The hardenability of low-carbon boron steels with different molybdenum and chromium contents was investigated using dilatometry, microstructural observations and secondary ion mass spectroscopy (SIMS), and then discussed in terms of the segregation and precipitation behaviors of boron. The hardenability was quantitatively evaluated by a critical cooling rate obtained from the hardness distribution plotted as a function of cooling rate. It was found that the molybdenum addition was more effective than the chromium addition to increase the hardenability of boron steels, in contrast to boron-free steels. The addition of 0.2 wt.% molybdenum completely suppressed the formation of eutectoid ferrite, even at the slow cooling rate of 0.2˚C/s, while the addition of 0.5 wt.% chromium did this at cooling rates above 3˚C/s. The SIMS analysis results to observe the boron distribution at the austenite grain boundaries confirmed that the addition of 0.2 wt.% molybdenum effectively increased the hardenability of boron steels, as the boron atoms were significantly segregated to the austenite grain boundaries without the precipitation of borocarbide, thus retarding the austenite-to-ferrite transformation compared to the addition of 0.5 wt.% chromium. On the other hand, the synergistic effect of molybdenum and boron on the hardenability of boron steels could be explained from thermodynamic and kinetic perspectives.

케이블지지 교량 건설의 증가로 인하여 이러한 시설물의 안전 점검에 대한 관심도 점차 증가하고 있다. 케이블지지 교량에서는 주 부재인 케이블의 성능 평가가 필수적으로 이루어져야 함에 불구하고, 기존의 점검 방식으로는 다양한 제한적인 요인 때문에 적절한 점검이 이루어지지 못하고 있는 실정이다. 이러한 문제점을 보완하기 위해 케이블 점검 로봇 제작이 필요하고, 본 연구에서는 기존의 개발된 케이블 점검 로봇의 성능을 향상시켜서 로봇의 운용 효율성을 높이는데 주목적을 두었다. 성능 보완 요소로는 대 구경 케이블(>200mm)에도 적용할 수 있도록 로봇의 가용범위를 조절할 수 있도록 하였으며, 주행능력도 향상시켜 점검의 효율성을 향상시켰다. 케이블의 내부 손상을 점검하기 위해 전자기센서를 탑재하였고, 실내 실험을 통해 다양한 케이블 손상 유형에 따른 손상 검출 시험을 실시하였다. 추가로 현재 공용중인 교량에서 현장 성능평가를 실시하였다. 그 결과로 본 연구에서 개발된 케이블 점검 로봇은 주행속도에서는 ~0.2m/s로 기존의 점검 로봇에 비해 향상 된 주행 능력을 보였으며, 케이블 내부 손상 점검 실험에서는 케이블 손상 부분을 검출을 할 수 있었다. 마지막으로, 케이블 점검 로봇의 현장 검증 실험에서는 실내 실험과 같은 성능을 보이는 것을 확인하였다.

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.

This paper presents a methodology for assessing the old-age level of facilities. In order to evaluate the retirement level, a method of selecting the indicators related to the old age was presented and a method of assessing the old age level through the measures of the selected indicators is suggested to improve the reliability of evaluation results and to develop evaluation algorithm. In the future, it is expected that it will be possible to efficiently manage the old facilities through the convergence of the old- level evaluation method and IoT sensor, big data, and artificial intelligence.

This research is a basic study to develop mid - and long - term data base platform for maintenance of aging infrastructure (bridges, tunnels, retaining walls, road facilities, etc. In this study, the degradation and damage data and experiment data obtained from various monitoring technologies are secured in the medium to long term, and the degradation environment and damage model are developed based on the data acquired later. Predicted and standardized services to the management or the people of the nation. In this study, the database will be constructed at the planning, design and implementation stage, and mid - and long - term data will be used for precision safety diagnosis report and monitoring measurement report.

In case of cable supported bridges, the cable system is a very important element that transfers the load of the girder to the pylon or substructure is the most important feature. The safety management of these cable systems is very important because they are directly linked to the safety of the entire bridge. This paper presents the applicability of the acoustic emission (AE) method is one of the non-destructive evaluation methods, is evaluated for the detection and monitoring of bridge cable damage. In order to verify the performance of the cable inspection method using the AE sensor, experiments were conducted. As a result, it is considered that the acoustic emission technique will be able to detect corrosion breakage and signs of rupture of cables if sufficient database of AE signal with various environmental conditions is secured.

본 연구에서는 음향 방출 기법을 사용하여 강연선(7-wire strand)의 손상을 감지하기 위한 기초 실험을 수행하였다. 강연선은 주로 교량에 추가적인 인장력을 제공하기 위해 널리 사용되는 건설 자재이다. 프리스트레스 교량 또는 사장교가 대표적인 경우이다. 그러나 교량 노화가 급격히 진행되면서 강연선 부식 문제가 대두되고 있다. 이러한 이유로 케이블 점검을 위한 다양한 비파괴 방법이 연구되고 있고 현장 적용 이 시도되고 있다. 비파괴 방법 ??중 하나인 음향 방출 기법은 케이블 손상 및 파단을 감지하는 효과적인 기술로 알려져 있다. 본 연구에서는 음향 방출 기법의 교량에 대한 적용 가능성을 평가하기 위해 강연선의 손상에 따른 음향 방출 신호 특성을 인장 실험을 분석 하고, 현장 적용을 위한 최적 센서 주파수 타입을 선정하였다. 결과적으로, 음향 방출 기법을 활용하여 향후 교량 케이블의 부식 파단 및 파단 징후를 감지 할 수 있다 고 여겨진다.

