Monitoring wood decay in poles by the vibroacoustic method

Despite recent advances in the development of new materials, wood continues to be used globally for the support of overhead cable networks used by telecommunications and electrical utility companies. As a natural material, wood is subject to decay and will eventually fail, causing disruption to services and danger to public and company personnel. The traditional method of testing poles for decay involves hitting them with a hammer and listening to the sound that results. However, evidence suggests that a large number of poles are replaced unnecessarily and a significant number of poles continue to fail unexpectedly in service. Therefore, a more accurate method for assessing the structural integrity of wooden poles is required. The underlying physical principles behind the 'pole tester's approach' have been identified and used in the development of a decay meter to enable objective monitoring of decay in wooden poles

Condition assessment of in-service timber utility poles utilizing advanced digital signal processing and multi-sensors array

University of Technology Sydney. Faculty of Engineering and Information Technology.Timber utility poles play a significant role in the infrastructure of Australia as well as many other countries. There are over 5 million timber utility poles currently used in Australian energy networks, which are more than 80% of total utility poles in the network. Due to the advanced age of Australia’s timber pole infrastructure, significant efforts are undertaken by state authorities on maintenance and asset management to prevent utility lines from failure. However, the lack of reliable information regarding their in-service condition, including the embedment length or the degree of deterioration or damage below ground level makes it extremely difficult for the asset managers to make decisions on the replacement/maintenance process with due consideration to economy, operational efficiency, risk/liability and public safety. For example, in order to avoid any failure and considering the public safety, each year approximately 300,000 poles are replaced in the Eastern States of Australia with up to 80% of them still being in a very good serviceable condition, resulting in significant waste of natural resources and money. In order to address this problem, an R&D program commenced in 2011 at the University of Technology Sydney in collaboration with the Electricity Network Association of Australia. The aim of this study is to design and develop a Non-Destructive Testing (NDT) method with acceptable accuracy, whilst being cost efficient for the condition assessment of the in-service timber utility poles. This research project contains three phases, which will be explained briefly in the following paragraphs. Several stress wave based NDT methods are currently available and have been used in field applications over the past decades as simple and cost-effective tools for identifying the condition and underground depth of embedded structures, such as poles or piles in service. In this regard, in the first phase of this research, the applicability and efficiency of the currently available NDT methods on the condition assessment of the timber utility poles is investigated through simulation and laboratory tests. Results of the first phase reveal that these surface NDT methods face significant challenges in the condition assessment of the timber utility poles. These challenges are due to presence of uncertainties such as complicated material properties and imperfect body (i.e. timber pole natural cracks), environmental conditions, interaction of soil and structure, defects and deteriorations as well as an impact excitation type. It is necessary to mention that access to the top of the in-service timber utility poles is prohibitive due to the presence of the electrical or communication wires. In this regard, the hammer impact is applied to the timber pole on its side. In order to address these complicating factors, in the second phase of this research some advanced digital signal processing methodologies are selected, modified, and employed from different groups of methodologies that can most probably provide solutions. The efficiency of these methodologies is investigated through simulation, laboratory, and field tests. Results of the second phase of this research illustrate that the behaviour of the timber pole under the lateral hammer impact excitation is very complicated. In fact, if dealing with this high level of complexities is not impossible, it is a very difficult task. In this regard, in the third phase of this research a novel, fast, and accurate ultrasonic narrowband NDT method is proposed as an alternative proposition for the condition assessment of the timber structures. The efficacy of the proposed methodology is verified through the laboratory experiments

Material characterization of timber utility poles using experimental approaches

University of Technology Sydney. Faculty of Engineering and Information Technology.Utility poles made of timber are a significant part of Australia’s infrastructure for power distribution and communication networks. Wood as a natural material deteriorates under the influence of environmental conditions such as weathering, fungus and insect attack which results in a reduction of the strength of the poles. Determining soundness and the remaining strength of timber utility poles in service is crucial in order to maintain a reliable and secure power network. This thesis presents an investigation of using static and dynamic material testing approaches to determine material properties and detecting internal damage of timber utility poles from two hardwood eucalyptus tree species, i.e. Spotted Gum and Tallowwood. The comparative study of static and dynamic tests based on the wave transmission time or time of flight (TOF) is necessary for the development of novel non-destructive testing (NDT) techniques for the health assessment of in-situ utility poles. In order to develop accurate non-destructive models, knowledge of the orthotropic material properties is necessary. In open literatures, comparative studies on orthotropic material properties are scarce to find for most eucalyptus species used for utility poles. Typically, material properties are only available in the longitudinal (i.e. along main wood fibre) direction, and most international standards cover only details on material testing in such direction with no coherent or comprehensive guidelines being given for the testing of the other two secondary directions (radial and tangential) of timber. TOF measurements were conducted by several researchers for a number of timber species, however non on high density woods such as the investigated eucalyptus species. Based the full set of material properties (Modulus of Elasticity and Poisson’s ratios) of two new utility poles determined with static tests in all three orthotropic directions (longitudinally, radially and tangentially), the dynamic tests were calibrated and used for the non-destructive material characterization and internal damage detection. The tests were also conducted taking into account varying moisture contents and different grain angles as they occur in the field. Ultimately, an orthotropic numerical model was created to simulate the experimental damage detection case which could be used to simulate further damage cases. The results revealed that the formulas used for the dynamic material characterization must be adjusted for the investigated species. The numerical model was capable of simulating the experimental case and predicting the TOF for damaged poles. The method has potential for the prediction of internal damage of eucalyptus timber poles in the field

