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CONTENTS
Volume 71, Number 5, September10 2019
 

Abstract
In this paper, hyperbolic shear deformation theory is used for free vibration analysis of piezoelectric rectangular plate made of porous core. Various types of porosity distributions for the porous material is used. To obtain governing equations of motion, Hamilton\'s principle is used. The Navier\'s method is used to obtain numerical results of the problem in terms of significant parameters. One can conclude that free vibration responses are changed significantly with change of important parameters such as various porosities and dimensionless geometric parameters such as thickness to side length ratio and ratio of side lengths.

Key Words
free vibration; porous material; hyperbolic shear deformation theory; Hamilton\'s principle; porosity distribution

Address
Department of Solid Mechanic, Faculty of Mechanical Engineering, University of Kashan, Kashan 87317-51167, Iran

Abstract
In this paper, an improved mathematical model is presented for the bending analysis of doubly curved functionally graded material (FGM) sandwich rhombic conoids. The mathematical model includes expansion of Taylor\'s series up to the third degree in thickness coordinate and normal curvatures in in-plane displacement fields. The condition of zero-transverse shear strain at upper and lower surface of rhombic conoids is implemented in the present model. The newly introduced feature in the present mathematical model is the simultaneous inclusion of normal curvatures in deformation field and twist curvature in strain-displacement equations. This unique introduction permits the new 2D mathematical model to solve problems of moderately thick and deep doubly curved FGM sandwich rhombic conoids. The distinguishing feature of present shell from the other shells is that maximum transverse deflection does not occur at its center. The proposed new mathematical model is implemented in finite element code written in FORTRAN. The obtained numerical results are compared with the results available in the literature. Once validated, the current model was employed to solve numerous bending problems by varying different parameters like volume fraction indices, skew angles, boundary conditions, thickness scheme, and several geometric parameters.

Key Words
functionally graded sandwich shell; conoids; finite element method; rhombic shell

Address
Md I. Ansari: Department of Architecture, Jamia Millia Islamia, New Delhi- 110025, India
Ajay Kumar and Ranja Bandyopadhyaya: Department of Civil Engineering, National Institute of Technology Patna, Patna- 800005, India

Abstract
In this research, the nonlinear static, buckling and vibration analysis of viscoelastic micro-composite beam reinforced by various distributions of boron nitrid nanotube (BNNT) with initial geometrical imperfection by modified strain gradient theory (MSGT) using finite element method (FEM) are presented. The various distributions of BNNT are considered as UD, FG-V and FG-X and also, the extended rule of mixture is used to estimate the properties of micro-composite beam. The components of stress are dependent to mechanical, electrical and thermal terms and calculated using piezoelasticity theory. Then, the kinematic equations of micro-composite beam using the displacement fields are obtained. The governing equations of motion are derived using energy method and Hamilton\'s principle based on MSGT. Then, using FEM, these equations are solved. Finally the effects of different parameters such as initial geometrical imperfection, various distributions of nanotube, damping coefficient, piezoelectric constant, slenderness ratio, Winkler spring constant, Pasternak shear constant, various boundary conditions and three material length scale parameters on the behavior of nonlinear static, buckling and vibration of micro-composite beam are investigated. The results indicate that with an increase in the geometrical imperfection parameter, the stiffness of micro-composite beam increases and thus the non-dimensional nonlinear frequency of the micro structure reduces gradually.

Key Words
nonlinear bending; buckling; vibration analysis; viscoelastic beam; various distributions of BNNTs; initial geometrical imperfection; MSGT; FEM

Address
S. Alimirzaei, M. Mohammadimehr: Department of Solid Mechanics, Faculty of Mechanical Engineering, University of Kashan, P.O. Box: 87317-51167, Kashan, Iran
Abdelouahed Tounsi: Department of Civil and Environmental Engineering, King Fahd University of Petroleum & Minerals,
31261 Dhahran, Eastern Province, Saudi Arabia
Material and Hydrology Laboratory, Faculty of Technology, Civil Engineering Department, University of Sidi Bel Abbes, Algeria

Abstract
Genetic Algorithms (GAs) have found the best design for reinforced concrete frames. The design of the optimum beam sections by GAs has been unified. The process of the optimum-design sections has satisfied axial, flexural, shear and torsion necessities based on the designing code. The frames\' function has contained the function of both concrete and reinforced steel besides the function of the frames\' formwork. The results have revealed that limiting the dimension of frame-beam with the dimension of frame-column have increased the optimum function of the structure, thereby reducing the reanalysis requirement for checking the optimum-designed structures through GAs.

