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CONTENTS
Volume 21, Number 2, September30 2005
 

Abstract
This paper presents the implementation of the Blatz-Ko hyperelastic compressible model in a finite element program to deal with large deformation problems. We show analytically and numerically that the minimum number of increment steps in the Newton-Raphson algorithm depends on material properties and applied loads. We also show that this dependence is related to the orientation preservation principle. So we propose a convergence criteria based on the sign of eigenvalues of the deformation gradient matrix.

Key Words
Blatz-Ko model; hyperelasticity; finite element; large deformation; Newton-Raphson.

Address
Francois Peyraut; Laboratoire MŽcatronique3M, Universite de Technologie de Belfort-MontbŽliard,
SŽvenans, 90010 Belfort cedex, France
Zhi-Qiang Feng; Laboratoire de MŽcanique d?vry, Universite d?vry-Val d?ssonne,40, rue du Pelvoux, 91020 Evry cedex, France
Nadia Labed; Laboratoire MŽcatronique3M, Universite de Technologie de Belfort-MontbŽliard,SŽvenans, 90010 Belfort cedex, France

Abstract
Dynamic analysis of dam-reservoir-foundation system is usually carried out by employing a simplified and approximate one-dimensional model to account for fluid-foundation interaction. The approximation introduced on this basis is examined thoroughly in this paper by comparing the method with the rigorous approach. It is concluded that the errors due to approximate method could be very significant both for horizontal and vertical ground motions.

Key Words
rigorous interaction; fluid-foundation interaction; concrete gravity dams; dynamic analysis.

Address
Civil Engineering Department, Amirkabir University, Tehran, Iran

Abstract
In this paper an energy method is presented for the linear buckling analysis of first order shear deformable plates. The displacement fields are defined in terms of the shape functions, which correspond to a set of predefined points and are composed of significantly high order polynomials. The locations of these points are found by mapping the geometry using the naturalized coordinates and bilinear shape functions. In order to evaluate the method, fully clamped and simply supported rectangular plates subjected to uniform uniaxial compressive loading on two opposite edges of the plate are investigated thoroughly and the results are compared with the exact solution given in the monograph of Timoshenko and Gere (1961). The method is extended to the analysis of perforated plates, wherein the negative stiffness computed over the opening area from in-plane and out-of-plane deformation modes is superimposed to the stiffness of the full plate. Numerical results are then favorably compared with those obtained by finite element methods. Other cases such as; rectangular plates with eccentrically located openings of different shapes are studied and reported in this paper with regards to the effect of aspect ratio, hole size, and hole position on the buckling. For a square plate with a large circular opening at the center, diameter being 80 percent of the length, the present method yields buckling coefficient 12.5 percent higher than the one from the FEM.

Key Words
meshless method; perforated plate; p-type formulation; buckling; negative stiffness.

Address
Department of Mechanical and Materials Engineering, The University of Western Ontario, London, Ontario, N6A 5B9, Canada

Abstract
This study deals with the free vibration of a circular plate in contact with a fluid; submerged in fluid, beneath fluid or on fluid. An analytical method based on the finite Fourier-Bessel series expansion and Rayleigh-Ritz method is suggested. The proposed method is verified by the finite element analysis using commercial program with a good accuracy. The normalized natural frequencies are obtained in order to estimate the relative added mass effect of fluid on each vibration mode of the plate. Also, the location of plate coupled with fluid and the cases of free and bounded fluid surface are studied for the effect on the vibration characteristics.

Key Words
circular plate; Fourier-Bessel series; Rayleigh-Ritz method; fluid-coupled system; normalized frequency.

Address
Myung Jo Jhung, Young Hwan Choi and Hho Jung Kim;
Korea Institute of Nuclear Safety, 19 Guseong-dong, Yuseong-gu, Daejeon 305-338, Korea
Kyeong Hoon Jeong; Korea Atomic Energy Research Institute, 150 Dukjin-dong, Yuseong-gu, Daejeon 305-353, Korea

Abstract
Variations in system parameters due to uncertainties may result in system performance deterioration. Uncertainties in modeling of structures are often considered to ensure that control system is robust with respect to response errors. Hence, the uncertain concept plays an important role in vibration control of the engineering structures. The paper discusses the robustness of the stability of vibration control systems with uncertain parameters. The vibration control problem of an uncertain system is approximated by a deterministic one. The uncertain parameters are described by interval variables. The uncertain state matrix is constructed directly using system physical parameters and avoided to use bounds in Euclidean norm. The feedback gain matrix is determined based on the deterministic systems, and then it is applied to the actual uncertain systems. A method to calculate the upper and lower bounds of eigenvalues of the close-loop system with uncertain parameters is presented. The lower bounds of eigenvalues can be used to estimate the robustness of the stability the controlled system with uncertain parameters. Two numerical examples are given to illustrate the applications of the present approach.

Key Words
uncertain systems; vibration active control; upper and lower bounds of eigenvalues; robustness analysis of the stability; interval analysis.

Address
Department of Mechanics, Nanling Campus, Jilin University, Changchun, 130025, P.R. China

Abstract
This paper presents the possibilities of adapting artificial neural networks (ANNs) to predict the dimensionless parameters related to the maximum contact pressures of an elasticity problem. The plane symmetric double receding contact problem for a rigid stamp and two elastic strips having different elastic constants and heights is considered. The external load is applied to the upper elastic strip by means of a rigid stamp and the lower elastic strip is bonded to a rigid support. The problem is solved under the assumptions that the contact between two elastic strips also between the rigid stamp and the upper elastic strip are frictionless, the effect of gravity force is neglected and only compressive normal tractions can be transmitted through the interfaces. A three layered ANN with backpropagation (BP) algorithm is utilized for prediction of the dimensionless parameters related to the maximum contact pressures. Training and testing patterns are formed by using the theory of elasticity with integral transformation technique. ANN predictions and theoretical solutions are compared and seen that ANN predictions are quite close to the theoretical solutions. It is demonstrated that ANNs is a suitable numerical tool and if properly used, can reduce time consumed.

Key Words
contact problem; contact pressure; contact length; elasticity; rigid stamp; backpropagation; artificial neural networks.

Address
Karadeniz Technical University, Civil Engineering Department, 61080, Trabzon, Turkey

Abstract
In this paper, the shear resistance behaviour of reinforced concrete (RC) dapped end beams is investigated by 24 tests until failure load. The main parameters considered are the dapped end height, the type and effective range to provided the stirrups and the bent form of the longitudinal reinforcement. The failure behaviour of dapped end beams is presented and some conclusions are given. Inclined stirrups and longitudinal bent reinforcement have more influence on the shear capacity than vertical stirrups. Additionally, the shear mechanism of dapped end beams is analysed. Relatively simple semi-empirical equations for shear strength have been derived based on the results of 22 dapped end beams. The predicted results are in close agreement with the experimental ones. Finally, some design suggestions for the ultimate shear strength of dapped end beams are presented.

Key Words
reinforced concrete (RC); dapped end beams; shear capacity; shear failure; ultimate shear strength; shear resistance mechanisms.

Address
Quanfeng Wang and Zixiong Guo; College of Civil Engineering, Huaqiao University, 362011 Quanzhou, Fujian, China
Pierre C.J. Hoogenboom; Department of Civil Engineering, Delft University of Technology, 2600 GA Delft, Netherlands


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