An experimental investigation of functionally graded reinforced concrete beams with layers of engineered cementitious composites was carried out. The main most objective was to evaluate the damage to the beams under free–free constraints using a non-destructive, vibration-based impact method. Damage levels were assessed at 50, 70 and 90% of ultimate load. Dynamic characteristics such as damping, fundamental natural frequencies, mode shapes and frequency response functions at each level were assessed by means of hammer excitation. The investigation showed that damage levels could be accurately evaluated through discrepancies in natural frequency compared to an undamaged beam. A finite-element analysis for the undamaged condition under free–free constraints was undertaken and compared with the experimental natural frequency values to validate the vibration-based test method.