An integrated vibration-based structural health monitoring system

Continuous monitoring of the health of a structure is a requirement desirable for many engineering structures, to obtain early warning of impeding disasters, which is important in both civil and aerospace applications. However, the complexity of large structures and the difficulty in accessing them makes the use of traditional non-destructive evaluation, such as visual inspection and instrument evaluation methods, impractical. An effective alternative is the use of methods that depend on vibration-based damage identification. These methods are based on measurement of changes in the modal characteristics of the structure, that is, its frequencies and mode shapes, to identify changes in its physical properties. However, vibration-based damage identification (VBDI) still faces a number of challenges that have not been fully resolved. The incompleteness of measured mode shapes, the challenges posed by the selection of the set of identification modes and ensuring the fidelity of the finite element model (FEM) of the monitored structure, and the mathematical complexity of the identification algorithm are the issues that must be addressed to ensure satisfactory performance of the VBDI techniques.; The objective of this work is to develop an improved approach to damage detection that may significantly enhance the ability of the optimal matrix update detection algorithms in identifying damage in complex structures, using limited number of measured degrees of freedom.; A new set of criteria is developed for an optimal selection of the response points. The selection criteria are used to determine the minimum number of measurement degrees of freedom, which would constitute an adequate modal database for model-based identification algorithms and at the same time preserve the identity of the set of identification modes. An existing mode selection criterion is modified for use in damage identification and for the selection of a FEM reduction/expansion technique that would have the ability of preserving the modal properties of the original model for a selected set of modes. A new combination of two simple mathematical algorithms, modal residual and nonlinear optimization, is used to identify damage location and extent.; The theoretical background of the proposed VBDI approach is derived. Computer simulation studies are presented. They show the feasibility of the proposed VBDI approach as well as its limitations. Some of the challenges are highlighted through modal tests designed to provide estimates of damage in a three dimensional eight-bay free-free frame used for the experimental validation of the proposed approach. The construction of a finite element model of the structure and its correlation with measured test data are described. Details of tests on a healthy structure as well as on a structure in which several predetermined damage scenarios have been introduced are presented. Test data and damage identification results are presented. The proposed VBDI approach is found to be successful in predicting single and multiple damage sites using a limited amount of modal data of a truncated set of incomplete identification modes, provided the damage is significant.