An Integrated Methodology for Damage Identification in Existing Buildings Using Optimal Sensor Placement Techniques

Abstract eng:
In this study, a complete methodology for vibration based damage identification in important buildings in seismically active areas is investigated. In the first phase of the study, the buildings are instrumented with sensors and their modal parameters are determined using system identification techniques. These modal properties belong to the damaged state of the structure. In the second step, a detailed finite element (FE) model of the structure is developed. This initial FE model is then updated iteratively by minimizing the differences between the modal parameters obtained from the possibly damaged structure and the modal parameters obtained from the FE model with respect to the unknown model parameters which are the stiffness reduction factors. This is an ongoing study. The system identification and the model updating part of this study is published separately. In this paper, the focus will be on the optimal sensor placement (OSP) techniques and their aplication in civil engineering structures. This paper addresses the application of six different optimal sensor placement (OSP) techniques on building type structures with flexible joints. Different techniques that are implemented are the Effective Independence Method (EFI), Optimal Driving Point (ODP) based method, Non-Optimal Driving Point (NODP) based method, the Effective Independence Driving Point Residue Method and the Singular Value Decomposition (SVD) based method. The techniques are compared using the determinant, trace and the condition number of the Fisher Information Matrix. The results show that the Effective Independence (EFI) Method is the best and results in a sensor configuration possessing a smaller estimate error covariance matrix yielding better state estimates than the other methods. This study also shows that the SVD based and the EFI methods give the same final sensor configurations and are essentially identical except for the fact that SVD based method brings a criteria for deleting more number of sensors at one iteration. Next, the robustness of each sensor placement technique to the presence of noise in the measurements is investigated by the Modal Assurance Criteria Values (MAC) between the mode shapes obtained from the FE model and the noisy measurements. The best correlations are obtained from the EFI method. The results obtained from this study show that in structures with complex damage patterns, the sensor configurations must be based on OSP techniques. Within this context, EFI method used for on-orbit modal identification and correlation of LSS is promising for widespread use in civil structures. Structural health monitoring, optimal sensor placement, system identification, finite element

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