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ENERGY (184 journals)                 | Last

Showing 1 - 200 of 406 Journals sorted alphabetically
ActaEnergetica     Open Access  
Advances in Building Energy Research     Hybrid Journal   (Followers: 9)
Advances in Energy and Power     Open Access   (Followers: 5)
Advances in High Energy Physics     Open Access   (Followers: 21)
Advances in Natural Sciences: Nanoscience and Nanotechnology     Open Access   (Followers: 28)
American Journal of Energy Research     Open Access   (Followers: 9)
Annals of Nuclear Energy     Hybrid Journal   (Followers: 6)
Annual Reports on NMR Spectroscopy     Full-text available via subscription   (Followers: 3)
Annual Review of Resource Economics     Full-text available via subscription   (Followers: 12)
Applied Nanoscience     Open Access   (Followers: 8)
Applied Solar Energy     Hybrid Journal   (Followers: 15)
Archives of Thermodynamics     Open Access   (Followers: 7)
Artificial Photosynthesis     Open Access   (Followers: 1)
Asian Bulletin of Energy Economics and Technology     Open Access   (Followers: 3)
Atomic Energy     Hybrid Journal   (Followers: 4)
Atoms for Peace: an International Journal     Hybrid Journal   (Followers: 3)
Batteries     Open Access   (Followers: 3)
Biofuel Research Journal     Open Access   (Followers: 4)
Biofuels     Hybrid Journal   (Followers: 10)
Biofuels Engineering     Open Access  
Biomass Conversion and Biorefinery     Partially Free   (Followers: 10)
Bulletin de droit nucleaire     Full-text available via subscription   (Followers: 1)
Canadian Journal of Remote Sensing     Full-text available via subscription   (Followers: 39)
Canadian Water Resources Journal     Hybrid Journal   (Followers: 20)
Carbon Management     Hybrid Journal   (Followers: 6)
Catalysis for Sustainable Energy     Open Access   (Followers: 5)
CERN courier. International journal of high energy physics     Free   (Followers: 7)
Chain Reaction     Full-text available via subscription   (Followers: 1)
Clefs CEA     Full-text available via subscription   (Followers: 1)
Computational Water, Energy, and Environmental Engineering     Open Access   (Followers: 4)
Dams and Reservoirs     Hybrid Journal   (Followers: 4)
Development of Energy Science     Open Access   (Followers: 4)
Distributed Generation & Alternative Energy Journal     Hybrid Journal   (Followers: 3)
E3S Web of Conferences     Open Access  
Economics and Policy of Energy and the Environment     Full-text available via subscription   (Followers: 8)
Electrical and Power Engineering Frontier     Open Access   (Followers: 21)
Electricity Journal     Partially Free   (Followers: 1)
ENERGETIKA. Proceedings of CIS higher education institutions and power engineering associations     Open Access   (Followers: 1)
Energy     Partially Free   (Followers: 24)
Energy & Environment     Hybrid Journal   (Followers: 16)
Energy & Fuels     Full-text available via subscription   (Followers: 25)
Energy and Buildings     Hybrid Journal   (Followers: 10)
Energy and Emission Control Technologies     Open Access   (Followers: 4)
Energy and Environment Focus     Free   (Followers: 6)
Energy and Environment Research     Open Access   (Followers: 11)
Energy and Environmental Engineering     Open Access   (Followers: 6)
Energy and Power     Open Access   (Followers: 8)
Energy and Power Engineering     Open Access   (Followers: 17)
Energy Conversion and Management     Hybrid Journal   (Followers: 10)
Energy Efficiency     Hybrid Journal   (Followers: 11)
Energy Harvesting and Systems : Materials, Mechanisms, Circuits and Storage     Hybrid Journal   (Followers: 3)
Energy Law Journal     Full-text available via subscription   (Followers: 4)
Energy Materials : Materials Science and Engineering for Energy Systems     Hybrid Journal   (Followers: 17)
Energy Policy     Partially Free   (Followers: 57)
Energy Prices and Taxes     Full-text available via subscription   (Followers: 5)
Energy Procedia     Open Access   (Followers: 2)
Energy Reports     Open Access   (Followers: 4)
Energy Research & Social Science     Full-text available via subscription   (Followers: 4)
Energy Science & Engineering     Open Access   (Followers: 3)
Energy Science and Technology     Open Access   (Followers: 12)
Energy Storage Materials     Full-text available via subscription   (Followers: 1)
Energy Strategy Reviews     Partially Free   (Followers: 9)
Energy Studies Review     Open Access   (Followers: 5)
Energy Systems     Hybrid Journal   (Followers: 13)
Energy Technology     Partially Free   (Followers: 5)
Energy Technology & Policy     Open Access   (Followers: 2)
Energy, Sustainability and Society     Open Access   (Followers: 17)
Environmental Progress & Sustainable Energy     Hybrid Journal   (Followers: 6)
EPJ Photovoltaics     Open Access   (Followers: 4)
Facta Universitatis, Series : Electronics and Energetics     Open Access  
Foundations and Trends® in Renewable Energy     Full-text available via subscription   (Followers: 1)
Frontiers in Energy     Hybrid Journal   (Followers: 3)
Frontiers in Energy Research     Open Access   (Followers: 2)
Fuel and Energy Abstracts     Full-text available via subscription   (Followers: 5)
Functional Materials Letters     Hybrid Journal   (Followers: 1)
Gcb Bioenergy     Open Access   (Followers: 2)
Geomechanics for Energy and the Environment     Full-text available via subscription  
Geothermal Energy     Open Access   (Followers: 3)
Green     Hybrid Journal   (Followers: 1)
Green Energy & Environment     Open Access   (Followers: 2)
IEA Electricity Information     Full-text available via subscription   (Followers: 2)
IEA Natural Gas Information     Full-text available via subscription   (Followers: 3)
IEEE Power and Energy     Full-text available via subscription   (Followers: 24)
IEEE Transactions on Energy Conversion     Hybrid Journal   (Followers: 11)
IEEE Transactions on Nuclear Science     Hybrid Journal   (Followers: 9)
IEEE Transactions on Power Systems     Hybrid Journal   (Followers: 27)
IET Power Electronics     Hybrid Journal   (Followers: 24)
Ingeniería Energética     Open Access  
Innovations : Technology, Governance, Globalization     Hybrid Journal   (Followers: 12)
International Journal of Alternative Propulsion     Hybrid Journal   (Followers: 6)
International Journal of Ambient Energy     Hybrid Journal   (Followers: 1)
International Journal of Applied Power Engineering     Open Access   (Followers: 4)
International Journal of Clean Coal and Energy     Open Access   (Followers: 5)
International Journal of Coal Science & Technology     Open Access   (Followers: 1)
International Journal of Electric and Hybrid Vehicles     Hybrid Journal   (Followers: 9)
International Journal of Emerging Electric Power Systems     Hybrid Journal   (Followers: 4)
International Journal of Emerging Multidisciplinary Fluid Sciences     Full-text available via subscription   (Followers: 2)
International Journal of Energy and Environmental Engineering     Open Access   (Followers: 4)
International Journal of Energy and Power     Open Access   (Followers: 9)
International Journal of Energy and Statistics     Hybrid Journal   (Followers: 2)
International Journal of Energy Engineering     Open Access   (Followers: 9)
International Journal of Energy Research     Hybrid Journal   (Followers: 8)
International Journal of Energy Science     Open Access   (Followers: 1)
International Journal of Flow Control     Full-text available via subscription   (Followers: 5)
International Journal of Global Energy Issues     Hybrid Journal   (Followers: 8)
International Journal of Green Energy     Hybrid Journal   (Followers: 9)
International Journal of Hydrogen Energy     Partially Free   (Followers: 12)
International Journal of Marine Energy     Full-text available via subscription   (Followers: 1)
International Journal of Nuclear Desalination     Hybrid Journal  
International Journal of Nuclear Energy Science and Technology     Hybrid Journal   (Followers: 2)
International Journal of Nuclear Governance, Economy and Ecology     Hybrid Journal   (Followers: 1)
International Journal of Nuclear Hydrogen Production and Applications     Hybrid Journal   (Followers: 1)
International Journal of Nuclear Knowledge Management     Hybrid Journal   (Followers: 1)
International Journal of Ocean and Climate Systems     Open Access   (Followers: 7)
International Journal of Power and Energy Conversion     Hybrid Journal   (Followers: 3)
International Journal of Smart Grid and Green Communications     Hybrid Journal  
International Journal of Sustainable Energy     Hybrid Journal   (Followers: 12)
International Journal of Sustainable Energy Planning and Management     Open Access   (Followers: 3)
International Journal of Sustainable Engineering     Hybrid Journal   (Followers: 7)
International Journal of Thermodynamics     Open Access   (Followers: 9)
Journal of Alternate Energy Sources & Technologies     Full-text available via subscription  
Journal of Building Performance Simulation     Hybrid Journal   (Followers: 6)
Journal of China Coal Society     Open Access  
Journal of Computational Multiphase Flows     Open Access  
Journal of Energy     Open Access  
Journal of Energy & Natural Resources Law     Hybrid Journal   (Followers: 2)
Journal of Energy Chemistry     Full-text available via subscription   (Followers: 1)
Journal of Energy in Southern Africa     Open Access   (Followers: 2)
Journal of Energy Storage     Full-text available via subscription  
Journal of Energy Technologies and Policy     Open Access   (Followers: 5)
Journal of Energy, Environment & Carbon Credits     Full-text available via subscription   (Followers: 2)
Journal of Fusion Energy     Hybrid Journal   (Followers: 3)
Journal of International Energy Policy     Open Access   (Followers: 3)
Journal of Modern Power Systems and Clean Energy     Open Access   (Followers: 8)
Journal of Nano Energy and Power Research     Full-text available via subscription   (Followers: 4)
Journal of Nuclear Energy Science & Power Generation Technology     Hybrid Journal  
Journal of Ocean Engineering and Marine Energy     Hybrid Journal   (Followers: 1)
Journal of Physical Chemistry C     Full-text available via subscription   (Followers: 28)
Journal of Power Electronics & Power Systems     Full-text available via subscription   (Followers: 7)
Journal of Radiological Protection     Full-text available via subscription   (Followers: 4)
Journal of Renewable Energy     Open Access   (Followers: 5)
Journal of Semiconductors     Full-text available via subscription   (Followers: 2)
Journal of Solar Energy     Open Access   (Followers: 8)
Journal of Solar Energy Engineering     Full-text available via subscription   (Followers: 17)
Journal of Sustainable Bioenergy Systems     Full-text available via subscription   (Followers: 1)
Journal of Sustainable Energy Engineering     Full-text available via subscription   (Followers: 1)
Journal of Technology Innovations in Renewable Energy     Hybrid Journal  
Materials for Renewable and Sustainable Energy     Open Access   (Followers: 7)
Natural Resources     Open Access   (Followers: 2)
Nature Energy     Hybrid Journal   (Followers: 4)
Nigerian Journal of Technological Research     Full-text available via subscription  
Nuclear Data Sheets     Full-text available via subscription  
Nuclear Engineering and Design     Hybrid Journal   (Followers: 10)
Nuclear Law Bulletin     Full-text available via subscription   (Followers: 2)
Nuclear Materials and Energy     Open Access   (Followers: 1)
Oil and Gas Journal     Full-text available via subscription   (Followers: 11)
Oil, Gas, Coal and Electricity - Quarterly Statistics - Electricite, charbon, gaz et petrole - Statistiques trimestrielles     Full-text available via subscription   (Followers: 9)
Open Journal of Energy Efficiency     Open Access   (Followers: 2)
Power Technology and Engineering     Hybrid Journal   (Followers: 3)
Proceedings of the Institution of Civil Engineers - Energy     Hybrid Journal   (Followers: 3)
Progress in Nuclear Energy     Hybrid Journal  
Radiochimica Acta     Hybrid Journal   (Followers: 5)
Radioprotection     Hybrid Journal   (Followers: 1)
Science and Technology of Nuclear Installations     Open Access   (Followers: 1)
Smart Grid and Renewable Energy     Open Access   (Followers: 8)
Solar Energy     Hybrid Journal   (Followers: 19)
Solar Energy Materials and Solar Cells     Hybrid Journal   (Followers: 31)
SourceOCDE Energie nucleaire     Full-text available via subscription  
SourceOECD Nuclear Energy     Full-text available via subscription   (Followers: 1)
South Pacific Journal of Natural and Applied Sciences     Hybrid Journal  
Strategic Planning for Energy and the Environment     Hybrid Journal   (Followers: 4)
Structural Control and Health Monitoring     Hybrid Journal   (Followers: 6)
Surface Science Reports     Full-text available via subscription   (Followers: 15)
Sustainable Energy     Open Access   (Followers: 1)
Sustainable Energy Technologies and Assessments     Full-text available via subscription  
Sustainable Energy, Grids and Networks     Hybrid Journal   (Followers: 1)
Technology Audit and Production Reserves     Open Access  
Universal Journal of Applied Science     Open Access   (Followers: 2)
Washington and Lee Journal of Energy, Climate, and the Environment     Open Access   (Followers: 3)
Waste Management     Hybrid Journal   (Followers: 11)
Water International     Hybrid Journal   (Followers: 13)
Wiley Interdisciplinary Reviews : Energy and Environment     Hybrid Journal   (Followers: 5)
Wind Energy     Hybrid Journal   (Followers: 2)
Wind Engineering     Hybrid Journal   (Followers: 2)

       | Last

Journal Cover Structural Control and Health Monitoring
  [SJR: 1.549]   [H-I: 35]   [6 followers]  Follow
   Hybrid Journal Hybrid journal (It can contain Open Access articles)
   ISSN (Print) 1545-2255 - ISSN (Online) 1545-2263
   Published by John Wiley and Sons Homepage  [1605 journals]
  • Implementation of a long-term monitoring approach for the operational
           safety of highway tunnel structures in a severely seismic area of China
    • Authors: Bo Wang; Zhe Zhang, Chuan He, Hao-long Zheng
      Abstract: With the rapid development of highway and railway transportation in China, many tunnels are constructed at the same time within the same region. It has become a challenge how to control dynamically such a large number of tunnel structures in long-term operation and ensure their safety. In this work, we focus on the construction of common characteristics of these tunnels built during the same period in the same region. In particular, we propose a concept and a systematic component of long-term health monitoring and develop a representative system of tunnel structure for such regional tunnels. Aiming at the engineering background, we consider the soft-rock tunnels in the Guang-Gan Expressway (GGE), which are located at the core of the Wenchuan earthquake zone, taking the Dujiashan Tunnel as a representative project. Based on the loading data of the secondary lining from long-term monitoring, the fuzzy model is employed to evaluate the structure conditions for its safety. On the basis of such theoretical analysis, we therefore establish the relationships between the representative project and other soft-rock tunnels, and then the structural safety status of the nonrepresentative project is deduced and achieved. The present study shows that the vast majority of segments of the soft-rock tunnels on the GGE are safe. At the same time, the network transmission hardware platform and security evaluation with the alerting software system are installed successfully for those tunnels. Using the long-term health monitoring and representative system of tunnel structure for soft-rock tunnels at the core of the Wenchuan earthquake zone, real-time monitoring and management of the safe status of all the soft-rock tunnels on the GGE across the entire life cycle can be realized.
