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Total 102 records

    Harmonic class loading for damage identification in beams using wavelet analysis

    , Article Structural Health Monitoring ; Volume 6, Issue 1 , 2007 , Pages 67-80 ; 14759217 (ISSN) Khatam, H ; Golafshani, A. A ; Beheshti Aval, S. B ; Noori, M ; Sharif University of Technology
    2007
    Abstract
    The harmonic displacement response of a beam is utilized as the input signal function in wavelet analysis. Sudden changes in the spatial variation of transformed response identify the location of damages and defects. The damage incurred causes a change in the stiffness or mass of the beam. This causes a localized singularity which can be identified by a wavelet analysis of the displacement response. In this article, it is shown that using harmonic response is superior to the static deflection response and this approach is more effective in the presence of noise and more sensitive to the versatility of the applied harmonic loads. © 2007 SAGE Publications  

    Deep learning-based Models for Distributed Damage Detection and Quantification in Concrete Using Sinusoidal Ultrasonic Response Signals

    , M.Sc. Thesis Sharif University of Technology Ranjbar, Iman (Author) ; Toufigh, Vahab (Supervisor)
    Abstract
    In this thesis, supervised and unsupervised deep learning-based frameworks were proposed for distributed damage detection and quantification in concrete using sinusoidal ultrasonic response signals. Before the main study on ultrasonic-based concrete damage assessment, a preliminary study was performed on deep learning-based concrete compressive strength prediction. In this study, convolutional neural networks were utilized to predict the compressive strength of concrete through its mix proportions. The Genetic algorithm was employed to find the optimum number of filters in each convolutional layer of the convolutional neural networks. The proposed framework demonstrated high accuracy in... 

    Damage detection in an offshore jacket platform using genetic algorithm based finite element model updating with noisy modal data

    , Article Procedia Engineering, Solo, Jawa Tengah ; Volume 54 , March , 2013 , Pages 480-490 ; 18777058 (ISSN); 9781627486354 (ISBN) Malekzehtab, H ; Golafshani, A. A ; Sharif University of Technology
    2013
    Abstract
    Offshore jacket platforms are one of the most motivating structures for damage detection due to their importance and productivity. In this study, the application of finite element model updating in damage detection of an offshore jacket platform is investigated. The objective function of this method is based on the measured and analytical modal data, including natural frequencies and mode shapes. However, the measured data is expected to be noisy. Also, to avoid obtaining false damage results, a penalty term is added to the objective function. To update the model, genetic algorithm is utilized as a robust global searching tool. Afterward, the efficiency of this method is evaluated on several... 

    A mode conversion-based algorithm for detecting rectangular notch parameters in plates using Lamb waves

    , Article Archive of Applied Mechanics ; Volume 85, Issue 6 , 2015 , Pages 793-804 ; 09391533 (ISSN) Ghadami, A ; Behzad, M ; Mirdamadi, H. R ; Sharif University of Technology
    Springer Verlag  2015
    Abstract
    In this paper, an algorithm for identifying rectangular notch parameters as damage in a plate using Lamb waves is presented. In this algorithm, a combination of pulse-echo and pitch-catch methods is used. The method is divided into two steps: notch localization and notch geometry detection. The bases for this algorithm are mode conversion and scattering phenomena because of interaction of Lamb wave modes with defects. The method is applied to some numerical examples, and the results show that it can successfully identify all of rectangular notch parameters, i.e., its location, depth, and width  

    Structural damage detection using principal component analysis of frequency response function data

    , Article Structural Control and Health Monitoring ; Volume 27, Issue 7 , 2020 Esfandiari, A ; Nabiyan, M. S ; Rahimzadeh Rofooei, F ; Sharif University of Technology
    John Wiley and Sons Ltd  2020
    Abstract
    In this paper, a new sensitivity-based model updating method is presented based on the changes of principal components (PCs) of frequency response function (FRF). Structural damage estimation, identification of damage location and severity, is conducted by an innovative sensitivity relation. The sensitivity relation is derived by incorporating PC analysis (PCA) data obtained from the incomplete measured structural responses in a mathematical formulation and is then solved by the least square method. In order to demonstrate the performance of the proposed method, it is applied to a truss and a frame model. The results prove the ability of the method as a robust damage detection algorithm in... 

