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Volume 27, Number 1, January 2021

In the present study, the free vibration analysis of a size-dependent micro composite Timoshenko beam model reinforced by various distributions of carbon nanotubes under temperature changes and two-dimensional magnetic field is investigated based on modified strain gradient theory. Also, the effects of environment are simulated by orthotropic elastic foundation and it is assumed that the material properties are temperature-dependent. Mathematical formulations are obtained using Hamilton's principle and the governing equations of motion are derived based on energy approach and variation method. These equations are solved using semi-analytical and numerical methods such as Navier's type solution, finite element method and generalized differential quadrature method for various boundary conditions. The obtained results of this study are compared with the other previous researches and there is a good agreement between them. The main purpose of this work is the comparison of various solution methods on the problem outputs. Thus, the results are compared together and the effects of solution approach on the dimensionless natural frequencies is developed. Moreover, the effects of length-to-thickness ratio, magnetic field, temperature changes, elastic foundation and carbon nanotubes volume fractions on the dimensionless natural frequencies are studied. The results of this article demonstrate that the micro composite Timoshenko beam reinforced by FG-O and FG-X CNTs have lowest and highest dimensionless natural frequency, respectively. It is investigated that the dimensionless natural frequency enhances by increasing the magnetic field in x and z-directions.

Key Words
2D magnetic field; free vibration analysis of Timoshenko micro beam; reinforced by carbon nanotubes; temperature-dependent material properties; orthotropic medium

(1) Mojtaba Mehrabi, Mehdi Mohammadimehr:
Department of Solid Mechanics, Faculty of Mechanical Engineering, University of Kashan, Kashan, Iran;
(2) Fatemeh S. Mousavinejad:
Department of Civil Engineering, Faculty of Engineering, University of Kashan, Kashan, Iran.

Structural health monitoring (SHM) is facilitated by new technologies that involve wireless sensor networks (WSNs). The main benefits of WSNs are that they are distributed, are inexpensive to install, and manage data effectively via remote control. In this paper, a wireless SHM system for the steel structure of Hangzhou East Railway Station in China is developed, since the state of the structural life cycle is highly complicated and the accompanying internal force redistribution is not known. The monitoring system uses multitype sensors, which include stress, acceleration, wind load, and temperature sensors, as the measurement components for the structural features, construction procedure, and on-site environment. The sensor nodes communicate with each other via a flexible tree-type network. The system that consists of 323 sensors is designed for the structure, and the data acquisition process will continue throughout its whole life cycle. First, a full-scale application of SHM using a WSN is described in details. Then, it focuses on engineering practice and data analysis. The current customized WSN has been demonstrated to have satisfactory durability and strong robustness; hence, it well satisfies the requirements for multi-type sensors to operate in a large area. The data analysis results demonstrate that the effects of the construction process and the environment on the super-large-scale structure have been captured accurately. Those effects include the stress variation throughout the construction process, the dynamic responses that are caused by passing trains, the strain variation caused by temperature change over the long term, and the delay in the wind-pressure history.

Key Words
wireless sensor network; life-cycle; structural health monitoring; railway station

(1) Yanbin Shen, Wenwei Fu, Yaozhi Luo, Chung-Bang Yun:
College of Civil Engineering and Architecture, Zhejiang University, Hangzhou 310058, China;
(2) Dun Liu:
CITIC General Institute of Architectural Design and Research Co., Ltd, Wuhan 430014, China;
(3) Pengcheng Yang:
Country Garden Holdings Company Limited, Hong Kong 999077, China;
(4) Guang Yang:
China Railway SIYUAN Survey & Design Group Co., Ltd, Wuhan 430063, China;
(5) Guangen Zhou:
Zhejiang Southeast Space Frame Company, Hangzhou 311209, China.

An automated unmanned aerial vehicle (UAV) based multi-hazard performance assessment system was developed to respond to rapid performance evaluation and performance prediction needs for river crossing reinforced concrete (RC) bridges. In the developed system, firstly the seasonally acquired UAV measurements were used to obtain the three-dimensional (3D) digital elevation models (DEMs) of the river bed. In conjunction with the flood simulation, the hydraulic model was verified with the previous flood event which corresponded to Q50 and the scour depths after a probable flood (Q500) were predicted by HEC-RAS software. Afterward, the 3D finite element model (FEM) of the bridge was constituted automatically with the developed code considering the scoured piles. The flood loads were exerted on the modeled bridge with regard to the HEC-RAS flood inundation map and relevant water depth estimations around the bridge piers. For the seismic evaluation, nonlinear time history analyses (THA) were conducted by using several scaled earthquake acceleration records that were acting in both principal axes of the bridge simultaneously as compatible with the region seismicity. The Boğaçay-II Bridge that was located in Antalya, Turkey was selected as the case study. In the analyses, as the scour depth increased, the lateral displacements and the pile internal forces were observed to increase while the pier column internal forces kept approximately constant. Thus, it was monitored that the seismic displacement and load demands migrated from pier columns to piles with increasing scour. Therefore, the applicability of the proposed system was verified using the case study bridge.

