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CONTENTS
Volume 22, Number 1, July 2018
 

Abstract
This study presents early crack detection of steel fiber-reinforced concrete (SFRC) under varying temperature and humidity conditions using an instantaneous electrical impedance acquisition system. SFRC has the self-sensing capability of electrical impedance without sensor installation thanks to the conductivity of embedded steel fibers, making it possible to effectively monitor cracks initiated in SFRC. However, the electrical impedance is often sensitively changed by environmental effects such as temperature and humidity variations. Thus, the extraction of only crack-induced feature from the measured impedance responses is a crucial issue for the purpose of structural health monitoring. In this study, the instantaneous electrical impedance acquisition system incorporated with SFRC is developed. Then, temperature, humidity and crack initiation effects on the impedance responses are experimentally investigated. Based on the impedance signal pattern observation, it is turned out that the temperature effect is more predominant than the crack initiation and humidity effects. Various crack steps are generated through bending tests, and the corresponding impedance damage indices are extracted by compensating the dominant temperature effect. The test results reveal that propagated cracks as well as early cracks are successfully detected under temperature and humidity variations.

Key Words
self-sensing concrete; electrical impedance; crack detection; steel fiber-reinforced concrete; structural health monitoring; temperature and humidity variation

Address
Man-Sung Kang and Yun-Kyu An:Department of Architectural Engineering, Sejong University, 209, Neungdong-ro, Gwangjin-gu, Seoul, 05006, Republic of Korea
Dong-Joo Kim: Department of Civil and Environmental Engineering, Sejong University, 209, Neungdong-ro, Gwangjin-gu, Seoul, 05006, Republic of Korea



Abstract
Pedro Gómez Bosque footbridge is a slender and lightweight structure that creates a pedestrian link over the Pisuerga River, Valladolid, Spain. This footbridge is a singular stress ribbon structure with one span of 85 m consisting on a steel plate and precast concrete slabs laying on it. Rubber pavement and a railing made of stainless steel and glass complete the footbridge. Because of its lively dynamics, prone to oscillate, a simple and affordable structural health monitoring system was installed in order to continuously evaluate its structural serviceability and to estimate its modal parameters. Once certain problems (conditioning and 3D orientation of the triaxial accelerometers) are overcome, the monitoring system is validated by comparison with a general purpose laboratory portable analyzer. Representative data is presented, including acceleration magnitudes and modal estimates. The evolution of these parameters has been analysed over one-year time.

Key Words
SHM; serviceability assessment; structural dynamics; modal parameters

Address
Norberto Iban and Carlos Casado: Centro Tecnológico CARTIF. Parque Tecnológico de Boecillo, 47151 Valladolid, Spain
Jose M. Soria and Ivan M. Diaz: E.T.S. de Ingenieros de Caminos, Canales y Puertos, Universidad Politécnica de Madrid, Calle del Profesor Aranguren 3, 28040 Madrid, Spain
Alvaro Magdaleno and Antolin Lorenzana: ITAP, Escuela de Ingenierías Industriales, Universidad de Valladolid, Paseo del Cauce 59, 47011 Valladolid, Spain


Abstract
The governing equations of motion are derived for analysis of a sandwich microbeam in this paper. The sandwich microbeam is including an elastic micro-core and two piezoelectric micro-face-sheets. The microbeam is subjected to transverse loads and two-dimensional electric potential. Higher-order sinusoidal shear deformation beam theory is used for description of displacement field. To account size dependency in governing equations of motion, strain gradient theory is used to mention higher-order stress and strains. An analytical approach for simply-supported sandwich microbeam with short-circuited electric potential is proposed. The numerical results indicate that various types of parameters such as foundation and material length scales have significant effects on the free vibration responses and dynamic results. Investigation on the influence of material length scales indicates that increase of both dimensionless material length scale parameters leads to significant changes of vibration and dynamic responses of microbeam.

