Measuring the exact cable tension force is important to cable supported bridge under construction and on service. This study was planned to propose EM(electro-magnetic) sensor-based method for measuring the tension force of MS(multi-strand) cable in cable-stayed and extradosed bridge. The tension force in each strand is the same due to MS cable construction using Iso-tensioning system. Therefore, In this prosed method, EM sensor was installed directly at a strand and the measurement model was established for estimating the tension force of strand via EM sensor by experiments. The measurement model was derived from the relation of tension force and magnetic permeability. Also, the magnetic permeability is shown to be different according to the magnetization characteristic of 1860MPa and 2200MPa high-strength strand. The difference is increased as tension force increases. Additional experiment was conducted to verify the measurement model. As a result, the distribution of strand tension calculated upon the EM sensor is similar to those of tension measured by load cell. This proposed approach can be an effective tool for monitoring and measuring the cable force of MS cable.

Membrane structure is a system that is stabilized by maintaining a tensile state of the membrane material that originally cannot resist the bending or pressure. Also, it is a system that allows the whole membrane structure to bear external loads caused by wind or precipitation such as snow, rain and etc. Tension relaxation phenomenon can transpire to the tension that is introduced to the fabric over time, due to the innate characteristics of the membrane material. Thus, it is important to accurately understand the size of the membrane tension after the completion of the structures, for maintenance and management purposes. The authors have proposed the principle of theoretically and indirectly measuring the tension by vibrating the membrane surface with sound waves exposures against the surface, which is compartmentalized by a rectangular boundary, and by measuring the natural frequency of the membrane surface that selectively resonates. The authors of this paper measured the tension of preexisting membrane structure for its maintenance by using the developed portable measurement equipment. Through analyzing the measurement data, the authors review the points that should be improved and the technical method for the new maintenance system of membrane tension.

In this paper, we study the calculation for the damage area of the tension specimens using image processing techniques. This study was able to calculate the area of the damage region on the basis of original image. Generally, to extract the area in the original image, we have to use opening operation, close operation, the Hit-or-Miss operation and bottom hat filter, top hat filter, etc. In particular, to extract the area of the composite specimen discussed in this study, we have to use the combination of the operations and filters because it is non-isotropic material, or should develop a new algorithm based on it.

In this paper, we study the calculation for the fracture area of the tension specimens using digital image processing techniques. This study was able to calculate the area of the fracture region on the basis of improved image. To extract the area in the original image, we have to use opening operation, close operation, the Hit-or-Miss operation and Bottom hat filter, Top hat filter, etc. In particular, to extract the area of the composite specimen discussed in this study, we have to use the combination of the operations and filters because it is non-isotropic material, or should develop a new algorithm based on it.

A damage case of parallel strand cable anchorage was introduced, in which 7 strands were slipped from each wedge at the anchorage of the cable stayed bridge in service. Also, a cable damage detection scheme was proposed on the basis of tension force measurement and model updating method by least square estimation to minimize tension variation. The proposed scheme has been verified from analytical simulations and the actual damage case. The damaged cable leading to tension variation more than noise level of cable force measurement was successfully detected with 7~8 strands damage indication of 2% error in the actual strand slippage case.

Currently, the cable safety management of cable supported bridges is calculated by the ratio of the measured tension to the design tension. The measurement of the tension is performed by indirectly estimating the acceleration measured at the cable surface in terms of the tension. The method of converting the cable vibration response (acceleration) into the tension is disadvantageous in that the damage of the individual strand (or wire) in the cable is not clearly reflected in the tension because the measurement is not reliable and is managed only by the total tension. The purpose of this study is to improve the cable safety management system by evaluating how the damage of individual strand of MS type cable, which is mainly applied to cable-stayed bridges, affects the safety level managed by level of cable tension.

In this study, the method of measuring cable tension using the vision-based system was proposed, and a portable digital camcorder was used as a sensor for the measurement of the cable tension positioned at remote distances, considering the user convenience and the cost-efficiency. The vibration method (accelerometer, vision-based system) was used to measure the cable tensions, and the result was compared and analyzed.

Because of the characteristics of long-span bridges, the cable tension is considered a critical item in their maintenance. In particular, because the evaluation of the cable tension in a suspension bridge is essential for understanding the general status of the structural system, identifying the initial values of this force in the construction of a bridge and then accurately predicting and comparing its estimated values during traffic use are very important tasks for the maintenance of a suspension bridge. In this paper, to verify the algorithm for estimating the cable tension of hanger cables using the back analysis technique, an ambient vibration test was conducted at a suspension bridge.

This paper presents the measurement of earth anchor tension using fiber optic OFDR sensor. Fiber optic OFDR sensor was configurated with tunable laser source, APD with polarization beam splitter and high speed DAQ system. Strains of pressure plate and anchor head were measured and compared using strain gage and fiber optic OFDR sensor. Fiber optic OFDR sensor signal showed linear increase in both tension and compression direction as tensional force increase. This results shows the capability of fiber optic OFDR sensor for monitoring earth anchor tension.

