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Modal-based damage-detection algorithms were used to identify the location of defects commonly found in timber and to estimate
their severities. In this study, the authors propose modifications to an existing damage-detection algorithm for locating
and evaluating damage by comparing the modal strain energy before and after damage using the first tw...
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... end support of the beam to the other end as shown in Fig. 1. The impact location, at 3/4 of the span length, was selected so that more modes can be excited, simultaneously. The HP VXI with LMS general acquisition monitor was used to record the dynamic response at 10,000 Hz sampling rate for 8,192 data points. LMS frequency domain direct measurement curve-fitting technique was used to obtain the modal frequencies and mode shapes from the measured FRFs. Using the EMA, five vibration modes, with a frequency bandwidth ranging from10Hz to 200 Hz, were captured. However in this paper, only the first two flexural modes were needed. From the nine- point experimental mode shape, a new mode shape vector with 41 points can be reconstructed using cubic spline interpolation technique. The reconstructed mode shape increases reliability and accuracy of damage detection when it is used in damage detection algorithms. In this investigation, the damage index method developed by Kim and Stubbs adopted and modified (named as modified damage index (MDI)) to detect the inflicted damage. The MDI pertaining to damage localisation is based on the relative differences in modal strain energy between an undamaged structure and that of the damaged structure. The modal strain energy utilises derivatives of mode shape, i.e. mode shape curvature, and the algorithm used to calculate the damage index for the j th element and the i th ...
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Citations
... Some damage indicators based on mode shapes, mode curvature, or statistic algorithms have been proposed for detecting and locating local damage with different severities, locations, and numbers in wooden beams (Yang et al. 2002(Yang et al. , 2003Hu and Afzal 2006). An improved damage detection algorithm by modal strain energy was attempted to accurately detect and locate the local damage for wooden beams (Choi et al. 2007). Modal strain energy (MSE)-based damage identification methods have been successfully applied to machinery, bridges, and other projects to achieve damage detection and localization (Shi et al. 1998;Liu et al. 2017;Ghiasi et al. 2018;Wang and Xu 2019;Khosravan et al. 2021). ...
... Because the degree and location of the damage to the damaged beam are unknown, j is also used in Eq. 3. According to the above equations, the damage index developed by Choi was adopted and modified as follows (Choi et al. 2007 ...
A damage detection and localization method for wooden beams was proposed based on the modal strain energy (MSE) change and evidence fusion. The fused damage indicator was deduced using the first three mode shapes of the wooden beams before and after damage. The finite element modal analysis of the free-supported undamaged and damaged wooden beams with different damage severities at one or two locations was performed. The first three mode shapes were extracted from the corresponding modal analysis, with which the damage indicator based on the MSE change and the fused damage indicator of each damage case were computed. The simulation results show that the fused damage indicator accurately detected and located the damage with different severities at one or two locations. Finally, the modal test was completed using the same damage cases as the finite element simulation. The frequency functions of the whole beam were first obtained, with which the first three experimental mode shapes were then acquired, and the damage indicator based on the MSE change and the fused indicator were further computed. The test results verified the validity and reliability of the proposed damage indicator.
... For instance, it is known from studies carried on wooden beams that rot, as well as other structural defects, reduce the stiffness of the material as quantified by the value of its MOE. As a consequence it is found that the frequency of resonance, or eigenfrequency, of the flexural modes is also diminished, however, without too appreciably affecting the shape of these bending modes (Yang et al 2002;Choi et al 2007). ...
Trees may be subject to rot-inducing agents that degrade the strength of the material making their trunk, and decrease the quality of their crop. Several techniques, both non-destructive and destructive, are available for assessing the extent of damage caused by rot in a tree trunk. The present work presents the results of a preliminary study conducted on a palm tree trunk for isolating a specific mode from its response to a vibrational excitation, namely the so-called “ovalling” mode. This latter is cross-sectional and in a circular cylinder manifests itself relatively locally, i.e. has little dependence on the lateral extension of the cylinder. An experimental modal analysis is made on a piece of a date palm tree trunk when set into vibration through a radial mechanical excitation, and the response is collected at points along a circumference on the trunk. The value of the resonance frequency of the ovalling mode was found to be somehow variable, probably resulting from some coupling phenomena between various modes of vibration due to the inhomogeneity, anisotropy and fibre-like structure of the trunk wood. As rot usually affects markedly the strength of the trunk wood, the frequency of the ovalling mode, which depends on the strength of the material, can be used for estimating the severity of rot attack in the trunk. A numerical simulation is also made to a cylinder as a simplified representation of a tree trunk.
