A Method of Modal Expansion for Structural Damage Detection LIU Hui 1 , QU Wei-lian 1, YUAN Run-zhang 2 (1.School of Civil Engineering and Architecture, Wuhan University of Technology, Wuhan 430070,China; 2.State Key Laboratory of Advanced Technology for Materials Synthesis and Processing, Wuhan University of Technology,Wuhan 430070,China)Measurements yield only partial mode shapes with respect to the total degrees-of-freedom corresponding to the finite-element model. The common practice to bridge the gap is to expand the measured mode shape to the total degrees-of-freedom of the finite-element model. Unfortunately, the damage detection method based on expansion modal shapes used dynamic expansion method or modal reduction method that can’t bring out right location. In order to use the measured incomplete mode shapes to detect damage,it put forward a new modal expansion method. Unmeasured modal shapes can be represented undamaged structural modal shapes and changes before and after the occurrence of damage in the structure. The complete modal shapes can be obtained by determining the changes before and after the occurrence of damage in the structure. At last, numerical example shows that this approach is effective for detecting structural damage using the optimum and incomplete modal shapes.complete mode; modal expansion; damage detection