• Wind and Structures
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• 제16권4호
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• pp.373-391
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• 2013

This is the first of two companion papers that analyse ten years of on-site monitoring data for the Confederation Bridge to determine the validity of the original wind speeds and wind loads predicted in 1994 when the bridge was being designed. The check of the original design values is warranted because the design wind speed at the middle of Northumberland Strait was derived from data collected at shore-based weather stations, and the design wind loads were based on tests of section and full-aeroelastic models in the wind tunnel. This first paper uses wind, tilt, and acceleration monitoring data to determine the static and dynamic responses of the bridge, which are then used in the second paper to derive the static and dynamic wind loads. It is shown that the design ten-minute mean wind speed with a 100-year return period is 1.5% less than the 1994 design value, and that the bridge has been subjected to this design event once on November 7, 2001. The dynamic characteristics of the instrumented spans of the bridge including frequencies, mode shapes and damping are in good agreement with published values reported by others. The on-site monitoring data show bridge response to be that of turbulent buffeting which is consistent with the response predicted at the design stage.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 1997년도 봄 학술발표회 논문집
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• pp.177-184
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• 1997

The Component Mode Synthesis Method for the -vibration analysis can be applied to the large-scaled structures, which have difficulty in modeling because of their intricate shapes and boundary conditions and need much time in computational calculations. This paper uses the Component Mode Synthesis Method to analyze the free vibration for the steel box bridge having the large number of D.O.F as an example of the large structural system. By comparing the CMS method to the other method (FEM), this paper proves the accuracy of the solution in techniques and the efficiency in time.

• 대한토목학회논문집
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• 제28권4A호
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• pp.507-515
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• 2008

본 연구에서는 모드분해기법을 이용한 변형률신호로부터 변위응답추정 방법을 개발하였다. 일반적으로 교량의 안정성평가는 완공 후에 초점이 맞추어져 있다. 하지만 가설 중에도 풍하중과 지진하중과 같은 동적하중에 노출되어 있으며, 이런 동적하중에 대한 안정성을 검토하기 위해 교량의 안정성 평가에 있어 중요한 인자인 변위를 추정하는 것이 중요하다. 그러나 건설현장에서의 적절한 변위측정 방법의 부재로 인하여 대형구조물의 전체적인 변위를 측정할 수 없는 것이 현실이다. 본 연구에서는 간접적으로 변위를 추정하는 방법인 변형률로 변위를 추정하는 방법을 제시하였으며, 광섬유 브래그 격자 센서(fiber optic Bragg-grating sensor)를 사용하여 변형률을 계측하였다. 기존에도 FBG센서를 이용한 변위추정 방법이 있었으며 기존의 방법으로는 정적하중에 대한 변위추정은 가능하였으나 고차 모드의 변형률신호와 노이즈의 영향 때문에 동적하중에 대한 변위추정은 많은 오차가 발생하여 정확한 변위추정이 어려웠다. 이런 오차를 줄이는 방법으로 모드분해기법을 사용하였다. 모드분해기법은 변형률신호로부터 proper orthogonal decomposition(POD)을 이용하여 추정한 모드형상과 empirical mode decomposition(EMD)을 이용하여 모드 분해한 변형률신호로 모드별 변위응답을 추정하고, 구조물의 주요 모드에 대한 변위응답을 합하여 전체변위응답을 추정하는 방법이다. 제안한 모드분해기법을 검증하기 위해 실내모형실험을 수행하였다.

• International Journal of Aeronautical and Space Sciences
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• 제14권1호
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• pp.46-57
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• 2013

Flutter stability and buffeting response have been the topics of most concern in the design state of long-span suspension bridges. Among approaches towards the aerodynamic stability, the aerodynamic-based control method which uses control surfaces to generate forces counteracting the unstable excitations has shown to be promising. This study focused on the mechanically controlled system using flaps; two flaps were attached on both sides of a bridge deck and were driven by the motions of the bridge deck. When the flaps moved, the overall cross section of the bridge deck containing these flaps was continuously changing. As a consequence, the aerodynamic forces also changed. The efficiency of the control was studied through the numerical simulation and experimental investigations. The values of quasi-steady forces, together with the experimental aerodynamic force coefficients, were proposed in the simulation. The results showed that the passive flap control can, with appropriate motion of the flaps, solve the aerodynamic instability. The efficiency of the flap control on the full span of a simple suspension bridge was also carried out. The mode-by-mode technique was applied for the investigation. The results revealed that the efficiency of the flap control relates to the mode number, the installed location of the flap, and the flap length.

