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CONTENTS
Volume 18, Number 1, July 2004
 

Abstract
The paper presents a numerical method for the limit analysis of structures made of a rigid no-tension material. Firstly, we formulate the constrained minimum problem resulting from the application of the kinematic theorem, which characterizes the collapse multiplier as the minimum of all kinematically admissible multipliers. Subsequently, by using the finite element method, we derive the corresponding discrete minimum problem in which the objective function is linear and the inequality constraints are linear as well as quadratic. The method is then applied to some examples for which the collapse multiplier and a collapse mechanism are explicitly known. Lastly, the solution to the minimum problem calculated via numerical codes for quadratic programming problems, is compared to the exact solution.

Key Words
limit analysis; masonry structures; finite elements.

Address
Silvia Degl\'Innocenti and Cristina Padovani; Istituto di Scienza e Tecnologie dell\'Informazione, \"Alessandro Faedo\" ISTI-CNR, Area della Ricerca CNR, Via Moruzzi, 1 56124 Pisa, Italy

Abstract
In this paper, we modify the L-L model (Li et al. 2003) and extend the application of this model to concrete confined by both steel reinforcement and CFRP. Thirty-six concrete cylinders with a dimension of j 30 ?60 cm were tested to verify the effectiveness of the proposed model. The experimental test results show that different types of steel reinforcement have a great effect on the compressive strength of concrete cylinders confined by steel reinforcement, but the different types of steel reinforcement have very little effect on concrete cylinders confined by both steel reinforcement and CFRP. Compared with the stress-strain curves of confined concrete cylinders, we can conclude that the proposed model can provide more effective prediction than others models.

Key Words
carbon fiber reinforced plastics; steel reinforcement; constitutive model; confined concrete.

Address
Yeou-Fong Li; Department of Civil Engineering, National Taipei University of Technology, No. 1, Sec. 3, Chung-Hsiao E. Rd., Taipei, 106-08, Taiwan, R.O.C.
Tsang-Sheng Fang; Department of Civil Engineering, National Taiwan University, Taiwan, R.O.C.

Abstract
The postbuckling behaviour of thin shells has fascinated researchers because the theoretical prediction and their experimental verification are often different. In reality, shell panels possess small imperfections and these can cause large reduction in static buckling strength. This is more relevant in thin laminated composite shells. To study the postbuckling behaviour of thin, imperfect laminated composite shells using finite elements, explicit incremental or secant matrices have been presented in this paper. These incremental matrices which are derived using Marguerre

Key Words
Marguerre\'s shell theory; secant matrices; postbuckling; nonlinear finite element analysis; shallow shells.

Address
S. Arul Jayachandran; Structural Engineering Research Centre, CSIR Campus, Taramani, Chennai 600 113, India
V. Kalyanaraman; Department of Civil Engineering, Indian Institute of Technology, Chennai 600 036, India
R. Narayanan; Structural Engineering Research Centre, CSIR Campus, Taramani, Chennai 600 113, India

Abstract
This paper is devoted to illustrate some numerical procedures to solve the boundary equilibrium problems of three-dimensional solids that are subjected to thermal strains. The constitutive equations take into account the bounded tensile strength of the material and they are presented in the framework of non-linear elasticity and small strains. The associated equilibrium problem is solved numerically by means of the finite element method and the numerical techniques, i.e. the Newton-Raphson method and the secant method, are revised in order to assure the solution convergence of the discretized problem. Some numerical examples are illustrated.

Key Words
masonry; thermal strain; bounded tensile strength; finite element.