케이블지지교량에서 케이블은 하중을 지지하는 주요 부재로, 케이블 장력은 교량의 건전성과 안전도 평가에 있어서 매우 중요한 변수이다. 케이블의 장력을 추정하는 기법으로, 로드셀 및 유압잭 등을 이용하여 케이블의 응력을 직접 측정하는 직접법과 케이블의 형상조건과 계측된 동특성을 활용하여 장력을 역산하는 진동법이 가장 많이 활용되고 있다. 최근 들어 케이블 내부 강재의 응력변화로 인하여 유발되는 자기장 변화를 탐지하는 EM 센서의 연구 및 활용이 증가하고 있다. 본 연구에서는 리프트오프 테스트, EM 센서 및 진동법(Vision-based System, Accelerometer)을 적용하여 장력을 측정하고 그 결과를 비교 분석하였다.

In this study, to verify the validity of the dynamic responses of cables with the image processing technique, the lift-off test and vibration method (Vision-based System) were used to measure the cable tensions, and the results were compared and analyzed.

When estimate Short Lenth External Tendon's tension by Vibration Measurement Method, We Consider Tendon's Boundary. This paper is a case about estimation of short lenth tendon's tension by using practical formula estimation and stiff string with clamped-clamped boundary conditions.

This study was performed to evaluate the cable tension of cable-stayed bridge by using vibration method and Lift-Off Test. As a result, cable tension by the vibration method and Lift-Off Test is most similar.

Membrane structure is a system that is stabilized by maintaining a tensile state of the membrane material that originally cannot resist the bending or pressure. Thus, it is important to accurately understand the size of the membrane tension after the completion of the structure, for maintenance and management purposes. The author of this paper measured the tension of preexisting membrane structure for its maintenance purpose by using the developed portable measurement equipment. Through analyzing the measurement data, the author check the points that should be improved and the technical method for the new maintenance system of membrane tension.

본 연구는 교량의 상시계측자료인 고유진동수 및 고유모드를 기준으로 계측기반모델을 구성하고, 구조해석을 수행하여 교량 공용상태에서 사장케이블 장력평가를 수행하였다. 케이블 설치 위치에 따라 하중유형별 케이블 장력이 다르다는 것을 알 수 있다. 고정하중과 활하중에 의한 케이블 계측장력은 케이블 설치위치에 따라 차이가 크지 않으나 설계하중을 적용한 해석결과보다 큰 값을 나타낸다. 계측기반모델에 대한 케이블장력분포는, 설계모델에 대한 장력보다 크지만, 계측장력과 유사한 분포를 나타낸다. 그러므로 장기거동을 고려하여 사장교 케이블설계는 계측기반모델의 해석결과를 반영할 필요가 있다. 이를 위하여 많은 계측자료를 이용한 장기거동 분석연구가 요구된다.

본 연구에서는 PC교량의 외부텐던의 장력을 평가하기 위하여 신속하고 경제적으로 적용할 수 있는 텐던의 진동을 이용한 고유진동수 측정 방법의 적용성을 검토하였다. 길이별로 다양한 여러 종류의 외부텐던 덕트 표면에 가속도 센서를 부착하고 고유진동수를 측정하였다.센서의 방향과 위치변경 등 여러 종류의 다양한 진동시험을 실시한 결과 고유진동수의 차이는 1% 이내로서 충분한 정확성을 확보하고 있음을 보였다. 측정된 고유진동수로부터 장력을 추정하기 위해서는 현의공식, 다중모드법, 저차 모드의 실용적 공식을 활용한 방법 (Zui et al., 1996), 양단고정 경계조건에 의한 휨강성을 고려한 현의공식 (Sagűѐs et al., 2006) 등의 장력 추정법을 적용하였고 그 결과값을 비교하였다. 휨강성을 반영하지 못한 현의 공식이나, 다중모드법은 길이가 짧은 텐던에 대해 장력을 과대평가하는 결과가 도출되어 텐던의 장력평가에 적절하지 않음을 알 수 있었다. 텐던의 장력 추정에 적절한 방법은 양단고정 경계조건과 휨강성을 고려한 단단한 현의 공식에 의한방법임을 알 수 있었으며, 이 방법을 실제 공용중인 PC 교량의 외부텐던에 적용한 결과 방향전환블록에 의한 마찰력으로 긴장단과 고정단에 텐던의 장력 차이가 발생한다는 것을 알 수 있었다.

The FBG sensor responses simultaneously to changes in thermal strain as well as elastic strain. Thus the total strain measured from a single FBG sensor shall be corrected to obtain the elastic strain by removing the temperature effect. This paper addresses how the temperature effect can be removed when the FBG sensor is encapsulated in a 7-wire steel strand. For this purpose, fundamental properties of the FBG sensor are identified through tests using a controlled temperature chamber. Then field measurements on a UHPC pi girder with the size of 11.0 m long, 5.0 m wide, and 0.6 m high have been conducted for about one year, and the prestressing force is estimated using the raw data from the FBG sensor and by applying temperature correction technique proposed in this study. Estimated results indicate that the proposed correction technique is executable for extracting the elastic strain from monitoring data using the FBG sensor in civil infrastructures.

In this study, natural frequency of the tendon is measured using acceleration sensors. Estimation of the tendon tension is performed by using many types of solutions such as string theory equation, stiff string with clamped-clamped boundary conditions. The results are compared with the measured value of load cell data. As a result, stiff string equation with clamped-clamped boundary conditions is more accurate than the other methods.