In view of the crucial role of bridges in transport networks and the ageing of Europe’s infrastructure, research into failure mechanisms of concrete bridges and advanced monitoring technologies has intensified in recent years. The OpenBridgeLab is a full-scale research bridge that was specifically constructed to enable controlled investigation of several failure modes and the trial of innovative sensing strategies. Given the complexity of the OpenBridgeLab, rigorous preparatory analyses are essential to ensure the safety and success of full-scale experimental tests. This paper presents the numerical workflow that was implemented to support a controlled full-scale load test on an instrumented girder of the OpenBridgeLab bridge. Two independent finite element (FE) models were developed using different commercial FE software packages and cross-validated to minimise software-specific bias and increase model confidence. The numerical modelling workflow is described in detail, covering geometric idealisation, discretisation strategy, explicit modelling of reinforcement and prestressing systems, and the applied boundary and loading conditions. Based on measurements obtained under uncritical, non-damaging loading, selected model parameters were adjusted in the linear-elastic range to achieve a plausible representation of the global structural response of the undamaged bridge. The calibrated models were subsequently used to support the planning of a staged load test by identifying critical structural regions and defining admissible load levels. The monitoring data obtained during the staged full-scale load test were used for a qualitative comparison with numerical results and to support a critical discussion of the modelling assumptions and their limitations. The paper emphasizes reproducible modelling and calibration procedures and summarises lessons learned regarding modelling uncertainties and potential sources of error, with the aim of supporting the cautious and informed use of the FE method in the assessment and load testing of prestressed concrete bridges.