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CONTENTS
Volume 34, Number 2, January30 2010
 

Abstract
This paper presents theoretical solutions for the three-dimensional (3D) stress field in an infinite isotropic elastic plate containing a through-the-thickness circular hole subjected to far-field inplane loads by using Kane and Mindlin\'s assumption. The dangerous position, where the premature fracture or failure of the plate will take place, the expressions of the tangential stress at the surface of the hole and the out-of-plane stress constraint factor are found in a concise, explicit form. Based on the present theoretical solutions, a comprehensive analysis is performed on the deviated degree of the in-plane stresses from the related plane stress solutions, stress concentration and out-of-plane constraint, and the emphasis has been placed on the effects of the plate thickness, Poisson\'s ratio and the far-field in-plane loads on the stress field. The analytical solution shows that the effects of the plate thickness and Poisson\'s ratio on the deviation of the 3D in-plane stress components is obvious and could not be ignored, although their effects on distributions of the in-plane stress components are slight, and that the effect of the farfield in-plane loads is just on the contrary of that of the above two. When only the shear stress is loaded at far field, the stress concentration factor reach its peak value about 8.9% higher than that of the plane stress solutions, and the out-of-plane stress constraint factor can reach 1 at the surface of the hole and is the biggest among all cases considered.

Key Words
three-dimensional stress field; through-the-thickness circular hole; thickness effect; stress concentration; out-of-plane constraint.

Address
Longchao Dai and Xinwei Wang: Institute of Structure and Strength, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, P.R. China
Feng Liu: College of Aviation Engineering, Civil Aviation Flight University of China, Guanghan, 618307, P.R. China

Abstract
Elastic buckling load of perforated steel plates is typically predicted using the finite element or conjugate load/displacement methods. In this paper an artificial neural network (ANN)-based formula is presented for the prediction of the elastic buckling load of rectangular plates having a circular cutout. By using this formula, the elastic buckling load of perforated plates can be calculated easily without setting up an ANN platform. In this study, the center of a circular cutout was chosen at different locations along the longitudinal x-axis of plates subjected to linearly varying loading. The results of the finite element method (FEM) produced by the commercial software package ANSYS are used to train and test the network. The accuracy of the proposed formula based on the trained ANN model is evaluated by comparing with the results of different researchers. The results show that the presented ANN-based formula is practical in predicting the elastic buckling load of perforated plates without the need of an ANN platform.

Key Words
artificial neural networks; plate buckling; perforated plates; linearly varying loading; explicit formula.

Address
Mustafa Sonmez and M. Aydin Komur: Dept. of Civil Engineering, Faculty of Engineering, Aksaray University, 68100 Aksaray, Turkey

Abstract
This paper deals with the buckling and postbuckling responses, and the progressive failure of square laminates of symmetric lay-up with a central rectangular cutout under in-plane shear load. A detailed investigation is made to show the effects of cutout size and cutout aspect ratio on the buckling and postbuckling responses, failure loads and failure characteristics of (+45/-45/0/90)2s, (+45/-45)4s and (0/90)4s laminates. The 3-D Tsai-Hill criterion is used to predict the failure of a lamina while the onset of delamination is predicted by the interlaminar failure criterion. In addition, the effects of boundary conditions on buckling loads, failure loads, failure modes, and maximum transverse deflection for a (+45/-45/0/90)2s laminate with and without a square cutout have been presented. It is concluded that because of early onset of delamination at the net section of cutouts before first-ply failure, total strength of the laminate with very small cutouts can not be utilized.

Key Words
buckling; postbuckling; in-plane shear; composite laminates; cutouts; strength; failure.

Address
S.B. Singh: Dept. of Civil Engineering, Birla Institute of Technology and Science, Pilani 333031, India
Dinesh Kumar: Dept. of Mechanical Engineering, Birla Institute of Technology and Science, Pilani 333031, India

Abstract
The behaviour of a reinforced concrete tension member is governed by the contribution of concrete between cracks, tension stiffening effect. Under highly repeated loading, this contribution is progressively reduced and the member response approximates that given by the fully cracked member. When focusing on the unloaded state, experiments show deformations larger than those of the naked reinforcement. This has been referred to as negative tension stiffening and is due to the fact that concrete carries compressive stresses along the crack spacing, even thought the tie is subjected to an external tensile force. In this paper a cycle-dependent approach is presented to reproduce the behaviour of the axially loaded tension member, paying attention to the negative tension stiffening contribution. The interaction of cyclic bond degradation and time-dependent effects of concrete is investigated. Finally, some practical diagrams are given to account for the negative tension stiffening effect in reinforced concrete elements.

