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ENERGY (188 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: 12)
Advances in High Energy Physics     Open Access   (Followers: 19)
Advances in Natural Sciences: Nanoscience and Nanotechnology     Open Access   (Followers: 30)
American Journal of Energy and Environment     Open Access   (Followers: 1)
American Journal of Energy Research     Open Access   (Followers: 10)
Annals of Nuclear Energy     Hybrid Journal   (Followers: 9)
Annual Reports on NMR Spectroscopy     Full-text available via subscription   (Followers: 4)
Annual Review of Resource Economics     Full-text available via subscription   (Followers: 12)
Applied Nanoscience     Open Access   (Followers: 8)
Applied Solar Energy     Hybrid Journal   (Followers: 18)
Archives of Thermodynamics     Open Access   (Followers: 8)
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: 6)
Biofuel Research Journal     Open Access   (Followers: 4)
Biofuels     Hybrid Journal   (Followers: 11)
Biofuels Engineering     Open Access   (Followers: 1)
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: 44)
Canadian Water Resources Journal     Hybrid Journal   (Followers: 22)
Carbon Management     Hybrid Journal   (Followers: 6)
Catalysis for Sustainable Energy     Open Access   (Followers: 7)
CERN courier. International journal of high energy physics     Free   (Followers: 7)
Chain Reaction     Full-text available via subscription  
Clefs CEA     Full-text available via subscription   (Followers: 1)
Computational Water, Energy, and Environmental Engineering     Open Access   (Followers: 4)
Current Alternative Energy     Hybrid Journal  
Dams and Reservoirs     Hybrid Journal   (Followers: 5)
Development of Energy Science     Open Access   (Followers: 4)
Distributed Generation & Alternative Energy Journal     Hybrid Journal   (Followers: 4)
E3S Web of Conferences     Open Access   (Followers: 1)
Economics and Policy of Energy and the Environment     Full-text available via subscription   (Followers: 8)
Electrical and Power Engineering Frontier     Open Access   (Followers: 24)
Electricity Journal     Partially Free   (Followers: 2)
ENERGETIKA. Proceedings of CIS higher education institutions and power engineering associations     Open Access   (Followers: 1)
Energy     Partially Free   (Followers: 31)
Energy & Environment     Hybrid Journal   (Followers: 20)
Energy & Fuels     Full-text available via subscription   (Followers: 32)
Energy and Buildings     Hybrid Journal   (Followers: 11)
Energy and Emission Control Technologies     Open Access   (Followers: 4)
Energy and Environment Focus     Free   (Followers: 6)
Energy and Environment Research     Open Access   (Followers: 14)
Energy and Environmental Engineering     Open Access   (Followers: 7)
Energy and Power     Open Access   (Followers: 10)
Energy and Power Engineering     Open Access   (Followers: 21)
Energy Conversion and Management     Hybrid Journal   (Followers: 11)
Energy Efficiency     Hybrid Journal   (Followers: 11)
Energy Harvesting and Systems : Materials, Mechanisms, Circuits and Storage     Hybrid Journal   (Followers: 4)
Energy Law Journal     Full-text available via subscription   (Followers: 4)
Energy Materials : Materials Science and Engineering for Energy Systems     Hybrid Journal   (Followers: 21)
Energy Policy     Partially Free   (Followers: 60)
Energy Prices and Taxes     Full-text available via subscription   (Followers: 5)
Energy Procedia     Open Access   (Followers: 2)
Energy Reports     Open Access   (Followers: 5)
Energy Research & Social Science     Full-text available via subscription   (Followers: 7)
Energy Science & Engineering     Open Access   (Followers: 5)
Energy Science and Technology     Open Access   (Followers: 12)
Energy Storage Materials     Full-text available via subscription   (Followers: 2)
Energy Strategy Reviews     Partially Free   (Followers: 10)
Energy Studies Review     Open Access   (Followers: 6)
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: 18)
Environmental Progress & Sustainable Energy     Hybrid Journal   (Followers: 7)
EPJ Photovoltaics     Open Access   (Followers: 5)
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: 4)
Frontiers in Energy Research     Open Access   (Followers: 4)
Fuel and Energy Abstracts     Full-text available via subscription   (Followers: 6)
Functional Materials Letters     Hybrid Journal   (Followers: 3)
Gcb Bioenergy     Open Access   (Followers: 2)
Geomechanics for Energy and the Environment     Full-text available via subscription   (Followers: 1)
Geothermal Energy     Open Access   (Followers: 4)
Geothermal Energy Science     Open Access   (Followers: 1)
Green     Hybrid Journal   (Followers: 1)
Green Energy & Environment     Open Access   (Followers: 2)
IEA Electricity Information     Full-text available via subscription   (Followers: 4)
IEA Natural Gas Information     Full-text available via subscription   (Followers: 3)
IEEE Power and Energy     Full-text available via subscription   (Followers: 27)
IEEE Transactions on Energy Conversion     Hybrid Journal   (Followers: 17)
IEEE Transactions on Nuclear Science     Hybrid Journal   (Followers: 10)
IEEE Transactions on Power Systems     Hybrid Journal   (Followers: 30)
IET Power Electronics     Hybrid Journal   (Followers: 38)
Ingeniería Energética     Open Access  
Innovations : Technology, Governance, Globalization     Hybrid Journal   (Followers: 12)
International Journal of Alternative Propulsion     Hybrid Journal   (Followers: 8)
International Journal of Ambient Energy     Hybrid Journal   (Followers: 1)
International Journal of Applied Power Engineering     Open Access   (Followers: 5)
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: 7)
International Journal of Energy and Environmental Engineering     Open Access   (Followers: 5)
International Journal of Energy and Power     Open Access   (Followers: 11)
International Journal of Energy and Statistics     Hybrid Journal   (Followers: 3)
International Journal of Energy Engineering     Open Access   (Followers: 11)
International Journal of Energy Research     Hybrid Journal   (Followers: 10)
International Journal of Energy Science     Open Access   (Followers: 2)
International Journal of Global Energy Issues     Hybrid Journal   (Followers: 9)
International Journal of Green Energy     Hybrid Journal   (Followers: 10)
International Journal of Hydrogen Energy     Partially Free   (Followers: 18)
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: 4)
International Journal of Nuclear Governance, Economy and Ecology     Hybrid Journal   (Followers: 2)
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: 8)
International Journal of Power and Energy Conversion     Hybrid Journal   (Followers: 3)
International Journal of Smart Grid and Green Communications     Hybrid Journal   (Followers: 1)
International Journal of Sustainable Energy     Hybrid Journal   (Followers: 13)
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)
International Journal of Turbomachinery, Propulsion and Power     Open Access   (Followers: 4)
Joule     Hybrid Journal  
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   (Followers: 2)
Journal of Energy & Natural Resources Law     Hybrid Journal   (Followers: 4)
Journal of Energy Chemistry     Full-text available via subscription   (Followers: 3)
Journal of Energy in Southern Africa     Open Access   (Followers: 3)
Journal of Energy Storage     Full-text available via subscription   (Followers: 3)
Journal of Energy Technologies and Policy     Open Access   (Followers: 5)
Journal of Fusion Energy     Hybrid Journal   (Followers: 3)
Journal of International Energy Policy     Open Access   (Followers: 4)
Journal of Modern Power Systems and Clean Energy     Open Access   (Followers: 10)
Journal of Nano Energy and Power Research     Full-text available via subscription   (Followers: 5)
Journal of Nuclear Energy Science & Power Generation Technology     Hybrid Journal   (Followers: 5)
Journal of Ocean Engineering and Marine Energy     Hybrid Journal   (Followers: 3)
Journal of Physical Chemistry C     Full-text available via subscription   (Followers: 35)
Journal of Power and Energy Engineering     Open Access   (Followers: 2)
Journal of Radiological Protection     Full-text available via subscription   (Followers: 4)
Journal of Renewable Energy     Open Access   (Followers: 8)
Journal of Semiconductors     Full-text available via subscription   (Followers: 4)
Journal of Solar Energy     Open Access   (Followers: 11)
Journal of Solar Energy Engineering     Full-text available via subscription   (Followers: 21)
Journal of Sustainable Bioenergy Systems     Full-text available via subscription   (Followers: 1)
Journal of Sustainable Energy Engineering     Full-text available via subscription   (Followers: 2)
Journal of Technology Innovations in Renewable Energy     Hybrid Journal  
Materials for Renewable and Sustainable Energy     Open Access   (Followers: 8)
Materials Today Energy     Hybrid Journal   (Followers: 1)
MRS Energy & Sustainability - A Review Journal     Full-text available via subscription  
Natural Resources     Open Access   (Followers: 2)
Nature Energy     Hybrid Journal   (Followers: 12)
Nigerian Journal of Technological Research     Full-text available via subscription   (Followers: 1)
Nuclear Data Sheets     Full-text available via subscription  
Nuclear Engineering and Design     Hybrid Journal   (Followers: 14)
Nuclear Law Bulletin     Full-text available via subscription   (Followers: 2)
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   (Followers: 2)
Protection and Control of Modern Power Systems     Open Access   (Followers: 2)
Radiochimica Acta     Hybrid Journal   (Followers: 5)
Radioprotection     Hybrid Journal   (Followers: 1)
Science and Technology of Nuclear Installations     Open Access   (Followers: 2)
Smart Grid and Renewable Energy     Open Access   (Followers: 8)
Solar Energy     Hybrid Journal   (Followers: 22)
Solar Energy Materials and Solar Cells     Hybrid Journal   (Followers: 38)
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: 9)
Surface Science Reports     Full-text available via subscription   (Followers: 20)
Sustainable Energy     Open Access   (Followers: 3)
Sustainable Energy Technologies and Assessments     Full-text available via subscription  
Sustainable Energy, Grids and Networks     Hybrid Journal   (Followers: 4)
Technology Audit and Production Reserves     Open Access   (Followers: 1)
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: 13)
Water International     Hybrid Journal   (Followers: 16)
Wiley Interdisciplinary Reviews : Energy and Environment     Hybrid Journal   (Followers: 6)
Wind Energy     Hybrid Journal   (Followers: 3)
Wind Engineering     Hybrid Journal   (Followers: 2)
Wireless Power Transfer     Full-text available via subscription   (Followers: 4)

       | Last

Journal Cover Structural Control and Health Monitoring
  [SJR: 1.549]   [H-I: 35]   [9 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  [1597 journals]
  • Issue Information
    • Abstract: No abstract is available for this article.
      PubDate: 2018-01-12T03:04:48.458496-05:
      DOI: 10.1002/stc.2092
  • Markov chain Monte Carlo-based Bayesian method for structural model
           updating and damage detection
    • Authors: Heung-Fai Lam; Jia-Hua Yang, Siu-Kui Au
      Abstract: This paper proposes a Bayesian method for structural model updating and damage detection using modal data. A recently developed Markov chain Monte Carlo algorithm is adopted to handle the model updating problem. The proposed Bayesian method focuses on calculation of the posterior probability distribution function of uncertain model parameters. In addition to the most probable values of the uncertain parameters, the associated uncertainties can be calculated with consideration of the effects of both the modeling error and the measurement noise. An experimental case study was carried out with a shear building model under laboratory conditions to study the identifiability of the model-updating problem following the proposed Bayesian method. The results demonstrate the change in the posterior probability distribution function of the uncertain parameters with the amount of measured information. It also demonstrates the ability of the proposed method to handle unidentifiable problems. The proposed Bayesian method is then applied for structural damage detection by calculating the probability distribution of the extent of damage to various structural components. To demonstrate the proposed Bayesian damage-detection method, ambient vibration tests were carried out on a 2-story steel frame with bolted connections. Joint damage was simulated by loosening some bolts at the target beam-column connection. The model-updating results show that the uncertainty associated with the rotational stiffness of the steel joints was very high, rendering the problem almost unidentifiable. Although the problem is almost unidentifiable, the calculated probability distribution of the damage extent can still locate the damaged joint and estimate the damage extent (i.e., the percentage reduction in rotational stiffness) together with the associated uncertainty.
