The importance of slim decks has led engineers to the exploration of high-strength materials and also of innovative shallow shear connectors, such as composite dowels in the case of composite constructions. Minimizing the overall slab depth often leads to composite girders being weakened by means of web openings that are necessary for installations such as ventilation ducts. Depending on the geometrical and loading conditions, some of the shear connectors are subjected to a combination of tensile and shear forces. However, the load-bearing behaviour of these connectors has only been rudimentarily investigated in the case of shear-tensile interaction. In addition, the load-bearing capacity of composite dowels under combined tensile and shear forces has not been investigated in cracked concrete. Earlier investigations under pure shear and pure tensile loading indicate a dependence of the connectors’ load-bearing behaviour on the crack width, so that under combined loading, a similar influence is expected. In this paper, experimental investigations on composite dowels in transversely cracked concrete under systematically varied shear-tension loading combinations are presented. Hereby, predefined crack widths and patterns were considered using a special test rig. Finally, a design approach for concrete failure of composite dowels under shear-tension loading is proposed based on the test results.

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.

Composite dowels as shear connectors between steel profiles and concrete sections have been investigated for decades. The long-term aim is to develop consistent design approaches and implement them within Eurocode 4 covering both fields of bridge and building construction. Especially in building construction, where the concrete slabs are dimensioned increasingly slimmer in contrast to bridge construction, the composite dowels are positioned unavoidably close to free concrete surfaces (1). This causes further failure modes which have not been entirely investigated yet. At University of Kaiserslautern experimental push-out tests were performed within a research project in cooperation with RWTH Aachen University focusing on the behaviour of these composite dowels in dependence of varying influence parameters, such as the dowel's distance to the edge, the concrete strength and the position of the reinforcement stirrups. Some results showed a significant reduction of the load-bearing capacity and an affection of the deformability, mostly accompanied by the spalling of the concrete cover. Based on the tests, numerical simulations were calibrated and utilized to understand more about the load transfer mechanisms and to interpolate between existing experimental results. This paper will particularly show the influence of three parameters and present considerations on the load transfer model including further primary, secondary and tertiary failure mechanisms leading to the overall failure of the specimens.

Rib shear connectors are gaining increasingly attention in the field of composite constructions. Especially in bridge constructions, rib shear connectors offer many advantages compared to conventional composite shear connectors such as headed studs. In order to describe the load‐bearing behaviour of rib shear connectors under cyclic loading, the successively increasing slip resulting from the cyclic loading of the shear connectors must be taken into account. The latter leads to the growth of the relative displacements along the composite joint and thus, to the degradation of the previously rigid shear connection. This effect leads to rearrangements of internal forces between the composite partners through which the load bearing behaviour and load bearing capacity of the structure alter. In this article results of experimental investigations on two cyclic single Push‐Out‐Tests (sPOT) and one full‐scale girder test regarding the degradation of the composite interconnection are presented and analysed. The investigated shear connectors in the full‐scale girder test are subjected to a comparable load history to that of the connectors in the sPOT. The results give insight into the effects of the degradation of the shear connection, as previously seen in sPOT, on the overall load bearing behaviour of composite girders.