      PubDate: 2017-02-16T01:25:55.616278-05:
      DOI: 10.1002/stc.1993
  • Damage detection under varying temperature using artificial neural
    • Authors: Jianfeng Gu; Mustafa Gul, Xiaoguang Wu
      Abstract: To avoid false alarms for vibration-based structural damage detection methods, temperature effects on damage-sensitive features should be eliminated. In this paper, a novel two-step damage identification method combining a multilayer neural network and novelty detection is developed to differentiate the changes in natural frequencies (one of the most commonly used damage features that can be obtained reliably and relatively easily) due to damage from those induced by temperature variations. In the first step, a multilayer artificial neural network, which resembles an auto-associative neural network but uses temperature variables in addition to the frequencies as the inputs, is explored to identify patterns in frequencies of undamaged structures under varying temperatures. Euclidean distance is then utilized as a novelty index to quantify the discordancy between patterns in undamaged cases and candidate cases. Numerical studies using a simply supported beam and finite element models based on an experimental grid structure, which simulate different levels of stiffness reductions under varying temperature conditions, are used to verify the detectability and robustness of the proposed approach. It is shown that the incorporation of the proposed artificial neural network with novelty detection enables one to robustly distinguish damage occurrence and severity regardless of temperature variations and noise perturbations. Using an unsupervised learning scheme, the proposed approach transforms a multivariate analysis using modal frequencies and temperature data into a straightforward univariate discordancy test using the novelty index. Given these competitive advantages, this approach is very attractive for the development of an automated continuous monitoring system in practical applications.
      PubDate: 2017-02-16T01:25:43.613289-05:
      DOI: 10.1002/stc.1998
  • Low-force magneto-rheological damper design for small-scale structural
    • Authors: Benjamin D. Winter; R. Andrew Swartz
      Abstract: Small-scale experimental testbeds fulfill an important role in the validation of multi-degree-of-freedom systems with distributed semi-active control, by providing a necessary platform for laboratory validation of key elements of control algorithms. Development of such small-scale testbeds is hampered by difficulties in actuator construction. In order to be a useful analog to full-scale structures, actuators for small-scale test beds should exhibit similar features and limitations as their full-scale counterparts. In particular, semi-active devices, such as magneto-rheological (MR)–fluid dampers, with limited authority (compared to alternatives such as active mass dampers) and nonlinear behavior are difficult to mimic over small force scales because of issues related to fluid containment and friction. In this study, a novel extraction-type small-force MR damper, which exhibits nonlinear hysteresis similar to a full-scale MR device, is proposed, and its behavior is characterized. This actuator is a necessary development to enable the function of small-scale structural control testbeds intended for experimental structural control validation studies. Experimental validation of this prototype as a structural control device is conducted using a three-story small-scale structure subjected to simulated seismic excitation. The actuator is commanded by a wired control computer that executes a linear-quadratic-Gaussian state feedback control law augmented by a modified Bouc–Wen lookup table, both previously developed for full-scale MR applications.
      PubDate: 2017-02-16T01:16:06.362645-05:
      DOI: 10.1002/stc.1990
  • A particle filter-based model selection algorithm for fatigue damage
           identification on aeronautical structures
    • Authors: Francesco Cadini; Claudio Sbarufatti, Matteo Corbetta, Marco Giglio
      Abstract: The early diagnosis of cracks in aeronautical structures is a fundamental task for the safe system operation and the optimization of maintenance policies, in view of the increasing interest in life extension programs of several high-investment industries. In principle, these tasks could be fulfilled within a condition-based framework, where direct or indirect observations of the degradation evolution are processed, possibly in real time, by proper diagnostic computational tools. In the past, several attempts have been made to build real-time monitoring systems collecting strain signals acquired from sensor networks. However, in real applications, some issues remain unresolved, for example, the large number of observations available to be handled within a unique diagnostic framework, their relationship with the underlying crack size, and their typical large uncertainties. In this paper, we provide a practical solution by innovatively combining a particle filtering-based model identification algorithm with a measurement system exploiting real-time observations of the crack length reconstructed by a committee of artificial neural networks. The artificial neural networks are trained by simulated strain fields generated by a finite element model. The resulting tool allows to perform an automatic, simultaneous, and real-time (a) selection of the model more properly describing the system state evolution, so as to detect the crack propagation onset time, (b) estimation of the model parameters, and (c) estimation of the crack length, within a unique probabilistic framework based on particle filtering. The methodology is demonstrated with reference to a real helicopter panel subject to fatigue and equipped with a fiber Bragg grating sensor network.
      PubDate: 2017-02-16T01:15:56.61959-05:0
      DOI: 10.1002/stc.2002
  • Bayesian model updating of a full-scale finite element model with
           sensitivity-based clustering
    • Authors: Jinwoo Jang; Andrew Smyth
      Abstract: Model updating based on vibration response measurements is a technique for reducing inherent modeling errors in finite element (FE) models that arise from simplifications, idealized connections, and uncertainties with regard to material properties. Updated FE models, which have relatively fewer discrepancies with their real structural counterparts, provide more in-depth predictions of the dynamic behaviors of those structures for future analysis. In this study, we develop a full-scale FE model of a major long-span bridge and update the model to improve an agreement between the identified modal properties of the real measured data and those from the FE model using a Bayesian model updating scheme. Sensitivity-based cluster analysis is performed to determine robust and efficient updating parameters, which include physical parameters having similar effects on targeted natural frequencies. The hybrid Monte Carlo method, one of the Markov chain Monte Carlo sampling methods, is used to obtain the posterior probability distributions of the updating parameters. Finally, the uncertainties of the updated parameters and the variability of the FE model's modal properties are evaluated.
      PubDate: 2017-02-16T01:10:53.545867-05:
      DOI: 10.1002/stc.2004
  • Bayesian model updating of a full-scale finite element model with
           sensitivity-based clustering
    • Authors: Jinwoo Jang; Andrew Smyth
      Abstract: Model updating based on vibration response measurements is a technique for reducing inherent modeling errors in finite element (FE) models that arise from simplifications, idealized connections, and uncertainties with regard to material properties. Updated FE models, which have relatively fewer discrepancies with their real structural counterparts, provide more in-depth predictions of the dynamic behaviors of those structures for future analysis. In this study, we develop a full-scale FE model of a major long-span bridge and update the model to improve an agreement between the identified modal properties of the real measured data and those from the FE model using a Bayesian model updating scheme. Sensitivity-based cluster analysis is performed to determine robust and efficient updating parameters, which include physical parameters having similar effects on targeted natural frequencies. The hybrid Monte Carlo method, one of the Markov chain Monte Carlo sampling methods, is used to obtain the posterior probability distributions of the updating parameters. Finally, the uncertainties of the updated parameters and the variability of the FE model's modal properties are evaluated.
      PubDate: 2017-02-16T01:10:53.545867-05:
      DOI: 10.1002/stc.2004
  • New approach for monitoring historic and heritage buildings: Using
           terrestrial laser scanning and generalised Procrustes analysis
    • Authors: Hasan Abdulhussein Jaafar; Xiaolin Meng, Andrew Sowter, Paul Bryan
      Abstract: Numerous different techniques and instruments can be used for structural monitoring with different requirements producing different results. For instance, some techniques need to use embedded sensors inside the building, such as geotechnical sensors. However, this method cannot be used for historic and heritage buildings. Other methods can offer high quality, but with a low point density and require fixed stations and targets, such as total stations. In such a case, the location of deformation tends to be known, such as dams, bridges, high-rise buildings, and so forth. Nevertheless, this is not the case for historic and heritage buildings where each block could be subject to deformation. The challenge in such a case is to detect the deformation without any previous knowledge. The aim of this research is to develop a new approach to detect and localise unpredictable deformation. It is based on terrestrial laser scanner measurements and generalised Procrustes analysis techniques to determine deformation vectors, although boxing structure and F-tests are used to detect and localise deformation. In summary, after applying this approach, the whole concerned building is represented as parts, for each of them, the displacement vector and deformation probability are estimated. Validation experiments have shown the capability of the proposed method to detect and localise deformation with magnitude less than noise level in simulated data and of subcentimetre level for ranges up to 10 m in real scan data. Finally, the new approach has been applied to an English Historic site, Bellmanpark Limeklins.
      PubDate: 2017-02-09T23:11:46.093351-05:
      DOI: 10.1002/stc.1987
  • Seismic FDD modal identification and monitoring of building properties
           from real strong-motion structural response signals
    • Authors: Fabio Pioldi; Rosalba Ferrari, Egidio Rizzi
      Abstract: In the present study, output-only modal dynamic identification and monitoring of building properties is attempted successfully by processing real earthquake-induced structural response signals. This is achieved through an enhanced version of a recently-developed refined Frequency Domain Decomposition (rFDD) approach, which in the earlier implementation was adopted to analyse synthetic seismic response signals only. Despite that short duration, nonstationary seismic response data and heavy structural damping shall not fulfil traditional Operational Modal Analysis assumptions, the present rFDD response-only algorithm allows for the effective estimation of strong-motion natural frequencies, mode shapes, and modal damping ratios, with real seismic response signals. The present rFDD enhancement derives from a preprocessing time-frequency analysis and from an integrated approach for Power Spectral Density matrix computation, which constitute crucial innovative issues for the treatment of real earthquake response data. A monitoring case study is analysed by taking the real strong-motion response records from a seven-storey reinforced concrete building in Van Nuys, California, from 1987 to the latest 2014 events (Center of Engineering Strong Motion Data database), as recorded before, during and after the 1994 Northridge earthquake, which severely damaged the building (then retrofitted). This paper proves the effectiveness of the proposed enhanced rFDD algorithm as a robust method for monitoring current structural modal properties under real earthquake excitations. This shall allow for identifying possible variations of structural features along experienced seismic histories, providing then a fundamental tool towards Earthquake Engineering and Structural Health Monitoring purposes.
      PubDate: 2017-02-09T22:50:53.539356-05:
      DOI: 10.1002/stc.1982
  • Improved semi-active control algorithm for hydraulic damper-based braced
    • Authors: Mohsen Azimi; Akbar Rasoulnia, Zhibin Lin, Hong Pan
      Abstract: Much research has been conducted on structural control systems to improve the seismic performance of structures under earthquakes and, ultimately, offer high performance-resilient buildings beyond life risk mitigation. Among various structural control algorithms, semi-active control strategies have been widely accepted for overcoming some limitations existed in either passive or active control systems, thereby leading to better structural performance over their counterparts. In this study, a new semi-active control algorithm with minimum control parameters is developed to drive the hydraulic damper for effective control of the dynamic deformation of low- and high-rise building structures under earthquake loadings. The new controller allows less input and computation for determining the damping coefficient of the hydraulic dampers while maintaining a higher performance. V-braced buildings with three varying heights are used as prototypes to demonstrate the effectiveness of the proposed semi-active damper. Two critical parameters, maximum drift and acceleration of stories, are defined for the performance criteria. The simulation results show that the developed semi-active damper can significantly improve the seismic performance of the buildings in terms of controlled story drift and acceleration. By use of less input and reduced time delay effects, the proposed control system is comparable with those of existing semi-active controllers. The findings in this study will help engineers to design control systems for seismic risk mitigation and effectively facilitate the performance-based seismic design.
      PubDate: 2017-02-08T03:02:08.230309-05:
      DOI: 10.1002/stc.1991
  • Numerical simulation of acoustic emission during crack growth in 3-point
           bending test
    • Authors: A. Berezovski; M. Berezovski
      Abstract: Numerical simulation of acoustic emission by crack propagation in 3-point bending tests is performed to investigate how the interaction of elastic waves generates a detectable signal. It is shown that the use of a kinetic relation for the crack tip velocity combined with a simple crack growth criterion provides the formation of waveforms similar to those observed in experiments.
      PubDate: 2017-02-07T01:50:44.453997-05:
      DOI: 10.1002/stc.1996
  • Spectral characteristics of asynchronous data in operational modal
    • Authors: Yi-Chen Zhu; Siu-Kui Au
      Abstract: Operational modal analysis (OMA) has gained popularity for identifying the modal properties of a structure for its high economy and feasibility. Conventionally, time synchronisation among data channels is required to determine mode shape. OMA can be conducted more flexibly if synchronisation is not required. The power spectral density (PSD) matrix of data and its spectral properties are often used for analysing potential modes. Conventionally known properties assume synchronous data and do not carry over to asynchronous data. This paper investigates the spectral properties of asynchronous OMA data. A stationary process with imperfect coherence is proposed that is conducive to OMA while capturing the key asynchronous characteristics. The theoretical properties of PSD matrix are derived and validated using synthetic and experimental data. Although conventional methods do not allow mode shape to be determined from asynchronous data, the present work reveals the possibility by noting that the data are measured under the same excitation and hence share a common PSD in the modal force. On this basis, a simple method is proposed for determining the mode shape. For perfectly incoherent data channels, it is not possible to determine the relative sense of their mode shape values, which is a fundamental limitation of such data. In implementation, the sense can be determined from intuition or estimated from the residual coherence between channels. Experimental application reveals practical issues in OMA with asynchronous data. This work aspires to provide the pathway for more flexible implementation of OMA, for example, using asynchronous data from multiple smart phones.
      PubDate: 2017-02-06T02:32:14.291209-05:
      DOI: 10.1002/stc.1981
  • Development and implementation of horizontal-plane settlement indication
           system for freeway health monitoring during underpass construction
    • Authors: Chih-Chung Chung; Chih-Ping Lin, Chi-Hsien Chin, Kun-Hsien Chou
      Abstract: This study introduced two major contributions for freeway health monitoring during the pipe roof construction and subsequent excavation to enlarge an existing underpass. First, a horizontal-plane settlement indication system (HSIS) was developed to monitor inevitable settlement due to shallow overburden above the steel pipes. Second, the experience gained from the field monitoring program was detailed with emphasis on encountered problems and countermeasures for freeway safety decision-making. On the basis of two microelectromechanical systems tilt sensors embedded as a differential pair, HSIS effectively minimizes the effect of ambient temperature whose fluctuation was expected at shallow depth. The measurement accuracy (≤4 mm) and repeatability (≤0.05 mm) were verified experimentally. Thereby, three HSIS arrays were positioned in the freeway pavement to continuously detect local settlement and based on which to issue possible alarm. The RS485 data acquisition protocol, which is characterized by fast synchronized communication, was applied for HSIS to reduce the dynamic error due to heavy traffics. The observed settlement was close to the alarm threshold, which is considered as the combination effects of the simulated settlement and the penetrating deviation during the pipe roof construction. Furthermore, an approach to account for false vertical drift due to instability of the fixed point of HSIS was proposed such that the settlement behavior during excavation phase could be effectively described. The unique implementation is a benefit to further HSIS application in practice.
