Nonlinear Restoring Force Identification Of MDOF Structures Under Limited Measurements

Based on the measured structures responses and basic principles of structure dynamics,the physical parameters of structures are identified.And then,the condition and the damage of structures can be described,which can be used for the state performance evaluation as a whole.It is crucial to retrofit and strengthen the structures,and improve the structural performance in the area of civil engineering.Actually,it is difficult to describe the structural nonlinear characteristics with an accurate parametric model.Furthermore,in all the responses of engineering structures,the acceleration responses are most easily measured.However,it is hard to realize that acceleration responses at all degrees of freedom are measured using the sensors in the structures,especially in the large-scale structures.Therefore,it is highly desired to develop a general structural damage approach in model free under limited measurements.Based on the above actual background,a general mas and structural hysteretic force identification approach was proposed.Acceleration responses and excitation at part of the degrees of the freedom are employed to develop the approach.It is of significance to identify the damage and evaluate the performance under strong dynamic loadings.The main contents of this thesis include:(1)A nonlinear restoring force and mass identification approach for MDOF structures based on double Chebyshev polynomial modal which is employed to describe the structural nonlinear restoring force using structural acceleration response at limited degree of freedoms(DOFs)with Extended Kalman Filter(EKF)and the Unscented Kalman Filter(UKF)was proposed at first.(2)In the numerical simulation study,the EKF was applied to identify the stiffness and damping coefficients of a multi-degree-of-freedom(MDOF)linear systems under unlimited and limited accelerations measurements.(3)And then,on the premise of known MR damper parametric model and assumption on the stiffness,damping and mass,the EKF was applied to a nonlinear system with MR dampers,an iterative structural hysteretic behavior and mass identification approach was proposed under limited acceleration responses.Furthermore,based on the UKF and the chebyshev polynomial model,without the use of any parametric models of the nonlinear restoring force,and assumption on the stiffness damping and mass,a nonlinear restoring force and mass distribution identification approach using limited acceleration measurements under incomplete excitation condition was proposed.(4)In the dynamic test,the feasibility of the proposed approach which uses the UKF and double Chebyshev polynomial modal to identify the structural nonlinear restoring force and mass by the limited measurements was illustrated with a four-story steel frame structure equipped with two MR dampers employed to simulate structural nonlinearity.The comparative analysis was made between the identification results and the measured nonlinear restoring force of MR dampers.