Key Words
UAV-photogrammetry; automated system; multi-hazard; bridge; scour; seismic performance; earthquake; flood

(1) Orkan Özcan:
Eurasia Institute of Earth Sciences, İstanbul Technical University, 34469, Istanbul, Turkey;
(2) Okan Özcan:
Department of Civil Engineering, Akdeniz University, 07058, Antalya, Turkey.

Gravel scattering, which occurs from snow-ice that develops on trains during winter, is a major cause of damage to train parts. An exothermic technology that uses copper wires to solve the problem of gravel scattering is ineffective on the snow-ice produced on the surface of the trains. Therefore, studies have been conducted to overcome the weaknesses of the conventional methods and to develop a paint-type surface exothermic technology that can be efficiently applied to complicated structures. However, multi-layered paint-type coatings can lead to problems such as a delamination or exfoliation of the layers when used for a long period of time within an environment undergoing variations in temperature. Therefore, this study assesses the long-term effects of temperature on multi-layered exothermic coating technology based on nano-solutions for an application of self-heating function on railway infrastructures. To do so, we developed an exothermic coating test specimen using the paint applied to train cars and commercial nano-solutions. To conduct an experiment on accelerated aging, the specimen was subjected to regular changes in the temperature within a thermal chamber. The results revealed that there is a nonlinear decline in the performance as the specimen is worn out in comparison to the exothermic performance achieved during the early stages. Further, it is possible to identify the structural causes of the decline in performance from the specimen applied thermal load by analyzing the morphology. However, it is possible to observe a high stability from noninvasive overheating or short-circuits based on the structural changes to the coating, which are observed during the assessment of the exothermic uniformity. Therefore, it can be concluded that a multi-layer exothermic coating, which can be effectively applied as an exothermic technology based on self-heating surfaces, can be applied for a long period to prevent disasters from freezing or snow-ice in trains during winter.

Key Words
long-term reliability; exothermic coating; self-heating surfaces; cyclic thermal load; exothermic performance

(1) Heonyoung Kim, Donghoon Kang:
Railroad Major Accident Research Team, Korea Railroad Research Institute, Uiwang 16105, Republic of Korea;
(2) Heonyoung Kim, Chulmin Joo:
Department of Mechanical Engineering, Yonsei University, Seoul 03722, Republic of Korea;
(3) Myeongcheol Kang, Mun-Young Hwang:
Department of Mechatronics Engineering and LANL-JBNU Engineering Institute-Korea, Jeonbuk National University, Jeonju 54896, Republic of Korea;
(4) Lae-Hyong Kang:
Department of Flexible and Printable Electronics Engineering, and LANL-JBNU Engineering Institute-Korea, Jeonbuk National University, Jeonju 54896, Republic of Korea.

In this study, a gain scheduling H controller based on Linear Parameter Varying (LPV) model was designed and applied to suppress the first out of plane bending vibration of a variable parameter smart beam equipped with Lead-Zirconium-Titanium (PZT) patches. This paper also introduces a novel LPV modelling technique which defalcates the zeros of the system. The controller design was carried out in three successive steps. In the first step, the variable parameter model of the beam with an added mass at its free end can rotate through a micro servo motor was experimentally obtained. In the second step, an original LPV model including the variable parameter model was obtained. Finally, H controller with gain scheduling was designed on LPV model. The obtained controller was then used both for simulations and experimental verifications. It was shown that in response to parameter changes in the system, the proposed controller is capable of suppressing the beam bending vibrations by also exhibiting a robust performance. In practice, the proposed LPV controller design strategy can be transacted for vibration control of aircraft wings, the parameters of which vary according to various load conditions changing in time and therefore deeply affects the passive characteristics of the system of interest.

Key Words
smart beam; robust control; H∞; gain scheduling; LPV model

(1) Abdullah Turan:
Department of Mechanical Engineering, Inonu University, Malatya, Turkey;
(2) Melin Sahin:
Department of Aerospace Engineering, Middle East Technical University, Ankara, Turkey;
(3) Cem Onat:
Department of Airframe and Power-plant, Firat University, Elazig, Turkey.

While in several publications the thermo-viscoelastic properties of solids have been documented, no attempt has been made to examine the action of coupled thermal and plasma wave in viscoelastic materials. In this paper, a new mathematical model for thermal and plasma transfer in an organic semiconductor was constructed with a time-fractional derivative of order

Key Words
organic semiconductor; thermo-viscoelasticity; photothermal theory; fractional calculus; fourier transforms; laplace transforms

Department of Mathematics, College of Science and Arts, Qassim University, Al-Bukairyah, Saudi Arabia.