Key Words
sandwich microbeam; piezoelectric face-sheets; micro-length-scale parameters; strain gradient theory; Pasternak\'s foundation

Address
Mohammad Arefi and Elyas Mohammad-Rezaei Bidgoli: Department of Solid Mechanics, Faculty of Mechanical Engineering, University of Kashan, Kashan 87317-51167, Iran
Ashraf M. Zenkour: Department of Mathematics, Faculty of Science, King Abdulaziz University, Jeddah 21589, Saudi Arabia;
Department of Mathematics, Faculty of Science, Kafrelsheikh University, Kafrelsheikh 33516, Egypt


Abstract
Damping ratio and frequency have influence on dynamic serviceability or instability such as vortex-induced vibration and displacement amplification due to earthquake and critical flutter velocity, and it is thus important to make determination of damping ratio and frequency accurate. As bridges are getting longer, small scale model test considering similitude law must be conducted to evaluate damping ratio and frequency. Analysis conditions modified by similitude law are applied to experimental test considering different scale ratios. Generally, Nyquist frequency condition based on natural frequency modified by similitude law has been used to determine sampling rate for different scale ratios, and total time length has been determined by users arbitrarily or by considering similitude law with respect to time for different scale ratios. However, Nyquist frequency condition is not suitable for multimode system with noisy signals. In addition, there is no specified criteria for determination of total time length. Those analysis conditions severely affect accuracy of damping ratio. The focus of this study is made on the determination of minimum analysis conditions for different scale ratios. Influence of signal to noise ratio is studied according to the level of noise level. Free initial value problem is proposed to resolve the condition that is difficult to know original initial value for free vibration. Ambient and free vibration tests were used to analyze the dynamic properties of a system using data collected from tests with a two degree-of-freedom section model and performed on full bridge 3D models of cable stayed bridges. The free decay is estimated with the stochastic subspace identification method that uses displacement data to measure damping ratios under noisy conditions, and the iterative least squares method that adopts low pass filtering and fourth order central differencing. Reasonable results were yielded in numerical and experimental tests.

Key Words
damping ratio; sampling rate; total time length; signal to noise ratio; free initial value problem; scale ratio

Address
Seungtaek Oh, Hoyeop Lee and Hak-Eun Lee: School of Civil, Environmental and Architectural Engineering, Korea University, Seoul 02841, Republic of Korea
Sung-Soon Yhim: Department of Civil Engineering, University of Seoul, Seoul 02504, Republic of Korea
Nakhyun Chun: Structural & Seismic Tech. Group, KEPCO Research Institute, Daejeon 34056, South Korea

Abstract
For the long-term structural health monitoring of civil structures, the effect of ambient temperature variation has been regarded as one of the critical issues. In this study, a principal component analysis (PCA)-based algorithm is proposed to filter out temperature effects on electromechanical impedance (EMI) monitoring of prestressed tendon anchorages. Firstly, the EMI monitoring via a piezoelectric interface device is described for prestress-loss detection in the tendon anchorage system. Secondly, the PCA-based temperature filtering algorithm tailored to the EMI monitoring of the prestressed tendon anchorage is outlined. The proposed algorithm utilizes the damage-sensitive features obtained from sub-ranges of the EMI data to establish the PCA-based filter model. Finally, the feasibility of the PCA-based algorithm is experimentally evaluated by distinguishing temperature changes from prestress-loss events in a prestressed concrete girder. The accuracy of the prestress-loss detection results is discussed with respect to the EMI features before and after the temperature filtering.

Key Words
electromechanical impedance; impedance monitoring; temperature effect; temperature filtering; principal component analysis; prestressed tendon anchorage; prestress-loss

Address
Thanh-Canh Huynh, Ngoc-Loi Dang and Jeong-Tae Kim: Department of Ocean Engineering, Pukyong National University, 599-1 Daeyeon 3-dong, Nam-gu, Busan 608-737, Republic of Korea


Abstract
The nonlinear vibration analysis of a magneto-rheological elastomer (MRE) sandwich plate is conducted experimentally. Experiments have been performed in order to construct the frequency-response curves in the vicinity of the fundamental natural frequency of an MRE sandwich plate (plate A) in either the absence or presence of a localised external magnetic field at 3 different geometrical locations, for both small and medium magnetic fields. Furthermore, experiments have also been conducted on a pure aluminium plate (plate B) with an equal thickness to the MRE sandwich plate (plate A) in order to examine the influence of the MRE layer on the nonlinear dynamics of the system. An electrodynamic shaker was used to directly force each system and the displacement at the centre of the plate was measured. Meanwhile, permanent magnets were used to apply a localised magnetic field for the experiments where the MRE sandwich plate was subject to an external magnetic field. It was observed all the MRE systems displayed strong hardening-type nonlinear behaviour, however, with increasing magnetic field this behaviour transitioned to a weak hardening-type nonlinearity.

