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Professor Jianchun Li

Biography

.
Image of Jianchun Li
Professor, School of Civil and Environmental Engineering
Director, Centre for Built Infrastructure Research
Core Member, Centre for Built Infrastructure Research
BSc (BUAA), MSc (BUAA), PhD (TCD)
 
Phone
+61 2 9514 2651
Room
CB11.11.116

Research Interests

Structural Health Monitoring and Nondestructive Evaluation

Smart Materials and Structure

Structural Dynamic  and Vibration Control

Bridge Condition Assessment and Rehabilitation with Fibre reinforced Polymer (FRP)

Fatigue and Fracture

Can supervise: Yes

Books

Li, J. & Taylor, D.A. 1993, Sourcebook on fatigue crack propagation: thresholds and crack closure, 1, Engineering Materials Advisory Services Ltd., UK.

Chapters

Samali, B., Li, J., Dackermann, U. & Choi, F. 2011, 'Vibration-Based Damage Detection for Timber Structures in Australia' in Chan, T.H.T. & Thambiratnam, D.P. (eds), Structural Health Monitoring in Australia, Nova Science Publishers, New York, USA, pp. 81-108.
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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-hased 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.
Samali, B., Li, J., Dackermann, U. & Choi, F.C. 2011, 'Vibration-based damage detection for timber structures in Australia' in Structural Health Monitoring in Australia, Nova Science Publishers, Inc., pp. 118-144.
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. ©2011 Nova Science Publishers, Inc. All rights reserved.
Aboura, K., Samali, B., Crews, K.I. & Li, J. 2009, 'The Use of Stochasatic Processes in Bridge Lifetime Assessment' in Agbinya, J.I., Biermann, E., Hamam, Y., Rocaries, F. & Lal, S.K. (eds), Biomedical and Environmental Sensing, River Publishers, Denmark, pp. 295-316.
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We introduce an approach for modelling the structural deterioration of components of bridges for maintenance optimization purposes. The Markov chain model is found in the maintenance and repair problems since the early 60's, is introduced to the maintenance of road infrastructure in the 1980's, and is made to drive the current bridge maintenance optimization systems. While this model results into solvable programming problems and provides a solution, there are a number of criticisms associated with it. We highlight the shortfalls of the Markov model for bridge lifetime assessment and promote the use of stochastic processes.