In this paper, a monitoring system containing a novel liquid metal-based pressure sensor and remote interactive monitoring devices are fabricated to monitor stress in geotechnical engineering. The pressure sensor with the dimension of 34 mm × 34 mm is designed and manufactured, which is mainly composed of 40CrMoV alloy steel shell, polydimethylsiloxane (PDMS) and liquid metal gallium indium alloy (EGaIn). It has the characteristics of high stability, can greatly improve the measurement range of the pressure sensor (0 to 20 MPa), and its resistance variation is from 0 mΩ to 800 mΩ. In addition, the linear regression analysis is carried out to verify the linear relationship between the resistance of sensor and the applied pressure. It is found that the performance of the pressure sensor is fine through experiments with three different loading rates and fatigue experiments. The remote interactive monitoring device can be suitable for the field monitoring environment, which is composed of monitoring stations (MS), remote communication base stations (RCBS) and indoor working platform. Finally, the monitoring system is successfully applied to the field measurements in geotechnical engineering, and the field monitoring data are in good agreement with the numerical results.

Key Words
geotechnical engineering; pressure sensor; polydimethylsiloxane (PDMS); liquid metal; field monitoring

(1) Yundong Shou, Xiaoping Zhou:
School of Civil Engineering, Wuhan University, Wuhan 430072, China;
(2) Xiaoping Zhou, Qingpeng Chang, Chao Liu:
School of Civil Engineering, Chongqing University, Chongqing 400045, China.

Concrete bridge decks may suffer local damage such as delamination, cracking, reinforcement corrosion and spalling during service. Visual inspection and nondestructive evaluation (NDE) technologies are extensively used for monitoring damage in bridge decks. This paper presents a damage detection method for decks of concrete girder bridges using the frequency obtained from an actively excited vehicle. First, the solution for the frequency of the deck with a concentrated mass is derived with Rayleigh's method, where the bridge deck is regarded as a slab supported on four sides, and the test vehicle is simplified as a concentrated mass. The validity of the proposed method that uses the frequency change to detect the local damage is verified. Then, the damage detection procedure for bridge decks is proposed, and the numerical analysis is performed on a typical concrete girder bridge to prove the validity of the method. Finally, the damage detection experiment for the plywood plate verifies the effectiveness of the proposed method. The results of this study provide an effective method for detecting damage in the decks of concrete girder bridges, which is time-saving and easier to implement.

Key Words
damage detection; bridge deck; actively excited vehicle; frequency change; Rayleigh's method

School of Civil Engineering, Dalian University of Technology, Dalian 116023, China.

This paper presents and compares the free and damped forced vibrations of layered and functionally graded composite beams. In the considered study, a cantilever beam subjected to a harmonic point load at the free end is investigated with layered and functionally graded materials. In the kinematics of the beam, the Timoshenko beam theory is used. The governing equations of problem are derived by using the Lagrange procedure. In the solution of the problem, the Ritz method is used. Algebraic polynomials are used with the trial functions for the Ritz method. In the obtaining of free vibration results, the eigenvalue procedure is implemented. In the solution of the damped forced vibration problem, the Newmark average acceleration method is used in the time history. In the damping effect, the Kelvin-Voigt viscoelastic model is used with the constitutive relations. In the numerical examples, the effects of material distribution parameter and dynamic parameters on the natural frequencies and forced vibration responses of functionally graded beams are obtained and compared with the results of the layered composite beam. Also, comparison studies are performed in order to validate the used formulations.

Key Words
functionally graded materials; layered materials; dynamic analysis; Timoshenko Beam Theory

(1) O. Kırlangıç:
The General Directorate of Highways, Ankara, Turkey;
(2) Ş.D. Akbaş:
Department of Civil Engineering, Bursa Technical University, 16330, Bursa, Turkey.

Experimental and discrete element methods were used to investigate the effects of both of the non-persistent joints and hole on the failure behaviour of rock pillars under uniaxial compressive test. Concrete samples with dimension of 150 mm × 150 mm × 50 mm were prepared. Within the specimen, two echelon non-persistent notches and one hole were provided. The hole was inserted at the middle of the specimen. two joints were distributed on the three diagonal planes. the angle of diagonal plane related to horizontal axis were 15°, 30° and 45°. The angle of joints related to diagonal plane were 30°, 45°, 60°. Totally, 9 different configuration systems were prepared. In these configurations, the length of joints was taken as 20 mm. diameter of hole was 20 mm. Similar to those for joints configuration systems in the experimental tests, 9 models with different echelon non-persistent joint were prepared in numerical model. The axial load was applied to the model by rate of 0.05 mm/min. the results show that the failure process was mostly governed by both of the non-persistent joint angle and diagonal plane angle. The compressive strengths of the specimens were related to the fracture pattern and failure mechanism of the discontinuities. It was shown that the shear behaviour of discontinuities is related to the number of the induced tensile cracks which are increased by increasing the joint angle. The strength of samples increases by increasing both of the joint angle and diagonal plane angle. The failure pattern and failure strength are similar in both methods i.e., the experimental testing and the numerical simulation methods.

Key Words
PFC2D; physical test; echelon non-persistent joint; joint angle; hole

(1) V. Sarfarazi:
Department of Mining Engineering, Hamedan University of Technology, Hamedan, Iran;
(2) S. Abharian, A. Ghorbani:
Department of Mining and Metallurgical Engineering, Amirkabir University, Tehran, Iran.

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