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CONTENTS
Volume 64, Number 6, December25 2017
 

Abstract
According to a generalized nonlocal strain gradient theory (NSGT), dynamic modeling and free vibrational analysis of nanoporous inhomogeneous nanoplates is presented. The present model incorporates two scale coefficients to examine vibration behavior of nanoplates much accurately. Porosity-dependent material properties of the nanoplate are defined via a modified power-law function. The nanoplate is resting on a viscoelastic substrate and is subjected to hygro-thermal environment and in-plane linearly varying mechanical loads. The governing equations and related classical and non-classical boundary conditions are derived based on Hamilton\'s principle. These equations are solved for hinged nanoplates via Galerkin\'s method. Obtained results show the importance of hygro-thermal loading, viscoelastic medium, in-plane bending load, gradient index, nonlocal parameter, strain gradient parameter and porosities on vibrational characteristics of size-dependent FG nanoplates.

Key Words
nanoporous plate; hygro-thermal environment; nonlocal strain gradient theory; four-variable plate theory

Address
Mohammad Reza Barati : Aerospace Engineering Department & Center of Excellence in Computational Aerospace, Amirkabir University of Technology, Tehran, Iran

Abstract
This paper investigates some general properties in the degenerate scale problem of antiplane elasticity or Laplace equation. For a given configuration, the degenerate scale problem is solved by using conformal mapping technique, or by using the null field BIE (boundary integral equation) numerically. After solving the problem, we can define and evaluate the degenerate area which is defined by the area enclosed by the contour in the degenerate configuration. It is found that the degenerate area is an important parameter in the problem. After using the conformal mapping, the degenerate area can be easily evaluated. The degenerate area for many configurations, from triangle, quadrilles and N-gon configuration are evaluated numerically. Most properties studied can only be found by numerical computation. The investigated properties provide a deeper understanding for the degenerate scale problem.

Key Words
degenerate scale problem; degenerate area; maximum property for degenerate area; laplace equation; conformal mapping

Address
Y.Z. Chen : Division of Engineering Mechanics, Jiangsu University, Zhenjiang, Jiangsu, 212013 P.R. China

Abstract
The experimental study of the behavior of dry medium and loose sandy soil under the action of a single impulsive load is carried out. Different falling masses from different heights were conducted using the falling weight deflectometer (FWD) to provide the single pulse energy. The responses of soils were evaluated at different locations (vertically below the impact plate and horizontally away from it). These responses include; displacements, velocities, and accelerations that are developed due to the impact acting at top and different depth ratios within the soil using the falling weight deflectometer (FWD) and accelerometers (ARH-500A Waterproof, and Low capacity Acceleration Transducer) that are embedded in the soil and then recorded using the multi-recorder TMR-200. The behavior of medium and loose sandy soil was evaluated with different parameters, these are; footing embedment, depth ratios (D/B), diameter of the impact plate (B), and the applied energy. It was found that increasing footing embedment depth results in: amplitude of the force-time history increases by about 10-30%. due to increase in the degree of confinement with the increasing in the embedment, the displacement response of the soil will decrease by about 25-35% for loose sand, 35-40% for medium sand due to increase in the overburden pressure when the embedment depth increased. For surface foundation, the foundation is free to oscillate in vertical, horizontal and rocking modes. But, when embedding a footing, the surrounding soil restricts oscillation due to confinement which leads to increasing the natural frequency, moreover, soil density increases with depth because of compaction, that is, tendency to behave as a solid medium.

Key Words
dry; medium sand; loose sand; impact; embedment; response

Address
Adnan F. Ali : Civil Engineering Department, University of Baghdad, Baghdad, Iraq

Mohammed Y. Fattah : Building and Construction Engineering Department, University of Technology, Baghdad, Iraq

Balqees A. Ahmed : Faculty Member, Civil Engineering Department, University of Baghdad, Baghdad, Iraq

Abstract
This paper studies on dynamic and stability behavior of a clamped-elastically restrained nanobeam under the action of a nonconservative force with an emphasis on the influence of surface properties on divergence and flutter instability. Using the Euler-Bernoulli beam theory incorporating surface effects, a governing equation for a clamped-elastically restrained nanobeam is derived according to Hamilton‟s principle. The characteristic equation is obtained explicitly and the forcefrequency interaction curves are displayed to show the influence of the surface effects, spring stiffness of the elastic restraint end on critical loads including divergence and flutter loads. Divergence and flutter instability transition is analyzed. Euler buckling and stability of Beck‟s column are some special cases of the present at macroscale.