Conferences

Yu, Y., Dackermann, U. & Li, J. 2015, 'A novel damage evaluation method for timber utility poles based on wavelet packet transform and support vector machine', Proceedings of 7th International Conference on Structural Health Monitoring of Intelligent Infrastructure, 7th International Conference on Structural Health Monitoring of Intelligent Infrastructure (SHMII7), Torino, Italy.
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In this paper, a novel damage evaluation approach based on wavelet package transform (WPT) and support vector machine (SVM) for the multi-sensor GW-based damage assessment of in-situ timber utility poles. First, WPT is utilized to extract energy features of guided wave signals. Then, to eliminate the multicollinearity between extracted features, principle component analysis (PCA) is adopted and energy features are replaced by a few principle components. Finally, a classifier model base on SVM is constructed to assess the pole condition. To improve the estimation accuracy of the model, particle swarm optimization (PSO) is used to optimize the parameters in SVM. The new method is validated on a number of laboratory timber specimen (undamaged and damaged) that are experimentally tested using an impact hammer for wave excitation and a multi-sensor array is utilised to capture transversal response wave signals. WPT-based energy feature extraction and PCA is subsequently applied to the recorded wave signals, and the health condition of the timber specimen is identified by the pre-trained classifier. The experimental results verify that the proposed method is effective achieving a high identification accuracy of up to 95%.
Yu, Y., Li, Y. & Li, J. 2014, 'A new hysteretic model for magnetorheological elastomer base isolator and parameter identification based on modified artificial fish swarm algorithm', 31st International Symposium on Automation and Robotics in Construction and Mining, ISARC 2014 - Proceedings, University of Technology Sydney, pp. 176-183.
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Magnetorheological elastomer (MRE) base isolator is a new semi-active control device that has recently acquired more attention. This paper proposes a new model for MRE base isolator to portray the nonlinear hysteresis between generated force and the displacement. In this model, a hyperbolic expression is proposed to compare with the classical Bouc-Wen model, which includes internal dynamics represented by a nonlinear differential equation. For the identification of model parameters, a modified artificial fish swarm algorithm is adopted using the experimental force-displacement/velocity data under different testing conditions. In this algorithm, a self-adaptive method for adjusting the algorithm parameters is introduced to improve the result accuracy. Besides, the behaviours in the algorithm are simplified to descend the algorithmic complexity. Parameter identification results are included to demonstrate the accuracy of the model and the effectiveness of the identification algorithm.
Li, J.C., Li, Y., Askari, M. & Ha, Q.P. 2014, 'Future intelligent civil structures: Challenges and opportunities', 31st International Symposium on Automation and Robotics in Construction and Mining, ISARC 2014 - Proceedings, University of Technology Sydney, pp. 72-79.
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An intelligent civil structure offers ultimate protection to its structure, contents and occupants in terms of safety and functionality against undesired dynamic loadings and structural deficiency. In this paper, the concept of the future intelligent civil structure featuring self-adaptive, selfprognostic, self-sensing, self-powering and self-repairing abilities, is proposed. A decade research efforts from Centre for Built Infrastructure Research, University of Technology Sydney, towards the development and concept proof of such intelligent structure is reviewed.
Dackermann, U., Smith, W.A., Li, J. & Randall, R.B. 2014, 'On the use of the cepstrum and artificial neural networks to identify structural mass changes from response-only measurements', Proceedings of ISMA 2014 - International Conference on Noise and Vibration Engineering and USD 2014 - International Conference on Uncertainty in Structural Dynamics, KU Leuven, pp. 3739-3750.
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This paper presents a damage identification technique based on response-only data utilising cepstrum analysis and artificial neural networks (ANNs) for the identification of added mass in a two-storey framed structure. The proposed technique applies cepstrum-based operational modal analysis (OMA) for the regeneration of frequency response functions (FRFs), and added mass is detected through the combined use of principal component analysis (PCA) for data compression and ANNs for feature extraction and pattern recognition. In particular, different treatments of the zeros in the curve-fitting of the transfer function cepstrum are investigated to improve the automation potential of the method for application in continuous online structural health monitoring (SHM). The proposed technique is validated on a laboratory structure tested on a large-scale shake table with ambient base loading. The results of the investigation show that the method is effective in identifying added mass based on response-only measurements.
Gardner, A.P., Willey, K., Vessalas, K. & Li, J. 2014, 'Experiences with flipped learning in subjects in consecutive stages of aCivil Engineering programme', Australasian Association for Engineering Education Annual Conference 2014, School of Engineering & Advanced Technology, Massey University, Turitea Campus, Palmerston North 4442, Wellington, NZ.
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CONTEXT Flipped learning is an instructional approach which allows instructors the opportunity to use a blending of online and face to face learning activities. The main affordance of flipped learning is the opportunity to free up class time to allow students and instructors to engage in collaborative learning activities designed to consolidate and deepen conceptual understanding of the subject material. Research has shown that participating in flipped instruction can change the way students approach their studies and improve motivation. PURPOSE OR GOAL We are interested in students' experience of the flipped environment, particularly their expectations of a learning environment, and the level of responsibility they take for their own learning. The purpose of this analysis is to create a baseline against which future instances of flipped learning can be compared. APPROACH Student perceptions of flipped instruction were investigated through survey responses and observations of students in a first year subject (Engineering Mechanics) a second year subject (Engineering Computations) and a third year subject (Construction Materials) in a Civil Engineering degree programme. In particular, students were asked to explain the impact of the flipped activities on their learning experience including any changes in how they approach their studies or managed their time. OUTCOMES Most students in each of the three subjects agreed that they 'liked' flipped instruction compared to the traditional lecture format. The majority of students in each subject also agreed that it is reasonable to expect students to prepare before attending a face to face session. However, some students made strong negative comments demonstrating how the flipped environment did not meet their expectations of how learning should be organised. This study suggests that students in the second and third year subjects were not necessarily showing signs of better self-regulation and time management sk...
Yu, Y., Dackermann, U., Li, J. & Yan, N. 2014, 'Guided-wave-based damage detection of timber poles using a hierarchical data fusion algorithm', Proceedings fo the 23rd Australasian Conference on the Mechanics of Structures and Materials, 23rd Australasian Conference on the Mechanics of Structures and Materials (ACMSM23), Southern Cross University, Byron Bay, Australia, pp. 1203-1208.
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This paper presents a hierarchical data fusion algorithm based on the combination of wavelet transform (WT), back propagation neural network (BPNN) and Dempster-Shafer (D-S) evidence theory for the multi-sensor guided-wave-based (GW-based) damage detection of in-situ timber utility poles. In the data-level fusion, noise elimination is performed on the original wave data to obtain single-mode signals using WT technology. Statistical information is extracted from the single-model signals as major characteristic parameters. In the feature-level fusion, for each sensor in the testing system, two sub-networks corresponding to different types of GW signals are constructed based on BPNN and characteristic parameters are sent to the networks for initial state recognition. In the decision-level fusion, the D-S evidence theory method is adopted to combine the initial results from different sensors for final decision making. The overall algorithm employs a hierarchical configuration, in which the results from the former level are regarded as input to the next level. To validate the proposed method, it was tested on GW signals from in-situ timber poles. The obtained damage detection results clearly demonstrate the effectiveness and accuracy of the proposed algorithm.
Nguyen, V.V.N., Li, J.L., Dackermann, U.D., Mustapha, S.M., Runcie, P.R. & Ye, L.Y. 2014, 'Damage identification of concrete arch beam utilising residual frequency response function', Proceedings of the 23rd Australasian Conference on the Mechanics of Structures and Materials, 23rd Australasian Conference on the Mechanics of Structures and Materials (ACMSM23), Southern Cross university, Byron Bay, Australia, pp. 1209-1214.
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One of the critical missions for bridge structural health monitoring (SHM) is to provide a reliable assessment technique to potential hazards caused by structural damage or other structural defects using continuously monitored vibration data. Recognising the needs and shortcomings of SHM, a project was established by NICTA, the University of Technology Sydney and The University of Sydney to develop reliable damage detection methods to provide robust and accurate assessment techniques for critical bridge infrastructure in Australia. This paper presents the progress of research and development of a vibration-based damage detection technique and its experimental validation in the laboratory. The proposed technique uses residual frequency response functions (FRFs) combined with principal component analysis (PCA) to form damage specific features (DSFs) that are incorporated in pattern recognition using artificial neural networks (ANNs). In the method, FRFs are obtained using modal analysis techniques and damage is identified using ANNs that innovatively map the DSF to damage characteristics, such as damage location and severity. The results of the experimental validation show that the proposed technique can successfully locate and quantify damage induced to a concrete arch beam simulating a real life structural component of the Sydney Harbour Bridge.
Dackermann, U., Yan, N.Y., Li, J.L. & Samali, B.S. 2014, 'A numerical investigation on the damage identification of timber utility poles based on wavelet packet energy', Proceedings of the 23rd Australasian Conference on the Mechanics of Structures and Materials, 23rd Australasian Conference on the Mechanics of Structures and Materials (ACMSM23), Southern Cross University, Byron Bay, Australia, pp. 1185-1190.
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Jozi, B.J., Dackermann, U., Braun, R.B., Li, J.L. & Samali, B.S. 2014, 'Application and improvement of conventional stress-wave-based non-destructive testing methods for the condition assessment of in-service timber utility poles', Proceedings of the 23rd Australasian Conference on the Mechanics of Structures and Materials, 23rd Australasian Conference on the Mechanics of Structures and Materials (ACMSM23), Southern Cross University, Byron Bay, Australia, pp. 1197-1202.
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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.
Mustapha, S., Nguyen, K., Runcie, P., Hu, Y., Dackermann, U., Nguyen, V.V., Li, J. & Ye, L. 2014, 'Structural health monitoring in civil structures based on the time series analysis', Austroads Publications Online, 9th Austroads Bridge Conference (ABS2014), Sydney, Australia.
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Yu, Y., Li, Y. & Li, J. 2014, 'Parameter Identification Of An Improved Dahl Model For Magnetorheological Elastomer Base Isolator Based On Enhanced Genetic Algorithm', 23rd Australasian Conference on the Mechanics of Structures and Materials (ACMSM23), Byron Bay, Australia, pp. 931-936.
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In view of the problems of high nonlinearity and multiple parameters in existing models of magnetorheological elastomer (MRE) base isolator, this paper proposes an improved Dahl model and an enhanced genetic algorithm (GA) for model parameter identification. In this model, the Dahl hysteresis operator is employed to depict the Coulomb force to avoid the estimation of many parameters and this model can perfectly capture the hysteretic behavior of the MRE base isolator at both small and large displacements. To improve the searching efficiency of identification process, adaptive crossover and mutation operators are introduced into the GA to avoid the algorithm falling into the local optimum, achieving faster convergence rate for optimal solutions. Furthermore, an appropriate stopping criterion is designed to reduce the calculation cost. Testing data from a practical MRE base isolator are utilized to validate the proposed algorithm with satisfactory parameter identification results.
Gu, X., Li, J. & Li, Y. 2014, 'Innovative semi-active storey isolation system utilising novel magnetorheological elastomer base isolators', 23rd Australasian Conference on the Mechanics of Structures and Materials (ACMSM23), Byron Bay, Australia, pp. 925-930.
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Seismic base isolation has been a widely adopted technique for earthquake protection of civil infrastructures. As the technology matures, new innovative designs of the base isolation systems become increasingly attractive to researchers, especially storey base isolation systems due to its design flexibility and better performance for seismic protection. Moreover, considering the unpredictable and diverse nature of earthquakes, the conventional base isolation systems have reached their limit due to their inherent passive nature which is incapable to adjust their isolation frequencies according to the characteristics of the earthquakes. A recent advance on the development of an adaptive magneto-rheological elastomer (MRE) base isolator provides an opportunity for the research and development on new adaptive base isolation systems. In this paper, an innovative semi-active storey isolation system utilising the novel magneto-rheological elastomer base isolator has been proposed. The proposed isolation system design incorporates adaptive magneto-rheological elastomer isolators under each storey of the structure instead of being only installed beneath of the entire structure. Such innovative system allows high authority semiactive control of storey responses by instantly changing stiffness of the isolator. Extensive simulation has been conducted to investigate such system using 5-storey international benchmark model under four benchmark earthquakes.
Li, Y. & Li, J. 2014, 'Base isolator with variable stiffness and damping: design, experimental testing and modelling', 23rd Australasian Conference on the Mechanics of Structures and Materials (ACMSM23), Byron Bay, Australia, pp. 913-918.
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Vulnerability in base isolation system of civil structures originated from passive nature of the rubber material raises the urgency of developing smart base isolation system with adaptive and controllable properties, i.e. variable stiffness and damping. To address this issue, this paper presents comprehensive investigations on a novel adaptive base isolator, including design, experimental testing and dynamic modelling. Smart rubber with field-dependent modulus and damping property is incorporated into the laminated base isolator design. Experimental testing is conducted utilising an advanced shake table facility to examine its performance under cycling loading. Results show that the adaptive base isolator possesses a stiffness increase of more than 16 times and damping ratio between 10% and 27%. With such features, it can be developed into a smart base isolation system to protect civil structures against any type of earthquake. Results also show that this device has high nonlinear hysteresis, i.e. shear stiffening behaviour. A mechanical model is thus required to describe the complex behaviour of new adaptive base isolator. A new strain stiffening element is proposed for this purpose. Comparison between the model and the experimental data verifies the fidelity and effectiveness of the proposed model.
Yu, Y., Li, Y. & Li, J. 2014, 'PARAMETER IDENTIFICATION OF AN IMPROVED DAHL MODEL FOR MAGNETORHEOLOGICAL ELASTOMER BASE ISOLATOR BASED ON ENHANCED GENETIC ALGORITHM', 23rd Australasian Conference on the Mechanics of Structures and Materials (ACMSM23), Byron Bay, Australia, pp. 931-936.
In view of the problems of high nonlinearity and multiple parameters in existing models of magnetorheological elastomer (MRE) base isolator, this paper proposes an improved Dahl model and an enhanced genetic algorithm (GA) for model parameter identification. In this model, the Dahl hysteresis operator is employed to depict the Coulomb force to avoid the estimation of many parameters and this model can perfectly capture the hysteretic behavior of the MRE base isolator at both small and large displacements. To improve the searching efficiency of identification process, adaptive crossover and mutation operators are introduced into the GA to avoid the algorithm falling into the local optimum, achieving faster convergence rate for optimal solutions. Furthermore, an appropriate stopping criterion is designed to reduce the calculation cost. Testing data from a practical MRE base isolator are utilized to validate the proposed algorithm with satisfactory parameter identification results.
Yu, Y., Li, Y. & Li, J. 2014, 'A Novel Strain Stiffening Model for Magnetorheological Elastomer Base Isolator and Parameter Estimation Using Improved Particle Swarm Optimization', Proceedings of the 6th edition of the World Conference of the International Association for Structural Control and Monitoring (IACSM), Sixth World Conference on Structural Control and Monitoring (6WCSCM), International Center for Numerical Methods in Engineering (CIMNE), Barcelona, Spain.
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In order to fully utilize the advantages of magnetorheological elastomer (MRE) base isolator for seismic protection of civil structures, a high fidelity model should be established to characterize its nonlinear hysteresis for its implementation in structural control. In this paper, a novel strain stiffening model is developed to capture this unique characteristic. In this model, a strain stiffening component, which described the unique viscos-elastic behavior of the device, is incorporated with a Voigt element, which portrays the solid-material behavior. The new model, as an attractive feature, maintains a relationship between the isolator parameters and physical force-displacement nonlinear phenomenon and decreases the complexity in other existing models. In addition to the proposed model, an improved optimization algorithm based on particle swarm optimization (IPSO) is designed to identify the model parameters by utilizing experimental force-displacement-velocity data acquired from various loading conditions. In this new algorithm, the mutation operation in genetic algorithm is utilized for helping the model solution avoiding the local optimum. The superiority of the proposed model and parameter solving algorithm is validated by comparing them with the classical Bouc-Wen model and other optimization algorithms through the error analysis, respectively. The comparison results show that the proposed model can exactly predict the force-displacement and force-velocity responses at both small and large displacements, and has a smaller root-mean-square (MSE) error than the Bouc-Wen model. Compared with other optimization algorithm, the IPSO not only has a faster convergence rate, but also obtains the satisfactory parameters identification results.
Li, J., Makki Alamdari, M. & Samali, B. 2014, 'Application Of Symbolic Time Series Analysis For Damage Localisation In Truss Structures', Proceedings of the 23rd Australasian Conference on the Mechanics of Structures and Materials, Australasian Conference on the Mechanics of Structures and Materials, Southern Cross University, Byron Bay, Australia, pp. 1179-1184.
Reliability of truss bridges can be significantly affected by local damages as damage changes the load path in the structure. As damage increases, the load-carrying capacity of the structure considerably reduces which might result in catastrophic failure. Hence, it is important to detect structural damages as early stage as possible to avoid further propagation. In the present work, a time series-based method is proposed to detect and localise damage in truss structures. The method works based on Symbolic Time Series Analysis (STSA) of time responses to localise a gradually evolving deterioration in the structure according to the changes in the statistical behaviour of symbol sequences. First, the symbol sequences are generated by transforming the measured time data to symbol space to reduce the dimension of information and then the probability vectors for each symbol sequence is created. Damage localisation is carried out by comparing the probability vectors of different measured locations. It is expected that the damaged member shows a higher degree of variation in the probability vector which is introduced as damage sensitive feature. Numerical demonstrations on a plane truss are presented to illustrate the accuracy and efficiency of the proposed method. Gradually evolving damage is introduced by the stiffness reduction in truss members. Finite element technique is employed to obtain the time response of the structure subjected to ambient vibration. The simulated responses are polluted with random noise to take into account the influence of practical uncertainties. Simulation results under various damage conditions demonstrate the effectiveness of the proposed algorithm in detection and localisation of gradually evolving damage in single or multiple states in presence of measurement noise up to 5%.
Jiang, X.Z., Li, Y.C. & Li, J.C. 2013, 'A novel piezoelectric wafer-stack vibration energy harvester', From Materials to Structures: Advancement Through Innovation - Proceedings of the 22nd Australasian Conference on the Mechanics of Structures and Materials, ACMSM 2012, pp. 399-404.
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Piezoelectric vibration-based energy harvesters are attractive as inexhaustible replacements for batteries in low-power requirement wireless electronic devices and thus have received increasing research interest in the last few years. This paper presents a novel piezoelectric harvester based on the wafer-stack configuration to convert the external vibration into usable electrical energy for this purpose. Both analytical and experimental investigations are undertaken at University of Technology Sydney. Firstly, an electromechanical model with a rectified circuit, considering both the mechanical and electrical factors of the harvester, is built to characterise the harvested electrical power across the external loadings. Exact closed-form expressions of the electromechanical model have been given to analyse conditions for maximum harvested power. Finally, a shake table experimental testing was conducted to evaluate the feasibility of the presented PZT wafer stack harvester under standard sinusoidal loadings. Test results show that the harvester can generate a maximum 16mW electrical power for sinusoidal loading with 40mm amplitude and 2Hz frequency. © 2013 Taylor & Francis Group.
Huang, S., Li, J., Samali, B. & Zobec, M. 2013, 'An experimental investigation of a thermal break composite faade mullion section', From Materials to Structures: Advancement Through Innovation - Proceedings of the 22nd Australasian Conference on the Mechanics of Structures and Materials, ACMSM 2012, pp. 513-517.
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This paper presents the experimental investigation into the behaviour of a typical thermal break composite faade mullion section under quasi-static loadings at various temperatures. Transverse tensile tests and shear tests were carried out according to the requirements of EN14024. Standard specimens specified by this standard were tested to determine characteristic shear strength and transverse tensile strength, as well as the elasticity constant. Tests were carried out at room temperature (23°C), low temperature (-20°C) and high temperature (80°C). Test results of shear strength and transverse tensile strength at various temperatures were presented in the graphs. These graphs showed both shear and tensile strength decreased with increased temperature under quasi-static loadings, as well as connectivity constant. © 2013 Taylor & Francis Group.
Li, Y.C., Li, J.C. & Samali, B. 2013, 'A novel adaptive base isolator utilising magnetorheological elastomer', From Materials to Structures: Advancement Through Innovation - Proceedings of the 22nd Australasian Conference on the Mechanics of Structures and Materials, ACMSM 2012, pp. 763-767.
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Base isolation is the most popular seismic protection technique for civil structures. However, research has revealed that the traditional base isolation system is vulnerable to two kinds of earthquakes, i.e. the near-fault and far-fault earthquakes, due to its passive nature.A great deal of effort has been dedicated to improve the performance of traditional base isolation systems for these two types of earthquakes. Controllable supplementary and energy-dissipation members, such as magnetorheological damper, friction damper or hydraulic fluid damper, have been proposed to reduce seismic responses of the building structures. However, with the introduction of additional control devices, the system complexity increases resulting difficulty in the system implementation and control system design. It would be ideal if a certain level of adaptability could be introduced into base isolation systems while maintaining the traditional outfit. This paper addresses the challenge facing the current base isolation practices and proposes a novel adaptive base isolator as a solution to the problem.A smart rubber, namely, magnetorheological elastomer (MRE), is utilised in this research for its magnetic field-sensitive material property as the main element in the novel device. The tradition base isolator design for a large-scale structure with laminated steel and MRE layers is adopted. To verify and characterise the performance of the MRE base isolator, experimental testing was conducted on UTS shake table facility. Experimental results show that after being energised with magnetic field, the maximum force and the stiffness of the novel device can increase by up to approximately 45% and 37%, respectively.With the field-dependent stiffness and damping, the proposed adaptive base isolator is very promising in meeting the challenges associated with the base isolation systems encountered in practice. © 2013 Taylor & Francis Group.
Makki Alamdari, M., Li, J. & Samali, B. 2013, 'A comparative study on the performance of the damage detection methods in the frequency domain', From Materials to Structures: Advancement Through Innovation - Proceedings of the 22nd Australasian Conference on the Mechanics of Structures and Materials, ACMSM 2012, pp. 867-872.
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During last two decades, a vast number of damage detection methods have been proposed either in frequency or time domain. These methods normally have their own advantages and limitations or suitable applications; the purpose of this study is to examine the performance of the some popular methods on localisation a possible damage on a sample structure. All of the chosen methods are based on the frequency domain data and work based on proposing a damage sensitive indicator which contains spatial information. Mode shape curvature, frequency response functions' curvature, modal strain energy, flexibility matrix and spatial wavelet transform were amongst those damage detection methods were chosen for this study. The case study considers a clamped-clamped beam which was modelled by solid elements in order to define several damage stages based on different crack depth. Damage was simulated by reduction in elastic modulus of the elements in damage zone. The transient response of the structure due to an external impact excitation was obtained by ANSYS and then polluted by different percentages of white noise. The time-domain responses at selected evenly-spaced locationswas then processed byMATLAB to achieve the FRFs and mode shapes respectively by applying Fourier transform and eigenvalue realization algorithm (ERA). Based on the obtained results, it was found that despite some of these methods were suggested by so many researchers, they completely fail in localising damage in the structure even at high level of damage severity. © 2013 Taylor & Francis Group.
Makki Alamdari, M., Li, J. & Samali, B. 2013, 'A FRF-based damage detection method utilising wavelet decomposition', From Materials to Structures: Advancement Through Innovation - Proceedings of the 22nd Australasian Conference on the Mechanics of Structures and Materials, ACMSM 2012, pp. 873-877.