      PubDate: 2017-02-06T02:31:54.767161-05:
      DOI: 10.1002/stc.1995
  • Low-cost simulation using model order reduction in structural health
           monitoring: Application of balanced proper orthogonal decomposition
    • Authors: N. Sepehry; M. Shamshirsaz, F. Bakhtiari Nejad
      Abstract: In this paper, both two powerful methods in structural health monitoring, Lamb wave propagation and electromechanical impedance method, are modeled, implemented, and tested to inspect the plate-like structure using piezoelectric wafer active sensor (PWAS). In order to detect damage in structure, introducing a model for advanced signal processing algorithm is essential. A three-dimensional spectral finite element method has been applied to model Lamb wave propagation and electromechanical impedance in plate with attached PWAS. In reality, Lamb wave generation and electromechanical impedance in high frequencies lead to a high degree of freedom in modeling and consequently to a low speed simulation in frequency and time domains calculation. For us to overcome this problem, balanced proper orthogonal decomposition (BPOD) has been developed and used as model order reduction for these methods in structural health monitoring. The experimental tests are carried out on aluminum plate with two attached PWAS. The simulation results obtained by BPOD and full-order method are validated by comparison with experimental ones. The results show that the proposed and implemented model order reduction method (BPOD) leads to increase significantly simulation speed without any distortion in accuracy. For Lamb wave method, CPU time consuming using BPOD is reduced 5.8 times (frequencies 40 and 150 kHz) comparing to full-order model application without any alteration of accuracy (less than 0.03 normalized voltage). For impedance method, the simulation time has been decreased 10 times less than using full-order model in frequency range 90–100 kHz while the error of impedance real part remains less than 0.025.
      PubDate: 2017-02-06T02:31:18.978718-05:
      DOI: 10.1002/stc.1994
  • New results concerning structural health monitoring technology
           qualification for transfer to space vehicles
    • Authors: Daniela Enciu; Ioan Ursu, Adrian Toader
      Abstract: This article reports the results of recent complex tests on the survival, in view of space applications, of structural health monitoring (SHM) methodology that uses piezo wafer active sensors (PWAS) and the electromechanical impedance spectroscopy (EMIS) method. Successive and then concomitant actions of the harsh conditions of outer space, including extreme temperatures and radiation, were simulated in a laboratory. The basis of the method consists in the fact that the real part of the bonded PWAS impedance spectrum, the so-called EMIS structure signature, follows the resonance behaviour of the structure vibrating under the PWAS excitation and, consequently, the onset and progress of structural damage with fidelity. The tests were conducted on the PWAS separately and aluminium discs with PWAS bonded on them as structural specimens. The conclusion of the tests is that the cumulative impact of severe conditions of temperature and radiation did not result in the decommissioning of the sensors or adhesive, which would have meant that the methodology was compromised. This conclusion occurs as a result of applying two new analysis methods to EMIS signatures. The first method, based on systematic observation of EMIS signatures during tests, makes it possible to distinguish between real damage with a mechanical origin and false damage, which is reversible and caused by the harsh environmental factors. A second method, based on the concept of entropy, shows how to identify mechanical damage at a certain distance from the PWAS. Moreover, an offline analysis of the EMIS “entropy” signatures supports the conclusion that the SHM technology survived the harsh environmental conditions.
      PubDate: 2017-02-03T00:25:42.83407-05:0
      DOI: 10.1002/stc.1992
  • Concrete dam deformation prediction model for health monitoring based on
           extreme learning machine
    • Authors: Fei Kang; Jia Liu, Junjie Li, Shouju Li
      Abstract: Structural health monitoring via quantities that can reflect behaviors of concrete dams, like horizontal and vertical displacements, rotations, stresses and strains, seepage, and so forth, is an important method to evaluate operational states of concrete dams correctly and predict the future structural behaviors accurately. Traditionally, statistical model is widely applied in practical engineering for structural health monitoring. In this paper, an extreme learning machine (ELM)-based health monitoring model is proposed for displacement prediction of gravity dams. ELM is one type of feedforward neural networks with a single layer of hidden nodes, where the weights connecting inputs to hidden nodes are randomly assigned. The model can produce good generalization performance and learns faster than networks trained using the back propagation algorithm. The advantages such as easy operating, high prediction accuracy, and fast training speed of the ELM health monitoring model are verified by monitoring data of a real concrete dam. Results are also compared with that of the back propagation neural networks, multiple linear regression, and stepwise regression models for dam health monitoring.
      PubDate: 2017-02-03T00:21:30.603982-05:
      DOI: 10.1002/stc.1997
  • A passive electromagnetic eddy current friction damper (PEMECFD):
           Theoretical and analytical modeling
    • Authors: Mohsen Amjadian; Anil K. Agrawal
      Abstract: The focus of this paper is on analytical modeling of a novel type of passive friction damper for seismic hazard mitigation of structures. The proposed seismic damping device, which is termed as passive electromagnetic eddy current friction damper, utilizes a solid-friction mechanism in parallel with an eddy current damping mechanism to maximize the dissipation of input seismic energy through a smooth sliding in the damper. In this passive damper, friction force is produced through magnetic repulsive action between two permanent magnetic sources magnetized in the direction normal to the friction surface, and the eddy current damping force is generated because of the motion of the permanent magnetic sources in the vicinity of a conductor. The friction and eddy current damping parts are able to individually produce ideal rectangular and elliptical hysteresis loops, respectively; which, when combined in the proposed device, are able to accomplish a higher input seismic energy dissipation than that only by the friction mechanism. This damper is implemented on a two-degree-of-freedom system to demonstrate its capability in reducing seismic responses of frame building structures. The numerical results show that the seismic performance of the proposed damper is comparable with that of passive magnetorheological damper of the same force capacity. However, the cost of the device is likely to be quite lesser than that of a magnetorheological damper.
      PubDate: 2017-02-03T00:16:40.968509-05:
      DOI: 10.1002/stc.1978
  • Monitoring of masonry historical constructions: 10 years of static
           monitoring of the world's largest oval dome
    • Authors: Rosario Ceravolo; Annunziata De Marinis, Marica L. Pecorelli, Luca Zanotti Fragonara
      Abstract: This paper presents the analyses conducted on the data acquired by the monitoring system of the “Regina Montis Regalis” Basilica of Vicoforte (Italy) in the decade 2004–2014. The Basilica is a building of great historical, architectural, and structural significance, owing its fame to its impressive masonry oval dome, the world's largest of this shape (internal axes of 37.23 by 24.89 m).The dome-drum system of the Basilica has suffered over the years of significant structural problems, partly due to the settlements of the building induced progressively by newly built masses and also to the sliding of the underground. In 1983, concerns over the severe settlements and cracking phenomena affecting the structure prompted the decision to undertake strengthening interventions. A special hooping system, consisting of 56 tie bars, placed around the oval perimeter of the dome, was thus conceived to limit the crack opening.The monitoring system of the Basilica installed in the early 1980s underwent several renovations, and in 2004, its acquisition procedure was automatized. One hundred twelve instruments, consisting of temperature sensors, crackmeters, load cells, pressure cells, wire gauges, hygrometer, piezometers, and hydrometer, are currently installed on the Basilica.This study is primarily focused on data acquired by the crackmeters, the extensometers along the main axes of dome, and the load cells placed at the ends of the tie bars. The main aim of the reported analysis is to evaluate the possible progression of the cracks on the Basilica, and the structural performance of the strengthening interventions put in place in 1985–1987.
      PubDate: 2017-02-03T00:11:21.013083-05:
      DOI: 10.1002/stc.1988
  • Structural damage diagnosis with uncertainties quantified using interval
    • Authors: Gang Liu; Zhu Mao
      Abstract: The in situ structural assessment by means of structural health monitoring (SHM) has received a great attention in all sorts of civil engineering applications. However, SHM implementations especially damage detections for real-world infrastructures are always overwhelmed with uncertainties of high dimensionality. A nonprobabilistic uncertainty-quantification-enhanced damage diagnosis method is proposed in this study with respect to interval analysis on SHM features. The diagonal elements of the vector auto-regressive model, constructed from the data measurements, are firstly extracted to form a vector, and this vector's Mahalanobis distance between pristine and unknown conditions is used as a damage-sensitive feature. Subsequently, the uncertainty sources, such as measurement inaccuracy and physical variability, are considered as influencing variables. A differential evolution algorithm is thereby introduced to convert the fluctuating interval of those variables into the uncertainty interval of Mahalanobis distance estimation. Finally, inspired by the idea of receiver operating characteristics when probability of detection is available, a modified mathematic metric is defined suited for interval analysis, and area under the modified receiver operating characteristics curve is employed to detect and localize damages. A contrived numerical mass-spring system and a laboratory-scale frame structure are used to validate the proposed framework; and in addition, the damage severity is able to be quantified via a proposed interval distance between pristine and inspection conditions.
      PubDate: 2017-02-03T00:05:41.287762-05:
      DOI: 10.1002/stc.1989
  • Radial basis function neural network algorithm for semi-active control of
           base-isolated structures
    • Authors: Agrahara Krishnamoorthy; Shubha Bhat, Dattatreya Bhasari
      Abstract: Curved surface slider (CSS) is considered as an effective isolation device for structures subjected to earthquake ground motions. Due to constant frequency, CSS may encounter a resonance problem when subjected to near-fault earthquake ground motions. To overcome this problem, we propose CSS combined with a control device in this study. The control device consists of variable orifice fluid damper, and its damping coefficient is controlled by a radial basis function-based neural network algorithm. Numerical simulations are performed to evaluate the effectiveness of the proposed technique for only one-directional horizontal seismic excitations without any evaluation concerning the durability of CSSs. The results of the investigation demonstrate that the proposed technique is effective to reduce both the base shear and the sliding displacement of the isolated structure. In addition, the response predicted by the proposed technique is almost similar to the response of isolated structure with passive damper at optimum damping ratio.
      PubDate: 2017-02-03T00:05:30.587509-05:
      DOI: 10.1002/stc.1984
  • Seismic resilience timber connection—adoption of shape memory alloy
           tubes as dowels
    • Authors: Haoyu Huang; Wen-Shao Chang
      Abstract: This study investigates a novel timber dowel-type connection system using superelastic shape memory alloy (SMA) bar and tubes as dowels, in order to provide self-centering effect. Double-shear connections with SMA and mild steel dowels were tested under dynamic loadings at different displacement levels. The results showed that SMA dowel-type connections have good self-centering behaviours and can mitigate the residual deformation effectively compared with steel dowel-type connections after excessive deformation; although the steel dowel-type connections present higher strength. These tests reveal that the connection with tube dowels show higher equivalent viscous damping ratio than those use solid bar as tube would allow larger deformation to dissipate energy. To demonstrate application of the benefit of this system, an analytical model of a 3-storey timber framed structure was built for parametric study. The results showed that the structures with conventional dowel-type type connections exhibit large unrecoverable deformation after timber framed structures experience an earthquake. In comparison, those with the connections developed in this project show limited unrecoverable deformation due to the self-centering capacity of the connections.
      PubDate: 2017-02-03T00:00:55.603377-05:
      DOI: 10.1002/stc.1980
  • Inertial mass damper for mitigating cable vibration
    • Authors: Lei Lu; Yuan-Feng Duan, Billie F. Spencer, Xilin Lu, Ying Zhou
      Abstract: Stay cables used in cable-stayed bridges are prone to vibration due to their low-inherent damping characteristics. Many methods have been implemented in practice to mitigate such vibration. Recently, negative stiffness dampers have gained attention because of their promising energy dissipation ability. The viscous inertial mass damper (VIMD) has been shown to have properties similar to negative stiffness dampers. This paper examines the potential of the VIMD to enhance the damping, and mitigate the vibration, of stay cables. First, a control-oriented model of the cable is employed to formulate a system level model of the cable–VIMD system for small in-plane motion. After carefully classifying and labeling the mode order, the modal characteristics of the system are analyzed, and the optimal damper parameters for the several lower frequency modes are determined numerically. The results show that the achievable modal damping ratio can be up to nearly an order of magnitude larger than that of the traditional linear viscous damper; note that the optimal parameters of the VIMD are distinct for each mode of interest. These results are further validated through analysis of the cable responses due to the distributed sinusoidal excitation. Finally, a case study is conducted for a cable with a length of 307 m, including the design of practical damper parameters, modal-damping enhancement, and vibration mitigation under wind loads. The results show that the VIMD is a promising practical passive damper that possesses greater energy dissipation capacity than the traditional viscous damper for such cable–damper systems.
      PubDate: 2017-02-02T23:59:51.473176-05:
      DOI: 10.1002/stc.1986
  • Detecting structural damage to bridge girders using radar interferometry
           and computational modelling
    • Authors: Maizuar Maizuar; Lihai Zhang, Saeed Miramini, Priyan Mendis, Russell G. Thompson
      Abstract: The process for assessing the condition of a bridge involves continuously monitoring changes to the material properties, support conditions, and system connectivity throughout its life cycle. It is known that the structural integrity of bridges can be monitored by measuring their vibration responses. However, the relationship between frequency changes and structural damage is still not fully understood. This study presents a bridge condition assessment framework which integrates computational modelling and noncontact radar sensor techniques (i.e., IBIS-S) to predict changes in the natural frequencies of a bridge girder as a result of a range of parameters that govern its structural performance (e.g., elastomeric bearing stiffness, concrete compressive stiffness, and crack propagation). Using a prestressed concrete bridge in Australia as a case study, the research outcomes suggest that vibration monitoring using IBIS-S is an efficient way for detecting the degradation of elastomeric bearing stiffness and shear crack propagation in the support areas that can significantly affect the overall structural integrity of a bridge structure. However, frequency measurements have limited capability for detecting the decrease in the material properties of a bridge girder.
