This paper presents the results of a numerical study carried out by the authors to better understand the structural behavior of prestressed beams with a complex geometry and to identify numerical modelling techniques that allow to adequately predict such behavior. UltraHigh Performance Fibre Reinfored Concrete (UHPC) beams with and without openings are considered, with a focus on shear controlled failure modes. For all the beams considered in this study, prestressing is used to resist the main bending moment. However, no other reinforcement is added to the beams in order to emphasize the structural contribution of the fibers and to focus on solutions that could be economically competitive for the precast industry. The results of non-linear simulations performed with existing finite elements codes are compared and validated against experimental results of tests carried out at the University of Applied Sciences of Western Switzerland. The main assumptions of the numerical simulations are discussed, as well as the results and the limits of the analysis.