Detection of Cracks in Beam Structures Using Modal Analysis

2011 ◽  
Vol 105-107 ◽  
pp. 689-694
Author(s):  
Pallab Das
Keyword(s):  
Natural Frequencies ◽  
Concrete Beams ◽  
Mode Shapes ◽  
Modal Parameters ◽  
Multiple Cracks ◽  
Flexibility Matrix ◽  
Numerical Studies ◽  
Linear Fracture ◽  
Eigen Value ◽  
Local Flexibility

In the present study, the modal parameters of cracked plain cement concrete beams have been studied theoretically. A crack in a beam element introduces considerable local flexibility, which has been expressed by local flexibility matrix, the dimension of which depends upon the numbers of degree of freedom considered. An approach based on linear fracture mechanics theory has been used to find flexibility matrix for the cracked element. The FEM program has been developed for eigen-value problems to determine the modal parameters of the cracked beams. Changes in natural frequencies and mode shapes between the damaged and intact beam have been observed. Numerical studies are performed by considering simply supported beam with single and multiple cracks at different locations with different crack depths.

Analysis of Modal Parameters of Adhesively Bonded Double-Strap Joints by the Modal Strain Energy Method

1993 ◽  
Author(s):  
Mohan D. Rao ◽  
Krishna M. Gorrepati
Keyword(s):  
Strain Energy ◽  
Natural Frequencies ◽  
Structural Parameters ◽  
Flexural Vibration ◽  
Mode Shapes ◽  
Modal Parameters ◽  
Adhesively Bonded ◽  
Modal Strain Energy ◽  
Joint System ◽  
Damping Material

Abstract This paper presents the analysis of modal parameters (natural frequencies, damping ratios and mode shapes) of a simply supported beam with adhesively bonded double-strap joint by the finite-element based Modal Strain Energy (MSE) method using ANSYS 4.4A software. The results obtained by the MSE method are compared with closed form analytical solutions previously obtained by the first author for flexural vibration of the same system. Good agreement has been obtained between the two methods for both the natural frequencies and system loss factors. The effects of structural parameters and material properties of the adhesive on the modal properties of the joint system are also studied which are useful in the design of the joint system for passive vibration and noise control. In order to evaluate the MSE and analytical results, some experiments were conducted using aluminum double-strap joint with 3M ISD112 damping material. The experimental results agreed well with both analytical and MSE results indicating the validity of both analytical and MSE methods. Finally, a comparative study has been conducted using various commercially available damping materials to evaluate their relative merits for use in the design of these joints.

scholarly journals Vibration-Based Damage Assessment in Gravity-Based Wind Turbine Tower under Various Waves

2019 ◽  
Vol 2019 ◽  
pp. 1-17 ◽  
Author(s):  
Cong-Uy Nguyen ◽  
So-Young Lee ◽  
Heon-Tae Kim ◽  
Jeong-Tae Kim
Keyword(s):  
Wind Turbine ◽  
Damage Assessment ◽  
Natural Frequencies ◽  
Modal Identification ◽  
Mode Shapes ◽  
Modal Parameters ◽  
Damage Scenarios ◽  
Wind Turbine Tower ◽  
Induced Variation ◽  
Wave Induced

In this study, the feasibility of vibration-based damage assessment in a wind turbine tower (WTT) with gravity-based foundation (GBF) under various waves is numerically investigated. Firstly, a finite element model is constructed for the GBF WTT which consists of a tower, caisson, and foundation bed. Eigenvalue analysis is performed to identify a few vibration modes of interest, which represent complex behaviors of a flexible tower, rigid caisson, and deformable foundation. Secondly, wave-induced dynamic pressures are analyzed for a few selected wave conditions and damage scenarios are also designed to simulate the main components of the target GBF WTT. Thirdly, forced vibration responses of the GBF WTT are analyzed for the wave-induced excitation. Then modal parameters (i.e., natural frequencies and mode shapes) are extracted by using a combined use of time-domain and frequency-domain modal identification methods. Finally, the variation of modal parameters is estimated by measuring relative changes in natural frequencies and mode shapes in order to quantify the damage-induced effects. Also, the wave-induced variation of modal parameters is estimated to relatively assess the effect of various wave actions on the damage-induced variation of modal parameters.

