• Title, Summary, Keyword: tower stiffness

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Experimental Investigation on the Energy Dissipation of Friction-type Reinforcing Members Installed in a Transmission Tower for Wind Response Reduction (송전철탑의 풍응답 감소를 위한 마찰형 보강기구의 에너지 소산특성 분석 실험)

  • Park, Ji-Hun;Moon, Byoung-Wook;Lee, Sung-Kyung;Min, Kyung-Won
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.17 no.7
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    • pp.649-661
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    • 2007
  • Friction-type reinforcing members(FRM) to enhance the resistance to wind loads of a transmission tower through both stiffness strengthening and damping increase are energy dissipation devices that utilize bending deflection of a tower leg. In this paper, the hysteretic behavior of the transmission tower structure with FRMs was experimentally investigated through cyclic loading tests on a half scale substructure model. Firstly, the variation of friction forces and durability of the FRM depending on the type of friction-inducing materials used in the FRM were examined by performing the cyclic loading tests on the FRM. Secondly, cyclic loading tests of a half-scale two-dimensional substructure model of a transmission tower with FRMs were conducted. Test results show that the FRM, of which desired maximum friction force is easily regulated by adjusting the amplitude of the torque applied to the bolts, have stable hysteretic behaviors and it is found that there exists the optimum torque depending on a design load by investigating the amount of energy dissipation of the FRMs according to the increase of torque.

Monitoring of tall slender structures by GPS measurements

  • Chmielewski, Tadeusz;Breuer, Peter;Gorski, Piotr;Konopka, Eduard
    • Wind and Structures
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    • v.12 no.5
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    • pp.401-412
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    • 2009
  • A method is applied for the estimation of structural damage of tall slender structures using natural frequency and displacements measurements by GPS. The relationship between the variation in the global stiffness matrix (or in the stiffness of each finite element) and the change in the natural frequencies of the structure is given. In engineering practice the number of frequencies which can be derived by GPS measurement of long-period structures will be equal to one, two or three first natural frequencies. This allows us in initial studies to detect damage with frequency changes based on forward methods in which the measured frequencies are compared with the predicted analytical data. This idea, of health monitoring from possible changes to natural frequencies, or from a statement of excessive displacements is applied to the Stuttgart TV Tower.

Vibration-Based Damage Detection Method for Tower Structure (타워 구조물의 진동기반 결함탐지기법)

  • Lee, Jong-Won;Kim, Sang-Ryul;Kim, Bong-Ki
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • pp.320-324
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    • 2013
  • A crack identification method using an equivalent bending stiffness for cracked beam and committee of neural networks is presented. The equivalent bending stiffness is constructed based on an energy method for a straight thin-walled pipe, which has a through-the-thickness crack, subjected to bending. Several numerical analysis for a steel cantilever pipe using the equivalent bending stiffness are carried out to extract the natural frequencies and mode shapes of the cracked beam. The extracted modal properties are used in constructing a training patterns of a neural network. The input to the neural network consists of the modal properties and the output is composed of the crack location and size. Multiple neural networks are constructed and each individual network is trained independently with different initial synaptic weights. Then, the estimated crack locations and sizes from different neural networks are averaged. Experimental crack detection is carried out for 3 damage cases using the proposed method, and the identified crack locations and sizes agree reasonably well with the exact values.

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Nonlinear Dynamic Behaviors of Offshore Guyed Towers (해양구조물 Guyed Tower의 비선형 동적거동)

  • Park, Woo-Sun;Pyen, Chong-Kun;Park, Young-Suk
    • Journal of Korean Society of Coastal and Ocean Engineers
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    • v.3 no.3
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    • pp.126-136
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    • 1991
  • This study is concerned with the nonlinear dynamic behaviors of guyed towers for wave loadings. In order to analyze the nonlinear responses of guyed towers efficiently, the main tower is modeled as an equivalent stick, the guyline system is idealized as a spring with nonlinear stiffness in the horizontal direction. and the pile foundation system is represented as a linear spring in the rotational direction. The wave forces on the main tower are evaluated by using Morison's equation. In order to consider adequately the nonlinearities of the guying system and drag forces due to fluid viscosity. the analyses are performed in the time domain. The mode superposition method is adopted for solving the nonlinear equation of motion efficiently. which is based on the Newmark integration scheme. Numerical analyses are carried out to investigate the sensitivity of two major design parameters for guyed towers. i.e., the clump weight conditions and the base renditions of the tower.

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Update the finite element model of Canton Tower based on direct matrix updating with incomplete modal data

  • Lei, Y.;Wang, H.F.;Shen, W.A.
    • Smart Structures and Systems
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    • v.10 no.4_5
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    • pp.471-483
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    • 2012
  • In this paper, the structural health monitoring (SHM) benchmark problem of the Canton tower is studied. Based on the field monitoring data from the 20 accelerometers deployed on the tower, some modal frequencies and mode shapes at measured degrees of freedom of the tower are identified. Then, these identified incomplete modal data are used to update the reduced finite element (FE) model of the tower by a novel algorithm. The proposed algorithm avoids the problem of subjective selection of updated parameters and directly updates model stiffness matrix without model reduction or modal expansion approach. Only the eigenvalues and eigenvectors of the normal finite element models corresponding to the measured modes are needed in the computation procedures. The updated model not only possesses the measured modal frequencies and mode shapes but also preserves the modal frequencies and modes shapes in their normal values for the unobserved modes. Updating results including the natural frequencies and mode shapes are compared with the experimental ones to evaluate the proposed algorithm. Also, dynamic responses estimated from the updated FE model using remote senor locations are compared with the measurement ones to validate the convergence of the updated model.