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Damage in a structure causes deviation in dynamic responses of the structure either in frequency or time domain in comparison with its healthy status. The purpose of this study is to present a new damage detection method in order to detect and localize the structural damage. This novel algorithm is based on the directly-measured frequency response functions (FRFs). The approach is composed of three major steps: first, developing the curvature of FRFs which produces spatially distributed shape functions at each frequency coordinate, secondly, normalization of FRFs' curvature in order to enhance the influence of the lower-frequency-band data; finally decomposition of the obtained profiles (normalized version of FRFs' curvature) by conducting wavelet analysis to detect any possible structural abnormality through structure. The combination of these three steps leads to a robust algorithm in detection and localisation of any damage in the structure even at small levels which other FRF-based methods were unable to detect. There are some benefits with the presented method: first, this method does not need higher-frequency-range data which is hard to obtain in most civil applications; second, there is no need for baseline data from the intact structure; This is particularly attractive for practical applications as it opens an opportunity for online monitoring of the structural integrity without demanding for any previous data records of the structure. The performance of the method is evaluated on a numerical model and the effect of different parameters such as the location of the excitation point, the level and the location of the damage was studied; the results demonstrated that the method can efficiently identify the location of the damage in the structure even for damage at small levels. © 2013 Taylor & Francis Group.
Askari, M., Li, J. & Samali, B. 2013, 'Adaptive multiple forgetting factor recursive least square (AMFF-RLS) for real-time structural identification', From Materials to Structures: Advancement Through Innovation - Proceedings of the 22nd Australasian Conference on the Mechanics of Structures and Materials, ACMSM 2012, pp. 879-884.
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System identification refers to any systematic way of deriving or improving models of systems through the use of experimental and field testing input-output data. In the field of civil engineering, identification of the state of the structure during the dynamic loads, such as earthquake, to predict the current state of the structure and detect any damage or hazard,when it occurs, has posed a great challenge to the research community. Therefore, online and real-time structural parameters identification has recently drawn more attractions, although few research works have been reported especially for cases where measurement data are contaminated by highlevel noise. The Recursive Least Square with single forgetting factor has been widely used in estimation and tracking of time-varying parameters in the fields of electrical and mechanical engineering. However, when there are multiple parameters that each (or some) varies with a different rate, this method cannot perform well. On the other hand, a priori information on the changing rate of the parameters might not be available, and the forgetting factors must be updated adaptively. This paper presents a new adaptive tracking technique, based on the Recursive Least Square (RLS) approach with Adaptive Multiple Forgetting Factors (AMFF). The proposed method considers an adaptive rule for each of the forgetting factors assigned to each of the parameters and thus, enables simultaneous estimation of the time-varying stiffness and damping of the storeys of the structure. Numerical examples show that results of this RLS-based approach are accurate and robust, even when the observed data are contaminated with different types and significantlevels of noise. © 2013 Taylor & Francis Group.
Dackermann, U., Li, J. & Samali, B. 2013, 'Transmissibility function analysis for boundary damage identification of a two-storey framed structure using artificial neural networks', From Materials to Structures: Advancement Through Innovation - Proceedings of the 22nd Australasian Conference on the Mechanics of Structures and Materials, ACMSM 2012, pp. 891-896.
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This paper presents a damage identification technique that uses output-only scalar transmissibility measurements of a structure to identify boundary conditions. A damage index is formulated based on output-only acceleration response measurements from ambient floor vibration. The damage index is analysed by a system of artificial neural networks (ANNs) to predict boundary condition changes of the structure. Using the data compression and noise filtering capabilities of principal component analysis (PCA), the size of the damage index is reduced in order to obtain suitable patterns for ANN training. To test the proposed method, it is applied to different models of a numerical two-storey framed structure with varying boundary conditions. Boundary damage is simulated by changing the condition of individual joint elements of the structure from fixed to pinned. The results of the investigation show that the proposed method is effective in identifying boundary damage in structures based on output-only response measurements. © 2013 Taylor & Francis Group.
Subhani, M., Li, J. & Samali, B. 2013, 'Behaviour of stress wave propagation in utility timber pole', From Materials to Structures: Advancement Through Innovation - Proceedings of the 22nd Australasian Conference on the Mechanics of Structures and Materials, ACMSM 2012, pp. 1077-1082.
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Non-destructive testing has been used for many years to evaluate the in situ condition of timber piles. Longitudinal impact is usually applied on the top of piles to induce longitudinal wave to detect faults in piles due to the fact that the longitudinalwave has less dispersive nature at lowfrequency. On the other hand,when it comes to evaluation of poles in situ, it is different as poles are partly embedded in soil and it is more practical to produce bending waves, as the top of the pole is not easily accessible. However, bending wave is known for its highly dispersive nature; especially in the low frequency range which is usually induced in low strain integrity testing. As bending wave can be considered as a hybrid of longitudinal and shear waves, it will be helpful, if it could detect the component of these twowaves separately.To do so, components of displacements or accelerations along radial and longitudinal directions need to be determined. By applying Fast Fourier Transform (FFT) on the signals, the dominant frequencies can be obtained. It has been found that, the longitudinal component decreases along radial direction which indicates the presence of bending wave component and this finding allows to the application of ContinuousWavelet Transform (CWT) on the longitudinal component of wave signals in order to obtain phase velocity. Phase velocities at different frequencies are then determined to draw the dispersive curve and compare with analytical phase velocity curve. The dispersion curve matched well with the analytical curve. © 2013 Taylor & Francis Group.
Jiang, X., Li, Y. & Li, J. 2013, 'Design of a novel linear permanent magnet vibration energy harvester', 2013 IEEE/ASME International Conference on Advanced Intelligent Mechatronics: Mechatronics for Human Wellbeing, AIM 2013, pp. 1090-1095.
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This paper presents a novel linear tubular permanent magnet (PM) energy harvester to scavenge energy from ambient vibrations. The proposed linear PM energy harvester consists of a mover attached with PMs and a slotted stator with build-in two-phase electromagnetic coils to induce the electromagnetic induction for converting vibrations into useful electrical energy. The magnetic circuit model of the PM harvester is built to analyze the parameters about scavenging energy and used to optimize the non-dimensional geometry factors and the structural parameters in order to maximize harvested energy under given vibration and space conditions. To confirm the design, dynamic FE simulations were conducted and compared with the analytical results. Simulation results indicate that the proposed PM harvester is able to scavenge about 100 W DC power when the RMS of vibration velocity equals to 0.4 m/s. Also, the harvested power increases as the vibration velocity increasing. © 2013 IEEE.
Li, Y., Li, J. & Li, W. 2013, 'Design and experimental testing of an adaptive magneto-rheological elastomer base isolator', 2013 IEEE/ASME International Conference on Advanced Intelligent Mechatronics: Mechatronics for Human Wellbeing, AIM 2013, pp. 381-386.
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Magnetorheological elastomer (MRE) is known for its field-sensitive shear modulus and damping property when it is exposed to a magnetic field. It has a great potential for the development of vibration reduction devices. Many research, mostly in mechanical engineering, have been focused on different kinds of vibration absorbers and vibration isolators, however few research addresses its potential in base isolation system in civil engineering application. The objective of this paper is to pilot the design and experimental testing of a novel device, an adaptive MRE base isolator, for the development of smart base isolation system. A large-scale design of the novel device with unique laminated structure of steel and MR elastomer layers is adopted. Detailed procedures on designing such adaptive base isolator are introduced. An innovative design on the magnetic circuit, with aim to provide strong and uniform magnetic field to the multi-layer MRES, is proposed to incorporate into the device design. Experimental investigation is conducted to examine its behavior under various cycling loadings when it is applied with different current inputs. Experimental results indicated that the force increase and the stiffness increase of the novel device are about 45% and 37%, respectively. To conclude, the MR elastomer base isolator will be a promising candidate to facilitate the development of adaptive base isolation system for civil structures. © 2013 IEEE.
Yan, N., Li, J., Dackermann, U. & Samali, B. 2013, 'Numerical and experimental investigations of stress wave propagation in utility poles under soil influence', From Materials to Structures: Advancement Through Innovation - Proceedings of the 22nd Australasian Conference on the Mechanics of Structures and Materials, ACMSM 2012, pp. 593-598.
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Over the past decades, different types of non-destructive testing (NDT) methods have been developed for the condition assessment of timber structures. Stress wave methods, which are based on stress wave propagation theory, are considered to be simple and cost-effective tools for identifying damage as well as embedment length of timber poles/piles. However, due to the lack of understanding on wave propagation in such structures, especially under the influence of surroundings such as soil, these methods encounter difficulties in producing reliable results. In this paper, an investigation was carried out on the wave propagation behaviour in utility timber poles with consideration of soil effects. The commercial finite element (FE) analysis software ANSYS was used to simulate stress wave propagation in a timber utility pole under the influence of soil. In order to verify the numerical findings, laboratory testing was also conducted in conjuction with the numerical modelling. © 2013 Taylor & Francis Group.
Li, J., Li, Y., Li, W. & Samali, B. 2013, 'Development of adaptive seismic isolators for ultimate seismic protection of civil structures', Proceedings of SPIE - The International Society for Optical Engineering.
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Base isolation is the most popular seismic protection technique for civil engineering structures. However, research has revealed that the traditional base isolation system due to its passive nature is vulnerable to two kinds of earthquakes, i.e. the near-fault and far-fault earthquakes. A great deal of effort has been dedicated to improve the performance of the traditional base isolation system for these two types of earthquakes. This paper presents a recent research breakthrough on the development of a novel adaptive seismic isolation system as the quest for ultimate protection for civil structures, utilizing the field-dependent property of the magnetorheological elastomer (MRE). A novel adaptive seismic isolator was developed as the key element to form smart seismic isolation system. The novel isolator contains unique laminated structure of steel and MR elastomer layers, which enable its large-scale civil engineering applications, and a solenoid to provide sufficient and uniform magnetic field for energizing the field-dependent property of MR elastomers. With the controllable shear modulus/damping of the MR elastomer, the developed adaptive seismic isolator possesses a controllable lateral stiffness while maintaining adequate vertical loading capacity. In this paper, a comprehensive review on the development of the adaptive seismic isolator is present including designs, analysis and testing of two prototypical adaptive seismic isolators utilizing two different MRE materials. Experimental results show that the first prototypical MRE seismic isolator can provide stiffness increase up to 37.49%, while the second prototypical MRE seismic isolator provides amazing increase of lateral stiffness up to 1630%. Such range of increase of the controllable stiffness of the seismic isolator makes it highly practical for developing new adaptive base isolation system utilizing either semi-active or smart passive controls. © 2013 SPIE.
Jiang, X., Li, Y. & Li, J. 2013, 'A piezoelectric wafer-stack vibration energy harvester for wireless sensor networks', Proceedings of SPIE - The International Society for Optical Engineering.
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Over the past few decades, wireless sensor networks have been widely used in civil structure health monitoring application. Currently, most wireless sensor networks are battery-powered and it is costly and unsustainable for maintenance because of the requirement for frequent battery replacements. As an attempt to address such issue, this paper presents a novel piezoelectric vibrational energy harvester to convert the structural vibration into usable electrical energy for powering wireless sensor networks. Unlike the normal cantilever beam structure, the piezoelectric harvester presented in this paper is based on the wafer-stack configuration which is suitable for applications where large force vibration occurs, and therefore can be embedded in civil structures to convert the force induced by vibration of large structures directly into electrical energy. The longitudinal mode of the piezoelectric wafer-stack was developed firstly to illustrate the force-to-voltage relationship of piezoelectric materials and to find the inter-medium force that will be used to convert vibration energy into electrical energy. Then, two electromechanical models (without and with a rectified circuit), considering both the mechanical and electrical aspects of the harvester, were developed to characterize the harvested electrical power under the external load. Exact closed-form expressions of the electromechanical models have been derived to analyze the maximum harvested power and the optimal resistance. Finally, a shake table experimental testing was conducted to prove the feasibility of the presented piezoelectric-wafer-stack harvester under standard sinusoidal loadings. Test results show that the harvester can generate a maximum 45mW (AC) or 16mW (DC) electrical power for sinusoidal loading with 40mm amplitude and 2Hz frequency, and the harvested electrical power is proportional to the levels of exciting vibrational loading. © 2013 SPIE.
Li, Y. & Li, J. 2013, 'Development and modeling of a highly-adjustable base isolator utilizing magnetorheological elastomer', ASME 2013 Conference on Smart Materials, Adaptive Structures and Intelligent Systems, SMASIS 2013, American Society of Mechanical Engineers.
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This paper presents a recent research breakthrough on the development of a novel adaptive seismic isolation system as the quest for seismic protection for civil structures, utilizing the field-dependent property of the magnetorheological elastomer (MRE). A highly-adjustable MRE base isolator was developed as the key element to form smart seismic isolation system. The novel isolator contains unique laminated structure of steel and MRE layers, which enable its large-scale civil engineering applications, and a solenoid to provide sufficient and uniform magnetic field for energizing the field-dependent property of MR elastomers. With the controllable shear modulus/damping of the MR elastomer, the developed adaptive base isolator possesses a controllable lateral stiffness while maintaining adequate vertical loading capacity. Experimental results show that the prototypical MRE base isolator provides amazing increase of lateral stiffness up to1630%. Such range of increase of the controllable stiffness of the base isolator makes it highly practical for developing new adaptive base isolation system utilizing either semi-active or smart passive controls. To facilitate the structural control development using the adaptive MRE base isolator, an analytical model was developed to stimulate its behaviors. Comparison between the analytical model and experimental data proves the effectiveness of such model in reproducing the behavior of MRE base isolator, including the observed strain stiffening effect. Copyright © 2013 by ASME.
Askari, M., Li, J. & Samali, B. 2013, 'A multi-objective subtractive FCM based TSK fuzzy system with input selection, and its application to dynamic inverse modelling of MR dampers', Lecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics), pp. 215-226.
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A new encoding scheme is presented for a fuzzy-based nonlinear system identification methodology, using the subtractive Fuzzy C-Mean clustering and a modified version of non-dominated sorting genetic algorithm. This method is able to automatically select the best inputs as well as the structure of the fuzzy model such as rules and membership functions. Moreover, three objective functions are considered to satisfy both accuracy and compactness of the model. The proposed method is then employed to identify the inverse model of a highly nonlinear structural control device, namely Magnetorheological (MR) damper. It is shown that the developed evolving Takagi-Sugeno-Kang (TSK) fuzzy model can identify and grasp the nonlinear dynamics of inverse systems very well, while a small number of inputs and fuzzy rules are required for this purpose. © 2013 Springer-Verlag.
Yan, N., Dackermann, U.D., Li, J.L. & Samali, B.J. 2013, 'NUMERICAL INVESTIGATIONS OF MATERIAL PROPERTY CHANGES AND STRESS WAVE BEHAVIOUR IN TIMBER UTILITY POLES', The 6th International Conference on Structural Health Monitoring of Intelligent Infrastructure, The 6th International Conference on Structural Health Monitoring of Intelligent Infrastructure, Hong Kong Polytechnic University, Hong Kong.
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Subhani, M., Li, J.C., Gravenkamp, H. & Samali, B. 2013, 'Effect of elastic modulus and poisson's ratio on guided wave dispersion using transversely isotropic material modelling', Advanced Materials Research, pp. 303-311.
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Timber poles are commonly used for telecommunication and power distribution networks, wharves or jetties, piling or as a substructure of short span bridges. Most of the available techniques currently used for non-destructive testing (NDT) of timber structures are based on one-dimensional wave theory. If it is essential to detect small sized damage, it becomes necessary to consider guided wave (GW) propagation as the behaviour of different propagating modes cannot be represented by one-dimensional approximations. However, due to the orthotropic material properties of timber, the modelling of guided waves can be complex. No analytical solution can be found for plotting dispersion curves for orthotropic thick cylindrical waveguides even though very few literatures can be found on the theory of GW for anisotropic cylindrical waveguide. In addition, purely numerical approaches are available for solving these curves. In this paper, dispersion curves for orthotropic cylinders are computed using the scaled boundary finite element method (SBFEM) and compared with an isotropic material model to indicate the importance of considering timber as an anisotropic material. Moreover, some simplification is made on orthotropic behaviour of timber to make it transversely isotropic due to the fact that, analytical approaches for transversely isotropic cylinder are widely available in the literature. Also, the applicability of considering timber as a transversely isotropic material is discussed. As an orthotropic material, most material testing results of timber found in the literature include 9 elastic constants (three elastic moduli and six Poisson's ratios), hence it is essential to select the appropriate material properties for transversely isotropic material which includes only 5 elastic constants. Therefore, comparison between orthotropic and transversely isotropic material model is also presented in this article to reveal the effect of elastic moduli and Poisson's ratios on di...
Dackermann, U., Elsener, R.E. & Li, J.L. 2013, 'Experimental investigations of the modulus of elasticity of timber utility poles using static and dynamic material testing approaches', 6th International Conference on Structural Health Monitoring of Intelligent Infrastructure (SHMII-6), Hong Kong.
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Jozi, B.J., Dackermann, U., Braun, R.B., Li, J.L. & Samali, B.S. 2013, 'Separation of bi-directional stress waves for the non-destructive condition assessment of in-service timber utility', 6th International Conference on Structural Health Monitoring of Intelligent Infrastructure (SHMII-6), Hong Kong.
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Timber utility poles represent a significant part of Australia's infrastructure for power distribution and communication networks. 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 tools for assessing the condition of in-service poles seriously jeopardizes the maintenance and asset management. For example, 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.
Zeng, J., Guo, Y., Zhu, J., Li, Y. & Li, J. 2012, 'Magnetic Hysteresis Properties Measurement for Magneto-Rheological Elastomer', the 13th International Conference on Electrorheological Fluids and Magnetorheological Suspensions: Book of Abstracts, Gazi University, Ankara, Turkey, pp. 1-2.
Askari, M., Li, J. & Samali, B. 2012, 'Application of extended, unscented, iterated extended and iterated unscented Kalman Filter for real-time structural identification', Advances in Applied Mechanics Research, Conference Proceedings - 7th Australasian Congress on Applied Mechanics, ACAM 2012, National Committee on Applied Mechanics, pp. 1041-1051.
System identification refers to any systematic way of deriving or improving models of dynamical systems through the use of experimental and field testing input-output data. In the field of civil engineering, identification of the state of a structure during service condition under dynamic loading, such as earthquake, in order to detect any damage as it occurs, has posed a great challenge to the research community. Therefore, online and real-time structural identification has attracted a great deal of attentions in the structural engineering research over the past decades, especially when input-output measurement data are contaminated by high-level noise. Among real-time identification methods, one of the most successful and widely used methods for estimation of states and parameters is the Kalman filter and its various nonlinear extensions like Extended Kalman Filter (EKF) and iterated Extended Kalman Filter (IEKF). However, these methods are not effective in the case of highly nonlinear problems. To overcome the problem, two filtering techniques, namely unscented Kalman filter (UKF) and iterated unscented Kalman filter (IUKF), have been recently developed to handle any functional nonlinearity. In this paper, an investigation has been carried out on the aforementioned methods for their effectiveness and efficiencies through a highly nonlinear SDOF structure as well as a two-storey linear structure. Results show that, although IEKF is an improved version of EKF, the IUKF, in most of cases, produces better results on state estimation and parameter identification than UKF and IEKF. IUKF is also more robust to measurement noise levels compared to the other approaches.
Askari, M., Li, J. & Samali, B. 2012, 'Adaptive multiple forgetting factor recursive least square (AMFF-RLS) for realtime structural identification with unknown input', Advances in Applied Mechanics Research, Conference Proceedings - 7th Australasian Congress on Applied Mechanics, ACAM 2012, National Committee on Applied Mechanics, pp. 1052-1061.
System identification refers to any systematic way of deriving or improving models of systems through the use of experimental and field testing input-output data. In the field of civil engineering, identification of the state of the structure during the dynamic loads, such as earthquake, to predict the current state of the structure and detect any damage or hazard, when it occurs, has posed a great challenge to the research community. Therefore, online and real-time structural parameters identification has recently drawn more attractions, although few research works have been reported especially for cases where measurement data are contaminated by high-level noise and some of the excitations are unknown. The Recursive Least Square with single forgetting factor has been widely used in estimation and tracking of time-varying parameters in the fields of electrical and mechanical engineering. However, when there are multiple parameters that each (or some) varies with a different rate, this method cannot perform well. On the other hand, a priori information on the changing rate of the parameters might not be available, and the forgetting factors must be updated adaptively. This paper presents a new adaptive tracking technique, based on the Recursive Least Square (RLS) approach with Adaptive Multiple Forgetting Factors (AMFF). The proposed method considers an adaptive rule for each of the forgetting factors assigned to each of the parameters and thus, enables simultaneous estimation of the time-varying stiffness and damping of the storeys of the structure. Numerical examples show that results of this RLS-based approach are accurate and robust, in identification of the unknown parameters such as damping, stiffness and unknown excitations, even when the observed data are contaminated with different types and significant levels of noise.
Dackermann, U., Li, J.L. & Subhani, M.M.S. 2012, 'R&D of NDTs for Timber Utility Poles in Service - Challenges and Applications (Extension for Bridge Sub-Structures and Wharf Structures)', Workshop on Civil Structural Health Monitoring (CSHM-4), Berlin, Germany.
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Li, Y., Li, J. & Samali, B. 2011, 'Design of new generation magnetorheological pins', Incorporating Sustainable Practice in Mechanics of Structures and Materials - Proceedings of the 21st Australian Conference on the Mechanics of Structures and Materials, pp. 807-812.
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Recently, research and development of smart materials and structures for civil engineering applications have attracted increasing attentions from researchers around theworld. Smart devices can be incorporated into civil structures as smart structural members with intelligent and controllable capacities for optimally detecting and reacting to the internal and external changes.Within the smart devices, magnetorheological (MR) based devices are one of the most promising smart devices to be considered for civil structures. This paper presents a novel design of a new-generation MR pin joint with high-torque capacity. An innovative design and analysis of MR pin with radial slots at the surface of the rotary plate is proposed. Theoretical modelling is undertaken based on the material, mechanical and magnetic analyses. Parametric analysis is conducted to optimise the shape, width and depth of the slots to best accommodate the design objectives. © 2011 Taylor & Francis Group, London.
Dackermann, U., Li, J. & Samali, B. 2011, 'Identification of added mass on a two-storey framed structure utilising FRFs and ANNs', Incorporating Sustainable Practice in Mechanics of Structures and Materials - Proceedings of the 21st Australian Conference on the Mechanics of Structures and Materials, pp. 757-762.
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This paper presents a vibration-based damage detection method that utilises frequency response functions (FRFs) to identify added mass on a two-storey framed structure. Added mass is used to simulate frequency changes due to structural damage. Artificial neural networks (ANNs) are employed to map changes in FRFs to locations of the added mass. In order to obtain suitable inputs for neural network training, principalcomponent analysis (PCA) techniques are adopted to reduce the size of the FRF data and to filter noise. A hierarchy of neural network ensembles is used to take advantage of individual measurement characteristics from different sensors. The method is tested on laboratory and numerical models of a two-storey framed structure. From the two kinds of structures, FRF data are determined and compressed utilising PCA techniques. The PCAreduced FRFs are then used as input patterns for training and testing of ANN ensembles predicting different locations of added mass. © 2011 Taylor & Francis Group, London.