      PubDate: 2018-01-11T04:25:57.757892-05:
      DOI: 10.1002/stc.2140
  • Utilising hydraulic transient excitation for fatigue crack monitoring of a
           cast iron pipeline using optical distributed sensing
    • Authors: Leslie Wong; Suranji Rathnayaka, Wing Kong Chiu, Jayantha Kodikara
      Abstract: Corrosion-induced failures are common in cast iron pipes used in water supply networks. Over times, cracks may initiate from the corroded pits and grow when subjected to fatigue internal loading. When the particular region of the pipe loses its structural capacity, it will eventually lead to leakage or even pipe burst. Thus, it is important to perform permanent and real-time integrity monitoring on these pipelines. Distributed optical fibre sensors (DOFS) have been proposed to monitor the structural health of water pipelines for the last few decades. Most of the previous studies have shown that DOFS is effective in monitoring the condition of a pipeline subjected to static operating pressure. This paper aims to experimentally demonstrate the ability of distributed optical fibre strain sensor to monitor the fatigue crack growth along the cast iron pipeline subjected to pressure transient. The fatigue test was conducted using a large-scale cyclic internal pressure loading facility. The DOFS was instrumented on the pipe to monitor the condition of the pipe when subjected to internal pressure loading approximation of water pressure loading (operating pressure and pressure transient) experienced in the field. The measured response will show the potential application of DOFS for crack detection, as well as monitoring the fatigue crack growth along the pipe. The results confirmed that DOFS is able to enhance the detection of cracks along the pipe subjected to pressure transient.
      PubDate: 2018-01-11T04:17:38.937897-05:
      DOI: 10.1002/stc.2141
  • Proposal of optimum tuning of semiactive TMDs used to reduce harmonic
           vibrations based on phase control strategy
    • Authors: Fernando Ferreira; Carlos Moutinho, Álvaro Cunha, Elsa Caetano
      Abstract: Tuned mass dampers (TMDs) are a well-established technology for passive structural vibration control involving harmonic vibrations. Some design issues are critical to guarantee the proper functioning of the device, in particular, the adequate tuning and the adequate space to accommodate the TMD stroke. With regard to the first aspect, semiactive TMDs were proposed as an alternative means of correcting the vibrating frequency of the device by adding a semiactive element between the TMD and the structure. In this case, several control strategies have been proposed, among which phase control has proven to lead to excellent results. However, in the framework of this control approach, the minimization of the structure displacements is often used as the main objective of the control, as the relative displacements of the TMDs mass are considered a secondary issue, which nevertheless may be a crucial aspect in some applications. In this context, this paper proposes a strategy to optimally tune the semiactive TMD, taking into account a balance between the level of the reduction of the structural response and the amplitude of the TMD stroke. The optimal tuning is found by minimizing the system stationary mechanical energy. The problem is formulated as an optimization process, and the corresponding results are presented and discussed.
      PubDate: 2018-01-11T03:21:34.782217-05:
      DOI: 10.1002/stc.2131
  • An UKF-based nonlinear system identification method using interpolation
           models and backward integration
    • Authors: Luyu Li; Han Qin
      Abstract: In this paper, a novel identification method for nonlinear systems is proposed. This method utilizes linear interpolation models to describe the nonlinear forces of the physical models, and the unscented Kalman filter (UKF) method is adopted for the task of nonlinear identification. With the help of a linear interpolation algorithm, the proposed method requires little prior knowledge of the form of the nonlinear stiffness. Therefore, this method takes advantage of both the independence of the linear interpolation points and the inherent mathematical properties of the UKF. The UKF method is also modified to better fit the needs of parameter identification. To further emphasize parameter identification, backward integration and observations of the previous states are used. Two numerical simulations of the nonlinear elastic stiffness and Bouc–Wen hysteresis are conducted to show the flexibility and efficiency of this method. In these 2 examples, the observation signals are generated by analytic models, and the identifications are conducted with a linear interpolation model.
      PubDate: 2018-01-05T04:32:28.001474-05:
      DOI: 10.1002/stc.2129
  • Ice monitoring of a full-scale wind turbine blade using ultrasonic guided
           waves under varying temperature conditions
    • Authors: Peng Wang; Wensong Zhou, Yuequan Bao, Hui Li
      Abstract: The icing of wind turbine blades is a common problem in cold climate area. Ice accretion on wind turbines, particularly turbine blades, can cause a variety of problems. The extreme icing may induce full stop of the turbine system. Thus, ice monitoring is one of the important issues for turbine blade icing solutions. The ice coating on the blade surface can change the primary propagation characteristics of the elastic waves. Therefore, Lamb waves are proposed to monitor the ice-forming processes of a full-scale wind turbine blade. Because the varying temperature is a remarkable and inevitably factor during ice monitoring, a principal component analysis (PCA)-based ice monitoring method is proposed to eliminate the temperature effects and is first demonstrated by a segment of the blade in the laboratory. Subsequently, the proposed method is applied on a full-scale blade in the frozen tunnel. The PZT wafers array is arranged to enhance the guided wave signals, and the tuning and attenuation characteristics are investigated on the clear surface of blade without ice. Finally, the PCA-based method is used to identify the ice formation again on both the tip and the middle segments of the full-scale blade under varying temperature conditions. The results indicate that the proposed ultrasonic guided wave combining PCA-based method is efficient and sensitive for ice monitoring of the full-scale wind turbine blade.
      PubDate: 2018-01-05T04:26:50.956814-05:
      DOI: 10.1002/stc.2138
  • Robust design of a multi-floor isolation system
    • Authors: Hamidreza Anajafi; Ricardo A. Medina
      Abstract: A multi-floor isolation (MFI) technique can provide a building with inherent dynamic vibration suppressors through decoupling different portions of floors masses from the superstructure. This paper evaluates the seismic effectiveness and robustness of the MFI technique using a test-bed 20-story building. First, a parametric study approach is utilized to optimize MFI configurations with different isolated mass ratios (IMRs) and different number of isolated floor subsystems (IFSs). The response quantity to be optimized is the sum of root-mean-square interstory drift responses of the superstructure under a stochastic excitation. The sensitivity of the seismic performance of the optimally designed MFI configurations with respect to uncertainties in the properties of the superstructure, IFSs, and the ground excitation is evaluated. Simulation results illustrate that with the presence of these uncertainties, the effectiveness of the optimally designed MFI configurations with low and high IMRs (e.g., 5% and 90%) is significantly impaired, whereas configurations with intermediate IMRs (e.g., 50%) exhibit a relatively stable performance. Evaluation of the optimal placement of IFSs along the building height, when the number of IFSs is limited, reveals that placing the IFSs at top stories can lead to a near-optimal system in terms of the spatial distribution of IFSs. A genetic algorithm is used to design a robust system for a selected configuration with top 10 IFSs and an IMR of 50%. The robust design is performed via minimizing the maximum deviation with respect to the design root-mean-square interstory drift response when the design parameters vary within a given uncertainty range.
      PubDate: 2018-01-05T04:21:02.516854-05:
      DOI: 10.1002/stc.2130
  • Structural damage identification using image-based pattern recognition on
           event-based binary data generated from self-powered sensor networks
    • Authors: Hadi Salehi; Saptarshi Das, Shantanu Chakrabartty, Subir Biswas, Rigoberto Burgueño
      Abstract: A continuing challenge in structural health monitoring is power availability for sensors to collect and communicate data. A way to minimize the communication power demand is to transmit the minimum amount of information, namely, one bit. Event-based binary signals are generated at sensor nodes according to local rules based on physical measurements, but interpretation at the global level requires dealing with discrete binary data, which implies system information with reduced resolution. This study presents an investigation on approaches for the interpretation of event-based binary data provided by a self-powered sensor network using a pulse-communication protocol for use in structural assessment and damage identification. Pattern recognition (PR) methods based on image data analysis techniques were adapted for such purpose. The methods used were classifiers based on anomaly detection, a Bayesian method, and a nearest neighbor method. To improve the performance of the approach, 2-dimensional principal component analysis and 2-dimensional linear discriminant analysis were used as feature extraction techniques along with a nearest neighbor classifier. The PR methods and the performance of the interpretation algorithms were evaluated by using virtual data from finite element simulations and real data from experiments on plates. The ability of the PR methods to identify service demands, load variations, and localized material degradation was examined. Results indicate that image-based PR methods can be effectively used for structural damage identification in plate-like structures using event-based binary data sets in novel wireless self-powered sensor networks.
      PubDate: 2018-01-02T03:41:46.345911-05:
      DOI: 10.1002/stc.2135
  • Local effects induced by dynamic load self-heating in NiTi wires of shape
           memory alloys
    • Authors: S. Casciati; V. Torra, M. Vece
      Abstract: The use of shape memory alloys wires in dampers devices for Civil Engineering applications is well documented in the literature. This paper develops a critical discussion on the wire macroscopic behavior and on the associated temperature effects with emphasis on the wire diameter. Vibration damping requires the absorption of mechanical energy and its conversion to heat via the action of hysteresis cycles. The experimental study is carried out on NiTi wires of different diameters. The flat cycles shown by thin wires (i.e., 0.5 mm of diameter or less) and the nonclassical S-shaped cycles (e.g., for diameter 2.46 mm) establish clear differences in the response of the samples. For this reason, a supplementary investigation is here reported to show that the flat cycles are coherent with the classical treatment of shape memory alloys as a first-order phase transition, but the S-shaped cycles of thick wires can be associated to an anomaly in the heat capacity.
      PubDate: 2017-12-21T22:41:13.476315-05:
      DOI: 10.1002/stc.2134
  • Sliding mode trajectory tracking control of a ball-screw-driven shake
           table based on online state estimations using EKF/UKF
    • Authors: Nima Rajabi; Amir Hossein Abolmasoumi, Mehdi Soleymani
      Abstract: In this paper, we propose a new trajectory tracking control of a ball-screw-driven servomechanism for a shaking table. Displacement and acceleration sensors are assumed available, but currents and velocity sensors are not. The design of this control strategy is based on sliding mode approach with state estimation by extended Kalman filter/unscented Kalman filter. The basic feature of this design is that high velocity and high positioning accuracy can be met despite of the fact that the controlled process suffers from noise, friction, and uncertainty. Torque/flux sliding mode controller with online estimation using extended Kalman filter and unscented Kalman filter is proposed to improve velocity sensorless trajectory tracking control of uniaxial earthquake simulator. Simulation works are carried out to show the ability of the proposed method to simulate the speed and acceleration of 2 important earthquakes. The results also demonstrate the activity of the proposed strategy at wide range of velocity operation with measurement noises.
      PubDate: 2017-12-21T22:31:53.550895-05:
      DOI: 10.1002/stc.2133
  • Evaluation of the dynamic characteristics of a super tall building using
           data from ambient vibration and shake table tests by a Bayesian approach
    • Authors: Feng-Liang Zhang; Carlos E. Ventura, Hai-Bei Xiong, Wen-Sheng Lu, Yu-Xin Pan, Ji-Xing Cao
      Abstract: The Shanghai Tower is a newly built 127-story and 632 m high super tall building. As of April 2017, it was ranked as the second tallest building in the world. Its main structural system is a mega-frame-tube-outrigger system with six outrigger trusses along the height. Due to its unique structural configuration, a series of field and laboratory model tests have been conducted to better understand its dynamic characteristics. Before its construction, a scaled model of the tower was tested on a shake table, and the results were used to refine the design of the tower. At the completion of the construction, full-scale ambient vibration tests were performed. A Bayesian method was used to perform operational modal analysis from the shake table and full-scale ambient vibration tests. The most probable value of the modal parameters and the associated posterior uncertainties were calculated using this method. The first eight modes were identified, including three translational modes in each principal direction and two torsional modes. Using these results, the dynamic characteristics and associated uncertainties obtained from the two tests were investigated and compared in this paper. Due to the scaling of the model, there are some discrepancies between the natural frequencies obtained from two different tests, but the identified mode shapes matched very well. Although the structure was designed in a very innovative manner, its dynamic characteristics are similar to regular tall buildings. The results from this investigation provide valuable information for an ongoing condition assessment of this super tall building.