• Smart Structures and Systems
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• 제15권3호
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• pp.645-663
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• 2015

Recently, an indirect displacement estimation method using data fusion of acceleration and strain (i.e., acceleration-strain-based method) has been developed. Though the method showed good performance on beam-like structures, it has inherent limitation in applying to more general types of bridges that may have complex shapes, because it uses assumed analytical (sinusoidal) mode shapes to map the measured strain into displacement. This paper proposes an improved displacement estimation method that can be applied to more general types of bridges by building the mapping using the finite element model of the structure rather than using the assumed sinusoidal mode shapes. The performance of the proposed method is evaluated by numerical simulations on a deck arch bridge model and a three-span truss bridge model whose mode shapes are difficult to express as analytical functions. The displacements are estimated by acceleration-based method, strain-based method, acceleration-strain-based method, and the improved method. Then the results are compared with the exact displacement. An experimental validation is also carried out on a prestressed concrete girder bridge. The proposed method is found to provide the best estimate for dynamic displacements in the comparison, showing good agreement with the measurements as well.

• Structural Engineering and Mechanics
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• 제43권5호
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• pp.691-709
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• 2012

This paper provides a variety of viewpoints to illustrate the mechanism of the deck-stay interaction with the appropriate initial shapes of cable-stayed bridges. Based on the smooth and convergent bridge shapes obtained by the initial shape analysis, the one-element cable system (OECS) and multi-element cable system (MECS) models of the Kao Ping Hsi Bridge in Taiwan are developed to verify the applicability of the analytical model and numerical formulation from the field observations in the authors' previous work. For this purpose, the modal analysis of the two finite element models are conducted to calculate the natural frequency and normalized mode shape of the individual modes of the bridge. The modal coupling assessment is also performed to obtain the generalized mass ratios among the structural components for each mode of the bridge. The findings indicate that the coupled modes are attributed to the frequency loci veering and mode localization when the "pure" deck-tower frequency and the "pure" stay cable frequency approach one another, implying that the mode shapes of such coupled modes are simply different from those of the deck-tower system or stay cables alone. The distribution of the generalized mass ratios between the deck-tower system and stay cables are useful indices for quantitatively assessing the degree of coupling for each mode. These results are demonstrated to fully understand the mechanism of the deck-stay interaction with the appropriate initial shapes of cable-stayed bridges.

• 한국구조물진단유지관리공학회 논문집
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• 제23권5호
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• pp.48-59
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• 2019

최근 들어 장대교량의 건설에 현수교, 사장교 등과 같은 케이블이 주 요소인 교량 형식이 급증하고 있다. 이와 같은 구조물에서 케이블이 미치는 영향은 매우 크며, 구조해석을 위해서 케이블에 대한 연구 및 케이블의 모드 특성에 따른 구조계의 변화를 연구해 볼 필요가 있다. 특히, 케이블은 거더에 가해지는 하중효과를 주탑으로 전달하는 캠버조절과 직결되고 전체 구조에서 중요한 부재로서, 가설시 가해지는 초기 장력과 시간이 경과후 장력을 비교하므로서 교량의 노후상태와 이상유무를 파악하는 데 기여하고자 본 연구를 수행하였다. 따라서 본 연구에서는 충격해머를 통한 모드 해석으로부터 케이블의 질량과 케이블의 길이변화에 따른 모드의 특성을 파악할 수 있었고, 공용중에 있는 케이블에서는 위상각의 변화가 비례관계임을 확인하였다. 또한 저차모드에서 지배모드가 결정되는 특성을 MAC분석을 통하여 알 수 있었다.

