• Title, Summary, Keyword: cable stiffness

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A Study on Numerical Simulation for Dynamic Analysis of Towed Low-Tension Cable with Nonuniform Characteristics (불균일 단면을 갖는 저장력 예인케이블의 동적해석을 위한 수치해석적 연구)

  • 정동호
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.16 no.1
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    • pp.69-76
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    • 2003
  • Low-tension cables have been increasingly used in recent years due to deep-sea developments and the advent of synthetic cables. In the case of low-tension cables, large displacements may happen due to relatively small restoring forces of tension and thus the effects of fluid and geometric non-linearities and bending stiffness. A Fortran program is developed by employing a finite difference method. In the algorithm, an implicit time integration and Newton-Raphson iteration are adopted. For the calculation of huge size of matrices, block tri-diagonal matrix method is applied, which is much faster than the well-known Gauss-Jordan method in two point boundary value problems. Some case studies are carried out and the results of numerical simulations are compared with a in-house program of WHOI Cable with good agreements.

Structural health rating (SHR)-oriented 3D multi-scale finite element modeling and analysis of Stonecutters Bridge

  • Li, X.F.;Ni, Y.Q.;Wong, K.Y.;Chan, K.W.Y.
    • Smart Structures and Systems
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    • v.15 no.1
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    • pp.99-117
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    • 2015
  • The Stonecutters Bridge (SCB) in Hong Kong is the third-longest cable-stayed bridge in the world with a main span stretching 1,018 m between two 298 m high single-leg tapering composite towers. A Wind and Structural Health Monitoring System (WASHMS) is being implemented on SCB by the Highways Department of The Hong Kong SAR Government, and the SCB-WASHMS is composed of more than 1,300 sensors in 15 types. In order to establish a linkage between structural health monitoring and maintenance management, a Structural Health Rating System (SHRS) with relevant rating tools and indices is devised. On the basis of a 3D space frame finite element model (FEM) of SCB and model updating, this paper presents the development of an SHR-oriented 3D multi-scale FEM for the purpose of load-resistance analysis and damage evaluation in structural element level, including modeling, refinement and validation of the multi-scale FEM. The refined 3D structural segments at deck and towers are established in critical segment positions corresponding to maximum cable forces. The components in the critical segment region are modeled as a full 3D FEM and fitted into the 3D space frame FEM. The boundary conditions between beam and shell elements are performed conforming to equivalent stiffness, effective mass and compatibility of deformation. The 3D multi-scale FEM is verified by the in-situ measured dynamic characteristics and static response. A good agreement between the FEM and measurement results indicates that the 3D multi-scale FEM is precise and efficient for WASHMS and SHRS of SCB. In addition, stress distribution and concentration of the critical segments in the 3D multi-scale FEM under temperature loads, static wind loads and equivalent seismic loads are investigated. Stress concentration elements under equivalent seismic loads exist in the anchor zone in steel/concrete beam and the anchor plate edge in steel anchor box of the towers.

Semi-active control of vibrations of spar type floating offshore wind turbines

  • Van-Nguyen, Dinh;Basu, Biswajit;Nagarajaiah, Satish
    • Smart Structures and Systems
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    • v.18 no.4
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    • pp.683-705
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    • 2016
  • A semi-active algorithm for edgewise vibration control of the spar-type floating offshore wind turbine (SFOWT) blades, nacelle and spar platform is developed in this paper. A tuned mass damper (TMD) is placed in each blade, in the nacelle and on the spar to control the vibrations for these components. A Short Time Fourier Transform algorithm is used for semi-active control of the TMDs. The mathematical formulation of the integrated SFOWT-TMDs system is derived by using Euler-Lagrangian equations. The theoretical model derived is a time-varying system considering the aerodynamic properties of the blade, variable mass and stiffness per unit length, gravity, the interactions among the blades, nacelle, spar, mooring system and the TMDs, the hydrodynamic effects, the restoring moment and the buoyancy force. The aerodynamic loads on the nacelle and the spar due to their coupling with the blades are also considered. The effectiveness of the semi-active TMDs is investigated in the numerical examples where the mooring cable tension, rotor speed and the blade stiffness are varying over time. Except for excessively large strokes of the nacelle TMD, the semi-active algorithm is considerably more effective than the passive one in all cases and its effectiveness is restricted by the low-frequency nature of the nacelle and the spar responses.