Samali, B., Li, J., Crews, K.I. & Choi, F. 2010, 'Damage evaluation of a repaired timber beam using modal-based method', Incorporating Sustainable Practice in Mechanics of Structures and Materials - Proceedings of the 21st Australasian Conference on the Mechanics of Structures and Materials (ACMSM21), Australasian Conference on the Mechanics of Structures and Materials, CRC Press/Balkema, Melbourne, Australia, pp. 751-755.
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For bridge structures, global damage evaluation and structural health monitoring using modal based damage identification methods have dominated recent worldwide research. However, to date there are few works reported on the effectiveness of the methods to evaluate the new conditions after the damaged structures have been repaired. In this paper, a modal based damage identification method for localisation of damage in a timber beam, utilising modal data from before and after damage as well as after repair, is presented based on expenmental resul!s. The method employs modal parameters that monitor changes in modal strain energy of damaged and repaired beams with respect to the undamaged one. Experimental modal analysis is used in the experimental work to acquire the modal parameters required by the method. The study aims to investigate the capability and limitations of the proposed method for identifying locations of damage in damaged and repaired timber structures.
Dackermann, U., Li, J. & Samali, B. 2011, 'Damage Identification on a Numerical Two-Storey Framed Structure using Ambient Vibration Response Analysis and Artificial Neural Networks', Proceeding of The 14th Asia Pacific Conferance, Dynamics for Sustainable Engineering, The Hong Kong Polytechnic University, Hong Kong, pp. 338-347.
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This paper presents a damage identification method based on ambient floor vibration measurements in multi-storey buildings. The proposed method uses ambient response vibration data to fannulate a damage index based on Frequency Response Functions (FRFs), which is used as input parameter to artificial neural networks (ANNs), to identify locations and severities of damage in a two-storey framed structure. By adopting principal component analysis (PCA) techniques, the Size of the derived damage index is reduced in order to obtain suitable patterns for ANN training. A hierarchy of neural network ensembles is designed to take advantage of individual characteristics of measurements from different floor locations. The proposed method is tested on finite element models of a complex two-storey framed structure inflicted with notch-type damage of different locations and severities (in total six damage cases). The results of the study show that the proposed algorithm is capable of accurately and reliably identifying damage in complex multi-storey structures based on response-only ambient floor vibration measurements.
Zad, A., Li, J., Samali, B. & Crews, K. 2011, 'Finite element evaluation of Non-Destructive Testing methods for embedded timber poles in service', Incorporating Sustainable Practice in Mechanics of Structures and Materials - Proceedings of the 21st Australian Conference on the Mechanics of Structures and Materials, pp. 909-914.
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This paper presents the results of numerical evaluation of surface Non-Destructive Testing methods for embedded timber poles in service. Main objective of the study is to investigate the influence of factors such as different boundary conditions, geotechnical conditions and material defects and imperfections of embedded timber poles, on reliability and accuracy of the prediction or evaluation using surface NDT. Firstly, the numerical evaluation of a free-end timber pole without embedmentwas conducted to gain an understanding of the behaviour of stress waves in timber poles in relation to selected surface NDT methods. Then the embedded timber poles are modelled to include effects of geotechnical conditions as in-service poles. Two types of typical decay patterns are simulated to study the effect of defect/damage on the Non-Destructive Testing results. Finally, the numerical results are compared with field test results obtained from field testing in Victoria. © 2011 Taylor & Francis Group, London.
Dackermann, U., Li, J., Samali, B., Choi, F. & Crews, K.I. 2011, 'Damage Severity Assessment of Timber Bridges using Frequency Response Functions (FRFs) and Artificial Neural Networks (ANNs)', International Conference on Structural Health Assessment of Timber Structures, International Conference on Structural Health Assessment of Timber Structures, Laboratorio Nacional de Engenharia Civil, Lisbon, pp. 63-71.
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This paper presents a novel vibration-based technique that utilises changes in frequency response functions (FRFs) to assess advancement of damage in timber bridges. In the proposed method, damage patterns embedded in FRF data are extracted and analysed by using a combination of principal component analysis (PCA) and artificial neural network (ANN) techniques for estimation of severity levels of damage. To demonstrate the method, it is applied to a laboratory four-girder timber bridge, which is gradually inflicted with accumulative damage at different locations and severities. To extract damage features in FRFs and to compress the large size of FRF data, FRFs are transferred to the principal component space adopting PCA techniques. PCA-compressed FRF data are then used as inputs to ANNs to identify severities of damage. The excellent severity predictions obtained from the ANNs show that FRF data can potentially be very good indicators for the assessment of damage advancements in timber bridges.
Saleh, A., Li, J. & Lucas, J. 2011, 'Internet-hosted assessment system for effective teaching and enhanced learning for engineering subjects', Proceedings of the 22nd Annual Conference for the Australasian Association for Engineering Education (AAEE2011) - Developing Engineers for Social Justice: Community Involvement, Ethics & Sustainability, AAEE - Annual Conference of Australasian Association for Engineering Education, Engineers Australia, Fremantle, WA, pp. 505-509.
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Despite of their popularity, online Learning Management Systems suffer serious limitations as a reliable and effective assessment tool in their implementation for engineering education, partly due to their demand for equation manipulation and multiple stage problem solving. An innovative spreadsheet based assessment tool (e-Task) which is designed to overcome such shortcoming and provides effective teaching and enhanced learning for engineering subjects has been proposed by the authors. The tool was developed for both formative and summative assessments with a capability to automatically collect not only results but also feedback from students on their perceived learning. Building on the previous work, this paper presents a further development by introducing a new deployment concept of the e-Task through internet-hosting of the system in order to enable effective teaching and enhanced learning of engineering subjects. The proposed internet-hosted assessment system (e-Task) integrates state-of-the-art cloud computing technology by incorporating a spreadsheet-like environment that can accommodate a wider range of users and course developers as well as enables easier expansion of the system in the future. It greatly enhances the fundamental concepts proposed in the original e-Taks by offering better accessibility, flexibility and controllability. It obviates any need of a specific software or hardware for the operational platform and requires only Internet access for its operation. Features of the Internet hosted e-Task include: the ability to access it by various Internet browsers, embedding learning and diagnostic feedback, individualised data sets for each students and automated marking & feedback.
Subhani, S., Li, J., Samali, B. & Dackermann, U. 2011, 'Determinations of Stress Wave Velocity in a Timber Pole using Wavelet Transform', Proceeding of The 14th Asia Pacific Conferance, Dynamics for Sustainable Engineering, The Hong Kong Polytechnic University, Hong Kong, pp. 222-231.
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This paper presents an application of Wavelet Transform (WT) for determination of stress wave velocity for Non-destructive Testing of timber utility poles in service. For surface Non-destructive Testing (NDT), the hammer impact, which produces generally broadband frequency excitation, is used to generate stress wave. Moreover, due to practicality the impact location for field testing of a utility pole is on the side of the pole and 1.5 m above ground level. And the geometry of utility pole could not guarantee non-dispersive longitudinal wave. All of these issues have resulted in lack of accuracy and reliability of results from surface NDT in field testing. In recognition of such problem, this research explores methods to reliably calculate desired wave velocity by isolating wave mode and studying dispersive nature of utility pole. Fast Fourier Transform (FFT) is firstly conducted to determine the suitable frequency from a stress wave data. Then WT is applied on the wave data mentioned to perform time-frequency analysis. Velocity can be determined by time history data of desired frequency from WT results which will be compared with the available analytical solution for longitudinal wave velocity. The results of the investigation showed that wavelet transform analysis can be a reliable signal processing tool for non-destructive testing in terms of velocity determination, which in turn also helps to determine the embedded length of the timber pole.
Askari, M., Li, J. & Samali, B. 2011, 'Semi-Active LQG Control of Seismically Excited Nonlinear Buildings using Optimal Takagi-Sugeno Inverse Model of MR Dampers', Procedia Engineering: The Proceedings of the Twelfth East Asia-Pacific Conference on Structural Engineering and Construction EASEC12, East Asia-Pacific Conference on Structural Engineering and Construction, Elsevier, Hong Kong, pp. 2765-2772.
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A novel semi-active control method for a seismically excited nonlinear benchmark building equipped with magnetorheological (MR) dampers is presented and evaluated in this paper. While Linear Quadratic Gaussian (LQG) controller is designed to estimate the optimal control force of a MR damper, the required voltage input for the damper to produce such control force is achieved by a proposed optimal Takagi- Sogeno(T-S) fuzzy inverse model. The proposed T-S fuzzy inverse model of dampers is derived using subtractive clustering, non-dominated sorting genetic algorithm II (NSGAII) and adaptive neuro-fuzzy inference systems (ANFIS). The effectiveness of this strategy is illustrated and verified using simulated response of a 20-storey full-scale nonlinear benchmark building excited by several historical earthquake records. The designed semi-active system is compared with the performances of active control as well as clipped optimal control (COC) systems, which are based on the same nominal controller as is used in this study. The results are discussed based on the evaluation criteria suggested for the benchmark problem by International Association for Structural Control and Monitoring (IASCM) for comparison with other algorithms and demonstrate the superiority of this scheme over other strategies.
Saleh, A. & Li, J. 2010, 'Innovative Assessment and Feedback System for Structural Engineering Education', Proceedings of the 21st Annual Conference for the Australasian Association for Engineering Education, Annual Conference of Australasian Association for Engineering Education, University of Technology, Sydney, Sydney, Australia, pp. 315-321.
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Commercial Online course management platforms are increasingly used in teaching and learning in many disciplines. However their use for setting assessment tasks in engineering education is often difficult and limited in achieving desired teaching and learning objectives. This is partly due to the nature of engineering exercise problems which often requires equation manipulation and multi-stage problem solving. This paper presents an innovative spreadsheet based tool which is designed to cater for this type of problem. The tool was developed for both formative and summative assessments and with a resource optimal capability to automate both marking and collecting timely feedback from students on their perceived learning. It aims to encourage active learning with activatable hints and to minimise plagiarism by generating individual assignment data for each student.
Li, J., Müller-Tomfelde, C. & Hyatt, A. 2010, 'Supporting collaborations across a biocontainment barrier', ACM International Conference Proceeding Series, pp. 320-323.
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We present the design process of a collaboration platform which allows research and diagnostics scientists in an animal health laboratory to work collaboratively across a biocontainment barrier. This Biosecurity Collaboration Platform (BCP) integrates high quality audio-video communications with a large shared interactive workspace. It enables real-time sharing of a broad range of data from various data repositories and computer applications, including microscope imaging. We describe the one-year design and development activities which included field study, scenario-based use case analysis, iterative design and evaluations. We highlight factors relating to the unique setting and the associated difficulties in information sharing and communication. We discuss the importance of an appropriate design approach and our solution of an integrated interaction and communication workspace with appropriate configurations to support the scientific collaborations. Copyright the author(s) and CHISIG.
Dackermann, U., Li, J.L. & Samali, B.S. 2010, 'Quantification of notch-type damage in a two-storey framed structure utilising frequency response functions and artificial neural networks'', 5th Fifth World Conference on Structural Control and Monitoring (5WCSCM), Tokyo, Japan.
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Choi, F., Li, J., Samali, B. & Crews, K.I. 2008, 'Non Destructive Testing of a Timber Beam using Vibration-Based Approach', The 9th International Conference on Motion and Vibration Control, Technique Universaetet, Munich.
Dackermann, U., Li, J., Samali, B., Choi, F. & Crews, K.I. 2008, 'Variation-Based Damage Identification in Civil Engineering Structures Utilising Artificial Neural Networks', Proc. Structural Faults & Repairs 2008 12th International Conference, Engineering Technics Press, Edinburgh, pp. 132-132.
Wang, Y., Li, J., Samali, B. & Sri Ravindrarajah, R. 2008, 'A New Damage Detection Method for Reinforced Concrete Beams Based on Modal Strain Energy', Proceedings of the 9th International Conference on Motion and Vibration Control, International Conference on Motion and Vibration Control, Technische Universitaet Muenchen, Munich, pp. 1-10.
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Choi, F., Li, J., Samali, B. & Crews, K.I. 2008, 'Overview of Dynamic Based Damage Detection for Timber Bridges', On-Site Assessment of Concrete, Masonry and Timber Structures - Volume 2, On Site Assessment of Concrete, Masonry and Timber Structures, RILEM Publications, Varena, Italy, pp. 1125-1135.
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Asset management of bridges throughout the world faces increasing challenges as a result of aging infrastructure and inadequate funding. Replacement of an old bridge is neither viable nor sustainable in many circumstances. As a consequence, there is an urgent need to develop and utilise state-of-the-art techniques to assess and evaluate the "health state" of existing bridges and to be able to understand and quantify the effects ofdegradation in regard to public safety. This paper presents an overview of experimental work for a project in developing and implementing several dynamic methods for evaluation of damage in timber bridges. The technique of detecting damage involved the use of modal strain energy commonly referred to in the literature as damage index methods. The project started with simple beams subjected to single and multiple damage and then was extended to a scale timber bridge constructed under laboratory conditions. It was found that after modification on the damage index method, it was well suited to detect single and multiple damage scenarios for a one-dimensional beam. For the laboratory bridge, the damage index method developed for plate-like structures was successful in detecting single and multiple damage with an acceptable degree of accuracy.
Li, J., Samali, B. & Xu, Y.L. 2008, 'A new modal based damage detection approach utilising added mass', Futures in Mechanics of Structures and Materials - Proceedings of the 20th Australasian Conference on the Mechanics of Structures and Materials, ACMSM20, pp. 789-793.
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To reliably detect structural damage and estimate damage severity at its early stage poses a great challenge to engineering community. Despite a great deal of research and development in the areas of damage detection and health monitoring, there are very few successful applications in real life damage detection in engineering practices. One of the main obstacles for successful application of damage detection algorithms to real life civil infrastructure is the complex nature of structures and the uncertainties associated with modelling and measurement. This paper presents a new modal based damage detection approach aiming to provide an effective means to improve reliability and accuracy of damage detection. The proposed approach requires measurement data from two states of the structure, i.e. data from the structure "as-is" and data from the structure after adding a known mass. By means of experimental modal analysis (EMA), the modal parameters of the structure with and without added mass can be obtained. With modal parameters of the said two states and the known added mass, the proposed method will be able to produce the "in-service" system stiffness matrix. With the element connectivity being known a priori (or assumed reasonably), the "in-service" element stiffness can be obtained. Location of damage as well as damage severity of the structure will therefore be known. Experimental verification of the proposed method was carried out using a three storey shear building model. The experimental results show that the proposed damage detection method is superior in both damage localisation and damage severity estimation. © 2009 Taylor & Francis Group, London.
Dackermann, U., Li, J., Samali, B., Choi, F. & Crews, K.I. 2008, 'Experimental Verification of A Vibration-Based Damage Identification Method In A Timber Structure Utilising Neural Network Ensembles', Proc. SACOMATIS 2008, On Site Assessment of Concrete, Masonry and Timber Structures, RILEM Publications, Italy, pp. 1049-1058.
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Dackermann, U., Li, J. & Samali, B. 2008, 'Damage Index Method for Damage Identification Utilising Artificial Nerual Networks', Proc. MOVIC 2008, MOVIC, Munich, pp. 1-10.
Dackermann, U., Samali, B. & Li, J.L. 2008, 'Damage Identification based on Modal Strain Energy utilising Nerual Network Ensembles', Proc. ASEC 2008, Australian Structural Engineering Conference, The Meeting Planners, Melbourne, pp. 1-10.
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Dackermann, U., Li, J. & Samali, B. 2008, 'Structural damage identification utilising PCA-compressed frequency response functions and neural network ensembles', Futures in Mechanics of Structures and Materials - Proceedings of the 20th Australasian Conference on the Mechanics of Structures and Materials, ACMSM20, pp. 803-809.
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This paper presents a damage detection method that utilises FRF data to identify damage in beam structures. The proposed method uses artificial neural networks (ANNs) to map changes in FRFs to damage characteristics. To obtain suitable patterns for ANN inputs, the size of the FRFs is reduced adopting Principal Component Analysis (PCA) techniques. A hierarchy of neural network ensembles is created to take advantage of individual differences from sensor signals. To simulate field applications, the time history data are polluted with white Gaussian noise. The method involves finite element modelling of undamaged and damaged steel beams. By performing transient analysis with the numerical beams, the time histories are obtained and subsequently polluted with different levels of white Gaussian noise. FRFs are determined and compressed utilising PCA techniques. The PCA-reduced FRFs are then used as input patterns for training and testing of neural network ensembles giving the characteristics of the damage. © 2009 Taylor & Francis Group, London.
Samali, B., Li, J. & Aboura, K. 2008, 'Monitoring bridge deterioration using sensors', Proceedings - 3rd International Conference on Broadband Communications, Informatics and Biomedical Applications, BroadCom 2008, pp. 64-69.
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Structural health monitoring is a vital part in the management of bridges, particulary as the structures begin to age. Detecting structural faults through the use of sensors is an emerging field that has seen considerable efforts this past decade. Similarly, the use of sensors in bridge management systems provides valuable data on the condition of bridges and external factors affecting the deterioration of bridges such as the traffic load endured by the structures. We review both cases of visual and vibration based monitoring of bridges and showcase an on-line monitoring system for the collection of traffic information. © 2008 IEEE.
Aboura, K., Samali, B., Crews, K. & Li, J. 2008, 'Stochastic deterioration processes for bridge lifetime assessment', Proceedings - 3rd International Conference on Broadband Communications, Informatics and Biomedical Applications, BroadCom 2008, pp. 437-442.
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The Markov chain model can be found in the maintenance and repair problems since the early 60's, is introduced to the maintenance of road infrastructure in the 1980's, and is made to drive the current bridge maintenance optimization systems. While this model results into solvable programming problems and provides a solution, there are a number of criticisms associated with it. In this article, we highlight the shortfalls of the Markov model for bridge infrastructure lifetime assessment and promote the use of stochastic processes. We use examples from a study for the modeling of the condition of bridges that considers more than 15 years of data. We argue for the applicability of the gamma process and other stochastic processes. © 2008 IEEE.
Aboura, K., Samali, B., Crews, K. & Li, J. 2008, 'Stochastic processes for modelling bridge deterioration', Futures in Mechanics of Structures and Materials - Proceedings of the 20th Australasian Conference on the Mechanics of Structures and Materials, ACMSM20, pp. 533-538.
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Traditionally, bridge management systems were designed using Markov chain models. Recently, researchers applied the gamma process successfully to structural deterioration problems. The stochastic process captures the temporal variability of degradation, and has been applied to a range of problems in structures. We report on a study for the modelling of the condition of bridges in the state of NSW. The study encompasses large amounts of data spanning more than 15 years. We argue for the applicability of the gamma process and other stochastic processes. While the gamma process has been adopted in the past decade on grounds of mathematical tractability and physical motivation, we also observe another distribution for the deterioration at different times. The finding promotes the stochastic process modelling direction taken in the past decade and brings forth new models for the time-dependent reliability analysis of bridges. © 2009 Taylor & Francis Group, London.
Choi, F., Li, J., Samali, B. & Crews, K.I. 2008, 'Overview of Dynamic Based Damage Detection of Timber Bridges', Proceedings of 12th International Conference STRUCTURAL FAULTS & REPAIR-2008, 12th International Conference STRUCTURAL FAULTS & REPAIR-2008, University of Edinburgh, Edinburgh, Scotland, pp. 1-13.
Asset management of bridges throughout the world faces increasing challenges as a result of ageing infrastructure and inadequate funding. Replacement of an old bridge is neither viable nor sustainable in many circumstances. As a consequence, there is an urgent need to develop and utilise state-of-the-art techniques to assess and evaluate the âthe state of healthâ? of existing bridges and to be able to understand and quantify the effects of degradation in regard to public safety. This paper presents an overview of part of the numerical work for a project recently completed by the authors to develop and implement dynamic methods for evaluation of damage in timber bridges. The damage detection technique involved the use of a modal strain energy based method, commonly referred to in the literature as damage index methods. The project started with simple beams subjected to single and multiple damage scenarios. The research was then extended to a scaled laboratory timber bridge. It was found that with proper modification, the damage index method was well suited to detect single and multiple damage scenarios for a onedimensional beam. For the laboratory timber bridge, the damage index method, developed for plate-like structures, can detect single and multiple damage locations with certain level of errors.
Li, Y., Li, J., Samali, B. & Wang, J. 2008, 'Theoretical and experimental studies on semi-active smart pin joint', Futures in Mechanics of Structures and Materials - Proceedings of the 20th Australasian Conference on the Mechanics of Structures and Materials, ACMSM20, pp. 723-728.
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An intelligent structural system equipped with smart structural members that are controllable in real-time is one effective solution to prevent structural damage and failure during hostile dynamic loadings, thereby leading to effective protection of structures and their occupants. The primary purpose of this study is to design, fabricate and characterise a prototype smart member, namely a semi-active magnetorheological (MR) pin joint, through theoretical modelling and experimental investigation. Design of prototype smart pin joints includes theoretical analysis relating to the rotary plate radius, the property of MR fluids and the gap between the rotary plate and the casing based on the requirements of the dynamics of MR pin joints. It is verified that an MR pin joint with a diameter of 180 mm can produce a torque of up to 30 Nm, which is deemed adequate for realisation of the semi-active control for multi-storey building models in the next stage of research. © 2009 Taylor & Francis Group, London.
Choi, F., Li, J., Samali, B. & Crews, K.I. 2006, 'Damage Evaluation of a timber Beam Using a Modal-based Method', Proceeding of the 19th Australasian Conference on the Mechanics of Structures and Materials - Progress in Mechanics of Structures and Materials, Australasian Conference on the Mechanics of Structures and Materials, Taylor and Francis, Christchurch, New Zealand, pp. 1005-1010.
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Li, J., Choi, F. & Samali, B. 2006, 'Modal-based damage identification methods for plate-like structures', Proceedings of the 19th Australasian Conference on the Mechanics of Structures and Materials - Progress in Mechanics of Structures and Materials, Australasian Conference on the Mechanics of Structures and Materials, Taylor and Francis, Christchurch, New Zealand, pp. 909-914.
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Li, J., Samali, B. & Crews, K.I. 2006, 'A cost effective approach for integrity assessment of timber bridges', Proceedings of the 19th Australasian Conference on the Mechanics of Structures and Materials - Progress in Mechanics of Structures and Materials, Australasian Conference on the Mechanics of Structures and Materials, Taylor and Francis, Christchurch, New Zealand, pp. 1037-1042.
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Widjaja, J., Samali, B. & Li, J. 2007, 'The use of displacement threshold for switching frequency strategy for structural vibration mitigation', Journal of Mechanical Science and Technology, pp. 865-869.
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This paper presents a study of controllable real-time frequency shift using a fluid pin damper, so called 'smart pin', mounted at a beam-column connection. Unlike the stationary frequency shifter, the pin can increase or decrease the rotational stiffness of the connection, leading to an actively adjustable structural frequency due to real-time responses of polarised magneto-rheological (MR) fluid, whose rheological properties can change in milliseconds. The feedback to the pin damper governs the structural frequency changes. To demonstrate this concept, a single storey plane steel frame model with one hinge and one 'smart pin' damper, mounted at each beam-column connection and subjected to two scaled earthquake excitations, namely El-Centro 1940 and Northridge 1994, which respectively represent near- and far-field excitations, was tested using the shake table at the University of Technology, Sydney (UTS) structures laboratory, for 'proof-of-concept' investigation. Further, the dynamic performance of the model using a proposed switching strategy with a displacement threshold as an indicator for alternately supplied current level (flip-flop) was examined, assuming the earthquake records were known. The results showed some potential use of this control technique for structural vibration mitigation, however, further study to optimize the performance of the switching strategy is still required.
