This paper presents an extensive experimental investigation on the effect of circular holes with and without reinforcement on glulam joists' behaviour. The tests consider the variability of hole position, number and strength class of the beam. Furthermore, a finite element model based on fracture mechanics was developed and validated against the experimental force-displacement curves of thirteen configurations. The model reproduces crack initiation and propagation through the adoption of cohesive contact layers. The satisfactory agreement with the experimental data has been the base of extensive parametric analyses considering multiple beam and hole geometry selections and two load arrangements at the upper and lower side of the beam. Finally, the results of the parametric analyses, initially used for a qualitative understanding of the structural behaviour, are used for calibrating probabilistic capacity models of the capacity of simply supported beams with circular holes. The mechanics-based probabilistic model calculates the capacity as the product between the analytical capacity associated with the reduced cross-section and an adimensional correction factor. The factor is expressed as a linear combination of a set of explanatory variables selected after a step-wise deletion process.