• Title, Summary, Keyword: tower stiffness

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Experimental and numerical investigations on seismic performance of a super tall steel tower

  • He, Minjuan;Li, Zheng;Ma, Renle;Liang, Feng
    • Earthquakes and Structures
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    • v.7 no.4
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    • pp.571-586
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    • 2014
  • This paper presents experimental and numerical study on seismic performance of a super tall steel tower structure. The steel tower, with a height of 388 meters, employs a steel space truss with spiral steel columns to serve as its main lateral load resisting system. Moreover, this space truss was surrounded by the spiral steel columns to form a steel mega system in order to support a 12-story platform building which is located from the height of 230 meters to 263 meters. A 1/40 scaled model for this tower structure was made and tested on shake table under a series of one- and two-dimensional earthquake excitations with gradually increasing acceleration amplitudes. The test model performed elastically up to the seismic excitations representing the earthquakes with a return period of 475 years, and the test model also survived with limited damages under the seismic excitations representing the earthquakes with a return period 2475 years. A finite element model for the prototype structure was further developed and verified. It was noted that the model predictions on dynamic properties and displacement responses agreed reasonably well with test results. The maximum inter-story drift of the tower structure was obtained, and the stress in the steel members was investigated. Results indicated that larger displacement responses were observed for the section from the height of 50 meters to 100 meters in the tower structure. For structural design, applicable measures should be adopted to increase the stiffness and ductility for this section in order to avoid excessive deformations, and to improve the serviceability of the prototype structure.

Flexural free vibration of cantilevered structures of variable stiffness and mass

  • Li, Q.S.
    • Structural Engineering and Mechanics
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    • v.8 no.3
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    • pp.243-256
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    • 1999
  • Using appropriate transformations, the differential equation for flexural free vibration of a cantilever bar with variably distributed mass and stiffness is reduced to a Bessel's equation or an ordinary differential equation with constant coefficients by selecting suitable expressions, such as power functions and exponential functions, for the distributions of stiffness and mass. The general solutions for flexural free vibration of one-step bar with variable cross-section are derived and used to obtain the frequency equation of multi-step cantilever bars. The new exact approach is presented which combines the transfer matrix method and closed form solutions of one step bars. Two numerical examples demonstrate that the calculated natural frequencies and mode shapes of a 27-storey building and a television transmission tower are in good agreement with the corresponding experimental data. It is also shown through the numerical examples that the selected expressions are suitable for describing the distributions of stiffness and mass of typical tall buildings and high-rise structures.

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.

Analysis of Characteristics of Connected-pile Foundations for Transmission Tower according to Changes of Load and Connection Beam Conditions in Clay (점토지반에서 하중특성 및 연결보조건에 따른 송전철탑용 연결형 말뚝기초의 특성 분석)

  • Kyung, Doohyun;Lee, Junhwan;Paik, Kyuho;Kim, Youngjun;Kim, Daehong
    • Journal of the Korean Geotechnical Society
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    • v.29 no.10
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    • pp.5-18
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    • 2013
  • The differential settlement between the foundations causes the critical damage on the transmission tower constructed in soft ground. Connected-pile foundation for transmission tower structures is an option to prevent the differential settlement. It consists of main foundations and connection beams that are placed between the individual foundations at each corner of tower. In this study, 24 model pile load tests were conducted at a construction site in jeonlabuk-do to investigate the effects of the connection beams on transmission tower foundation. In model tests, various load conditions and connection beam conditions were considered. As the test results, the displacements of connected-pile foundation differed in accordance with load directions. The settlements of connected-pile foundation decreased with the increased stiffness of connection beams, lateral load capacity decreased in accordance with load height, and the lateral load capacity on the failure criteria was similar regardless of load direction.

Free Vibration Analysis of Lattice Type Structure by Transfer Stiffness Coefficient Method (전달 강성계수법에 의한 격자형 구조물의 자유 진동 해석)

  • 문덕홍;최명수;강화중
    • Journal of KSNVE
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    • v.8 no.2
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    • pp.361-368
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    • 1998
  • Complex and large lattice type structures are frequently used in design of bridge, tower, crane and aerospace structures. In general, in order to analyze these structures we have used the finite element method(FEM). This method is the most widely used and powerful tool for structural analysis. However, it is necessary to use a large amount of computer memory and computation time because the FEM resuires many degrees of freedom for solving dynamic problems exactly for these complex and large structures. For overcoming this problem, the authors developed the transfer stiffness coefficient method(TSCM). This method is based on the concept of the transfer of the nodal dynamic stiffness coefficient which is related to force and displacement vector at each node. In this paper, the authors formulate vibration analysis algorithm for a complex and large lattice type structure using the transfer of the nodal dynamic stiffness coefficient. And we confirmed the validity of TSCM through numerical computational and experimental results for a lattice type structure.

