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CONTENTS
Volume 18, Number 2, August 2016
 

Abstract
The increased speed of a train causes increased loads that act on the track substructures. To ensure the safety of the track substructures, proper maintenance and repair are necessary based on an accurate characterization of strength and stiffness. The objective of this study is to develop and apply a cone penetrometer incorporated with the dynamic cone penetration method (CPD) for investigating track substructures. The CPD consists of an outer rod for dynamic penetration in the ballast layer and an inner rod with load cells for static penetration in the subgrade. Additionally, an energy-monitoring module composed of strain gauges and an accelerometer is connected to the head of the outer rod to measure the dynamic responses during the dynamic penetration. Moreover, eight strain gauges are installed in the load cells for static penetration to measure the cone tip resistance and the friction resistance during static penetration. To investigate the applicability of the developed CPD, laboratory and field tests are performed. The results of the CPD tests, i.e., profiles of the corrected dynamic cone penetration index (CDI), profiles of the cone tip and friction resistances, and the friction ratio are obtained at high resolution. Moreover, the maximum shear modulus of the subgrade is estimated using the relationships between the static penetration resistances and the maximum shear modulus obtained from the laboratory tests. This study suggests that the CPD test may be a useful method for the characterization of track substructures.

Key Words
dynamic penetration; shear modulus; static penetration; track substructures; transferred energy

Address
Won-Taek Hong, ang Yeob Kim and Jong-Sub: School of Civil, Environmental and Architectural Engineering, Korea University, 145 Anam-ro, Seongbuk-gu, Seoul 136-713, Republic of Korea
Yong-Hoon Byun: Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign,
205 North Mathews Ave., Urbana, IL 61801-2352, USA



Abstract
The present work aims to develop piezoresistive sensors of excellent piezoresistive response attributable to change in nanoscale structures of multi-wall carbon nanotube (MWNT) embedded in cement. MWNT was distributed in a cement matrix by means of polymer wrapping method in tandem with the ultrasonication process. DC conductivity of the prepared samples exhibited the electrical percolation behavior and therefore the dispersion method adopted in this study was deemed effective. The integrity of piezoresistive response of the sensors was assessed in terms of stability, the maximum electrical resistance change rate, and sensitivity. A composite sensor with MWNT 0.2 wt.% showed the lowest stability and sensitivity, while the maximum electrical resistance change rate exhibited by this sample was the highest (96 %) among others and even higher than those found in the literature. This observation was presumably attributed by the percolation threshold and the tunneling effect. As a result of the MWNT content (0.2 wt.%) of the sensor being near the percolation threshold (0.25 wt.%), MWNTs were close to each other to trigger tunneling in response of external loading. The sensor with MWNT 0.2 wt.% was able to maintain the repeatable sensing capability while sustaining a vehicular loading on road, demonstrating the feasibility in traffic flow sensing application.

Key Words
piezoresistive sensor; multi-wall carbon nanotube; cement composite; percolation threshold; sensitivity and stability

Address
I.W. Nam: Infrastructure Research Center, K-water Institute, 125, 1689 beon-gil, Youseongdae-ro, Yuseong-gu, Daejeon 34045, Republic of Korea
H. Souri: Center of Advanced Composite Materials (CACM), Department of Mechanical Engineering, The University of Auckland, Khyber pass road, New market, Auckland 1010, New Zealand
H.K. Lee: Department of Civil and Environmental Engineering, Korea Advanced Institute of Science and Technology (KAIST), 291 Daehak-ro, Yuseong-gu, Daejeon 34141, Republic of Korea




Abstract
The vibration characteristic analysis of sandwich cylindrical shells subjected with magnetorheological (MR) elastomer and constraining layer are considered in this study. And, the discrete finite element method is adopted to calculate the vibration and damping characteristics of the sandwich cylindrical shell system. The effects of thickness of the MR elastomer, constraining layer, applied magnetic fields on the vibration characteristics of the sandwich shell system are also studied in this paper. Additionally, the rheological properties of the MR elastomer can be changed by applying various magnetic fields and the properties of the MR elastomer are described by complex quantities. The natural frequencies and modal loss factor of the sandwich cylindrical shells are calculated for many designed parameters. The core layer of MR elastomer is found to have significant effects on the damping behavior of the sandwich cylindrical shells.

Key Words
cylindrical shells; damping; magnetorheological; discrete layer finite element

Address
Jia-Yi Yeh: Department of Information Management, Chung Hwa University of Medical Technology, 89, Wen-Hwa 1st ST. Jen-Te Hsiang , Tainan Hsien 717 Taiwan, R.O.C.