      PubDate: 2017-12-18T04:59:58.384625-05:
      DOI: 10.1002/stc.2121
  • Comprehensive investigation of leakage problems for concrete gravity dams
           with penetrating cracks based on detection and monitoring data: A case
    • Authors: Jiang Hu; Fuheng Ma, Suhua Wu
      Abstract: The leakage amount is an important indicator evaluating the seepage behavior of a dam. Due to the complex behavior, crack development judgment and leakage behavior identification for concrete gravity dams remain a challenging task. The paper is concerned with comprehensive investigation of leakage problems for concrete gravity dams with penetrating cracks. A case study on Shimantan Reservoir Dam was taken to examine the utilization of the comprehensive investigation method. Deficiency investigations were undertaken to identify the nature and sources of defects responsible for the serious leakage. Based on the information acquired from field visual inspections and ground-penetrating radar tests, it is apparent that several transverse cracks penetrate the dam crest and propagate downward into the dam body. The results of the remedial grouting, X-ray diffraction analyses and water injection tests reflect the appearance of penetrating leakage paths in the dam body. Subsequently, 2 behavior models including the special hydrostatic-seasonal-time model and the inverse analysis model were conducted to distinguish the contribution of penetrating cracks to leakage amount. The special hydrostatic-seasonal-time model was modified to address the influence of leakage flow in real microcracks in concrete dams based on the Navier–Stokes equation. The result shows that the proposed models provide an acceptable accuracy in analyzing leakage monitoring data for gravity dams with penetrating cracks. Leakage flow in penetrating cracks plays a dominant role in the dam seepage field. The execution flow in this paper could be readily employed in investigations of similar problems of concrete dams.
      PubDate: 2017-12-08T03:16:16.470699-05:
      DOI: 10.1002/stc.2127
  • Theoretical study and experimental validation on the energy dissipation
           mechanism of particle dampers
    • Authors: Zheng Lu; Biao Huang, Ying Zhou
      Abstract: An energy dissipation factor was proposed to quantify the energy dissipation mechanism of particle dampers based on theoretical analysis and was further validated by free vibration tests and wind tunnel tests. The vibration energy of the main structure was consumed by impact and friction between particles and between particles and the container. An elastoplastic collision model and a simplified frictional-elastic collision model were used to analyze the energy dissipation due to impact and friction, respectively. Then, an energy dissipation factor, reflecting the vibration energy consumption of a particle damper, was defined. Finally, free vibration tests and aero-elastic wind tunnel tests of a benchmark model unattached or attached with particle dampers were conducted to validate the relationship between the vibration reduction performances and the energy dissipation factors, and the experimental results were in qualitative agreement with the theoretical results. Consequently, the energy dissipation factor indicated the energy dissipation mechanism of particle dampers and can be used to select the proper material of the particles, helping to maximize the vibration control effects from the material's perspective. It was shown that the material of higher kinetic friction coefficient, higher modulus of elasticity, and lower yield strength usually leads to better energy dissipation effects.
      PubDate: 2017-12-08T03:15:54.884719-05:
      DOI: 10.1002/stc.2125
  • Detection of structural faults in piers of masonry arch bridges through
           automated processing of laser scanning data
    • Authors: A. Sánchez-Rodríguez; B. Riveiro, B. Conde, M. Soilán
      Abstract: This paper introduces a new methodology for the automated processing of large point clouds for the diagnosis of structural pathologies in piers of masonry arch bridges. This method starts with the automatic segmentation of the global point cloud of the entire bridge in its different structural elements (piers, arches, spandrel walls, etc.). Later, piers were further segmented in order to be able to detect and quantify structural pathologies. Particularly, faults are based in geometric anomalies (tilts and skews) of the pier walls that might be indicators of stability problems of the entire bridge. The methodology was validated using several samples of representative masonry arch bridges. The obtained results demonstrate that this method can provide useful information about the structural health of the bridge requiring neither training in the technology nor advanced knowledge in the processing of laser scanning data.
      PubDate: 2017-12-08T03:11:00.490813-05:
      DOI: 10.1002/stc.2126
  • Deflection distribution estimation of tied-arch bridges using long-gauge
           strain measurements
    • Authors: Qingqing Zhang; Jian Zhang, Wenhui Duan, Zhishen Wu
      Abstract: Deflection, as a critical indicator for structural performance evaluation, is difficult to be measured accurately for long-span bridges, though various deformation sensors and devices have been developed. In this paper, a new scheme using long-gauge fiber optic sensors for estimating the deflection distribution of tied-arch bridges is proposed. First, the complex strain state of the tied-arch bridge is investigated, in which a cubic function describing the axial strain distribution of the tie beam is obtained. Second, the bending strain is separated from the measured long-gauge strain which is a combination of axial and bending components by a sensor layout scheme. Finally, the separated bending strain is utilized to estimate the deflection distribution of the tied-arch bridge through an improved conjugate beam method. Numerical and experimental examples are studied to illustrate the effectiveness of the proposed method for deflection estimation of tied-arch bridges in static and dynamic loading cases.
      PubDate: 2017-12-05T04:26:59.6229-05:00
      DOI: 10.1002/stc.2119
  • Real-time hybrid testing of a structure with a piezoelectric friction
           controllable mass damper by using a shake table
    • Authors: Shih-Yu Chu; Lyan-Ywan Lu, Shih-Wei Yeh
      Abstract: A structure with semi-active control devices is usually a highly nonlinear system. To investigate the aseismic performance of such a system, real-time hybrid testing (RTHT) can be a cost-effective experimental method. However, a substructure with a semi-active friction device is difficult to be tested by the RTHT, because the dynamic behavior of a friction device, which consists of sliding and sticking phases, is determined by the exerted force of the primary structure, rather than its displacement response. To overcome this problem, a methodology of RTHT with a shake table (RTHT-ST) is utilized in this study. In the RTHT-ST, which is an experimental technique combining shaking table test and RTHT, the shake table is employed to mimic the acceleration response of the primary structure that is simulated by a numerical model and imposed to the substructure, which is mounted on the shake table. In order to verify the feasibility of the experimental method, a semi-active piezoelectric friction controllable mass damper substructure is tested by using the RTHT-ST. The test results of the RTHT-ST are compared with those of a full shaking table test, in which the integrated primary structure and piezoelectric friction controllable mass damper system have been physically tested. Moreover, to evaluate the accuracy of the RTHT-ST result, one category of indicators called root-mean-square energy error index is also proposed. Unlike previously existing hybrid-testing indices, the root-mean-square energy error index is able to distinguish modeling error from control system error.
      PubDate: 2017-11-27T04:18:10.692469-05:
      DOI: 10.1002/stc.2124
  • Posterior uncertainty, asymptotic law and Cramér-Rao bound
    • Authors: Siu-Kui Au; Binbin Li
      Abstract: In a globally identifiable Bayesian system identification problem, the uncertainty of model parameters can be quantified by their “posterior covariance matrix” calculated for a particular data set. When the data is modeled to be distributed as the likelihood function (i.e., no modeling error), a statistical law analogous to the law of large numbers results, where the posterior covariance matrix is asymptotic to a deterministic quantity that depends on the “information content” of data rather than its particular (stochastic) details. This was referred as the “uncertainty law” in a recent study of the achievable precision of modal parameters in operational modal analysis (OMA). Deriving the uncertainty law involves asymptotics techniques and leveraging on the mathematical structure of the likelihood function, which was found to be tedious. As a sequel to the development, this work shows that for long data and up to a Gaussian approximation of the posterior distribution, the uncertainty law is asymptotic to the inverse of the Fisher information matrix, which coincides with the tightest Cramér-Rao bound in classical statistics. A parametric study is presented to illustrate the theoretical results in the context of OMA. As a direct application with practical relevance, the relationship provides a systematic means for deriving the uncertainty laws in OMA. Applied and interpreted properly, the posterior covariance matrix (for given data), uncertainty law, and Cramér-Rao bound can provide a powerful means for quantifying and managing the uncertainties in structural health monitoring.
      PubDate: 2017-11-27T04:16:35.27562-05:0
      DOI: 10.1002/stc.2113
  • Shaking table test of a four-tower high-rise connected with an isolated
           sky corridor
    • Authors: Xilin Lu; Qing Lu, Wensheng Lu, Ying Zhou, Bin Zhao
      Abstract: A 4-tower high-rise building connected with an isolated sky corridor on the top is designed in the seismic region of China. The 300-meter long sky-corridor bridges the four 230-m-high towers at the top floor. The seismic design of the building is challenging due to the structural complexity. Passive control strategy is employed to reduce earthquake responses and member forces of the towers and the sky corridor. Connections between the towers and the sky corridor are designed as flexible links. Curved surface sliders (CSSs) and viscous dampers (VDs) are installed at the connection joints. The characteristics of the seismic isolation system should remain unchanged during the service life, and the CSSs shall be protected strictly from humidity and dust. To study the seismic performance of the 4-tower connected structure, a 1/25 scale model is tested by shaking table tests subject to minor, moderate, and major earthquake. According to the Chinese code, peak ground accelerations subject to the 3 levels are specified as 0.025, 0.07, and 0.175 g. Eight earthquake records with different frequency spectrum properties were selected to test the model structure. Detailed dynamic similitude design of towers, CSSs, and VDs are described. The maximum acceleration and deformation responses of the towers and the sky corridor are measured, as well as the seismic performance of the CSSs and VDs, the dynamic characteristics, and the cracking pattern of the building. Results show that no serious damage occurs on the 4-tower connected structure. The protective system that consists of the CSSs and VDs reduces the seismic responses of the sky corridor. The sky corridor keep in elastic state under the high-intensity earthquake.
      PubDate: 2017-11-17T07:02:42.47187-05:0
      DOI: 10.1002/stc.2109
  • Visual–inertial displacement sensing using data fusion of vision-based
           displacement with acceleration
    • Authors: Jong-Woong Park, Do-Soo Moon, Hyungchul Yoon, Fernando Gomez, Billie F. Spencer Jr; Jong R. Kim
      Abstract: In recognition of the importance of the displacement associated with assessing structural condition, many displacement measurement methods have been proposed to date. With advances in optics and electronics, displacement measurement relying on computer-vision techniques to convert pixel movement into structural displacement has drawn much attention recently, thanks to its simplicity in installation and relatively inexpensive cost. Despite numerous advantages, 2 major obstacles that prohibit the use of vision-based method are (a) resolution, which is a function of distance between the camera and the structure, and (b) limited frame rate, which both lower dynamic displacement-capturing capability. In this paper, to enhance the quality of vision-based displacement measurement, data fusion with acceleration measurement is proposed to improve the dynamic range of displacements while lowering signal noise. To achieve fusion between vision-based displacement and acceleration, complementary filters and a time synchronization method between 2 different sources were proposed. The proposed methods were verified through numerical analysis and an experimental test, the results of which showed the validity of proposed data fusion.