Key Words
optimum-design; GA; space frame; reinforced concrete

Address
Chuanhua Xu, Xiliang Zhang: State Key Laboratory of Safety and Health for Metal Mines, Sinosteel Maanshan Institute of Mining Research, Co., Ltd., Anhui, Maanshan 243000, China
James H. Haido: Department of civil engineering, college of engineering, University of Duhok, Kurdistan Region, Iraq
Peyman Mehrabi: Department of Civil Engineering, K.N. Toosi University of Technology, Tehran, Iran
Ali Shariati: Department of Civil Engineering, Faculty of engineering, University of Malaya, Kuala Lumpur, Malaysia
Edy Tonnizam Mohamad: Centre of Tropical Geoengineering (GEOTROPIK), School of Civil Engineering, Faculty of Engineering, Universiti Teknologi Malaysia, 81310 Johor Bahru, Malaysia
Hoang Nguyen:Institute of Research and Development, Duy Tan University, Da Nang 550000, Vietnam
Karzan Wakil: Research Center, Sulaimani Polytechnic University, Sulaimani 46001, Kurdistan Region, Iraq

Abstract
The present study deals with the simulation of low velocity impact on prestressed and reinforced concrete (RC) slabs supported with different end conditions. The prestress is pre-applied on the RC slab in an analytical approach for the prestressed slab. RC slabs with dimensions 500x600x60 mm, 500x600x80 mm and 500x600x120 mm were used by changing support condition in two different ways; (i) Opposite sides simply supported, (ii) Adjacent sides simply supported with opposite corner propped. Deflection response of these specimens were found for the impact due to three different velocities. The effect of grade of concrete on deflection due to the impact of these slabs were also studied. Deflection result of 500x500x50 mm slab was calculated numerically and compared the result with the available experimental result in literature. Finite element analyses were performed using commercially available ANSYS 16.2 software. The effectiveness of prestressing on impact resistant capacity of RC slabs are demonstrated by the way of comparing the deflection of RC slabs under similar impact loadings.

Key Words
finite element; prestressing; low velocity impact; concrete; support conditions; floor slab

Address
Partheepan Ganesan: Department of Civil Engineering, MVGR College of Engineering, Vizianagaram - 535 005
S. Venkata Sai Kumar: Department of Civil Engineering, Baba Institute of Technology and Sciences, Vizag - 530 041
Andhra Pradesh, India

Abstract
In the present study, buckling and free vibration analyses of annular thin sector plate made of functionally graded materials (FGMs) resting on visco-elastic Pasternak foundation, subjected to external radial, circumferential and shear in-plane loads is investigated. Material properties are assumed to vary along the thickness according to an power law with Poisson\'s ratio held constant. First, based on the classical plate theory (CPT), the governing equation of motion is derived using Hamilton\'s principle and then is solved using the generalized differential quadrature method (GDQM). Numerical results are compared to those available in the literature to validate the convergence and accuracy of the present approach. Finally, the effects of power-law exponent, ratio of radii, thickness of the plate, sector angle, and coefficients of foundation on the fundamental and higher natural frequencies of transverse vibration and critical buckling loads are considered for various boundary conditions. Also, vibration and buckling mode shapes of functionally graded (FG) sector plate have been shown in this research. One of the important obtained results from this work show that ratio of the frequency of FG annular sector plate to the corresponding values of homogeneous plate are independent from boundary conditions and frequency number.

Key Words
buckling and free vibration; annular thin sector FGM plate; visco- elastic Pasternak medium; generalized differential quadrature method

Address
Mehdi Mohammadimehr, Hasan Afshari, M. Salemi, K. Torabi and Mojtaba Mehrabi: Department of Solid Mechanics, Faculty of Mechanical Engineering, University of Kashan, Kashan, Iran
Hasan Afshari: Department of Mechanical Engineering, Khomeinishahr Branch, Islamic Azad University, Khomeinishahr/Isfahan, Iran
K. Torabi and Mojtaba Mehrabi: Department of Mechanics, Faculty of Engineering, University of Isfahan, Isfahan, Iran

Abstract
The analysis and design of complex structures like sandwich-panel elements are difficult; the use of finite element method for the analysis is complicated and time consuming when non-linear effects are considered. On the other hand, artificial neural network (ANN) models can capture the non-linear effects and its application requires lesser computational demand. Two ANN models were trained, tested and validated to compute the force for a given displacement of a sandwich-type roof element; 2555 force and element deformation pairs were used for training the ANN models. For the models trained without considering the damping effect, there were two values in the input layer: maximum displacement and current displacement, and for the model considering damping, displacement from the previous step was used as an additional input. Totally, 400 ANN models were trained. Results show that there is a good agreement between the experimental and simulated data, and the models showed a good performance with a mean square error value of 4548.85. Both the ANN models could simulate the inelastic behaviour, loss of rigidity, and evolution of permanent displacements. The models could also interpolate and extrapolate, which enables them to be used as an analysis and design tool for such complex elements.

