Dynamic identification techniques to numerically detect the structural damage (original) (raw)
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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.
MODAL CURVATURE AND MODE SHAPE BASED DAMAGE IDENTIFICATION OF STRUCTURE FROM INCOMPLETE MODAL DATA
Modal curvature and Mode shape are two powerful damage estimation parameters. In this paper, an error equational error is formed by accommodating the separate errors obtained by considering both the modal characteristics and allowing equal weightage for the both. Thereafter with the help of sensitivity analysis, changes due to damage in the parameter i.e. flexural rigidity for beam model are successfully identified. The effectiveness of the proposed method can be underlined from the fact that the minimal errors were obtained from both noisy and noise free data analysis. The validation of this technique is performed with the help of a cantilever beam taken as an example and comparisons of both analytical with measured experimental data. Apart from the cantilever beam, a simple supported beam has also been taken as an example to affirm the effectiveness of the algorithm.
Damage detection in bridges using accurate modal parameters
Finite Elements in Analysis and Design, 2004
Damage identiÿcation in civil engineering structures using the dynamic system parameters has become an important area of research. A reliable, time and cost e ective method is therefore required to evaluate and localize damage using the changes in dynamic parameters between the intact and damage states. The dynamic parameters must be calculated in as accurate manner as possible. In the present work, eigenvalue analysis is carried out using Lanczos algorithm in an adaptive h-version ÿnite element environment in order to control the discretization error for accurate evaluation of modal parameters. Standard Ahmed Shell elements have been used for the discretization of bridge deck. Changes of natural frequencies between the damaged and intact model have been observed. A better localization of damage could be done by considering curvature of the mode shapes, which shows more sensitivity than the mode shapes themselves. Numerical studies are conducted to demonstrate the necessity of adaptive eigenfrequency analysis by considering simply supported and continuous bridges containing damaged parts at di erent locations and their usefulness in the application for damage detection in the ÿeld.
Damage Detection in Large Structures Using Modes Shapes and Its Derivatives
International Journal of Research in Engineering and Technology, 2015
Synopsis: Many techniques for structural damage detection using modal parameters have been developed over few years because the modal parameters are easily obtained from free, forced and ambient conditions. Many of the techniques have shown that mode shape curvature is efficient to localize damage in continuous system. Focusing on the damage detection/localization of typical Indian Railway bridges, in this paper, a numerical model of an existing steel truss Indian Railway Bridge (discrete system) was developed to check the validity of the mathematical model for continuous shear beam. Numerical model was based on the design drawings of the structure and Eigen value analysis was performed to extract modal parameters. Damage was simulated by modifying the member properties of particular truss members. Results demonstrate that change in fundamental mode shape due damage to a member is an excellent indicator of damage localization because it is discontinuous at damage location. Change in higher derivatives (slope and curvature) of the fundamental mode shape is found to have improved sensitivity in damage localization. These results are similar to those of the shear beams. However, the damage signature is different. Further studies are needed to understand such signatures for meaningful application of the method for existing structures.
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.
A Numerical Study of Using Changes in Mode Shapes for Structural Damage Detection
Damage detection using changes in global dynamic characteristics has been a hot research topic in recent years. In this paper, a numerical study of the relationship between damage characteristics and the changes in the dynamic characteristics is presented. It is shown that both slope and curvature mode shapes are sensitive indicators of damage. The numerical results clarify that the curvature mode shape is more localized than the slope mode shape, which is suitable to detect damage. Furthermore, it is found that finer grid of measurements is needed to increase the sensitivity of these two indices, especially, in using the changes in slope mode shapes.
Damage Identification in a Plate-Like Structure Using Modal Data
Aviation, 2013
In this paper, an on-going research effort aimed at detecting and localising damage in plate-like structures by using mode shape curvature–based damage detection algorithms is described. Two alternative damage indexes are examined. The first one uses exclusively mode shape curvature data from the damaged structure. This method was originally developed for beam-like structures. In this paper, the method is generalised to plate-like structures that are characterised by two-dimensional mode shape curvature. To examine limitations of the method, several sets of simulated data are applied and damage detection results are compared to the damage identification method that requires mode shape information from both the undamaged and the damaged states of the structure. The modal frequencies and the corresponding mode shapes for the first 15 modes of a plate are obtained via finite element models. Simulated test cases include damage of various levels of severity. In order to ascertain the sen...
Damage identification in plate-like structure using mode shape derivatives
In this paper, a newdamage indicator based onmodal data, such as mode shapes and its derivatives, is presented for damage identification in plate-like structures. The proposed indicator is determined using modal analysis information extracted from a finite element code in MATLAB. After obtaining the mode shapes, the slope and curvature of the plate in each mode are calculated based on central finite difference methods. A numerical example with and without noise is considered to evaluate the exact location of different damage scenarios. In order to validate the proposed indicator for structural damage detection, the obtained results have been compared with another study which was based on experimental data. Moreover, in order to better assess the performance of the proposed indicator, a comparison has been made between the proposed indicator and two well-known indicators found in the literature. The results indicate that the proposed damaged indicator is able to detect precisely the location of single and multiple damage cases having different characteristics in plate-like structures.
Archives of Civil and Mechanical Engineering, 2011
A new algorithm to determine the damage magnitude in structural elements by combining modal parameters is proposed in this study. The algorithm is based on the combined effect of both the natural frequencies and mode shapes when a change in stiffness of the structural element occurs. In order to demonstrate the significance and capability of this new algorithm, the magnitude of damage was calculated from a finite element model of a beam-like structure model and comparisons with previous algorithms were carried out. The new technique CPI (Combined Parameter Index) compares the factor of reduction in stiffness according to reduction in natural frequencies and also the factor of reduction in stiffness according to change in mode shape. Different damage levels starting from reduction in stiffness of 1% were adopted to validate the sensitivity of the new algorithm CPI to detect the damage at different levels of severity. Mid-span and quarter-span damage positions were adopted to verify the capability of the new damage algorithm CPI to detect the damage location. Moreover damage in support condition was investigated in order to ascertain that the new damage algorithm CPI can also identify support damage cases. The results indicate that the new algorithm has better ability and higher sensitivity to determine the severity of the damage due to stiffness changes in the element or support. In addition, the CPI exhibits sensitivity to detect lower level of damage occurring at earlier stage by having the ability to detect a damage of 1% reduction in the structural element stiffness or elastic bearing stiffness.
Archives of Civil and Mechanical Engineering, 2011
A new index for detecting the damage severity in structural elements by combining modal parameters is proposed in this study. The index is based on the combined effect of both the natural frequencies and mode shapes when a change in stiffness of the structural element occurs. In order to demonstrate the significance and capability of this new algorithm, the magnitude of damage was calculated from a finite element model of a beam-like structure model and comparisons with previous algorithms were carried out. The new index called Combined Parameter Index (CPI) compares the factor of reduction in stiffness according to reduction in natural frequencies and also the factor of reduction in stiffness according to change in mode shape. Various damage levels starting from reduction in stiffness of 1% were adopted to validate the sensitivity of the new index to detect the damage severity at various deterioration levels. Mid-span and quarter-span damage positions were adopted to verify the capability of the new damage index to detect the damage severity at various locations. Moreover, damage in support condition was investigated in order to ascertain that the new damage index can also identify support damage cases. The results indicate that the new index has better ability and higher sensitivity to determine the severity of the damage due to stiffness changes in the element or support. In addition, the CPI exhibits sensitivity to detect lower level of damage occurring at earlier stage by having the ability to detect a damage of 1% reduction in the structural element stiffness or elastic bearing stiffness. www.sciencedirect.com/science/article/pii/S1644966512601034