      PubDate: 2017-11-17T06:56:29.421715-05:
      DOI: 10.1002/stc.2122
  • A novel time reversal sub-group imaging method with noise suppression for
           damage detection of plate-like structures
    • Authors: Weihang Gao; Guangmin Zhang, Hongnan Li, Linsheng Huo, Gangbing Song
      Abstract: In this paper, a new time reversal imaging (TRI) algorithm with noise suppression is developed for the application of imaged based structural damage detection of plate-like structures. The conventional TRI method suffers from performance degradation in high noise condition. The proposed method addresses the aforementioned issues. First, an array of detection transducers is used and is divided into several subgroups. Then, the echo signals of the subgroups are time reversed and reemitted via numerical computation. Finally, the cross-correlation functions of the summation of refocused time reversed signals in each subgroup are obtained to locate damages. The time reversed signals at the reference time are irrelevant to the noise, meanwhile, the multiple refocused signals in each subgroup are first added and then cross-correlated. Therefore, the proposed method can effectively suppress noise. To validate the effectiveness of proposed method, 2 experiments were performed. The 2 experiments involved 2 aluminum plate specimens. Each specimen was equipped with 4 surface-bonded lead zirconate titanate transducers. One specimen involved a simulated damage (an addition of a mass), and the other one involved an actual through-hole damage. The experimental performances of the proposed method are compared to those of the conventional TRI method. The imaging results demonstrated that the damage on both specimens was clearly displayed with high spatial resolution by the proposed method even under the low signal-to-noise ratio condition. On the contrary, the location of the damage computed by the conventional TRI method was submerged in noise and cannot be distinguished.
      PubDate: 2017-11-17T06:51:31.58417-05:0
      DOI: 10.1002/stc.2111
  • Characterization of stationary and walking people on vertical dynamic
           properties of a lively lightweight bridge
    • Authors: Wei He; Wei-ping Xie
      Abstract: This paper investigates the effect of both stationary and walking people on vertical dynamic characteristics of structures based on an experimental program. A lively lightweight bridge was designed and constructed for the experiments. Dynamic properties of the bridge are obtained based on ambient vibration testing method. Stationary tests of straight knees and bent knees postures under different crowd sizes were performed using heel-impact method. Synchronized walking tests were conducted considering walking frequencies ranging from 1.6 to 2.4 Hz and different group sizes of the participants. Random walking activities were also performed. Results of stationary people tests show a decrease in natural frequency and an increase in damping ratio of the occupied structure with respect to the empty structure as number of people increases, for both straight knees and bent knees postures. However, the structural damping tends to be “stable” (or “saturated”) when number of occupants exceeds a critical value. Theoretical modeling of standing people–structure interaction system reflects similar trend. Results of walking tests also show a decrease in natural frequency and an increase in damping ratio of the structure. Comparison of all test data implies that structural properties, structural weight, load frequency, and crowd size all contribute to structural responses, among which load frequency plays a decisive role. Furthermore, both higher harmonics of walking load and higher vibration modes may contribute remarkably to total structural response for lightweight structures.
      PubDate: 2017-11-17T06:31:47.597969-05:
      DOI: 10.1002/stc.2123
  • The MIT Green Building benchmark problem for structural health monitoring
           of tall buildings
    • Authors: Hao Sun; Oral Büyüköztürk
      Abstract: This paper presents a benchmark problem for the structural health monitoring community to study tall buildings. The benchmark building is called the Green Building located at the Massachusetts Institute of Technology campus, with 21 stories above the ground (83.7 m) and a basement (3.8 m) connecting to the Massachusetts Institute of Technology tunnel system. This building was constructed as cast-in-place reinforced concrete and instrumented with 36 accelerometers to measure the building translational, torsional and vertical responses. The benchmark problem includes the detailed description of this building, 7 field measurement data sets (4 ambient data sets, 1 data set under an unidentified event, 1 data set under the excitation of fireworks, and 1 earthquake data set), and finite element models (both full-scale and condensed models). The Green Building has an identifiable soil-structure interaction behavior and the base rocking movement brings significant components into the building response. To decouple the rocking effect, storey measurement condensation and rocking response determination are discussed in this paper. A blind source separation approach is finally applied to identify the modal characteristics and quantify the rocking components. The benchmark data and models are open to the public for algorithmic development and validation.
      PubDate: 2017-11-17T06:01:47.11076-05:0
      DOI: 10.1002/stc.2115
  • Mitigation of offshore wind turbine responses under wind and wave loading:
           Considering soil effects and damage
    • Authors: Chao Sun
      Abstract: The present paper studies the mitigation of monopile offshore wind turbines subjected to wind and wave loading. Soil effects (SE) and damage are considered. A semiactive tuned mass damper (STMD) capable of retuning its natural frequency and damping property in real time is utilized to mitigate the nacelle/tower top dynamic response. Based on the Euler–Lagrangian equation, an analytical model of the wind turbine coupled with an STMD is established wherein the interaction between the blades and the tower is modeled. Wind turbulence is generated via mapping a three-dimensional wind field profile onto the rotating blades. Aerodynamic loading is computed using the blade element momentum method where the Prandtl's tip loss factor and the Glauert correction are considered. Wave loading is computed using Morison's equation together with the strip theory. The National Renewable Energy Laboratory monopile 5-MW baseline wind turbine model is employed to examine the performance of the STMD. It is found that the SE and damage presence in the foundation or/and the tower can change the dominant frequency, thereby rendering the conventional TMD detuned and ineffective. In comparison, the STMD retuned in real time by the proposed algorithm can mitigate the nacelle/tower and foundation response more effectively with a smaller stroke. Results indicate that the STMD has significant effectiveness improvement over the TMD when the SE and/or damage are considered.
      PubDate: 2017-11-17T06:01:11.376616-05:
      DOI: 10.1002/stc.2117
  • Development of a smart-device-based vibration-measurement system:
           Effectiveness examination and application cases to existing structure
    • Authors: Ashish Shrestha; Ji Dang, Xin Wang
      Abstract: After the 2011 Great East Japan Earthquake, long-term vibration measurement using high-density instruments is one of the most critical issues for structural-health-monitoring owing to increasing deterioration and threat of future large earthquakes. Because of the high initial and running costs of traditional monitoring systems, smart-device-based measurement system is considered as a simple and easy solution. In this paper, the effectiveness of in-built sensor, data transfer via wireless local area network, data acquisition to a synchronize cloud server, and trigger function using shaking table tests were firstly examined. A measurement system including a group of sensors has been established successfully based on the “control center” from which the trigger command can be send to other sensors immediately as any sensor/sensors is/are triggered. Then, the system is applied to seismic-response and environment-vibration measurement at existing structures. Results show that the observable acceleration level of smart devices is more than 5 gal in the frequency range of 0.1 to 10 Hz. The possible sampling rate is 100 Hz. Though it is unstable, correction methods have been proposed. Continuous measurement and data transfer is possible without data loss. Dynamic properties extracted from smart-device-based system is very similar to those extracted from high-quality-sensor-based system.
      PubDate: 2017-11-17T05:52:29.752717-05:
      DOI: 10.1002/stc.2120
  • Measurement of strains by optical fiber Bragg grating sensors embedded
           into polymer composite material
    • Authors: V.P. Matveenko; I.N. Shardakov, A.A. Voronkov, N.A. Kosheleva, D.S. Lobanov, G.S. Serovaev, E.M. Spaskova, G.S. Shipunov
      Abstract: This paper presents the experimental results of strain measurements made by the fiber Bragg grating sensors embedded into polymer composite materials (PCMs). A series of performed experiments are described to demonstrate the capability of fiber optic sensors to measure strains in the case of their pronounced gradient distribution within the material, under compression and tension, at cyclic variation of strains with time and at different temperatures. A measuring technique is presented, and the results of strain measurements during the process of preparation of PCM including measurements of residual process-induced strains are discussed.The results of strain measurements made by fiber optic strain sensors (FOSS) are compared with the results of numerical modeling based on the finite element method and independent measurement data obtained with the use of a digital optical system Vic-3D and other experimental devices. The comparison made shows good agreement between the results obtained by the experimental methods and numerical simulation.The results of numerical computations demonstrate that the embedment of optical fibers in a PCM introduces perturbations in the strain distribution pattern in the vicinity of optical fibers but practically does not cause changes in the value of the strain tensor component measured by the FOSS. The conclusions about applicability range of FOSS embedded into PCM were made based upon the numerical simulation. The interrelation model between Bragg wavelength peak shift and the strain of the optical fiber in the fiber Bragg grating area for the sensor that is not affected by the environment is proposed.
      PubDate: 2017-11-09T05:40:40.029654-05:
      DOI: 10.1002/stc.2118
  • Study on self-adjustable tuned mass damper with variable mass
    • Authors: Weixing Shi; Liangkun Wang, Zheng Lu
      Abstract: Tuned mass dampers (TMDs) represent a quite mature technology for controlling human-induced vibrations of footbridges, when they are tuned to the primary structure's fundamental frequency. However, the TMD is very sensitive to even a small change in the tuning ratio. This paper proposes a novel TMD named self-adjustable variable mass TMD (SAVM-TMD), which is capable of varying its mass and retuning its frequency on the basis of the acceleration ratio between the primary system and the TMD. The accelerations are obtained from two acceleration sensors, and the frequency adjustment is achieved by using a microcontroller and actuating devices. The acceleration ratio limit value should be set in the microcontroller firstly, and when the adjustment begins, the microcontroller will retune the TMD to a reasonable frequency region, under a specific harmonic excitation. The SAVM-TMD can be regarded as a passive control device capable of adjusting its frequency. The performance of SAVM-TMD is studied via both experimental studies and numerical simulations under different pedestrian excitations. It is found that the SAVM-TMD is effective in reducing the response and improving the equivalent damping ratio of the primary system when the structural frequency changes, with little power consumption. The results obtained from the experimental studies and the numerical simulations agree with each other very well. More pedestrian vibration situations are studied in the numerical simulations, and the results also show that the SAVM-TMD has excellent performance in controlling human-induced vibrations.
      PubDate: 2017-11-09T04:40:57.294817-05:
      DOI: 10.1002/stc.2114
  • Environmental-effects-embedded model updating method considering
           environmental impacts
    • Authors: Shanglian Zhou; Wei Song
      Abstract: In structural health monitoring, one practical challenge is to separate the change of structural characteristics (e.g., natural frequency and mode shape) due to environmental impacts from those induced by actual damage. Generally, data-driven regression models are applied to remove the environmental impacts before model updating takes place. Model selection and training procedures are required in constructing these regression models, which are often subjective, prone to overfitting issue, and human errors. This paper proposes a novel physics-based Environmental-Effects-Embedded model updating method. By embedding physical mechanisms of environmental impacts into the formulation of the finite element model, the proposed method is capable of considering these impacts during the finite element model updating. A comparative numerical study is performed by applying both the Environmental-Effects-Embedded model updating method and traditional method on a pedestrian bridge model subjected to structural damage, temperature variation, and boundary condition change. Comparison between the proposed and traditional methods has demonstrated that the proposed method can offer more accurate results in localizing and quantifying the structural damage under environmental impacts.
      PubDate: 2017-10-27T04:46:31.084201-05:
      DOI: 10.1002/stc.2116
  • Effect of horizontal loading direction on performance of prototype square
           unbonded fibre reinforced elastomeric isolator
    • Authors: Thuyet V. Ngo; Sajal K. Deb, Anjan Dutta
      Abstract: Unbonded fibre reinforced elastomeric isolator (U-FREI) is lightweight and facilitates easier installation in comparison to conventional steel reinforced elastomeric isolators. Most of the previous studies were focused to investigate the behaviour of scaled models of square U-FREIs in 0° or 45° horizontal loading directions. However, the angle of incidence of earthquake to a structure may be from any directions. This paper presents influence of different loading directions (0°, 15°, 30°, and 45°) on the horizontal response of a sample prototype square U-FREI on the basis of both experimental investigation and three-dimensional finite element analysis. Mechanical properties and deformed configurations of the prototype U-FREI computed using finite element analyses are observed to be in good agreement with those obtained from experimental study. It is further observed that as the loading direction changes from 0° to 45°, the effective horizontal stiffness of U-FREI increases, whereas the damping value decreases. Thus, the seismic performance of U-FREI will also vary depending on the direction of load acting on them.
