Strain field distributions within a beam are frequently calculated using linear theory. However, linear beam theory does not provide solutions in the areas close to force application points, due to local strain perturbations caused by the force. Hence, interpretation of strain measurements taken by long-gauge sensors in proximity of force application point is difficult, as the measurements cannot be directly compared with analytical models. In addition, due to perturbation, sensors with different gauge lengths installed at that same location provide different values of measured strain. This paper explores and develops a potential analytical model for strain field perturbation in a beam's regions close to force application points, and investigates the influence of sensor gauge length on strain measurement in these areas. An analytical model derived by Seewald is modified in order to fit the sensor measurements. Based on the model, evaluation of strain measurement is performed taking into account the gauge length of the sensor. Results are validated using data from a real structure, Streicker Bridge at Princeton University campus.