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CONTENTS
Volume 35, Number 2, May30 2010
 

Abstract
This paper focuses on a number of criteria that enable controlling the influence of geometric simplification on the quality of finite element (FE) computations. To perform the mechanical simulation of a component, the corresponding geometric model typically needs to be simplified in accordance with hypotheses adopted regarding the component\'s mechanical behaviour. The method presented herein serves to compute an a posteriori indicator for the purpose of estimating the significance of each feature removal. This method can be used as part of an adaptive process of geometric simplification. If a shape detail removed during the shape simplification process proves to be influential on mechanical behaviour, the particular detail can then be reinserted into the simplified model, thus making it possible to readapt the initial simulation model. The fields of application for such a method are: static problems involving linear elastic behaviour, and linear thermal problems with stationary conduction.

Key Words
adaptive modelling; geometric simplification; a posteriori mechanical indicator; structural simulation; finite element; CAD; feature removal.

Address
P. Marin: 3SR Laboratory, National Polytechnic Institute of Grenoble, B.P. 95, 38402 St., Martin d\'Heres, France

Abstract
In this paper a boundary element method is developed for the general flexural-torsional buckling analysis of Timoshenko beams of arbitrarily shaped cross section. The beam is subjected to a compressive centrally applied concentrated axial load together with arbitrarily axial, transverse and torsional distributed loading, while its edges are restrained by the most general linear boundary conditions. The resulting boundary value problem, described by three coupled ordinary differential equations, is solved employing a boundary integral equation approach. All basic equations are formulated with respect to the principal shear axes coordinate system, which does not coincide with the principal bending one in a nonsymmetric cross section. To account for shear deformations, the concept of shear deformation coefficients is used. Six coupled boundary value problems are formulated with respect to the transverse displacements, to the angle of twist, to the primary warping function and to two stress functions and solved using the Analog Equation Method, a BEM based method. Several beams are analysed to illustrate the method and demonstrate its efficiency and wherever possible its accuracy. The range of applicability of the thin-walled theory and the significant influence of the boundary conditions and the shear deformation effect on the buckling load are investigated through examples with great practical interest.

Key Words
flexural-torsional buckling; nonuniform torsion; elastic stability; warping; flexural; bar; beam; twist; boundary element method; shear deformation.

Address
E.J. Sapountzakis: School of Civil Engineering, National Technical University, Zografou Campus, GR-157 80, Athens, Greece
J.A. Dourakopoulos: School of Civil Engineering, National Technical University, Zografou Campus, GR-157 80, Athens, Greece

Abstract
One of the intractable problems in multiresolution structural analysis is the decoupling computation between scales, which can be realized by the operator-orthogonal wavelets based on the lifting scheme. The multiresolution finite element space is described and the formulation of multiresolution finite element models for structural problems is discussed. Various operator-orthogonal wavelets are constructed by the lifting scheme according to the operators of multiresolution finite element models. A dynamic multiresolution algorithm using operator-orthogonal wavelets is proposed to solve structural problems. Numerical examples demonstrate that the lifting scheme is a flexible and efficient tool to construct operator-orthogonal wavelets for multiresolution structural analysis with high convergence rate.

Key Words
multiresolution finite element; lifting scheme; operator-orthogonal wavelet.

Address
Youming Wang: State Key Lab for Manufacturing Systems Engineering, Xi\'an Jiaotong University, Xi\'an 710049, People\'s Republic of China
Xuefeng Chen: State Key Lab for Manufacturing Systems Engineering, Xi\'an Jiaotong University, Xi\'an 710049, People\'s Republic of China
Yumin He: State Key Lab for Manufacturing Systems Engineering, Xi\'an Jiaotong University, Xi\'an 710049, People\'s Republic of China
Zhengjia He: State Key Lab for Manufacturing Systems Engineering, Xi\'an Jiaotong University, Xi\'an 710049, People\'s Republic of China

Abstract
To investigate the critical buckling load and post-buckling behavior of an axially loaded pile entirely embedded in soil, the non-linear large deflection differential equation for a pinned pile, based on the Winkler-model and the discretionary distribution function of the foundation coefficient along pile shaft, was established by energy method. Assuming that the deflection function was a power series of some perturbation parameter according to the boundary condition and load in the pile, the non-linear large deflection differential equation was transformed to a series of linear differential equations by using perturbation approach. By taking the perturbation parameter at middle deflection, the higher-order asymptotic solution of load-deflection was then found. Effect of ratios of soil depth to pile length, and ratios of pile stiffness to soil stiffness on the critical buckling load and performance of piles (entirely embedded and partially embedded) after flexural buckling were analyzed. Results show that the buckling load capacity increases as the ratios of pile stiffness to soil stiffness increasing. The pile performance will be more stable when ratios of soil depth to pile length, and soil stiffness to pile stiffness decrease.

Key Words
pile buckling load capacity; post-buckling equilibrium; perturbation approach; ratio of soil depth to pile depth; ratio of pile stiffness to soil stiffness.