Address
Giovanni Pimpinelli; Dipartimento di Ingegneria Civile e Ambientale,
Politecnico di Bari, Via Orabona 4, 70125 Bari, Italy

Abstract
A high precision shear deformable triangular element has been proposed for bending analysis of triangular plate. The element has twelve nodes at the three sides and four nodes inside the element. Initially the element has thirty-five degrees of freedom, which has been reduced to thirty by eliminating the degrees of freedom of the internal nodes through static condensation. Plates having different boundary conditions, side ratios (b/a) and thickness ratios (h/a = 0.001, 0.1 and 0.2) have been analyzed using the proposed shear locking free element. Concentrated and uniformly distributed transverse loads have been used for the analysis. The formulation is made based on first order shear deformation theory. For validation of the present element and formulation few results of thin triangular plate have been compared with the analytical solutions. Results for thick plate have been presented as new results.

Key Words
shear locking free element; first order shear deformation theory; static condensation; triangular.

Address
S. Haldar; Department of Applied Mechanics, B. E. College (D.U.), Howrah-711103, India
P. Das; Department of Computer Science, M.C.K.V. Institute of Engineering, Howrah-711204, India
M. C. Manna; Department of Applied Mechanics, B. E. College (D.U.), Howrah-711103, India

Abstract
Concrete is a composite material and at meso-level, may be assumed to be composed of three phases: aggregate, mortar-matrix and aggregate-matrix interface. It is postulated herein that although non-linear material parameters are generally used to model this composite structure by finite element method, linear elastic fracture mechanics principles can be used for modelling at the meso level, if the properties of all three phases are known. For this reason, a novel meso-mechanical approach for concrete fracture which uses the composite material model with distributed-phase for elastic properties of phases and considers the size effect according to linear elastic fracture mechanics for strength properties of phases is presented in this paper. Consequently, the developed model needs two parameters such as compressive strength and maximum grain size of concrete. The model is applied to three most popular fracture mechanics approaches for concrete namely the two-parameter model, the effective crack model and the size effect model. It is concluded that the developed model well agrees with considered approaches.

Key Words
concrete; fracture mechanics; numerical modelling; two-parameter model; effective crack model; size effect model.

Address
R. Ince; Engineering Faculty, Civil Engineering Department, Firat University, Elazig, Turkey

Abstract
The information on local stress acting in a bridge is required in many occasions such as fatigue assessment. The analysis by beam elements cannot yield this class of information adequately, while the finite element modeling of an entire long-span bridge by shell elements is impractical. In the present study, the hybrid modeling is tried out: only part of a bridge in which the point of interest is located is discretized by shell elements and the remaining part is modeled by beam elements. By solving a simple box girder problem, the effectiveness of this approach is discussed. This technique is then applied to the Rama IX Bridge for local stress evaluation. The numerical results compare very well with the results of a full-scale static loading test. The present research thus offers a practical yet accurate technique for the stress analysis of a long-span cable-stayed bridge.

Key Words
three-dimensional finite element modeling; cable-stayed bridge; hybrid modeling; local stress analysis; full-scale static loading test.

Address
Chartree Lertsima and Taweep Chaisomphob; Civil Engineering Program, Sirindhorn International Institute of Technology, Thammasat University, Pathumthani 12121, Thailand
Eiki Yamaguchi; Department of Civil Engineering, Kyushu Institute of Technology, Tobata, Kitakyushu 804-8550, Japan

Abstract
Industrial structure systems may have nonlinearity, and are also sometimes exposed to the danger of random excitation. This paper proposes a method to analyze response and reliability design of a complex nonlinear structure system under random excitation. The nonlinear structure system which is subjected to random process is modeled by finite element method. The nonlinear equations are expanded sequentially using the perturbation theory. Then, the perturbed equations are solved in probabilistic methods. Several statistical properties of random process that are of interest in random vibration applications are reviewed in accordance with the nonlinear stochastic problem.

Key Words
response analysis; modal analysis; multi-DOF system; mdeling of complex system; finite element method; structural vibration.

Address
Byung-Young Moo, Gyung-Ju Kang and Beom-Soo Kang;
Department of Aerospace Engineering, Pusan National University, Gumjung-ku, Busan 609-735, Korea
Dae-Seung Cho; Department of Naval Architecture and Ocean Engineering, Pusan National University, Gumjung-ku, Busan 609-735, Korea


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