      PubDate: 2017-10-24T23:17:00.409726-05:
      DOI: 10.1002/stc.2112
  • Reliability analysis of active tendon-controlled wind turbines by a
           computationally efficient wavelet-based probability density evolution
    • Authors: Weifeng Tao; Biswajit Basu, Jie Li
      Abstract: We propose a computationally efficient stochastic framework and an associated mathematical formulation to assess the improvement in the vibration response of wind turbines with active structural controllers. Uncertainties in the turbulent wind speed as well as in the structural parameters are considered in the formulation for analyzing the 2 important (rated and cut-out) wind speed conditions. A multimodal wind turbine model based on a NREL 5-MW wind turbine model is adopted for analysis, and an active tendon controller is used to develop the stochastic framework. Dynamic interaction between the rotor blades and the supporting tower, as well as the coupling induced by the pretwist of the blades, and a collective pitch controller are considered. A time-evolving phase spectrum method together with a phase delay spectrum model is used to simulate the stochastic wind field, which is computationally less expensive. The probability density contours and the extreme value distributions of the blade tip displacements with and without the active controller are obtained by the wavelet-based probability density evolution method, followed by the computation of the corresponding failure probabilities. It is observed that the improvement in reliability and performance of the rotor blades with the controller becomes statistically more effective as the wind speed increases (e.g., significant beneficial effects are noticed from the probability distributions in terms of the spread at the cut-out wind speed).
      PubDate: 2017-10-24T23:16:28.731013-05:
      DOI: 10.1002/stc.2078
  • Development of a divergent fluid wall damper for framed structures
           subjected to dynamic loads
    • Authors: Soheil Nikpour; Farzad Hejazi, Mohd Saleh Jaafar
      Abstract: This study developed a new adaptive design for a divergent fluid wall damper (DFWD). This design decreases the dynamic vibration in reinforced concrete (RC) structures subjected to dynamic forces caused by earthquakes, wind, tsunamis, and explosions. The DFWD comprises a tank connected to the lower floor that is filled with a fluid and a plate with fins located inside the tank connected to the upper floor. The DFWD uses a bypass system mechanism that circulates fluid inside the wall damper tank through a divergent pipe and controls the fluid pressure during vibration using a double-acting valve. To evaluate the performance of the DFWD in RC-frame structures, we fabricated and experimentally evaluated a prototype of the device based on a new adjustable design. Two RC frames, a bare frame and a frame with DFWD, were cast with the same geometric specifications. These frames were then examined in terms of the time history of applied displacement with a maximum amplitude of 40 mm under the same conditions. The valves in the design of the DFWD were adjustable, and the fully open valve condition was examined. The results indicated that the failure capacity of the frame was significantly improved compared to that of the bare frame as the DFWD absorbed more dynamic force. The ductility of the RC-frame structure equipped with the DFWD was improved by almost 17.8% compared to that of the bare frame.
      PubDate: 2017-10-19T03:36:44.242065-05:
      DOI: 10.1002/stc.2108
  • Effect of hysteretic properties of SMAs on seismic behavior of
           self-centering concentrically braced frames
    • Authors: Hetao Hou; Han Li, Canxing Qiu, Yichen Zhang
      Abstract: Shape memory alloys (SMAs) exhibit nearly ideal superelastic properties when the ambient temperature is above the austenite finish temperature, which enables them to recover deformation and dissipate energy for the seismic-resisting structures. This unique hysteretic properties of SMAs indicate they are very promising in developing self-centering structures. As such, recent studies installed SMAs in concentrically braced frames (CBFs) to form SMA-based self-centering CBFs (SCCBFs) and illustrated that the structures performed excellently with controlled peak drift and eliminated residual drift upon earthquakes. SMAs show variability in the hysteretic parameters due to the difference in metal types, crystallographic structure, component ratios, and heating treatments in producing process. Thus, this necessitates an investigation into the associated effect on the seismic performance of SMA-based SCCBFs. To this end, this study selects 3 SMAs, proposes a bracing form, and installs SMA braces in the CBFs. Prior to the seismic analysis, all 3 frames are designed by an ad hoc design method. The focus of this paper is to understand the effect of hysteretic properties on the seismic behavior of SMA-based SCCBFs. Intensive nonlinear time history analyses are carried out to assess the seismic performance of these structures under frequently occurred earthquakes and design basis earthquakes. The analytical results indicate the properly designed SCCBFs are able to meet prescribed performance targets and display comparable seismic demands, irrespective of the SMA types. This study suggests that using SMAs with greater hysteretic parameters is more favorable, from the perspective of saving material consumption and controlling acceleration demands.
      PubDate: 2017-10-16T02:41:24.071983-05:
      DOI: 10.1002/stc.2110
  • Structural damage detection based on l1 regularization using natural
           frequencies and mode shapes
    • Authors: Rongrong Hou; Yong Xia, Xiaoqing Zhou
      Abstract: Conventional vibration-based damage detection methods employ the Tikhonov regularization in model updating to deal with the problems of underdeterminacy and measurement noise. However, the Tikhonov regularization technique tends to provide over smooth solutions that the identified damage is distributed to many structural elements. This result does not match the sparsity property of the actual damage scenario, in which structural damage typically occurs at a small number of locations only in comparison with the total elements of the entire structure. In this study, an l1 regularization-based model updating technique is developed by utilizing the sparsity of the structural damage. Both natural frequencies and mode shapes are employed during the model updating. A strategy of selecting the regularization parameter for the l1 regularization problem is also developed. A numerical and an experimental examples are utilized to demonstrate the effectiveness of the proposed damage detection method. The results showed that the proposed l1 regularization-based method is able to locate and quantify the sparse damage correctly over a large number of elements. The effects of the mode number on the damage detection results are also investigated. The advantage of the present l1 regularization over the traditional l2 regularization method in damage detection is also demonstrated.
      PubDate: 2017-09-29T11:14:39.415502-05:
      DOI: 10.1002/stc.2107
  • Bayesian identification of soil-foundation stiffness of building
    • Authors: Nima Shirzad-Ghaleroudkhani; Mojtaba Mahsuli, S. Farid Ghahari, Ertugrul Taciroglu
      Abstract: A probabilistic method is presented for identifying the dynamic soil-foundation stiffnesses of building structures. It is based on model updating of a Timoshenko beam resting on sway and rocking springs, which respectively represent the superstructure and the soil-foundation system. Unlike those previously employed for this particular problem, the proposed method is a Bayesian one, which accounts for the prevailing uncertainties due to modeling and measurement errors. As such, it yields the probability distribution of the system parameters as opposed to average/deterministic values. In this approach, the joint probability density function of the parameters that control the flexible-base Timoshenko beam model, together with the fundamental natural frequency and mode shape of the system, forms the prior distribution. Using Bayes' theorem, a posterior distribution is obtained by updating the prior distribution with a sparsely measured mode shape and frequency. The most probable realizations of the system parameters are then determined by maximizing the posterior distribution. For this purpose, first- and second-order derivatives of the objective function are analytically computed via direct differentiation. The proposed method is verified using a synthetic example. Additionally, sensitivity analyses are carried out on both the system parameters and standard deviations of the sources of error. Subsequently, the proposed method is applied to real-life data recorded at the Millikan Library building, which is located at the California Institute of Technology campus in Pasadena, California, and the results are compared with a previous deterministic study.
      PubDate: 2017-09-25T05:40:48.020962-05:
      DOI: 10.1002/stc.2090
  • Operational modal identification and finite element model updating of a
           coupled building following Bayesian approach
    • Authors: Jun Hu; Heung-Fai Lam, Jia-Hua Yang
      Abstract: This paper presents a comprehensive study of the full-scale ambient vibration test, modal analysis, finite element (FE) modeling, and model updating of a coupled building in Hong Kong. The coupled building comprised a main part and a complementary part. To capture the dynamic properties of the building, a 21-setup ambient vibration test was designed and conducted. The modal parameters of each setup were identified following a fast Bayesian fast Fourier transform approach, and the partial mode shapes from the different setups were assembled following the least squares method. The identified modal parameters were analyzed and discussed in detail, revealing certain features of the coupling effects between the main and complementary parts. To determine the equivalent Young's moduli of various structural components, an FE model of the coupled building was developed and updated with the identified modal parameters. The Bayesian approach was followed to explicitly handle the uncertainties induced by modeling error and measurement noise. To ensure the model updating method is applicable even in unidentifiable cases, a Markov chain Monte Carlo simulation was employed in the proposed method to generate samples for approximating the posterior probability density functions of uncertain model parameters. The close match between the modal parameters calculated from the updated FE model and those identified from the measured time-domain data verified the validity of the proposed FE model. This study provides valuable experience and information for the development of structural model updating and structural health monitoring of building systems.
      PubDate: 2017-09-25T05:36:45.982305-05:
      DOI: 10.1002/stc.2089
  • Damping and frequency of a model cable attached with a pre-tensioned shape
           memory alloy wire: Experiment and analysis
    • Authors: Haijun Zhou; Shengke Qi, Guozao Yao, Linbai Zhou, Limin Sun, Feng Xing
      Abstract: This study proposed a system consisting of a stay cable transversely attached with a pre-tensioned shape memory alloy (SMA) wire. Cyclic tension loading test of pre-tensioned 0.5-mm-diameter NiTi wire was conducted first. The effective modulus and energy dissipation per unit volume were obtained from the tested hysteretic loops of the pre-tensioned SMA wire. The effects of prestrain on the energy dissipation and effective modulus of the SMA wire was discussed. Preliminary fatigue testing of 0.5-mm- and 1.0-mm-diameter SMA wires was carried out, and a vibration mitigation experiment with a model stay cable transversely attached with a pre-tensioned SMA wire was then conducted. Both the first and the second in-plane mode vibrations were tested. The effects of the SMA wire installation location and pre-tension level on the frequency and damping ratio of the model-cable-SMA-wire system were discussed. The test results confirmed there was an optimal pre-tension level of the SMA wire for maximum mode damping, and in this test, the maximum damping ratio was larger than 0.50%. A preliminary linearized theoretical study was also carried out to further explore the dynamics of the model-cable-SMA-wire system. The comparison results showed good agreement of theoretical frequency and damping to the tested version. The study confirmed the potential application of pre-tensioned SMA wires as cross-ties for stay cable vibration mitigation.
      PubDate: 2017-09-25T05:31:04.503597-05:
      DOI: 10.1002/stc.2106
  • Partial mass isolation system for seismic vibration control of buildings
    • Authors: Hamidreza Anajafi; Ricardo A. Medina
      Abstract: In a previous study, the authors studied a partial mass isolation (PMI) system that through isolating different portions of story masses can provide a building with multiple inherent vibration suppressors. It was shown that the PMI strategy with isolated mass ratios (IMRs) of 0.05 or 0.90 could perform as effectively as an equivalent tuned mass damper or a base isolation system, respectively. In the present paper, the PMI system is examined in structural models with different fundamental periods. PMI configurations in a wide IMR range of (0.05:0.025:0.90) are optimized illustrating that applying an IMR of 0.25–0.50 can provide an efficient system, simultaneously satisfying the constraints related to different performance objectives (i.e., mitigating the overall building seismic responses and controlling isolated components' (ICs) responses while integrating these components into the building architecture). Simulation results reveal that using identical ICs at different stories, which have the advantage of facilitating the design and construction of the system, can lead to a near-optimal solution. It is also demonstrated that in terms of the spatial distribution of ICs, an adequate seismic performance improvement can be achieved by allocating ICs only at a subset of upper stories (e.g., top half stories), which can further simplify the PMI systems' construction.
