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Abstract
The present paper discusses the behavior of the reinforced concrete beams subjected to
torsion by applying the endochronic plastic model in conjunction with the softened truss model. The
endochronic constitutive equations are developed to describe the behavior of concrete. The mechanical
behavior of concrete is decomposed into hydrostatic part and deviatoric part. New definition of the bulk
modulus and the shear modulus are defined in terms of compressive strength of concrete. Also, new
deviatoric hardening function is developed. Then, the endochronic constitutive equations of concrete are
applied with the softened truss model for the behavior of the reinforced concrete beams subjected to
torsion. The theoretical results obtained based on the present model are compared with the experimental
data. The present model has shown the ability to describe the behavior of reinforced concrete beams
subjected to torsion.

Key Words
endochronic model for concrete; reinforced concrete beam; softened truss model.

Address
Jun-Kai Lu and Wen-Hsiung Wu, Department of Civil Engineering, National Pingtung University of Science and Technology, Pingtung, Taiwan 912, ROC.

Abstract
The linear constitutive relations and the failure criteria of composite materials made of
thermoviscoelastic solids are presented. The post-failure material behavior is proposed and the dynamic
finite element equations are formulated. However, a nonlinear term is kept in the energy equation because
it represents the effect of the second law of thermodynamics. A general purpose nonlinear three-dimensional
dynamic finite element program COMPASS is upgraded and employed in this work to investigate the
interdependence among stress wave propagation, stress concentration, failure progression and temperature
elevation in composite materials. The consequence of truthfully incorporating the second law of thermodynamics is
clearly observed: it will always cause temperature rise if there exists a dynamic mechanical process.

Key Words
dynamic finite element analysis; second law of thermodynamics; thermo-mechanical coupling; thermoviscoelasticity; composite materials; wave propagation.

Address
Siyuan J. Shen, Jens C. Pfister and James D. Lee, Department of Mechanical and Aerospace Engineering, The George Washington University, Washington, DC 20052, U.S.A.

Abstract
This paper presents a method of elastic-plastic analysis for planar steel frames that provides
the accuracy of distributed plasticity methods with the computational efficiency that is greater than that of
distributed plasticity methods but less than that of plastic-hinge based methods. This method accounts for
the effect of spread of plasticity accurately without discretization through the cross-section of a beam-column
element, which is achieved by the following procedures. First, nonlinear equations describing the
relationships between generalized stresses and strains of the cross-section are derived analytically. Next,
nonlinear force-deformation relationships for the beam-column element are obtained through lengthwise
integration of the generalized strains. Elastic-plastic flexibility coefficients are then calculated by
differentiating the above element force-deformation relationships. Finally, an elastic-plastic stiffness matrix
is obtained by making use of the flexibility-stiffness transformation. Adding the conventional geometric
stiffness matrix to the elastic-plastic stiffness matrix results in the tangent stiffness matrix, which can
readily be used to evaluate the load carrying capacity of steel frames following standard nonlinear
analysis procedures. The accuracy of the proposed method is verified by several examples that are
sensitive to the effect of spread of plasticity.

Key Words
second-order analysis; steel frames; spread of plasticity; flexibility matrix.

Address
Liang-Jenq Leu and Ching-Huei Tsou, Department of Civil Engineering, National Taiwan University, Taipei, 10617 Taiwan, R.O.C.

Abstract
This paper presents an effective application of a variable-node axisymmetric solid element
designated as AQV (Axisymmetric Quadrilateral Variable-node element). The variable-node element with
physical midside nodes helps to overcome some problems in connecting the different layer patterns on a
quadrilateral mesh in the adaptive h-refinement. This element alleviates the necessity of imposing
displacement constraints on irregular (hanging) nodes in order to enforce the inter-element compatibility.
Therefore, the elements with variable mid-side nodes can be used effectively in the local mesh refinement
for the axisymmetric structures which have stress concentrations. A modified Gaussian quadrature should
be adopted to evaluate the stiffness matrices of the variable-node elements mainly because of the slope
discontinuity of assumed displacement within the elements. Some numerical examples show the usefulness
of variable-node axisymmetric elements in the practical application.

Key Words
quadrilateral axisymmetric element; irregular node; variable-node element; transition element; adaptive h-refinement.

Address
Chang-Koon Choi and Eun-Jin Lee, Department of Civil Engineering, KAIST, Taejon 305-600, Korea
Wan-Hoon Lee, Department of Civil & Environment Engineering, Chungwoon University, Chungnam 350-701, Korea

Abstract
The aim of this work is to establish the coefficient that defines the critical buckling load for
isotropic annular plates of variable thickness whose outer boundary is simply supported and subjected to
uniform pressure. It is assumed that the plate thickness varies in a continuous way, according to an
exponential law. The eigenvalues are determined using an optimized Rayleigh-Ritz method with
polynomial coordinate functions which identically satisfy the boundary conditions at the outer edge. Good
engineering agreement is shown to exist between the obtained results and buckling parameters presented
in the technical literature.