      PubDate: 2017-02-02T23:25:29.031281-05:
      DOI: 10.1002/stc.1985
  • Control of underground blast induced building vibration by
           shape-memory-alloy rubber bearing (SMARB)
    • Authors: Papiya D. Mondal; Aparna D. Ghosh, Subrata Chakraborty
      Abstract: This paper focuses on the performance of shape-memory-alloy rubber bearings (SMARBs) compared to conventional lead-plug or New-Zealand (N-Z) bearings in control of building vibration due to underground blast induced ground motion (BIGM). The performance is evaluated with regard to maximum acceleration and isolator displacement obtained by nonlinear time history analysis. In doing so the Bouc–Wen's model is used to represent the nonlinear behaviour of the N-Z bearing and the superelastic behaviour of nickel–titanium-based shape-memory alloy is represented by the Graesser–Cozzarelli model. The underground BIGM input is modelled by exponentially decaying function. It is observed that though the N-Z bearing is fairly effective in controlling the structural accelerations due to BIGM without excessive bearing displacements, there remains a problem with the residual bearing displacements. The latter, however, is found to be dealt with very effectively by the SMARB. Furthermore, the procedure to obtain the optimum design parameters of the base isolators under study is obtained by optimizing two mutually conflicting objective functions, that is, the minimization of peak acceleration as well as peak bearing displacement by converting the multiobjective optimization problem to a single composite objective function. The improved and robust control performance of SMARB compared to N-Z bearing is elucidated through numerical study by considering a five-storied shear building frame.
      PubDate: 2017-02-02T23:20:30.575149-05:
      DOI: 10.1002/stc.1983
  • Issue Information
    • Abstract: No abstract is available for this article.
      PubDate: 2017-01-18T02:21:14.324467-05:
      DOI: 10.1002/stc.1940
  • Utilization of structural health monitoring in long-span bridges: Case
    • Authors: Zhen Sun; Zilong Zou, Yufeng Zhang
      Abstract: Structural health monitoring (SHM) of bridges has gained rapid development in the past few years. This paper describes application of SHM on long-span bridges in China, with the aim to illustrate its practical value. A short review of its development and practice is firstly introduced. Three case studies are subsequently presented on utilization of SHM data in engineering practice. In the first case study, a ship collision incident is analyzed using SHM data. An alarm is sent and confirmed when the collision occurred, and mode parameters are identified with GPS measurements to evaluate the bridge condition. In the second case study, damage of expansion joints in a suspension bridge is assessed with girder end displacement measurements. Malfunction of viscous damper is found to correlate with cumulative displacement. The results show that cumulative displacement can be used for condition assessment of expansion joints. In the third case study, the performance of tuned mass dampers is evaluated with wind and vibration measurements before and after tuned mass damper installation. Through explanation of these case studies, the paper illustrates how to distill useful insights from SHM data, which could be instructive for further research in this field.
      PubDate: 2017-01-06T05:36:01.302483-05:
      DOI: 10.1002/stc.1979
  • Eulerian-based virtual visual sensors to measure dynamic displacements of
    • Authors: Ali Shariati; Thomas Schumacher
      Abstract: Vibration measurements provide useful information about a structural system's dynamic characteristics and are used in many fields of science and engineering. Here, we present an alternative noncontact approach to measure dynamic displacements of structural systems using digital videos. The concept is that intensity measured at a pixel with a fixed (or Eulerian) coordinate in a digital video can be regarded as a virtual visual sensor. The pixels in the vicinity of the boundary of a vibrating structural element contain useful frequency information, which we have been able to demonstrate in earlier studies. Our ultimate goal, however, is to be able to compute dynamic displacements, i.e., actual displacement amplitudes in the time domain. In order to achieve that, we introduce the use of simple black-and-white targets that are mounted on locations of interest on the structure. By using these targets, intensity can be directly related to displacement, turning a video camera into a simple, computationally inexpensive, and accurate displacement sensor with notably low signal-to-noise ratio. We show that subpixel accuracy with levels comparable to computationally expensive block matching algorithms can be achieved using the proposed targets. Our methodology can be used for laboratory experiments, on real structures, and additionally, we see educational opportunities in K-12 classroom. In this paper, we introduce the concept and theory of the proposed methodology, present and discuss a laboratory experiment to evaluate the accuracy of the proposed black-and-white targets, and discuss the results from a field test of an in-service bridge.
      PubDate: 2016-12-23T01:26:16.847281-05:
      DOI: 10.1002/stc.1977
  • Performance of tuned tandem mass dampers for structures under the ground
    • Authors: Yunzhi Yang; Chunxiang Li
      Abstract: It is widely acknowledged that the tuned mass damper (TMD) is one of the most effective and simplest passive control devices, but its limited control performance is still a troubling problem. In order to surmount the shortage of TMD, the tuned tandem mass dampers (referred herein to as TTMD) have been proposed for mitigating the undesirable oscillation of structures under the ground acceleration. Based on the formulation of the mode-generalized system in the specific vibration mode being controlled, the analytical expression is then derived for the dynamic magnification factor of the structure furnished with a TTMD. The optimum criterion can thereby be defined as minimization of the minimum values of the maximum dynamic magnification factor with a set of optimization variables embedded so as to give full play to the control device potential. The optimization implementation of TTMD is carried out by the MATLAB-based coding and debugging. For the purpose of a mutual authentication to the optimization results, three metaheuristic algorithms, namely, genetic algorithm, particle swarm optimization, and simulated annealing, are concurrently taken into consideration. Results demonstrate that the proposed TTMD endows with the superior stroke performance with respect to TMD.
      PubDate: 2016-12-22T00:51:05.605001-05:
      DOI: 10.1002/stc.1974
  • Using water hammer to enhance the detection of stiffness changes on an
           out-of-round pipe with distributed optical-fibre sensing
    • Authors: Leslie Wong; Kenneth Lim, Wing Kong Chiu, Jayantha Kodikara, Nabil Chowdhury
      Abstract: Over the last few decades, distributed optical fibre sensor (DOFS) has been introduced to monitor the structural health of water pipelines. Most of the previous studies show that DOFS is very effective as a static measurement and monitoring platform. However, there is still a lack of research being done using DOFS to monitor the dynamic response of the pipeline. This paper will first demonstrate the dynamic capability of optical frequency domain reflectometry-based DOFS on a pipe. To be specific, the primary monitoring work is conducted on an out-of-round plastic pipe subjected to water hammer. It is important to monitor the dynamic response of the pipe as it is well known that water hammer can occur in any pressurised pipeline system due to changes in the operating conditions. The ability to detect local stiffness irregularity on the noncircular pipe subjected to water hammer is also demonstrated. The result shows that the presence of the local stiffness change is accentuated when the pipe is subjected to water hammer. The dynamic capability of DOFS facilitates the application of water hammer as a stimulus and hence shows the potential to enhance pipeline health monitoring.
      PubDate: 2016-12-21T23:41:07.817743-05:
      DOI: 10.1002/stc.1975
  • Shake table real-time hybrid simulation techniques for the performance
           evaluation of buildings with inter-story isolation
    • Authors: Ruiyang Zhang; Brian M. Phillips, Shun Taniguchi, Masahiro Ikenaga, Kohju Ikago
      Abstract: Interstory isolation systems have recently gained popularity as an alternative for seismic protection, especially in densely populated areas. In inter-story isolation, the isolation system is incorporated between stories instead of the base of the structure. Installing inter-story isolation is simple, inexpensive, and disruption free in retrofit applications. Benefits include nominally independent structural systems where the accelerations of the added floors are reduced when compared to a conventional structural system. Furthermore, the base shear demand on the total structure is not significantly increased. Practical applications of inter-story isolation have appeared in the United States, Japan, and China, and likewise new design validation techniques are needed to parallel growing interest. Real-time hybrid simulation (RTHS) offers an alternative to investigate the performance of buildings with inter-story isolation. Shake tables, standard equipment in many laboratories, are capable of providing the interface boundary conditions necessary for this application of RTHS. The substructure below the isolation layer can be simulated numerically while the superstructure above the isolation layer can be tested experimentally. This configuration provides a high-fidelity representation of the nonlinearities in the isolation layer, including any supplemental damping devices. This research investigates the seismic performance of a 14-story building with inter-story isolation. A model-based acceleration-tracking approach is adopted to control the shake table, exhibiting good offline and online acceleration tracking performance. The proposed methods demonstrate that RTHS is an accurate and reliable means to investigate buildings with inter-story isolation, including new configurations and supplemental control approaches.
      PubDate: 2016-12-21T03:25:37.460926-05:
      DOI: 10.1002/stc.1971
  • Damage detection in elastic properties of masonry bridges using coda wave
    • Authors: Marcello Serra; Gaetano Festa, Maurizio Vassallo, Aldo Zollo, Antonino Quattrone, Rosario Ceravolo
      Abstract: Structures may be subjected to damage and deterioration over different timescales, and monitoring their health status may allow to perform maintenance actions before the functionality limit is reached. Masonry arch bridges, in particular, are sensitive to the bearings loss produced by scour of the streambed soil at the pier foundations. In this study, we measured the changes in the elastic properties of a 1:2 scaled model of a masonry arch bridge built in the laboratory to study the evolution of the damage mechanism related to the application of foundation movements. Specifically, the bridge is realized to model the effect of erosion of the ground underneath the central pier. We analysed the accelerometric records acquired along the structure generated by a sledgehammer hitting the bridge walls. We used the method of coda wave interferometry to detect the changes in the elastic properties of the medium. After selecting the specific frequency band exciting coda waves, we progressively measured the time lag between signals acquired in the intact and two damaged stages of the bridge for each source–receiver couple, and we fit the data to get the relative wave velocity changes. We found that the average relative velocity changes for the two damaged steps are Δv/v = −5.08 ± 0.08% and Δv/v = −8.2 ± 0.6%, consistently measured at all the analysed source–receiver couples. These values correspond to an average estimation of the velocity changes occurred within the structure, because the associated wavelengths are comparable with the bridge size and the damage is spread over a large portion of the structure.
      PubDate: 2016-12-20T03:55:48.31577-05:0
      DOI: 10.1002/stc.1976
  • Crack propagation monitoring using an image deformation approach
    • Authors: D. Dias-da-Costa; J. Valença, E. Júlio, H. Araújo
      Abstract: An image deformation method is herein proposed to monitor the crack propagation in structures. The proposed approach is based on a computational algorithm that uses displacements measured by photogrammetry or image correlation to generate a virtual image of the surface, from an initial input to any given stage of analysis. This virtual image is then compared with the real image of the specimen to identify any discontinuities that appeared or evolved during the monitored period. The procedure was experimentally validated in the characterisation of crack propagation in concrete specimens. When compared with other image processing techniques, for instance, based on edge detectors, the image deformation approach showed insensitiveness to any discontinuity previously existing on the surface, such as cracks, stains, voids, or shadows, and did not require any specific surface treatments or lighting conditions. With this approach, the global crack maps could be extracted from the surface of the structure and extremely small changes occurring within a given time interval could be characterised, such as the movement associated with the opening of cracks. It is highlighted that the proposed procedure is general and therefore applicable to detect and characterise surface discontinuities in different materials and test set-ups.
      PubDate: 2016-12-20T03:27:06.88695-05:0
      DOI: 10.1002/stc.1973
  • Damage detection in beam and truss structures by the inverse analysis of
           the static response due to moving loads
    • Authors: Nadir Boumechra
      Abstract: The detection and the localization of damages in a bridge have been always one of the major concerns of infrastructure managers, engineers, and researchers. In addition to the dynamic techniques that were well imposed in the diagnosis of bridges, several static methods have been developed. The idea of this work is to exploit the measurement results about a bridge deflection submitted to a moving load. By using the displacements response, important data about the displacement of a structural point could be gathered. When the structure's geometry and the material characteristics are known, a finite element model, supposed to be the most similar, could be developed. The numerical structural model and the static displacements data are used to develop an equilibrium equations system where unknowns are the possible stiffness changes in the finite element model. Thus, the global stiffness matrix of the studied structure is a polynomial matrix. The equilibrium equations system is a static inverse problem requiring resolution. To facilitate the mathematical development, the inverse of the global stiffness matrix is expressed by a Neumann series. Then, the resolution of the system is done by a code developed in Matlab. To confirm the good convergence of the developed mathematical method, numerical tests are carried out by considering beams and a 3D truss bridge subjected to a moving load. Thereafter, an analysis concerning the influence of the noise in the displacements data on the accuracy of the inverse analysis and the convergence of the results is made. It has been shown that the large number of data reduces the noises effect and the damages detection can be ensured.
      PubDate: 2016-12-16T02:25:49.402413-05:
      DOI: 10.1002/stc.1972
  • Structural time-dependent reliability assessment of the vibration active
           control system with unknown-but-bounded uncertainties
    • Authors: Lei Wang; Xiaojun Wang, Yunlong Li, Guiping Lin, Zhiping Qiu
      Abstract: The active control system for structural vibration is extremely sensitive to the parametric uncertainty so that more and more concerns of its reliability estimation have been given recently. In view of the insufficiency of the uncertainty information in practical engineering, a non-probabilistic time-dependent reliability method that combines the active vibration control theory with interval analysis is proposed in this paper to effectively estimate the dynamic safety of the controlled structures, in which circumstances the unknown-but-bounded uncertainties in structural parameters are considered. The uncertain structural responses based on the closed-loop control are firstly analyzed and embodied by the interval process model. By virtue of the first-passage theory, an integral procedure of non-probabilistic time-dependent reliability analysis of the active control system for structural vibration is then conducted. Two engineering examples and one experimental application are eventually presented to demonstrate the validity and applicability of the methodology developed.
      PubDate: 2016-12-02T01:47:24.385306-05:
      DOI: 10.1002/stc.1965
  • Experimental image and range scanner datasets fusion in SHM for
           displacement detection
    • Authors: Javier Rivera-Castillo; Wendy Flores-Fuentes, Moisés Rivas-López, Oleg Sergiyenko, Felix F. Gonzalez-Navarro, Julio C. Rodríguez-Quiñonez, Daniel Hernández-Balbuena, Lars Lindner, Luis C. Básaca-Preciado
      Abstract: Optical images and signals can be used to detect displacement in civil engineering structures. This paper presents a technical experimentation of a vision-based technology and artificial intelligence algorithms methodology for structural health monitoring of new and aging structures, by a noncontact and nondestructive system. The experimental study emphasis is on the outdoor urban environment, by the detection of spatial coordinate displacement on the structures, in order to perform a damage assessment. Also, the experimental study contains both theoretical and experimental aspects of the fusion of image and range scanner datasets created using intelligent algorithms. A camera and an optical scanning system were used to generate high resolution and quality images for 2D imaging, and 3D accuracy range data from optoelectronic sensor signals. Scans at a specific area of an engineering structure were performed to measure spatial coordinates displacements, successfully verifying the effectiveness and the robustness of the proposed non-contact and non-destructive monitoring approach.