Key Words
experiments; sandwich plate; magneto-rheological elastomer; frequency-response; nonlinear dynamics

Address
Jiawei Zhang and Weihua Li: School of Mechanical, Materials and Mechatronics Engineering, University of Wollongong, NSW 2522, Australia
Tanju Yildirim: College of Chemistry and Environmental Engineering, Shenzhen University, Shenzhen 518060, Guangdong, China
Gursel Alici: School of Mechanical, Materials and Mechatronics Engineering, University of Wollongong, NSW 2522, Australia;
ARC Centre of Excellence for Electromaterials Science, University of Wollongong, Innovation Campus, NSW 2522, Australia
Shiwu Zhang: Department of Precision Machinery and Precision Instrumentation, University of Science and Technology of China, Hefei, Anhui 230027, China



Abstract
Automatic Generation Control (AGC) has functionally controlled the interchange power flow in order to suppress the dynamic oscillations of frequency and tie-line power deviations as a perturbation occurs in the interconnected multi-area power system. Furthermore, Flexible AC Transmission Systems (FACTS) can effectively assist AGC to more enhance the dynamic stability of power system. So, Static Synchronous Series Compensator (SSSC), one of the well-known FACTS devices, is here applied to accurately control and regulate the load frequency of multi-area multi-source interconnected power system. The research and efforts made in this regard have caused to introduce the Fractional Order Proportional Integral Derivative (FOPID) based SSSC, to alleviate both the most significant issues in multi-area interconnected power systems i.e., frequency and tie-line power deviations. Due to multi-objective nature of aforementioned problem, suppression of the frequency and tie-line power deviations is formularized in the form of a multi-object problem. Considering the high performance of Multi Objective Bees Algorithm (MOBA) in solution of the non-linear objectives, it has been utilized to appropriately unravel the optimization problem. To verify and validate the dynamic performance of self-defined FOPID–SSSC, it has been thoroughly evaluated in three different multi-area interconnected power systems. Meanwhile, the dynamic performance of FOPID–SSSC has been accurately compared with a conventional controller based SSSC while the power systems are affected by different Step Load Perturbations (SLPs). Eventually, the simulation results of all three power systems have transparently demonstrated the dynamic performance of FOPID–SSSC to significantly suppress the frequency and tie-line power deviations as compared to conventional controller based SSSC.

Key Words
power system dynamic stability; simultaneous optimization scheme; FOPID-SSSC; AGC; MOBA

Address
Department of Electrical Engineering, Shadegan Branch, Islamic Azad University, Shadegan, Iran

Abstract
Active vibration control via inertial mass actuators has been shown as an effective tool to significantly reduce human-induced vertical vibrations, allowing structures to satisfy vibration serviceability limits. However, a lot of practical obstacles have to be solved before experimental implementations. This has motivated simple control techniques, such as direct velocity feedback control (DVFC), which is implemented in practice by integrating the signal of an accelerometer with a band-pass filter working as a lossy integrator. This work provides practical guidelines for the tuning of DVFC considering the damping performance, inertial mass actuator limitations, such as stroke and force saturation, as well as the stability margins of the closed-loop system. Experimental results on a full scale steel-concrete composite structure (behaves similar to a footbridge) with adjustable span are reported to illustrate the main conclusions of this work.