    Damage detection of offshore jacket structures using frequency domain selective measurements

    , Article Journal of Marine Science and Application ; Volume 12, Issue 2 , June , 2013 , Pages 193-199 ; 16719433 (ISSN) Kianian, M ; Golafshani, A. A ; Ghodrati, E ; Sharif University of Technology
    2013
    Abstract
    The development of damage detection techniques for offshore jacket structures is vital to prevent catastrophic events. This paper applies a frequency response based method for the purpose of structural healthCgreater detection efficiency. In addition, the performance of the proposed method was evaluated in relation to multiple damages. The aforementioned points are illustrated using the numerical study of a two dimensional jacket platform, and the results proved to be satisfactory utilizing the proposed methodology  

    A semi-baseline damage identification approach for complex structures using energy ratio correction technique

    , Article Structural Control and Health Monitoring ; Volume 25, Issue 2 , February , 2018 ; 15452255 (ISSN) Alem, B ; Abedian, A ; Sharif University of Technology
    John Wiley and Sons Ltd  2018
    Abstract
    Because damage identification results based on the Lamb waves propagation approach can be influenced by varying environmental and operational conditions, development of a robust monitoring system with no need of the prior measured data of the structure has gained much attention recently. The instantaneous baseline damage detection technique is one of the promising methods that overcome the mentioned obstacles. For this, the material properties, electromechanical characteristics, and the geometric features must be identical. Also, sensor distances in similar paths and the geometric dimensions of the transducers must be the same. So, implementing the instantaneous baseline damage... 

    Optimal sensors layout design based on reference-free damage localization with lamb wave propagation

    , Article Structural Control and Health Monitoring ; Volume 27, Issue 4 , 10 January , 2020 Keshavarz Motamed, P ; Abedian, A ; Nasiri, M ; Sharif University of Technology
    John Wiley and Sons Ltd  2020
    Abstract
    This study presents a new approach for designing optimal sensors layout based on accuracy of defect mapping. It is obtained from combination of the reference-free damage detection technique and the probability-based diagnostic imaging method. Considering damage indices based on continuous wavelet transform of sensors signals, the core of this study involves with development of a database of continuous wavelet transform features of a crack. In fact, the database contains the data from 594 different states in crack positions, orientations, and the considered sensing path lengths. Eventually, this database is used for localization of damage by interpolating the stored data collected from the... 

    Health monitoring of structures using few frequency response measurements

    , Article Scientia Iranica ; Volume 17, Issue 6 A , NOVEMBER-DECEMBER , 2010 , Pages 493-500 ; 10263098 (ISSN) Golafshani, A. A ; Kianian, M ; Ghodrati, E ; Sharif University of Technology
    2010
    Abstract
    The development of damage detection techniques for offshore jacket structures is vital for preventing catastrophic events. This paper applies a frequency response based method for the purpose of structural health monitoring. In this approach, the concept of a minimum rank perturbation theory is used. The feasibility of using a finite number of sensors and its effect on damage detection capabilities is investigated. In addition, the performance of the proposed method is evaluated in the case of multiple damages. The aforementioned points are illustrated using the numerical study of a two dimensional jacket platform  

    Reference-Free damage identification in Plate-Like structures using Lamb-Wave propagation with embedded piezoelectric sensors

    , Article Journal of Aerospace Engineering ; Volume 29, Issue 6 , 2016 ; 08931321 (ISSN) Alem, B ; Abedian, A ; Nasrollahi nasab, K ; Sharif University of Technology
    American Society of Civil Engineers (ASCE) 
    Abstract
    Structural health monitoring (SHM) has been adopted in the aircraft and civil industries over the last two decades. The ultrasonic guided wave propagation technique is a promising damage detection approach in airplane thin wall structures because of their long distance traveling ability and low attenuation. In fact, by efficiently designing the pattern of sensors one can effectively pick up the changes that happen in propagated signals due to presence of any kind of structural damage. This detection approach could be effectively assisted by numerical simulation techniques like finite-element modeling. To obtain a damage detection algorithm based on instantaneous baseline data, the... 

