This study investigates the corrosion characteristics of prestressing strands and reinforcing bars using mold specimens. These components such as prestressing strands and reinforcing bars are critical for the durability and structural safety of prestressed and reinforced concrete structures, as they bear loads in tensile regions. Prestressing strands, which are constantly under high tensile stress, are particularly susceptible to corrosion. The presence of poorly compacted grout or the infiltration of de-icing agents from an upper girder can accelerate corrosion in these strands, potentially leading to their failure and significantly compromising structural safety. The extent of corrosion in the prestressing strands and reinforcing bars was quantitatively evaluated based on the charge transmitted through a specified circuit over a specified period, following Faraday's law. The methodology proposed in this study offers an accurate assessment of the corrosion characteristics observed in the prestressing strands and reinforcing bars. This study provided predictions of corrosion amount and depth for both types of reinforcements, depending on variations in the accelerated corrosion experiments. These findings are expected to aid in modeling corrosion in full-sized specimens, setting environmental parameters, and forecasting corrosion rates relative to the service life of the structures

Mountain railways are constructed on terrains with steep gradients and operate under unique conditions as they climb slopes at low speeds using rack rails. Recently, mountain railway systems in the form of embedded rail systems (ERSs) have been developed to minimize environmental damage caused by the construction of new roads. However, the use of ERS in mountain railway tracks is still limited, and research on their safety and behavior is lacking. Therefore, this study was conducted to evaluate the safety profile and behavioral responses of mountain-ERS under a steep gradient condition of 180‰. The effects of using high-strength concrete materials for precast concrete panels were investigated in this study, and the safety profile and behavioral response of mountain-ERS based on changes in the gradient and after adjusting the thickness of the subgrade of mountain-ERS was assessed. Under load conditions, the maximum tensile stress in the concrete elements did not exceed the tensile strength of the concrete. In the structural behavioral analysis, the patterns of stress variation were analyzed by applying stress to the concrete elements. The safety assessment and behavioral analysis results obtained in this study are considered valuable foundational research data for analytical studies on mountain-ERSs.

This paper presents a nonlinear analysis procedure for evaluating the seismic performance of reinforced concrete (RC) bridge columns with lap splices using a novel plastic hinge element considering shear deformation. To accurately assess the inelastic behavior of RC bridge columns, reliable three-dimensional (3D) constitutive models are required. However, developing a 3D nonlinear material model is difficult and computationally intensive. In this study, to address these issues, a new plastic hinge element considering shear deformation for RC bridge columns is developed. The new plastic hinge element is based on the Timoshenko beam theory and utilizes two-noded zero length element with six degrees of freedom. The finite element model was implemented in a computer program named Reinforced Concrete Analysis in Higher Evaluation System Technology (RCAHEST) developed by the authors. The developed plastic hinge element for seismic performance assessment of RC bridge columns with lap splices was validated through comparison of the numerical and experimental results.

Currently, a mountain railway system using existing mountain roads is being developed in Korea. Considering the alignment of domestic mountain roads with many sharp curves, the maximum radius of curvature of the mountain railway is about 10 m. Therefore, the 50 N rail applied to the track structure of the mountain railway must be manufactured with a radius of curvature of 10 m at the factory. In this study, the material properties of 50 N Rails were analyzed through indoor tests and the behavioral characteristics according to bending processing (R = 10 m) were analyzed to evaluate their applicability to sharp curves on mountain railways.

The purpose of this study is to assess the seismic performance of reinforced concrete wall piers for out-of-plane seismic loads, and to provide a method for developing a new evaluation procedure. A non-linear finite element analysis program, RCAHEST (Reinforced Concrete Analysis in Higher Evaluation System Technology), is used to carry out all the seismic analyses of reinforced concrete wall piers. The wall piers were modelled using a combination of reinforced concrete shell elements and newly developed interface elements with six degrees of freedom. The reinforced concrete shell interface element is used to account for local discontinuous deformations at the boundary plane caused by abrupt changes in stiffness where members with different thickness are connected. Novel damage indices were modified to provide a means of quantifying numerically the seismic performance level in wall piers sustained under earthquake loading. Six reinforced concrete wall pier specimens were loaded in the weak direction under cyclic loading. The failure mode of the wall piers was either compression failure of the concrete or fracture of the longitudinal reinforcing bars due to low-cycle fatigue. The proposed numerical method for the seismic performance assessment of reinforced concrete wall piers for out-of-plane seismic loads is verified by comparison with the experimental and analytical results.

