• Smart Structures and Systems
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• 제20권5호
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• pp.549-562
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• 2017

The US railroad network carries 40% of the nation's total freight. Railroad bridges are the most critical part of the network infrastructure and, therefore, must be properly maintained for the operational safety. Railroad managers inspect bridges by measuring displacements under train crossing events to assess their structural condition and prioritize bridge management and safety decisions accordingly. The displacement of a railroad bridge under train crossings is one parameter of interest to railroad bridge owners, as it quantifies a bridge's ability to perform safely and addresses its serviceability. Railroad bridges with poor track conditions will have amplified displacements under heavy loads due to impacts between the wheels and rail joints. Under these circumstances, vehicle-track-bridge interactions could cause excessive bridge displacements, and hence, unsafe train crossings. If displacements during train crossings could be measured objectively, owners could repair or replace less safe bridges first. However, data on bridge displacements is difficult to collect in the field as a fixed point of reference is required for measurement. Accelerations can be used to estimate dynamic displacements, but to date, the pseudo-static displacements cannot be measured using reference-free sensors. This study proposes a method to estimate total transverse displacements of a railroad bridge under live train loads using acceleration and tilt data at the top of the exterior pile bent of a standard timber trestle, where train derailment due to excessive lateral movement is the main concern. Researchers used real bridge transverse displacement data under train traffic from varying bridge serviceability levels. This study explores the design of a new bridge deck-pier experimental model that simulates the vibrations of railroad bridges under traffic using a shake table for the input of train crossing data collected from the field into a laboratory model of a standard timber railroad pile bent. Reference-free sensors measured both the inclination angle and accelerations of the pile cap. Various readings are used to estimate the total displacements of the bridge using data filtering. The estimated displacements are then compared to the true responses of the model measured with displacement sensors. An average peak error of 10% and a root mean square error average of 5% resulted, concluding that this method can cost-effectively measure the total displacement of railroad bridges without a fixed reference.

• 한국지반공학회논문집
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• 제22권6호
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• pp.5-13
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• 2006

지하수 급속저하와 같은 비배수 상태에서는 흙과 보강재 사이의 경계면(interface)에서 발생하는 과잉간극수압으로 인하여 유효응력이 감소할 수도 있으며, 이는 보강재의 인발력 감소로 이어지기도 한다. 본 연구에서는 각기 다른 종류의 흙(순수모래, 5, 10, 15, 35% 실트질 모래)과 상재하중(30, 100, 200kPa)을 대상으로 배수 및 비배수 실내인발시험을 실시하여 최대 배수인발력과 최대 비배수인발력을 서로 비교하였다. 시험결과 배수인발력과 비배수인발력 모두 실트 함유량에 의해 영향을 받고, 흙의 내부마찰각이 증가함에 따라 인발력 또한 증가하는 것으로 나타났다. 또한, 상재하중이 증가함에 따라 인발력도 증가하였으며, 최대인발력에 도달하는데 소요되는 인발거리도 증가하였다. 비배수 시험에서는 과잉간극수압이 발생함에 따라 보강재에 작용하는 유효응력이 감소하였으며, 그 결과 배수 조건과 비교하여 인발력과 인발거리가 감소하였다.

• 한국지반공학회논문집
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• 제25권5호
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• pp.17-28
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• 2009

연약지반상 성토시, 성토하중은 연약지반에 편재하중으로 작용하게 되어 기초 연약지반의 과도한 침하와 측방유동을 야기할 수 있다. 연약지반의 과도한 변형은 결국 성토체 자체와 인접 지반 및 구조물의 안전을 위협하게 된다. 연약지반의 변형거동에 영향을 미치는 요인은 크게 성토하중 조건과 지반조건으로 구분할 수 있다. 따라서 본 연구에서는 이들 조건을 달리한 5회의 모형실험을 수행하여, 성토하중 재하가 기초 연약지반의 변형거동에 미치는 영향을 평가하였다. 모형실험 결과, 성토하중 재하가 지중 측방변위 발생에 영향을 미치는 영향거리는 성토체 선단부로부터 재하폭의 2배까지인 것으로 나타났다. 또한 모형실험 결과를 근거로, 성토속도(v, kPa/day)와 일평균 침하량(${\Delta}s$, mm/day) 사이의 관계식과 성토속도와 일평균 지중 최대수평변위(${\Delta}y_m$, mm/day) 사이의 상관관계식을 제안하였다.