    Online nonlinear structural damage detection using hilbert Huang transform and artificial neural networks

    , Article Scientia Iranica ; Volume 26, Issue 3A , 2019 , Pages 1266-1279 ; 10263098 (ISSN) Vazirizade, M ; Bakhshi, A ; Bahar, O ; Sharif University of Technology
    Sharif University of Technology  2019
    Abstract
    In order to implement a damage detection strategy and assess the condition of a structure, Structural Health Monitoring (SHM) as a process plays a key role in structural reliability. This paper aims to present a methodology for online detection of damages that may occur during a strong ground excitation. In this regard, Empirical Mode Decomposition (EMD) is superseded by Ensemble Empirical Mode Decomposition (EEMD) in the Hilbert Huang Transformation (HHT). Although analogous with EMD, EEMD brings about more appropriate Intrinsic Mode Functions (IMFs). IMFs are employed to assess the first-mode frequency and mode shape. Afterwards, Artificial Neural Network (ANN) is applied to predict story... 

    Online nonlinear structural damage detection using hilbert huang transform and artificial neural networks

    , Article Scientia Iranica ; Volume 26, Issue 3A , 2019 , Pages 1266-1279 ; 10263098 (ISSN) Vazirizade, M ; Bakhshi, A ; Bahar, O ; Sharif University of Technology
    Sharif University of Technology  2019
    Abstract
    In order to implement a damage detection strategy and assess the condition of a structure, Structural Health Monitoring (SHM) as a process plays a key role in structural reliability. This paper aims to present a methodology for online detection of damages that may occur during a strong ground excitation. In this regard, Empirical Mode Decomposition (EMD) is superseded by Ensemble Empirical Mode Decomposition (EEMD) in the Hilbert Huang Transformation (HHT). Although analogous with EMD, EEMD brings about more appropriate Intrinsic Mode Functions (IMFs). IMFs are employed to assess the first-mode frequency and mode shape. Afterwards, Artificial Neural Network (ANN) is applied to predict story... 

    Experimental Investigations into Damage Detection Techniques in Concrete Beams

    , M.Sc. Thesis Sharif University of Technology Shafieyoon, Amirhossein (Author) ; Joghataie, Abdolreza (Supervisor)
    Abstract
    A simply supported reinforced concrete beam has been built at the concrete laboratory of Sharif University of Technology. The cross section of the beam has been rectangular and all the reinforcing steel bars have been placed at the bottom of the beam. A progressive damage has been applied to the beam first by cutting the concrete cover and then by cutting the reinforcing bars one at a time. The beam has been tested using forced vibration test where an impact hammer has been used to apply the external load. The acceleration of the beam has been recorded based on which the FRFs and then the corresponding modal parameters have been determined. Finally natural frequencies, MAC, COMAC and mode... 

    Identification of Damage Type and Location in Reinforced Concrete Piers of Slab– Beam Bridges Using Numerical Methods

    , M.Sc. Thesis Sharif University of Technology Hemmati, Omid (Author) ; Ahmadizadeh, Mahdi (Supervisor)
    Abstract
    Bridges are among the crucial elements of transportation networks, and play an important role in facilitating emergency relief efforts following earthquakes. For this reason, it is emparative to monitor their damages to ensure about their performace in earthquakes. The structure of a bridge is divided into two parts, namely the superstructure and substructure. Due to the relatively high rigidity and strength of superstructures, most of structural damage is usually concentrated in substructures, which may ultimately affect the overall stability of the bridge. Therefore, assessing the level of damage in the substructure is of utmost concern. This research attempts to evaluate the damage in the... 

    WT-SOBI Method Towards Blind System Identification of Structures

    , M.Sc. Thesis Sharif University of Technology Saremi, Shervin (Author) ; Kazemi , Mohammad Taghi (Supervisor)
    Abstract
    Blind source separation methods such as independent component analysis (ICA) and second order blind identification (SOBI) have shown considerable potential in the area of ambient vibration system identification. The objective of these methods is to separate the modal responses, or sources, from the measured output responses, without the knowledge of excitation. Several frequency domain and time domain methods have been proposed and successfully implemented in the literature. Whereas frequency-domain methods pose several challenges typical of dealing with signals in the frequency-domain, popular time domain methods such as NExT/ERA and SSI pose limitations in dealing with noise, low sensor... 