Samali, B., Choi, F., Li, J. & Crews, K.I. 2007, 'Experimental investigations on a laboratory timber bridge using Damage Index Method for plate-like structures', Proceedings of the 5th Australasian Congress on Applied Mechanics, ACAM 2007, Australasian Congress on Applied Mechanics, Engineers Australia, Brisbane, Australia, pp. 114-119.
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A great deal of work has been done in the area of damage identification in structures using changes of modal parameters before and after damage. Most of the developments have been based on beam theory and applied to beam-like or truss structures. Few researchers have made contributions to damage identification of plate-like structures employing a damage index method, especially for timber structures. In this paper, experimental investigations on a laboratory timber bridge using damage index method for plate-like structures are reported. Experimental modal analysis was performed to extract essential modal parameters from test data. Mode shape curvatures derived from the mode shapes were utilised in a damage index method for plate-like structures to detect single and two damage scenarios in a timber bridge. The purpose of the study is to explore feasibility of using modal strain energy based methods for damage identification of plate-like structures. The results show that the damage index method for plate-like structures using higher modes provides reasonable damage localisation for single and multiple damage cases.
Nguyen, M.T., Kwok, N.M., Ha, Q.P., Li, J. & Samali, B. 2007, 'Semi-active direct control of civil structure seismic responses using magneto-rheological dampers', Automation and Robotics in Construction - Proceedings of the 24th International Symposium on Automation and Robotics in Construction, pp. 157-162.
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As building structures frequently collapse and cause losses of lives and properties, due to excessive vibrations induced during earthquake periods, it is crucial to reduce the structural vibrations. This paper develops a Lyapunov-based controller for Magnetorheological (MR) dampers embedded in building structures to mitigate quake-induced vibrations. In this work, MR dampers are used as semi-active devices, taking the advantages of the fail-safe operation and low power requirement. To enhance the system performance, a Lyapunov-based controller is proposed here for direct control of the supply currents of the MR dampers placed in a multi-storey building. The effectiveness of the proposed technique is verified in simulation by using a ten-storey building model subject to quake-like excitations.
Nguyen, M., Kwok, N., Ha, Q.P., Li, J. & Samali, B. 2007, 'Mitigation of Seismic Responses in Building Structures using Magneto-rheological Dampers', Proceedings of the 24th International Symposium on Automation and Robotics in Construction (ISARC 2007), International Symposium of Automation and Robotics in Construction, Indian Institute of Technology Madras, Kochi, Kerala, India.
Kwok, N., Nguyen, T., Ha, Q.P., Li, J. & Samali, B. 2006, 'Parameter Identification for a simple MR Damper model using Particle Swarm Optimisation', Disgest Book of the Asia Pacific Symposium on Applied Electromagnetic and Mechanics, Asia Pacific Symposium on Applied Electromagnetics and Mechanics, UTS, Sydney, Australia, p. 11.
Nguyen, T., Kwok, N., Ha, Q.P., Li, J. & Samali, B. 2006, 'Symmetric Quantized Sliding Model Control for Civil Structures Using Magnetorcheological Dampers', Digest Book of the Asia-Pacific Symposium on Applied Electromagnetics and Mechanics, Asia Pacific Symposium on Applied Electromagnetics and Mechanics, UTS, Sydney, Australia, p. 47.
Li, J., Samali, B., Crews, K.I., Choi, F., Brown, P.W., Al-Dawod, M. & Shrestha, R. 2005, 'theoretical and Experimental Studies on Assessment of Bridges Using Simple Dynamic Procedures', Australian Structural Engineering Conference 2005: Structural Engineering - Preserving and Building Into the Future, Australian Structural Engineering Conference, Tour Hosts Pty Ltd, Newcastle, Australia.
Widjaja, J.H., Samali, B., Li, J. & Reizes, J. 2005, 'Seismic Structural Control Investigations Using a Prototype Magneto-rheological Shear Damper', Australian Structural Engineering Conference 2005: Structural Engineering - Preserving and Building into the Future, Australian Structural Engineering Conference, Tour Hosts Pty Ltd, Newcastle, Australia.
Samali, B., Dowling, D.M. & Li, J. 2005, 'Dynamic Response of U-Shaped Adobe-Mudbrick Wall Units', Austrlaian Structural Engineering Conference 2005: Structural Engineering - Preserving and Building Into the Future, Australian Structural Engineering Conference, Tour Hosts Pty Ltd, Newcastle, Australia.
Choi, F.C., Li, J., Samali, B. & Crews, K. 2006, 'Impact of different numerical techniques on damage identification in structures', Materials, Experimentation, Maintenance and Rehabilitation - Proceedings of the 10th East Asia-Pacific Conference on Structural Engineering and Construction, EASEC 2010, pp. 111-116.
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Damage identification techniques have been widely investigated and used for structural damage evaluation. Many researchers have shown good results in detecting, locating and quantifying damage in structures using various damage identification algorithms and methods. One of the popular and promising damage identification methods is modified damage index (MDI) which utilises modal strain energy (MSE) and a statistical approach. However, when using this damage identification method, numerical techniques used in realising the damage detection algorithm plays an important role for the final outcome. The use of different techniques in detection of damage has not been widely investigated. In this paper, a finite element (FE) model of a timber beam was developed as a test structure. Modal responses of the test structure were generated using a FE software package. The damage index algorithm, utilising modal strain energy as its damage indicator, was computed. In the computation process, different numerical techniques at different stages were utilised to process the data. Since in practice, the number of modal data is usually limited, it is recommended that the mode shape data to be expanded using mode shape reconstruction technique. Thus, the raw data was reconstructed using two different mode shape reconstruction techniques, namely Shannon's sampling theorem and cubic spline. The computation of MDI is enabled by numerical integration method. In this paper, two numerical integration methods were performed viz trapezoidal and rectangular rules. The manipulated data is subsequently transformed into standard normal space. The mode shape was mass normalised and the mode shape curvature was normalised with respect to the maximum value of each considered mode. For practicality purposes, the first two flexural mode shapes were used in the algorithms computation. Among the two proposed numerical integration methods, the rectangular rule has shown greater potential. The cubic spli...
Li, J., Choi, F., Samali, B. & Crews, K.I. 2006, 'Damage Localisation and Severity Evaluation of a Beam-like timber Structure based on modal strain energy and flexibility approaches', Proceedings of the Eleventh International Conference on Structural Faults and Repair 2006, International Conference on Structural Faults and Repairs, Engineering Technics Press, Edinburgh, U.K., pp. 1-9.
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Li, J., Choi, F., Samali, B. & Crews, K.I. 2006, 'Damage Detection in a Timber Beam', Proceedings of the Eleventh International Conference on Structural Faults and Repair 2006, International Conference on Structural Faults and Repair, Engineering Technics Press, Edinburgh, U.K., pp. 1-10.
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Nguyen, T., Kwok, N., Ha, Q.P., Li, J. & Samali, B. 2006, 'Adaptive sliding mode control for civil structure using magnetorheological dampers', Proceedings 23rd International Symposium on Automation and Robotics in Construction, International Symposium of Automation and Robotics in Construction, Japan Robot Association, Tokyo, Japan, pp. 636-641.
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Choi, F., Samali, B., Crews, K.I. & Li, J. 2006, 'Calibration of a Laboratory Timber Bridge Finite Element Model using the Experimental Modal Data', Proceedings CD of WCTE 2006 - 9th World Conference on Timber Engineering, World Conference on Timber Engineering, WCTE 2006, Portland, Oregon, USA, pp. 1-8.
In recent years, a great deal of attention has been focused on the condition and safety of aging timber bridges in Australia. Vibration-based damage identification techniques to detect structural deterioration at an early stage have significant potential to reduce the costs and down-time associated with repair of damaged members as well as enhancing the safety and reliability of timber bridges. In this paper, the process of developing and calibrating a scale timber bridge, which accurately simulates the behaviour of a ?real? bridge under laboratory conditions, is presented. A finite element (FE) model has been developed and calibrated with experimental modal data. The FE model shows acceptable correlations when compared to the experimental data, with minor adjustment of the actual material properties. It forms a tool for predicting the behaviour of the damaged laboratory bridge, as well as potential identification of damage in real timber bridges.
Kwok, N., Ha, Q.P., Li, J. & Samali, B. 2005, 'Parameter Identification for a Magnetorheological Fluid Damper: An Evolutionary Computation Approach', Proceedings of the 6th International Symposium on Intelligent Technologies, International Symposium on Intelligent Technologies in Tech'05, Faculty of Science and Technology, Assumption University, Phuket, Thailand, pp. 115-122.
Samali, B., Dowling, D.M. & Li, J. 2004, 'Dynamic Testing of Unreinforced U-Shaped Adobe-Mudbrick Wall Unit', Developments in Mechanics of Structures and Materials, Australasian Conference on the Mechanics of Structures and Materials, A A Balkema, Perth, Australia, pp. 505-510.
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Samali, B., Widjaja, J.H., Li, J. & Reizes, J. 2004, 'Smart Braced Frame Systems', Developments in Mechanics of Structures and Materials, Australasian Conference on the Mechanics of Structures and Materials, A. A. Balkema, Perth, Australia, pp. 401-406.
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Samali, B., Widjaja, J.H., Li, J., Dackermann, U. & Brown, P.W. 2005, 'Amplitude Frequency Characteristics of 'Smart'-Pin Frame System', Proceedings of the 11th Asia Pacific Vibration Conference, Asia Pacific Vibration Conference, Universiti Teknologi Malaysia, Langkawi, Malaysia, pp. 228-233.
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Samali, B., Dowling, D.M. & Li, J. 2005, 'Dynamic Response of U-Shaped Adobe-Mudbrick Wall Units', Australian Structural Engineering Conference 2005: Structural Engineering - Preserving and Building into the Future, Australian Structural Engineering Conference, Tour Hosts Pty Limited, Newcastle, Australia, pp. 1-9.
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Widjaja, J.H., Samali, B., Li, J. & Reizes, J. 2005, 'Seismic Structural Control Investigations Using a Prototype Magnetorheological Shear Damper', Australian Structural Engineering Conference 2005: Structural Engineering - Preserving and Building into the Future, Australian Structural Engineering Conference, Tour Hosts Pty Limited, Newcastle, Australia, pp. 1-11.
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Widjaja, J.H., Samali, B., Li, J. & Reizes, J. 2005, 'Dynamic Frequency De-Tuning Using Controllable Beam-Column Semi-Rigid Connections', Proceedings of 4th Australasian Congress on Applied Mechanics, Australasian Congress on Applied Mechanics, Institute of Materials Engineering Australasia Ltd, Melbourne, Australia, pp. 807-813.
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Choi, F., Samali, B., Li, J., Brown, P.W. & Dackermann, U. 2005, 'Investigation on the Dynamic Response of a Damaged Bridge', Proceedings of the 11th Asia-Pacific Vibration Conference, Asia Pacific Vibration Conference, Universiti Teknologi Malaysia, Langkawi, Malaysia, pp. 274-280.
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Choi, F.C., Samali, B., Crews, K. & Li, J. 2005, 'Static and dynamic evaluation of continuity effect of corbels in timber bridges', 4th Australasian Congress on Applied Mechanics, ACAM 2005, pp. 285-291.
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This paper presents part of the ongoing experimental and analytical work to investigate the effect of corbels on continuity in timber bridges. Full scale beams with corbels were erected for testing the extreme boundary conditions such as simply supported and fixed end conditions. The states of continuity in the test beams were assessed through a three span beam loading test set up. Dynamic tests were performed on the test beams and the modal parameters extracted were compared against those obtained for simply supported beams without corbel. Analytical investigations were conducted and then compared with the experimental results. The static experimental results obtained showed changes in the vertical displacement for different boundary conditions. The magnitude of reduction in the measured vertical displacement was fairly sensitive to the change of boundary conditions. Hence, changes in vertical displacement at mid-span can be used as an indicator for different boundary conditions, which relate to the effect of corbel on both continuity and effective span length in a structural system, especially for timber bridges. A comparative analysis of the first natural frequency for each boundary condition was then undertaken with reference to a simply supported benchmark. The analysis confirmed that the effects of changes in the boundary can be detected using modal parameters. © Institute of Materials Engineering Australasia Ltd 2005.
Dowling, D.M., Samali, B. & Li, J. 2005, 'An Improved Means of Reinforcing Adobe Walls-External Vertical Reinforcement', Sismo Adobe 2005, Sismo Adobe 2005, Arquitectura, Construccion y Convervacion de Edificaciones de Tierra en Areas Sismicas, Pontificia Universidad Catolica del Peru, Lima, Peru, p. CD Rom.
Li, J. & Samali, B. 2005, 'Fuzzy Sliding Mode Control of Seismically Excited Structure Using Magnetorheological Dampers', Developments in Mechanics of Structures and Materials, Australasian Conference on the Mechanics of Structures and Materials, A A Balkema, Perth, Australia, pp. 479-484.
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Li, J., Samali, B., Choi, F. & Dackermann, U. 2005, 'Damage Identification of Timber Bridge Using Vibration Based Methods', Proceedings of the 11th Asia-Pacific Vibration Conference, Asia Pacific Vibration Conference, Universiti Teknologi Malaysia, Langkawi, Malaysia, pp. 662-668.
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Li, J., Samali, B., Crews, K.I. & Shestha, R. 2005, 'Theoretical and Experimental Studies on Assessment of Bridges Using Simple Dynamic Procedures', Australian Structural Engineering Conference 2005: Structural Engineering - Preserving and Building into the Future, Australian Structural Engineering Conference, Tour Hosts Pty Limited, Newcastle, Australia, pp. 1-11.
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Li, J., Samali, B. & Smith, S.T. 2005, 'Stiffness estimation and damage detection of fibre reinforced polymer strengthened reinforced concrete beams using a vibration-based method', 4th Australasian Congress on Applied Mechanics, ACAM 2005, pp. 663-669.
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Reinforced concrete (RC) structural elements can be strengthened by bonding high-strength, noncorrosive fibre reinforced polymer (FRP) composites to their surfaces. In the majority of strengthening situations the existing structure would have been subjected to extreme loading at some stage of its life. It is of great interest to designers and users of structures to be aware of the condition of the structural elements, particularly with regards to damage, prior to the design and application of FRP strengthening measures. This paper reports the results of a vibration-based method for assessing damage in RC beams prior to and after the application of FRP strengthening. The vibration-based method measures the vibrations of beams with and without additional mass and provides an assessment of the degree of damage as well as stiffness of the structural element. A simply supported RC beam was constructed and initially damaged by loading to 50% of its flexural capacity. FRP strengthening was then applied and the beam tested to failure. Vibration measurements were taken prior to and after damage of the plain beam as well as after application of the FRP strengthening. The proposed method was used for detecting damage and evaluating the repair as well as quantitatively estimating in-service stiffness of the beams. Good correlation between dynamic results and static load test results is found, thus demonstrating the potential of the vibration-based method. © Institute of Materials Engineering Australasia Ltd 2005.
Kwok, N., Nguyen, T., Ha, Q.P., Li, J. & Samali, B. 2005, 'MR Damper Structural Control Using a Multi-Level Sliding Mode Controller', Australian Earthquake Engineering Society Proceedings of the 2005 Conference, Australian Earthquake Engineering Conference, Australian Earthquake Engineering Society, Albury, New South Wales, Australia, pp. 1-7.
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Li, J. & Samali, B. 2004, 'Recent studies on structural control of five storey benchmark model', 4th International Workshop for Structural Control, 4th International Workshop for Structural Control, DEStech Publications, Inc, New York, USA, pp. 110-115.
As one of the benchmark models encouraged by the International Association for Structural Control (IASC), a five story experimental benchmark building model was designed and fabricated by the University of Technology Sydney in 1999. In the past four years, a number of structural control studies have been carried out on the benchmark model including passive, active and semi-actice controls. In this paper, the benchmark model is presented and a review is given on the benchmark model related research, especially the experimental studies.
Dackermann, U., Samali, B.S., Li, J.L. & Dowling, D.M.D. 2005, 'Experimental modal analysis of u-shaped adobe-mudbrick wall units', 2005 Australian Earthquake Engineering Conference, Albury, Australia.
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Ha, Q.P., Wu, Y., Samali, B. & Li, J. 2004, 'Earthquake Response of a Building Model with Base-Isolated Active Control', Preprints of the 3rd IFAC Symposium on Mechatronics Systems, IFAC Symposium on Mechatronic Systems, Casual Productions, Glenelg North, SA, Sydney, Australia, pp. 687-692.
Place published ?- CD ROM
Dowling, D.M., Samali, B. & Li, J. 2004, 'Shake Table Testing of Unreinforced and Highly Reinforced U-shape Adobe-Mudbrick Wall Units', Australian Earthquake Engineering in the New Millenium, Australian Earthquake Engineering Society 2004 Conference, Australian Earthquake Engineering Society, Mt Gambier, Australia, pp. 1-6.
Crews, K.I., Samali, B. & Li, J. 2004, 'Reliable assessment of aged timber bridges using dynamic procedures', Proceedings of the 8th World Conferences on Timber Engineering, WCTE 2004, WCTE, Lahti, Finland, pp. 1001-1006.
Since late 2001, a new assessment method has been developed by the authors that incorporates two significant innovations enabling reliable prediction of the strength of the old timber bridges. The first innovation is the use of a dynamic based testing method that accurately determines the global stiffness of a bridge deck, whilst reducing both the time required and cost of testing to about 20% of that for traditional static load tests. The dynamic testing procedure involves the attachment of accelerometers underneath the bridge girders, which are then excited by a modal hammer. The method analyses the dynamic responses with and without extra mass, so that the overall flexural stiffness of the bridge can be obtained. Recent refinements by the authors have also enabled determination of the individual member stiffness and identification of defective members in the bridge structure. The second innovation involves the development of a reliability based strength model, which has been derived from analysis of extensive test data using a probabilistic relationship between the measured girder stiffness and the bending moment capacity of the timber girders. This paper describes research and development of the method and discusses its application in successfully undertaking testing of some 100 âoldâ? timber bridges in Australia.
Samali, B., Widjaja, J.H., Li, J. & Reizes, J. 2003, 'Magneto-rheological Shear Dampers; Quasi-static Modelling and Simulation', Proceedings of the 10th Asia Pacific Vibration Conference, Asia Pacific Vibration Conference, Queensland University of Technology, Gold Coast, Queensland, Australia, pp. 1-6.
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Samali, B., Djajakesukma, S., Nguyen, H.T. & Li, J. 2003, 'An Experimental Study of a Five Storey Steel Frame Using Semi-active Control System', Proceedings of the 10th Asia Pacific Vibration Conference, Asia Pacific Vibration Conference, Queensland University of Technology, Gold Coast, Queensland, Australia, pp. 604-609.
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Mayol, E., Samali, B., Kwok, K.C. & Li, J. 2003, 'Vibration Control of An Experimental Benchmark Model To Earthquake Using Liquid Column Vibration Absorbers (LCVAs)', Proceedings of the 10th Asia Pacific Vibration Conference, Asia Pacific Vibration Conference, Queensland University of Technology, Gold Coast, Queensland, Australia, pp. 451-456.
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Wu, Y., Samali, B. & Li, J. 2003, 'Seismic Response of Torsionally Sensitive Building Models', Proceedings of the 10th Asia Pacific Vibration Conference, Asia Pacific Vibration Conference, Queensland University of Technology, Gold Coast, Queensland, Australia, pp. 765-770.
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Li, J., Samali, B. & Crews, K.I. 2003, 'Determining Individual Member Stiffness of Bridge Structure Using a Simple Dynamic Procedure', Proceedings of the 10th Asia Pacific Vibration Conference, Asia Pacific Vibration Conference, Queensland University of Technology, Gold Coast, Queensland, Australia, pp. 379-384.
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Crews, K.I., Samali, B., Li, J. & Bakoss, S.L. 2002, 'Assessing the Load Capacity of Timber Bridges Using Dynamic Methods', Proceedings of the NSW IPWEA State Conference 2002 - Coffs Harbour, NSW IPWEA State Conference 2002 - Coffs Harbour, IPWEA, coffs Harbour, Australia, pp. 1-10.
Samali, B., Bakoss, S.L., Li, J., Saleh, A. & Wije, A. 2003, 'Assessing the Structural Adequacy of a 3-span Steel-Concrete Bridge Using Dynamic Methods: A case study', Abstracts of the Tenth International Conference: Structural Faults & Repair Abstracts, ENGINEERING TECHNICS PRESS, London, UK.
Li, J., Samali, B. & Chapman, C. 2002, 'Experimental realisation of active control of a five storey building model using SMA actuators', Advances in Mechanics of Structures and Materials, The 17th Australasian Conference on the Mechanics of Structures and Materials, A.A. Balkema Publishers, Gold Coast, Australia, pp. 699-704.
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Samali, B., Wu, Y. & Li, J. 2002, 'Torsional response of a base-isolated eccentric building model', Advances in Mechanics of Structures and Materials, The 17th Australasian Conference on the Mechanics of Structures and Materials, A.A. Balkema Publishers, Gold Coast, Australia, pp. 769-774.
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Wu, Y., Samali, B. & Li, J. 2002, 'Earthquake resistance performance of laminated and lead core rubber bearings', Applied Mechanics Progress and Applications, Australasian Congress on Applied Mechanics, World Scientific, Sydney, Australia, pp. 659-664.
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Li, J., Samali, B. & Ha, Q.P. 2002, 'Fuzzy sliding mode control of a five storey benchmark model equipped with active mass driver (AMD)', Proc. the Int. Conference on Motion Control and Vibration (MOVIC'02), International Conference on Motion and Vibration Control, Proc. the Int. Conference on Motion Control and Vibration (MOVICâ02), Saitama Japan, pp. 172-177.
Li, J., Samali, B. & Chapman, C. 2002, 'Variable structure control of seismically excited structure with shape memory alloy actuators', Applied Mechanics Progress and Applications, Australasian Congress on Applied Mechanics, World Scientific, Sydney, Australia, pp. 665-670.
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Samali, B., Al-Dawod, M. & Li, J. 2002, 'Performance of a five storey benchmark model using an active mass driver and a fuzzy controller', Proceedings of the Third Australasian Congress on Applied Mechanics, Australasian Congress on Applied Mechanics, World Scientific Publishing, Gold Coast, Australia, pp. 647-652.
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Benitez-Martinez, F.M. & Li, J. 2002, 'Static and Dynamic Evaluation of a Timber Bridge (Cattai Ck. Bridge, NSW, Australia)', Timber Construction in New Millenniem, World Conference in Timber Engineering 2002, University of Technoiogy, Mara, Malaysia.
Li, J., Djajakesukma, S., Samali, B. & Nguyen, H.T. 2002, 'Modeling and Identificaion of MR Damper for Semi-Active Control Devices', The 6th International Conference on Motion and Vibration Control MOVIC 2002, MOVIC, Japan.
Samali, B., Al-Dawod, M. & Li, J. 2002, 'Performance of An Active Mass Driver System on A Five Storey Benchmark Model', The 6th International Conference on Motion and Vibration Control, MOVIC 2002, MOVIC, Japan.
Ha, Q.P., Li, J., Hong, G. & Samali, B. 2001, 'Active structural control using dymanic output feedback sliding mode', Proceedings of the Australian Conference on Robotics and Automation ACRA'01, Australasian Conference on Robotics and Automation, Australian Robotics & Automation Association, Sydney, pp. 20-25.
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Li, J. & Samali, B. 2001, 'Comparison of Different Control Algorithms For SMA Actuators', 8th East Asia-Pacific Conference on Structural Engineering and Construction, East Asia-Pacific Conference on Structural Engineering and Construction, School of Civil and Environmental Engineering, Nanyang Technological University, Singapore, Signapore.
Li, J. & Samali, B. 2001, 'Sliding Mode Control Of Five Storey Benchmark Model With Magnetorheological (MR) Damper', Eighth East Asia-Pacific Conference on Structural Engineering and Construction, East Asia-Pacific Conference on Structural Engineering and Construction, School of Civil and Environmental Engineering, Nanyang Technological University, Singapore, Singapore.
Wu, Y.M., Samali, B., Li, J. & Mayol, E. 2001, 'Experimental modal analysis of a five-storey benchmark model', Proceedings of the International Modal Analysis Conference - IMAC, pp. 1579-1584.
This paper reports the results of experimental modal analysis of a five-storey benchmark model with impact excitation using HP-VXI data acquisition system and LMS CADA-X software. A numerical was also conducted. The benchmark building model was identified both in terms of its dynamic parameters, namely, natural frequencies, mode shapes and damping ratios as well as its structural properties, namely, the mass, stiffness and damping matrices. The results showed a good agreement between the analytical and experimental results. These parameters enabled further analysis and modeling of the building frame in the presence of various control devices using different control algorithms, aimed at reducing earthquake-induced building vibrations.
Li, J. & Samali, B. 2000, 'Control of a Five Storey Building Model Under Benchmark Earthquake Using SMA Actuators', The 5th International Conference on Motion and Vibration Control, Centre for Built Infrastructure Research, University of Technology, Sydney, Sydney, Australia.
Wu, Y., Samali, B., Li, J. & Bakoss, S.L. 2000, 'Shock Test and Stress Analysis of a Heavy Metal Forge', The 7th International Symposium of Structural Failure and Plasticity, Pergamon an imprint of Elsevier Science, Melbourne, Australia.
Li, J., Samali, B. & Wu, Y. 1999, 'Qualification Testing of Network Cabinets Using a Shake', The 10th Anniversary of the Newcastle Earthquake, Australian Earthquake Engineering Society, Sydney, Australia, p. 11.
Wu, Y., Samali, B., Li, J. & Nguyen, H.T. 1999, 'Modal Analysis of XBJ2 Automobile', International Conference on Application of Modal Analysis '99, The University of Queensland, Queensland, Australia.
Li, J., Samali, B. & Wu, Y. 1999, 'Improving Seismic Behaviour of Network System Enclosures Using Modal Analysis', The International Conference of Applications of Modal Analysis '99, The University of Queensland, Queensland, Australia.
Samali, B., Li, J., Mayol, E. & Wu, Y. 1999, 'System Identification of a Five Storey Benchmark Model Using Exprimental Modal Analysis', The International Conference on Application of Modal Analysis '99, The University of Queensland, Queensland, Australia.
Bakoss, S.L., Samali, B. & Li, J. 1997, 'A Facility for Dynamic Testing and Research', The 1997 Conference of the Australian Earthquake Engineering Society, Australian Earthquake Engineering Society, Brisbane, Australia.
Li, J. & Taylor, D.A. 1997, 'A New Method of Short Crack Closure', 9th International Conference on Fracture, Pergamon, Syndey, Australia.
Li, J. & Kwok, K.C. 1994, 'A Plan for Full-Scale Measurement of Transmission Line Tower Under Wind Load', The 4th National Workshop on Wind Engineering, Australian Wind Engineering Society Australia, Sydney, Australia.

