• Title, Summary, Keyword: cable stiffness

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Hybrid Control with a Bang-Bang Type Controller (Bang-Bang 형태의 제어기를 갖는 복합제어)

  • 박규식;정형조;조상원;이인원
    • Proceedings of the Computational Structural Engineering Institute Conference
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    • pp.193-200
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    • 2003
  • This paper presents a hybrid (i.e., integrated passive-active) system for seismic response control of a cable-stayed bridge. Because multiple control devices are operating, a hybrid control system could alleviate some of the restrictions and limitations that exist when each system is acting alone. Lead rubber bearings are used as passive control devices to reduce the earthquake-induced forces in the bridge and hydraulic actuators are used as active control devices to further reduce the bridge responses, especially deck displacements. In the proposed hybrid control system, a linear quadratic Gaussian control algorithm is adopted as a primary controller. In addition, a secondary bang-bang type (i.e., on-off type) controller according to the responses of lead rubber bearings is considered to increase the controller robustness. Numerical simulation results show that control performances of the hybrid control system are superior to those of the passive control system and slightly better than those of the fully active control system. Furthermore, it is verified that the hybrid control system with a bang-bang type controller is more robust for stiffness perturbation than the active controller with μ-synthesis method and there are no signs of instability in the overall system whereas the active control system with linear quadratic Gaussian algorithm shows instabilities in the perturbed system. Therefore, the proposed hybrid protective system could effectively be used to seismically excited cable-stayed bridges.

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Seismic Analysis of a 3-dimensional Cable-Stayed Bridge with an Unsymmetric Girder Cross-section (주형단면의 비대칭성을 고려한 3차원 사장교의 지진해석)

  • Kim, Chul Young;Chang, Sung Pil
    • Journal of The Korean Society of Civil Engineers
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    • v.12 no.2
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    • pp.11-20
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    • 1992
  • In general, the cross-section of a girder of a bridge has only one axis of symmetry. Therefore, lateral forces such as earthquake and wind may cause torsion coupled with lateral bending in the gider. This induces additional stresses especially in cables arranged in double-planes. Since this effect cannot be considered by using the conventional frame elements, the stiffness and the mass matrices of the geometrically nonlinear thin-walled frame element have to be used in order to model the girder. Theoretical development and verification of the frame element used in this study were made through a-previously presented paper. In this paper, seismic analysis of a three dimensional cable-stayed bridge considering the unsymmetry of the girder cross-section is performed to investigate the coupled flexural-torsional behaviors.

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Dynamic characteristics of hybrid tower of cable-stayed bridges

  • Abdel Raheem, Shehata E.
    • Steel and Composite Structures
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    • v.17 no.6
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    • pp.803-824
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    • 2014
  • The dynamic characterization is important in making accurate predictions of the seismic response of the hybrid structures dominated by different damping mechanisms. Different damping characteristics arise from the construction of the tower with different materials: steel for the upper part; reinforced concrete for the lower main part and interaction with supporting soil. The process of modeling damping matrices and experimental verification is challenging because damping cannot be determined via static tests as can mass and stiffness. The assumption of classical damping is not appropriate if the system to be analyzed consists of two or more parts with significantly different levels of damping, such as steel/concrete mixed structure - supporting soil coupled system. The dynamic response of structures is critically determined by the damping mechanisms, and its value is very important for the design and analysis of vibrating structures. An analytical approach capable of evaluating the equivalent modal damping ratio from structural components is desirable for improving seismic design. Two approaches are considered to define and investigate dynamic characteristics of hybrid tower of cable-stayed bridges: The first approach makes use of a simplified approximation of two lumped masses to investigate the structure irregularity effects including damping of different material, mass ratio, frequency ratio on dynamic characteristics and modal damping; the second approach employs a detailed numerical step-by step integration procedure in which the damping matrices of the upper and the lower substructures are modeled with the Rayleigh damping formulation.