Vibratory Parameters of Blades From Coordinate Measurement Machine (CMM) Data

2005 ◽  
Author(s):  
Alok Sinha ◽  
Benjamin Hall ◽  
Brice Cassenti ◽  
Gary Hilbert
Keyword(s):  
Finite Element ◽  
Proper Orthogonal Decomposition ◽  
Natural Frequencies ◽  
Orthogonal Decomposition ◽  
Mode Shapes ◽  
Modal Parameters ◽  
Coordinate Measurement ◽  
Coordinate Measurement Machine ◽  
Bladed Rotor ◽  
Proper Orthogonal

This paper deals with the development of a procedure to model geometric variations of blades. Specifically, vibratory parameters of blades are extracted from CMM data on an integrally bladed rotor (IBR). The method is based on proper orthogonal decomposition (POD) of CMM data, solid modeling and finite element techniques. In addition to obtaining natural frequencies and mode shapes of each blade on an IBR, statistics of these modal parameters are also computed and characterized. Numerical results are validated by comparison with experimental results.

Detection of Concrete Spalling Using Changes in Modal Flexibility

2010 ◽  
Vol 163-167 ◽  
pp. 2598-2602
Author(s):  
Nadia Hajihasani ◽  
Norhisham Bakhary
Keyword(s):  
Natural Frequencies ◽  
Mode Shapes ◽  
Modal Parameters ◽  
Dynamic Parameters ◽  
Numerical Example ◽  
Damage Location ◽  
Modal Flexibility ◽  
Vibration Parameters

This paper presents a study in the effect of spalling to dynamic parameters such as natural frequencies and mode shapes. Numerical example of a slab is used as an example in this study. The slab will be modelled using ANSYS 11.0 and various types of spalling are imposed. The changes of vibration parameters are monitored and compared. To compare the sensitivity of modal parameters to spalling is determined using the flexibility method. Based on the results it is found that by incorporating mode shapes using flexibility method, damage location and severity can be obtained.

scholarly journals Identifying the stiffness parameters of a structure using a subspace approach and the Gram–Schmidt process in a wavelet domain

2017 ◽  
Vol 9 (7) ◽  
pp. 168781401770764 ◽  
Author(s):  
Wei-Chih Su ◽  
Chiung-Shiann Huang ◽  
Ho-Cheng Lien ◽  
Quang-Tuyen Le
Keyword(s):  
Stiffness Matrix ◽  
Natural Frequencies ◽  
Shaking Table Test ◽  
State Space Model ◽  
Measured Data ◽  
Shaking Table ◽  
Mode Shapes ◽  
Modal Parameters ◽  
Wavelet Domain ◽  
Space Model

This article presents a procedure to improve the accuracy of calculated stiffness matrix of a structure based on the identified modal parameters from its measured responses. First, a continuous wavelet transform is applied to the measured responses of a structure, and the state–space model can be reconstructed by the wavelet coefficients of acceleration that can be obtained from the measured noisy responses. The modal parameters are identified using the subspace approach. Second, the identified mode shapes are corrected via Gram–Schmidt process. Finally, the identified natural frequencies and the corrected mode shapes in previous steps are utilized to build the stiffness matrix of structure. The accuracy of the proposed approach is numerically confirmed, and the noise effects on the ability to precisely identify the stiffness matrix are also investigated. The measured data of two eight-story steel frames in a shaking table test are analyzed to demonstrate the applicability of the procedure to real structures.

Role of Dynamic Testing in Assessment of Bridges

1997 ◽  
Vol 1594 (1) ◽  
pp. 115-124 ◽  
Author(s):  
P. C. Das ◽  
J. S. Owen ◽  
B. J. Eccles ◽  
M. A. Woodings ◽  
B. S. Choo
Keyword(s):  
Reinforced Concrete ◽  
Natural Frequencies ◽  
Concrete Beams ◽  
Dynamic Testing ◽  
Reinforced Concrete Beams ◽  
Mode Shapes ◽  
Ambient Conditions ◽  
Frequency Changes ◽  
Frequency Ratios

Six reinforced concrete beams were loaded incrementally up to failure. After each increment the load was removed and measurements of the modal properties of the beams were made by impulse testing. The variation of the natural frequencies, frequency ratios, mode shapes, and the level of damage were investigated. It was found that on completion of the tests the natural frequencies of the beams had been reduced by an average of 25 percent in each mode. However, changes in mode shape were very small, and appreciable differences were only observed when the damage was highly localized. Modeling of the beam by using finite elements predicted trends that compared well with experimental observations. It is concluded that if dynamic testing were used in monitoring reinforced concrete structures, then the changes in frequency due to initial concrete cracking or yield of the reinforcement could be detected. More useful information associated with the spread and type of cracking through a structure may be detectable, although the level of the frequency changes is of the same order as those due to changes in ambient conditions.

