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CONTENTS
Volume 23, Number 1, May10 2006
 

Abstract
Structural cracks may cause variations in structural stiffness and thus produce bilinear vibrations to structures. This study examines the dynamic behavior of structures with breathing cracks. A generalized algorithm based on the finite element method and bilinear theory was developed to study the influence of a breathing crack on the vibration characteristic. All the formulae derived in the time domain were applied to estimate the period of the overall bilinear motion cycle, and the contact effect was considered in the calculations by introducing the penetration of the crack surface. Changes in the dynamic characteristics of cracked structures are investigated by assessing the variation of natural frequencies under different crack status in either the open or closed modes. Results in estimation with vibrational behavior variation are significant compared with the experimental results available in the literature as well as other numerical calculations.

Key Words
breathing crack; cracked structure; finite element analysis.

Address
Tzuo-Liang Luo and James Shih-Shyn Wu;
Institute of Mechanical Engineering, Nat. Chung-Hsing University, 250, Kuo-Kuang Rd., Taichung, Taiwan 402, ROC
Jui-Pin Hung; Institute of Precision Machinery and Manufacturing Technology, National Chin-Yi Institute of Technology, 35, Lane. 215, Sec. 1, Chung-Shan Rd., Taiping, Taichung, Taiwan 411, ROC

Abstract
A locally varying temperature field or a mixture of two or more different materials can cause local variation of elasticity properties of a beam. In this paper, a new Euler-Bernoulli beam element with varying Young? modulus along its longitudinal axis is presented. The influence of axial forces according to the linearized 2nd order beam theory is considered, as well. The stiffness matrix of this element contains the transfer constants which depend on Young? modulus variation and on axial forces. Occurrence of the polynomial variation of Young? modulus has been assumed. Such approach can be also used for smooth local variation of Young? modulus. The critical loads of the straight slender columns were studied using the new beam element. The influence of position of the local Young? modulus variation and its type (such as linear, quadratic, etc.) on the critical load value and rate of convergence was investigated. The obtained results based on the new beam element were compared with ANSYS solutions, where the number of elements gradually increased. Our results show significant influence of the locally varying Young? modulus on the critical load value and the convergence rate.

Key Words
FEM; beam-column; variation of Young? modulus; FGM.

Address
Department of Mechanics, Slovak University of Technology, Faculty of Electrical Engineering and
Information Technology, Ilkovi ova 3, Bratislava, 81219, Slovakia

Abstract
This paper describes the design scheme of the three-dimensional structures based on the concept of the cellular automata simulation. The cellular automata simulation is performed according to the local rule. In this paper, the local rule is derived in the mathematical formulation from the optimization problem. The cell density is taken as the design variable. Two objective functions are defined for reducing the total weight of the structure and obtaining the fully stressed structure. The constraint condition is defined for defining the local rule. The penalty function is defined from the objective functions and the constraint condition. Minimization of the penalty function with respect to the design parameter leads to the local rule. The derived rule is applied to the design of the three-dimensional structure first. The final structure can be obtained successfully. However, the computational cost is expensive. So, in order to reduce the computational cost, the material parameters c1 and c2 and the value of the cell rejection criterion (CRC) are changed. The results show that the computational cost depends on the parameters and the CRC value.

Key Words
structural design; cellular automata; local rule; finite element method.

Address
E. Kita; Graduate School of Information Sciences, Nagoya University, Japan
H. Saito; Graduate School of Human Informatics, Nagoya University, Japan
T. Tamaki; Ube National College of Technology, Japan
H. Shimizu; Graduate School of Information Sciences, Nagoya University, Japan
Y. M. Xie; School of Civil and Chemical Engineering, Royal Melbourne Institute of Technology, Australia

