With the occurrence of higher and more frequent axle loads on roads, in particular bridge deck slabs are more severely solicitated by fatigue loading. To avoid heavy interventions for strengthening of deck slabs, an improved building material is used, namely Ultra-High Performance Fibre Reinforced Concrete with steel rebars (reinforced UHPFRC = R-UHPFRC). By adding a thin (30 to 50 mm) layer of R-UHPFRC on top of the bridge deck slab, the required fatigue resistance and load carrying capacity may be restored and improved. In addition, the R-UHPFRC layer is waterproof which provides durability. This paper presents a model to describe the fatigue behaviour of reinforced concrete (RC) slab-like beams strengthened with R-UHPFRC leading to RU-RC beams. The model determines stress and deformation evolution in components of the RU-RC beam by considering decrease of UHPFRC stiffness due to fatigue. Comparison with available experimental results shows that the model can accurately represent the beam behaviour. Force distribution among components of the RU-RC beam reveals efficient fatigue resistant behaviour of the RU-RC beam, by which R-UHPFRC is demonstrated to be an effective element for fatigue strengthening of RC member.