Analysis of Modal Parameters of Adhesively Bonded Double-Strap Joints by the Modal Strain Energy Method

1996 ◽  
Vol 118 (1) ◽  
pp. 28-35 ◽  
Author(s):  
K. M. Gorrepati ◽  
M. D. Rao
Keyword(s):  
Strain Energy ◽  
Natural Frequencies ◽  
Structural Parameters ◽  
Flexural Vibration ◽  
Mode Shapes ◽  
Modal Parameters ◽  
Adhesively Bonded ◽  
Modal Strain Energy ◽  
Joint System ◽  
Damping Material

This paper presents the analysis of modal parameters (natural frequencies, damping and mode shapes) of a simply supported beam with adhesively bonded double-strap joint by the finite-element based Modal Strain Energy (MSE) method using ANSYS 4.4A software. The results obtained by the MSE method are compared with closed form analytical solutions previously obtained by the author for flexural vibration of the same system. Good agreement has been obtained between the two methods for both the natural frequencies and system loss factors. The effects of structural parameters and material properties of the adhesive on the modal properties of the joint system are also studied which are useful in the design of the joint system for passive vibration and noise control. In order to evaluate the MSE and analytical results, some experiments were conducted using aluminum double-strap joints with 3M ISD112 damping material. The experimental results agreed well with both analytical and MSE results indicating the validity of both analytical and MSE methods. Finally, a comparative study has been conducted using various commercially available damping materials to evaluate their relative merits for use in the design of these joints.

A Normalized Modal Eigenvalue Approach for Resolving Modal Interaction

1997 ◽  
Vol 119 (3) ◽  
pp. 647-650 ◽  
Author(s):  
M.-T. Yang ◽  
J. H. Griffin
Keyword(s):  
Monte Carlo ◽  
Eigenvalue Problem ◽  
Perturbation Analysis ◽  
Material Properties ◽  
Natural Frequencies ◽  
Mode Shapes ◽  
Modal Parameters ◽  
Modal Interaction ◽  
Eigenvalue Approach ◽  
The Difference

Modal interaction refers to the way that the modes of a structure interact when its geometry and material properties are perturbed. The amount of interaction between the neighboring modes depends on the closeness of the natural frequencies, the mode shapes, and the magnitude and distribution of the perturbation. By formulating the structural eigenvalue problem as a normalized modal eigenvalue problem, it is shown that the amount of interaction in two modes can be simply characterized by six normalized modal parameters and the difference between the normalized frequencies. In this paper, the statistical behaviors of the normalized frequencies and modes are investigated based on a perturbation analysis. The results are independently verified by Monte Carlo simulations.

scholarly journals Finite Element Modeling of the Dynamic Properties of Composite Steel–Polymer Concrete Beams

Materials ◽  
2020 ◽  
Vol 13 (7) ◽  
pp. 1630
Author(s):  
Paweł Dunaj ◽  
Stefan Berczyński ◽  
Marcin Chodźko ◽  
Beata Niesterowicz
Keyword(s):  
Finite Element ◽  
Frequency Response ◽  
Natural Frequencies ◽  
Concrete Beams ◽  
Dynamic Properties ◽  
Mode Shapes ◽  
Polymer Concrete ◽  
Response Functions ◽  
Full Agreement ◽  
High Agreement

This paper presents a method for modeling the dynamic properties of steel–polymer concrete beams, the basic structural components of machine tools, assembly lines, vibratory machines, and other structures subjected to time-varying loads during operation. The presented method of modeling steel–polymer concrete beams was developed using the finite element method. Three models of beams differing in cross-sectional dimensions showed high agreement with experimental data: relative error in the case of natural frequencies did not exceed 5% (2.2% on average), the models were characterized by the full agreement of mode shapes and high agreement of frequency response functions with the results of experimental tests. Additionally, the developed beam models supported the reliable description of complex structures, as demonstrated on a spatial frame, obtaining a relative error for natural frequencies of less than 3% (on average 1.7%). Full agreement with the mode shapes and high agreement with the frequency response functions were achieved in the analyzed frequency range.

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