Journal articles

Li, Y. & Li, J. 2015, 'A Highly Adjustable Base Isolator Utilizing Magnetorheological Elastomer: Experimental Testing and Modeling', JOURNAL OF VIBRATION AND ACOUSTICS-TRANSACTIONS OF THE ASME, vol. 137, no. 1.
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Yu, Y., Li, Y. & Li, J. 2015, 'Forecasting hysteresis behaviours of magnetorheological elastomer base isolator utilizing a hybrid model based on support vector regression and improved particle swarm optimization', Smart Materials and Structures, vol. 24, no. 3.
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© 2015 IOP Publishing Ltd. Due to its inherent hysteretic characteristics, the main challenge for the application of a magnetorheological elastomer- (MRE) based isolator is the exploitation of the accurate model, which could fully describe its unique behaviour. This paper proposes a nonparametric model for a MRE-based isolator based on support vector regression (SVR). The trained identification model is to forecast the shear force of the MRE-based isolator online; thus, the dynamic response from the MRE-based isolator can be well captured. In order to improve the forecast capacity of the model, a type of improved particle swarm optimization (IPSO) is employed to optimize the parameters in SVR. Eventually, the trained model is applied to the MRE-based isolator modelling with testing data. The results indicate that the proposed hybrid model has a better generalization capacity and better recognition accuracy than other conventional models, and it is an effective and suitable approach for forecasting the behaviours of a MRE-based isolator.
Li, Y. & Li, J. 2015, 'Finite element design and analysis of adaptive base isolator utilizing laminated multiple magnetorheological elastomer layers', Journal of Intelligent Material Systems and Structures.
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Available magnetorheological elastomer devices normally consist one to two layers of small-size magnetorheological elastomer materials. To be used in large-scale structures, magnetorheological elastomer devices with multiple larger magnetorheological elastomer materials are expected. This article addresses the critical issue in designing a large-scale device with multiple layers of low magnetic conductive magnetorheological elastomer materials, that is, magnetic circuit design. The primary target in magnetic circuit design for magnetorheological elastomer devices is to provide sufficient and uniform magnetic field to all magnetorheological elastomer layers in the device. In this article, finite element investigations are conducted. An innovative magnetic circuit design is proposed for magnetorheological elastomer base isolator with multi-layer of magnetorheological elastomer materials. In the design, laminated magnetorheological elastomer and steel structure is adopted as part of the magnetic core together with two steel blocks. Cylindrical steel tube is used as the yoke of the magnetic circuit. Two plates are placed on the top and bottom of the device to form enclosed magnetic path in the device. Finite element results showed that such innovative magnetic design is able to provide sufficient and uniform magnetic field to all magnetorheological elastomer layers, that is, 25 magnetorheological elastomer layers with thickness of 1 mm and diameter of 120 mm in this case. Finally, the influence of lateral deformation of the magnetorheological elastomer base isolator on the magnetic field is investigated. It is found that the magnetic field in magnetorheological elastomer materials deteriorates when the deformation of the device increases.
Yu, Y., Li, Y. & Li, J. 2015, 'Parameter identification and sensitivity analysis of an improved LuGre friction model for magnetorheological elastomer base isolator', Meccanica.
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The recently-developed magnetorheological elastomer (MRE) base isolator can provide an instant change in the shear modulus and damping property under applied magnetic field, which makes it as an ideal device for the semi-active control in buildings and bridges. Previous studies show that this new device is featured with its nonlinear and hysteretic responses, and it is necessary to sufficiently understand its behaviour when adopting this device in control system. Although there are several models presented to predict the hysteresis of MRE base isolator, they are always suffered from some application limitations, e.g. high computation demand or complex model. To better interpret this complicated feature of the device, this work presents an improved LuGre friction model, which has been successfully used in modelling other magnetorheological device i.e. MR damper. In addition, an improved fruit fly optimization algorithm (IFFOA) is also proposed to identify the model parameters. In the improved algorithm, a transfer factor based on a self-adaptive step is added together with a three-dimensional searching space. This improvement can enhance the convergence rate of the algorithm and avoid the local optimum. Furthermore, to reduce the complexity of the model, the local and global parameter sensitivity analyses are conducted for model simplification. Eventually, the experimental measurements of device displacement, velocity and shear force are used to evaluate the performance of the proposed model and IFFOA.
Gu, X., Li, J., Li, Y. & Askari, M. 2015, 'Frequency control of smart base isolation system employing a novel adaptive magneto-rheological elastomer base isolator', Journal of Intelligent Material Systems and Structures.
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Makki Alamdari, M., Li, J. & Samali, B. 2014, 'FRF-based damage localization method with noise suppression approach', Journal of Sound and Vibration, no. 14, pp. 3305-3320.
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In this paper a noise-robust damage identification method is presented for localization of structural damage in presence of heavy noise influences. The method works based on Frequency Response Functions (FRFs) of the damaged structure without any prior knowledge of the healthy state. The main innovation of this study starts with convolving FRFs with Gaussian kernel to suppress the noise. Denoised signals are then used to develop shape signals according to the second derivative of the operational mode shapes at frequencies in the half-power bandwidth of the center resonant frequencies. The scheme is followed by normalization of shape signals to create a two-dimensional map indicating the damage pattern. The validation of the method was carried out based on simulated data and experimental measurements. The simulated data polluted with 10 percent random noise considering four different conditions: (i) un-correlated noise with Gaussian distribution (ii) noise with non-Gaussian exponential distribution (iii) noise with non-Gaussian Log-normal distribution and (iv) correlated colored noise. The robustness of the method was examined with respect to the damage severity with various damage conditions. Finally, damage detection experiments of a fixed-fixed steel beam are presented to illustrate the feasibility and effectiveness of the proposed method. According to the numerical and experimental investigations, it was demonstrated that the proposed approach presents satisfactory damage indices both in single and multiple damage states in presence of high level noise. Hence, the method can overcome the problems of output measurement noise and deliver encouraging results on damage localization.
Makki Alamdari, M., Samali, B. & Li, J. 2014, 'Damage localization based on symbolic time series analysis', Structural Control and Health Monitoring.
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The objective of this paper is to localize damage in a single or multiple state at early stages of development on the basis of the principles of symbolic dynamics. Symbolic time series analysis (STSA) of noise-contaminated responses is used for feature extraction to detect and localize a gradually evolving deterioration in the structure according to the changes in the statistical behaviour of symbol sequences. Basically, in STSA, statistical features of the symbol sequence can be used to describe the dynamic status of the system. Symbolic dynamics has some useful characteristics making it highly demanded for implementation in real-time observation application such as SHM. First, it significantly reduces the dimension of information and provides information-rich representation of the underlying data. Second, symbolic dynamics and the set of statistical measures built upon it represent a solid framework to address the main challenges of the analysis of nonstationary time data. Finally, STSA often allows capturing the main features of the underlying system whilst alleviating the effects of harmful noise. The method presented in this paper consists of four primary steps: (i) acquisition of the time series data; (ii) creating the symbol space to produce symbol sequences on the basis of the wavelet transformed version of time series data; (iii) developing the symbol probability vectors to achieve anomaly measures; and (iv) localizing damage on the basis of any sudden variation in anomaly measure of different locations. The method was applied on a flexural beam and a 2-D planar truss bridge subjected to varying Gaussian excitation in presence of 2% white noise to examine the efficiency and limitations of the method. Simulation results under various damage conditions confirmed the efficiency of the proposed approach for localization of gradually evolving deterioration in the structure; however, for the future work, the method needs to be verified by experimental data. © ...
Alamdari, M.M., Li, J. & Samali, B. 2014, 'A novel FRF-based damage localisation method using random vibration', Applied Mechanics and Materials, vol. 553, pp. 713-718.
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This paper presents a novel damage localization method based on the measured Frequency Response Functions (FRFs) without demanding any previous data records of the structure in its healthy state. The main innovation of this study starts with reconstruction of FRFs curvature to develop spatial shape functions. It is demonstrated that reconstructed data significantly magnifies the influence of low-frequency spectra in damage detection procedure which is considered the milestone of this approach as excitation of the higher frequencies is not easy to obtain in most practical applications. The modified curvature data in all measured frequencies and locations is interpreted as a two dimensional image and then processed by employing 2-D discrete wavelet transform to detect any abrupt variation at damage site. Level one wavelet decomposition is utilised to provide the finest detail coefficients. It is illustrated that this approach presents a more recognizable pattern at damage site in all measured frequencies. The pattern can be described by a horizontal line parallel to the frequency spectra in 2-D image. Hence, the horizontal detail coefficients are utilised to detect this pattern as they are more sensitive to perturbation with orientation parallel to horizontal axis in the image. The main contribution of this approach lies in the fact that the proposed technique is able to detect the structural damage in all measured frequencies and the effectiveness of the method is independent of the excitation location. Moreover, the results provide a better visualisation at damage site which other FRF-based damage detection methods could not obtain. Applying broadband FRF data in this approach and the fact that there is no need for data from the healthy state of the structure are other advantages accompanying this method. The robustness of the proposed damage identification method was examined with various damage conditions in both single and multiple states. Moreover, the feasib...
Dackermann, U., Crews, K., Kasal, B., Li, J., Riggio, M., Rinn, F. & Tannert, T. 2014, 'In situ assessment of structural timber using stress-wave measurements', Materials and Structures/Materiaux et Constructions, vol. 47, no. 5, pp. 787-803.
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This paper summarizes the test recommendations for in situ assessment of structural timber using stress wave measurements as developed by members of the RILEM Technical Committee AST 215 "In-situ assessment of structural timber". In the first part, the basic principles, the equipment, and the practical application of stress-wave-based testing using the time-of-flight method are described. A detailed testing procedure provides hands-on information on the execution of in-field stress wave testing. A typical example is given to demonstrate step-by-step on how to evaluate stress wave readings and the health state of the inspected timber member. The latter part of the paper gives a short overview of the use of acoustic tomography and ultrasonic echo methods. © 2013 RILEM.
Jiang, X., Wang, J., Li, Y. & Li, J. 2014, 'Design and modelling of a novel linear electromagnetic vibration energy harvester', INTERNATIONAL JOURNAL OF APPLIED ELECTROMAGNETICS AND MECHANICS, vol. 46, no. 1, pp. 165-183.
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Li, Y. & Li, J. 2014, 'Dynamic characteristics of a magnetorheological pin joint for civil structures', Frontiers of Mechanical Engineering, vol. 9, no. 1, pp. 15-33.
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Magnetorheological (MR) pin joint is a novel device in which its joint moment resistance can be controlled in real-time by altering the applied magnetic field. The smart pin joint is intended to be used as a controllable connector between the columns and beams of a civil structure to instantaneously shift the structural natural frequencies in order to avoid resonance and therefore to reduce unwanted vibrations and hence prevent structural damage. As an intrinsically nonlinear device, modelling of this MR fluid based device is a challenging task and makes the design of a suitable control algorithm a cumbersome situation. Aimed at its application in civil structure, the main purpose of this paper is to test and characterise the hysteretic behaviour of MR pin joint. A test scheme is designed to obtain the dynamic performance of MR pin joint in the dominant earthquake frequency range. Some unique phenomena different from those of MR damper are observed through the experimental testing. A computationally-efficient model is proposed by introducing a hyperbolic element to accurately reproduce its dynamic behaviour and to further facilitate the design of a suitable control algorithm. Comprehensive investigations on the model accuracy and dependences of the proposed model on loading condition (frequency and amplitude) and input current level are reported in the last section of this paper. © 2014 Higher Education Press and Springer-Verlag Berlin Heidelberg.
Jiang, X., Li, Y., Li, J., Wang, J. & Yao, J. 2014, 'Piezoelectric energy harvesting from traffic-induced pavement vibrations', Journal of Renewable and Sustainable Energy, vol. 6, no. 4.
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This paper focuses on the development and experimental testing of a potential clean energy source for powering the remote equipment used in transportation infrastructure. Traditional power sources (i.e., power cables and batteries) are excessively expensive or infeasible in this type of application. A compression-based roadway energy harvester has been developed that can be embedded into pavement to scavenge electrical energy from traffic-induced vibrations. The proposed roadway harvester employs a group of piezoelectric harvesting units to convert traffic-induced vibrations into electrical energy, and each single harvesting unit contains three piezoelectric multilayer stacks. According to the linear theory of piezoelasticity, a two-degree-of-freedom electromechanical model of the piezoelectric harvesting unit was developed to characterize its performance in generating electrical energy under external excitations. Experimental testing in the laboratory was conducted to investigate the output power properties of the harvesting unit and shows good agreement with the theoretical analysis. Based on the testing results of the harvesting unit, the capability of the proposed roadway harvester has been theoretically evaluated and demonstrated that it has the ability to generate sufficient energy for driving common electrical equipment used in transportation infrastructure. © 2014 AIP Publishing LLC.
Alamdari, M.M., Li, J., Samali, B., Ahmadian, H. & Naghavi, A. 2014, 'Nonlinear joint model updating in assembled structures', Journal of Engineering Mechanics, vol. 140, no. 7.
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Dynamic response of mechanical structures is significantly affected by joints. Joints introduce remarkable frictional damping and localized flexibility to the structure; hence, to obtain a more accurate representation of a system's dynamics, it is crucial to take these effects into account. This paper investigates the application of finite-element model updating on characterization of a nonlinear joint interface. A thin layer of virtual elements is used at a joint location to represent the nonlinear behavior of the coupling in the tangential direction. The material properties of the elements are described by a nonlinear constitutive stress-strain equation that defines the nonlinear state of the joint interface. In this study, Richard-Abbot elastic-plastic material was considered, which is capable of characterizing energy dissipation and softening phenomena in a joint at a nonlinear state. Uncertain material parameters are adjusted to minimize the residual between the numerical and experimental nonlinear frequency responses. Minimization was carried out based on iterative sensitivity-based optimization. The procedure was implemented on an assembled structure consisting of two steel threaded pipes coupled to each other by a nut interface. It was demonstrated that the proposed technique significantly reduced the uncertainties in the joint modeling and led to a more reliable description of the assembled structure. © 2014 American Society of Civil Engineers.
Jiang, X.Z., Li, Y.C., Wang, J. & Li, J.C. 2014, 'Electromechanical modeling and experimental analysis of a compression-based piezoelectric vibration energy harvester', International Journal of Smart and Nano Materials, vol. 5, no. 3, pp. 152-168.
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Over the past few decades, wireless sensor networks have been widely used in the field of structure health monitoring of civil, mechanical, and aerospace systems. Currently, most wireless sensor networks are battery-powered and it is costly and unsustainable for maintenance because of the requirement for frequent battery replacements. As an attempt to address such issue, this article theoretically and experimentally studies a compression-based piezoelectric energy harvester using a multilayer stack configuration, which is suitable for civil infrastructure system applications where large compressive loads occur, such as heavily vehicular loading acting on pavements. In this article, we firstly present analytical and numerical modeling of the piezoelectric multilayer stack under axial compressive loading, which is based on the linear theory of piezoelectricity. A two-degree-of-freedom electromechanical model, considering both the mechanical and electrical aspects of the proposed harvester, was developed to characterize the harvested electrical power under the external electrical load. Exact closed-form expressions of the electromechanical models have been derived to analyze the mechanical and electrical properties of the proposed harvester. The theoretical analyses are validated through several experiments for a test prototype under harmonic excitations. The test results exhibit very good agreement with the analytical analyses and numerical simulations for a range of resistive loads and input excitation levels. © 2014 The Author(s).
Dackermann, U., Skinner, B. & Li, J. 2014, 'Guided wave-based condition assessment of in situ timber utility poles using machine learning algorithms', Structural Health Monitoring, vol. 13, no. 4, pp. 374-388.
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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.
Xiao, R.H., Li, J.C. & Shrestha, R.J. 2014, 'Investigations of vibration based condition assessment of timber beams strengthened with fiber reinforced polymer', Advanced Materials Research, vol. 831, pp. 53-57.
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In recent years, research trend on structural condition assessments have largely shifted toward utilizing vibration based methods for structural damage detection and evaluation. On the other hand, research and applications on use of fiber reinforce polymer (FRP) on timber for strengthening or repair damaged timber members in various types of timber structures has also become increasingly popular. Although the application of FRP for repair and/or strengthening of structures has been researched for a long time, research on non-destructive assessment or evaluation of the effectiveness and reliability after FRP repairing or strengthening is yet to be carried out. In this paper, the authors made an attempt on investigation of such issue utilizing Damage Index method, which is a robust vibration-based approach for damage detection. The investigation was aiming at localizing and quantifying damage in timber beams and, more importantly evaluating the effectiveness after the damage was repaired. An experimental program was carried out on five laminated veneer lumber (LVL) beams. Various damage scenarios (i.e. severe, medium, light damage) are introduced on these beams and then repaired with carbon fiber reinforced polymer (CFRP). Experimental results indicate that the use of CFRP was effective in repairing the damaged timber beams. Utilizing Damage Index method can accurately detect the damage location. However, the investigation also shows that direct application of the Damage Index for evaluation of the effectiveness of rehabilitation of the damaged timber beam is not satisfactory. Further investigation and modification of the Damage Index method will be carried out in next stage research. © (2014) Trans Tech Publications, Switzerland.
Yu, Y., Li, Y. & Li, J. 2014, 'Parameter identification of a novel strain stiffening model for magnetorheological elastomer base isolator utilizing enhanced particle swarm optimization', Journal of Intelligent Material Systems and Structures.
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This article presents a novel model to describe the nonlinear relationships between shear force and displacement/velocity in a magnetorheological elastomer base isolator. The proposed model, containing a strain stiffening element, is able to portray the distinct dynamic behaviors of magnetorheological elastomer base isolator. To identify the model parameters, an enhanced particle swarm optimization is used on force–displacement/velocity data sampled under different loading conditions. In this algorithm, a self-adaptive inertia weight replaces the general linear weight, enhancing the convergence rate of iteration process. Besides, the mutation operator in genetic algorithm is adopted for finding global optimum. Testing data of the device displacement, velocity and force from magnetorheological elastomer base isolator are utilized to validate the proposed model and corresponding parameter identification algorithm.
Li, Y., Li, J., Tian, T. & Li, W. 2014, 'Erratum: A highly adjustable magnetorheological elastomer base isolator for applications of real-time adaptive control (Smart Materials and Structures (2013) 22 (095020))', Smart Materials and Structures, vol. 23, no. 12.
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Li, Y., Li, J., Li, W. & Du, H. 2014, 'A state-of-the-art review on magnetorheological elastomer devices', Smart Materials and Structures, vol. 23, no. 12.
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During the last few decades, magnetorheological (MR) elastomers have attracted a significant amount of attention for their enormous potential in engineering applications. Because they are a solid counterpart to MR fluids, MR elastomers exhibit a unique field-dependent material property when exposed to a magnetic field, and they overcome major issues faced in magnetorheological fluids, e.g. the deposition of iron particles, sealing problems and environmental contamination. Such advantages offer great potential for designing intelligent devices to be used in various engineering fields, especially in fields that involve vibration reduction and isolation. This paper presents a state of the art review on the recent progress of MR elastomer technology, with special emphasis on the research and development of MR elastomer devices and their applications. To keep the integrity of the knowledge, this review includes a brief introduction of MR elastomer materials and follows with a discussion of critical issues involved in designing magnetorheological elastomer devices, i.e. operation modes, coil placements and principle fundamentals. A comprehensive review has been presented on the research and development of MR elastomer devices, including vibration absorbers, vibration isolators, base isolators, sensing devices, and so on. A summary of the research on the modeling mechanical behavior for both the material and the devices is presented. Finally, the challenges and the potential facing magnetorheological elastomer technology are discussed, and suggestions have been made based on the authors' knowledge and experience.
Krause, M., Dackermann, U. & Li, J. 2014, 'Elastic wave modes for the assessment of structural timber: ultrasonic echo for building elements and guided waves for pole and pile structures', Journal of Civil Structural Health Monitoring, vol. 5, no. 2, pp. 221-249.
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This paper presents the state-of-the-art of using non-destructive testing (NDT) methods based on elastic waves for the condition assessment of structural timber. Two very promising approaches based on the propagation and reflections of elastic waves are described. While the first approach uses ultrasonic echoes for the testing of wooden building elements, the second approach uses guided waves (GW) for the testing of timber pole and pile structures. The basic principle behind both approaches is that elastic waves induced in a timber structure will propagate through its material until they encounter a change in stiffness, cross-sectional area or density, at which point they will reflect back. By measuring the wave echoes, it is possible to determine geometric properties of the tested structures such as the back wall of timber elements or the underground length of timber poles or piles. In addition, the internal state of the tested structures can be assessed since damage and defects such as rot, fungi or termite attacks will cause early reflections of the elastic waves as well as it can result in changes in wave velocity, wave attenuation and wave mode conversion. In the paper, the principles and theory of using elastic wave propagation for the assessment of wooden building elements and timber pole/pile structures are described. The state-of-the-art in testing equipment and procedures is presented and detailed examples are given on the practical application of both testing approaches. Recent encouraging developments of cutting edge research are presented along with challenges for future research.
Mustapha, S., Lu, Y., Li, J. & Ye, L. 2014, 'Damage detection in rebar-reinforced concrete beams based on time reversal of guided waves', Structural Health Monitoring, vol. 13, no. 4, pp. 347-358.
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Li, Y., Li, J., Li, W. & Samali, B. 2013, 'Development and characterization of a magnetorheological elastomer based adaptive seismic isolator', Smart Materials and Structures, vol. 22, no. 3.
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One of the main shortcomings in current base isolation design/practice is lack of adaptability. As a result, a base isolation system that is effective for one type earthquake may become ineffective or may have adverse effect for other earthquakes. The vulnerability of traditional base isolation systems can be exaggerated by two types of earthquakes, i.e. near-field earthquakes and far-field earthquakes. This paper addresses the challenge facing current base isolation design/practice by proposing a new type of seismic isolator for the base isolation system, namely an adaptive seismic isolator. The novel adaptive seismic isolator utilizes magnetorheological elastomer (MRE) for its field-sensitive material property. Traditional seismic isolator design with a unique laminated structure of steel and MRE layers has been adopted in the novel MRE seismic isolator. To evaluate and characterize the behavior of the MRE seismic isolator, experimental testing was conducted on a shake table facility under harmonic cycling loading. Experimental results show that the proposed adaptive seismic isolator can successfully alter the lateral stiffness and damping force in real time up to 37% and 45% respectively. Based on the successful development of the novel adaptive seismic isolator, a discussion is also extended to the impact and potential applications of such a device in structural control applications in civil engineering. © 2013 IOP Publishing Ltd.
Subhani, M., Li, J., Samali, B. & Yan, N. 2013, 'Determination of the embedded lengths of electricity timber poles utilizing flexural wave generated from impacts', Australian Journal of Structural Engineering, vol. 14, no. 1, pp. 85-96.
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Round timbers are extensively used as utility poles in Australia for electricity distribution and communication. Lack of information on their conditions results in great difficulties on asset management for industries. Despite the development of various non-destructive testing (NDT) techniques for evaluating the condition of piles, few NDTs are reported for applications on timber poles. This paper addresses challenges and issues on development of NDTs for condition assessment and embedded length of timber poles. For this paper, it is mainly focusing on determining the embedded length of the pole considering loss of the sufficient embedment length is a main factor compromising capacity and safety of timber poles. Since it is impractical for generating longitudinal waves by impacting from the top of poles, utilizing flexural wave from side impact on poles becomes attractive. However, the flexural wave is known by its highly dispersive nature. In this paper, one dimensional wave theory, guided wave theory and advanced signal processing techniques have been introduced in order to provide a solution for the problem. Two signal processing techniques, namely short kernel method and continuous wavelet transform, have been investigated for processing flexural wave signals to evaluate wave velocity and embedment length of timber poles in service. © Institution of Engineers Australia, 2013.