콘크리트 도상은 총 생애주기와 비용측면에서 장점과 보편성에도 불구하고 열차 운행 시 차륜과 레일간 마찰소음을 반사하여 자갈도상에 비하여 주행소음이 크다. 소음저감방안으로 도상용 흡음블럭을 개발한 업체가 다수 있으나, 운영기관에서 시공성과 유지보수 측면에서 도상용 흡음블럭의 경량화 연구가 필요하다는 의견이 대두되었다. 따라서 본 연구에서는 경량화의 방법으로 흡음블럭의 재료 특성을 파악하고 배합조건을 달리하여 압축강도와 흡음률을 측정하여 비교분석하였다. 연구결과 내구성능과 흡음성능이 KRS 기준에 만족하는 경량화가 가능한 천연경량골재와 인공경량골재의 비율이 약 3:1로 산출되었다.

In sections with poor ground conditions, it is difficult to apply the commonly used NATM tunnel method; thus, applications of the non-open cut tunneling method are increasing. This section is a tunnel crossing area under the national road in which the Panel method is to be applied to the section where a deeply buried layer and a loose weathered soil layer are distributed. Therefore, the stability of the upper road, the amount of settlement, and the stability of the tunnel structure were reviewed for each construction stage by using MIDAS GTX. Through the installation of measuring instruments in the tunnel area, the results of the numerical analysis were reviewed and the stability during and after construction was evaluated. Therefore, it is likely that the Panel method is an appropriate countermeasure in the downtown area and in areas with soft ground sections where the application of the general tunnel excavation method is difficult.

The roadbed reinforcement method using cuboidal fiber reinforcement is an eco-friendly method that compensates for the shortcomings of various existing roadbed reinforcement technologies. A rectangular parallelepiped fiber reinforcement was installed in section oo of the existing line where fine-grained gravel, floating sleepers, and sleeper cracks occurred. The basic physical property test of the upper subgrade was conducted, and the vertical displacement and acceleration of rails and sleepers were compared and analyzed according to the train operation of the reinforced and non-reinforced sections. A comparative analysis of the vertical displacement and acceleration according to train operation after laying the rectangular parallelepiped fiber reinforcement demonstrated that the vertical displacement and acceleration were reduced by up to 84% and 80%, respectively. The dynamic movement of the rail was reduced owing to the reinforcing effect of the rectangular parallelepiped reinforcement, thereby improving the roadbed bearing capacity and stability.

In this study, a full-scale model of a railway track structure using an asphalt concrete trackbed with concrete slab panel (ACTSP) is developed. Slab panels are very important to develop asphalt concrete (AC) track system for minimizing the roadbed pressure due to the trainload and reducing the plastic deformation of the AC. The purpose of this study is to analyze the performance of the subgrade and the AC trackbed under different AC layer concepts. Static and dynamic loads were applied to the whole track system by using the Railway Loading System (RLS). Based on the data acquisition and instrument systems, the displacement of the rail/sleeper, the strain at the bottom of the asphalt concrete, and the pressure characteristics of each subgrade was measured. The pressure distribution efficiency along the track system was also investigated. Based on the full-scale test results, the application of asphalt concrete trackbed is very promising since this technology will noticeably mitigate the impact of pressure on the track system from the trainload. The effectiveness is more prominent in railway structures having an AC trackbed thickness of around 35 cm. In this condition, the dynamic train load results reveal that plastic deformation and tensile strain of rail and panel can substantially be reduced up to 20 and 50%, respectively, compared to the condition of 20 cm trackbed thickness. The results also indicate that the pressure distribution along the panel is improved by using a thicker AC layer roadbed concept. Overall, the findings in the research suggest that asphalt concrete trackbed with slab panel is a novel technology that will reinforce the durability of track components and prolong the service life of railway track structure. (C) 2021 Elsevier Ltd. All rights reserved.

