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CONTENTS
Volume 24, Number 6, December20 2006
 

Abstract
In this study, an improved finite element formulation with a scheme of solution for the large deflection analysis of inextensible prismatic and nonprismatic slender beams is developed. For this purpose, a three-noded Lagrangian beam-element with two dependent degrees of freedom per node (i.e., the vertical displacement, y, and the actual slope, dy/ds = sinq, where s is the curved coordinate along the deflected beam) is used to derive the element stiffness matrix. The element stiffness matrix in the global xy-coordinate system is achieved by means of coordinate transformation of a highly nonlinear (6

Key Words
ADINA; finite element; large deflection; nonprismatic beams; quasi-linearization.

Address
Samir Z. AL-Sadder; Department of Civil Engineering, Faculty of Engineering, Hashemite University, Zarqa 13115, Jordan
Ra

Abstract
A vibration-based nondestructive damage evaluation technique for a curved thin beam is introduced. The proposed method is capable of detecting, locating, and sizing structural damage simultaneously by using a few of the lower natural frequencies and their corresponding mode shapes before and after a small damage event. The proposed approach utilizes modal flexibilities reconstructed from measured modal parameters. A rigorous system of equations governing damage and curvature of modal flexibility is derived in the context of elasticity. To solve the resulting system of governing equations, an efficient pseudo-inverse technique is introduced. The direct inspection of the resulting solutions provides the location and severity of damage in a curved thin beam. This study confirms that there is a strong linear relationship between the curvature of modal flexibility and flexural damage in the selected class of structures. Several numerical case studies are provided to justify the performance of the proposed approach. The proposed method introduces a way to avoid the singularity and mode selection problems from earlier attempts.

Key Words
damage detection; flexural damage index; curvature of mode shape; modal flexibility; curved thin beam; circular arch.

Address
Byeong Hwa Kim; Research Institute of Industrial Science & Technology, Steel Structure Research Lab, 79-5 Yeongcheon, Dongtan, Hwaseong, Gyeonggi 445-813, Korea
Hwan Joong Joo and Taehyo Park; Department of Civil Engineering, Hanyang University, 17 Haengdang-dong, Seoul 133-791, Korea

Abstract
The accurate dynamic analysis of concrete arch dams relies heavily on employing a three-dimensional semi-infinite fluid element. The usual method for calculating the impedance matrix of this fluid hyper-element is dependent on the solution of a complex eigen-value problem for each frequency. In the present study, an efficient procedure is proposed which simplifies this procedure amazingly, and results in great computational time saving. Moreover, the accuracy of this technique is examined thoroughly and it is concluded that efficient procedure is incredibly accurate under all practical conditions.

Key Words
efficient fluid hyper-element; concrete arch dams; dynamic analysis.

Address
Civil Engineering Department, Amirkabir University of Technology, Tehran, Iran

Abstract
In the paper, a direct method of solution of the Navier equation is presented. An orthotropic thick hollow cylinder under a one-dimensional steady-state temperature distribution and a uniform magnetic field with general types of thermal and mechanical boundary conditions is considered. The Navier equation in terms of displacement is derived and solved analytically by the direct method, and magnetothermoelastic responses and perturbation of the magnetic field vector in the orthotropic thick hollow cylinder is described. The present method is suitable for orthotropic thick hollow cylinders placed in an axial magnetic field with arbitrary thermal and mechanical boundary conditions. Finally, numerical examples are carried out and discussed.

Key Words
magnetothermoelastic; orthotropic hollow cylinder; perturbation of magnetic field vector.

Address
Department of Engineering Mechanics, Hunan University, Changsha, 410082, Hunan Province, P. R. China