Key Words
active control; human-induced vibrations; band-pass filter; direct velocity feedback control; inertial mass actuator

Address
Xidong Wang, Iván M. Díaz and Jaime H. García-Palacios: E.T.S. Ingenieros de Caminos, Canales y Puertos, Universidad Politécnica de Madrid, Calle del Profesor Aranguren 3, Madrid, Spain
Emiliano Pereira: Department of Signal Processing and Communications, Universidad de Alcalá, Alcalá de Henares (Madrid), Spain



Abstract
In this paper, the nonlinear free and forced vibration responses of sandwich nano-beams with three various functionally graded (FG) patterns of reinforced carbon nanotubes (CNTs) face-sheets are investigated. The sandwich nano-beam is resting on nonlinear Visco-elastic foundation and is subjected to thermal and electrical loads. The nonlinear governing equations of motion are derived for an Euler-Bernoulli beam based on Hamilton principle and von Karman nonlinear relation. To analyze nonlinear vibration, Galerkin\' decomposition technique is employed to convert the governing partial differential equation (PDE) to a nonlinear ordinary differential equation (ODE). Furthermore, the Multiple Times Scale (MTS) method is employed to find approximate solution for the nonlinear time, frequency and forced responses of the sandwich nano-beam. Comparison between results of this paper and previous published paper shows that our numerical results are in good agreement with literature. In addition, the nonlinear frequency, force response and nonlinear damping time response is carefully studied. The influences of important parameters such as nonlocal parameter, volume fraction of the CNTs, different patterns of CNTs, length scale parameter, Visco-Pasternak foundation parameter, applied voltage, longitudinal magnetic field and temperature change are investigated on the various responses. One can conclude that frequency of FG-AV pattern is greater than other used patterns.

Key Words
euler-bernoulli beam theory; reinforcement carbon nano-tube composite; sandwich beams; nonlocal strain gradient theory; non-linear vibration

Address
Ali Ghorbanpour Arani, Mahmoud Pourjamshidian and Mohammad Arefi: Department of Solid Mechanics, Faculty of Mechanical Engineering, University of Kashan, Postal Code: 87317-53153, Kashan, Iran


Abstract
This research investigates the free vibration analysis of advanced composite plates such as functionally graded plates (FGPs) resting on a two-parameter elastic foundations using a hybrid quasi-3D (trigonometric as well as polynomial) higher-order shear deformation theory (HSDT). This present theory, which does not require shear correction factor, accounts for shear deformation and thickness stretching effects by a sinusoidal and parabolic variation of all displacements across the thickness. Governing equations of motion for FGM plates are derived from Hamilton\' s principle. The closed form solutions are obtained by using Navier technique, and natural frequencies are found, for simply supported plates, by solving the results of eigenvalue problems. The accuracy of the present method is verified by comparing the obtained results with First-order shear deformation theory, and other predicted by quasi-3D higher-order shear deformation theories. It can be concluded that the proposed theory is efficient and simple in predicting the natural frequencies of functionally graded plates on elastic foundations.

Key Words
free vibration; functionally graded plates; high-order theory; two-parameter elastic foundations; stretching effect

Address
Hicham Zakaria Guerroudj: University of SAIDA Dr MOULAY TAHAR, Faculty of Technology, Department of Civil Engineering and Hydraulics, PBox 138 City En-Nasr 20000 SAIDA, Algeria;
Laboratory of Ressources Hydriques et Environnement, University Dr MOULAY TAHAR, PBox 138 City En-Nasr 20000 SAIDA, Algeria
Redha Yeghnem and Abdelhakim Kaci: University of SAIDA Dr MOULAY TAHAR, Faculty of Technology, Department of Civil Engineering and Hydraulics, PBox 138
City En-Nasr 20000 SAIDA, Algeria;
Material and Hydrology Laboratory, University of SIDI BEL ABBES, Algeria
Fatima Zohra Zaoui: Department of Mechanical Engineering, Faculty of Science and Technology, University of MOSTAGANEM, Algeria
Samir Benyoucef: Material and Hydrology Laboratory, University of SIDI BEL ABBES, Algeria
Abdelouahed Tounsi: Material and Hydrology Laboratory, University of SIDI BEL ABBES, Algeria;
Department of Civil Engineering and Public Works, Faculty of Technology, University of SIDI BEL ABBES , Algeria






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