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CONTENTS
Volume 30, Number 1, September10 2008
 

Abstract
The dynamic characteristics of the passive, semi-active, and active tuned-liquidcolumn dampers (or TLCDs) are studied in this paper. The design of the latter two are based on the first one. A water-head difference (or simply named as water head in this paper) of a passive TLCD is pre-set to form the so-called semi-active one in this paper. The pre-set of water head is released at a proper time instant
during an earthquake excitation in order to enhance the vibration reduction of a structure. Two propellers are installed along a shaft inside and at the center of a passive TLCD to form an active one. These two propellers are driven by a servo-motor controlled by a computer to provide the control force. The seismic responses of a five-story shear building with a passive, semiactive, and active TLCDs are computed for demonstration and discussion. The responses of this building with a tuned mass damper (or TMD) are also included for comparison. The small-scale shaking-table experiments of a pendulum-like system with a passive or active TLCD to harmonic and seismic excitations are conducted for verification.

Key Words
TLCDs; modelling; controls; experiments.

Address
Yung-Hsiang Chen: Dept. of Civil Engineering, National Taiwan University, Taipei, Taiwan, R.O.C.
Ying-Jan Ding: Construction and Planning Agency, Ministry of the Interior, Taipei, Taiwan, R.O.C.

Abstract
The static response of a finite beam resting on a tensionless Pasternak foundation and subjected to a concentrated vertical load is assessed in this study. The concentrated vertical load may be applied at the center of the beam, or it may be offset from the center. The tensionless character of the foundation results in the creation of lift-off regions between the beam and the foundation. An analytical/numerical solution is obtained from the governing equations of the contact and lift-off regions to determine the extent of the contact region. Although there is no nonlinear term in the equations, the problem shows a nonlinear character since the contact region is not known in advance. Due to that nonlinearity, the essentials of the problem (the coordinates of the lift-off points) are calculated numerically
using the Newton-Raphson technique. The numerical results are presented in figures to illustrate the behaviours of the free-free and pinned-pinned beams under symmetric or asymmetric loading. The figures
illustrate the effects of the shear foundation parameter and the symmetric and asymmetric loading options on the variation of the contact lengths and the displacement of the beam.

Key Words
Pasternak foundation; finite beam; lift-off.

Address
Irfan Coskun: Faculty of Civil Engineering, Yildiz Technical University, 34349 Yildiz, lstanbul, Turkey
Hasan Engin: Faculty of Civil Engineering,lstanbul Technical University, 34469 Maslak, lstanbul, Turkey
Aydin Ozmutlu: Dept. of Civil Engineering, Trakya University, 2250 Karaagac, Edirne, Turkey

Abstract
This paper focuses on the nonlinear vibrations of stay cables and evaluates the dynamic characteristics of stay cables by using the nonlinear enhanced MECS approach and the approximate approach. The nonlinear enhanced MECS approach is that both the girder-tower vibrations and the cable vibrations including parametric cable vibrations are simultaneously considered in the numerical analysis of cable-stayed bridges. Cable finite element method is used to simulate the responses including the parametric vibrations of stay cables. The approximate approach is based on the assumption that cable vibrations have a small effect on girder-tower vibrations, and analyzes the local cable vibrations after obtaining the girder-tower responses. Under the periodic excitations or the moderate ground motion, the
differences of the responses of stay cables between these two approaches are evaluated in detail. The effect of cable vibrations on the girder and towers are also discussed. As a result, the dynamic
characteristics of the parametric vibrations in stay cables can be evaluated by using the approximate approach or the nonlinear enhanced MECS approach. Since the different axial force fluctuant of stay
cables in both ends of one girder causes the difference response values between two approach, it had better use the nonlinear enhanced MECS approach to perform the dynamic analyses of cable-stayed
bridges.

Key Words
stay cable; parametric vibrations; cable-stayed bridge; nonlinear enhanced MECS approach; approximate approach; finite element method.

Address
Qingxiong Wu: College of Civil Engineering, Fuzhou University, 523 Gongye Road, Fuzhou, Fujian, China
Kazuo Takahashi: Dept. of Civil Engineering, Faculty of Engineering, Nagasaki University, 1-14, Bunkyo-machi, Nagasaki, Japan
Baochun Chen: College of Civil Engineering, Fuzhou University, 523 Gongye Road, Fuzhou, Fujian, China

Abstract
Limit cycle oscillations of a two-dimensional airfoil with quadratic and cubic pitching nonlinearities are investigated. The equivalent stiffness of the pitching stiffness is obtained by combining the linearization and harmonic balance method. With the equivalent stiffness, the equivalent linearization method for nonlinear flutter analysis is generalized to address aeroelastic system with quadratic
nonlinearity. Numerical example shows that good approximation of the limit cycle can be obtained by the generalized method. Furthermore, the proposed method is capable of revealing the unsymmetry of the
limit cycle; however the ordinary equivalent linearization method fails to do so.

