Identification Of Structures And Unknown Excitations Under Partial Response Measurements And Unknown Mass

The deterioration even cumulative damage of civil structures occurred by natural environment or human reasons may deteriorate the safety of structures and people.Therefore,it is of great importance to carry out health monitoring and damage detection of structures.In the past two decades,many researchers studied structural parameter identification and damage detection.However,a known structural mass is requested in this approach.Inaccuracy in the mass estimation can lead to errors in the structural identification results.Since the mass distribution information of civil infrastructures in service may be hard to be directly and correctly estimates.In addition,structural mass is likely to change under operational conditions.In the past decades,some researchers have studied structural identification without the mass information,but there are still some limitations:When the excitations are known,some researchers utilized the excitations and all response measurements forstructural identification,some methods considered partial responses for chain-like structures but with low efficiency.When structures under ambient excitations,some researchers utilized all response measurements for structural identification,and excitations are assumed as stationary ambient excitations.Some researchers considered structures under unknown external excitation,but the number of sensors and the placement position are required to meet the conditions,and excitations cannot be identified.Some structural identification methods are proposed for chain-like structures under unknwon seismic excitation by using the mass and response measurements of specific DOFs.Mowever,the relative accelerations cannot be observed under unknown ground motion.Recently,the research group has improved the extended Kalman filter(EKF)method:the extended Kalman filter with unknown excitation(EKF-UI)method for the simultaneous identification of structural and unknown excitation,and the generalized extended Kalman filter with unknown excitation(GEKF-UI)method which need not observe the responses at the excitation location while the EKF-UI have to.However,these EKF-based methods assume a known mass.Structural and unknown excitation identification methods under unknown mass are proposed in this thesis.The structural identification methods for chain-like structures and the beam-like structures under known excitation are proposed in the first part,which only needs the partial acceleration response observations.For chain-like structures,the structural element mass is directly identified based on the EKF method because of the lumped mass matrix.For the beam-like structures,structural masses are identified based on the EKF method and the least square method iteratively.The structural identification method for chain-like structures under ambient excitation and unknown mass information is proposed in the second part.with the mass information of any one DOF,structural mass and stiffness can be identified.Besides,Mass and stiffness changes can be identified with partial accerleration measurements but without the mass and the ambient excitation.This method considers stationary and non-stationary ambient excitation with good anti-noise capability.The third part focus on structural and unknown excitation identification methods for chain-like and beam-like structures under unknwon external excitation by using the partial acceleration and displacement responses.For chain-like structures,with any DOF’s mass information,the mass and excitation can be obtained.Besides,the parameter changes can be calculated without any mass information.For beam-like structures,as the mass is not lumped mass,it can be obtained based on the EKF-UI and least square method iteratively.The fourth chapter extend the method in the second part to the unknwon seismic excitation.The proposed method is based on the GEKF-UI method.With the mass information of any one DOF,structural element mass stiffness and the excitation can be identified.Besides,it can identify the the mass and stiffness changes of chain-like structures and the unknown seismic excitation without any structural mass information.The proposed method can directly use the partial absolute acceleration measurements,with displacement measurements to perform parameter identification and damage detection when the seismic excitation is unknwon.