Studies on methodological developments in structural damage identification (original) (raw)
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Assessment of vibration-based damage identification techniques
Journal of Sound and Vibration, 2006
In this paper some usual vibration-based damage identification techniques (VBDIT) will be reviewed and used for structural damage evaluation. With the help of a simple supported beam with different damage levels the reliability of these techniques will be investigated. The techniques reviewed herein are based on measured modal parameters which use only few mode shapes and/or modal frequencies of the structure that can be easily obtained by dynamic tests. In other words, by realizing two sets of dynamic measurements, corresponding to two moments of the structure lifetime, the dynamic modal parameters can be obtained. In order to assess properly the performance of these techniques different noise levels are randomly introduced to the response signals of a simulated beam which is exited by a random force. For different levels of damage and noise, the probabilities of damage detection and the probabilities of false alarm for the total number of simulations is evaluated. It can be concluded that among the evaluated techniques the strain energy method presents the best stability regarding noisy signals; however, the detection judgement depends on a threshold level which is discussed in this paper. The change in mode shape curvature, change in flexibility and change in flexibility curvature methods are also capable to detect and localise damaged elements but in the case of complex and simultaneous damages these techniques show less efficiency. r
2012
In this paper dynamic testing of some civil engineering structures is presented. The investigated objects are prestressed and non-prestressed industrially produced concrete slab elements under laboratory conditions, as well as an in situ prestressed concrete bridge. In order to achieve damage assessment, different analyses based on modal parameters changes are done. To this end, the structures are artificially damaged by cutting locally their passive or prestressed steel reinforcement. Moreover, to cause cracks, the structures are loaded with a varying experimental mass. For modal analysis all objects are excited sinusoidally by an electrodynamic shaker in the laboratory and by special exciters in the case of the bridge. In this article, a set of modal parameters, i.e. eigenfrequencies and modes shapes are determined and compared according the damage states. It results that the shift of the eigenfrequencies is a valuable damage indicator whereas the modeshapes variations are small and more difficult to interpret. Further, the modal parameters are used to calculate the flexibility, i.e. the inverse stiffness matrix and their changes revealing clear differences according to the damage at the correct locations. In addition, the mode shape slope and curvature, as well as the bending and strain fractional energy method for the bridge are presented, indicating the loss of stiffness and hence the damage.
AN OVERVIEW OF MODAL-BASED DAMAGE IDENTIFICATION METHODS
This paper provides an overview of methods that examine changes in measured vibration response to detect, locate, and characterize damage in structural and mechanical systems. The basic idea behind this technology is that modal parameters (notably frequencies, mode shapes, and modal damping) are functions of the physical properties of the structure (mass, damping, and stiffness). Therefore, changes in the physical properties will cause detectable changes in the modal properties. The motivation for the development of this technology is first provided. The methods are then categorized according to various criteria such as the level of damage detection provided, model-based vs. non-model-based methods and linear vs. nonlinear methods. This overview is limited to methods that can be adapted to a wide range of structures (i.e., are not dependent on a particular assumed model form for the system such as beam-bending behavior and methods and that are not based on updating finite element models). Next, the methods are described in general terms including difficulties associated with their implementation and their fidelity. Past, current and future-planned applications of this technology to actual engineering systems are summarized. The paper concludes with a discussion of critical issues for future research in the area of modal-based damage identification.
Structural damage identification: a survey
Trends in computational structures …
This chapter is devoted to the description of several methods found in the literature that were developed and applied to solve the problem of structural damage identification. Because of the economical and safety advantages of its solution, the damage identification problem has been attracting the attention of the Civil, Mechanical and Aeronautical Engineering communities for several decades. The present survey is mainly focused on the inverse problems methodology and only deals with methods based on structural dynamic characteristics. In this survey, the methods are categorised in chronological order of appearance in the literature and grouped by the dynamic characteristics (e.g. natural frequencies and mode shapes) and the mathematical techniques (e.g. least squares) in which they are based. Since each method is, typically, only appropriated to certain type of structures, their characteristics are also described. The nature of the data used (numerical, experimental or numerical-experimental) to perform the damage identification is also pointed out. availability of a universal method which can be applied to all kinds of structures and damages types.