Abstract
An investigation of the effectiveness of the interface treatment when column concrete jacketing is performed is presented. Alternative methods of interface connection were used in order to investigate the performance of strengthened concrete columns. These connecting techniques involved roughening the surface of the original column, embedding steel dowels into the original column and a combination of these two techniques. The experimental program included three strengthened specimens, one original specimen (unstrengthened) and one as-built specimen (monolithic). The specimens represented half height full-scale old Greek Code (1950?) designed ground floor columns of a typical concrete frame building. The jackets of the strengthened specimens were constructed with shotcrete. All specimens were subjected to displacement controlled earthquake simulation loading. The seismic performance of the strengthened specimens is compared to both the original and the monolithic specimens. The comparison was performed in terms of strength, stiffness and hysteretic response. The results demonstrate the effectiveness of the strengthening methods and indicate that the proper construction of a jacket can improve the behaviour of the specimens up to a level comparable to monolithic behaviour. It was found that different methods of interface treatment could influence the failure mechanism and the crack patterns of the specimens. It was also found that the specimen that combined roughening with dowel placement performed the best and all strengthened columns were better at dissipating energy than the monolithic specimen.

Key Words
concrete columns; strengthening; shotcrete; jacketing; interface connection; roughening; dowels; seismic performance.

Address
University of Patras, Department of Civil Engineering, 26500, Patras, Greece

Abstract
In this paper, the scattering of harmonic elastic anti-plane shear waves by two collinear cracks in functionally graded materials is investigated by means of nonlocal theory. The traditional concepts of the non-local theory are extended to solve the fracture problem of functionally graded materials. To overcome the mathematical difficulties, a one-dimensional non-local kernel is used instead of a two-dimensional one for the anti-plane dynamic problem to obtain the stress field near the crack tips. To make the analysis tractable, it is assumed that the shear modulus and the material density vary exponentially with coordinate vertical to the crack. By use of the Fourier transform, the problem can be solved with the help of a pair of triple integral equations, in which the unknown variable is the displacement on the crack surfaces. To solve the triple integral equations, the displacement on the crack surfaces is expanded in a series of Jacobi polynomials. Unlike the classical elasticity solutions, it is found that no stress singularities are present at crack tips.

Key Words
crack; nonlocal theory; functionally graded materials; lattice parameter; stress waves.

Address
Zhen-Gong Zhou; P.O. Box 1247, Center for Composite Materials, Harbin Institute of Technology, Harbin 150001, P. R. China
Biao Wang; School of Physics and Engineering, Sun Yat-Sen University, Guangzhou 510275, China

Abstract
Two-step identification approaches for effective bridge health monitoring are proposed to alleviate the issues associated with many unknown parameters faced in real structures and to improve the accuracy in the estimate results. It is suitable for on-line monitoring scheme, since the damage assessment is not always needed to be carried out whereas the alarming for damages is to be continuously monitored. In the first step for screening potentially damaged members, a damage indicator method based on modal strain energy, probabilistic neural networks and the conventional neural networks using grouping technique are utilized and then the conventional neural networks technique is utilized for damage assessment on the screened members in the second step. The effectiveness of the proposed methods is investigated through a field test on the northern-most span of the old Hannam Grand Bridge over the Han River in Seoul, Korea.

Key Words
bridge health monitoring; two-step approach; modal strain energy; probabilistic neural networks; neural networks; field tests.

Address
Jong Jae Lee; Department of Civil & Environmental Engineering, University of California Irvine,Irvine, CA, 92697, USA
Chung Bang Yun; Smart Infra-Structure Technology Center, Korea Advanced Institute of Science and Technology, Yusong-gu, Daejeon 305-701, Korea

Abstract
A simply supported hybrid plate consisting of top and bottom functionally graded elastic layers and an intermediate actuating or sensing homogeneous piezoelectric layer is investigated by an elasticity (piezoelasticity) method, which is based on state space formulations. The general spring layer model is adopted to consider the effect of bonding adhesives between the piezoelectric layer and the two functionally graded ones. The two functionally graded layers are inhomogeneous along the thickness direction, which are approached by laminate models. The effect of interlaminar bonding imperfections on the static bending and free vibration of the smart plate is discussed in the numerical examples.

Key Words
functionally graded material; piezoelectric layer; state space approach; spring layer model.

Address
Z. G. Bian; Department of Civil Engineering, Zhejiang University, Hangzhou 310027, P. R. China
J. Ying; Department of Mechanical Engineering, Zhejiang University, Hangzhou 310027, P. R. China
W. Q. Chen and H. J. Ding; Department of Civil Engineering, Zhejiang University, Hangzhou 310027, P. R. China


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