이 연구는 소성힌지모델과 파이버 보-기둥요소를 이용하여 겹침이음부를 갖는 철근콘크리트 교각의 내진성능평가를 위한 해석적 연구이다. 보-기둥요소 파이버의 이력거동은 콘크리트와 철근 각각의 1축 구성관계를 따른다. 겹침이음부의 비탄성변형에 의해 소성힌지 영역에서 소성 회전이 발생한다. 소성힌지는 주로 겹침이음부 같은 비선형 특성에 영향을 받는다. 특히, 교각의 끝단에서 주로 발생하게 되는 균열에 의한 겹침이음 철근의 부착슬립 효과는 철근응력과 부착슬립과의 관계를 정의함으로써 고려하였다. 이 연구에서 제안한 해석기법을 신뢰성 있는 연구자의 실험결과 및 해석결과와 비교하여 그 타당성을 입증하였다.

The roadbed reinforcement method, in which a rectangular parallelepiped fiber reinforcement sack is used, is ecofriendly and overcomes the disadvantages of the conventional roadbed reinforcement method. Through large-scale tests, the effects of improving the bearing capacity, stability, and constructability according to the train speed were confirmed. Physical property investigations of the field test were conducted to analyze the conditions of the roadbed. The settlement degree of the site, where the reinforced section and unreinforced section were placed, was measured and analyzed. A rectangular parallelepiped fiber reinforcement sack was laid. Based on the physical properties determined during the field tests, this section was found to be soft ground composed of silt sand with a low bearing capacity. In addition, through comparison and analysis of the degree of settlement caused by the laying of rectangular parallelepiped fiber reinforcement sack, the dynamic vertical displacement of rails and sleepers decreased by at least 84%. It was shown that the track stability improved when the rectangular-parallelepiped fiber reinforcement sack was laid, which reduced the dynamic behavior along and improved the track support.

열차의 증속으로 콘크리트 슬래브궤도구간에서 높은 소음이 발생하고 있고, 이에 대한 대책이 필요한 실정이다. 따라서 본 논문에서는 콘크리트 슬래브 도상용 흡음재료 및 구조시스템을 설계하고 시제품을 개발, 실내적용시험후 콘크리트 슬래브 도상구간 현장에 부설하였다. 환경소음기준인 ISO와 EN의 시험방법을 따라 열차의 단계별 증속으로 인한 여러 속도대역에서 흡음블럭 설치구간과 미설치구간으로 구분하여 철도연변에서의 소음저감량을 측정하였다. 개발한 흡음블럭을 현장에 부설한후 열차의 증속시험에 따른 다양한 속도대역에서 최대 5.9dB, 350km/h 이상의 속도대역에서는 3dB이상의 소음이 저감되었으며 약 10개월간 현장 부설후 슬래브 도상용 흡음블럭이 열차 운행시 발생하는 소음저감 비교분석을 수행하였다.

철도노반 하부에 연약지반이 위치할 경우 치환 및 그라우팅 공법이 있으나 철도역사 구조물, 본선 박스구조물의 저성토구간등에 공기단축 및 노반보강에 적합한 시공법 연구가 필요하며, 현재 기존 구조물 하부 보강공법은 대형장비 사용으로 인해 진동과 소음으로 민원이 발생하기 쉽다. 이에 본 논문에서는 철도구조물 하부에 직육면체 섬유보강재를 이용한 보강공법을 제안하고, 재료물성시험과 실물가속실험을 통하여 성능평가를 수행하였다. 제안된 직육면체 섬유보강재 공법은 내부에 격벽과 트러스밴드를 추가하여, 철도 하중을 균등하게 하고 지반의 구속효과와 지지강성을 확보하는 방법이다. 섬유보강재의 물성시험은 재료의 인장강도, 수직투수계수, 인장신도를 시험하였다. 또한 실물가속시험항목은 하중재하횟수별 누적침하량, 열차하중 재하로 인한 토압분포, 노반의 진동가속도이며, 비교검토를 통한 성능 평가를 통하여 보강단면과 비보강단면에 대한 시험을 수행하였다. 실물가속시험 결과, 노반보강방법이 침하제어와 진동가속도 및 토압저감으로 구조적 안정성을 향상시키는 것으로 나타났다.