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.

3-D Configuration Effects of Prestressing Cable Bracing Used for Retrofitting a RC Frame Subjected to Seismic Damage (RC 골조의 내진 보강을 위한 예압 가새의 3-D 배치)

  • Lee, Jin-Ho;Oh, Sang-Gyun;Hisham, El-Ganzori
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.7 no.3
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    • pp.183-191
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    • 2003
  • A four-story reinforced concrete moment resisting frame damaged from an ultimate limit state earthquake is upgraded with prestressing cable bracing. The purpose of this study is to investigate the bracing configuration effects on the 3-D building response using thee different locations of the bracing systems for the retrofitted building. Since the previous work done by the author proved that static incremental loads to collapse analysis as a substitute to dynamic non-linear time history analysis was a valid alternative tool. Thus, static load to collapse analysis is solely applied to evaluate the seismic performance parameters of both the original and upgraded buildings in this study. In results, the exterior bracing system is effective in restraining torsional behavior of the structure under seismic loads, and no sudden failure occurs in this system that enhances the ductility of the building due to the gradual change of building stiffness as the lateral load increases.

Hybrid System Controlled by a $\mu-Synthesis$ Method for a Seismically Excited Cable-Stayed Bridge (지진하중을 받는 사장교를 위한 $\mu$-합성법을 이용한 복합시스템)

  • Park, Kyu-Sik;Jung, Hyung-Jo;Choi, Kang-Min;Lee, Jong-Heon;Lee, In-Won
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • pp.574-577
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    • 2004
  • This paper presents a hybrid system combining lead rubber bearings and hydraulic actuators controlled by a $\mu-synthesis$ method for seismic response control of a cable-stayed bridge. A hybrid system could alleviate some of restrictions and limitations that exist when each system is acting alone because multiple control devices are operating. Therefore, the overall control performance of a hybrid system may be improved compared to each system, however the overall system robustness may be negatively impacted by active device in the hybrid system or active controller may cause instability due to small margins. Therefore, a $\mu-synthesis$ method that guarantees the robust performance is considered to enhance the possibility of real applications of the control system. The performances of the proposed control system are compared with those of passive, active, semiactive control systems and hybrid system controlled by a LQG algorithm. Furthermore, an extensive robust analysis with respect to stiffness and mass matrices perturbation and time delay of actuator is performed. Numerical simulation results show that the performances of the proposed control system are superior to those of passive system and slightly better than those of active and semiactive systems and two hybrid systems show similar control performances. Furthermore, the hybrid system controlled by a f-synthesis method shows the good robustness without loss of control performances. Therefore, the proposed control system could effectively be used to seismically excited cable-stayed bridge which contains many uncertainties.

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The Sensitivity Analysis and Safety Evaluations of Cable Stayed Bridges Based on Probabilistic Finite Element Method (확률유한요소해석에 의한 사장교의 민감도 분석 및 안전성 평가)

  • Han, Sung-Ho;Cho, Tae-Jun;Bang, Myung-Seok
    • Journal of the Korea institute for structural maintenance and inspection
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    • v.11 no.1
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    • pp.141-152
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    • 2007
  • Considering uncertainties of random input data, it is more reasonable to use probabilistic method than the conventional deterministic method for the design of structures or for the assessment of the responses of structures, which are designed as safe even under extreme loads. Therefore, to assess the quantitative effects of the constructed cable stayed bridge by the input random variables, a sensitivity analysis is studied. Using perturbation method, an analysis program is developed for the iterative probabilistic finite element analyses and sensitivity analyses of the cable stayed bridge, except the initial shape analysis. Monte-Carlo Simulations were used for the verification of the developed program. The results of sensitivity analysis shows the governing effects of external loads. Because the results also provide the sensitive effects of the stiffness of members and the magnitudes of prestressing force of cables, the developed

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.

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
    • Journal of The Korean Society of Civil Engineers
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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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