      PubDate: 2017-09-25T05:17:24.644268-05:
      DOI: 10.1002/stc.2088
  • Wireless structural control using stochastic bandwidth allocation and
           dynamic state estimation with measurement fusion
    • Authors: Benjamin D. Winter; R. Andrew Swartz
      Abstract: Wireless sensor networks are becoming more popular for structural monitoring because of their low installation costs; in addition, coupling structural control with wireless data acquisition can also yield advantages. However, these systems have limited communication bandwidth, limiting their effectiveness as the number of devices in control networks grows large if centralized control approaches are used. Traditional methods for collocating data in wireless structural control network rely on time-budgeted bandwidth or spatial decentralization, where the network is divided into smaller subnetworks. These methods are largely static and typically do not take into account any measure of data quality to prioritize transmissions. This study presents a dynamic approach for bandwidth allocation in wireless structural control networks that relies on an application-specific, autonomous, and controller-aware, carrier sense multiple access with collision detection protocol. Stochastic parameters are derived to strategically alter back-off times in the carrier sense multiple access with collision detection algorithm based on nodal observability and output estimation error. Inspired by data fusion approaches, this paper presents 2 different methods for neighborhood state estimation using a dynamic form of measurement-only fusion. Upon receiving data from the contended wireless medium, each wireless unit fuses incoming data using a precalculated static Kalman gain matrix for the corresponding dynamic neighborhood. Onboard, each wireless unit contains a library of Kalman gain matrices, to accommodate any possible set of communicated data. Both numerical simulations and small-scale laboratory experimental results are presented.
      PubDate: 2017-09-20T06:40:59.331015-05:
      DOI: 10.1002/stc.2104
  • A semi-baseline damage identification approach for complex structures
           using energy ratio correction technique
    • Authors: Behrouz Alem; Ali Abedian
      Abstract: Because damage identification results based on the Lamb waves propagation approach can be influenced by varying environmental and operational conditions, development of a robust monitoring system with no need of the prior measured data of the structure has gained much attention recently. The instantaneous baseline damage detection technique is one of the promising methods that overcome the mentioned obstacles. For this, the material properties, electromechanical characteristics, and the geometric features must be identical. Also, sensor distances in similar paths and the geometric dimensions of the transducers must be the same. So, implementing the instantaneous baseline damage identification in complex structures is rather complicated due to the inherent non-homogeneities involved. To ease the complexity, this article proposes a semi-instantaneous baseline damage identification approach by modifying an existing instantaneous baseline method. This is used to detect and characterize fatigue cracks that initiate around the rivet holes of lap joint structures. In this method, an active sensing network is mounted on the lap joint, and a robust and effective feature called energy ratio change is extracted from the collected time-domain signals using the wavelet transform. The introduced “identicality coefficient” for all the sensing paths in pristine condition of the structure is obtained and used to remove any inequalities that may occur to the signals of each path. The obtained results show that the proposed method can detect fatigue cracks around the lap joint rivet holes and estimate the crack size. An experiment as well as numerical simulations is performed to verify the method.
      PubDate: 2017-09-15T06:32:15.293467-05:
      DOI: 10.1002/stc.2103
  • Experimental study of local and modal approaches to active vibration
           control of elastic systems
    • Authors: A.K. Belyaev; A.V. Fedotov, H. Irschik, M. Nader, V.A. Polyanskiy, N.A. Smirnova
      Abstract: Two different methods, local and modal, are suggested to control systems with distributed parameters, each of them having its own advantages and drawbacks. The aim of the present research is to carry out experiments aiming in comparison of these 2 methods for the problem of suppression of forced bending vibrations of a thin metal beam. Two pairs of piezoelectric sensors and actuators are attached to the beam in each control system considered. Their locations are chosen so as to provide the most efficient measurement and excitation of the first and second vibration modes of the beam. Frequency methods of the automatic control theory are employed to design stable control systems that can efficiently suppress bending vibrations of the beam with the first and second resonance frequencies. As a result, control systems with the desired performance are created on the basis of both local and modal methods. The obtained modal system works efficiently for both resonances, whereas the local systems demonstrate appropriate performance either at the first or at the second resonance frequency only. This difference is due to the fact that in the case of modal control, each control loop corresponds to a particular vibration mode and can be designed to provide optimal performance at the required frequency. The performed benchmark study demonstrates the advantages of the modal method over the local one for the cases where it is necessary to suppress vibrations in the frequency range that contains more than one resonance frequency of the control object.
      PubDate: 2017-09-15T06:27:12.012802-05:
      DOI: 10.1002/stc.2105
  • Adaptive constrained unscented Kalman filtering for real-time nonlinear
           structural system identification
    • Authors: Andrea Calabrese; Salvatore Strano, Mario Terzo
      Abstract: The unscented Kalman filter (UKF) is often used for nonlinear system identification in civil engineering; nevertheless, the application of the UKF to highly nonlinear structures could not provide accurate results. In this paper, an improvement of the UKF algorithm has been adopted. This methodology can consider state constraints, and it can estimate the measurement noise covariance matrix. The results obtained adopting a modified UKF have been compared to the ones obtained using the UKF for parameter estimation of a single degree of freedom nonlinear hysteretic system. The second part of this work shows results of an experimental activity on a base-isolated prototype structure. Both numerical and experimental results underline that the adopted algorithm produces better state estimation and parameter identification than the UKF, being capable of taking into account parameter boundaries. The adopted algorithm is more robust than the standard UKF in the case of measuring noise variation.
      PubDate: 2017-09-05T23:11:31.637249-05:
      DOI: 10.1002/stc.2084
  • Optimal tuned mass-damper-inerter (TMDI) design for seismically excited
           MDOF structures with model uncertainties based on reliability criteria
    • Authors: A. Giaralis; A.A. Taflanidis
      Abstract: The tuned mass-damper-inerter (TMDI) is a recently proposed linear passive dynamic vibration absorber for the seismic protection of buildings. It couples the classical tuned mass damper (TMD) with an inerter, a two-terminal device resisting the relative acceleration of its terminals, in judicial topologies, achieving mass-amplification and higher-modes-damping effects compared to the TMD. This paper considers an optimum TMDI design framework accommodating the above effects while accounting for parametric uncertainty to the host structure properties, modeled as a linear multi degree of freedom system, and to the seismic excitation, modeled as stationary colored noise. The inerter device constant, acting as a TMD mass amplifier, is treated as a design variable, whereas performance variables sensitive to high-frequency structural response dynamics are used to account for the TMDI influence to the higher structural modes. Reliability criteria are adopted for quantifying the structural performance, expressed through the probability of occurrence of different failure modes related to the trespassing of acceptable thresholds for the adopted performance variables: floor accelerations, interstory drifts, and attached mass displacement. The design objective function is taken as a linear combination of these probabilities following current performance-based seismic design trends. Analytical and simulation-based tools are adopted for the efficient estimation of the underlying stochastic integral defining the structural performance under uncertainty. A 10-story building under stationary Kanai-Tajimi stochastic excitation is considered to illustrate the design framework for various TMDI topologies and attached mass values. It is shown that the TMDI achieves enhanced structural performance and robustness to building and excitation uncertainties compared to same mass/weight TMDs.
      PubDate: 2017-09-05T23:06:27.430928-05:
      DOI: 10.1002/stc.2082
  • Optimal design of semiactive MR-TLCD for along-wind vibration control of
           horizontal axis wind turbine tower
    • Authors: Saptarshi Sarkar; Arunasis Chakraborty
      Abstract: Present study aims to address the design of smart vibration control scheme for horizontal axis wind turbine tower using magneto-rheological tuned liquid column damper. With this in view, a reduced order model of the blade-tower system is used, considering centrifugal stiffening and gravitational effects that lead to time-dependent dynamic stiffness matrix. Aerodynamic load on the blades is modeled using blade element momentum theory. Semiactive control law in linear quadratic regulator framework is developed to mitigate the along-wind vibration of the tower. To implement the control law, multiblade coordinate transformation is adopted that converts the system matrices in the nonrotating framework to tackle its time dependency. The performance of the proposed control algorithm is demonstrated using numerical simulations with and without controller. Clipped optimality of the control force is imposed to keep the parameters of magneto-rheological tuned liquid column damper in the feasible range. Finally, sensitivity analysis is carried out to demonstrate the performance envelope of the proposed control algorithm for different operational scenario. Results presented in this paper clearly demonstrate that the proposed algorithm can be employed for effective along-wind vibration control of large HWAT tower.
      PubDate: 2017-09-05T23:01:45.5231-05:00
      DOI: 10.1002/stc.2083
  • Wave-based SHM of sandwich structures using cross-sectional waves
    • Authors: Christophe Droz; Olivier Bareille, Jean-Pierre Lainé, Mohamed N. Ichchou
      Abstract: The identification of structural damage in composite waveguides is a critical issue in aerospace and transportation industries. Frequently, these structures involve periodic patterns or dissipative components that considerably reduce the range, robustness, and available bandwidth of ultrasonic structural health monitoring techniques. On the other hand, wave-based methods provide more accurate information on a defect's type, size, and location than modal analysis techniques. This paper focuses on a low-frequency wave-based method for structural integrity assessment of complex waveguides. The wave finite element method is employed to compute the dispersion curves of non-standard cross-sectional waves exhibiting increased strain energy. The spectral results are used to analyse the diffusion of guided elastic waves through representative localized defects in a laminated sandwich panel. To validate the diffusion model, reflection and transmission coefficients are determined for several wave pulses on typical defects using time-domain virtual experiments and cross-sectional energy acquisition. Results demonstrate that using cross-sectional waves provides a sensitivity to damage up to 2.8× higher than flexural waves in the low-frequency range. These results are explained by the presence of local resonances within the cross section, producing wavelengths in the transverse direction of propagation. These waves may prove suitable for cost-effective structural health monitoring applications because they can travel long distances through heterogeneous and periodic structures.
      PubDate: 2017-09-05T04:07:05.778806-05:
      DOI: 10.1002/stc.2085
  • Optimal design of double-skin façades as vibration absorbers
    • Authors: Giovanni Pipitone; Giorgio Barone, Alessandro Palmeri
      Abstract: In this paper, several layouts of double-skin façades (DSFs) used as mass dampers to reduce the vibrations in structures under seismic events are analyzed. First, the mathematical coupled problem is studied considering a non-classically damped system excited by a set of accelerograms. The design problem aims to determine the optimal values of four parameters, namely, the flexural stiffness and damping of the DSF panel and the stiffnesses of the elements that connect the DSF to the primary structure. Second, four objective functions are investigated. Two of these functions aim to minimise, respectively, the variance of displacements and accelerations of the primary structure for each earthquake record. The remaining two, instead, minimise the average of the displacements and accelerations calculated for all the selected accelerograms. Finally, numerical analyses are performed on a 6-storey building and four DSF designs are proposed. The particle swarm optimisation is used to estimate the optimal parameters. Comparisons among the DSF layouts are presented in terms of minima of the objective functions and in terms of energy transfer functions, and a simplified design method for the connection elements is discussed.
      PubDate: 2017-08-25T05:31:07.490956-05:
      DOI: 10.1002/stc.2086
  • Using the signal-to-noise ratio of GPS records to detect motion of
    • Authors: Ioulia Peppa; Panos Psimoulis, Xiaolin Meng
      Abstract: Although major breakthroughs have been achieved during the last decades in the use of Global Positioning System (GPS) technology on structural health monitoring, the mitigation of the biases and errors impeding its positioning accuracy remains a challenge. This paper tests an alternative approach that can increase the reliability of the GPS system in structural monitoring by using the spectral content of the signal-to-noise ratio (SNR) of GPS signals to detect frequencies of antenna vibrations. This approach suggests the potential of using SNR data analysis as a supplement to low-quality positioning solution or as a near real-time alert of excessive vibration proceeding the position solution calculation. Experiments, involving a GPS antenna subjected to vertical vibrations of 0.4- to 4.5-cm amplitude at a range of frequencies between 0.007 and 1 Hz, examine the dynamic multipath-induced SNR response corresponding to the antenna motion. Synchronised fluctuations in the SNR time series were observed to reflect the antenna motion and their spectral content to include the frequencies of motion. SNR records from the GPS monitoring of the Wilford suspension bridge were used to validate the SNR sensitivity to controlled vibrations of the bridge deck. The natural frequency of 1.64 Hz was extracted from SNR measurements using spectral analysis on a 6-mm amplitude vibration, and the frequency of the semistatic displacement (∼0.02 Hz) was revealed in the SNR records permitting, after appropriate filtering, the estimation of a few millimetre semistatic displacement from the GPS time series without the need for any other sensor.
