Sharif Digital Repository

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  

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... 

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  

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... 

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  

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... 

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... 

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  

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... 

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... 

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... 

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... 

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... 

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... 

Estimation of damage to structures after severe earthquakes is important for loss estimation and is an essential step for rescue program. Using seismic or spectral parameters could be a quick method for this purpose. In this article damage estimation for some world's destructive earthquakes has been carried out. For this purpose some earthquake seismic parameters, response spectra and damage indices have been calculated and compared. Damage indices are calculated for three types of intermediate sway concrete frame buildings, i.e. low-rise, mid-rise and high-rise, designed according to Iranian Seismic Code and ACI 318-95. Finally the trend between earthquake seismic parameters, response...