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Elasto-plastic time history analysis of an asymmetrical twin-tower rigid-connected structure

  • Wu, Xiaohan;Sun, Yanfei;Rui, Mingzhuo;Yan, Min;Li, Lishu;Liu, Dongze
    • Computers and Concrete
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    • v.12 no.2
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    • pp.211-228
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    • 2013
  • The structure analyzed in this paper has particular building style and special structural system. It is a rigid-connected twin-tower skyscraper with asymmetrical distribution of stiffness and masses in two towers. Because of the different stiffness between the north and the south towers, the torsion seismic vibration is significant. In this paper, in order to study the seismic response of the structure under both frequent low-intensity earthquakes as well as rare earthquakes at the levels of intensity 7, the analysis model is built and analyzed with NosaCAD. NosaCAD is an nonlinear structure analysis software based on second-development of AutoCAD with ObjectARX. It has convenient modeling function, high computational efficiency and diversity post-processing functions. The deformations, forces and damages of the structure are investigated based on the analysis. According to the analysis, there is no damage on the structure under frequent earthquakes, and the structure has sufficient capacity and ductility to resist rare earthquakes. Therefore the structure can reach the goal of no damage under frequent earthquakes and no collapse under rare earthquakes. The deformation of the structure is below the limit in Chinese code. The time sequence and distribution of damages on tubes are reasonable, which can dissipate some dynamic energy. At last, according to forces, load-carrying capacity and damage of elements, there are some suggestions on increasing the reinforcement in the core tube at base and in stiffened stories.

Forced Vibration Analysis of Lattice Type Structure by Transfer Stiffness Coefficient Method (전달강성계수법에 의한 격자형 구조물의 강제진동 해석)

  • 문덕홍;최명수
    • Journal of KSNVE
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    • v.8 no.5
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    • pp.949-956
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    • 1998
  • Complex and large lattice type structures are frequently used in design of bridge, tower, crane and aerospace structures. In general, in order to analyze these structures we have used the finite element method(FEM). This method is the most widely used and powerful method for structural analysis lately. However, it is necessary to use a large amount of computer memory and computational time because the FEM requires many degrees of freedom for solving dynamic problems exactly for these complex and large structures. For analyzing these structures on a personal computer, the authors developed the transfer stiffness coefficient method(TSCM). This method is based on the concept of the transfer of the nodal dynamic stiffness coefficient matrix which is related to force and displacement vector at each node. And we suggested TSCM for free vibration analysis of complex and large lattice type structures in the previous report. In this paper, we formulate forced vibration analysis algorithm for complex and large lattice type structures using extened TSCM. And we confirmed the validity of TSCM through computational results by the FEM and TSCM, and experimental results for lattice type structures with harmonic excitation.

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A Study on the Evaluation of Structural Properties of Wind Turbine Blade-Part2 (풍력터빈의 구조특성 평가에 관한 연구-Part2)

  • Lee, Kyoung-Soo;Huque, Ziaul;Kommalapati, Raghava;Han, Sang-Eul
    • Journal of the Korean Association for Spatial Structures
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    • v.15 no.1
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    • pp.65-73
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    • 2015
  • This paper presents the structural model verification process of whole wind turbine blade including blade model which proposed in Part1 paper. The National Renewable Energy Laboratory (NREL) Phase VI wind turbine which the wind tunnel and structural test data has publicly available is used for the study. In the Part1 of this paper, the processes of structural model development and verification process of blade only are introduced. The whole wind turbine composed by blade, rotor, nacelle and tower. Even though NREL has reported the measured values, the material properties of blade and machinery parts are not clear but should be tested. Compared with the other parts, the tower which made by steel pipe is rather simple. Since it does not need any considerations. By the help of simple eigen-value analysis, the accuracy of structural stiffness and mass value of whole wind turbine system was verified by comparing with NREL's reported value. NREL has reported the natural frequency of blade, whole turbine, turbine without blade and tower only models. According to the comparative studies, the proposed material and mass properties are within acceptable range, but need to be discussing in future studies, because our material properties of blade does not match with NREL's measured values.

A Study of Natural Frequency of Offshore Wind Turbine JACKET (해상 풍력 발전 JACKET의 고유 진동수에 관한 연구)

  • Lee, Jung-Tak;Son, Choong-Yul;Lee, Kang-Su;Won, Jong-Bum;Kim, Sang-Ho;Kim, Tae-Yong
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • pp.434-438
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    • 2006
  • The purpose of this paper is that investigates the Natural Frequency behavior characteristic of Wind Turbine Jacket Type Tower model, and calculated that the stress values of Thrust Load, Wave Load, Wind Load, Current Loda, Gravity Load, etc., environment evaluation analysis during static Operating Wind Turbine Jacket Type Tower model, carried out of Natural Frequency analysis of total load case to stress matrix, Frequency calculated that calculated Add Natural Frequency to stiffness matrix for determinant to stress results. The finite element analysis is performed with commercial F.E.M program (ANSYS) on the basis of the natural frequency and mode shape.

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A Study of Natural Frequency of Offshore Wind Turbine JACKET (해상 풍력 발전 JACKET의 고유진동수에 관한 연구)

  • Lee, Kang-Su;Lee, Jung-Tak;Son, Choong-Yul
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.17 no.2
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    • pp.130-135
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    • 2007
  • The purpose of this paper is that investigates the Natural Frequency behavior characteristic of wind turbine jacket type tower model, and calculated that the stress values of thrust load, wave load, wind load, current loda, gravity load, etc., environment evaluation analysis during static operating wind turbine jacket type tower model, carried out of natural frequency analysis of total load case to stress matrix, frequency calculated that calculated add natural frequency to stiffness matrix for determinant to stress results. The finite element analysis is performed with commercial F.E.M program (ANSYS) on the basis of the natural frequency and mode shape.