Lu, Y., Li, J., Ye, L. & Wang, D. 2013, 'Guided waves for damage detection in rebar-reinforced concrete beams', Construction And Building Materials, vol. 47, no. 1, pp. 370-378.
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The propagation properties of ultrasonic waves in rebar-reinforced concrete beams were investigated for the purpose of damage detection. Two types of piezoelectric (PZT) elements were used in experiments in which PZT disks were attached on the surfaces of concrete beams to observe wave propagation in concrete before and after a four-point bending test, while rectangular PZT patches were attached at the exposed ends of the rebar to monitor wave transmission along the rebar with and without simulated corrosion in the form of partial material removal from the rebar. Experimental testing demonstrated that the surface-attached PZT disks were capable of detecting the change in material properties due to the existence of cracking. In consideration of the inevitable discrepancies in different concrete beams due to specimen preparation and sensor installation, principal component analysis based on statistical parameters extracted from wave signals was applied to highlight the difference between benchmark and damaged rebar. The results show the potential of the principal components as damage indices for quantifying integrity conditions of concrete structures.
Li, Y., Li, J. & Samali, B. 2013, 'On the magnetic field and temperature monitoring of a solenoid coil for a novel magnetorheological elastomer base isolator', Journal of Physics: Conference Series, vol. 412, no. 1.
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Following a successful experimental validation of a magnetorheological elastomer (MRE) base isolator, this study presents one of the major concerns, the heating of the magnetic coil, in the design and development of the adaptive MRE based isolator. In this research, the MRE materials, with a total thickness of nearly 150 mm, are placed as the magnetic core of the device to best utilize the magnetic energy provided by the coil. A series of tests are undertaken to investigate the magnetic fields inside the coil with or without the MRE materials. Thermocouples are used to monitoring the surface temperature of the coil when it is applied with various currents for 10 min. It is shown that the measurement of field inside the solenoid when no MRE is placed inside agrees with the theoretical analysis. It is also shown that the temperature of the coil increase dramatically when a current is applied. Cooling of the coil may takes even longer, about 4 h, till down to the room temperature. Dropping of the magnetic field is observed when the temperature goes high. © Published under licence by IOP Publishing Ltd.
zhang, J., Xu, Y., Li, J., Xia, Y. & Li, J. 2013, 'Statistical moment-based structural damage detection method in time domain', EARTHQUAKE ENGINEERING AND ENGINEERING VIBRATION, vol. 12, pp. 13-23.
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A novel structural damage detection method with a new damage index, i.e., the statistical moment-based damage detection (SMBDD) method in the frequency domain, has been recently proposed. The aim of this study is to extend the SMBDD method in the frequency domain to the time domain for building structures subjected to non-Gaussian and non-stationary excitations. The applicability and effectiveness of the SMBDD method in the time domainis verified both numerically and experimentally. Shear buildings with various damage scenarios are fi rst numerically investigated in the time domain taking into account the effect of measurement noise. The applicability of the proposed method in the time domain to building structures subjected to non-Gaussian and non-stationary excitations is then experimentally investigated through a series of shaking table tests, in which two three-story shear building models with four damage scenarios aretested. The identifi ed damage locations and severities are then compared with the preset values. The comparative results are found to be satisfactory, and the SMBDD method is shown to be feasible and effective for building structures subjected to non-Gaussian and non-stationary excitations.
Dackermann, U., Li, J. & Samali, B. 2013, 'Identification of member connectivity and mass changes on a two-storey framed structure using frequency response functions and artificial neural networks', Journal of Sound and Vibration, vol. 332, no. 16, pp. 3636-3653.
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This paper presents a structural health monitoring (SHM) technique that utilises pattern changes in frequency response functions (FRFs) as input parameters for a system of artificial neural networks (ANNs) to assess the structural condition of a structure. To verify the proposed method, it is applied to numerical and experimental models of a two-storey framed structure, on which structural damage is induced by member connectivity and mass changes, respectively. For the numerical structure, simulated time-history data are polluted with various levels of white Gaussian noise in order to realistically represent field-testing conditions. As a damage indicator, residual FRFs are used, which are derived by calculating the differences in FRF data between the undamaged/baseline structure and the structure with changed joint conditions or added mass. To obtain suitable patterns for neural network training, principal component analysis (PCA) techniques are adopted to reduce the size of the residual FRF data and to filter noise. A hierarchical system of individual ANNs, termed network ensemble, is then trained to map changes in PCA-reduced residual FRFs to damage conditions. The results obtained for both damage investigations, namely joint damage and mass changes, demonstrate that the proposed SHM technique is accurate and reliable in assessing the condition of the test structure numerically and experimentally based on direct FRF measurements and network ensemble analysis. From the outcomes of the individual networks, it is found that the proposed hierarchical network ensemble approach is highly efficient in filtering poor results of underperforming networks obtained from measurement locations with low damage sensitivity. © 2013 Elsevier Ltd.
Li, Y., Li, J., Tian, T. & Li, W. 2013, 'A highly adjustable magnetorheological elastomer base isolator for applications of real-time adaptive control', Smart Materials and Structures, vol. 22, no. 9.
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Inspired by its controllable and field-dependent stiffness/damping properties, there has been increasing research and development of magnetorheological elastomer (MRE) for mitigation of unwanted structural or machinery vibrations using MRE isolators or absorbers. Recently, a breakthrough pilot research on the development of a highly innovative prototype adaptive MRE base isolator, with the ability for real-time adaptive control of base isolated structures against various types of earthquakes including near- or far-fault earthquakes, has been reported by the authors. As a further effort to improve the proposed MRE adaptive base isolator and to address some of the shortcomings and challenges, this paper presents systematic investigations on the development of a new highly adjustable MRE base isolator, including experimental testing and characterization of the new isolator. A soft MR elastomer has been designed, fabricated and incorporated in the laminated structure of the new MRE base isolator, which aims to obtain a highly adjustable shear modulus under a medium level of magnetic field. Comprehensive static and dynamic testing was conducted on this new adaptive MRE base isolator to examine its characteristics and evaluate its performance. The experimental results show that this new MRE base isolator can remarkably change the lateral stiffness of the isolator up to 1630% under a medium level of magnetic field. Such highly adjustable MRE base isolator makes the design and implementation of truly real-time adaptive (e.g. semi-active or smart passive) seismic isolation systems become feasible. © 2013 IOP Publishing Ltd.
Ha, Q.P., Nguyen, M.T., Li, J. & Kwok, N.M. 2013, 'Smart structures with current-driven MR dampers: Modeling and second-order sliding mode control', IEEE/ASME Transactions on Mechatronics, vol. 18, no. 6, pp. 1702-1712.
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Smart structures are civil or mechanical structures that can automatically and intelligently react to external dynamic loadings such as vibration shocks, strong winds, destructive waves, and earthquakes. The use of magnetorheological (MR) dampers has been of increasing interest in smart structures as they have reliable, stable and fail-safe operations, small energy requirements, and fast responses. The challenges of MR damper structural control rest with the complex dynamics involved, high nonlinearity due to the force-velocity hysteresis, nonaffinity, and constraints of the control system with the magnetization current as its input. To address these problems, this paper presents the modeling and control design as well as the implementation results of a second-order sliding mode controller for the MR dampers embedded in the building structures subject to quake-induced vibrations. Based on the static hysteresis model of the MR damper using computationally tractable algebraic expressions, algorithms are proposed to control directly the magnetization current to the dampers, configured in a differential mode to counteract the offset force. The effectiveness of the proposed technique is verified in simulation by using a building model under quake-like excitations. The experimental results are provided on a laboratorial setup tested on a shake table. © 2013 IEEE.
Yang, J., Du, H., Li, W., Li, Y., Li, J., Sun, S. & Deng, H.X. 2013, 'Experimental study and modeling of a novel magnetorheological elastomer isolator', Smart Materials and Structures, vol. 22, no. 11.
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This paper reports an experimental setup aiming at evaluating the performance of a newly designed magnetorheological elastomer (MRE) seismic isolator. As a further effort to explore the field-dependent stiffness/damping properties of the MRE isolator, a series of experimental testing were conducted. Based upon the analysis of the experimental responses and the characteristics of the MRE isolator, a new model that is capable of reproducing the unique MRE isolator dynamics behaviors is proposed. The validation results verify the model's effectiveness to portray the MRE isolator. A study on the field-dependent parameters is then provided to make the model valid with fluctuating magnetic fields. To fully explore the mechanism of the proposed model, an investigation relating the dependence of the proposed model on every parameter is carried out. © 2013 IOP Publishing Ltd.
Zeng, J., Guo, Y., Li, Y., Zhu, J. & Li, J. 2013, 'Two-dimensional magnetic property measurement for magneto-rheological elastomer', Journal of Applied Physics, vol. 113, no. 17.
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Magneto-rheological elastomer (MRE) is a new kind of smart material. Its rheological properties can be altered and controlled in a real time manner when it is applied an external magnetic field. For calculating magnetic properties of MRE material, usually Maxwell-Garnet equation is used to acquire an approximately effective permeability. This equation treats the magnetic property of particles as linear. However, when the applied magnetic field is alternating or rotating, the nonlinearity of magnetic property and magnetic hysteresis cannot be neglected. Hence, the measurement and modelling of the magnetic properties under alternating and rotating magnetic fields are essential to explore new applications of the material. This paper presents the investigation on the magnetic hysteresis properties of MRE material under one-dimensional (1-D) alternating and two-dimensional (2-D) rotating magnetic field excitations. A kind of MRE material, consisting of 70 carbonyl iron particles, 10 silicone oil, and 20 silicone rubber, was used to investigate the magnetic properties. The diameter of carbonyl iron particles is 3-5 ?m. The measurement results, such as the relations between magnetic field intensity (H) and magnetic flux density (B) under different magnetic field excitations on the MRE sample, have been obtained and analyzed. These data would be useful for design and analysis of MRE smart structures like MR dampers. © 2013 American Institute of Physics.
Subhani, M., Li, J. & Samali, B. 2013, 'A comparative study of guided wave propagation in timber poles with isotropic and transversely isotropic material models', Journal of Civil Structural Health Monitoring, vol. 3, no. 2, pp. 65-79.
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Guided wave (GW) has been used for many years in non-destructive testing (NDT). There are various ways to generate the guided wave, including impact or impulse either manually or using devices. Although the method of impact or impulse is considered to be simple and practical in guided wave generation, it produces waves with broadband frequencies, which often make analysis much more difficult. The frequency bandwidth produced by manual impacts is usually at the low end, and is therefore justified when dealing with one dimensional wave propagation assumption in low strain integrity testing of cylindrical structures. Under such assumption if the velocity is known accurately, NDTs can produce reasonably good results for the condition assessment of the structure. However, for guided wave propagation in timber pole-like structures, it is rather complicated as timber is an orthotropic material and wave propagation in an orthotropic medium exhibits different characteristics from that in isotropic medium. It is possible to obtain solutions for guided wave propagation in orthotropic media for cylindrical structures, even though the orthotropic material greatly complicates GW propagation. In this paper, timber has been considered as a transversely isotropic (i.e. simplified orthotropic) material and a comparative study of GW propagation in a timber pole is conducted considering isotropic and transversely isotropic modelling. Phase velocity, group velocity and attenuation are the main parameters for this comparative study. Moreover, tractionfree situation and embedded geotechnical condition are also taken into consideration to evaluate the effect of boundary. Displacement profile, wave propagation pattern and power flow at particular frequency are utilized to determine different displacement components of longitudinal and flexural waves along and across the timber pole. Effect of temperature and moisture content (in terms of modulus of elasticity) in timber pole is also comp...
Elsener, R., Dackermann, U., Li, J.C., Samali, B. & Crews, K. 2013, 'Experimental investigations of material properties of timber utility poles using various material testing approaches', Advanced Materials Research, vol. 778, pp. 265-272.
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This paper presents an investigation of using different material testing approaches to determine material properties of timber utility poles from two hardwood tree species, i.e. Spotted Gum and Tallowwood. The material properties investigated are the Modulus of Elasticity (MOE), the Modulus of Rupture (MOR) and the compression strength (CS) in longitudinal direction as well as radial and tangential directions of the cross section of the poles. These material properties are needed for the accurate modelling of timber poles using Finite Element Method (FEM) for the study of stress wave propagation and damage detection in timber utility poles. In open literatures, for most timber species such comprehensive material property data are scarce to find. Typically, material properties available are only in the longitudinal direction. Furthermore, most international standards cover only details on material testing in longitudinal direction and no coherent nor comprehensive guidelines are given for the testing of the full orthotropic material properties of timber. Hence, an extensive study is deemed necessary to investigate a suitable approach to determine full material properties of timber. Two hardwood timber species, namely Spotted Gum and Tallowwood are selected for this investigation. Beside full material properties, the investigation is extended to examine different material testing approaches (bending, compression and tension testing) for the determination of the same material properties. The presented material testing is conducted on numerous small clear specimens as well as on four full scale 5 m long timber pole specimens of the two mentioned hardwood tree species. © (2013) Trans Tech Publicutions, Switzerland.
Chen, P., Wong, L. & Li, J. 2012, 'Detection of outlier residues for improving interface prediction in protein heterocomplexes', IEEE/ACM Transactions on Computational Biology and Bioinformatics, vol. 9, no. 4, pp. 1155-1165.
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Sequence-based understanding and identification of protein binding interfaces is a challenging research topic due to the complexity in protein systems and the imbalanced distribution between interface and noninterface residues. This paper presents an outlier detection idea to address the redundancy problem in protein interaction data. The cleaned training data are then used for improving the prediction performance. We use three novel measures to describe the extent a residue is considered as an outlier in comparison to the other residues: the distance of a residue instance from the center instance of all residue instances of the same class label (Dist), the probability of the class label of the residue instance (PCL), and the importance of within-class and between-class (IWB) residue instances. Outlier scores are computed by integrating the three factors; instances with a sufficiently large score are treated as outliers and removed. The data sets without outliers are taken as input for a support vector machine (SVM) ensemble. The proposed SVM ensemble trained on input data without outliers performs better than that with outliers. Our method is also more accurate than many literature methods on benchmark data sets. From our empirical studies, we found that some outlier interface residues are truly near to noninterface regions, and some outlier noninterface residues are close to interface regions. © 2012 IEEE.
Samali, B., Dackermann, U. & Li, J. 2012, 'Location and severity identification of notch-type damage in a two-storey steel framed structure utilising frequency response functions and artificial neural network', Advances in Structural Engineering, vol. 15, no. 5, pp. 743-757.
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This paper presents a vibration-based damage identification method that utilises damage fingerprints embedded in frequency response functions (FRFs) to identify location and severity of notch-type damage in a two-storey framed structure. The proposed method utilises artificial neural networks (ANNs) to map changes in FRFs to damage characteristics. To enhance damage fingerprints in FRF data, residual FRFs, which are differences in FRF data between the undamaged and the damaged structures, are used for ANN inputs. By adopting principal component analysis (PCA) techniques, the size of the residual FRF data is reduced in order to obtain suitable patterns for ANN inputs. A hierarchy of neural network ensembles is created to take advantage of individual characteristics of measurements from different locations. The method is applied to laboratory and numerical two-storey framed structures. A number of single notch-type damage scenarios of different locations and severities are investigated. To simulate field-testing conditions, numerically simulated data is polluted with white Gaussian noise of up to 10% noise-to-signal-ratio. The results from both numerical and experimental investigations show the proposed method is effective and robust for detecting notch-type damage in structures.
Li, Z., He, Y., Wong, L. & Li, J. 2012, 'Progressive dry-core-wet-rim hydration trend in a nested-ring topology of protein binding interfaces', BMC Bioinformatics, vol. 13, no. 1.
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Background: Water is an integral part of protein complexes. It shapes protein binding sites by filling cavities and it bridges local contacts by hydrogen bonds. However, water molecules are usually not included in protein interface models in the past, and few distribution profiles of water molecules in protein binding interfaces are known.Results: In this work, we use a tripartite protein-water-protein interface model and a nested-ring atom re-organization method to detect hydration trends and patterns from an interface data set which involves immobilized interfacial water molecules. This data set consists of 206 obligate interfaces, 160 non-obligate interfaces, and 522 crystal packing contacts. The two types of biological interfaces are found to be drier than the crystal packing interfaces in our data, agreeable to a hydration pattern reported earlier although the previous definition of immobilized water is pure distance-based. The biological interfaces in our data set are also found to be subject to stronger water exclusion in their formation. To study the overall hydration trend in protein binding interfaces, atoms at the same burial level in each tripartite protein-water-protein interface are organized into a ring. The rings of an interface are then ordered with the core atoms placed at the middle of the structure to form a nested-ring topology. We find that water molecules on the rings of an interface are generally configured in a dry-core-wet-rim pattern with a progressive level-wise solvation towards to the rim of the interface. This solvation trend becomes even sharper when counterexamples are separated.Conclusions: Immobilized water molecules are regularly organized in protein binding interfaces and they should be carefully considered in the studies of protein hydration mechanisms. © 2012 Li et al; licensee BioMed Central Ltd.
Huang, Q., Xu, Y.L., Li, J.C., Su, Z.Q. & Liu, H.J. 2012, 'Structural damage detection of controlled building structures using frequency response functions', Journal of Sound and Vibration, vol. 331, no. 15, pp. 3476-3492.
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If a building structure requires both a vibration control system and a health monitoring system, the integration of the two systems will be cost-effective and beneficial. One of the key problems of this integrated system is how to use control devices to enhance system identification and damage detection. This paper presents a new method for system identification and damage detection of controlled building structures equipped with semi-active friction dampers through model updating based on frequency response functions. The two states of the building are first created by adding a known stiffness using semi-active friction dampers. A scheme based on the frequency response functions of the two states of the building is then presented to identify stiffness parameters of structural members in consideration of structural connectivity and transformation information. By applying the proposed model updating scheme to the damaged building, a damage detection scheme is proposed based on the identified stiffness parameters of structural members of both the original and damaged buildings. The feasibility of the proposed schemes is finally demonstrated through a detailed numerical investigation in terms of an example building, in which the effects of measurement noise and excitation conditions are discussed. The numerical results clearly show that the proposed method can locate and quantify damage satisfactorily even though measurement noise is taken into consideration. © 2012 Elsevier Ltd. All rights reserved.
Li, J., Subhani, S. & Samali, B. 2012, 'Determination of Embedment Depth of Timber Poles and Piles Using Wavelet Transform', Advances in Structural Engineering, An International Journal, vol. 15, no. 5, pp. 759-770.
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This paper presents an investigation on the wave propagation in timber poles with Wavelet Transform (WT) analysis for identification of the condition and underground depth of embedded timber poles in service. Most of non-destructive testing (NDT) applications for timber poles using wave-based methods consider only single wave mode and no dispersion. However, for wave propagations in timber poles (damaged/undamaged), such simplification may not be correct, especially for broad band excitation using impulse impact. To investigate the problem, a 5m timber pole was investigated numerically and experimentally. A dispersion curve is generated from the numerical results to provide guidance on the velocity and wave mode selection. Continuous wavelet transform (CWT) is applied on the same signal to verify the presence of modes and to process data from experimental testing. The results are presented in both time domain and time-frequency domain for comparison. The results of the investigation showed that, wavelet transform analysis can be a reliable signal processing tool for NDT in terms of condition and embedment length determination.
Nguyen, T.T., Ngo, H.H., Guo, W., Phuntsho, S. & Li, J. 2011, 'A new sponge tray bioreactor in primary treated sewage effluent treatment', Bioresource Technology, vol. 102, no. 9, pp. 5444-5447.
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The new attached growth sponge tray bioreactor (STB) was evaluated at different operating conditions for removing organics and nutrients from primary treated sewage effluent. This STB was also assessed when using as a pre-treatment prior to micro-filtration (MF) for reducing membrane fouling. At a short hydraulic retention time (HRT) of 40min, the STB could remove up to 92% of DOC and 40-56% of T-N and T-P at an organic loading rate (OLR) of 2.4kg COD/m3 spongeday. This OLR is the best for the STB as compared to the OLRs of 0.6, 1.2 and 3.6kg COD/m3 spongeday. At 28mL/min of flow velocity (FV), STB achieved the highest efficiencies with 92% of DOC, 87.4% of T-P, and 54.8% of T-N removal. Finally, at the optimal OLR and FV, the STB could remove almost 90% of organic and nutrient, significantly reduce membrane fouling with HRT of only 120min. © 2010 Elsevier Ltd.
Li, J., Dackermann, U., Xu, Y.-.L. & Samali, B. 2011, 'Damage identification in civil engineering structures utilizing PCA-compressed residual frequency response functions and neural network ensembles', Structural Control and Health Monitoring, vol. 18, no. 2, pp. 207-226.
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This paper presents a non-destructive, global, vibration-based damage identification method that utilizes damage pattern changes in frequency response functions (FRFs) and artificial neural networks (ANNs) to identify defects. To extract damage features and to obtain suitable input parameters for ANNs, principal component analysis (PCA) techniques are applied. Residual FRFs, which are the differences in the FRF data from the intact and the damaged structure, are compressed to a few principal components and fed to ANNs to estimate the locations and severities of structural damage. A hierarchy of neural network ensembles is created to take advantage of individual information from sensor signals. To simulate field-testing conditions, white Gaussian noise is added to the numerical data and a noise sensitivity study is conducted to investigate the robustness of the developed damage detection technique to noise. Both numerical and experimental results of simply supported steel beam structures have been used to demonstrate effectiveness and reliability of the proposed method. © 2009 John Wiley & Sons, Ltd.
Qin, Z., Su, G., Zhang, J., Ouyang, Y., Yu, Q. & Li, J. 2010, 'Identification Of Important Factors For Water Vapor Flux And Co2 Exchange In A Cropland', Ecological Modelling, vol. 221, no. 4, pp. 575-581.
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Water vapor flux and carbon dioxide (CO2) exchange in croplands are crucial to water and carbon cycle research as well as to global warming evaluation. In this study, a standard three-layer feed-forward back propagation neural network technique associate
Dackermann, U., Li, J. & Samali, B. 2010, 'Dynamic-based damage identification using neural network ensembles and damage index method', Advances in Structural Engineering, vol. 13, no. 6, pp. 1001-1016.
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This paper presents a vibration-based damage identification method that utilises a "damage fingerprint" of a structure in combination with Principal Component Analysis (PCA) and neural network techniques to identify defects. The Damage Index (DI) method is used to extract unique damage patterns from a damaged beam structure with the undamaged structure as baseline. PCA is applied to reduce the effect of measurement noise and optimise neural network training. PCA-compressed DI values are, then, used as inputs for a hierarchy of neural network ensembles to estimate locations and severities of various damage cases. The developed method is verified by a laboratory structure and numerical simulations in which measurement noise is taken into account with different levels of white Gaussian noise added. The damage identification results obtained from the neural network ensembles show that the presented method is capable of overcoming problems inherent in the conventional DI method. Issues associated with field testing conditions are successfully dealt with for numerical and the experimental simulations. Moreover, it is shown that the neural network ensemble produces results that are more accurate than any of the outcomes of the individual neural networks.
Sun, S., Huang, Z., Zhong, H., Dai, D., Liu, H. & Li, J. 2010, 'Efficient Monitoring Of Skyline Queries Over Distributed Data Streams', Knowledge And Information Systems, vol. 25, no. 3, pp. 575-606.
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Data management and data mining over distributed data streams have received considerable attention within the database community recently.
Samali, B., Li, J., Choi, F.C. & Crews, K. 2010, 'Application of the damage index method for plate-like structures to timber bridges', Structural Control and Health Monitoring, vol. 17, no. 8, pp. 849-871.