... Fan [7] established a finite-element model of a wooden frame and adopted a damage identification method combining the wavelet packet analysis method and stochastic resonance theory to evaluate the damage location and degree of damage of the structure. Choi [8] adopted a model-based damage detection method to identify the locations of common damage defects in wood and estimate the degree of damage. Hu and Afzal [9] proposed a new statistical algorithm, which was validated by the numerical simulation of different degrees of damage and damage locations of wooden beams. ...
A damage location method for the autocorrelation peak value change rate based on the vibration response of a random vibration structure is established. To calculate the autocorrelation function of the vibration response of each measurement point, we transformed the maximum values into an autocorrelation peak vector. Under a good condition, the autocorrelation peak vector has a fixed shape; hence, it can be used as a basis for structural damage identification. The two adjacent measurement points with the largest change corresponding to the two nodes of the damage unit and the damage location are determined to calculate the change rate of the autocorrelation peak values between damaged and intact structures. When the degree of damage is 5%, the autocorrelation peak value change rate of the acceleration response on the two nodes of the damage unit is significantly greater than that of the other points, which can accurately determine the damage location, indicating that the damage location index constructed has good damage sensitivity. The damage location index can determine a single damage, as well as a double damage. The antinoise capability of the damage location index gradually improves with an increase in the degree of damage. At 45% degree of damage and signal-to-noise ratio (SNR) of 0 dB, the damage location index can still accurately determine the damage location, which has good antinoise interference capability. The Xi’an Bell Tower is used as a case study, and the feasibility of this method is verified, which provides a new method for the study of damage location of ancient timber structures.
... Osterloh et al. [5] achieved the high-quality images with X-rays or gamma radiation to establish the location and extent of the timber damage. Choi et al. [6] proposed a modified damage index algorithm to locate the multiple damages and to evaluate the severity of timber damage, by normalizing the modal shape curvature and strain energy. However, generally speaking, complex equipment and algorithms are always needed for these methods. ...
Nowadays, the electromechanical impedance method has been widely used in the field of structural healthy monitoring, especially for the concrete and steel materials. However, the electromechanical impedance studies on damage detection for timber are limited due to the anisotropic and ununiform biomaterial properties. As a low-cost and environment-friendly building material, timber has been widely used in the construction. Thus, it is beneficial to develop electromechanical impedance technique for structural healthy monitoring of timber so as to ensure the stability and safety of the entire timber structures. In this paper, two damage factors, i.e., the damage location factor and the damage size factor of timber specimens are investigated by using the electromechanical impedance method. The method is implemented by using a patch of Lead Zirconate Titanate transducer both as an actuator to generate stress waves and a sensor to detect stress waves after propagating across the timber specimens. Then, the damage index-root mean square deviation is employed to evaluate the damage severity of the timber specimens. The results indicate that the damage index changes consistently with the change of damage location and size factors, and the proposed method using electromechanical impedance technique can efficiently estimate the damage and its severity.
... This approach requires that the correlation between the model parameters and the damage is known. It is therefore necessary that preliminary tests on damaged specimens are performed [59]. ...
... The presence of delaminations or cracks changes the dynamic behaviour of the element and this could be detected by changes in the dynamic properties. These techniques have been successful in detecting and locating damage under laboratory conditions [59], but are highly dependent on the support conditions of the members, which could change depending on re-tightening of bolts or friction in the connections. In addition, the lower modal frequencies typically measured during vibration tests are less sensitive to damage than higher frequencies, which are more difficult to measure, and the number of sensors required to correctly identify dynamic properties and locate the crack can be quite high. ...
