In the sensors of control systems for civil structures faults may occur due to strong earthquakes and affect the control results.This paper focuses on the semi-active fault tolerance control of structures using MR dampers.First

the semi-active H∞ control based on state observer is studied and applied to the seismic response control of building structures using MR damper.The modified Bouc-Wen model is used to calculate the control force of MR dampers.The H∞ based active control law is obtained by solving a Riccati equation and a state observer equation.Then the clipped-optimal method is applied to implement the semi-active control.The faults of sensors are diagnosed online based on the output residual signals by a series of observers and the magnitudes of fault are acquired by comparing the state values of the state observers.The measured value of faulted sensor is modified to eliminate the influence of sensor faults on the closedloop system and to implement semi-active H∞ fault tolerance control.The numerical simulation results show that the proposed method can achieve the great fault tolerance control effect on the earthquake-excited structures.