• 한국구조물진단유지관리공학회 논문집
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• 제15권2호
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• pp.153-160
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• 2011

최근들어 사장교나 현수교와 같은 케이블 형식의 장대교량이 많이 건설되거나 계획중에 있다. 하지만 도로교 설계기준에 제시된 풍하중 산정시 중요한 요인인 기본풍속 산정함에 있어서 1995년까지 측정된 풍속자료를 근거로 한 일반교량에 적합한 풍속을 명시하고 있어 장대교량에 적합한 풍속에 대한 재검토가 필요한 상황이다. 본 연구에서는 태풍의 빈도가 높고 대부분의 장대교량이 건설되고 있는 서남해안지역으로 구체화하였다. 풍하중기준과 같이 극치I형분포(Gumbel분포)에 의해 일반교량에 적용할 100년, 장대교량에 적용할 200년 재현기대풍속을 적률법과 최소자승법의 두 가지 방법으로 추정하고, 극한 상황인 해상에서 불어오는 풍속으로 보정하여 지상풍속보다 약 17%정도 큰 값을 추정하였다. RMS error 방법에 의해 재현기대풍속의 적합성을 평가한 결과 최소자승법이 서남해안지역의 경우 적합성이 우수하였다.

• Wind and Structures
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• 제32권4호
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• pp.293-308
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• 2021

For the past three decades a significant amount of research has been conducted on bridge flutter. Wind tunnel tests for a 2000 m class twin-box suspension bridge have revealed that a twin-box deck carrying 4 m tall 50% open area ratio wind screens at the deck edges achieved higher critical wind speeds for onset of flutter than a similar deck without wind screens. A result at odds with the well-known behavior for the mono-box deck. The wind tunnel tests also revealed that the critical flutter wind speed increased if the bridge deck assumed a nose-up twist relative to horizontal when exposed to high wind speeds - a phenomenon termed the "nose-up" effect. Static wind tunnel tests of this twin-box cross section revealed a positive moment coefficient at 0° angle of attack as well as a positive moment slope, ensuring that the elastically supported deck would always meet the mean wind flow at ever increasing mean angles of attack for increasing wind speeds. The aerodynamic action of the wind screens on the twin-box bridge girder is believed to create the observed nose-up aerodynamic moment at 0° angle of attack. The present paper reviews the findings of the wind tunnel tests with a view to gain physical insight into the "nose-up" effect and to establish a theoretical model based on numerical simulations allowing flutter predictions for the twin-box bridge girder.

• Wind and Structures
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• 제6권5호
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• pp.387-402
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• 2003

In the past decades, much effort has been made towards the study of single-mode-based vibration controls with dynamic energy absorbers such as single or multiple Tuned Mass Dampers(TMDs). With the increase of bridge span length and the tendency of the bridge cross-section being more slender and streamlined, multi-mode coupled vibrations as well as their controls have become very important for large bridges susceptible to strong winds. As a simple but effective device, the TMD system especially the semi-active one has become a promising option for such coupled vibration controls. However, despite various studies of optimal controls of single-mode-based vibrations with TMDs, research on the corresponding controls of the multi-mode coupled vibrations is very rare so far. For the development of a semi-active control strategy to suppress the multi-mode coupled vibrations, a comprehensive parametric analysis on the optimal variables of this control is substantial. In the present study, a multi-mode control strategy named "three-row" TMD system is discussed and the general numerical equations are developed at first. Then a parametric study on the optimal control variables for the "three-row" TMD system is conducted for a prototype Humen Suspension Bridge, through which some useful information and a better understanding of the optimal control variables to suppress the coupled vibrations are obtained. This information lays a foundation for the design of semi-active control.

• 한국안전학회지
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• 제22권6호
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• pp.55-62
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• 2007

The structural safety of long span bridges such as suspension bridges is smaller under the construction stage than in the completion. But the importance of construction sequences has been neglected in most of safety check programs. On this study is developed the structural analysis method of suspension bridges considering construction sequences and structural analyses are performed by step by step during construction. This can be used to determine the safest erection method. The results shows that the more critical structural behavior appears under construction than after completion.

• Wind and Structures
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• 제20권2호
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• pp.349-361
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• 2015

Higher-mode vertical vortex-induced vibrations (VIV) have been observed on several steel box-girder suspension bridges where different vertical modes are selectively excited in turn with wind velocity in accordance with the Strouhal law. Understanding the relationship of VIV amplitudes for different modes of vibration is very important for wind-resistant design of long-span box-girder suspension bridges. In this study, the basic rectangular cross-section with side ratio of B/D=6 is used to investigate the effect of different modes on VIV amplitudes by section model tests. The section model is flexibly mounted in wind tunnel with a variety of spring constants for simulating different modes of vibration and the non-dimensional vertical amplitudes are determined as a function of reduced velocity U/fD. Two 'lock-in' ranges are observed at the same onset reduced velocities of approximately 4.8 and 9.4 for all cases. The second 'lock-in' range, which is induced by the conventional vortex shedding, consistently gives larger responses than the first one and the Sc-normalized maximum non-dimensional responses are almost the same for different spring constants. The first 'lock-in' range where the vibration frequency is approximately two times the vortex shedding frequency is probably a result of super-harmonic resonance or the "frequency demultiplication". The main conclusion drawn from the section model study, central to the higher-mode VIV of suspension bridges, is that the VIV amplitude for different modes is the same provided that the Sc number for these modes is identical.