Key Words
critical buckling load; annular plates; variable thickness.

Address
P.M. Ciancio and J.A. Reyes, Department of Civil Engineering, Universidad Nacional del Centro de la Provincia de Buenos Aires. Av. Del Valle 5737, 7400 Olavarria, Argentina

Abstract
A new beam system comprising two cantilever stems and an interspan composite beam has
been developed and its design philosophy is described in this paper. The system provides the equivalent
of a semi-continuous beam without the requirement to calculate the moment rotation capacity of the
beam-to-column connection. The economy of braced frames using the system has been investigated and
compared with simple, continuous or semi-rigid systems. It is shown that the costs of the proposed system
are similar to the semi-rigid system and cheaper than both the simply supported and rigid beam systems.
Two tests have been carried out on 6 meter span beams, which also incorporated an asymmetric flange
steel section. The behaviour of the system is presented and the test results are compared with those
obtained from the theory.

Key Words
continuous stem girder system (csgs); asymmetric steel section beam (asb); economy of braced frames; semi-rigid connection.

Address
Boksun Kim, Scott Sutherland School of Architecture, Robert Gordon University, Garthdee Road, Aberdeen AB10 7QB, UK
Howard D Wright and Roy Cairns, Department of Civil Engineering, University of Strathclyde, 107 Rottenrow, Glasgow G4 0NG, UK

Abstract
Modern soft computing methods, such as neural networks, evolutionary models and fuzzy
logic, are mainly inspired by the problem solving strategies the biological systems use in nature. As such,
the soft computing methods are fundamentally different from the conventional engineering problem
solving methods, which are based on mathematics. In the author

Key Words
soft computing; newral networks; genetic algorithm; structural mechanics; inverse problems.

Address
Jamshid Ghaboussi, Department of Civil and Environmental Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, U.S.A.

Abstract
In this paper, the procedure for deriving an infinite element that is compatible with the
quadrilateral Q8 element is first summarized. Enhanced by a self mesh-expansion procedure for generating
the impedance matrices of different frequencies for the region extending to infinity, the infinite element is
used to simulate the far field of the soil-structure system. The structure considered here is of the box type
and the soils are either homogeneous or resting on a bedrock. Using the finite/infinite element approach, a
parametric study is conducted to investigate the effect of open and in-filled trenches in reducing the
structural vibration caused by a train passing nearby, which is simulated as a harmonic line load. The key
parameters that dominate the performance of wave barriers in reducing the structural vibrations are
identified. The results presented herein serve as a useful guideline for the design of open and in-filled
trenches concerning wave reduction.

Key Words
finite/infinite element method; in-filled trench; infinite element; open trench; traffic-induced vibration; wave barrier.

Address
Hsiao-Hui Hung, Jenny Kuo and Yeong-Bin Yang, Department of Civil Engineering, National Taiwan University, Taipei, Taiwan, R.O.C.

Abstract
The effects of the initial imperfections on the nonlinear behaviors and ultimate strength of
the thin-walled members subjected to the axial loads, obtained by the finite element stability analysis, are
examined. As the initial imperfections, the buckling mode shapes of the members are adopted. The
buckling mode shapes of the thin-walled members are obtained by the transfer matrix method. In the
finite element stability analysis, isoparametric degenerated shell element is used, and the geometrical and
material nonlinearity are considered based on the Green Lagrange strain definition and the Prandtl-Reuss
stress-strain relation following the von Mises yield criterion. The U-, box- and I-section members
subjected to the axial loads are adopted for numerical examples, and the effects of the initial
imperfections on the nonlinear behaviors and ultimate strength of the members are examined.

Key Words
finite element stability analysis; initial imperfection; nonlinear behavior; thin-walled member; ultimate strength.

Address
M. Ohga, Department of Civil and Environmental Engineering, Ehime University, Matsuyama 790-8577, Japan
A. Takaue, Chodai Ltd., Takamatsu 760-0017, Japan
T. Shi gematsu and T. Hara, Tokuyama Technical College, Tokuyama 745-8585, Japan

Abstract
A new p-adaptive analysis scheme for hp-clouds method is presented. In the scheme, refined
global equations are resolved into two parts, one of them being related to the newly appended dof

Key Words
meshless method; meshfree method; hp-clouds method; p-refinement; dof splitting; p-adaptive meshless method; DSPMM.

Address
Myung-Seok Kang and Sung-Kie Youn, Department of Mechanical Engineering, KAIST, Taejon 305-701, Korea

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