Equivalent Suspension Bridge Model for Tower Design of Multi-span Suspension Bridges (다경간 현수교 주탑 설계를 위한 등가 현수교 모델)

  • Choi, Dong-Ho;Na, Ho-Sung;Yi, Ji-Yop;Gwon, Sun-Gil
    • Journal of Korean Society of Steel Construction
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    • v.23 no.6
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    • pp.669-677
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    • 2011
  • The multi-span suspension bridge generally has more than three towers and two main spans. To economically and effectively design a multi-span suspension bridge, the proper stiffness ratio of the center tower to the side tower must be determined. This study was conducted to propose a method of figuring out briefly the structural behavior of the towers in a multi-span suspension bridge. In the equivalent suspension bridge model, the main cable of the multi-span suspension bridge is idealized as an equivalent cable spring, and the external loads of horizontal and vertical forces that were calculated using the tensile forces of the main cable were applied on top of the towers. The equilibrium equations of the equivalent multi-span suspension bridge model were derived and the equations were solved via nonlinear analysis. To verify the proposed method, a sample four-span suspension bridge with a main span length of 3,000 m was analyzed using thefinite element method. The displacements and moment reactions of each tower in the proposed method were compared with the FEM analysis results. Consequently, the results of the analysis of the equivalent suspension bridge model tended to be consistent with the results of the FEM analysis.

The Behavior and Resistance of Connected-pile Foundations for Transmission Tower from In-situ Lateral Load Tests (송전용 철탑기초의 현장수평재하시험을 통한 연결형 말뚝기초의 거동 및 지지력특성)

  • Kyung, Doo-Hyun;Lee, Jun-Hwan;Paik, Kyu-Ho;Kim, Dae-Hong;Kim, Dae-Hak
    • Journal of the Korean Geotechnical Society
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    • v.28 no.2
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    • pp.57-70
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    • 2012
  • For soft ground, a pile foundation is typically used as a substructure of transmission tower. However, differential settlement between the foundations can cause structural damage of transmission tower. The connected-pile foundation is a type of group foundation consisting of four foundations connected with beams, and it was suggested in USA and Japan. In this study, a series of 1/8 scale model pile tests were performed to investigate the effect of load direction and stiffness of connecting beam on the responses of connected-pile foundation. As a result, the load capacities of the connected-pile foundation were larger than those of the conventional group pile foundation. For example, under the given test conditions in this paper, the resistibility against differential settlement was improved significantly for connected-pile foundation and its efficiency was maximized when the stiffness of connecting beams is about 25% of the mat foundation.

Vibration-based damage detection in wind turbine towers using artificial neural networks

  • Nguyen, Cong-Uy;Huynh, Thanh-Canh;Kim, Jeong-Tae
    • Structural Monitoring and Maintenance
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    • v.5 no.4
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    • pp.507-519
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    • 2018
  • In this paper, damage assessment in wind-turbine towers using vibration-based artificial neural networks (ANNs) is numerically investigated. At first, a vibration-based ANNs algorithm is designed for damage detection in a wind turbine tower. The ANNs architecture consists of an input, an output, and hidden layers. Modal parameters of the wind turbine tower such as mode shapes and frequencies are utilized as the input and the output layer composes of element stiffness indices. Next, the finite element model of a real wind-turbine tower is established as the test structure. The natural frequencies and mode shapes of the test structure are computed under various damage cases of single and multiple damages to generate training patterns. Finally, the ANNs are trained using the generated training patterns and employed to detect damaged elements and severities in the test structure.

Numerical evaluation for vibration-based damage detection in wind turbine tower structure

  • Nguyen, Tuan-Cuong;Huynh, Thanh-Canh;Kim, Jeong-Tae
    • Wind and Structures
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    • v.21 no.6
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    • pp.657-675
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    • 2015
  • In this study, the feasibility of vibration-based damage detection methods for the wind turbine tower (WTT) structure is evaluated. First, a frequency-based damage detection (FBDD) is outlined. A damage-localization algorithm is visited to locate damage from changes in natural frequencies. Second, a mode-shape-based damage detection (MBDD) method is outlined. A damage index algorithm is utilized to localize damage from estimating changes in modal strain energies. Third, a finite element (FE) model based on a real WTT is established by using commercial software, Midas FEA. Several damage scenarios are numerically simulated in the FE model of the WTT. Finally, both FBDD and MBDD methods are employed to identify the damage scenarios simulated in the WTT. Damage regions are chosen close to the bolt connection of WTT segments; from there, the stiffness of damage elements are reduced.

The Measurement Test of Stiffness and Natural Frequencies for Bearingless Rotor System of Helicopter (헬리콥터용 무베어링 로터 시스템의 강성 및 고유 진동수 측정)

  • Yun, Chul Yong;Kim, Deog-kwan
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.25 no.12
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    • pp.881-887
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    • 2015
  • The stiffness and natural frequencies for blades, flexbeam, and torque tube of bearingless rotor system are measured to determine the material input properties such as mass distributions and stiffness distribution for the rotor dynamics and load analysis. The flap stiffness, lag stiffness, and torsional stiffness are calculated by measuring section strain or twist angle, gages position, and applied loads through bending and twist tests. The modal tests are undertaken to find out the natural frequencies for flap, lag, torsion modes in non-rotating conditions. The stiffness values and mass properties are tuned and updated to match prediction frequencies to the measured frequencies. The rotorcraft comprehensive code(CAMRAD II) is used to analyze the natural frequencies of the specimens. The analysis results with the updated material properties agree well with the measured frequencies. The updated properties will be used to analyze the rotor stability, dynamic characteristics and loads for the rotor rotation test in a whirl tower.