Key Words
aeroelastic system; quadratic nonlinearity; limit cycle; equivalent linearization method.

Address
Y.M. Chen and J.K. Liu: Dept. of Mechanics, SunYat-sen University, Guangzhou 510275, China

Abstract
In this paper, a strut-and-tie model approach has been proposed to directly calculate the amount of reinforcements in deep beams, and the force transfer mechanisms for this approach were investigated using linear finite element analysis. The proposed strut-and-tie model provides quite similar force transfer mechanisms to the results of linear finite element analysis for the 28 deep beams. The loadcarrying
capacities calculated from the proposed method are both accurate and conservative with little scatter or trends for the 214 deep beams. The deep beams have different concrete strengths including highstrength,
various combinations of web reinforcements, and wide range of and a/d ratios. Good accuracy was also obtained using VecTor2, nonlinear finite element analysis tool based on the Modified Compression
Field Theory. Since the proposed method provides a safe and reliable means for design of deep beams, this can serve to improve design provisions in future adjustments and development of design guidelines.

Key Words
strut-and-tie model; shear strength; force transfer mechanism; reinforced concrete; deep beams.

Address
Jung-Woong Park and Seung-Eock Kim: Dept. of Civil and Environmental Engineering, Sejong University, 98 Gunja-dong, Gwangjin-gu, Seoul 143-747, Korea

Abstract
This paper presents a comprehensive approach to the evaluation of macroscopic material parameters for natural stone and quarry masonry. To that end, a reliable non-linear material model on a meso-scale is developed to cover the random arrangement of stone blocks and quasi-brittle behaviour of both basic components, as well as the impaired cohesion and tensile strength on the interface between the blocks and mortar joints. The paper thus interrelates the following three problems: (i) definition of a suitable periodic unit cell (PUC) representing a particular masonry structure; (ii) derivation of material parameters of individual constituents either experimentally or running a mixed numerical- experimental problem; (iii) assessment of the macroscopic material parameters including the tensile and compressive strengths and fracture energy.

Key Words
meso-scale; macro-scale; homogenization; finite element analysis; fracture energy; masonry.

Address
J. Sejnoha and M. Sejnoha: Dept. of Mechanics, Faculty of Civil Engineering, CTU in Prague, Thakurova 7, 166 29 Praha 6, Czech Republic
Centre for Integrated Design of Advanced Structures, CTU in Prague, Thakurova 7, 166 29 Praha 6, Czech Republic
J. Zeman, J. Sykora and J. Vorel: Dept. of Mechanics, Faculty of Civil Engineering, CTU in Prague, Thakurova 7, 166 29 Praha 6, Czech Republic

Abstract
A small strain and elastoplastic formulation of Polygonal Element Method (PEM) is developed for efficient analysis of elastoplastic solids. In this work, the polygonal elements are constructed based on traditional triangular finite meshes. The construction method of polygonal mesh can directly utilize the sophisticated triangularization algorithm and reduce the difficulty in generating polygonal elements. The Wachspress rational finite element basis function is used to construct the approximations of polygonal elements. The incremental variational form and a von Mises type model are
used for non-linear elastoplastic analysis. Several small strain elastoplastic numerical examples are presented to verify the advantages and the accuracy of the numerical formulation.

Key Words
elastoplasticity; polygonal finite element method; Wachspress basis functions; meshless methods.

Address
Yong-chang Cai and He-hua Zhu: Key Laboratory of Geotechnical and Underground Engineering of Ministry of Education, Department of Geotechnical Engineering, Tongji University, 200092, P.R. China
Sheng-yong Guo: Ertan Hydropower Development Company, Ltd., 98 Shuanglin Road, Chengdu, 610021, P.R. China

Abstract
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Key Words
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Address
M. M. G. V. Shyamalee, C. K. Pathirana, H. Abeyruwan and K. R. B. Herath: Dept. of Civil Engineering, University of Peradeniya, Peradeniya, Sri Lanka


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