LRB-based hybrid base isolation systems for cable-stayed bridges (사장교를 위한 LRB-기반 복합 기초격리 시스템)

  • Jung, Hyung-Jo;Park, Kyu-Sik;Spencer, Billie-F.Jr.;Lee, In-Won
    • Journal of the Earthquake Engineering Society of Korea
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    • v.8 no.3
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    • pp.63-76
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    • 2004
  • This paper presents LRB-based hybrid base isolation systems employing additional active/semiactive control devices for mitigating earthquake-induced vibration of a cable-stayed 29 bridge. Hybrid base isolation systems could improve the control performance compared with the passive type-base isolation system such as LRB-installed bridge system due to multiple control devices are operating. In this paper, the additional response reduction by the two typical additional control devices, such as active type hydraulic actuators controlled by LQG algorithm and semiactive-type magnetorheological dampers controlled by clipped-optimal algorithm, have been evaluated bypreliminarily investigating the slightly modified version of the ASCE phase I benchmark cable-stayed bridge problem (i.e., the installation of LRBs to the nominal cable-stayed bridge model of the problem). It shows from the numerical simulation results that all the LRB based hybrid seismic isolation systems considered are quite effective to mitigate the structural responses. In addition, the numerical results demonstrate that the LRB based hybrid seismic isolation systems employing MR dampers have the robustness to some degree of the stiffness uncertainty of in the structure, whereas the hybrid system employing hydraulic actuators does not. Therefore, the feasibility of the hybrid base isolation systems employing semiactive additional control devices could be more appropriate in realfor full-scale civil infrastructure applications is clearly verified due to their efficacy and robustness.

Section Model Study on the Aerodynamic Behaviors of the Cable-Stayed Bridges with Two I-Type Girders Considering Structural Damping and Turbulence Intensity (2개의 I형 거더를 가진 사장교의 구조감쇠비 및 난류강도를 고려한 공기역학적 거동에 관한 단면모형실험 연구)

  • Cho, Jae-Young;Kim, Young-Min;Cho, Young-Rae;Lee, Hak-Eun
    • KSCE Journal of Civil and Environmental Engineering Research
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    • v.26 no.6A
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    • pp.1013-1022
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    • 2006
  • Although the cable-stayed bridges with two I-type girders inherently do not have good aerodynamic characteristics, a lot of the bridges with this type girders are constructed in Korea recently because of an economical merit. This paper investigated the aerodynamic characteristics of the cable-stayed bridges with two I-type girders. Section model tests were conducted in order to investigate the aerodynamic behaviors of this section with varying of the angles of attack, turbulence intensity and damping ratios. Two deck section configurations with different torsional stiffness were studied under construction and after completion respectively. Three types of the fairings were investigated to improve the aerodynamic characteristics of the bridges. The result of this study showed that the traditional section model test in uniform flow estimates the aerodynamic behavior rather pessimistically. The wind induced responses of the bridges were severely varied in accordance with the turbulence intensity and the structural damping ratio. The proposed fairing reduced the magnitude of the vortex-shedding vibrations and buffeting responses. It also increased the wind speed at which flutter occurs. It is expected that these investigations would provide a lot of information for the design of the cable stayed bridges with two I-type girders regarding wind resistance.

