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CONTENTS
Volume 44, Number 1, October10 2012
 

Abstract
In this paper the dynamic behavior of a viscoelastic Timoshenko beam subjected to a concentrated moving load are studied analytically and numerically. The viscoelastic properties of the beam obey the linear standard model in shear and incompressible in bulk. The governing equation for Timoshenko beam theory is obtained in viscoelastic form using the correspondence principle. The analytical solution is based on the Fourier series and the numerical solution is performed with finite element method. The effects of the material properties and the load velocity are investigated on the responses by numerical and analytical methods. In addition, the results are compared with the Euler beam results.

Key Words
viscoelastic timoshenko beam; moving load; analytical solution; linear standard model; FE

Address
Mohammad Tehrani and H.R. Eipakchi: Mechanical Engineering Faculty, Shahrood University of Technology, P.O. Box 316, Shahrood, I.R. Iran

Abstract
In the present paper, an improved high-order theory is used for bending analysis of soft-core sandwich plates. Third-order plate assumptions are used for face sheets and quadratic and cubic functions are assumed for transverse and in-plane displacements of the orthotropic soft core. Continuity conditions for transverse shear stresses at the interfaces as well as the conditions of zero transverse shear stresses on the upper and lower surfaces of the plate are satisfied. Also, transverse flexibility and transverse normal strain and stress of the orthotropic core are considered. The equations of motion and boundary conditions are derived by principle of minimum potential energy. Analytical solution for bending analysis of simply supported sandwich plates under various transverse loads are presented using Navier\'s solution. Comparison of the present results with those of the three-dimensional theory of elasticity and some plate theories in the literature confirms the accuracy of the proposed theory.

Key Words
bending analysis; sandwich plate; high-order theory; analytical solution; soft core

Address
M.M. Kheirikhah: Faculty of Industrial and Mechanical Engineering, Qazvin Branch, Islamic Azad University, Qazvin, Iran
S.M.R. Khalili: Centre of Excellence for Research in Advanced Materials & Structures, Faculty of Mechanical
Engineering, K.N. Toosi University of Technology, Tehran, Iran
K. Malekzadeh Fard: Department of Structural Engineering and Simulation, Space Research Institute, Tehran-karaj Highway, Tehran, Iran

Abstract
A series of fatigue test were carried out on scarfed lap joints (SLJ) using in airfoil siding to explore the effect of structural details, such as rows of rivets, lap angles, on its fatigue performance. Finite element (FE) analysis was employed to explore the effect of lap angle on load transfer and the stress evolution around the rivet hole. At last, the fatigue lives were predicted by nominal stress approach and critical plane approach. Both of the test results and predicted results showed that fatigue life of SLJ was remarkably increased after introducing lap angle into the faying surface. Specimen with the lap angle of 1.68o exhibits the best fatigue performance in the present study.

Key Words
fatigue life; scarfed lap joint; lap angle; critical plane approach; finite element method

Address
W.Z. Yan, H.S. Gaoa, X. Yuanb, F.S. Wangc and Z.F. Yue: Institute of Aircraft Reliability Engineering, School of Mechanics, Civil Engineering and Architecture, Northwestern Polytechnical University, Xi\'an 710129, PR China

Abstract
Concrete sleepers are essential components of the conventional railway. As support elements, sleepers are always subjective to a variety of time-dependent loads attributable to the train operations, either wheel or rail abnormalities. It has been observed that the sleepers may deteriorate due to these loads, inducing the formation of hairline cracks. There are two areas along the sleepers that are more prone to crack: the central and the rail seat sections. Several non-destructive methods have been developed to identify failures in structures. Health monitoring techniques are based on vibration responses measurements, which help engineers to identify the vibration-based damage or remotely monitor the sleeper health. In the present paper, the dynamic effects of the cracks in the vibration signatures of the railway pre-stressed concrete sleepers are investigated. The experimental modal analysis has been used to evaluate the modal bending changes in the vibration characteristics of the sleepers, differentiating between the central and the rail seat locations of the cracks. Modal parameters changes of the \'healthy\' and cracked sleepers have been highlighted in terms of natural frequencies and modal damping. The paper concludes with a discussion of the most suitable failure indicator and it defines the vibration signatures of intact, central cracked and rail seat cracked sleepers.

Key Words
experimental modal analysis (EMA); concrete sleeper; structural health monitoring; crack; damping

Address
J.I. Real, M.E. Sanchez: Department of Transportation Engineering and Infrastructures, School of Civil Engineering, Technical University of Valencia, 14 Camino de Vera, 46022 Valencia, Spain
T. Real: Department of Construction Engineering, Public Works and Urban Infrastructure, School of Engineering,
University of Alicante, Campus de SantVicent del Raspeig, PO Box 99, E-03080 Alicante, Spain
F.J. Ssnchez: Railway Division of Precon S.A.U., 13C Apolonio Morales, 28036 Madrid, Spain
C. Zamorano: Foundation for the Research and Engineering in Railways, 160 Serrano, 28002 Madrid, Spain

Abstract
The paper is on contact analysis of a spherical ball with a deformable flat, considering the effect of tangent modulus on the contact parameters of a non-adhesive frictionless elastic-plastic contact. The contact analysis of this model has been carried out using analysis software Ansys and Abaqus. The contact parameters such as area of contact between two consecutive steps, volume of bulged material are evaluated from the formulated equations. The effect of the tangent modulus is considered for determining these parameters. The tangent modulus are accounted between 0.1E and 0.5E of materials E/Y value greater than 500 and less than 1750. Result shows that upto an optimal tangent modulus values the elastic core push up to the free surface in the flat. The simulation is also carried out in Abaqus and result provide evidence for the volume of bulged material in the contact region move up and flow into the free surface of the flat from the contact edge between the ball and flat. The strain energy of the whole model is varied between 20 to 40 percentage of the stipulated time for analysis.