In this study, the durability rating was evaluated to evaluate the safety of bridges considering the factors affecting the corrosion of cables in cable-stayed bridges and suspension bridges. Corrosion factors were considered for salinity, sulfur dioxide concentration and relative humidity. In addition, the durability level was calculated by applying the corrosion rates given in KS D ISO 9223 ~ 9226.

The corrosion is one of the main causes of cable damages. The use of dehumidification system can be an alternative for this issue. Therefore, the authors have been evaluated for efficiency of the cable dehumidification system for the main cables of a suspension bridge. This study was initiated to develop an efficient and economical management strategy to operate the cable dehumidification system for suspension bridges built in the coastal region of South Korea.

This study presents the investigation for relationship between local damage and structural performance of the 7-wire strand. This strand is often used additional reinforcement of bridges such as PSC (Prestressed Concrete) bridge and cable-stayed bridge. Stay cables are continuously damaged after completion and corrosion is the main cause of damage. Due to its structural characteristics, it is difficult to quantitatively evaluate the degradation cable damage. Therefore the relationship between local damages on strand and structural performance is experimentally and analytically evaluated in this study. The results can be used for the safety management of the cable supported bridges in the future.

This paper presents the assessment of 7-wire strand monitoring using acoustic emission technique for bridges. 7-wire strand is widely used construction materials to provide additional tensile force to bridges. PSC (PreStressed Concrete) bridge and cable-stayed bridge are representatives for such cases. However, as the bridge aging progresses recently, corrosion problems of strand are emerging. For this reason, various NDT (Non-Destructive Test) methods for cable inspection are being studied and applied to the field. One of the NDT methods, acoustic emission technique, is known as an effective technique to detect cable damage and breakage. In this study, to evaluate the applicability of acoustic emission technique to bridges, acoustic emission signals according to presence or absence of the strand were acquired and analyzed by tensile test. As a result, it is considered that the acoustic emission technique will be able to detect corrosion breakage and signs of rupture.

This paper aims to evaluate the safety of the cable supported bridges under the occurrence of damages on cable system. There are more than 50 cable supported bridges currently built in the Korean peninsula and efficient and systematic maintenance and management are in great demand. However, safety of the bridges cannot be under estimated and should be properly evaluated. In this paper, two bridges (one cable-stayed bridge and one suspension bridge) in South Korea were investigated their safety based on the damage scenario of cable system. FEM analysis for safety evaluation of the two bridges was conducted and the results were explained. The result could be used by operators and owners of bridges for the future maintenance and management.

For suspension bridges, the super-structure is supported by main cables and hangers which carry the dead and live loads to the pylons and anchorages. Due to the fact that the difficultly of repair and strengthening for damaged cables, it is very important to find an efficient way of maintenance methods for cables. The corrosion is one of main causes for cable damages. The use of dehumidification system can be an alternative for this issue. Therefore, the authors have been evaluated for efficiency of the cable dehumidification system for main cables of suspension bridge. This study was initiated to develop an efficient and economical management strategy to operate the cable dehumidification system for suspension bridges built in South Korea.

Numerical analysis was performed to predict for deflection of reinforced concrete (RC) beams in flexure strengthened with textile reinforced concrete (TRC) in this study. TRC is new reinforcing material to strengthen for deteriorated RC structures. TRC consists of fiber reinforced polymer (FRP) reinforcement of textile form and concrete using fine aggregate. This paper presents both results and process of nonlinear analysis method for experimental results published in 2015 by Jung et al. Nonlinear analysis method proposed by Cho et al. was used to predict the displacement at the cross-section of mid-span for RC beams in flexure strengthened with TRC. At the three states of the RC beams such as occurrence of initial flexural crack in tensile concrete, the yield of tensile rebar, and ultimate in accordance with debonding of TRM. Displacements of beams were calculated at the three state and load-displacement curves by predicting results were compared to the collected test results. As a result, nonlinear analysis method accurately predicted the deflection of RC beams strengthened with TRC.

Numerical analysis was performed to predict for deflection of reinforced concrete (RC) beams in flexure strengthened with textile reinforced concrete (TRC) in this study. TRC is new reinforcing material to strengthen for deteriorated RC structures. TRC consists of fiber reinforced polymer (FRP) reinforcement of textile form and concrete using fine aggregate. This paper presents both results and process of nonlinear analysis method for experimental results published in 2015 by Jung et al. Nonlinear analysis method proposed by Cho et al. was used to predict the displacement at the cross-section of mid-span for RC beams in flexure strengthened with TRC. At the three states of the RC beams such as occurrence of initial flexural crack in tensile concrete, the yield of tensile rebar, and ultimate in accordance with debonding of TRM. Displacements of beams were calculated at the three state and load-displacement curves by predicting results were compared to the collected test results. As a result, nonlinear analysis method accurately predicted the deflection of RC beams strengthened with TRC.

This study was conducted to develop a bended steel-hybrid GFRP (Glass Fiber Reinforced Polymer) bar. The steel-hybrid GFRP bar was to develop for replacing steel rebar for RC structures which were built in the corrosive environment. To be used for RC structures, a bended type of steel-hybrid GFRP bar is required. This study explains the results of current status of the project.

In this research, experiment and simulation plans for evaluating the performance of the cables used for cable-stayed type bridges is presented. 27 cables are prepared where each of the cables are introduced with either corrosion or/and fatigue damage. Then the acquired data is analyzed with the vibration characteristics to evaluate the performance of the cables subjected to the two damage types.

This study was conducted to build an emergency action plan (EAP) for cable-supported bridges in South Korea. First, accidents happened on Cable-supported bridges were investigated and categorized based on the types. Second, accident scenarios were built-up regarding the types. Two bridges were selected for planning the emergency action following the accident scenarios. The emergency action plan established in this study could be used for the management of cable-supported bridges in the future.