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The Optimum Design of Spatial Structures by TABU Algorithm (터부 알고리즘에 의한 대공간 구조물의 최적설계)

  • 한상을;이상주;조용원;김민식
    • Proceedings of the Computational Structural Engineering Institute Conference
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    • pp.171-178
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    • 2004
  • The purpose of optimum design for structures is to minimize the cost and to obtain the reasonable structural systems. This design algorithm have many objective functions including discrete variables as sections, weight, stiffness and shapes. Simulated annealing, Genetic algorithm and TABU algorithm are used search for these optimum values in the structural design. TABU algorithm is applied to many types structures to search for section and distribution optimization and compared with the results of Genetic algorithm for evaluating the efficiency of this algorithm. In this paper, the plane truss of 10 elements and the space truss of 25 element having 10 nodes, star dome and cable dome are analyzed as analytical models.

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Type Suggestion and Parameter Study for Long-Span Bridge of High-Speed Railway without the REJ considering CWR Axial Force (장대레일 축력을 고려한 REJ 미적용 고속철도 특수교량 형식 제시 및 변수별 분석)

  • Lee, Jong-Soon;Joo, Hwan-Joong;Shin, Jai-Yeoul;Yoon, Sung-Sun;Park, Sun-Hee;Nam, Hyoung-Mo
    • Proceedings of the KSR Conference
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    • pp.1254-1261
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    • 2011
  • Application of long-span bridge, which is affected by parameters such as span length, shoe boundary condition, track property and stiffness of superstructure and substructure etc., can vary. Especially, by CWR aspects of the axial force, long-span high speed railway bridges are limited at type and span length. In this study, in terms of CWR axial force, the long-span high-speed railway bridges without REJ(Rail Expansion Joint) is to propose the bridge type. Various Parameters analysis performed for the proposed type(Arch bridge, Cable-stayed bridge).

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Determining the Bilateral and Unilateral Mechanisms of Tensegrity Systems

  • Shekastehband, B.
    • International journal of steel structures
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    • v.17 no.3
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    • pp.1049-1058
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    • 2017
  • Tensegrity systems as kinematically and statically indeterminate pin-jointed systems are characterized by mechanisms and self-stress states. Taking into account the unilateral rigidity of cables may cause other mechanisms (unilateral) rather than bilateral infinitesimal mechanisms to be produced. Two numerical methods are presented for determining of bilateral mechanisms in tensegrity structures which are based on the geometrical characteristics and positive-definiteness of the tangent stiffness matrix, respectively. These methods allows distinction between first-order and higher order mechanisms. A numerical method is submitted for determining the unilateral mechanisms of these systems which uses the basis of the self-stress states for identifying prestressed and non-prestressed cable elements.

Effect of Initial Tension on Natural Periods for a Suspension Bridge (현수교 초기장력이 고유주기 산정에 미치는 영향)

  • 김호경;이재홍
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • pp.450-454
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    • 2003
  • Natural periods are usually determined by the so-called linearized finite displacement theory even for a suspension bridge. This linearized method, with formulating structural stiffness by taking dead-load tension into consideration, calculates the natural periods of the bridge. As a result, the assumed initial tensions for each cable member may affect the accuracy of calculated natural periods and some other dynamic responses. This paper mainly demonstrates the effect of initially introduced tension accuracy on the evaluation of dynamic characteristics for a suspension bridge.

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Shape Finding of Cable-Net Structures by Using Modified Dynamic Relaxation Method (변형된 동적이완법을 이용한 케이블-네트 구조물의 형상해석)

  • 하창우;김재열;권택진
    • Proceedings of the Computational Structural Engineering Institute Conference
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    • pp.51-58
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    • 2000
  • Dynamic relaxation method is a shape finding analysis method for flexible structures by introducing the dynamic equilibrium equation. However, it is difficult for shape finding to estimate the most appropriate values for the mass and damping on each shape because the values are random one. In this study, the unit mass, the unit damping and the principal direction stiffness are utilized to avoid the random values, and the Newmarks assumption is introduced during the dynamic analysis. By introducing variant time increment method presented, the convergence time is reduced, that is, it can be reduced the total times for analysis.

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