• Structural Engineering and Mechanics
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• 제34권6호
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• pp.719-738
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• 2010

The aim of this paper concerns with the nonlinear analysis of cable-stayed bridges including the vibration effect of cable stays. Two models for the cable stay system are built up in the study. One is the OECS (one element cable system) model in which one single element per cable stay is used and the other is MECS (multi-elements cable system) model, where multi-elements per cable stay are used. A finite element computation procedure has been set up for the nonlinear analysis of such kind of structures. For shape finding of the cable-stayed bridge with MECS model, an efficient computation procedure is presented by using the two-loop iteration method (equilibrium iteration and shape iteration) with help of the catenary function method to discretize each single cable stay. After the convergent initial shape of the bridge is found, further analysis can then be performed. The structural behaviors of cable-stayed bridges influenced by the cable lateral motion will be examined here detailedly, such as the static deflection, the natural frequencies and modes, and the dynamic responses induced by seismic loading. The results show that the MECS model offers the real shape of cable stays in the initial shape, and all the natural frequencies and modes of the bridge including global modes and local modes. The global mode of the bridge consists of coupled girder, tower and cable stays motion and is a coupled mode, while the local mode exhibits only the motion of cable stays and is uncoupled with girder and tower. The OECS model can only offers global mode of tower and girder without any motion of cable stays, because each cable stay is represented by a single straight cable (or truss) element. In the nonlinear seismic analysis, only the MECS model can offer the lateral displacement response of cable stays and the axial force variation in cable stays. The responses of towers and girders of the bridge determined by both OECS- and MECS-models have no great difference.

• Computers and Concrete
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• 제14권6호
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• pp.745-765
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• 2014

In this paper, it is aimed to determine the finite element model updating effects on the structural behavior of long span concrete highway bridges. Birecik Highway Bridge located on the 81stkm of Sanliurfa-Gaziantep state highway over Firat River in Turkey is selected as a case study. The bridge consist of fourteen spans, each of span has a nearly 26m. The total bridge length is 380m and width of bridge is 10m. Firstly, the analytical dynamic characteristics such as natural frequencies and mode shapes are attained from finite element analyses using SAP2000 program. After, experimental dynamic characteristics are specified from field investigations using Operational Modal Analysis method. Enhanced Frequency Domain Decomposition method in the frequency domain is used to extract the dynamic characteristics such as natural frequencies, mode shapes and damping ratios. Analytically and experimentally identified dynamic characteristics are compared with each other and finite element model of the bridge is updated to reduce the differences by changing of some uncertain parameters such as section properties, damages, boundary conditions and material properties. At the end of the study, structural performance of the highway bridge is determined under dead load, live load, and dynamic loads before and after model updating to specify the updating effect. Displacements, internal forces and stresses are used as comparison parameters. From the study, it is seen that the ambient vibration measurements are enough to identify the most significant modes of long span highway bridges. Maximum differences between the natural frequencies are reduced averagely from %46.7 to %2.39 by model updating. A good harmony is found between mode shapes after finite element model updating. It is demonstrated that finite element model updating has an important effect on the structural performance of the arch type long span highway bridge. Maximum displacements, shear forces, bending moments and compressive stresses are reduced %28.6, %21.0, %19.22, and %33.3-20.0, respectively.

• 한국초전도저온공학회:학술대회논문집
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• 한국초전도저온공학회 2003년도 학술대회 논문집
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• pp.43-46
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• 2003

The dc reactor type high-Tc superconducting fault current limiter(SFCL) is composed of three parts, a power converter, a magnetic core reactor(MCR) and a dc reactor. This study concerned with the power converter of the DC reactor type high-Tc SFCL. The rectifying devices which power converter of 6.6kV/200A SFCL consists of have to endure high voltage. We propose the dual mode power converter to reduce the voltage which each rectifying device endures. In the single phase the experiment and simulation of dual mode power converter and the simulation of power converter with one bridge rectifier are performed. The current of each system with different power converter has a same tendency and the voltage which rectifying device of dual mode power converter endures is reduced in half by comparison with that of power converter with one bridge rectifier. We found dual mode power converter can be applied to SFCL.