    Structural Health Monitoring Considering Nonlinear Behavior of Structures Using the Sensitivity of Time-Varying Modal Parameters

    , M.Sc. Thesis Sharif University of Technology Hosseini, Anahita Sadat (Author) ; Bakhshi, Ali (Supervisor)
    Abstract
    The process of implementing a damage detection strategy for aerospace, civil and mechanical engineering infrastructure is referred to as Structural Health Monitoring (SHM). Many portions of our technical infrastructure are approaching or exceeding their initial design life. As a result of economic issues, these civil, mechanical and aerospace structures are being used in spite of aging and the associated damage accumulation. Therefore, the ability to monitor the health of these structures is becoming increasingly important. In many cases, damage causes a structure that initially behaves in a predominantly linear manner to exhibit nonlinear response when subject to its operating environment.... 

    Estimating structural damage of steel moment frames by Endurance Time method

    , Article Journal of Constructional Steel Research ; Volume 64, Issue 2 , 2008 , Pages 145-155 ; 0143974X (ISSN) Estekanchi, H. E ; Arjomandi, K ; Vafai, A ; Sharif University of Technology
    2008
    Abstract
    In Endurance Time (ET) method, structures are subjected to gradually intensifying accelerograms and their performance is judged based on the maximum time duration in which they can satisfy the predefined endurance criteria. Damage indexes are used in ET method as the endurance criteria. In this paper, correlation between the values of various damage indexes as obtained from nonlinear time-history analysis of steel moment frames subjected to scaled earthquakes are compared with those from ET method at the same level of spectral acceleration. It is shown that the average value of various damage indexes can be estimated from ET analysis results. Advantages, accuracy and limitations of this... 

    Online detection of the breathing crack using an adaptive tracking technique

    , Article Acta Mechanica ; Volume 188, Issue 3-4 , 2007 , Pages 139-154 ; 00015970 (ISSN) Sholeh, K ; Vafai, A ; Kaveh, A ; Sharif University of Technology
    2007
    Abstract
    Early detection of structural damage is an important goal of any structural health monitoring system. Among numerous data analysis techniques, those which are used for online damage detection have received considerable attention recently, although the problem of online detection in continuous structures, for example beams, is quite challenging. In this paper, it is shown how the type, the size and the location of breathing cracks are identified online with the use of the records which are gathered from a continuous beam. For determining the existence of a breathing crack in a beam, its vibrating behavior is simulated. The algorithm of the least square estimation with the use of adaptive... 

    An empirical time-domain trend line-based bridge signal decomposing algorithm using Savitzky–Golay filter

    , Article Structural Control and Health Monitoring ; Volume 28, Issue 7 , 2021 ; 15452255 (ISSN) Kordestani, H ; Zhang, C ; Masri, S. F ; Shadabfar, M ; Sharif University of Technology
    John Wiley and Sons Ltd  2021
    Abstract
    This paper develops a trend line-based algorithm for signal decomposition in which the adjusted Savitzky–Golay filter is utilized to initiate the decomposition process. In this line, the proposed algorithm determines some special trend lines, mainly composed of the natural frequency of a bridge. An easy-to-implement algorithm is then provided to formulate this process and to decompose the given signal into its components in a systematic way. Additionally, a residual signal is generated by the proposed algorithm to store the detected noise and to reconstruct the original signal. To verify the proposed algorithm in the field of bridge health monitoring, a set of numerical and experimental... 

    Fatigue damage detection in large thin wall plate based on ultrasonic guided wave by using a piezoelectric sensor network

    , Article 29th Congress of the International Council of the Aeronautical Sciences, ICAS 2014 ; 2014 Alem, B ; Abedian, A ; Sharif University of Technology
    Abstract
    Today, structural Health monitoring is a major concern in the engineering community. Multisite fatigue damage, hidden cracks and corrosion in hard-to-reach locations are among the major flaws encountered in today's extensive diagnosis and/or prognosis of aircraft structures. Ultrasonic waves, lamb waves are particularly advantageous because of their propagation at large distances with little damp in thin-wall structures. In this paper a new rectangular shape array of embedded piezoelectric sensors is developed to detect some damages in large planar structures. An artificial neural network is trained to identify the damage state and its location. Output signals of each sensor due to various...