. Especially in the field of small and medium span bridges, composite dowels offer many advantages in comparison to other shear connectors. In contrast to headed studs, where initial steel cracks already occur after a few load cycles, composite dowels have a better resistance against dynamic loading and thus an increased lifetime. The bearing capacity of composite dowels is mainly characterized by the compression of the multiaxial stressed concrete in front of the composite dowel, where shear forces are transferred between steel and concrete. Here, the multiaxial compressive stress leads to increasing strains, that accumulate over the load cycles and lead to a cyclic growth of relative displacements in the composite connection. These relative displacements subsist of two strain‐components, the elastic and the plastic strains. The plastic strain remains constant in the connection, even after release of external loading. These permanent displacements are called inelastic slip. Due to this inelastic slip the characteristics of the static dowel curve might change significantly over the lifetime of the composite structure. The initially rigid connection between steel and concrete degrades over the lifetime and rearrangements of internal forces between the composite partners occur, which may impact the fatigue behaviour of the construction. The degradation of the composite connection can be considered by a cyclic dowel curve, which may be developed from the static dowel curve by introducing the inelastic slip. In this paper, results of cyclic shear tests are presented, in which the inelastic slip between steel and concrete and the relative slip of the steel dowel to the steel web are measured and compared.