      PubDate: 2016-12-02T01:12:21.63409-05:0
      DOI: 10.1002/stc.1967
  • Laboratory validation of buried piezoelectric scour sensing rods
    • Authors: Faezeh Azhari; Kenneth J. Loh
      Abstract: Scour, or the erosion of soil and sediments near bridge piers and abutments, accounts for the majority of overwater bridge failures. This study focuses on evaluating the use of a driven piezoelectric scour sensing rod, where the real-time dynamics of the voltage response of the sensing rod is used to determine scour depths using the inverse relation between natural frequency and the rod's exposed length. A poly (vinylidene fluoride) polymer strip forms the main sensing component of this prototype sensor. After confirming the viability of the sensing concept through various idealized tests, the response of the sensors was studied in scour conditions simulated in a laboratory flume. The sensors were driven into the soil surrounding a cylindrical pier. As the scour hole evolved, the exposed length of the sensors changed, causing the measured natural frequencies to also vary. Scour depth at each sensor location was determined using a simple cantilever beam eigenfrequency analysis where the soil support fixity was modeled with a rotational spring. The results were promising in that the sensors were capable of detecting scour depths and the scour hole topography with reasonable accuracy. As is the case with other rod-like scour sensors, vulnerability to debris and installation difficulties are some of the limitations that need to be addressed in future real-world implementations.
      PubDate: 2016-12-02T01:03:26.821367-05:
      DOI: 10.1002/stc.1969
  • Optimal sensor placement for damage detection of bridges subject to ship
    • Authors: Y.L. Guo; Y.Q. Ni, S.K. Chen
      Abstract: Ship collisions threaten the safety of bridges over navigable waterways in modern times. Postcollision damage and condition assessment is thus of significant importance for decision making on whether closure of bridge to traffic is necessary and for planning the consequent bridge strengthening or retrofitting. Online structural health monitoring systems provide a unique approach to monitor bridge responses during ship collisions and detect the structural damage. The damage information contained in the monitoring data, which is critical for damage detection, however, is largely dependent on the sensor layout. In this paper, an optimal sensor placement method targeting postcollision damage detection of bridges is proposed for selecting the optimal sensor set so that the measured data are most informative for damage detection. The sensor configuration is optimized by a multi-objective optimization algorithm, which simultaneously minimizes the information entropy index for each possible ship-bridge collision scenario. One advantage of the proposed method is that it can handle the uncertainty of ship collision position. It also guarantees a redundancy of sensors for the most informative regions and leaves a certain freedom to determine the critical elements for monitoring. The proposed method is applicable in practice to determine the sensor placement, prior to field testing, with the intention of identifying postcollision damage. The cable-stayed Ting Kau bridge in Hong Kong is employed to demonstrate the feasibility and effectiveness of the proposed method.
      PubDate: 2016-11-28T03:30:34.187252-05:
      DOI: 10.1002/stc.1963
  • Online structural damage identification technique using constrained dual
           extended Kalman filter
    • Authors: Subhamoy Sen; Baidurya Bhattacharya
      Abstract: Periodic health assessment of large civil engineering structures is an effective way to ensure safe performance all through their service lives. Dynamic response-based structural health assessment can only be performed under normal/ambient operating conditions. Existing Kalman filter-based parameter identification algorithms that consider parameters as the only states require the measurements to be sufficiently clean in order to achieve precise estimation. On the other hand, appending parameters in an extended state vector in order to jointly estimate states and parameters is reported to have convergence issues. In this article, a constrained version of the dual extended Kalman filtering (cDEKF) technique is employed in which two concurrent extended Kalman filters simultaneously filter the measurement response (as states) and estimate the elements of state transition matrix (as parameters). Constraints are placed on stiffness and damping parameters during the estimation of the gain matrix to ensure they remain within realistic bounds. The proposed method is compared against the existing Kalman filter-based parameter identification techniques on a three-degrees-of-freedom mass-spring-damper system adopting both unconstrained and constrained estimation approaches. cDEKF is then employed on a numerical six-story shear frame and a 3D space truss to validate its robustness and efficacy in identifying structural damage. The results suggest that cDEKF algorithm is an efficient online damage identification scheme that makes use of ambient vibration response.
      PubDate: 2016-11-23T23:00:31.056891-05:
      DOI: 10.1002/stc.1961
  • Health monitoring of rail structures using guided waves and
           three-dimensional diagnostic imaging
    • Authors: Chao Zhou; Chunliang Zhang, Zhongqing Su, Xia Yue, Jianhua Xiang, Guiyun Liu
      Abstract: With the rapid development of high-speed railway around the world, more advanced nondestructive evaluation (NDE) and structural health monitoring (SHM) techniques are required to detect structural damage in its forming stage before the damage jeopardizes the safety of the structures. In this aspect, guided-wave-based diagnostic imaging is a recent research focus, aimed at intuitionally showing the healthy status of the structure under inspection. However, the present diagnostic imaging techniques are mostly two-dimensional imaging methods, which fail to inspect complicated solid structures. In this study, a novel three-dimensional diagnostic imaging technique was developed in conjunction with an active sensor network, capable of real-time monitoring complex solid engineering structures. The ToF-based signal features were extracted from captured guided waves signals, and subsequently applied to define field values. The effectiveness of the approach was examined by identifying a crack introduced into a part of the real rail structure using both FE simulation and experiments. Results have revealed that the developed three-dimensional imaging approach is able to quantitatively visualizing structural damage in complicated solid engineering structures.
      PubDate: 2016-11-20T21:51:24.46578-05:0
      DOI: 10.1002/stc.1966
  • Optimization of an artificial neural network for fatigue damage
           identification using analysis of variance
    • Authors: Claudio Sbarufatti
      Abstract: Artificial neural networks (ANN) are extensively utilized in structural health monitoring. Nevertheless, the definition of a rigorous method for the optimization of their structure is still an unresolved issue, especially when applied to safety critical systems. In this paper, an approach typically adopted in the design of experiments and based on the analysis of variance (ANOVA) is used to statistically determine the number of hidden neurons in a three-layer ANN structure. Repeated trainings of the same network structure provide multiple observations of the performance index here, based on the root mean square error. Different levels of network structure complexity are statistically compared, based on the number of hidden nodes. ANOVA is used to determine whether there is statistical evidence that the network performance is influenced by the number of hidden nodes. This analysis allows defining the threshold number of hidden nodes above which there is no statistical evidence of a performance benefit by the increase of the ANN structure complexity. The method is applied to the optimization of a set of algorithms for the diagnosis of fatigue damage on a typical aeronautical structure, consisting of a metallic panel with a riveted skin-stringer construction. The ANNs for damage detection, localization, and quantification are trained and validated with finite element simulated strain data and are finally tested on experimental strain signals, acquired in real-time in a fatigue crack growth laboratory test program including a skin crack artificially initiated in a panel bay and two stringers that had failed naturally under fatigue load.
      PubDate: 2016-11-18T01:15:42.223166-05:
      DOI: 10.1002/stc.1964
  • Real-time hybrid simulation of the size effect of tuned liquid dampers
    • Authors: Fei Zhu; Jin-Ting Wang, Feng Jin, Li-Qiao Lu, Yao Gui, Meng-Xia Zhou
      Abstract: The use of tuned liquid dampers (TLDs) is an effective passive control technique to suppress structural vibration under wind and seismic loads. This paper investigates the size effect of TLDs on control efficiency. Given the advantages of real-time hybrid simulation, two issues affecting the control performance of TLD are addressed: (a) the geometric size and (b) the experimental model scale. A series of real-time hybrid simulations is performed, in which TLD devices with various sizes (including full-scale and small-scale) are experimentally modeled as physical substructures; the controlled structures are numerically simulated as numerical substructures. Results demonstrate that TLD performance is size dependent; a shallow liquid in TLD with lower relative liquid depth may be more efficient for both peak and root-mean-square response control. Scaled TLD models that are usually used in conventional shaking table tests generally overestimate the control performance of prototype TLD devices, indicating that full-scale TLD experiments should be pursued to ensure proper performance evaluation.
      PubDate: 2016-11-10T01:12:59.419872-05:
      DOI: 10.1002/stc.1962
  • Singular spectrum analysis combined with ARMAX model for structural damage
    • Authors: K. Lakshmi; A. Rama Mohan Rao, N. Gopalakrishnan
      Abstract: Time series analysis is being used popularly in structural health monitoring mainly because of its output-only and non-modal approach. Generally, the damage features are extracted either from the coefficients or the prediction errors of the time series models. However, when the incipient damage is small like minor cracks, the damage features of popularly used time series models, constructed using only the coefficients/prediction errors, are not sensitive. Therefore, identifying the presence or exact spatial damage location becomes difficult. In view of this, in this paper, we present an approach to enhance the sensitivity of the damage features by augmenting Singular Spectrum Analysis (SSA) to ARMAX model, enabling it to locate the smaller damage like cracks. The damage index is obtained from the Cepstral distance between any two ARMAX models. Numerical simulation studies have been carried out by considering an example of a simply supported beam girder with single and multiple cracks. Experimental studies on a simply supported RCC beam is conducted to demonstrate the effectiveness of the proposed algorithm. A benchmark problem associated with the bookshelf frame structure, proposed by Engineering Institute –Los Alamos National Laboratory, is used as another example for experimental verification of the proposed technique. SSA is found to improve the sensitivity of the damage features devised from the ARMAX models for detection of minor damage and damage localization on the structures.
      PubDate: 2016-11-08T03:10:14.278872-05:
      DOI: 10.1002/stc.1960
  • Optimal control of supersonic pre-twisted rotating functionally graded
           thin-walled blades
    • Authors: Mohammadreza Naghmehsanj; Behrooz Rahmani
      Abstract: In this paper, the optimal vibration control of a rotating, pre-twisted, single-celled box thin-walled beam made of functionally graded material is discussed. This beam is under aerothermoelastic loading and warping restraint. A first-order shear deformation theory enabling satisfaction of traction-free boundary conditions is employed to achieve governing dynamical model. These equations include the effects of the presetting angle, the secondary warping, temperature gradient through the wall thickness of the beam, and also the rotational speed. Moreover, quasi-steady aerodynamic pressure loadings are determined using first-order piston theory, and steady beam surface temperature is obtained from gas dynamics theory. The extended Galerkin method is then used to transform the blade partial differential equations into a set of ordinary differential equations. Transversely isotropic sensor-actuator piezoelectric pairs that are surface embedded along the blade are also considered for the purpose of closed-loop control. An optimal observer-based output feedback control scheme is used to stabilize the closed-loop system. Simulation studies demonstrate the effectiveness of the proposed method.
      PubDate: 2016-10-24T03:15:42.115671-05:
      DOI: 10.1002/stc.1957
  • Comparison of different statistical approaches for removing
           environmental/operational effects for massive data continuously collected
           from footbridges
    • Authors: Wei-Hua Hu; Álvaro Cunha, Elsa Caetano, Rolf.G. Rohrmann, Samir. Said, Jun Teng
      Abstract: The implementation of continuous dynamic monitoring systems in two bridges, in Portugal, is enabled to detect the occurrence of very significant environmental and operational effects on the modal properties of these bridges, based on automated processing of massive amounts of monitoring data collected by a set of accelerometers and thermal sensors over several years.In order to remove or mitigate such environmental/operational effects with the purpose of damage detection, two different statistical methods have been adopted. One of them is the multiple linear regression by performing nonlinear correlation analysis between measured modal properties and environmental/operational variables. Another one is principal component regression based on the identification of the linear subspace within the modal properties without using measured values of environmental and operational variables.This paper presents a comparison of the performance of these two alternative approaches on the basis of continuous monitoring data acquired from two instrumented bridges and simulated damage scenarios. It is observed that different methods show similar capacity in removing environmental effects, and the multiple linear regression method is slightly more sensitive to structural damage.
      PubDate: 2016-10-21T00:15:41.861053-05:
      DOI: 10.1002/stc.1955
  • Real-time structural monitoring of Building 350 at Del Valle University
    • Authors: Lisandro Arturo Jiménez-Roa; Johannio Marulanda-Casas, Alejandro Cruz-Escobar
      Abstract: Design errors, misuse, and natural or accidental events can cause small and cumulative damages or large and sudden damages that can deteriorate structural systems or cause their collapse. Structural monitoring consists in the permanent real-time tracking of information about the condition and performance of a structure. This paper presents the development, validation, and implementation of the structural monitoring system for building 350 at Del Valle University, located in Santiago de Cali, Colombia. The system uses the SSI and natural excitation technique with the eigensystem realization algorithm methodologies for modal identification and a specialized event-recognition algorithm based on the standard deviation analysis of vibrations. The dynamic behavior monitoring of the building has been conducted in real-time since January 2012, and six seismic events have been successfully recognized. The computational tool was validated using a finite element model with which the effect of variation in mass was evaluated.
      PubDate: 2016-10-18T02:11:02.437979-05:
      DOI: 10.1002/stc.1959
  • AOSID: An analytical solution to the output-only system identification
           problem to estimate physical parameters and unknown input simultaneously
    • Authors: Mostafa Ghobadi; Manoranjan Majji, Ehsan T. Esfahani
      Abstract: This paper studies an analytical solution for the identification problem of linear systems, where inputs are unknown and only output data are accessible. A linear output-only model (LOM) is developed and employed along with physical constraints in state space to simultaneously identify two subspace models, one of which represents the physical system and the other describes the behavior of the unknown input by reconstructing its history. Inputs are assumed to be an arbitrary combination of harmonic signals with constant or time varying exponential amplitudes with non-overlapping frequency ranges with natural frequencies of the physical system. The identification is first performed by a zero-input eigensystem realization algorithm in time domain that estimates the LOM in a generic form; we call it unfixed form, which contains both physical system model and input model in a coupled configuration. By transforming the LOM into a canonical form and utilizing the physical constraints, an analytical approach is developed to decouple the physical model from the input dynamics. The proposed method of analytical output-only system identification (AOSID) is evaluated through simulation of a set of scenarios to demonstrate its capabilities. To this end, we study the effects of type of sensor models, level of measurement noise, and complexity level of the problem on the estimation error. The accuracy of the identified LOM demonstrates that the AOSID method is capable of simultaneous identification of physical model and unknown inputs in the presence of measurement noise with a considerable accuracy at a modest computational expense. Furthermore, AOSID method demonstrates a considerable robustness against nonlinear inputs and white noise disturbances which challenge the assumptions initially made in the theoretical development of the model.