Journal of Structural …, 2004
The paper reports on relative performance of inverse eigensensitivity and response function methods for structural damage detection, location and quantification using vibration data. In implementing each of these methods, a validated baseline finite element (FE) model for the structure, in its undamaged state, is assumed to be available. Depending on this, a matrix of sensitivity of structural dynamic characteristics, in frequency or modal domains, to changes in values of structural parameters, is constructed. An inverse procedure, based on pseudoinverse theory of matrices, is subsequently applied to identify structural damages based on observed changes in vibration response of the structure. Issues arising out of mismatch between degrees of freedom of the FE model and number of measured degrees of freedom are dealt with by using alternative model reduction/expansion schemes. Illustrative examples on synthetically and experimentally generated vibration data on cantilever beams and a three-storied building frame are presented.
The purpose of this paper is to present an innovative application within the Non Destructive Testing field based upon vibration measurements developed by the authors during these past four years at the Department of Aeronautical Engineering of the University of Naples "Federico II" (Italy). This proposed new method is based upon the acquisition and comparison of the Frequency Response Functions (FRFs) of the monitored structure before and after damage occurs. Structural damage modifies the dynamic behaviour of a structure affecting its mass, stiffness and damping, and consequently the FRFs of a damaged structure, when compared with the FRFs of a sound structure, makes the identification, localization and quantification of structural damage possible. The activities presented in this paper focus mainly on a new FRFs processing technique based upon the determination of a representative "Damage Index" for identifying and analysing damage on real-scale aeronautical st...
Dynamic identification techniques to numerically detect the structural damage
Damage detection in civil engineering structures using changes in measured modal parameters is an area of research that has received notable attention in literature in recent years. In this paper two different experimental techniques for predicting damage location and severity have been considered: the Change in Mode Shapes Method and the Mode Shapes Curvature Method. The techniques have been applied to a simply supported finite element bridge model in which damage is simulated by reducing opportunely the flexural stiffness EI. The results show that a change in modal curvature is a significant damage indicator, while indexes like MAC and COMAC-extensively and correctly used for finite element model updating-lose their usefulness in order to damage detection.
Journal of Sound and Vibration, 2016
This paper presents numerical and experimental studies on modal behavior of cylindrical, lightly damped beam structures containing a notch-like crack with variable position and geometry. The numerical investigation utilizes the Finite-Element-Method (FEM) and a discretization strategy is developed that enables a crack to be represented in three dimensions. A test procedure capable of delivering a broadband impulse excitation to a flexible supported test specimen was developed. The customized excitation unit was used in conjunction with a Laser-Scanning-Vibrometer (LDV) to analyze a frequency range up to 40 kHz. The first 15 bending mode shape pairs with their corresponding eigenfrequencies are numerically and experimentally identified. The model updating is performed for the elastic parameters and the boundary conditions to minimize the deviation between experimentally determined and numerically calculated results in terms of eigenfrequencies. The acquired data are used in a two-stage damage identification procedure, in which suitable start vectors are found by the evaluation of objective function plots. Subsequently, geometrical crack parameters are identified. The deviations between real and determined crack positions range between 0.05 and 0.28 percent for crack depth/ diameter ratios of less than 7 percent.
Structural Damage Identification Using Modal Curvature Differences
Structural health monitoring is gaining high importance in conjunction with damage assessment and safety evaluation of structures. Vibration based damage identification techniques are global methods that are able to assess the condition of the entire structure at once. These methods are based on the fact that damage in a structure alters dynamic characteristics of the structure. The change is characterized by changes in the eigen parameters that are natural frequency, damping values and the mode shapes associated with each natural frequency. Damage can be identified by comparing the identified dynamic properties of the damage and undamaged structure. Modal-based damage detection methods, have received considerable attention in civil engineering applications. In the present work, method of modal curvature difference is employed for identifying and locating damage in beam models. Damage is considered as a localized reduction in structural stiffness. From the numerical simulations, it is observed that the absolute changes in modal curvature are localized in the region of damage and hence can be used to detect damage in a structure. The method is found successful for detecting and locating the damage in the beam models with different boundary conditions.