Abstract:a method is proposed for structural damage detection of multi-story shear buildings under unknown earthquake excitation with partial observations of absolute acceleration responses. Based on sequential application of the extended Kalman estimator and least squares estimation, structural parameters above the first story of a building can be identified. Then, structural parameters of the first story can be identified from the frequency equation. Finally, the unknown earthquake excitation can be identified via the numerical solution of a first-order differential equation. It is shown by a numerical example that the proposed method can identify structural parameters and the earthquake excitation with good accuracy. Structural damage under unknown earthquake excitation can be detected by tacking the degrading of structural stiffness parameters.