Abstract
A bimorph piezoelectric energy harvester is developed for harvesting energy under the vortex induced vibration and it is integrated to a host structure of a trapezoidal plate without changing its passive dynamic properties. It is aimed to select trapezoidal plate as similar to a vertical fin-like structure which could be a part of an air vehicle. The designed energy harvester consists of an aluminum beam and two identical multi fiber composite (MFC) piezoelectric patches. In order to understand the dynamic characteristic of the trapezoidal plate, finite element analysis is performed and it is validated through an experimental study. The bimorph piezoelectric energy harvester is then integrated to the trapezoidal plate at the most convenient location with minimal structural displacement. The finite element model is constructed for the new combined structure in ANSYS Workbench 14.0 and the analyses performed on this particular model are then validated via experimental techniques. Finally, the energy harvesting performance of the bimorph piezoelectric energy harvester attached to the trapezoidal plate is also investigated through wind tunnel tests under the air load and the obtained results indicate that the system is a viable one for harvesting reasonable amount of energy.

Key Words
piezoelectric energy harvesting; finite element; experimental modal analysis; wind tunnel test

Address
Ahmet Levent Avsar and Melin Sahin: Department of Aerospace Engineering, Middle East Technical University, Ankara, Turkey

Abstract
In this research work, an exact analytical solution for thermal buckling analysis of functionally graded material (FGM) sandwich plates with clamped boundary condition subjected to uniform, linear, and non-linear temperature rises across the thickness direction is developed. Unlike any other theory, the number of unknown functions involved is only four, as against five in case of other shear deformation theories. The theory accounts for parabolic distribution of the transverse shear strains, and satisfies the zero traction boundary conditions on the surfaces of the plate without using shear correction factor. A power law distribution is used to describe the variation of volume fraction of material compositions. Equilibrium and stability equations are derived based on the present refined theory. The non-linear governing equations are solved for plates subjected to simply supported and clamped boundary conditions. The thermal loads are assumed to be uniform, linear and non-linear distribution through-the-thickness. The effects of aspect and thickness ratios, gradient index, on the critical buckling are all discussed.

Key Words
functionally graded plates; refined theory; sandwich plate; clamped boundary conditions; thermal buckling

Address
Zohra Abdelhak: Université Ahmed Zabana, R Bourmadia, 48000 Relizane, Algérie;
Laboratoire des Matériaux & Hydrologie, Université de Sidi Bel Abbes, 22000 Sidi Bel Abbes, Algérie
Lazreg Hadji and T. Hassaine Daouadji: Laboratoire des Matériaux & Hydrologie, Université de Sidi Bel Abbes, 22000 Sidi Bel Abbes, Algérie;
Université Ibn Khaldoun, BP 78 Zaaroura, 14000 Tiaret, Algérie
E.A. Adda Bedia: Laboratoire des Matériaux & Hydrologie, Université de Sidi Bel Abbes, 22000 Sidi Bel Abbes, Algérie


Abstract
Seismic isolation is often used in protecting mission-critical structures including hospitals, data centers, telecommunication buildings, etc. Such structures typically house vibration-sensitive equipment which has to provide continued service but may fail in case sustained accelerations during earthquakes exceed threshold limit values. Thus, peak floor acceleration is one of the two main parameters that control the design of such structures while the other one is peak base displacement since the overall safety of the structure depends on the safety of the isolation system. And in case peak base displacement exceeds the design base displacement during an earthquake, rupture and/or buckling of isolators as well as bumping against stops around the seismic gap may occur. Therefore, obtaining accurate peak floor accelerations and peak base displacement is vital. However, although nominal design values for isolation system and superstructure parameters are calculated in order to meet target peak design base displacement and peak floor accelerations, their actual values may potentially deviate from these nominal design values. In this study, the sensitivity of the seismic performance of structures equipped with linear and nonlinear seismic isolation systems to the aforementioned potential deviations is assessed in the context of a benchmark shear building under different earthquake records with near-fault and far-fault characteristics. The results put forth the degree of sensitivity of peak top floor acceleration and peak base displacement to superstructure parameters including mass, stiffness, and damping and isolation system parameters including stiffness, damping, yield strength, yield displacement, and post-yield to pre-yield stiffness ratio.

Key Words
sensitivity analysis; seismic isolation; linear isolation system; nonlinear isolation system; seismic performance

Address
Cenk Alhan and Kemal Hisman: Department of Civil Engineering, Istanbul University, 34320 Avc

Abstract
Structural Health Monitoring System (SHMS) works as an efficient platform for monitoring the health status and performance deterioration of engineering structures during long-term service periods. The objective of its installation is to provide reasonable suggestions for structural maintenance and management, and therefore ensure the structural safety based on the information extracted from the real-time measured data. In this paper, the SHMS implemented on a world-famous kilometer-level cable-stayed bridge, named as Sutong Cable-stayed Bridge (SCB), is introduced in detail. The composition and core functions of the SHMS on SCB are elaborately presented. The system consists of four main subsystems including sensory subsystem, data acquisition and transmission subsystem, data management and control subsystem and structural health evaluation subsystem. All of the four parts are decomposed to separately describe their own constitutions and connected to illustrate the systematic functions. Accordingly, the main techniques and strategies adopted in the SHMS establishment are presented and some extension researches based on structural health monitoring are discussed. The introduction of the SHMS on SCB is expected to provide references for the establishment of SHMSs on long-span bridges with similar features as well as the implementation of potential researches based on structural health monitoring.

