A new damage identification method for a coupled rod system with close and repeated natural frequencies is presented. The equation of motion for the coupled system is established from finite element analysis. The dynamic responses of the system are obtained from state-space method. And the dynamic responses of the system are used for damage detection. The local damage of the system is modeled by a reduction in the elemental tensile stiffness. The dynamic response sensitivity with respect to the damage parameter (elemental tensile stiffness) is then derived. In the inverse analysis

the local damages in the system are identified from dynamic response sensitivity-based finite element model updating method. It is found that the local damage(s) can be identified successfully from several dynamic response measurements. The effect of artificial measurement noise on the identified results is also discussed. Numerical simulation shows that the proposed method is insensitive to the measurement noise and with very good accuracy. This shows that the proposed method has the potential for real application.