• 한국지반공학회논문집
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• 제21권4호
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• pp.123-134
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• 2005

비선형 말뚝두부강성을 고려한 3차원 군말뚝기초 해석기법(YSGroup)을 개발하였으며 이를 기타 해석기법들(탄성 변위법, Croup 6.0, FBPier 3.0)과 비교${\cdot}$분석하였다. 본 해석기법은 말뚝캡을 평면쉘요소로, 교각은 3차원 보요소로, 그리고 개개 말뚝들은 보-기둥요소로 모델링 하였다. 교각 상단에 수평하중을 받는 $2\times2$배열 군말뚝기초에서 지반을 선형으로 가정한 경우를 대상으로 탄성변위법, Group 6.0, FBPier 3.0, 그리고 본 해석기법(YSGroup)을 이용하여 해석한 결과, 본 해석기법과 탄성변위법, Group 6.0은 서로 유사한 말뚝두부변위가 산정되었으나 FBPier 3.0는 다소 큰변위가 산정되었다. 지반의 비선형성이 고려된 상부구조물(교각)의 변위는 본 해석기법(YSGroup)과 FBPier 3.0을 통해 산정 가능하였는데, 이는 본 해석기법과 FBPier 3.0은 유한요소법을 이용하여 상부구조물을 직접 모델링하였기 때문이다. 말뚝두부조건이 힌지조건인 경우의 군말뚝은 말뚝캡의 과다한 회전이 발생할 가능성이 큼을 알 수 있었다.

• Structural Engineering and Mechanics
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• 제59권4호
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• pp.719-737
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• 2016

The present study investigated the earthquake behavior of R/C structures considering the vertical earthquake motion with the help of a comparative study. For this aim, the linear time-history analyses of a high-rise R/C structure designed according to TSC-2007 requirements were conducted including and excluding the vertical earthquake motion. Earthquake records used in the analyses were selected based on the ratio of vertical peak acceleration to horizontal peak acceleration (V/H). The frequency-domain analyses of the earthquake records were also performed to compare the dominant frequency of the records with that of the structure. Based on the results obtained from the time-history analyses under the earthquake loading with (H+V) and without the vertical earthquake motion (H), the value of the overturning moment and the top-story vertical displacement were found to relatively increase when considering the vertical earthquake motion. The base shear force was also affected by this motion; however, its increase was lower compared to the overturning moment and the top-story vertical displacement. The other two parameters, the top-story lateral displacement and the top-story rotation angle, barely changed under H and H+V loading cases. Modal damping ratios and their variations in horizontal and vertical directions were also estimated using response acceleration records. No significant change in the horizontal damping ratio was observed whereas the vertical modal damping ratio noticeably increased under H+V loading. The results obtained from this study indicate that the desired structural earthquake performance cannot be provided under H+V loading due to the excessive increase in the overturning moment, and that the vertical damping ratio should be estimated considering the vertical earthquake motion.

• Smart Structures and Systems
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• 제8권2호
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• pp.173-190
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• 2011

As a practical and effective seismic resisting technology, the base isolation system has seen extensive applications in buildings and bridges. However, a few problems associated with conventional lead-rubber bearings have been identified after historical strong earthquakes, e.g., excessive permanent deformations of bearings and potential unseating of bridge decks. Recently the applications of shape memory alloys (SMA) have received growing interest in the area of seismic response mitigation. As a result, a variety of SMA-based base isolators have been developed. These novel isolators often lead to minimal permanent deformations due to the self-centering feature of SMA materials. However, a rational design approach is still missing because of the fact that conventional design method cannot be directly applied to these novel devices. In light of this limitation, a displacement-based design approach for highway bridges with SMA isolators is proposed in this paper. Nonlinear response spectra, derived from typical hysteretic models for SMA, are employed in the design procedure. SMA isolators and bridge piers are designed according to the prescribed performance objectives. A prototype reinforced concrete (RC) highway bridge is designed using the proposed design approach. Nonlinear dynamic analyses for different seismic intensity levels are carried out using a computer program called "OpenSees". The efficacy of the displacement-based design approach is validated by numerical simulations. Results indicate that a properly designed RC highway bridge with novel SMA isolators may achieve minor damage and minimal residual deformations under frequent and rare earthquakes. Nonlinear static analysis is also carried out to investigate the failure mechanism and the self-centering ability of the designed highway bridge.

• 한국지반환경공학회 논문집
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• 제7권4호
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• pp.53-62
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• 2006

