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Volume 11, Number 1, January 2001

This paper discusses the elastic stability of unbraced frames under non-proportional loading
based on the concept of storey-based buckling. Unlike the case of proportional loading, in which the load
pattern is predefined, load patterns for non-proportional loading are unknown, and there may be various
load patterns that will correspond to different critical buckling loads of the frame. The problem of
determining elastic critical loads of unbraced frames under non-proportional loading is expressed as the
minimization and maximization problem with subject to stability constraints and is solved by a linear
programming method. The minimum and maximum loads represent the lower and upper bounds of critical
loads for unbraced frames and provide realistic estimation of stability capacities of the frame under
extreme load cases. The proposed approach of evaluating the stability of unbraced frames under non-proportional
loading has taken into account the variability of magnitudes and patterns of loads, therefore,
it is recommended for the design practice.

Key Words
non-proportional loading; frame stability; storey-based buckling; linear programming; critical load; unbraced frame; lean-on column.

L. Xu, Y. Liu and J. Chen, Department of Civil Engineering, University of Waterloo, Waterloo, Ontario, Canada N2L 3G1

An improved method has been developed for the computation of the section forces and
stiffness in nonlinear finite element analysis of RC plane frames. The need for a new approach arises
because the conventional technique may have a questionable level of efficiency if a large number of
layers is specified and a questionable level of accuracy if a smaller number is used. The proposed
technique is based on automatically dividing the section into zones of similar state of stress and tangent
modulus and then numerically integrating within each zone to evaluate the sectional stiffness parameters
and forces. In the new system, the size, number and location of the layers vary with the state of the
strains in the cross section. The proposed method shows a significant improvement in time requirement
and accuracy in comparison with the conventional layered approach. The computer program based on the
new technique has been used successfully to predict the experimental load-deflection response of a RC
frame and good agreement with test and other numerical results have been obtained.

Key Words
computation; computer analysis; concrete structures; finite element analysis; layered systems; nonlinear analysis; nonlinear response; efficiency.

Ahmed B. Shuraim, Civil Engineering Department, College of Engineering, King Saud University, P.O. Box 800, Riyadh 11421, Saudi Arabia

The objective of this study is to investigate the stability behavior of steel cable-stayed
bridges by comparing the buckling loads obtained by means of finite element methods with eigen-solver.
In recent days, cable-stayed bridges dramatically attract engineers

Key Words
stability analysis; cable-stayed bridges; steel and bridge.

Chia-Chih Tang, Hung-Shan Shu and Yang-Cheng Wang, Department of Civil Engineering, Chinese Military Academy, Taiwan, 1 Hwang-Poo Road, Feng-Shan, 83000, Taiwan, ROC

This paper is concerned with a study on thermo-elastoplastic characteristics of functionally
graded composite. Compared to the classical layered composites, it shows a wide range of thermo-elastoplastic
characteristics according to the choice of two major parameters, the thickness-wise volume
fraction of constituents and the relative thickness ratio of the graded layer. Therefore, by selecting an
appropriate combination of the two parameters, one is expected to design the most suitable heat-resisting
composite for a given thermal circumstance. Here, we address the parametric investigation on its characteristics together with theoretical study on thermo-elastoplasticity and numerical techniques for its finite
element approximations. Through the numerical experiments, we examine the influence of two parameters
on the thermo-elastoplastic characteristics.

Key Words
functionally graded material (FGM); graded layer; volume fraction; relative thickness ratio; material properties; stress concentration; thermo-elastoplastic characteristics.

Jin-Rae Cho and Dae-Yul Ha, School of Mechanical Engineering, Pusan National University, Pusan 609-735, Korea

A frequency domain response analysis is presented for building frames passively controlled
by viscoelastic dampers, under harmonic ground excitation. Three different models are used to represent
the linear dynamic force-deformation characteristics of viscoelastic dampers namely, Kelvin model, Linear
hysteretic model and Maxwell model. The frequency domain solution is obtained by (i) an iterative
pseudo-force method, which uses undamped mode shapes and frequencies of the system, (ii) an
approximate modal strain energy method, which uses an equivalent modal damping of the system in each
mode of vibration, and (iii) an exact method which uses complex frequency response function of the
system. The responses obtained by three different methods are compared for different combinations of
viscoelastic dampers giving rise to both classically and non-classically damped cases. In addition, the
effect of the modelling of viscoelastic dampers on the response is investigated for a certain frequency
range of interest. The results of the study are useful in appropriate modelling of viscoelastic dampers and
in understanding the implication of using modal analysis procedure for building frames which are
passively controlled by viscoelastic dampers against base excitation.

Key Words
viscoelastic dampers; base excitation; storage and loss moduli; pseudo-force; modal strain energy.

A.K. Shukla and T.K. Datta, Civil Engineering Department, Indian Institute of Technology, New Delhi 110 016, India

This paper reviews the author

Key Words
plates; Kirchhoff; Mindlin; bending; buckling; vibration; relationships; shear deformation.

C.M. Wang, Department of Civil Engineering, The National University of Singapore, Kent Ridge, Singapore 119260

A new three-dimensional 13-node hexahedral element with rotational degrees of freedom,
which is designated as MR-H13 element, is presented. The proposed element is established by adding five
nodes to one of the six faces of basic 8-node hexahedral element. The new element can be effectively
used in the connection between the refined mesh and the coarser mesh. The derivation of the current
element in this paper is based on the variational principles in which the rotation and skew-symmetric
stress are introduced as independent variables. Numerical examples show that the performance of the new
element is satisfactory.

Key Words
13-node hexahedral element; rotation; variable-node element; finite element method.

Chang-Koon Choi, Keun-Young Chung and Eun-Jin Lee, Department of Civil Engineering, Korea Adavanced Institute of Science and Technology, Taejon 305-701, Korea

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