Load capacity prediction of in-service timber utility poles considering wind load

© 2016, Springer-Verlag Berlin Heidelberg. This paper presents a numerical investigation on the influence of different types of damage to the load capacity of in-service timber utility poles. Current design codes do not highlight a pole’s strength performance due to different types of damage. However, damages typically found in ageing timber poles, such as damage due to fungus or termite attack, have very different characteristics and result in various effects on the strength properties of timber poles. Hence, the presented study investigates the influence of typical common types of damage to the strength properties and load capacities of timber utility poles. The study considers the damage type, location and severity. Wind load is considered as critical load due to the practical issue. The research shows that external damages at ground level significantly affect the load capacity of a timber pole. While internal damage, such as termite nests, has less influence on the load capacity regardless of the damage location and severity

Numerical modelling and condition assessment of timber utility poles using stress wave techniques

University of Technology Sydney. Faculty of Engineering and Information Technology.Timber utility poles are traditionally used for electricity and telecommunication distribution and represent a significant part of the infrastructure for electricity distribution and communication networks in Australia and New Zealand. Nearly 7 million timber poles are in service and about $40-$50 million is spent annually on their maintenance and asset management. To prevent the ageing poles from collapse, about 300,000 electricity poles are replaced in the Eastern States of Australia every year. However, up to 80% of the replaced poles are still in a very good condition (Nguyen et al., 2004). Therefore, huge natural resources and money is wasted. Accordingly, a reliable non-destructive evaluation technique is essential for the condition assessment of timber poles/piles to ensure public safety, operational efficiency and to reduce the maintenance cost. Several non-destructive testing (NDT) methods based on stress wave propagation have been used in practice for the condition assessment of timber poles. However, stress wave propagation in timber poles especially with the effect of soil embedment coupled with unknown pole conditions below ground line (such as deterioration, moisture etc.) is complicated, and therefore it hindered the successful application of these NDT methods for damage identification of timber poles. Moreover, some stress wave based NDT methods are often based on over-simplified assumptions and thus fail to deliver reliable results. In the presented study, in order to gain an in-depth understanding of the propagation of stress waves in damaged poles and to develop an effective damage detection method, a solid numerical study of wave behaviour is undertaken and novel wavelet packet energy (WPE) method is investigated for damage identification. Numerical studies utilises finite element (FE) models to track the wave propagation behaviour characteristics considering different boundary conditions, material properties as well as impact and sensing locations. WPE is a sensitive indicator for structural damage and has been used for damage detection in various types of structures. This thesis presents a comprehensive investigation on the novel use of WPE for damage identification in timber utility poles using FE models. The research study comprises several aspects of investigations such as a comparative study between 2D and 3D models, a sensitivity study of mesh density for 2D models, and a study of the novel WPE-based technique for damage classification and detection in timber poles. Support vector machine (SVM) is imported for damage classification and particle swarm optimisation (PSO) is selected to achieve the classification. The results clearly show the effectiveness of the proposed novel WPE based damage identification technique. Damage prediction based on optimisation procedure is also carried out in this thesis. Several numerical models with different damage conditions are created and the damage size is predicted according to optimisation procedure based on information from sample damaged model. Genetic algorithm and artificial fish swarm algorithm are used as optimisation algorithms and the comparative study is conducted based on the prediction results. The influence of damage on the strength of timber utility poles is also studied in this thesis. The damage conditions are changes in diameter, length as well as location. Wind is considered as a main reason to cause the collapse of timber utility poles in this research. Wind load is defined based on Australian standards and the Ausgrid manual, and the corresponding stress is calculated through FE analysis. According to this analysis, it can be found that under specific damage conditions, some small damage may cause collapse; however, for certain conditions, the timber poles can still be safe even when large damage exists. In conclusion, a novel WPE based damage detection method has been successfully developed to address the limitations of existing methods for condition assessment of timber utility poles. The numerical verification has shown the method is effective for identification of the classification and severity of damage