      PubDate: 2017-08-25T05:27:08.299478-05:
      DOI: 10.1002/stc.2080
  • The wavelet transform as a Gaussian process for damage detection
    • Authors: Konstantinos Balafas; Anne S. Kiremidjian, Ram Rajagopal
      Abstract: This paper presents a novel statistical model for the wavelet transform of the acceleration response of a structure based on Gaussian process theory with applications to earthquake damage detection. The proposed model considers the wavelet coefficients at each time sample as a realization of a Gaussian process that depends solely on the damage state of the structure. Damage is then detected by identifying changes in the distribution of the model parameters. The model is purely data driven; it requires no prior knowledge of the structural properties, and all the parameters are learned directly from the measured data. The estimation of the model parameters is transformed to an optimization problem and the convexity of the objective function is investigated. An efficient algorithm for the parameter estimation is proposed and tested for accuracy. Finally, the statistical model is applied to the data obtained from a series of shake table experiments conducted at the University of Nevada, Reno. The results of the application of the proposed statistical model and implementation methodology are presented, and the validity of the model assumptions and damage detection capability are illustrated. A damage detection scheme based on the model parameters and statistical hypothesis testing is proposed and evaluated using the experimental dataset.
      PubDate: 2017-08-25T05:26:06.486597-05:
      DOI: 10.1002/stc.2087
  • Multiresolution Bayesian nonparametric general regression for structural
           model updating
    • Authors: Ka-Veng Yuen; Gilberto A. Ortiz
      Abstract: A novel Bayesian method, namely, multiresolution Bayesian nonparametric general regression (MR-BNGR), is proposed for structural model updating using modal data, that is, identified natural frequencies and mode shapes. In this method, the model updating problem is posed as a non-linear regression problem from the modal data to the structural parameters. The proposed method is nonparametric, so it does not require an explicit functional form of this mapping. Instead, it utilizes the input–output data to adaptively model its relationship. Its multiresolution nature allows to zoom into the significant region in stages to search the optimal point. Furthermore, the estimation uncertainty can be quantified. Training of the MR-BNGR network is very straightforward and computationally economical. Examples of a 20-storey shear building and a three-dimensional truss are provided to demonstrate the capabilities of the proposed MR-BNGR method, and the results confirm the effectiveness of this novel method.
      PubDate: 2017-08-22T04:05:59.036547-05:
      DOI: 10.1002/stc.2077
  • Ambient vibration test-based deflection prediction of a posttensioned
           concrete continuous box girder bridge
    • Authors: Yongding Tian; Panjie Li, Jian Zhang
      Abstract: Ambient vibration test generally only outputs basic modal parameters including frequencies, damping ratios, and unscaled mode shapes, which cannot directly support decision making of structural maintenance and management. In this article, structural deep-level parameters including unscaled and scaled flexibility identification of a posttensioned concrete continuous box girder bridge are studied by performing ambient vibration test, which is able to predict structural deflections by multiplying the static load with the identified flexibility. Ambient vibration test of the bridge and basic modal identification are firstly performed. Then, the method of unscaled flexibility identification is proposed by investigating the relationship between the frequency response function estimated from ambient test data and the analytical one. Finally, a mass-changing strategy is utilized to identify the scaled flexibility from output-only data, in which the key issue is to identify mass-normalized scaling factors by performing ambient vibration tests of tested structure before and after changing its mass. Numerical simulation of a simply supported beam and field test of a three-span bridge has been conducted to verify the capability and reliability of the proposed method. The good agreement between the predicted deflections from the identified flexibility and those measured from the static test successfully illustrates the effectiveness of the proposed method.
      PubDate: 2017-08-22T04:05:40.112582-05:
      DOI: 10.1002/stc.2070
  • An improved equivalent force control algorithm for hybrid seismic testing
           of nonlinear systems
    • Authors: Zhen Wang; Bin Wu, Guoshan Xu, Oreste S. Bursi
      Abstract: The equivalent force control (EFC) algorithm is a hybrid seismic testing method based on both an implicit integration algorithm and force feedback control. As it performs the computation of the numerical substructure with a fixed sampling number and some evaluations are not necessary, the EFC method is believed to be time-consuming for seismic testing of nonlinear systems with complicated numerical substructure model. In order to tackle this problem, the EFC method with varying sampling number (vEFC) has been conceived. The analysis of the vEFC method has shown that 2 traditional pseudodynamic testing (PDT) variants on the basis of implicit time integration schemes and numerical iteration, that is, the IPDT1 method and the IPDT2 method, can be recovered from the vEFC method. Moreover, the advantages of the vEFC method, such as fast response rate and compensation for control errors and possible slippage, are demonstrated.
      PubDate: 2017-08-15T03:06:04.120635-05:
      DOI: 10.1002/stc.2076
  • Modeling method for predicting seepage of RCC dams considering
           time-varying and lag effect
    • Authors: Bowen Wei; Minghan Gu, Huokun Li, Wei Xiong, Zhenkai Xu
      Abstract: This paper deduces the expressions for equivalent water level and equivalent rainfall. Different factors and methods were considered, such as the lag characteristics of the reservoir water level and rainfall on the seepage of roller-compacted concrete dams, combining the characteristics of layered pouring of the dam body, the time-varying effects of the factors affecting dam seepage, statistical regression, multilevel recursive method, and the numerical analysis method of the model with its corresponding implementation procedures. The safety monitoring model of spatial seepage, which can comprehensively reflect the seepage characteristics of roller-compacted concrete dams is set up. The engineering example shows that this model is obviously better than the statistical model in terms of fitting accuracy and searching ability. The forecast results of this model closely approach the actual monitoring state of the dam and can also be applied to the analysis of the foundation and bypass seepage of dams.
      PubDate: 2017-08-11T04:45:45.574555-05:
      DOI: 10.1002/stc.2081
  • A statistical model of deformation during the construction of a concrete
           face rockfill dam
    • Authors: Yuqun Shi; Juanjuan Yang, Jielian Wu, Jinping He
      Abstract: Monitoring data collected during dam construction are important in complete series of monitoring data. These data play a significant role in dam safety monitoring and the analysis of structural conditions. The traditional statistical model of the deformation of a concrete face rockfill dam (CFRD) with filling height and time factors is associated with serious multicollinearity issues during the construction phase. This study uses the Longbeiwan CFRD as an engineering model, and the internal settlement of the dam is the research focus. The traditional statistical model of deformation includes internal settlement data from the construction period and the filling height factor. Subsequently, the filling height component of the statistical model is established, and an improved statistical model is proposed with additional factors not included in the traditional statistical model. The model analysis indicates that the improved statistical model can effectively eliminate or reduce multicollinearity issues between the filling height and time factors in the traditional statistical model. The model analysis also provides a new and reasonable modeling approach for quantitatively analyzing deformation monitoring data during CFRD construction.
      PubDate: 2017-08-08T05:16:07.827469-05:
      DOI: 10.1002/stc.2074
  • Identification framework for cracks on a steel structure surface by a
           restricted Boltzmann machines algorithm based on consumer-grade camera
    • Authors: Yang Xu; Shunlong Li, Dongyu Zhang, Yao Jin, Fujian Zhang, Na Li, Hui Li
      Abstract: This paper proposes an identification framework based on a restricted Boltzmann machine (RBM) for crack identification and extraction from images containing cracks and complicated background inside steel box girders of bridges. The original images that include fatigue crack and other background information are obtained by a consumer-grade camera inside the steel box girder. The original images are cut into a number of elements with small size as the input dataset, and a state representation vector is artificially labeled to every image element used for the crack identification. A deep learning model or network consisting of multiple processing RBM layers to learn the abstract features is constructed to match the input image elements with corresponding state representation vectors. Next, a three-layer RBM with 500; 500; and 2,000 hidden units is trained as the hidden layers in the deep learning network. A contrastive divergence learning algorithm is employed for training the deep network to update and obtain the optimal parameters (i.e., the biases and weights). The new input image elements labeled as crack are sorted out and assembled to form an output image. A deep network is modeled through the consumer-grade camera images containing cracks and complicated background information using the proposed approach. The accuracy and ability to identify cracks from new images with different resolutions using the trained deep network are validated. Furthermore, effects of element size on reconstruction error and identification accuracy are investigated. The results show that there exists optimal element size; that is, too small and too large element sizes both increase the reconstruction error and decrease the identification accuracy.
      PubDate: 2017-08-04T06:41:28.641713-05:
      DOI: 10.1002/stc.2075
  • Performance-based seismic design of multistory frame structures equipped
           with crescent-shaped brace
    • Authors: Omar Kammouh; Stefano Silvestri, Michele Palermo, Gian Paolo Cimellaro
      Abstract: The primary objective of the “performance-based seismic design” is to provide stipulated seismic performances for building structures. However, a certain degree of design freedom is needed for matching a specific seismic response. This design freedom is not obtainable by the conventional lateral resisting systems because their stiffness and strength are coupled. Here, we put emphasis on the role of the unconventional lateral resisting systems in adding more flexibility to the design. In this paper, we seek to explore the seismic design of moment-resisting frame structures equipped with an innovative hysteretic device, known as “crescent-shaped brace.” One conspicuous feature of this device is its distinctive geometrical configuration, which is responsible for the enhanced nonlinear force-displacement behavior exhibited by the device. A new performance-based approach for the seismic design of the crescent-shaped brace is proposed. The performance of the device is evaluated, and its application in multistory shear-type structures is investigated. Two case studies were established to illustrate the design methodology. The first is a new two-story RC structure, and the second is an existing three-story RC structure. Nonlinear time history and pushover analyses are performed to evaluate the behavior of the controlled structures. The analyses show that for each of the two case studies, the acceleration–displacement capacity spectrum conforms to the performance objectives curve. This finding confirms the validity of the proposed design approach and the effectiveness of the new hysteretic device in resisting lateral forces.
      PubDate: 2017-08-04T06:26:03.300826-05:
      DOI: 10.1002/stc.2079
  • Energy regenerative tuned mass dampers in high-rise buildings
    • Authors: Wenai Shen; Songye Zhu, You-Lin Xu, Hong-ping Zhu
      Abstract: This study investigates a novel energy regenerative tuned mass damper (TMD) with dual functions—vibration control and energy harvesting—in a high-rise building. The energy regenerative TMD consists of a pendulum-type TMD, an electromagnetic damper, and an energy-harvesting circuit. A simple optimal design method for energy regenerative TMD is proposed, in which a fixed duty-cycle buck-boost converter is employed as the energy-harvesting circuit to optimize the energy-harvesting efficiency and damping coefficient of the TMD. This study is organized into two main tasks: (a) characterizing and modeling the energy regenerative TMD through laboratory testing of a scaled prototype and (b) evaluating the vibration control and energy-harvesting performance of the energy regenerative TMD when applied in a 76-story wind-excited benchmark building in consideration of the nonlinearities in the energy regenerative TMD. The simulations reveal that the harvested electric power averages from hundreds of watts to kilowatts level when the mean wind speed ranges 8–25 m/s. Meanwhile, the building vibration is mitigated with the control performance comparable to the optimally designed passive TMD in a wide range of wind speed. The results in this study clearly demonstrate the effectiveness of the dual-function energy regenerative TMD when applied to building structures.