      PubDate: 2016-10-18T01:40:50.088738-05:
      DOI: 10.1002/stc.1951
  • Multi-scale model updating of a transmission tower structure using Kriging
    • Authors: F.Y. Wang; Y.L. Xu, S. Zhan
      Abstract: A multi-scale model is often constructed using different finite elements and consists of a global scale model for the structural system and a few local scale models for critical structural components so that the multi-scale simulation can concurrently exhibit both global performance and local behavior of the structure. To ensure the multi-scale model can best represent the real structure, multi-scale model updating technique shall be developed accordingly. This paper thus presents a multi-scale model updating method for a transmission tower structure using the Kriging meta-model that actually is a surrogate for the multi-scale model. Firstly, the multi-scale model of a transmission tower is established by using beam elements to simulate global structure and solid elements to simulate local joints with bolt connections. Secondly, the multi-objective optimization problem that involves multiple objective functions is established to update key parameters of the multi-scale model so that the errors between the measured and predicted structural dynamic characteristics and multi-scale responses can be minimized. To improve the computational efficiency and accuracy of optimization, the Kriging meta-method is used to find the updated key parameters of the tower after a comparison with other meta-methods is made. Finally, the proposed method is applied to a physical transmission tower model, which has been tested in a laboratory, to demonstrate the feasibility and accuracy of the proposed model-updating method. The updated results show that the proposed updating method can improve the accuracy of the multi-scale model of the tower in both global and local structural responses.
      PubDate: 2016-10-09T23:25:38.564386-05:
      DOI: 10.1002/stc.1952
  • Elastic-wave-based synthetic aperture focusing technique imaging system
           for detecting voids inside concrete structures
    • Authors: Jian-Hua Tong; Chin-Lung Chiu
      Abstract: In this paper, an elastic-wave-based imaging system was proposed for adopting synthetic aperture focusing technique to reveal the voids inside concrete structures. Design concept of each component in this system, including an impact source generator, a transducer, a signal capturing unit, and operation software, is clearly described. Relation between contact time and impact source selection was discussed and verified by an experiment of steel ball free-falling on a concrete specimen. A displacement transducer and corresponding signal capturing unit were carefully designed to get higher quality signals for Synthetic aperture focusing technique processing. A calibration experiment was conducted to ensure the capability of proposed point-source/point-receiver scheme for proper elastic wave generation and receiving. Besides, a concrete slab with an artificial defect was cast for experiment for usability evaluation. A 2D plane-stress finite difference simulation on corresponding numerical module was carried out for comparison. The experimental result shows good agreement with the numerical result not only on the B-scan diagram but also on the resultant image. It exhibits the potential of the proposed imaging system in inspecting defects of in-situ concrete structures by image.
      PubDate: 2016-10-06T02:40:45.55464-05:0
      DOI: 10.1002/stc.1956
  • Optimal placement of triaxial sensors for modal identification using
           hierarchic wolf algorithm
    • Authors: Ting-Hua Yi; Guang-Dong Zhou, Hong-Nan Li, Chuan-Wei Wang
      Abstract: Optimal triaxial sensor placement plays a crucial role in tridimensional modal identification; however, few studies have been conducted on this topic. In this paper, a holistic approach, including a tridimensional optimal criterion and solution method, is proposed for finding the optimal locations to deploy triaxial sensors. The tridimensional optimal criterion is established by combining the tridimensional modal assurance criterion and the redundancy function. The tridimensional modal assurance criterion is deduced from the one-dimensional modal assurance criterion by using the widely accepted Fisher information matrix, adopted to ensure the linear independence of identified tridimensional mode shapes. The redundancy function, which is defined by the similarity index among nodes, is developed to measure the information redundancy and to maintain effective visualization of the identified tridimensional mode shapes. To efficiently find the optimal triaxial sensor configuration with the proposed tridimensional optimal criterion, the hierarchic wolf algorithm (HWA) is developed by imitating the swarm intelligence embedded in the wolf pack. Five strategies, which are termed as coding and spreading wolves, searching behaviors, attacking behaviors, hierarchic population, and distributing food process, are employed to enhance the global searching ability of the HWA. The proposed approach is verified by a benchmark bridge model. The results indicate that the established tridimensional optimal criterion has the capability of ensuring optimal triaxial sensor configurations that make the identified tridimensional mode shapes have features of excellent linear independence and good visualization, and the HWA has strong ability and high efficiency in determining the global optimal triaxial sensor configuration.
      PubDate: 2016-10-06T02:36:35.040736-05:
      DOI: 10.1002/stc.1958
  • Structural damage identification via response reconstruction under unknown
    • Authors: C.D. Zhang; Y.L. Xu
      Abstract: The restriction of limited sensors for measurement acquisition and the presence of unknown excitation usually bring about more challenges in the vibration-based damage identification of large-scale civil structures. To explore the potential benefits of utilizing multitype dynamic responses and alleviate the necessity of deploying dense sensors and measuring excitations for structural damage identification, this study investigates a novelty damage identification method via response reconstruction when the external excitations acting on the structure are unknown. Response and excitation are reconstructed simultaneously through the implementation of Kalman filter under unknown input. Radial-basis-function network is employed to predict the mode shapes using modal properties extracted by experimental modal analysis after damage occurrence. The reconstructed response and excitation are finally integrated into to sensitivity based finite element model updating for localizing and quantifying the damage. A numerical simulation study is conducted on an overhanging steel beam under unknown excitation. The feasibility and effectiveness of the proposed method are further ascertained by laboratory tests of the beam.
      PubDate: 2016-10-04T23:15:36.473299-05:
      DOI: 10.1002/stc.1953
  • A pounding spacer damper and its application on transmission line
           subjected to fluctuating wind load
    • Authors: Xing Fu; Hong-Nan Li, Jia-Xiang Li, Peng Zhang
      Abstract: In this paper, a new pounding spacer damper (PSD) is proposed, and the control effect on the transmission line under the fluctuating wind load is validated. At first, the schematic of the proposed PSD is provided, and the mechanical models of elastic, damping, and pounding forces are then obtained. After that, the dynamic equations of transmission line equipped with the PSD are derived. On the basis, the finite element model of transmission line–PSD system with the ANSYS software is established, and the pounding force of the PSD is calculated and applied through the ANSYS Parametric Design Language. Then the response induced by the fluctuating wind load is simulated, and meanwhile, the control effects of the PSD and spacer damper without pounding force are compared, of which the results illustrate that the minimal reduction ratio for the conductor span can reach to 11.10%, indicating that the proposed PSD can effectively control the vibration of the conductor span under the fluctuating wind load. In addition, the parametric analysis of gap, frequency, and damping ratios is conducted and demonstrates that the gap and frequency ratio have great impact on the control effect while the influence of damping ratio is not very significant.
      PubDate: 2016-09-29T23:40:53.145074-05:
      DOI: 10.1002/stc.1950
  • Integrated distributed fiber optic sensing technology-based structural
           monitoring of the pound lock
    • Authors: Zhan-Pu Song; Dan Zhang, Bin Shi, Shen-En Chen, Meng-Fen Shen
      Abstract: In this paper, an integrated distributed fiber optic sensing technology, which includes Raman optical time-domain reflectometry (ROTDR), Brillouin optical time-domain analysis (BOTDA), and fiber Bragg grating (FBG) sensing technologies, is adopted to monitor the temperature and the stress/strain variations of a reinforced concrete pound lock structure during the construction process. The Raman optical time-domain reflectometry was used to monitor the internal temperature variation throughout the concrete curing process when concrete hydration heat was released in the base plate of the lock head. The FBG temperature sensors were adopted to measure the surface temperature of the concrete, and the temperature data were used to compensate the results that are measured by BOTDA sensing technology to get the real concrete strain of the base plate. To better understand the stress/strain state of the base plate before and after filling water in the lock, the BOTDA sensing cable and FBG temperature sensors monitoring continued throughout the whole construction process. The observation provided a positive indication that the proposed integrated distributed fiber optic sensing technology may have great potential in performance monitoring of hydraulic structures.
      PubDate: 2016-09-29T23:35:48.534607-05:
      DOI: 10.1002/stc.1954
  • Vibration-based bridge scour detection: A review
    • Authors: Ting Bao; Zhen Liu
      Abstract: Scour around bridge foundations is regarded as one of the predominant causes of bridge failures. Traditional methods primarily employ underwater instruments to detect bridge scour depths, which thus have difficulties in instrument installations and operations. The concept of scour detection derived from vibration-based damage detection has been explored in recent years to address such difficulties by investigating the natural frequency spectrum of a bridge or a bridge component. This paper presents a comprehensive review of existing studies on scour detection using the natural frequency spectrum of a bridge or a bridge component. Underlying mechanisms, laboratory and field tests, numerical studies, and data processing schemes are reviewed to summarize the state of the art, which are absent but urgently needed. Updates on recently developed scour monitoring sensors are also provided to complement the introduction. Based on the review, in-depth discussions in existing studies are made regarding a few controversial and unsolved issues to shed light on future research, highlighting issues such as the soil–structure interaction, locations of the sensor installation, and the influence of shapes of scour holes.
      PubDate: 2016-09-29T23:10:38.716567-05:
      DOI: 10.1002/stc.1937
  • Monitoring and time‐dependent analysis of vertical deformations of the
           tallest building in China
    • Authors: Qiusheng Li; Yinghou He, Hui Wang, Kang Zhou, Bowen Yan
      Abstract: Ping‐An Finance Center (PAFC) in Shenzhen, with a structural height of 597 m and a total height of 660 m, is currently the second tallest building in the world and the tallest in China. In this paper, based on the outputs of a structural health monitoring system installed in PAFC, a combined study of both on‐site measurements and numerical analysis of the vertical deformations (axial shortenings) of the super tall building during its various construction stages is carried out. It is worth noting that a novel strategy to adjust the elevation of each floor of PAFC was implemented in the design and construction of the super tall building, in which the floor‐to‐floor height is modestly increased to compensate for the axial shortenings of gravity load bearing elements during the construction process and in‐service stage. This design strategy is referred to as elevation reservation, and its effectiveness is verified through the field measurements of the vertical deformations in this study. A good agreement is found between the numerical results and the field measurements, which validates the finite element models of PAFC at different construction stages. The finite element models are further used to investigate the time‐dependent effects due to the construction sequence and the shrinkage and creep of concrete on the vertical deformations. The numerical results show that the vertical deformations would be seriously underestimated without consideration of the time‐dependent effects. The outcomes of this study would be of interest and practical use for engineers and researchers involved in the structural design, construction, and structural health monitoring of super tall buildings.
      PubDate: 2016-09-16T03:12:06.119661-05:
      DOI: 10.1002/stc.1936
  • Structural health assessment of historical timber structures combining
    • Authors: Mariapaola Riggio; Nicola Macchioni, Cristiano Riminesi
      Abstract: Examining the timber structure supporting the roof of Giotto's bell tower in Florence, this paper discusses the combination of non‐destructive (NDT), wave‐based methods for the characterization of timber structural elements. In particular, it analyses the on‐site applicability of selected wave‐based techniques for the identification of decay, damage, defects, and moist areas in structural timber. The applied NDT techniques are IR termography, microwave reflectometry, time‐of‐flight tomography, and mapping by means of elastic waves. Experimental results are compared with data obtained by means of consolidated NDT techniques, such as the electric resistance method for moisture content estimation and the drill‐resistance test for decay characterization. These can be considered non‐destructive, although they are invasive. The wave‐based NDT methods are found to be a value‐added complement to routine methodologies for a holistic diagnosis of timber members. Normal practice based on visual inspection, decay detection through point measurements of drill resistance, and moisture content estimation through local readings of electric resistance, can be substantially improved through full‐field, multi‐sensor, multi‐resolution imaging. Nevertheless, while the diverse NDT methods illustrated here can be useful for screening large areas in a completely non‐invasive way, local measurements (i.e., the drill resistance and the electric resistance measurements) are still necessary.
      PubDate: 2016-09-16T03:01:27.493721-05:
      DOI: 10.1002/stc.1935
  • Event‐driven strain cycle monitoring of railway bridges using a wireless
           sensor network with sentinel nodes
    • Authors: Nemanja Popovic; Glauco Feltrin, Khash‐Erdene Jalsan, Michal Wojtera
      Abstract: Due to the increasing traffic volume on the European railway network, the remaining fatigue life of existing steel bridges is a major concern. Several investigations demonstrated that supplementing the assessment with monitoring data enables to achieve more reliable remaining fatigue life estimations. In this paper, an event‐driven monitoring system based on a wireless sensor network that consists of two functionally different components was designed and tested. Sentinel nodes, which were mounted on the track, were used for detecting approaching trains and alerting with alarm messages the monitoring nodes. These nodes, which were mounted on the bridge, started strain sensing and data recording after receiving the alarm message and went back to a power saving mode upon completion. An embedded data processing algorithm transformed the recorded raw data into a much smaller data set representing strain cycles. A test deployment on a railway bridge demonstrated that train detection and alarming was fast and reliable. The combination of event‐driven monitoring and embedded data processing allowed to extend the battery lifetime of monitoring nodes to several months.
      PubDate: 2016-09-16T02:57:47.760465-05:
      DOI: 10.1002/stc.1934
  • Analysis of measurement and simulation errors in structural system
           identification by observability techniques
    • Authors: Jun Lei; José Antonio Lozano‐Galant, María Nogal, Dong Xu, José Turmo
      Abstract: During the process of structural system identification, errors are unavoidable. This paper analyzes the effects of measurement and simulation errors in structural system identification based on observability techniques. To illustrate the symbolic approach of this method a simply supported beam is analyzed step‐by‐step. This analysis provides, for the very first time in the literature, the parametric equations of the estimated parameters. The effects of several factors, such as errors in a particular measurement or in the whole measurement set, load location, measurement location or sign of the errors, on the accuracy of the identification results are also investigated. It is found that error in a particular measurement increases the errors of individual estimations, and this effect can be significantly mitigated by introducing random errors in the whole measurement set. The propagation of simulation errors when using observability techniques is illustrated by two structures with different measurement sets and loading cases. A fluctuation of the observed parameters around the real values is proved to be a characteristic of this method. Also, it is suggested that a sufficient combination of different load cases should be utilized to avoid the inaccurate estimation at the location of low curvature zones. Copyright © 2016 John Wiley & Sons, Ltd.
      PubDate: 2016-09-05T22:20:37.845282-05:
      DOI: 10.1002/stc.1923
  • Structural model updating using incomplete transfer function and modal
    • Authors: Maria Farshadi; Akbar Esfandiari, Maryam Vahedi
      Abstract: Structural damage detection by non‐destructive techniques has been investigated widely by researchers in recent years, and several response‐based Structural Health monitoring techniques have been developed. In this paper, a vibration‐based damage detection algorithm through model updating utilizing incomplete frequency response function and modal data is presented. First, a modified sensitivity equation is presented to relate the changes of mode shapes to the changes of unknown structural parameters. Then, the developed equations are used to correlate changes of frequency response functions to the changes of structural parameters. Parameter estimation is conducted through least square solution of sensitivity equations. In order to prove the capability of the proposed method for structural damage detection purpose, a numerical example using error contaminated data is presented. Results exhibit robustness of method against measurement and mass modeling errors.