Key Words
surface elasticity; flutter instability; divergence instability; nanocantilever; elastically restrained end

Address
Qiu-Xiang Xiao : School of Civil Engineering, Central South University, Changsha 410075, PR China

Jiaqi Zou : School of Civil Engineering, Central South University, Changsha 410075, PR China

Kang Yong Lee : State Key Laboratory of Structural Analysis for Industrial Equipment and Department of Engineering Mechanics,
Dalian University of Technology, Dalian 116024, PR China

Xian-Fang Li : School of Civil Engineering, Central South University, Changsha 410075, PR China; State Key Laboratory of Structural Analysis for Industrial Equipment and Department of Engineering Mechanics, Dalian University of Technology, Dalian 116024, PR China

Abstract
Friction Pendulum isolators are tools developed in the past few decades. The simplest form of these isolators, are FPS whose main disadvantages are having a constant frequency independent of the frequency of the structure. For this reason, researchers have invented VFPI isolator whose frequency is variable and depends on displacement. Another friction pendulum isolator is DCFP isolator which is a combination of two FPS isolators. In this article, first by changing the geometry of DCFP isolator plates from spherical to elliptical, the motion and frequency equations of DVFPI isolators are defined, and then the seismic behavior of DVFPI isolators are analyzed in various geometric and plate friction settings using motion equations, and confirmed using ABAQUS software. The most important results of this study are that the hysteresis behavior of DVFPI isolators are severely nonlinear, its curve follows two distinct curvatures, and that the restoring force is faced with softening mechanism that limits the seismic force transmitted to the structure, whereas the restoring force in DCFP isolators increases linearly with increasing displacement.

Key Words
earthquake engineering; passive control; base isolation; DCFP; cyclic behaviour; VFPI

Address
Gholamreza Abdollahzadeh : Faculty of Civil Engineering, Babol Noshirvani University of Technology, Iran

Reza Darvishi : Faculty of Civil Engineering, Babol Noshirvani University of Technology, Iran

Abstract
A new quasi-3D higher shear deformation theory (quasi-3D HSDT) for functionally graded plates is proposed in this article. The theory considers both shear deformation and thickness-stretching influences by a hyperbolic distribution of all displacements within the thickness, and respects the stress-free boundary conditions on the upper and lower surfaces of the plate without using any shear correction factor. The highlight of the proposed theory is that it uses undetermined integral terms in displacement field and involves a smaller number of variables and governing equations than the conventional quasi-3D theories, but its solutions compare well with 3D and quasi-3D solutions. Equations of motion are obtained from the Hamilton principle. Analytical solutions for buckling and dynamic problems are deduced for simply supported plates. Numerical results are presented to prove the accuracy of the proposed theory.

Key Words
buckling; vibration; sandwich plate; functionally graded materials; quasi-3D HSDT

Address
Mohamed Sekkal : Laboratoire de Modélisation et Simulation Multi-échelle, Département de Physique, Faculté des Sciences Exactes,
Département de Physique, Université de Sidi Bel Abbés, Algeria

Bouazza Fahsi : Faculty of Technology, Civil Engineering Department, Material and Hydrology Laboratory, University of Sidi Bel Abbes, Algeria

Abdelouahed Tounsi : Faculty of Technology, Civil Engineering Department, Material and Hydrology Laboratory, University of Sidi Bel Abbes, Algeria; Laboratoire de Modélisation et Simulation Multi-échelle, Département de Physique, Faculté des Sciences Exactes,
Département de Physique, Université de Sidi Bel Abbés, Algeria; Laboratoire des Structures et Matériaux Avancés dans le Génie Civil et Travaux Publics, Université de Sidi Bel Abbes,
Faculté de Technologie, Département de Génie Civil, Algeria

S.R. Mahmoud : Department of Mathematics, Faculty of Science, King Abdulaziz University, Saudi Arabia

Abstract
This article deals with the buckling behaviour of multilayered magneto-electro-elastic (MEE) plate subjected to uniaxial and biaxial compressive (in-plane) loads. The constitutive equations of MEE material are used to derive a finite element (FE) formulation involving the coupling between electric, magnetic and elastic fields. The displacement field corresponding to first order shear deformation theory (FSDT) has been employed. The in-plane stress distribution within the MEE plate existing due to the enacted force is considered to be equivalent to the applied in-plane compressive load in the pre-buckling range. The same stress distribution is used to derive the potential energy functional. The non-dimensional critical buckling load is accomplished from the solution of allied linear eigenvalue problem. Influence of stacking sequence, span to thickness ratio, aspect ratio, load factor and boundary condition on critical buckling load and their corresponding mode shape is investigated. In addition, static deflection of MEE plate under the sinusoidal and the uniformly distributed load has been studied for different stacking sequences and boundary conditions.