Abstract
In this paper the buckling and post-buckling behavior of slender bars under self-weight are studied. In order to study the post-buckling behavior of the bar, a geometrically exact formulation for the non-linear analysis of uni-directional structural elements is presented, considering arbitrary load distribution and boundary conditions. From this formulation one obtains a set of first-order coupled non-linear equations which, together with the boundary conditions at the bar ends, form a two-point boundary value problem. This problem is solved by the simultaneous use of the Runge-Kutta integration scheme and the Newton-Raphson method. By virtue of a continuation algorithm, accurate solutions can be obtained for a variety of stability problems exhibiting either limit point or bifurcational-type buckling. Using this formulation, a detailed parametric analysis is conducted in order to study the buckling and post-buckling behavior of slender bars under self-weight, including the influence of boundary conditions on the stability and large deflection behavior of the bar. In order to evaluate the quality and accuracy of the results, an experimental analysis was conducted considering a clamped-free thin-walled metal bar. As this kind of structure presents a high index of slenderness, its answers could be affected by the introduction of conventional sensors. In this paper, an experimental methodology was developed, allowing the measurement of static or dynamic displacements without making contact with the structure, using digital image processing techniques. The proposed experimental procedure can be used to a wide class of problems involving large deflections and deformations. The experimental buckling and post-buckling behavior compared favorably with the theoretical and numerical results.

Key Words
instability; post-buckling behavior; large deflections; self-weight; experimental analysis.

Address
Paulo B. Goncalves; Civil Engineering Department, Catholic University, PUC-Rio, 22453-900 Rio de Janeiro, RJ, Brazil
Daniel Leonardo B. R. Jurjo, Carlos Magluta and Ney Roitman;
Civil Engineering Department, Federal University of Rio de Janeiro, COPPE-UFRJ,
21941-972 Rio de Janeiro, RJ, Brazil
Djenane Pamplona; Civil Engineering Department, Catholic University, PUC-Rio, 22453-900 Rio de Janeiro, RJ, Brazil

Abstract
A simple plane-strain solution is derived in this paper for the functionally graded multilayered isotropic elastic cylinder under static deformation. The solution is obtained using method of separation of variables and is expressed in terms of the summation of the Fourier series in the circumferential direction. While the solution for order n = 0 corresponds to the axisymmetric deformation, that for n = 2 includes the special deformation frequently utilized in the upper and lower bounds analysis. Numerical results for a three-phase cylinder with a middle functionally graded layer are presented for both axisymmetric (n = 0) and general (n = 2) deformations, under either the traction or displacement boundary conditions on the surface of the layered cylinder. The solution to the general deformation case (n = 2) is further utilized for the first time to find the upper and lower bounds of the effective shear modulus of the layered cylinder with a functionally graded middle layer. These results could be useful in the future study of cylindrical composites where FGMs and/or multilayers are involved.

Key Words
elasticity; analytical solution; micromechanics; functionally graded material; fiber/matrix bond; effective modulus; three-phase cylinder.

Address
E. Pan; Department of Civil Engineering, The University of Akron, Akron, OH 44325-3905, USA
A. K. Roy; Air Force Research Laboratory, Materials and Manufacturing Directorate, AFRL/MLBC, 2941 P St., WPAFB, OH 45433-7750, USA

Abstract
The time-dependent analysis of prestressed concrete bridges built adopting the incremental launching technique is presented. After summarizing the well known results derived from the elastic analysis, the problem is approached in the visco-elastic domain taking into account the effects consequent to the complex load history affecting the structure. In particular, the effects produced by prestressing applied both in the launching phase and after it and by application of imposed displacements and of delayed restraints during the launching phases are carefully investigated through a refined analytical procedure. The reliability of the proposed algorithm is tested by means of comparisons with reference cases for which exact solutions are known. A case study of general interest is then discussed in detail. This case study demonstrates that a purely elastic approach represents a too crude approximation, which is unable to describe the specific character of the problem.

Key Words
prestressed concrete bridges; creep; launched bridges.

Address
M. Mapelli; SPEA Ingegneria Europea, Via Vida 11, 20127 Milan, Italy
F. Mola and M. A. Pisani; Department of Structural Engineering, Politecnico di Milano, Piazza Leonardo da Vinci 32, 20133 Milan, Italy

Abstract
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Key Words
crack detection; strain gage; elasticity; pseudo-3-D problem; body force method; notch; detection limit.

Address
Hiroshi Noguchi; Dept. of Mechanical Engineering Science, Fac. of Engineering, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan
Toyomitsu Harada; Department of Mechanical Engineering, Kurume National College of Technology, 1-1-1 Komorino, Kurume 830-8555, Japan

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