• Smart Structures and Systems
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• 제12권3_4호
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• pp.363-379
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• 2013

Dynamic displacement of structures is an important index for in-service structural condition and behavior assessment, but accurate measurement of structural displacement for large-scale civil structures such as long-span bridges still remains as a challenging task. In this paper, a vision-based dynamic displacement measurement system with the use of digital image processing technology is developed, which is featured by its distinctive characteristics in non-contact, long-distance, and high-precision structural displacement measurement. The hardware of this system is mainly composed of a high-resolution industrial CCD (charge-coupled-device) digital camera and an extended-range zoom lens. Through continuously tracing and identifying a target on the structure, the structural displacement is derived through cross-correlation analysis between the predefined pattern and the captured digital images with the aid of a pattern matching algorithm. To validate the developed system, MTS tests of sinusoidal motions under different vibration frequencies and amplitudes and shaking table tests with different excitations (the El-Centro earthquake wave and a sinusoidal motion) are carried out. Additionally, in-situ verification experiments are performed to measure the mid-span vertical displacement of the suspension Tsing Ma Bridge in the operational condition and the cable-stayed Stonecutters Bridge during loading tests. The obtained results show that the developed system exhibits an excellent capability in real-time measurement of structural displacement and can serve as a good complement to the traditional sensors.

• 한국구조물진단유지관리공학회 논문집
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• 제9권4호
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• pp.127-134
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• 2005

최근 컴퓨터 기술의 발달로 장대교량의 설계 및 시공이 증가하고 있다. 특히 케이블 요소를 갖는 사장교와 현수교는 장대교량을 대표한다 할 수 있을 것이다. 따라서 본 논문에서는 사장교로 시공중인 제2진도대교에 대하여 시공단계별로 전체케이블에 대한 장력을 측정하여 시공오차 등에 따른 장력보정값을 현장에서 즉시 제시하여 시공정밀도를 향상하고자 하였다. 이에 적용된 장력측정방법은 간접법인 가속도센서를 이용한 진동법을 적용하였다. 직접법에 비해 비교적 간편한 간접인 진동법을 통하여 보다 쉽게 장력을 추정할 수 있었으며, 시공의 정밀도를 향상시키기 위하여 전체 케이블을 4가지 시공단계별로 장력변화량을 모니터링하여 케이블 가설시 시공오차에 대한 장력보정값을 현장에서 제시하였다. 또한, 최종장력값을 설계값과 비교한 결과 간접법을 이용한 장력값과 유사한 것을 알 수 있었다. 그리고 온도 변화에 따른 케이블의 장력변화를 추후 유지관리 계측시 관리한계치 설정에 참고자료로 활용할 수 있도록 장력변화를 파악하였다.

• Smart Structures and Systems
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• 제29권5호
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• pp.715-728
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• 2022

Recently, numbers of long span pedestrian suspension bridges have been constructed worldwide. While recent tragedies regarding pedestrian suspension bridges have shown how these bridges can wreak havoc on the society, there are no specific guidelines for construction standards nor safety inspections yet. Therefore, a structural health monitoring system that could help ensure the safety of pedestrian suspension bridges are needed. System identification is one of the popular applications for structural health monitoring method, which estimates the dynamic system. Most of the system identification methods for bridges are currently adapting output-only system identification method, which assumes the dynamic load to be a white noise due to the difficulty of measuring the dynamic load. In the case of pedestrian suspension bridges, the pedestrian load is within specific frequency range, resulting in large errors when using the output-only system identification method. Therefore, this study aims to develop a system identification method for pedestrian suspension bridges considering both input and output of the dynamic system. This study estimates the location and the magnitude of the pedestrian load, as well as the dynamic response of the pedestrian bridges by utilizing artificial intelligence and computer vision techniques. A simulation-based validation test was conducted to verify the performance of the proposed system. The proposed method is expected to improve the accuracy and the efficiency of the current inspection and monitoring systems for pedestrian suspension bridges.

• Wind and Structures
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• 제23권1호
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• pp.19-43
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• 2016

In the present study, a new methodology is presented to study the ride comfort and bridge responses of a long-span bridge-traffic-wind coupled vibration system considering stochastic characteristics of traffic flow and bridge surface progressive deterioration. A three-dimensional vehicle model with 24 degrees-of-freedoms (DOFs) including a three-dimensional non-linear suspension seat model and the longitudinal vibration of the vehicle is firstly presented to study the ride comfort. An improved cellular automaton (CA) model considering the influence of the next-nearest neighbor vehicles and a progressive deterioration model for bridge surface roughness are firstly introduced. Based on the equivalent dynamic vehicle model approach, the bridge-traffic-wind coupled equations are established by combining the equations of motion of both the bridge and vehicles in traffic using the displacement relationship and interaction force relationship at the patch contact. The numerical simulations show that the proposed method can simulate rationally the ride comfort and bridge responses of the bridge-traffic-wind coupled system; and the vertical, lateral, and longitudinal vibrations of the driver seat model can affect significantly the driver's comfort, as expected.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2003년도 가을 학술발표회 논문집
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• pp.235-242
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• 2003

This paper deals with numerical analysis of static and dynamic wind effects on civil engineering structures. Aeroelastic analysis becomes a prime criterion to be confirmed during the structural design because the long-span suspension bridges are prone to the aerodynamic instabilities caused by wind. If the wind velocity exceeds the critical velocity that the bridge can withstand, then the bridge fails due to the phenomenon of flutter. The aeroelastic simulation is carried out using both Computational Fluid Dynamic(CFD) and Computational Structural Dynamic(SCD) schemes.