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The paper presents a research recently completed by the authors utilizing a method of damage evaluation for identifying damage in timber bridges, numerically and experimentally. The method utilizes changes in modal strain energy between the undamaged and damaged states of plate-like structures. A finite element model of a laboratory timber bridge was developed to investigate the capabilities and limitations of the method to detect damage. A simple four-girder bridge was fabricated and tested in a laboratory to verify the method. The numerical studies showed that the method can correctly identify single and multiple damage locations within the bridge. The experimental studies also showed promising results for detecting severe damage, but less effective for light and medium damage. Copyright © 2009 John Wiley & Sons, Ltd.
Li, Y., Li, J. & Samali, B. 2010, 'Dynamic performance of a novel magnetorheological pin joint', MOVIC 2010 - 10th International Conference on Motion and Vibration Control, Proceedings.
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Magnetorheological fluid (MRF) has received significant attention lately and MRF based devices have been proposed for structural control applications in recent years. The unique characteristics of MR fluid lies in its abilities to reversibly, repeatedly and instantly change from a free flowing liquid to a semi-solid state when exposed to a magnetic field. The electric power required to drive the MR devices can be easily provided by a battery. Possessing such unique properties, MR fluid based devices, such as MR damper, have become promising candidates in the semi-active control for civil structure applications. However, most of the published research has focused on application of MR dampers instead of exploring other type of MR devices. In addition, MR based devices exhibit complex nonlinear hysteresis behaviour and thus making their modelling a challenging task. In this paper, a novel MR fluid based device, namely MR pin joint, is proposed as smart structural members in development of an intelligent civil structure that can suppress unwanted vibrations to ensure safety and serviceability of the structure. After design and fabrication, experiments have been conducted to characterise dynamic behaviours of the new device under different harmonic excitations with various input currents. Test data shows that the MR pin joint possesses a unique behaviour in the moment-angular velocity plot. A hyperbolic hysteresis model is proposed to model such unique behaviour. The investigation presented in the paper explores dynamic performance of MR pin joint. Finally, a parametric model is developed following the investigation on the correlation of coefficients in the proposed model with the loading conditions and applied currents.
Samali, B., Crews, K.I., Aboura, K. & Li, J. 2009, 'The Use of Stochastic Processes in Bridge Maintenance Optimisation', African Journal of Information & Communication Te..., vol. 5, no. 1, pp. 43-53.
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We introduce an approach for modelling the structural deterioration of components of bridges for maintenance optimization purposes. The Markov chain model is found in the maintenance and repair problems since the early 60's, is introduced to the maintenance of road infrastructure in the 1980's, and is made to drive the current bridge maintenance optimization systems. While this model results into solvable programming problems and provides a solution, there are a number of criticisms associated with it. We highlight the shortfalls of the Markov model for bridge lifetime assessment and promote the use of stochastic processes.
Li, Y., Li, J., Samali, B. & Wang, J. 2009, 'Design considerations and experimental studies on semi-active smart pin joint', Frontiers of Mechanical Engineering in China, vol. 4, no. 4, pp. 363-370.
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Hostile dynamic loadings such as severe wind storms, earthquakes, and sudden impacts can cause severe damage to many civil engineering structures. An intelligent structural system equipped with smart structural members that are controllable in real-time is an effective solution to structural damage and failure during such situations. Civil intelligent structures with controllable properties to adapt to any changes due to dynamic loadings can lead to effective protection of structures and their occupants. In this paper, design and testing of a semi-active magnetorheological (MR) pin joint, in which the moment resistance can be controlled in real-time by altering the magnetic field, is reported with the view of using it as a potential candidate for smart members in the development of intelligent structures. Design of prototype smart pin joints includes theoretical analysis related to the radius of the rotary plate, the property of MR fluids and the gap between the rotary plate and the casing based on the requirements of the dynamics of MR pin joints. FEM analysis was deployed to study the distribution of the magnetic field along the gap. It is found, from the theoretical analysis and experimental verification, that the MR pin joint with a diameter of 180 mm can produce a torque of up to 30 Nm, which meets requirements for semi-active members in a multi-storey prototype building model in the next stage of research and development. © Higher Education Press and Springer-Verlag 2009.
Xu, Y.L., Zhang, J., Li, J.C. & Xia, Y. 2009, 'Experimental investigation on statistical moment-based structural damage detection method', Structural Health Monitoring, vol. 8, no. 6, pp. 555-571.
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Although vibration-based structural damage detection methods have demonstrated various degrees of success, the damage detection of civil structures still remains as a challenging task. The main obstacles include the insensitivity to local damage and the high sensitivity to measurement noise. A new structural damage detection method based on the statistical moments of dynamic responses of a structure has been recently proposed by the authors, and the numerical study manifested that the proposed method is sensitive to local structural damage but insensitive to measurement noise. The experimental investigation on this method is presented in this article. Three shear building models with and without damage were built and subjected to ground motions generated by a shaking table. The displacement and acceleration responses of each building model at each floor were recorded. The recorded ground motion and building responses as well as identified structural damping ratios were then used to identify damage locations and severities using the statistical moment-based damage detection method. The identified damage locations and severities were compared with the theoretical values. The comparison is found satisfactory, and the method proposed is effective and feasible. © The Author(s), 2009.
Dackermann, U., Li, J. & Samali, B. 2009, 'Damage identification in timber bridges utilising the damage index method and neural network ensembles', Australian Journal of Structural Engineering, vol. 9, no. 3, pp. 181-194.
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Many of Australia's timber bridges are in aged and decayed conditions. In order to ensure the reliability of these structures and the safety of the public, condition assessment, damage detection and safety evaluation is necessary. This paper presents a damage identification procedure, which is based on global change of vibration characteristics of a structure. The developed method utilises the damage index (DI) method in combination with neural network techniques to identify damage in numerical and experimental timber beam structures. The neural network ensemble approach is utilised in order to respect important diversities of different modes and to integrate individual characteristics of vibrational mode separated damage features. The method considers field testing issues associated with measurement noise, limited number of sensor arrays and environmental fluctuations. The results of damage detection using the proposed approach demonstrate its ability to determine the location and severity of all present damage cases. The outcomes show that the developed damage detection method is effective, robust and reliable. © Institution of Engineers Australia, 2009.
Samali, B., Dowling, D.M. & Li, J. 2008, 'Dynamic testing and analysis of adobe-mudbrick structures', Australian Journal of Structural Engineering, vol. 8, no. 1, pp. 63-75.
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Traditional, unreinforced adobe-mudbrick houses are highly susceptible to damage and destruction during seismic events. Research at the University of Technology Sydney has included shake table testing of 10 scale model (1:2) u-shaped adobe wall units to assess the performance of different reinforcement systems and evaluate the response to out-of-plane seismic forces. This paper describes the qualitative and quantitative performance of one unreinforced and two reinforced adobe structures. Results confirm the importance of using appropriately time-scaled input spectra to ensure dynamic similitude and induce damaging near-resonance conditions. The testing and analysis revealed both internally and externally reinforced structures to be effective at impeding initial cracking, as well as delaying major structural damage and ultimate collapse. The system incorporating external vertical reinforcement performed significantly better and has the clear advantage of being simpler to construct, as well as being a viable option for the retrofit-strengthening of existing dwellings. © Institution of Engineers Australia, 2008.
Ha, Q.P., Ha, Q.P., Kwok, N.M., Nguyen, M.T., Li, J. & Samali, B. 2008, 'Mitigation of seismic responses on building structures using MR dampers with Lyapunov-based control', Structural Control and Health Monitoring, vol. 15, no. 4, pp. 604-621.
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As losses of human lives and damages to buildings frequently occur during earthquake periods, it is crucial to mitigate structural vibrations. This paper describes the development of a Lyapunov-based control approach for magnetorheological (MR) dampers integrated in building structures to suppress quake-induced vibrations. In this work, MR dampers are used as semi-active devices, taking the advantages of the fail-safe operation and low power consumption. The control of MR dampers is, however, hindered by their hysteretic force-velocity responses and usually leads to indirect strategies compromising controllability and performance. To enhance the system performance, a Lyapunov-based controller is proposed here for direct control of the supply currents to the dampers for a multi-storey building. The dampers are configured in a differential mode to counteract the force-offset problem from the use of a single damper. The effectiveness of the proposed technique is verified, in simulations, by using a building model subject to quake-like excitations. Copyright © 2007 John Wiley & Sons, Ltd.
Samali, B., Dowling, D.M. & Li, J. 2008, 'Static and dynamic testing of adobe-mudbrick structures', Australian Journal of Structural Engineering, vol. 8, no. 2, pp. 159-170.
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Each decade major earthquakes highlight the vulnerability of traditional adobemudbrick houses, especially in developing countries. This paper describes two series of tests (static and dynamic) designed to investigate simple and effective methods of improving the structural capacity of adobe-mudbrick buildings. The static tests presented in this paper include compressive, shear and flexural bond strength testing, and consider a variety of simple modifications to the brick laying technique (effects of brick surface moisture content, mortar thickness and curing load). Results show that a significant improvement in the shear and flexural bond strength of adobe-mudbrick masonry can be practically achieved by wetting the surface of each brick prior to laying, using a thin mortar joint and applying a normal load during curing. The dynamic testing component of this paper provides a summary of the shake table testing of 10 u-shaped adobe wall units, and details the preparation and testing of a 1:2 scale model house that was retrofit-strengthened with vertical bamboo poles, horizontal wire and a timber ring beam. Results confirm that these additions, when securely tied together, create an integrated matrix that restrains movement and enhances the overall strength of the structure. The model house performed extremely well, even during repeated high intensity shake table testing, with catastrophic failure and collapse prevented in all cases. © Institution of Engineers Australia, 2008.
Choi, F.C., Li, J., Samali, B. & Crews, K. 2008, 'Application of the modified damage index method to timber beams', Engineering Structures, vol. 30, no. 4, pp. 1124-1145.
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In this paper the use of two existing algorithms developed for global nondestructive evaluation to locate and evaluate localised damage in timber beams is investigated using a finite element model. These damage localisation algorithms were found, through this investigation, not to be effective in locating multiple damage scenarios and unable to evaluate the severity of damage. Hence, modifications on damage index algorithms as well as a hybrid algorithm are proposed to overcome the problems. In this study, experimental modal analysis (EMA) was used as a tool to extract mode shapes for calculating the damage index in the proposed method which utilises changes in modal strain energy between the undamaged and the damaged timber beam model. The modified damage index (MDI) method normalises the mode shape curvature and the hybrid algorithm combines the modified damage index and changes in flexibility algorithms which reflect the changes of natural frequency and mode shape. Analytical evaluations were performed to compare and verify the ability of original and modified damage localisation algorithms in locating single and multiple damage in timber beams. The modified damage index (MDI) algorithm and the hybrid damage algorithm are also used in the experimental studies to validate the effectiveness of the methods to locate and evaluate damage within timber beams by laboratory experiments. © 2007 Elsevier Ltd. All rights reserved.
Widjaja, J.H., Samali, B. & Li, J. 2007, 'The Use of Displacement Threshold for Switching Frequency Strategy for Structural Vibration Mitigation', Journal of Mechanical Science and Technology, vol. 21, no. 6, pp. 865-869.
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Choi, F.C., Li, J., Samali, B. & Crews, K. 2007, 'Application of modal-based damage-detection method to locate and evaluate damage in timber beams', Journal of Wood Science, vol. 53, no. 5, pp. 394-400.
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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 two flexural modes of vibration. Experimental verification was performed on pin-pin supported timber beams by employing the algorithms with extracted modal parameters using experimental modal analysis. Single and multiple cases of damage used to simulate pocket(s) of rot with various severities were inflicted by removing sections of timber beam specimens. The proposed damage indicator, computed from the first two flexural modes, was capable of detecting all damage locations. It was also able to estimate, with reasonable accuracy, the severity of damage in term of loss of sectional moment of inertia. The modified damage index method is generally reliable in detecting the location and estimating the severity of simulated defects in timber beams. © 2007 The Japan Wood Research Society.
Kwok, N.M., Ha, Q.P., Nguyen, M.T., Li, J. & Samali, B. 2007, 'Bouc-Wen model parameter identification for a MR fluid damper using computationally efficient GA', ISA Transactions, vol. 46, no. 2, pp. 167-179.
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A non-symmetrical Bouc-Wen model is proposed in this paper for magnetorheological (MR) fluid dampers. The model considers the effect of non-symmetrical hysteresis which has not been taken into account in the original Bouc-Wen model. The model parameters are identified with a Genetic Algorithm (GA) using its flexibility in identification of complex dynamics. The computational efficiency of the proposed GA is improved with the absorption of the selection stage into the crossover and mutation operations. Crossover and mutation are also made adaptive to the fitness values such that their probabilities need not be user-specified. Instead of using a sufficiently number of generations or a pre-determined fitness value, the algorithm termination criterion is formulated on the basis of a statistical hypothesis test, thus enhancing the performance of the parameter identification. Experimental test data of the damper displacement and force are used to verify the proposed approach with satisfactory parameter identification results. © 2007 ISA.
Hong, S., Nguyen, M., Kwok, N., Ha, Q.P. & Li, J. 2007, 'Hysteretic model for magnetorheological fluid dampers using a curve fitting approach', Journal of JSAEM, Japanese Society of Applied Electromagnetics and Mechanics, vol. 15, pp. 176-179.
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Li, J., Choi, F., Samali, B. & Crews, K.I. 2007, 'Damage Localisation and Severity Evaluation of a Beam-Like Timber Structure Based on Modal Strain Energy and Flexibility Approaches', Journal of Building Appraisal, vol. 2, no. 4, pp. 323-334.
Samali, B., Li, J., Crews, K.I. & Al-dawod, M. 2007, 'Load rating of impaired bridges using a dynamic method', Electronic Journal of Structural Engineering, vol. 7, pp. 66-75.
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Local Government in Australia is responsible for the operational management and maintenance of over 20,000 bridges. More than 70% of these bridges comprise aging timber bridges, the load capacity and structural adequacy of many of which have been impaired over time. This is partly due to increased vehicular loads with little attention to consequence of such increases. It is now necessary to determine the load carrying capacity of these bridges using simple yet reliable methods to allow local authorities to upgrade, replace or sign post at-risk bridges. In this paper a novel dynamic based method is presented by which the in-service stiffness of the bridge is estimated first. From this stiffness the load carrying capacity of the bridge is estimated following a statistically based analysis.
Choi, F.C., Li, J., Samali, B. & Crews, K. 2007, 'An experimental study on damage detection of structures using a timber beam', Journal of Mechanical Science and Technology, vol. 21, no. 6, pp. 903-907.
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Using vibration methods for the damage detection and structural health monitoring in bridge structures is rapidly developing. However, very little work has so far been reported on timber bridges. This paper intends to address such shortcomings by experimental investigation on a timber beam using a vibration based method to detect damage. A promising damage detection algorithm based on modal strain energy was adopted and modified to locate/evaluate damage. A laboratory investigation was conducted on a timber beam inflicted with various damage scenarios using modal tests. The modal parameters obtained from the undamaged and damaged state of the test beam were used in the computation of damage index, were then applied using a damage detection algorithm utilising modal strain energy and a statistical approach to detect location of damage. A mode shape reconstruction technique was used to enhance the capability of the damage detection algorithm with limited number of sensors. The test results and analysis show that location of damage can be accurately identified with limited sensors. The modified method is less dependent on the number of modes selected and can detect damage with a higher degree of confidence.
Al-Dawod, M., Samali, B. & Li, J. 2006, 'Experimental verification of an active mass driver system on a five-storey model using a fuzzy controller', Structural Control and Health Monitoring, vol. 13, no. 5, pp. 917-943.
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This paper reports experimental tests conducted on a five-storey model using an active mass driver (AMD) system, where the control action was achieved by using a fuzzy logic controller (FLC) and the UTS state-of-the-art shake table facility. The performance of the fuzzy controller was checked against El Centro 1940, Hachinohe 1968, Northridge 1994, and Kobe 1995 earthquakes to verify the potential of using the fuzzy controller in real applications for active control of structures. Fuzzy logic is one of few mathematical model-free approaches to system identification and control. Other advantages of fuzzy logic controllers are that they can be nonlinear, adaptive, admit a high degree of parallel implementation, and tolerate uncertainty in the system. The building model under consideration is a large-scale five-storey, 3.6-m-tall, steel frame designed and manufactured at the University of Technology, Sydney. The paper details the experimental set up of the five-storey model with AMD system and the instrumentation used to measure the response, the design process of the Fuzzy Controller, and the earthquake excitations used in the experimental tests. The results of the experimental tests confirm the potential of using the adopted fuzzy controller for the active structural control using, an active mass driver (AMD) system. Copyright © 2005 John Wiley & Sons, Ltd.
Kwok, N.M., Ha, Q.P., Nguyen, T.H., Li, J. & Samali, B. 2006, 'A novel hysteretic model for magnetorheological fluid dampers and parameter identification using particle swarm optimization', Sensors and Actuators, A: Physical, vol. 132, no. 2, pp. 441-451.
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Non-linear hysteresis is a complicated phenomenon associated with magnetorheological (MR) fluid dampers. A new model for MR dampers is proposed in this paper. For this, computationally-tractable algebraic expressions are suggested here in contrast to the commonly-used Bouc-Wen model, which involves internal dynamics represented by a non-linear differential equation. In addition, the model parameters can be explicitly related to the hysteretic phenomenon. To identify the model parameters, a particle swarm optimization (PSO) algorithm is employed using experimental force-velocity data obtained from various operating conditions. In our algorithm, it is possible to relax the need for a priori knowledge on the parameters and to reduce the algorithmic complexity. Here, the PSO algorithm is enhanced by introducing a termination criterion, based on the statistical hypothesis testing to guarantee a user-specified confidence level in stopping the algorithm. Parameter identification results are included to demonstrate the accuracy of the model and the effectiveness of the identification process. © 2006 Elsevier B.V. All rights reserved.
Li, J., Samali, B. & Crews, K. 2004, 'Determining individual member stiffness of bridge structures using a simple dynamic procedure', Acoustics Australia, vol. 32, no. 1, pp. 9-12.
A reliable determination of the structural condition of timber bridges presently requires costly load testing. A new dynamic based testing method was developed by authors to reduce the cost and shorten the testing time. The method has been successfully used to undertake field-testing of more than 40 timber bridges across NSW. The dynamic testing procedure involves the attachment of accelerometers underneath the bridge girders. The bridge girders are then excited by a modal hammer. The method requires tests with and without extra mass, so that the overall flexural stiffness of the bridge can be obtained. However, in order to accurately estimate the load carrying capacity of the bridge, it is necessary to obtain the stiffness values of individual members from test results without complicating the current testing procedure. In this paper, the authors review the dynamic testing procedure and propose a method to determine individual member stiffness for a bridge structure based on the field dynamic testing data. The outcomes of this work not only enable more accurate prediction of the load carrying capacity of the bridge but will also identify defective members of the bridge structure.
Samali, B., Al-Dawod, M. & Li, J. 2003, 'Performance of an active mass driver system on a five storey benchmark model', JSME International Journal, Series C: Mechanical Systems, Machine Elements and Manufacturing, vol. 46, no. 3, pp. 848-853.
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This paper reports the experimental tests conducted on a 5-storey benchmark model defined by Samali, using an Active Mass Driver (AMD) system, where the control action is achieved by using Fuzzy Logic controller and UTS state-of-the-art shake table facility. The performance of the Fuzzy controller is checked against Hachinohe 1968 and Northridge 1994 earthquake records as input excitation to the benchmark model. The main advantage of the Fuzzy controller is its inherent robustness and ability to handle any non-linear behaviour of the structure. The results of the experimental tests show the ability of the adopted Fuzzy controller to reduce the building responses for the two earthquake records used.
Samali, B., Wu, Y. & Li, J. 2003, 'Shake table tests on a mass eccentric model with base isolation', Earthquake Engineering & Structural Dynamics, vol. 32, no. 9, pp. 1353-1372.
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Widjaja, J.H., Samali, B. & Li, J. 2003, 'A Mathematical Hysteretic Model for ER/MR Fluid Dampers', Journal Of Engineering Mechanics-asce, vol. 129, no. 2, pp. 1459-1465.
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A quasi-steady duct flow through a parallel plate model for electrorheological ~ER! and magnetorheological ~MR! fluids under shear-flow mode is investigated mathematically. To do so Herschel-Bulkley power law constitutive model for ER and MR fluid is adopted to account for postyield shear thinning or shear thickening conditions as indicated in recent research. This approach is selected in order to obtain a more flexible representation of ER or MR postyield behavior rather than using the mostly adopted Bingham plastic model. This will lead to developing a theoretical method for prediction of ER or MR force characteristics.
Widjaja, J.H., Samali, B. & Li, J. 2003, 'Electrorheological and magnetorheological duct flow in shear-flow mode using Herschel-Bulkley constitutive model', Journal Of Engineering Mechanics-ASCE, vol. 129, no. 12, pp. 1459-1465.
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Li, J., Samali, B., Ye, L. & Bakoss, S. 2002, 'Behaviour of concrete beam-column connections reinforced with hybrid FRP sheet', Composite Structures, vol. 57, no. 1-4, pp. 357-365.
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Modelling complex concrete column-beam connection with hybrid fibre reinforced plastic (FRP) reinforcement properly requires understanding of the behaviour of such component and supporting from some experimental data for model updating and refinement. This paper, through a comprehensive experimental work, investigates the behaviour of reinforced concrete frame specimens designed to represent the column-beam connections in plane frames. As a follow-up to the previous reported work, it focuses on details of experimental analyses, in particular, a comprehensive strain analysis. Results of the analysis show that designed hybrid FRP reinforcement greatly improve the stiffness and load carrying capacity of its concrete counterpart. It also delays the crack initiation at the joint through confinement due to FRP reinforcement. © 2002 Published by Elsevier Science Ltd.
Zhang, X., Li, J., Wang, C.H., Mai, Y. & Ye, L. 2002, 'Prediction of short fatigue crack propagation behaviour by characterisation of both plasticity and roughness induced crack closures', International Journal Of Fatigue, vol. 24, no. 5, pp. 529-536.
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Li, J., Bakoss, S.L., Samali, B. & Ye, L. 2000, 'Reinforcement of concrete beam-column connections with hybrid FRP', Composite Structures, vol. Volume 1, no. 0, pp. 805-812.
Zhang, X.P., Wang, C.H., Li, J.C., Mai, Y.-.W. & Ye, L. 2000, 'A combined model of short crack closure accounting for both plasticity and roughness induced crack closures', Key Engineering Materials, no. 187 PART 1, pp. 217-222.
A new model combining both plasticity-induced and surface roughness-induced crack closures is proposed to describe short fatigue crack growth. The numerical results obtained using this model agree well with the analytical predictions of Budiansky-Hutchinson and are reasonably close to the experimental data. © 2000 Trans Tech Publications.
Zhang, X.P., Wang, C.H., Li, J.C., Mai, Y.-.W. & Ye, L. 2000, 'Combined model of short crack closure accounting for both plasticity and roughness induced crack closures', Key Engineering Materials, vol. 183.
A new model combining both plasticity-induced and surface roughness-induced crack closures is proposed to describe short fatigue crack growth. The numerical results obtained using this model agree well with the analytical predictions of Budiansky-Hutchinson and are reasonably close to the experimental data.
Taylor, D.A., Li, J. & Giese, A. 1995, 'Short fatigue crack growth in cast iron described using P-a curves', International Journal Of Fatigue, vol. 17, no. 3, pp. 201-206.
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A new approach to the description of short crack growth - the P - a curve - has been tested using extensive data on submillimetre cracks in a grey cast iron. It is shown that this approach, in which the probability of growth is plotted as a function of crack length, is valid in that it produces a plot that is consistent from specimen to specimen and is a function of both crack length and stress level. The growth probability, Pg, can be defined systematically in terms of the average amount of crack growth, Îcmean within a given interval of cycles, ÎN; this leads to the concept that Pg characterizes growth at a particular rate: Îcmean/ÎN. Predictions were made of the endurance, Nf, using a numerical model that simulates the growth of a large number of cracks. Crack coalescence was found to be a critical feature, both of the model and of the experimental findings. The great majority of crack growth was found to occur by coalescence; a simple model of coalescence, based on fracture mechanics, was successfully incorporated into the predictions.
Zhengneng, L. & Li, J. 1992, 'Study on the single-peak over-load retardation effect of three-dimensional small cracks', Acta Aeronautica et Astronautica Sinica, vol. 3.
Li, J., Maohua, W. & Qingzhi, H. 1986, 'Study in Mixed Mode Fatigue Crack Propagation in a Stiffened Sheet', Acta Aeronautica et Astronautica Sinica, vol. 7.