Key Words
tangent modulus; E/Y ratio; elastic-plastic; elastic core; strain energy

Address
V.C. Sathish Gandhi: Department of Mechanical Engineering, University College of Engineering Nagercoil, Anna University, Tirunelveli Region, Konam, Nagercoil - 629004, Tamilnadu, India
S. Ramesh: Department of Mechanical Engineering, Sona College of Technology, Salem, Tamilnadu, India
R. Kumaravelan: Department of Mechanical Engineering, Velalar College of Engineering and Technology, Erode, Tamilnadu, India
M. Thanmanaselvi: Department of Civil Engineering, University College of Engineering Nagercoil, Anna University, Tirunelveli Region, Konam, Nagercoil - 629004, Tamilnadu, India

Abstract
This paper strongly addresses to the problem of the mechanical systems in which parameters are uncertain and bounded. Interval calculation is used to find sharp bounds of the structural parameters for infilled frame system modeled with finite element method. Infill walls are generally treated as nonstructural elements considerably to improve the lateral stiffness, strength and ductility of the structure together with the frame elements. Because of their complex nature, they are often neglected in the analytical model of building structures. However, in seismic design, ignoring the effect of infill wall in a numerical model does not accurately simulate the physical behavior. In this context, there are still some uncertainties in mechanical and also geometrical properties in the analysis and design procedure of infill walls. Structural uncertainties can be studied with a finite element formulation to determine sharp bounds of the structural parameters such as wall thickness and Young\'s modulus. In order to accomplish this sharp solution as much as possible, interval finite element approach can be considered, too. The structural parameters can be considered as interval variables by using the interval number, thus the structural stiffness matrix may be divided into the product of two parts which correspond to the interval values and the deterministic value.

Key Words
interval analysis; interval finite elements; masonry infilled wall; uncertainty

Address
Ayse Erdolen and Bilge Doran: Civil Engineering Department, Yildiz Technical University, Davutpasa Campus, 34210 Esenler, Istanbul, Turkey

Abstract
The building frame and its foundation along with the soil on which it rests, together constitute a complete structural system. In the conventional analysis, a structure is analysed as an independent frame assuming unyielding supports and the interactive response of soil-foundation is disregarded. This kind of analysis does not provide realistic behaviour and sometimes may cause failure of the structure. Also, the conventional analysis considers infill wall as non-structural elements and ignores its interaction with the bounding frame. In fact, the infill wall provides lateral stiffness and thus plays vital role in resisting the seismic forces. Thus, it is essential to consider its effect especially in case of high rise buildings. In the present research work the building frame, infill wall, isolated column footings (open foundation) and soil mass are considered to act as a single integral compatible structural unit to predict the nonlinear interaction behaviour of the composite system under seismic forces. The coupled isoparametric finite-infinite elements have been used for modelling of the interaction system. The material of the frame, infill and column footings has been assumed to follow perfectly linear elastic relationship whereas the well known hyperbolic soil model is used to account for the nonlinearity of the soil mass.

Key Words
finite element method; infilled frame; infill wall; nonlinear analysis; hyperbolic soil model; differential settlement; decay pattern; infinite elements; truncation boundary

Address
Ramakant Agrawal: Department of Civil Engineering,TRUBA Institute of Engineering and Information Technology, Bhopal, India
M.S. Hora: Department of Applied Mechanics, Maulana Azad National Institute of Technology, Bhopal, India

Abstract
Post-buckling behavior of Timoshenko beams subjected to uniform temperature rising with temperature dependent physical properties are studied in this paper by using the total Lagrangian Timoshenko beam element approximation. The beam is clamped at both ends. In the case of beams with immovable ends, temperature rise causes compressible forces end therefore buckling and post-buckling phenomena occurs. It is known that post-buckling problems are geometrically nonlinear problems. Also, the material properties (Young\'s modulus, coefficient of thermal expansion, yield stress) are temperature dependent: That is the coefficients of the governing equations are not constant in this study. This situation suggests the physical nonlinearity of the problem. Hence, the considered problem is both geometrically and physically nonlinear. The considered highly non-linear problem is solved considering full geometric non-linearity by using incremental displacement-based finite element method in conjunction with Newton- Raphson iteration method. The beams considered in numerical examples are made of Austenitic Stainless Steel (316). The convergence studies are made. In this study, the difference between temperature dependent and independent physical properties are investigated in detail in post-buckling case. The relationships between deflections, thermal post-buckling configuration, critical buckling temperature, maximum stresses of the beams and temperature rising are illustrated in detail in post-buckling case.

Key Words
temperature dependent physical properties; thermal post-buckling analysis; total lagrangian finite element model; Timoshenko beam; uniform temperature rise

Address
Seref Doguscan Akbas and Turgut Kocaturk: Department of Civil Engineering, Yildiz Technical University, Davutpasa Campus, 34210 Esenler, Istanbul, Turkey


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