Key Words
Artificial Neural Networks; inelastic behavior; composed panels; non-traditional structures; permanent displacement

Address
María E. Marante, Wilmer J. Barreto and Ricardo A. Picón: Laboratory of Structural Mechanics, Lisandro Alvarado University, Barquisimeto, Venezuela
Wilmer J. Barreto and Ricardo A. Picón: Departamento de Obras Civiles y Geología, Facultad de Ingeniería, Universidad Católica de Temuco, Temuco, Chile


Abstract
This paper presents the results of a study into the dynamic behaviour of a support structure of a mobile elevating work platform. The vibrations of the mechanical system of the observed structure are examined analytically, numerically, and experimentally. Within the analytical examination, a simple mathematical model is developed to describe free and forced vibrations. The dynamic analysis of the mechanical system is conducted using a discrete dynamic model with a reduced number of vibrational degrees of freedom. On the basis of the expression for the system energy, and by applying Lagrange\'s equations of the second kind, differential equations are derived for system vibrations, frequencies are determined, and the laws of forced platform vibration are established. At the same time, a nonlinear FEM model is developed and the laws of free and forced vibration are determined. The experimental and numerical part of the study deal with the examination of the real structure in extreme conditions, taking into account: the lowest eigenfrequency, forced actions that could endanger the general stability, the maximal amplitudes, and the acceleration of the work platform. The obtained analytical and numerical results are compared with the experiments. The experimental verification points to the adverse behaviour of the platform in excitation cases – swaying. In such a situation, even a relatively small physical force can lead to unacceptably high amplitudes of displacement and acceleration – exceeding the usual work values.

Key Words
experiment; FEM; frame structures; incidental dynamic analysis; mechanical model; numerical simulation

Address
Miomir L.J. Jovanović and Vladimir S. Stojanović: University of Niš, Faculty of Mechanical Engineering, Str. Al. Medvedev 14, Niš 18000, Serbia
Goran N. Radoičić: University

Abstract
According to The Concrete Centre, in the UK shear walls have become an inseparable part of almost every reinforced concrete frame building. Recently, the construction industry has questioned the need for shear walls in low to mid-rise RC frame buildings. This study tried to address the issue in two stages: The first stage, the feasibility of removing shear walls in an existing design for a residential building where ETABS and CONCEPT software were used to investigate the structural performance and cost-effectiveness respectively. The second stage, the same structure was examined in various locations in the UK to investigate regional effects. This study demonstrated that the building without shear wall could provide adequate serviceability and strength within the safe range defined by Eurocodes. As a result, construction time, overall cost and required concrete volume are reduced which in turn enhance the sustainability of concrete construction.

Key Words
low-rise RC buildings; wind actions; sustainability; non-linear static analysis; cost-effectiveness

Address
Reza Keihani: School of Computing and Engineering, University of West London, London, UK, W5 5RF
Ali Bahadori-Jahromi: Civil Engineering, School of Computing and Engineering, University of West London, London, UK, W5 5RF
Charles Goodchild: the Concrete Centre, London, UK, SW1V 1HU

Abstract
The paper investigates the influence of the rheological parameters which characterize the creep time, the long-term values of the mechanical properties of viscoelastic materials and a form of the creep function around the initial state of a deformation of the materials of the hollow bi-layered cylinder on the dispersion of the flexural waves propagated in this cylinder. Constitutive relations for the cylinder\'s materials are given through the fractional exponential operators by Rabotnov. The dispersive attenuation case is considered and numerical results related to the dispersion curves are presented and discussed for the first and second modes under the first harmonic in the circumferential direction. According to these results, it is established that the viscosity of the materials of the constituents causes a decrease in the flexural wave propagation velocity in the bi-layered cylinder under consideration. At the same time, the character of the influence of the rheological parameters, as well as other problem parameters such as the thickness-radius ratio and the elastic modulus ratio of the layers\' materials on the dispersion curves, are established.

Key Words
flexural waves; rheological materials; viscoelastic material; wave dispersion; fractional-exponential operator; bi-layered hollow cylinder

Address
Tarik Kocal: Department of Marine Engineering Operations, Yildiz Campus, 34349 Besiktas, Istanbul, Turkey
Surkay D. Akbarov: Department of Mechanical Engineering, Yildiz Technical University, Yildiz Campus, 34349, Besiktas, Istanbul, Turkey
Institute of Mathematics and Mechanics of the National Academy of Sciences of Azerbaijan, 37041, Baku, Azerbaijan


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