Key Words
cracking; bond mechanics; reinforced concrete; tension stiffening; repeated loads.

Address
Carlos Zanuy: Dept. of Continuum Mechanics and Structures, E.T.S. Ingenieros de Caminos, Canales y Puertos, Universidad Politecnica de Madrid, Av. Profesor Aranguren s/n, 28040 Madrid, Spain

Abstract
An analytical method is proposed for the evaluation of the static response of a prestressedribbon concrete pedestrian bridge, which may also be applied for the roofing of large areas. On the basis of an established analogy with a suspension bridge system, a procedure is presented for the prestressedribbon direct analysis, leading to the introduction of two dimensionless parameters as governing factors of the design, namely the thinness and the prestressing steel ratio. The exposed procedure, applied by a simple computer program, allows a quick evaluation of the response and permits the investigation of the influence of the aforementioned parameters on it, by means of comprehensive diagrams. The presented diagrams may be directly used for the preliminary design of a pedestrian bridge of this type, for the whole practical range of span lengths. A design example is also included, showing the applicability of the proposed procedure.

Key Words
stress-ribbon; bridge; suspension bridge; static analysis; design.

Address
Leonidas T. Stavridis: Structural Engineering, National Technical University of Athens, Vas. Sofias 100-11528
Athens, Greece

Abstract
Vibration analysis of rotating beams is a topic of constant interest in mechanical engineering. The differential quadrature method (DQM) is used to obtain the natural frequencies of free transverse vibration of rotating beams. As it is known the DQM offers an accurate and useful method for solution of differential equations. And it is an effective technique for solving this kind of problems as it is shown comparing the obtained results with those available in the open literature and with those obtained by an independent solution using the finite element method. The beam model is based on the Timoshenko beam theory.

Key Words
rotating beam; Timoshenko beam theory; free vibration; differential quadrature method.

Address
D.V. Bambill: Dept. of Engineering, Universidad Nacional del Sur, Av. Alem 1253, 8000 Bahia Blanca, Argentina
Comision Nacional de Investigaciones Cientificas y Tecnicas, Argentina
D.H. Felix and R.E. Rossi: Dept. of Engineering, Universidad Nacional del Sur, Av. Alem 1253, 8000 Bahia Blanca, Argentina

Abstract
In this study, experimental, numerical, and analytical approaches were carried out to evaluate the behavior and prestressing effect of prestressed composite beam by external tendon and cover plate. Behavior of prestressed composite beam, load-carrying capacity, effects of prestressing, and ultimate strength were estimated. The contribution of the section increase of the prestressing method using tendon was less than the prestressing method using cover plate. In accordance with numerical and analytical approaches, the ultimate strength of the prestressed composite beam is shown to be the same value because strength is determined according to the plastic resistance moment and the plastic neutral axis; however, both plastic resistance moment and neutral axis are not affected by prestressing force but affected by sectional stiffness of the prestressing member. Based on these approaches, we concluded that the prestressing method using tendon can be useful in applications without an increase in self-weight, and the prestressing method using high-strength cover plate can be applied to reduce the deflection of the composite beam. The prestressing method using high-strength cover plate can also be used to induce prestress of the composite beam in the case of a large deflection due to a smaller sectional stiffness of the composite beam.

Key Words
prestressing; prestressing member; load-carrying capacity; tendon; cover-plate; composite beam.

Address
Jin-Hee Ahn, Chi-Young Jung and Sang-Hyo Kim: School of Civil and Environmental Engineering, Yonsei University, Seoul 120-749, Korea

Abstract
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Key Words
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Address
C.S. Tsai: Dept. of Civil Engineering, Feng Chia University, Taichung, Taiwan, R.O.C.
Wen-Shin Chen: Graduate Institute of Civil and Hydraulic Engineering, Feng Chia University, Taichung, Taiwan, R.O.C.
Tsu-Cheng Chiang: Earthquake Proof Systems, Inc., Taichung, Taiwan, R.O.C.

Abstract
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Key Words
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Address
Tan Yong-Gang, Zhang Zhe, Yu Yang and Zhao Xu: School of Civil & Hydraulic Engineering, Dalian University of Technology, Dalian, China


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