Significant developments in structural health monitoring (SHM) and in non-destructive testing (NDT) and damage identification techniques for structural timber elements have led to an increasing interest in the application of these technologies. However, specific aspects of timber structures (anisotropy, moisture dependency, high variability), the wide range and novelty of available systems, and the need to adapt them for each configuration, makes specifying and implementing a SHM system a non-trivial task, heavily dependent on previous experience. This article presents a comprehensive review of available SHM and NDT methods, case studies, and a survey on the implementation of SHM in timber structures.
... Moreover, studies conducted on wood beams indicated that rot, as well as other structural defects, reduce the strength of the material as quantified by the value of its MoE. Therefore, the frequency of resonance of the flexural, or bending, modes are also diminished without significantly affecting the shape of these modes (Choi et al. 2007). Henceforth, this study focuses on a specific mode of vibration, the ovalling mode, in which the particles of the wood material in the trunk are moving radially with respect to the axis of the trunk. ...
Palm trees, like all other tree species, are living entities that may be subject to the attack of several natural agents which affect the strength of the trunk. The most serious of these damaging agents are parasites and rot fungi, which proliferate in the substance of the stem, destroying its cells and fibers and weakening it. Consequently, this decay affects the physical characteristics of the modes of vibration in the tree trunk regarding resonance frequency, shape, and damping. Advanced stages of rot infection in a tree trunk may reach such an extreme level that substantial amounts of its solid mass are removed, ultimately leading to a hollow trunk rather than one of substance. In cases like these, the trunk presents less resistance to forced vibrations, and the active modes affecting the cross section of the trunk exhibit decreased resonance frequency values. This paper aims to present a method based on vibrations which might be employed for tracking a specific mode of radial vibrations known as the ovalling mode. To achieve this goal, the trunk of a palm tree was set into vibration via mechanical excitation in the radial direction and its response at some specific point on the trunk was examined. This method uses a single concentrated source of excitation and two vibration sensors, which are diametrically positioned and fastened to the surface of the tree trunk. The ovalling mode might be extracted from the frequency response by adding the signals recorded by the two sensors, which are in phase for a test specimen with a perfectly circular, cylindrical shape made of homogeneous, isotropic material. This study provides a preliminary investigation into the feasibility and reliability of this nondestructive method when applied for the identification of rot hosting by the trunks of standing trees, wooden poles, and logs, as well as the level of severity of rot attack.
... Pin impact tests, stress wave detection, and drilling resistance detection are the more common methods , but it is difficult to carry out a comprehensive and accurate assessment of the internal damage of wooden structures using only one method. To make up for the shortcomings of each method, different detection methods have been combined to analyze quantitatively and qualitatively the internal damage of wood Ge et al. 2014;Wang and Allison 2008;Ouis and Zerizer 2006;Choi et al. 2007). Moreover, there are already several publications reporting on the determination of weights related to the combination of different nondestructive tests (Chang et al. 2016a,b;Dai et al. 2017;Chang et al. 2019;Wang et al. 2019). ...
In order to improve the detection precision of internal defect in the ancient wooden structures, defect simulation tests on pine and elm commonly used in ancient buildings were performed by using stress wave detection and drilling resistance detection. Based on detection data, three typical evaluation criteria, which are the information entropy, the correlation coefficient, and residual sum of squares, were selected as a priori information. Combining with the expert's fuzzy evaluation value, Bayesian formula was used to modify the prior information to determine the weight coefficients of the two detection methods, and a combined prediction model was established. The results show that the combination of subjectivity and objectivity enables the revised weights to more reasonably and accurately reflect the relative importance of each detection method in prediction evaluation, which reduces the forecasting error. Specifically speaking, the mean error of the combined model was reduced by 49.8% and 59.8%, respectively, compared with stress wave detection and drilling resistance detection. Moreover, the five error indicators of this combined forecasting model are the smallest in all methods, indicating the proposed method has a better forecasting effect. It provides an effective application tool for the practice of forecasting the internal defects of wooden components in ancient buildings.
... Nowadays, the most commonly used timber connections [5][6][7][8][9] in industries include the mortise-tenon joint, connections through screws, bolts, nails, dowels, tooth plates, rings, and glued connections. With the development of timber constructions [10], the investigations and optimal design of timber connection have received increasing attention over the past decades [11]. ...