      PubDate: 2016-09-01T02:55:32.093935-05:
      DOI: 10.1002/stc.1932
  • Impact event identification in thin plates through real strain
    • Authors: Mijia Yang; Saeed Ahmari, Majura Selekwa
      Abstract: Impact event identification is a primary concern in many structural health monitoring applications. Model‐based inverse analysis is a common approach for system identification as long as the physical model can accurately capture the behavior of structure. A layered analysis including estimation of impact location in the first layer and refinement and reconstruction of impact load time history through inverse analysis in the second layer was proposed and verified well with the numerical results previously. Due to unavoidable noises, implementation of the theory with a modified inverse scheme on a simply supported plate structure is conducted in this study. The real signal data is first prefiltered using a low pass filter. Different alternatives are then proposed for the inverse scheme, and a new parameter, normalized signal energy, is adopted for layer 1 due to its convenience and accuracy compared with the traditional one, that is, the time of flight method. Signal power and filtered signal data are used for layer 2 of the inverse procedure. The results indicate that the modified inverse scheme is capable of detecting impact location and reconstructing impact load time history with a satisfactory precision.
      PubDate: 2016-08-30T03:41:19.927668-05:
      DOI: 10.1002/stc.1933
  • A method of pipeline corrosion detection based on hoop‐strain
           monitoring technology
    • Authors: Liang Ren; Tao Jiang, Dong‐sheng Li, Peng Zhang, Hong‐nan Li, Gang‐bing Song
      Abstract: A pipeline is often an important structure with very long service life. It is of great significance to monitor the corrosion level of a pipeline to ensure its safety operation. This paper aims to develop a new nondestructive method to detect the pipeline corrosion. It is assumed that the pipeline corrosion will result in a variation of the circumferential strain. The nondestructive detection method is based on a novel fiber Bragg grating (FBG) hoop‐strain sensor, which can accurately measure the circumferential strain of a pipeline. In this paper, the theoretical study and numerical analysis based on finite element method are detailed in our initial work. Then, tests are conducted on three steel pipes to verify the effectiveness and accuracy of this method. The results demonstrate that the FBG hoop‐strain sensor has good performance in the circumferential strain measurement and is sensitive to the variation of the circumferential strain caused by different corrosion level. The FBG hoop‐strain sensor is considered to be a promising device in pipeline corrosion monitoring. Copyright © 2016 John Wiley & Sons, Ltd.
      PubDate: 2016-08-30T03:30:33.837977-05:
      DOI: 10.1002/stc.1931
  • Optimal sensor placement methodology for uncertainty reduction in the
           assessment of structural condition
    • Authors: Wei Yang; Limin Sun, Gang Yu
      Abstract: This paper introduces a novel approach for selecting sensor positions for uncertainty reduction in the assessment of structural condition, where the main difficulty is how to quantify the uncertainty. In order to tackle this problem, a condition index, which is a linear combination of the finite‐element model parameters, is defined. By taking the multiplying coefficient equal to the vulnerability index corresponding to each model parameter, the linearized condition index is able to reflect the influence of local damage on the global damage condition. The uncertainty in the estimate of this linearized condition index can be readily quantified from the uncertainty in the updated model parameters. Bayesian finite‐element model updating is applied for uncertainty quantification in the model parameters. The procedure of the proposed method is illustrated by designing the optimal sensor configuration for a truss structure model. The simulated damage and condition assessment of the truss structure shows that the proposed method is effective in reducing the uncertainty in the condition assessment. Furthermore, it is demonstrated that the proposed method is useful for a more important reason: it can reduce the uncertainty in the damage assessment of vulnerable substructure. Copyright © 2016 John Wiley & Sons, Ltd.
      PubDate: 2016-08-30T03:28:01.759033-05:
      DOI: 10.1002/stc.1927
  • A state estimation method for wireless structural control systems
    • Authors: Z. Sun; G. Ou, S. J. Dyke, C. Lu
      Abstract: Structural control systems based on wireless sensors offer a convenient, flexible and cost‐effective alternative to their wired counterparts. Although wireless control systems (WCSs) have several attractive features, some challenges do remain related to the persistent presence of network‐induced time delays, and potential for sensor data losses and in extreme cases, sensor failures. The consequences of these challenges should be investigated, and solutions should be developed to achieve highly effective and robust control systems. The availability of such solutions will also encourage the adoption of WCSs in real structures. Here, an estimator switching method intended to minimize the influence of potential faults is developed and validated for WCSs. In this method, the switching gains are pre‐calculated to enable real‐time implementation. The proposed method is verified through numerical simulations of a seismically excited, three‐story structure considering various sensor data loss and sensor failure scenarios. The robustness of this estimation method in the presence of measurement noise and modeling uncertainty is also investigated. In addition, the estimation switching method is incorporated into a closed‐loop WCS in experiment. The results demonstrate the effectiveness of the proposed state estimation method in mitigating the impact of sensor data loss and sensor failure. Copyright © 2016 John Wiley & Sons, Ltd.
      PubDate: 2016-08-15T23:00:43.49285-05:0
      DOI: 10.1002/stc.1929
  • Decentralised one‐class kernel classification‐based damage
           detection and localisation
    • Authors: James Long; Oral Büyüköztürk
      Abstract: In this paper, a data‐based damage detection algorithm that uses a novel one‐class kernel classifier for detection and localisation of damage is presented. The demands of wireless sensing are carefully considered in the development of this fully decentralised and automated methodology. The one‐class kernel classifier proposed in this paper is trained through a faster and simpler to implement iterative procedure than other kernel classification methods, while retaining the same advantages over parametric methods, making it especially attractive for embedded damage detection. Acceleration time series at each sensor location are processed into autoregressive and continuous wavelet transform‐based damage‐sensitive features. Baseline values of these features are used to train the classifier, which can then classify features from new tests as damaged or undamaged, as well as outputting a localisation index, which can be used to identify the location of damage in the structure. This methodology is evaluated using acceleration data taken from a steel‐frame laboratory structure under various damage scenarios. A number of parametric studies are also conducted to investigate the effect of sampling frequency and baseline data sample size. Copyright © 2016 John Wiley & Sons, Ltd.
      PubDate: 2016-08-15T22:45:36.566149-05:
      DOI: 10.1002/stc.1930
  • Genetic-based EM algorithm to improve the robustness of Gaussian mixture
           models for damage detection in bridges
    • Authors: Adam Santos; Eloi Figueiredo, Moisés Silva, Reginaldo Santos, Claudomiro Sales, João C. W. A. Costa
      Abstract: During the service life of bridges, the bridge management systems (BMSs) seek to handle all performed assessment activities by controlling regular inspections, evaluations, and maintenance of these structures. However, the BMSs still rely heavily on qualitative and visual bridge inspections, which compromise the structural evaluation and, consequently, the maintenance decisions as well as the avoidance of bridge collapses. The structural health monitoring appears as a natural field to aid the bridge management, providing more reliable and quantitative information. Herein, the machine learning algorithms have been used to unveil structural anomalies from monitoring data. In particular, the Gaussian mixture models (GMMs), supported by the expectation-maximization (EM) on the parameter estimation, have been proposed to model the main clusters that correspond to the normal and stable state conditions of a bridge, even when it is affected by unknown sources of operational and environmental variations. Unfortunately, the performance of the EM algorithm is strongly dependent on the choice of the initial parameters. This paper proposes a hybrid approach based on a standard genetic algorithm (GA) to improve the stability of the EM algorithm on the searching of the optimal number of clusters and their parameters, strengthening the damage classification performance. The superiority of the GA-EM-GMM approach, over the classic EM-GMM one, is tested on a damage detection strategy implemented through the Mahalanobis-squared distance, which permits one to track the outlier formation in relation to the chosen main group of states, using real-world data sets from the Z-24 Bridge, in Switzerland. Copyright © 2016 John Wiley & Sons, Ltd.
      PubDate: 2016-05-29T23:05:39.214157-05:
      DOI: 10.1002/stc.1886
  • Damage detection for high-speed train axle based on the propagation
           characteristics of guided waves
    • Authors: Jianxi Qiu; Fucai Li, Jifeng Wang
      Abstract: The currently defect identification techniques based on guided wave is not feasible for high-speed train axle because the structure complicates wave propagation. A novel damage detection method especially for train axle is proposed in this paper. Piezoelectric patches are used as actuator to excite waves in the axle. Guided wave generated by single actuator and circumferential, limited number of actuator configurations is discussed to optimize the transducer network. The axle is simplified to a variable cross-sectional and thick-walled hollow cylindrical structure. Eight piezoelectric actuators that evenly distributed at the axle end surface are used to excite simplex longitudinal waves. Signals of circumferential and axial displacement of the monitoring points are researched before and after introducing the flaw on the surface, and their sensitivity to the depth and length of defect are also discussed. From the view of practical feasibility, the difference of signals from two axisymmetrical measure points of same axial position is proposed for the defect identification. Experimental verification is conducted, and the results demonstrate that the proposed approach is reliable in the axle inspection. Copyright © 2016 John Wiley & Sons, Ltd.
      PubDate: 2016-05-29T22:40:41.038835-05:
      DOI: 10.1002/stc.1891
  • Identification of time-varying cable tension forces based on adaptive
           sparse time-frequency analysis of cable vibrations
    • Authors: Yuequan Bao; Zuoqiang Shi, James L. Beck, Hui Li, Thomas Y. Hou
      Abstract: For cable bridges, the cable tension force plays a crucial role in their construction, assessment and long-term structural health monitoring. Cable tension forces vary in real time with the change of the moving vehicle loads and environmental effects, and this continual variation in tension force may cause fatigue damage of a cable. Traditional vibration-based cable tension force estimation methods can only obtain the time-averaged cable tension force and not the instantaneous force. This paper proposes a new approach to identify the time-varying cable tension forces of bridges based on an adaptive sparse time-frequency analysis method. This is a recently developed method to estimate the instantaneous frequency by looking for the sparsest time-frequency representation of the signal within the largest possible time-frequency dictionary (i.e. set of expansion functions). In the proposed approach, first, the time-varying modal frequencies are identified from acceleration measurements on the cable, then, the time-varying cable tension is obtained from the relation between this force and the identified frequencies. By considering the integer ratios of the different modal frequencies to the fundamental frequency of the cable, the proposed algorithm is further improved to increase its robustness to measurement noise. A cable experiment is implemented to illustrate the validity of the proposed method. For comparison, the Hilbert–Huang transform is also employed to identify the time-varying frequencies, which are then used to calculate the time-varying cable-tension force. The results show that the adaptive sparse time-frequency analysis method produces more accurate estimates of the time-varying cable tension forces than the Hilbert–Huang transform method. Copyright © 2016 John Wiley & Sons, Ltd.
      PubDate: 2016-05-29T22:35:37.479509-05:
      DOI: 10.1002/stc.1889
  • Dynamic investigation of a large historical cathedral
    • Authors: Ahmed Elyamani; Oriol Caselles, Pere Roca, Jaime Clapes
      Abstract: The presented research aimed at studying the dynamic behavior of Mallorca cathedral (Mallorca Island, Spain) under ambient sources of vibration and seismic events. The cathedral is one of the greatest built masonry structures worldwide. It is characterized for its audacious dimensions and slender structural members. Because of it, the study of its dynamic behavior is a clear concern. The cathedral dynamic properties were firstly identified using ambient vibration testing. Afterwards, a dynamic monitoring system was implemented to continuously measure, record, and wirelessly transfer the acceleration records without having to set up an activating threshold. This monitoring type was implemented because of the low seismic intensity of Mallorca Island with a basic ground acceleration of only 0.04 g according to the Spanish seismic standard. The continuous monitoring allowed for capturing some seismic events and some drops in the natural frequencies were noticed because of a breathing crack effect. Using both ambient vibration testing and continuous monitoring system, global modes could be more accurately identified than more local ones. The identification of the global modes was more attainable than in the case of more local ones. The temperature was a more influential environmental parameter than humidity and wind for all of the identified modes except for one more directly depended on wind. Copyright © 2016 John Wiley & Sons, Ltd.
      PubDate: 2016-05-29T22:20:55.347784-05:
      DOI: 10.1002/stc.1885
  • A trajectory method for vibration based damage identification of
           underdetermined problems
    • Authors: Stavros Chatzieleftheriou; Nikos D. Lagaros
      Abstract: The problem of structural damage identification based on vibration measurements (eigenfrequencies and incomplete mode shapes) is generally formulated as an inverse problem aiming to identify changes encountered on the global stiffness matrix. In most cases, the measured quantities are less than the damage parameters to be identified; thus, an infinite number of possible damage configurations are expected to satisfy the measurements. Therefore, damage identification problems are often proven to be ill-conditioned. The problem becomes more complex when measurements' noise and model uncertainties are considered. Therefore, depending on the structural system, damage scenario and available vibration measurements, additional eigenmode data may need to be considered in order to increase the robustness of the damage identification procedure. In this work, a new two-loop trajectory method is presented, that relies on an iterative nonlinear sensitivity analysis procedure. The main advantage of the proposed method is its ability to identify damage scenarios that match the measured data with high accuracy as well as to explore effectively the solution space. This feature can be exploited in order to assess the adequacy of the measurements in noisy and/or uncertain environment. Copyright © 2016 John Wiley & Sons, Ltd.
      PubDate: 2016-05-26T23:35:48.701966-05:
      DOI: 10.1002/stc.1883
  • Optimal configurations for a linear vibration suppression device in a
           multi-storey building
    • Authors: Sara Ying Zhang; Jason Zheng Jiang, Simon Neild
      Abstract: This paper investigates the use of a two-terminal vibration suppression device in a building. The use of inerter-spring-damper configurations for a multi-storey building structure is considered. The inerter has been used in Formula 1 racing cars and applications to various systems such as road vehicles have been identified. Several devices that incorporate inerter(s), as well as spring(s) and damper(s), have also been identified for vibration suppression of building structures. These include the tuned inerter damper and the tuned viscous mass damper. In this paper, a three-storey building model with a two-terminal absorber located at the bottom subjected to base excitation is studied. The brace stiffness is also taken into consideration. Four optimum absorber layouts, in terms of how spring, damper and inerter components should be arranged, for minimising the maximum relative displacements of the building are obtained with respect to the inerter's size and the brace stiffness. The corresponding parameter values for the optimum absorber layouts are also presented. Furthermore, a real-life earthquake data is used to show the advantage of proposed absorber configurations. Copyright © 2016 John Wiley & Sons, Ltd.
