The monitoring of timber bridges during their service life is important for the maintenance plans of these structures. Numerical modelling can integrate the monitoring techniques by reducing the needed inspections and the maintenance costs. In this paper a 3D computational model based on a well assessed multi-Fickian theory is implemented in Abaqus FEM code. The hygro-thermal response of a timber pedestrian bridge is simulated during a period of its service life. The numerical results are in agreement with measurements taken by a sensor-based technique. Conclusions are given on the moisture gradients which could generate the so-called moisture induced stresses (MIS).