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CONTENTS
Volume 4, Number 1, March 2017
 

Abstract
Installation of sensors networks for continuous in-service monitoring of structures and their efficiency conditions is a current research trend of paramount interest. On-line monitoring systems could be strategically useful for road infrastructures, which are expected to perform efficiently and be self-diagnostic, also in emergency scenarios. This work researches damage detection in composite concrete-steel structures that are typical for highway overpasses and bridges. The techniques herein proposed assume that typical damage in the deck occurs in form of delamination and cracking, and that it affects the peak power spectral density of dynamic curvature. The investigation is performed by combining results of measurements collected by long-gauge fiber optic strain sensors installed on monitored structure and a statistic approach. A finite element model has been also prepared and validated for deepening peculiar aspects of the investigation and the availability of the method. The proposed method for real time applications is able to detect a documented unusual behavior (e.g., damage or deterioration) through long-gauge fiber optic strain sensors measurements and a probabilistic study of the dynamic curvature power spectral density.

Key Words
bridge; traffic; PDF; detection; output-only; fiber optic sensors

Address
M. Domanesch: Politecnico di Torino, Department of Structural, Geotechnical and Building Engineering, Turin, Italy

D. Sigurdardottir: Ramböll, Stockholm Branch, Sweden

B. Glisic: Princeton University, Department of Civil and Environmental Engineering, Princeton NJ, USA

Abstract
Since extensometers are used to determine the absolute deformation of foundation and abutments and all results are obtained in reference to the base rod, the accuracy of these results has been constantly a subject of debate. In this regard, locating and installing extensometers outside the range of effect zone is also another challenge. The main purpose of this paper is to investigate and modify extensometers results based on the mentioned issues. For this aim, the concrete RCC Zhaveh dam in Iran was selected as the case study. To study the results of extensometers installed in this dam, first, the 3DEC_DP 5.00 software was applied for numerical modeling. Parameters such as discontinuities, dead load and piezometric pressure in the interface of concrete and rock were considered. Next, using the results obtained from 6 extensometers in foundation and abutments and 4 clinometers in dam body, the numerical model was calibrated through back analysis method. The results indicate that the base rod is moved and is not recommended being used as the base point. In other words, because installation of base anchor outside the range of effect zone is not possible due to the operational and economic considerations, the obtained results are not accurate enough. The results indicate a considerable 2-3 mm displacement of the base rod (location of the base anchor) in reference to the real zero point location, which must be added to the base rod results.

Key Words
extensometer; clinometer; geomechanical parameters; dead load; piezometric pressure; 3DEC_DP 5.00.software

Address
Ahad Ziaei, Kaveh Ahangari: Department of Mining Engineering, Science and Research Branch, Islamic Azad University, Tehran, Iran

Parviz Moarefvand: Department of Mining and Metallurgical Engineering, Amir Kabir University of technology, Tehran, Iran

Hasan Mirzabozorg: Department of Civil Engineering, KN Toosi University of technology, Tehran, Iran

Abstract
A cantilever beam with a breathing crack is studied to improve the breathing crack identification sensitivity by the parametric optimization of sample entropy and wavelet transformation. Crack breathing is a special bi-linear phenomenon experienced by fatigue cracks which are under dynamic loadings. Entropy is a measure, which can quantify the complexity or irregularity in system dynamics, and hence employed to quantify the bi-linearity/irregularity of the vibration response, which is induced by the breathing phenomenon of a fatigue crack. To improve the sensitivity of entropy measurement for crack identification, wavelet transformation is merged with entropy. The crack identification is studied under different sinusoidal excitation frequencies of the cantilever beam. It is found that, for the excitation frequencies close to the first modal frequency of the beam structure, the method is capable of detecting only 22% of the crack depth percentage ratio with respect to the thickness of the beam. Using parametric optimization of sample entropy and wavelet transformation, this crack identification sensitivity is improved up to 8%. The experimental studies are carried out, and experimental results successfully validate the numerical parametric optimization process.

Key Words
structural health monitoring; breathing cracks; crack identification; parametric optimization; sample entropy; wavelet transformation

Address
Department of Mechanical Engineering, University of Manitoba, Winnipeg, Manitoba, R3T 5V6, Canada

Abstract
The response sensitivity method in time domain has been applied extensively for damage identification. In this paper, the relationship between the error of damage identification and the sensitivity matrix is investigated through perturbation analysis. An index is defined according to the perturbation amplify effect and an optimal sensor placement method is proposed based on the minimization of that index. A sequential sub-optimal algorithm is presented which results in consistently good location selection. Numerical simulations with a two-dimensional high truss structure are conducted to validate the proposed method. Results reveal that the damage identification using the optimal sensor placement determined by the proposed method can identify multiple damages of the structure more accurately.

Key Words
sensor selection; damage identification; response sensitivity; perturbation amplify effect; sequential algorithm

Address
Beijing

Abstract
Delamination is the most common failure mode in layered composite materials. The author have found that the electrical potential change (EPC) technique using response surfaces method is very effective in assessment delamination in basalt fiber reinforced polymer (FRP) laminate composite pipe by using electrical capacitance sensor (ECS). In the present study, the effect of the electrodes number on the method is investigated using FEM analyses for delamination location/size detection by ANSYS and MATLAB, which are combined to simulate sensor characteristic. Three cases of electrodes number are analyzed here are eight, twelve and sixteen electrodes, afterwards, the delamination is introduced into between the three layers [0

Key Words
delamination monitoring; Electrical Capacitance Sensor (ECS); basalt FRP pipe; FEM; response surfaces method; least square error method

Address
International Institute for Urban Systems Engineering, Southeast University, Nanjing (210096), China

Department of Mechanical Engineering, Faculty of Engineering,
Alexandria University, Alexandria (21544), Egypt

Abstract
Monitoring is the most important part of the construction and operation of the embankment dams. Applied instruments in these dams should be determined based on dam requirements and specifications. Instruments selection considered as one of the most important steps of monitoring plan. Competent instruments selection for dams is very important, as inappropriate selection causes irreparable loss in critical condition. Lack of a systematic method for determining instruments has been considered as a problem for creating an efficient selection. Nowadays, decision making methods have been used widely in different sciences for optimal determination and selection. In this study, the Multi-Attribute Decision Making is applied by considering 9 criteria and categorisation of 8 groups of geotechnical instruments. Therefore, the Analytic Hierarchy Process and Multi-Criteria Optimisation and Compromise Solution methods are employed in order to determine the attributes

Key Words
risk management; decision analysis; embankments dams; geotechnical instrument; monitoring; multi-attribute decision making; Analytic Hierarchy Process; Multi-Criteria Optimisation and Compromise Solution

Address
Isa Masoumi, Kaveh Ahangari: Department of Mining Engineering, Science and Research Branch, Islamic Azad University, Tehran, Iran

Ali Noorzad: Faculty of Civil, Water and Environmental Engineering, Shahid Beheshti University, Tehran, Iran


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