Vibration-based damage detection for timber structures in Australia

© 2014 by Nova Science Publishers, Inc. All rights reserved. The use of non-destructive assessment techniques for evaluating structural conditions of aging infrastructure, such as timber bridges, utility poles and buildings, for the past 20 years has faced increasing challenges as a result of poor maintenance and inadequate funding. Replacement of structures, such as an old bridge, is neither viable nor sustainable in many circumstances. Hence, there is an urgent need to develop and utilize state-of-the-art techniques to assess and evaluate the ?health state? of existing infrastructure and to be able to understand and quantify the effects of degradation with regard to public safety. This paper presents an overview of research work carried out by the authors in developing and implementing several vibration methods for evaluation of damage in timber bridges and utility poles. The technique of detecting damage involved the use of vibration methods, namely damage index method, which also incorporated artificial neural networks for timber bridges and time-based non-destructive evaluation (NDE) methods for timber utility poles. The projects involved successful numerical modeling and good experimental validation for the proposed vibration methods to detect damage for simple beams subjected to single and multiple damage scenarios and was then extended to a scaled timber bridge constructed under laboratory conditions. The time-based NDE methods also showed promising trends for detecting the embedded depth and condition of timber utility poles in early stages of that research

A numerical investigation on the damage identification of timber utility poles based on wavelet packet energy

Timber utility poles are traditionally used for electricity and telecommunication distribution. Due to the old age of many distribution networks, the health condition of these timber poles needs to be assessed. Non-destructive testing (NDT) methods based on stress wave propagation have successfully been used in practice for the condition assessment of timber poles. However, for the successful application of these methods for damage identification, some limitations exist. To overcome these limitations, this paper proposes the use of wavelet packet energy (WPE) for the stress wave data analysis and damage identification. WPE is a sensitive indicator for structural damage and has been used for damage detection in various types of structures. This paper presents a comprehensive investigation on the novel use of WPE for the damage identification in timber utility poles using finite element (FE) models. The research study comprises of the following investigations: i) a comparative study between 2D and 3D models, ii) a sensitivity study of mesh density for 2D models, and iii) a study of the novel WPE-based technique for damage detection in timber poles. The results of the new method clearly show the effectiveness of the proposed damage identification technique based on WPE

Application and improvement of conventional stress-wave-based non-destructive testing methods for the condition assessment of in-service timber utility poles

Timber utility poles represent a significant part of Australia’s infrastructure for power distribution and communication networks. Due to their advanced age, significant efforts are undertaken to prevent utility lines from failure. However, the lack of reliable tools for assessing the condition of in-service poles seriously jeopardizes the maintenance and asset management. Non-destructive testing (NDT) methods based on stress wave propagation can potentially offer simple and cost-effective tools for the condition assessment of in-service timber poles. Based on the impact direction and location, mainly two wave types can be excited in a pole, i.e. longitudinal and bending waves. A conventional stresswave- based method that analyses longitudinal waves is the Sonic Echo (SE) method; and a typical signal processing method for the analysis of bending waves (BW) is the Short Kernel Method (SKM). In this paper, firstly, the application of the conventional SE method and the BW method with SKM data analysis is investigated for the condition assessment of timber poles from a signal processing perspective. Secondly, to improve limitations of the current methods, the application of a multisensors array is proposed for more reliable and accurate results. The new method is validated on numerical data of a timber pole modelled with both isotropic and orthotropic material properties

Guided wave-based condition assessment of in situ timber utility poles using machine learning algorithms

This paper presents a machine-learning-based approach for the structural health monitoring (SHM) of in-situ timber utility poles based on guided wave (GW) propagation. The proposed non-destructive testing method combines a new multi-sensor testing system with advanced statistical signal processing techniques and state-of-the-art machine learning algorithms for the condition assessment of timber utility poles. Currently used pole inspection techniques have critical limitations including the inability to assess the underground section. GW methods, on the other hand, are techniques potentially capable of evaluating non-accessible areas and of detecting internal damage. However, due to the lack of solid understanding on the GW propagation in timber poles, most methods fail to fully interpret wave patterns from field measurements. The proposed method utilises an innovative multi-sensor testing system that captures wave signals along a sensor array and it applies machine learning algorithms to evaluate the soundness of a pole. To validate the new method, it was tested on eight in-situ timber poles. After the testing, the poles were dismembered to determine their actual health states. Various state-of-the-art machine learning algorithms with advanced data pre-processing were applied to classify the poles based on the wave measurements. It was found that using a support vector machine classifier, with the GW signals transformed into autoregressive coefficients, achieved a very promising maximum classification accuracy of 95.7±3.1% using 10-fold cross validation on multiple training and testing instances. Using leave-one-out cross validation, a classification accuracy of 93.3±6.0% for bending wave and 85.7±10.8% for longitudinal wave excitation was achieved. © The Author(s) 2014