      PubDate: 2017-07-28T06:23:29.611364-05:
      DOI: 10.1002/stc.2072
  • Wavelet energy ratio index for health monitoring of hysteretic dampers
    • Authors: Elisabet Suarez; Amadeo Benavent-Climent, Ruben Molina-Conde, Antolino Gallego
      Abstract: This paper presents new contributions to evaluate the damage suffered on a particular type of hysteretic damper called web plastifying damper (WPD) for the passive control of structures subjected to earthquakes. WPDs consist of several I-section steel segments arranged to form a brace-type structural element. Energy input by the earthquake is dissipated by the WPD through plastic deformations of the web of the I-sections. These devices, properly installed in reinforced concrete test models, were tested under successive seismic simulations of increasing magnitude with a shaking table. To assess the damage of the web of the I-section after each seismic simulation, a new damage index called wavelet energy ratio (WER) was developed; it uses the signals collected by piezoelectric sensors in simple vibration tests. The index is based on wavelet package decomposition and energy calculation of properly chosen wavelet coefficients. It was correlated with a mechanical energy-based damage index—ID—proposed in past research, which has proven to accurately characterize the level of damage yet requires costly instrumentation to acquire the load–displacement curve needed for its computation. The experiments reported in this paper demonstrate a good correlation between WER and ID indices in a realistic seismic loading scenario. On the basis of this correlation, it is possible to estimate ID indirectly from the WER, which involves much simpler and less expensive instrumentation, easily applicable for in situ continuous monitoring of the dampers.
      PubDate: 2017-07-28T06:21:38.987513-05:
      DOI: 10.1002/stc.2071
  • Multisource information fusion-based approach diagnosing structural
           behavior of dam engineering
    • Authors: Huaizhi Su; Zhiping Wen, Xiaoran Sun, Xiaoqun Yan
      Abstract: Considering the effect of many factors on structural behavior, the diagnosing problem on structural behavior of dam engineering is investigated. Dempster–Shafer theory of evidence (DST) and set pair theory (SPT) are combined to fuse the multisource space–time information on dam safety. The structural behavior of dam engineering is identified and its development is forecasted by implementing the information fusions with 3 levels, namely, data fusion, feature fusion, and decision fusion. First, a multisource information fusion system on dam safety is built and an information fusion-based flowchart is presented to diagnose the dam structural behavior. Second, the batch estimation algorithm is adopted to implement the data fusion on same type information. Third, DST and SPT are applied to the decision fusion on heterogeneous information of dam safety. The index connection number and partial connection number in SPT are introduced to determine the basic probability assignment in DST and identify the dam structural behavior, respectively. Last, one actual dam undergoing structural reinforcements is taken as an example. Its structural behavior is diagnosed, and the reinforcement effect is assessed. It is indicated that the proposed approach is more suitable to be used to evaluate the safety status and reinforcement effect of dangerous dam.
      PubDate: 2017-07-28T06:16:09.773851-05:
      DOI: 10.1002/stc.2073
  • Hybrid simulation of structural systems with online updating of concrete
           constitutive law parameters by unscented Kalman filter
    • Authors: Zhu Mei; Bin Wu, Oreste S. Bursi, Ge Yang, Zhaoran Wang
      Abstract: Online model updating in hybrid simulation (HS) can represent an effective technique to reduce modeling errors of parts numerically simulated, that is, numerical substructures, especially when only a few critical components of a large system can be tested, that is, physical substructures. As a result, in an enhanced HS with online model updating, parameters of constitutive relationship can be identified based on experimental data provided by physical substructures and updated in numerical substructures. This paper proposes a novel method to identify constitutive parameters of concrete laws with unscented Kalman filter (UKF). In order to implement UKF, parts of the source codes of the OpenSEES software were modified to compute estimated measurements. Prior to experimental HS, a parametric study of UKF constitutive law parameters was conducted. As a result, the effectiveness of the UKF combined with OpenSEES was validated through numerical simulations, a monotonic loading test on a concrete column and real-time HSs of a reinforced concrete frame run with both standard and model-updating techniques based on UKF.
      PubDate: 2017-07-27T02:16:05.522309-05:
      DOI: 10.1002/stc.2069
  • Active detection of block mass and notch-type damages in metallic plates
           using a refined time-reversed Lamb wave technique
    • Authors: Jitendra Kumar Agrahari; Santosh Kapuria
      Abstract: A recently proposed refined time-reversed Lamb wave method for baseline-free damage detection is tested experimentally for detecting block mass and notch-type damages in isotropic plates. The experimental results were compared with finite element simulations. The frequency of best reconstruction has been determined experimentally for the actuator–plate–sensor system by performing the time reversal process for a range of frequency, which is found to be very different from the sweet spot frequency exciting a single mode, hitherto recommended for improving the performance of the time reversal process-based techniques. It is shown that the damage indices (DIs) computed by using the conventional main wave packet of the reconstructed signal are less sensitive to the presence of damage, which is consistent with some recently reported experimental results by other groups. The present method with extended wave packet shows excellent sensitivity to damage for both block mass and notch-type damages and also ensures a low threshold for the undamaged case when used at the best reconstruction frequency. The refined DIs reflect the true severity of damage. It was observed that a putty on the plate has no significant change in the DIs in the present method, whereas a baseline method would identify it as a damage due to very significant scattering by the putty.
      PubDate: 2017-07-27T02:06:34.143166-05:
      DOI: 10.1002/stc.2064
  • Free parameter search of multiple tuned mass dampers by using artificial
           bee colony algorithm
    • Authors: Ali Bozer; Şaban S. Özsarıyıldız
      Abstract: In optimization of multiple tuned mass dampers (MTMDs), certain restrictions or preconditions such as uniform distribution of stiffness, mass, or frequency spacing had been applied for simplification, but in turn, solution of individual stiffness and damping parameters are not the true optima. The main purpose of this paper is to obtain the true optima of individual stiffness and damping parameters of MTMD system. In the proposed method, parameters of TMD units are treated as free search optimization variables, and an efficient optimization algorithm, namely, artificial bee colony algorithm has been utilized in obtaining optimum parameters of MTMDs. Performance proposed method with respect to uncontrolled structure is verified through numerical analyses and compared with other reported methods. Comparisons show a superior performance of proposed approach. The basic properties of optimum design, the effectiveness, and robustness with respect to number of dampers are also discussed.
      PubDate: 2017-07-27T02:00:28.086227-05:
      DOI: 10.1002/stc.2066
  • Structural control with tuned inertial mass electromagnetic transducers
    • Authors: Takehiko Asai; Yoshikazu Araki, Kohju Ikago
      Abstract: This paper investigates the validity of the tuned inertial mass electromagnetic transducer (TIMET) applied to building structures subjected to seismic motions. The TIMET is a device inspired by two innovative structural control devices proposed recently, that is, tuned viscous mass damper and electromagnetic transducer. The TIMET consists of a spring, an inertial mass produced by a ball screw mechanism, and an electromagnetic transducer part composed of a motor and an electrical circuit. The stiffness of the spring is tuned such that the inertial mass resonates with the vibrating building. This makes the motor installed in parallel with the inertial mass run up in an efficient way, and the vibration energy is converted to electrical energy effectively. As a result, vibration of the building decays fast and electrical energy is stored. This generated energy that is reusable for the self-powered control systems, structural health monitoring, emergency power source, and so on. In this paper, through numerical simulation studies employing the scaled three-story building model proposed for benchmark studies, the vibration reduction and energy harvesting capabilities of the TIMET is explored and the application potentiality to civil structures is discussed.
      PubDate: 2017-07-26T04:13:35.333149-05:
      DOI: 10.1002/stc.2059
  • Investigation of wind load on 1,000 m-high super-tall buildings based on
           HFFB tests
    • Authors: Bo Li; Qingshan Yang, Giovanni Solari, Di Wu
      Abstract: This paper studies the wind load on 1,000 m-high super-tall buildings and provides basic reference for design, including the utilization of passive and active control devices. High-frequency force balance wind tunnel tests of super-tall buildings with different height are carried out to investigate the effects of building height and wind flow on the wind load. Both monsoon and typhoon climate wind flows are simulated based on target models suggested in literatures. The simulation of typhoon climate wind flows is carried out by a newly developed technique. The analysis of the experimental results confirms that the aerodynamic force is very sensitive to both building height and wind flow. In monsoon climate, the turbulence intensity decreases on increasing the height above ground. Thus, on increasing the building height, vortex shedding becomes increasingly intense and excites stronger structural vibrations in the across-wind direction, though the across-wind fluctuating overturning moment coefficient is almost the same. In typhoon climate, both the mean and the fluctuating overturning moment coefficients increase with the building height. This is mainly caused by the decreasing mean wind speed. The vortex excitation becomes weaker on increasing the building height, and this phenomenon is different from that observed in the monsoon climate. In order to better explain vortex-shedding excitation, a new parameter referred to as the characteristic turbulence intensity is defined herein as a weighted mean value of the turbulence intensity in the range of the building height. It provides a robust interpretation of the vortex excitation of super-tall buildings located in different wind flow and climate conditions.
      PubDate: 2017-07-20T03:37:06.803706-05:
      DOI: 10.1002/stc.2068
  • Enhanced hybrid active tuned mass dampers for structures
    • Authors: Liyuan Cao; Chunxiang Li
      Abstract: Based on the recent research by Li and Cao in 2015, now taking the stroke mitigation as a target, the enhanced hybrid active tuned mass dampers (EHATMD) have been proposed in order to attenuate undesirable oscillations of structures under the ground acceleration. In accordance with the mode generalized system in the specific vibration mode being controlled (simply referred herein to as the structure) and continuing to make use of the negative normalized acceleration feedback gain factors scheme, the dynamic magnification factor (DMF) has been formulated for the structure furnished with an EHATMD. Then, the criterion for the optimum searching can be determined as the minimization of the minimum values of the maximum DMF (min.min.max.DMF). Employing the genetic algorithm, the effects of varying the key parameters on the optimum performance of EHATMD have been scrutinized in order to capture the expected performance. Furthermore, for a comparison, the optimum results of hybrid active tuned mass dampers (HATMD) with the same initial design parameters using both the genetic algorithm and negative normalized acceleration feedback gain factor scheme are also taken into consideration. Results of analysis have demonstrated that EHATMD outperforms HATMD and thereby may be regarded as a novel extension of HATMD.
      PubDate: 2017-07-16T23:25:40.78846-05:0
      DOI: 10.1002/stc.2067
  • Damage imaging in composites using nonlinear vibro-acoustic wave
    • Authors: L. Pieczonka; L. Zietek, A. Klepka, W.J. Staszewski, F. Aymerich, T. Uhl
      Abstract: The paper deals with the application of nonlinear vibro-acoustic modulation technique for detection and localization of impact damage in a laminated composite plate. An imaging procedure—based on the nonlinear vibro-acoustic modulation sidebands—is proposed. The procedure relies on simultaneous low-frequency modal and high-frequency ultrasonic excitations. Laser scanning vibrometry is used to analyze the amplitude of modulation sidebands in vibro-acoustic responses. This analysis is performed for different positions on monitored structure to reveal the location and shape of damage. The method is illustrated using a simple example of impact damage detection in a composite plate. The experimental damage detection results are compared with the results obtained from the previously used approach on the basis of higher harmonic generation. The proposed method demonstrates better ability to locate damage in these comparative tests without the need to increase the measurement bandwidth to the higher harmonics regime. The work shows that the local defect resonance analysis can improve damage detection results of both compared approaches.
      PubDate: 2017-07-16T23:21:01.380626-05:
      DOI: 10.1002/stc.2063
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