Fatigue assessment includes estimation of the expected damage accumulation and the remaining life-time of the structure. This work is based on output-only vibration measurements at a limited number of locations provided by a sensor network installed on the structure. For the fatigue damage assessment, the stress time responses are obtained by using the vibration sensor data and a modal expansion approach enabling predictions of stresses at positions where sensor installation is not possible. A methodology for the prediction of stresses based on the combination of a finite element numerical model and the accelerations recorded at measurement locations is presented in this paper.