Key Words
magneto-electro-elastic plate; FSDT; finite element; buckling analysis; static studies; in-plane loads

Address
M.C. Kiran : Department of Mechanical Engineering, National Institute of Technology Karnataka, Surathkal 575025, India

S.C. Kattimani : Department of Mechanical Engineering, National Institute of Technology Karnataka, Surathkal 575025, India

Abstract
The out-of-plane response of infill walls has recently gained a growing attention and has been recognised fundamental in the damage assessment of reinforced concrete and steel framed buildings subjected to seismic loads. The observation of damage after earthquakes highlighted that out-of-plane collapse of masonry infills may occur even during seismic events of low or moderate intensity, causing both casualty risks and unfavourable situations affecting the overall structural response. Even though studies concerning the out-of-plane behaviour of infills are not as many as those focused on the in-plane response, in the last decades, a substantial number of researches have been carried out on the out-of-plane behaviour of infills. In this study, the out-of-plane response is investigated considering different aspects. First, damages observed after past earthquakes are examined, with the aim of identifying the main parameters involved and the most critical configurations. Secondly, the response recorded in about 150 experimental tests is deeply examined, focusing on the influence of geometrical characteristics, boundary conditions, prior in-plane damage, presence of reinforcing elements and openings. Finally, different theoretical capacity models and code provisions are discussed and compared, giving specific attention to those based on the arching theory. The reliability of some of these models is herein tested with reference to experimental results. The comparison between analytically predicted and experimental values allows to appreciate the extent of approximation of such methods.

Key Words
infill walls; masonry; frames; out-of-plane loads; experimental tests; predicting models; out-of-plane capacity

Address
Monica Pasca : Department of Structural and Geotechnical Engineering,

Abstract
Carbon Fiber Reinforced Polymer (CFRP) laminates are used widely either for repairing or strengthening of existing structures. When CFRP laminates are used for strengthening of RC continuous T-beams in the Hogging Moment Zone (HMZ); above and around the intermediate supports, it is important to study the expected positions of the laminates across the width of the beam flange. Although, it is traditional to consider CFRP laminates added above the beam web, this is not practical since walls and columns are located in such positions in general. This paper examines the effect of changing the positions of CFRP laminates used for the strengthening of the hogging moment zone across the beam flange of two-span-T-section beams. The Finite Element (FE) Package ANSYS is used to create 3-D theoretical models needed for the study. It can be concluded that changing the position of CFRP strengthening across the beam flange, in the hogging moment zone, is effective upon the overall behavior. The best locations are either above the web or at the flange just beside the web, due to the presence of walls and/or columns.

Key Words
CFRP; continuous beam; RC; ANSYS; strengthening; hogging moment; position; flange

Address
Mohammad Mohie Eldin : Department of Civil Engineering, Faculty of Engineering, Beni-Suef University, Egypt

Ahmed M. Tarabia : Department of Structural Engineering, Faculty of Engineering, Alexandria University, Egypt

Rahma F. Hasson : Department of Civil Engineering, Faculty of Engineering, Sirte University, Libya

Abstract
The damage of concrete due to the expansion of alkali-aggregate reaction (AAR) and thermal-chemical reactions affecting the strength of concrete is studied. The empirical equations for the variations of expansion of AAR, compressive strength and degradation of the modulus of elasticity with time, and compressive strength with degradation of the modulus of elasticity are proposed by analysing numerous experimental data. It is revealed that the expansion of AAR and compressive strength increase with time. The proposed combination of the time variations of chemical and mechanical parameters provides a satisfactory prediction of the concrete strength. Seismic analysis of the aged Koyna dam is conceded for two different long-term experimental data of concrete incorporating the proposed AAR based properties. The responses of aged Koyna dam reveal that the crest displacement of the Koyna dam significantly increases with time while the contour plots show that major principal stress at neck level reduces with time. As the modulus of elasticity decreases with ages the stress generated in the concrete structure get reduces. On the other hand with lesser value of modulus of elasticity the structure becomes more flexible and the crest displacement becomes very high that cause the seismic safety of the dam reduce