In recent years, leakages in aged pipelines for water and sewage in urban areas have frequently induced ground loss, resulting in cavities and ground subsidence, causing roadbed settlement greater than the allowable value.In this study, FLAC 3D , which is a three-dimensional finitedifference numerical modeling software, is used to perform stability and risk level assessment for the roadbed adjacent to urban railways with respect to various groundwater levels and the geometric characteristics of cavities.Numerical results show that roadbed settlement increases as the diameter (D) of the cavity increases and the distance (d) between the roadbed and the cavity decreases.The regression analyses results show that, as D/d is greater than 0.2 and less than 0.3, the roadbed is in the status of caution or warning.It requires a database of measurement sensors for realtime monitoring of the roadbed, structures and groundwater to prevent disasters in advance.As D/d exceeds 0.35, the roadbed settlement substantially increases and the roadbed is in danger.Since this may result in highly probable traffic accidents, train operation should be stopped and the roadbed should be reinforced or repaired.The effects of groundwater level on roadbed settlement are examined and the analysis results indicate that roadbed settlement is highly influenced by groundwater levels to an extent greater than even the influence of the size of the cavity.

원형모형실험을 통해 철도노반재료로 사용되는 흙을 대상으로 함수비 변화에 따른 침하관계를 평가하였다. 초기 함수비에서 침하량비($R_e$)는 2.08이었으나, 초기함수비보다 2배 이상으로 함수비가 증가되었을 때 침하량비($R_e$)는 4.06으로 4배 이상의 침하가 발생하였다. 또한 실제 공용중인 콘크리트궤도에서 계측된 강우데이타를 기반으로 약 1년여간 현장에 매설된 함수비 측정장비를 통해 장기 함수비 변화추이를 관찰하였다. 콘크리트궤도의 직하부에 위치한 함수비는 강우강도에 따라 변화가 거의 없는 수준이며, 사면부에서는 최대 강우강도 20mm/hr가 초과되는 경우 약 4% 정도의 함수비 변화가 생기는 것을 볼 수 있다. 이러한 변화정도를 볼 때 콘크리트 궤도의 경우 배수성능이 적절히 유지된다면 노반 내부의 함수비 변화는 강우에 대하여 영향이 매우 미비할 것으로 판단된다. In this study, it was performed in characteristics of settlement of roadbed materials with variation of water content using cylinder model device. The ratio of settlement ($R_e$) of subgrade soils in the initial water content were about 2.08, whereas it was increased about 4.06 which resulted in increase two times in the initial water content. Also, it was monitoring long-term to measure variation of the field water contents at concrete track using rainfall measuring sensors. The water content at directly underneath of concrete track rarely seems to affect the variation of water content, but it was increased by about 4% than intial water content with 20 mm/hr rainfall index at slope section. As for the result from the field date, it was determined that the water content of the inner subgrade layer was rarely affect caused by more than 20 mm/h rainfall index during if good drainage system at concrete track properly maintained.

지하수위 하강에 따른 침하량은 1차 압밀 침하량에 비해 비교적 작기 때문에 잔류침하량 산정시 별도로 고려하지 않는다. 그러나 고속철도 콘크리트 궤도에서의 허용잔류침하량은 30mm로 작기 때문에 예기치 못한 과도한 지하수위 하강으로 인하여 허용잔류침하량을 초과할 수 있다. 본 연구에서는 응력-간극수압 유한요소 해석을 통하여 지하수위 변동에 따른 침하 영향을 분석하여 해석결과와 실측자료를 비교하였다. 그 결과 허용잔류침하량을 만족하기 위한 탄성계수 범위를 제시 하였으며 설계 시 지하수위 저하 영향이 반영되는 것이 타당하다고 판단된다. Unlike the primary consolidation settlement, the settlement of ground water lowering is not considered separately because of relatively small residual settlement. But the allowed residual settlement (30 mm) of the concrete track in the high-speed railway may be exceeded due to unexpected excessive ground water lowering. This study analyzed the effect of the settlement according to the ground water level change using finite element analysis of stress-pore pressure coupling model, and compared the analysis results with the measured data. As a result, the range of elasticity modulus satisfying the allowable settlement was proposed, and it is suggested that settlement due to ground water level changes should be reflected in the design.

In recent days, underground excavations and water pipeline damages have caused a lot of soil losses especially in urban areas. For instance, large-scale cavities were found at the roads adjacent to both Seokchon subway station and Incheon subway line No.2. Since a lot of people use urban subway every day, a big accident leads fatal life loss. Therefore, urban railway should be secured and the risk factors influencing on the railway stability should be examined. In this study, a three-dimensional finite difference model using the commercial program FLAC3D is adopted to estimate the stability of railway roadbed adjacent to cavity as a train loading is applied. Roadbed settlements were estimated, with respect to various depths, widths, and lengths of the cavities located at a 20-m distance from the center of railway, to examine the stability of the roadbed.