Key Words
structural health monitoring system; Sutong Cable-stayed Bridge; subsystem; extension and application of SHMS

Address
Hao Wang, Tianyou Tao and Aiqun Li: Key Laboratory of C&PC Structures of Ministry of Education, Southeast University, No. 2 Sipailou, Nanjing 210096, China
Yufeng Zhang: Jiangsu Transportation Institute, No. 2200 Chengxin Street, Nanjing 211112, China

Abstract
This contribution presents an extended one-dimensional theory for piezoelectric beam-type structures with non-ideal electrodes. For these types of electrodes the equipotential area condition is not satisfied. The main motivation of our research is originated from passive vibration control: when an elastic structure is covered by several piezoelectric patches that are linked via resistances and inductances, vibrational energy is efficiently dissipated if the electric network is properly designed. Assuming infinitely small piezoelectric patches that are connected by an infinite number of electrical, in particular resistive and inductive elements, one obtains the Telegrapher\'s equation for the voltage across the piezoelectric transducer. Embedding this outcome into the framework of Bernoulli-Euler, the final equations are coupled to the wave equations for the longitudinal motion of a bar and to the partial differential equations for the lateral motion of the beam. We present results for the wave propagation of a longitudinal bar for several types of electrode properties. The frequency spectra are computed (phase angle, wave number, wave speed), which point out the effect of resistive and inductive electrodes on wave characteristics. Our results show that electrical damping due to the resistivity of the electrodes is different from internal (=strain velocity dependent) or external (=velocity dependent) mechanical damping. Finally, results are presented, when the structure is excited by a harmonic single force, yielding that resistive-inductive electrodes are suitable candidates for passive vibration control that might be of great interest for practical applications in the future.

Key Words
piezoelectric effect; conductive electrodes; linear elastic beam and bar modeling; vibration control; wave propagation

Address
Juergen Schoeftner: Johannes Kepler University, Institute of Technical Mechanics, Altenbergerstrasse 69, 4040 Linz, Austria
Gerda Buchberger: Johannes Kepler University, Institute of Biomedical Mechatronics, Altenbergerstrasse 69, 4040 Linz, Austria
Ayech Benjeddou: SUPMECA, 3 rue Fernand Hainaut, 93407 Saint Ouen CEDEX, France


Abstract
This paper presents and compares a one-dimensional (1D) bending theory for piezoelectric thin beam-type structures with resistive-inductive electrodes to ANSYS three-dimensional (3D) finite element (FE) analysis. In particular, the lateral deflections and vibrations of slender piezoelectric beams are considered. The peculiarity of the piezoelectric beam model is the modeling of electrodes in such a manner that is does not fulfill the equipotential area condition. The case of ideal, perfectly conductive electrodes is a special case of our 1D model. Two-coupled partial differential equations are obtained for the lateral deflection and for the voltage distribution along the electrodes: the first one is an extended Bernoulli-Euler beam equation (second-order in time, forth order in space) and the second one the so-called Telegrapher\'s equation (second-order in time and space). Analytical results of our theory are validated by 3D electromechanically coupled FE simulations with ANSYS. A clamped-hinged beam is considered with various types of electrodes for the piezoelectric layers, which can be either resistive and/or inductive. A natural frequency analysis as well as quasi-static and dynamic simulations are performed. A good agreement between the extended beam theory and the FE results is found. Finally, the practical relevance of this type of electrodes is shown. It is found that the damping capability of properly tuned resistive or resistive-inductive electrodes exceeds the damping performance of beams, where the electrodes are simply linked to an optimized impedance.

Key Words
piezoelectric effect; conductive electrodes; linear piezoelectric beam and bar modeling; passive vibration control; bending vibration; finite element analysis

Address
Juergen Schoeftner: Johannes Kepler University, Institute of Technical Mechanics, Altenbergerstrasse 69, 4040 Linz, Austria
Gerda Buchberger: Johannes Kepler University, Institute of Biomedical Mechatronics, Altenbergerstrasse 69, 4040 Linz, Austria
Ayech Benjeddou: SUPMECA, 3 rue Fernand Hainaut, 93407 Saint Ouen CEDEX, France


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