Timber structures have been widely used due to their low-cost and environmental-friendly properties. It is essential to monitor connection damage to ensure the stability and safety of entire timber structures since timber connection damage may induce catastrophic incidents if not detected in a timely manner. However, the current investigations on timber connections focus on mechanical properties and failure modes, and the damage detection of timber connection receives rare attention. Therefore, in this paper, we investigate the damage detection of four common timber connections (i.e., the screw connection, the bolt connection, the decussation connection, and the tooth plate connection) by using the active sensing method. The active sensing method was implemented by using a pair of lead zirconate titanate (PZT) transducers: one PZT patch is used as an actuator to generate stress waves, and the other works as a sensor to detect stress waves after propagating across the timber connection. Based on the wavelet packet energy analysis, the signal energy levels of received stress waves under different damage extent are quantified. Finally, by comparing the signal energy between the intact status and the damage status of the timber connection, we find that the energy attenuates with increasing severity of the connection damage. The experimental results demonstrate that the active sensing method can realize real-time monitoring of timber connection damage, which can guide further investigations.
... All this includes diagnostics using vibration based damage detection methods [4][5][6]. Therefore, at present, the requirements to methods for diagnosing the state of building structures are increasing -they should enable to quickly and fully evaluate the actual characteristics of structural elements and structures, and be simple and mobile to be used at the design, construction, operation, repair and reconstruction stages [7][8]. ...
Conducting surveys of multi-storey buildings is a laborious task, because large volumes of visual and instrumental research should be carried out. Reduction of labor costs with an increase in the reliability of information about the state of damage and technical condition is an actual scientific and practical task. One of the ways to solve it is to use non-destructive vibration diagnostic methods. The purpose of carrying out diagnostics with the use of vibration based damage detection methods is to search for damages in structural elements that can cause the deviation of the dynamic parameters of a structure from calculated ones. Determination of the dynamic parameters of the structure, in particular natural frequencies and mode shapes of mechanical systems, is one of the most important tasks that allows obtaining integral information about the state of a structure. This article presents the results of calculations for the localization of slabs defects in a multi-storey building with a transverse crack, span L = 4.5 (m), height H = 0.2 (m), with prestressed reinforcement d = 0.05 (m). Vibration based Damage Index method was used to localize the defect. During the study, reliable localization values of the defect area of the slab were obtained, this indicates that the vibration method for determining the damage index with a sufficient degree of accuracy allowed predicting the site of damage to the structure.
... Timber, which is a ubiquitous natural resource, is used widely across many countries as a building material [1,2]. Timber is an inhomogeneous, anisotropic organic material whose mechanical properties are affected by several factors, such as its specific cellular structure, as well as the physical, and chemical conditions of the surrounding environment. ...
In recent years, the piezoceramic transducer-enabled active sensing technique has been extensively applied to structural damage detection and health monitoring, in civil engineering. Being abundant and renewable, timber has been widely used as a building material in many countries. However, one of the more challenging applications of timber, in construction, is the potential damage caused by moisture. Increased moisture may cause easier warping of timber components and encourage corrosion of integrated metal members, on top of potentially causing rot and decay. However, despite numerous efforts to inspect and monitor the moisture content of timber, there lacks a method that can provide truly real time, quantitative, and non-invasive measurement of timber moisture. Thus, the research presented in this paper investigated the feasibility of moisture-content monitoring using an active sensing approach, as enabled by a pair of the Lead Zirconate Titanate (PZT) transducers bonded on the surface of a timber specimen. Using a pair of transducers in an active sensing scheme, one patch generated a designed stress wave, while another patch received the signal. While the active sensing was active, the moisture content of the timber specimen was gradually increased from 0% to 60% with 10% increments. The material properties of the timber correspondingly changed under varying timber moisture content, resulting in a measurable differential in stress wave attenuation rates among the different specimens used. The experimental results indicated that the received signal energy and the moisture content of the timber specimens show a parabolic relationship. Finally, the feasibility and reliability of the presented method, for monitoring timber moisture content, are discussed.