      PubDate: 2016-05-26T23:15:35.854082-05:
      DOI: 10.1002/stc.1887
  • Acoustic emission-based analysis of bond behavior of corroded
           reinforcement in existing concrete structures
    • Authors: Ahmed A. Abouhussien; Assem A. A. Hassan
      Abstract: This experimental study exploits acoustic emission (AE) monitoring to assess the bond behavior of corroded bars in reinforced concrete prism samples under pull-out tests. The analysis of AE parameters obtained in this study including amplitude, duration, cumulative number of hits, and signal strength was performed to identify different stages of bond degradation. The results of bond behavior and free end slip were analyzed and compared with the corresponding AE data. An intensity analysis of AE signal strength was also completed to quantify the bond damage using two additional AE parameters: historic index (H (t)) and severity (Sr). The outcomes of AE analysis enabled the detection of early stages of bond deterioration (micro-cracking) as well as identification of the macro-cracking stage prior to the occurrence of bond splitting failure. The results also showed a good correlation between AE cumulative number of hits and AE signal strength parameters with the steel-to-concrete bond degradation because of corrosion. Finally, the results of H (t) and Sr were employed to generate intensity classification charts to characterize the stages of micro- and macro-cracking and range of slip of corroded reinforcement. Copyright © 2016 John Wiley & Sons, Ltd.
      PubDate: 2016-05-26T23:10:34.517081-05:
      DOI: 10.1002/stc.1893
  • Online Bayesian model assessment using nonlinear filters
    • Authors: Thaleia Kontoroupi; Andrew W. Smyth
      Abstract: Model assessment is an integral part of many engineering applications, because any analytical or numerical mathematical model used for predictive purposes is only an approximation of the real system. The Bayesian approach to model assessment requires the calculation of the evidence of each candidate model considered given the available measured data, which is a nontrivial task, and it is usually attempted offline, e.g., by using a stochastic simulation scheme or some deterministic approximation. Very few authors, in general, and hardly any in the field of structural dynamics, have investigated online application of model assessment. The current work explores how Bayesian model assessment and an online identification scheme for joint state and parameter estimation, in particular the unscented Kalman filter, whose computational efficiency has been widely recognized, could be integrated into a single method. This hierarchical Bayesian modeling approach involves two inference levels, namely, model assessment and parameter estimation. There is the possibility of adding another level within the hierarchy for noise estimation. An illustrative example involving several hysteretic candidate models is presented to demonstrate the implementation of the proposed procedure in structural health monitoring applications. Copyright © 2016 John Wiley & Sons, Ltd.
      PubDate: 2016-05-19T04:35:30.849928-05:
      DOI: 10.1002/stc.1880
  • Correlation between global damage and local damage of RC frame structures
           under strong earthquakes
    • Authors: Zheng He; Yichao Xu
      Abstract: In order to reasonably incorporate local and global monitoring response data into dynamic update in the weighted combination models for a closer correlation between global damage and local damage, a logical time-variant correlation between global damage and local damage is established for reinforced concrete structures under strong earthquakes. Two sets of dynamic weight coefficients used to characterize the relative damage contribution of floors through modal information and energy information are suggested in the correlation. The modal information-based weight coefficients that are defined as the normalized accumulative times of reserved floors could be capable of retaining the necessary information of relatively weak floors or sensitive regions with localized damage significance, while the energy information-based weight coefficients based on the normalized curvature difference of ‘jerk energy’ are helpful to quantify the relative degree of floor damages accumulated by hysteretic dissipated energy. The combination factors corresponding to the proposed dynamic weight coefficients, together with static weight coefficients, are calibrated by a macroscopic global seismic damage model. The results from the example study indicate that these factors show different changing rules with increasing peak ground acceleration level. Modal information-based weight coefficients have been found to have a desirable agreement with the inter-story pure translation ratios. Copyright © 2016 John Wiley & Sons, Ltd.
      PubDate: 2016-05-19T04:31:30.934734-05:
      DOI: 10.1002/stc.1877
  • Particle filtering and marginalization for parameter identification in
           structural systems
    • Authors: Audrey Olivier; Andrew W. Smyth
      Abstract: In structural health monitoring, one wishes to use available measurements from a structure to assess structural condition, localize damage if present, and quantify remaining life. Nonlinear system identification methods are considered that use a parametric, nonlinear, physics-based model of the system, cast in the state-space framework. Various nonlinear filters and parameter learning algorithms can then be used to recover the parameters and quantify uncertainty. This paper focuses on the particle filter (PF), which shows the advantage of not assuming Gaussianity of the posterior densities. However, the PF is known to behave poorly in high dimensional spaces, especially when static parameters are added to the state vector. To improve the efficiency of the PF, the concept of Rao–Blackwellisation is applied, that is, we use conditional linearities present in the equations to marginalize out some of the states/parameters and infer their conditional posterior pdf using the Kalman filtering equations. This method has been studied extensively in the particle filtering literature, and we start our discussion by improving upon and applying two well-known algorithms on a benchmark structural system. Then, noticing that in structural systems, high nonlinearities are often localized while the remaining equations are bilinear in the states and parameters, a novel algorithm is proposed, which combines this marginalization approach with a second-order extended Kalman filter. This new approach enables us to marginalize out all the states/parameters, which do not contribute to any high nonlinearity in the equations and, thus, improve identification of the unknown parameters. Copyright © 2016 John Wiley & Sons, Ltd.
      PubDate: 2016-05-19T04:25:52.892868-05:
      DOI: 10.1002/stc.1874
  • Improving performance of a super tall building using a new eddy-current
           tuned mass damper
    • Authors: Xilin Lu; Qi Zhang, Dagen Weng, Zhiguang Zhou, Shanshan Wang, Stephen A. Mahin, Sunwei Ding, Feng Qian
      Abstract: Two kinds of methods have been primarily used to improve the vibration performance of high-rise buildings. One approach is to enhance the structural lateral stiffness, which may increase the component size and inefficiently use material. The other approach is to employ vibration control devices, such as tuned mass dampers (TMDs), tuned liquid dampers (TLD) and other supplemental damping devices. This latter approach has proved to be quite economical and efficient, and as such, increasingly used in practice. The Shanghai Center Tower (SHC) is a super high-rise landmark building in China, with a height of 632 m. In order to mitigate its vibration during wind storms, a new eddy-current TMD was installed at the 125th floor. Special protective mechanisms were incorporated to prevent excessively large amplitude motion of the TMD under extreme wind or earthquake scenarios. Results of reduced-scale laboratory tests and field tests are presented in this paper to characterize the dynamic properties of the damping device and validate the fidelity of the numerical results. Results of structural analyses indicate that for SHC the eddy-current TMD was able to reduce wind-induced structural acceleration by 45%–60% and earthquake-induced structural displacement by 5%–15%. The installation of the TMD was completed in December 2014, and the performance observed to date is judged to be good. Copyright © 2016 John Wiley & Sons, Ltd.
      PubDate: 2016-05-18T04:12:42.556007-05:
      DOI: 10.1002/stc.1882
  • A model-based method for damage detection with guided waves
    • Authors: Pouria Aryan; Andrei Kotousov, Ching-Tai Ng, Benjamin Cazzolato
      Abstract: Defect detection techniques, which utilise guided waves, have received significant attention over the past twenty years. Many of these techniques implement the baseline signal subtraction approach for damage diagnosis. In this approach, the baseline signal previously recorded for a defect-free structure is compared with/or subtracted from the actual signal recorded during routine inspections. A significant deviation between these two signals (or residual signal/time-trace) can be treated as an indication of the presence of critical damage. However, the accuracy of this common approach can be compromised by various uncontrolled factors, which include ambient temperature variations, unavoidable inconsistencies in the PZT installation procedure and degradation of mechanical properties with time. This paper presents a new method for reconstruction of the baseline signal, which can compensate for the above influences and improve the accurateness of damage diagnosis. The method utilises 3D laser vibrometry measurements in conjunction with high-fidelity FE simulations. This paper also describes an application of this method to the reconstruction of the baseline signal and detection of damage in beam and plate structures. Copyright © 2016 John Wiley & Sons, Ltd.
      PubDate: 2016-05-18T04:12:11.718728-05:
      DOI: 10.1002/stc.1884
  • Assessing the effect of nonlinearities on the performance of a tuned
           inerter damper
    • Authors: Alicia Gonzalez-Buelga; Irina F. Lazar, Jason Z. Jiang, Simon A. Neild, Daniel J. Inman
      Abstract: In this paper, the use of a tuned inerter damper (TID) as a vibration absorber is studied numerically and experimentally, with civil engineering applications in mind. Inerters complete the analogy between mechanical and electrical networks, as the mechanical element equivalent to a capacitor and were developed in the 2000s. Initially, inerters were used for applications in automotive engineering, where they are known as J-dampers. Recently, research has suggested that inerter-based networks could be used for civil engineering applications, offering interesting advantages over traditional tuned mass dampers. In the civil engineering context, research has been mainly theoretical, considering ideal inerters. Because the dynamics of an inerter device include nonlinearities, especially at the low frequencies associated with civil engineering applications, the performance of the TID device using an off-the-shelf inerter has been experimentally tested in the work presented here. The chosen system, comprising a host structure with a TID attached to it, was tested using real-time dynamic substructuring (RTDS) or hybrid testing. The inerter was tested physically, while the remaining components of the TID device, the spring and damper, together with the host structure, were simulated numerically. Displacements and forces at the interface between numerical and physical components are updated in real time. This numerical–physical split allows the optimisation of the TID parameters, because the values of the spring and the damper can be changed without altering the experimental setup. In addition, this configuration takes into account the inerter's potentially complex dynamics by testing it experimentally, together with the characteristics of the host structure. Developing RTDS tests for physical inertial substructures, where part of the fed back interface forces are proportional to acceleration, is a challenging task because of delays arising at the interface between the experimental and the numerical substructures. Problems associated with stability issues caused by delay and causality arise, because we are dealing with neutral and advanced delayed differential equations. A new approach for the substructuring algorithm is proposed, consisting of feeding back the measured force deviation from the ideal inerter instead of the actual force at the interface. The experimental results show that with appropriate retuning of the components in the TID device, the performance in the TID incorporating the real inerter device is close to the ideal inerter device. © 2016 The
      Authors . Structural Control and Health Monitoring published by John Wiley & Sons, Ltd.
      PubDate: 2016-05-15T22:40:32.973161-05:
      DOI: 10.1002/stc.1879
  • Real-time experimental validation of a novel semi-active control scheme
           for vibration mitigation
    • Authors: Mohammad S. Miah; Eleni N. Chatzi, Vasilis K. Dertimanis, Felix Weber
      Abstract: This study performs an experimental investigation of a novel, semi-active control strategy for effective vibration mitigation. The implemented approach comprises a combination of the linear quadratic regulator with a nonlinear observer, namely, the unscented Kalman filter, for the control of systems described by uncertainties. Indeed, numerical models of structural systems often result as inadequate because of inherent uncertainties, such as noise, modeling errors, unknown system properties, or influence of varying operational and environmental conditions. In tackling this issue, the unscented Kalman filter is herein employed for adaptive joint state and parameter estimation refining the accuracy of the model employed by the controller and resulting in enhanced vibration mitigation. A scaled five-story shear frame attached to a hydraulic cylinder comprises the tested structure, where actuation is provided by means of a rotational magnetorheological damper operating on the relative motion between the ground floor and the first floor plate. The experimentally obtained results demonstrate a good agreement with simulations and encourage further implementation of the proposed framework in field applications of structural control. Copyright © 2016 John Wiley & Sons, Ltd.
      PubDate: 2016-05-15T22:35:57.414218-05:
      DOI: 10.1002/stc.1878
  • Vibration-based system identification of wind turbine system
    • Authors: Chin-Hsiung Loh; Kenneth J. Loh, Yuan-Sen Yang, Wan-Ying Hsiung, Yu-Ting Huang
      Abstract: The goal of this study was to investigate the use of vibration-based system identification methods for detecting wind turbine blade delamination during operating conditions and when subjected to other excitations such as earthquake ground motion. In particular, multivariate singular spectrum analysis and two subspace identification techniques were tested for detecting the dynamic characteristics of the wind blade. A total of two series of experiments was conducted to verify the proposed algorithms. In both cases, accelerometers were installed on the blades for measuring their vibration response. The first test series were performed in the laboratory; a motor spun a small-scale customized wind turbine at controlled angular velocities, and the shaking table excited the entire structure. Artificial damage was introduced by loosening bolts at the blade-rotor connection. The second test was conducted in the field, and vibration data was collected from an operating small-scale wind turbine. The blade's vibration response was analyzed through time-frequency analyses and subspace identification. These tests confirmed that the estimation of dynamic characteristics of blade and rotating frequency of the turbine system was feasible, and the results will guide future monitoring studies planned for larger-scale systems. Copyright © 2016 John Wiley & Sons, Ltd.
      PubDate: 2016-05-10T03:15:55.377285-05:
      DOI: 10.1002/stc.1876
  • Distributed sensing of a masonry vault during nearby piling
    • Authors: Sinan Acikgoz; Loizos Pelecanos, Giorgia Giardina, James Aitken, Kenichi Soga
      Abstract: Piles were constructed inside historic brick barrel vaults during the London Bridge Station Redevelopment. In order to ensure safe operation of the tracks above, movements of the vaults were monitored regularly by total stations. Concurrently, two distributed sensing technologies, fibre optic cables and laser scanners, were used to investigate the vault response to settlements. This paper discusses the monitoring data retrieved from these ‘point’ and ‘distributed’ sensing technologies and evaluates their use in structural assessment. The total station data are examined first. It is characterized by high precision and limited spatial coverage due to the use of optical targets. As a result, the total station data are useful for threshold detection but do not provide a detailed understanding of structural response or damage. In contrast, by utilizing distributed fibre optic sensors based on Brillouin optical domain reflectometry, the strain development in the structure during piling is quantified. The location and width of resulting crack openings are also determined, providing useful indicators for damage evaluation. The comparison of point clouds from laser scanners obtained at different stages of pile construction further expands the spatial coverage by detecting global movement of the structure on all visible surfaces. Using these data, the two hinge-response mechanism of the vault is revealed. The rich distributed data enable the calibration of the 2D mechanism and the finite element models, elucidating the contribution of arch stiffness, arch and backfill interaction, potential lateral movements and inter-ring sliding to the response. © 2016 The
      Authors . Structural Control and Health Monitoring published by John Wiley & Sons, Ltd.
      PubDate: 2016-05-10T03:00:37.839851-05:
      DOI: 10.1002/stc.1872
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