Several New Methods For Vibration-based Damage Identification Of Structures

The vibration-based damage identification technique can identify, localize and quantify the damage of structures through analysing vibration responses with intelligent algorithms; it can be used in real time monitoring and fast periodical detection whenever necessary, also it can save manpower. Since the late1970s, vibration-based damage identification methods have received considerable attention and many methods have been developed. However, it still suffers from some limitations, such as high sensitivity to noise, high-dependence on accuracy of structural numerical models and low sensitivity to damage; challenges still remain.The present work is about the study of vibration-based structural damage identification methods (damage localization and damage severity identification), and the main purpose is to develop some new damage identification methods which are model-free, robust enough against the noise and also sensitive to the small damage. The research contents are listed in detail as follows:(1) A guidance has been provided regarding the conditions under which the respective formulations of the observation matrix C should be used, which results in the higher accuracy of the damage identification. The present work has studied the SDLV method from its key (i.e. the extraction of Q matrix without the excitation information) to the influence of different C matrices on Q matrix. Additionally, several strategies of sensor layout to achieve the effective performance with the SDLV method with limited measured nodes of two common truss structures have been explored based on the force balance method. The present work has also proposed the precise damage localization based on the SDLV method for local damage on some key truss members. Experimental and numerical validation of these points have been achieved based on two common truss structures.(2) The present work has proposed a damage localization method based on LU(QR) decomposition of the proportional flexibility matrix. The modal flexibility matrix can be extracted only with the first several modal parameters. However, the mass-normalized mode shapes can be achieved when input excitation (or at least at one measured point) is known, which is usually not available in practice. The proportional flexibility matrix is used and different damage indices based on its LU(QR) decomposition are used for various types of structures, and it has been validated based on a shear building model and a truss model. (3) The above two methods have been only designed as damage localization methods, damage quantification has not been considered. Here, four cost functions and the corresponding damage severity identification methods have been proposed. Pulse responses/the first several mode shapes at the damaged elements/and the substructure including the damaged elements have been selected as objective vectors; correlation coefficient and modal assurance criterion have been selected as mathematical tools to describe the similarity between the objective vectors and the corresponding vectors in the updated finite element model. Finally, finite element model updating-based four cost functions have been validated using a beam model and a truss model through experiments and simulations.(4) The present work has studied/proposed five structural damage features:fractal dimension, approximate entropy, logarithmic acceleration energy, degree of dispersion and jerk energy. Moreover, the curvature method, mean and probability method are combined to deal with the proposed damage features. As a result, two methods, i.e. the mean normalized curvature difference method and the curvature difference probability method for every damage feature are developed. Their feasibility has been validated in several types of laboratory models with numerical simulation and experiments with different noise levels. Moreover, damage localization of suspenders (hangers) and cables in the long-span bridges have been studied based on the above five and another new (i.e. the improved logarithmic acceleration energy) damage features. The results show these methods are sensitive to small damage, robust enough against the noise, and these methods do not require the finite element model of the measured structures, which avoid the error in the process of parameter identification and finite element modeling.The proposed methods in this work can be used in the vibration-based damage identification for real-time health monitoring or periodical detection. The research objects refer to the following numerical examples and laboratory models:a shear building model, a beam model, a truss model, a suspension bridge numerical model, an arch bridge numerical model and a cable-stayed bridge numerical model.