Address
M.H. Zhao: College of Civil Engineering, Hunan University, Changsha, Hunan 410082, P.R. China
W. He: School of Civil Engineering and Architecture, Changsha University of Science and Technology, Changsha, Hunan 410076, P.R. China
Q.S. Li: College of Civil Engineering, Hunan University, Changsha, Hunan 410082, P.R. China

Abstract
Recently, earthquake proof technology has been widely applied to both new and existing structures and bridges. The analysis of bridge systems equipped with structural control devices, which possess large degrees of freedom and nonlinear characteristics, is a result in time-consuming task. Therefore, a piecewise exact solution is proposed in this study to simplify the seismic mitigation analysis process for bridge systems equipped with sliding-type isolators. In this study, the simplified system having two degrees of freedom, to reasonably represent the large number of degrees of freedom of a bridge, and is modeled to obtain a piecewise exact solution for system responses during earthquakes. Simultaneously, we used the nonlinear finite element computer program to analyze the bridge responses and verify the accuracy of the proposed piecewise exact solution for bridge systems equipped with sliding-type isolators. The conclusions derived by comparing the results obtained from the piecewise exact solution and nonlinear finite element analysis reveal that the proposed solution not only simplifies the calculation process but also provides highly accurate seismic responses of isolated bridges under earthquakes.

Key Words
multiple friction pendulum system; bridges; base isolator; base isolation system; earthquake engineering; structural control; passive control.

Address
C.S. Tsai: Department of Civil Engineering, Feng Chia University, Taichung, Taiwan
Yung-Chang Lin: Graduate Institute of Civil and Hydraulic Engineering, Feng Chia University, Taichung, Taiwan
Wen-Shin Chen: Graduate Institute of Civil and Hydraulic Engineering, Feng Chia University, Taichung, Taiwan
Tsu-Cheng Chiang: Earthquake Proof Systems, Inc., Taichung, Taiwan
Bo-Jen Chen: Department of Research and Development, Earthquake Proof Systems, Inc., Taichung, Taiwan

Abstract
A semi-analytical method is presented for accurately prediction of the free vibration behavior of generally laminated composite plates with arbitrary boundary conditions. The method employs the technique of separation of spatial variables within Hamilton\'s principle to obtain the equations of motion, including two systems of coupled ordinary homogeneous differential equations. Subsequently, by applying the laminate constitutive relations into the resulting equations two sets of coupled ordinary differential equations with constant coefficients, in terms of displacements, are achieved. The obtained differential equations are solved for the natural frequencies and corresponding mode shapes, with the use of the exact state-space approach. The formulation is exploited in the framework of the first-order shear deformation theory to incorporate the effects of transverse shear deformation and rotary inertia. The efficiency and accuracy of the present method are demonstrated by obtaining solutions to a wide range of problems and comparing them with finite element analysis and previously published results.

Key Words
extended Kantorovich method; laminated composite plates; free vibration; arbitrary boundary conditions; shear deformation; rotary inertia.

Address
A.M. Naserian-Nik: Department of Mechanical Engineering, Faculty of Engineering, Ferdowsi University of Mashhad, Mashhad, Iran
M. Tahani: Department of Mechanical Engineering, Faculty of Engineering, Ferdowsi University of Mashhad, Mashhad, Iran

Abstract
The interaction between steel tube and concrete core is the key issue for understanding the behavior of concrete-filled steel tube columns (CFTs). This study investigates the force transfer by natural bond or by mechanical shear connectors and the interaction between the steel tube and the concrete core under three types of loading. Two and three-dimensional nonlinear finite element models are developed to study the force transfer between steel tube and concrete core. The nonlinear finite element program ABAQUS is used. Material and geometric nonlinearities of concrete and steel are considered in the analysis. The damage plasticity model provided by ABAQUS is used to simulate the concrete material behavior. Comparisons between the finite element analyses and own experimental results are made to verify the finite element models. A good agreement is observed between the numerical and experimental results. Parametric studies using the numerical models are performed to investigate the effects of diameterto-thickness ratio, uniaxial compressive strength of concrete, length of shear connectors, and the tensile strength of shear connectors.

Key Words
composite columns; concrete-filled steel tube; bond stress; load transfer; mechanical shear connectors; confinement; test; finite element analysis; parametric study.

Address
Uwe Starossek: Structural Analysis and Steel Structures Institute, Hamburg University of Technology (TUHH), Denickestrasse 17, D-21073 Hamburg, Germany
Nabil Falah: Structural Analysis and Steel Structures Institute, Hamburg University of Technology (TUHH), Denickestrasse 17, D-21073 Hamburg, Germany
Thomas Lohning: Structural Analysis and Steel Structures Institute, Hamburg University of Technology (TUHH), Denickestrasse 17, D-21073 Hamburg, Germany

Abstract


Key Words


Address
Hakan Gokdag: Faculty of Engineering and Architecture, Mechanical Engineering Department, Uludag University, 16059 Gorukle – Bursa, Turkey
Osman Kopmaz: Faculty of Engineering and Architecture, Mechanical Engineering Department, Uludag University, 16059 Gorukle – Bursa, Turkey

Abstract


Key Words


Address
Wei-Ren Chen: Department of Mechanical Engineering, Chinese Culture University, Taipei, Taiwan, R.O.C.


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