Key Words
degradation of concrete; alkali-aggregate reaction; aged concrete dam; thermo-chemical reaction; compressive strength of aged concrete; numerical modeling

Address
Nik Zainab Nik Azizan : School of Civil Engineering, Universiti Sains Malaysia, Penang, Malaysia; School of Environmental Engineering, Universiti Malaysia Perlis, Perlis, Malaysia

Angshuman Mandal : Department of Civil Engineering, Indian Institute of Technology, Kharagpur, India

Taksiah A. Majid : School of Civil Engineering, Universiti Sains Malaysia, Penang, Malaysia

Damodar Maity : Department of Civil Engineering, Indian Institute of Technology, Kharagpur, India

Fadzli Mohamed Nazr : School of Environmental Engineering, Universiti Malaysia Perlis, Perlis, Malaysia

Abstract
Structural health monitoring has increasingly been a focus within the civil engineering research community over the last few decades. With increasing application of sensor networks in large structures and infrastructure systems, effective use and development of robust algorithms to analyze large volumes of data and to extract the desired features has become a challenging problem. In this paper, we grasp some precautions and key points of the signal processing approach, wavelet, establish a relative reliable framework, and analyze three problems that require attention when applying wavelet based damage detection approach. The cases studies how to use optimal scales for extracting mode shapes and modal curvatures in a reinforced concrete beam and how to effectively identify damages using maximum curves of wavelet coefficient differences. Moreover, how to make a recognition based on the wavelet multi-resolution analysis, wavelet packet energy, and fuzzy sets is a meaningful topic that has been addressed in this work. The relative systematic work that compasses algorithms, structures and evaluation paves a way to a framework regarding effective structural health monitoring, orientation, decision and action.

Key Words
mode shape; curvature mode; wavelet coefficient differences; multi-resolution analysis; damage identification; artificial neural network; fuzzy pattern recognition; reinforced concrete beam

Address
Ying Zhao : International Institute for Urban Systems Engineering, Southeast University, Nanjing, 210096, China

Mohammad Noori : International Institute for Urban Systems Engineering, Southeast University, Nanjing, 210096, China; Mechanical Engineering, California Polytechnic State University, San Luis Obispo, California 93405, USA

Wael A. Altabey :International Institute for Urban Systems Engineering, Southeast University, Nanjing, 210096, China; Department of Mechanical Engineering, Faculty of Engineering, Alexandria University, Alexandria 21544, Egypt

Abstract
The effects of thermocycling procedure and material shade on the mechanical properties and wear resistance of resin-based dental restorative materials are investigated. The modulus of elasticity, hardness, plasticity index and wear resistance are determined for the conventional composite, the nanohybrid composite and the nanofilled dental composites. Disc-shape samples are prepared from each material to investigate the effects of thermocycling procedure on the mechanical properties and wear resistance of different types of dental restorative materials. In this respect, a group of samples is thermocycled and the other group is stored in ambient conditions. Then nano-indentation and nano-scratch tests are performed on the samples to measure their mechanical properties and wear resistance. Results show that the A1E shade of the dental nanocomposite possesses higher modulus of elasticity and hardness values compared to the two other shades. According to the experimental results, the mean values for the modulus of elasticity and hardness of the A1E shade of the nanocomposite are 13.71 GPa and 1.08 GPa, respectively. The modulus of elasticity and hardness of the conventional dental composite increase around 30 percent in the oral environment due to the moisture and temperature changes. The wear resistance of the dental composites is also significantly affected by moisture and temperature changes in the oral conditions. It is observed that thermocycling has no significant effect on the hardness, plasticity index and wear resistance of the nanohybrid composite and the nanocomposite dental materials.

Key Words
dental restorative polymers; nano-indentation experiment; nano-scratch experiment; surface analysis; thermocycling effect

Address
A. Karimzadeh : Fatigue and Fracture Laboratory, Center of Excellence in Experimental Solid Mechanics and Dynamics

Majid R. Ayatollahi : Fatigue and Fracture Laboratory, Center of Excellence in Experimental Solid Mechanics and Dynamics

M. Nikkhooyifar : Fatigue and Fracture Laboratory, Center of Excellence in Experimental Solid Mechanics and Dynamics

A.R. Bushroa : Department of Mechanical Engineering, Faculty of Engineering, University of Malaya, Kuala Lumpur 50603, Malaysia; Centre of Advanced Manufacturing and Mechanical Engineering, Faculty of Engineering, University of Malaya,
Kuala Lumpur 50603, Malaysia


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