## 2 State of the Art of Fibre Design  
The intended softening respectively ductile material behaviour of fibre concretes can only be achieved, if the tested fibre design leads to fibre pullout instead of fibre rupture [1, 2]. Therefore, the fibres have to match to the strength properties of the concrete. Not all fibre types are in the same way suitable for each concrete type. This means, for example, that valuable high-strength micro steel fibres are much more suitable for concretes with higher strengths like UHPC [3, 4] and conventional hooked macro fibres are suitable for normal performance concrete (NPC). Studies on fibre pullout in high- and ultra-high performance concrete were carried out, e.g., in [5, 6, 7, 8, 9, 10].  
[PERSON] [5] points out that inclined embedded steel fibres exhibit higher pullout resistances compared to straight embedded fibres. The deflection of the fibre at the exit point of the fibre channel, where the fibre rubs against the wall, results in high frictional and therefore higher pullout forces. However, it might also be possible that inclined fibres cause spalling of concrete fragments at the edges to the main crack, which then reduce the rubbing and bending effects. In addition, high amounts of fibres in concrete lead to a very close fibre location and mechanical interaction of fibres in components might be expected.  
[PERSON] [6] investigates the dependence of the pullout resistance of micro steel fibres on the water-cement ratio (w/c ratio) and the embedment depth. A high w/c ratio leads to a higher porosity in the bond zone and lowers the pullout resistance, whereas a higher embedment depth increases the pullout resistance. In all carried out pullout tests the fibre pullout was always initiated under quasi-static loading.  
[PERSON] [7] states that pullout forces of inclined fibres are 1.8-2.7 times higher, compared to a straight fibre pullout. In addition, fibre rupture occurred in the pullout tests for fibres with a mechanical end anchorage. On the other hand, no fibre rupture was observed in pullout tests with straight fibres and no end anchorage.  
Refs. [8, 9, 10] contain fibre pullout test of high-strength steel fibres without mechanical anchorage in ultra-high-performance concrete. In all studies, continuous fibre pullout took place, which means that the activated bond stresses did not exceed the tensile strength of the fibre material. Furthermore, [10] includes pullout tests of individual fibres and fibre groups with different orientations. Similar to [5], concrete breakout at the fibre exit point was observed affecting the mechanical properties.  
In all the aforementioned works, no fibre rupture occurred under quasi-static loading, unless the fibres have a mechanical anchorage. However, the literature review does not clarify what happens with embedded fibres under cyclic loading. It could be possible that the fatigue resistance of the bare fibre material is higher than the fatigue resistance of the bond zone between fibre and concrete or vice versa. This might lead to either fibre rupture or fibre pullout.  
Results of investigations on the load-bearing behaviour of UHPC components with a 3D-fibre distribution under cyclic tensile loading are partly available, however, they are mainly limited to the derivation of S/N-curves [11, 12, 13]. The findings of the investigationsleave the question unanswered, whether embedded fibres pull out of the concrete matrix or rupture in the crack area under cyclic loading.