최근 우리나라는 연약지반으로 구성된 서해안과 남해안의 해안매립지역에 도로, 신항 등 건설사업 진행시 수평하중이 말뚝두부에 작용할 경우, 지반은 부동의 상태에서 말뚝의 이동에 저항하여 작용하는 연약지반의 측방유동과 수동말뚝에 대한 문제점이 종종 논의되고 있다. 본 연구에서는 인천 ${\bigcirc}{\bigcirc}{\bigcirc}{\bigcirc}$ 부두 건설공사 과정에서 발생되는 측방유동에 따른 구조물 및 지반의 변형을 분석하기 위하여 현장계측을 실시하였고, 유한요소 해석 프로그램인 AFFIMEX Version 3.4를 이용하여 현장계측 결과와 비교분석하였다. 수치해석에 의한 변위 결과는 시공단계별로 초기응력상태, 말뚝항타, 모래치환, 사석층설치, 준설매립, 배수층설치, 상재하중재하, 상재하중재하 및 제하 후 방치 등으로 구분하여 구조물과 기초지반에 발생된 연직 및 측방 변위를 분석하였다. 현장계측과 수치해석 결과, 안벽호안의 침하량은 계측이 시작된 시점으로부터는 이미 많은 침하가 발생된 것으로 나타났으며, 계측일로부터는 준설매립에 의한 성토작업을 개시하는 시점에서 가장 많은 양의 침하가 발생되었고, 성토가 완료된 시점으로부터 침하량은 수렴하였다. 전체적으로 수치해석에 의한 결과치가 계측을 통한 결과치보다 크게 나타났다.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2009년도 세계 도시지반공학 심포지엄
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• pp.660-670
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• 2009

Neighboring construction becomes mainstream of Ground excavation in downtown area. This causes the displacement, deformation, stress condition, etc of the ground surroundings. Therefore Neighboring construction have an effect on Neighboring structure. All these years a lot of Neighboring construction carried out, and the accumulation of technology also get accomplished. But earth retaining structure collapse happens yet. Types of earth retaining structure collapse are 12. 1. Failure of anchor or strut system, 2. Insufficiency of penetration, 3. H-pile Failure on excessive bending moment, 4. Slope sliding failure, 5. Excessive settlement of the back, 6. Deflection of H-pile, 7. Joint failure of coupled H-pile, 8. Rock failure when H-pile penetration is rock mass, 9. Plane arrangement of support systems are mechanically weak, 10. Boiling, 11. Heaving, 12. Over excavation. But field collapses are difficult for classification according to the type, because collapse process are complex with various types. When we consider the 12 collapse field, insufficient recognition of ground condition is 4 case. Thorough construction management prevents from fault construction. For limitations of soil survey, It is difficult to estimate ground condition exactly. Therefore, it should estimate the safety of earth retaining system, plan for necessary reinforcement, according to measurement and observation continuously.

• Geomechanics and Engineering
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• 제21권2호
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• pp.171-178
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• 2020

Mountainous areas cover more than 70% of Korea. With the rapid increase in tunnel construction, tunnel-collapse incidents and excessive deformation are occurring more frequently. In addition, longer tunnel structures are being constructed, and geologically weaker ground conditions are increasingly being encountered during the construction process. Tunnels constructed under weak ground conditions exhibit long-term deformation behavior that leads to tunnel instability. This study analyzes the behavior of the bottom region of tunnels under geological conditions of long-term deformation. Long-term deformation causes various types of damage, such as cracks and ridges in the packing part of tunnels, as well as cracks and upheavals in the pavement of tunnels. We observed rapid tunnel over-displacement due to the squeezing of a fault rupture zone after the inflow of a large amount of groundwater. Excessive increments in the support member strength resulted in damage to the support and tunnel bottom. In addition, upward infiltration pressure on the tunnel road was found to cause severe pavement damage. Furthermore, smectite (a highly expandable mineral), chlorite, illite, and hematite, were also observed. Soil samples and rock samples containing clay minerals were found to have greater expansibility than general soil samples. Considering these findings, countermeasures against the deformation of tunnel bottoms are required.

• 한국터널지하공간학회 논문집
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• 제10권4호
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• pp.397-404
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• 2008

본 연구는 인천국제공항철도 신설 공사구간 중 서울지하철 2호선 하부에서 TRcM 공법으로 통과하는 구간의 수리 및 굴착 안정성에 대해 검토한 내용이다. 본 검토 대상 구간에서는 터널 굴착과정에서 하루 최대 86.4 ton의 예상치 못한 과다 용출수가 발생하였으며, 과다 용출수의 발생에 대한 원인 분석을 위해 관측정에서 계측된 지하수위 저하거동과 가장 적합한 수리해석 파라미터를 찾기 위한 수리 역해석을 실시하였다. 본 수리 역해석에서는 TRcM 구간에 접한 홍익대학교 정거장 굴착시의 측정된 자료중 TRcM 구간 굴착전까지의 지하수위 계측결과를 사용하였다. 암종별 수리전도계수와 서울지하철 2호선의 배수경계조건, 과업구간의 강우강도 등을 변화시켜가며 수리 역해석을 수행하였다. 그 결과 계측된 자료와 유사한 최종 지하수위 및 지하수위 저하 경향을 보이는 수리해석 조건을 얻을 수 있었다. 다음, 지반의 굴착에 의한 역학적 영향을 분석하기 위해 지하수를 고려하지 않은 역학적 해석을 수행하였다. 순수 역학적 해석 결과, 지표침하 0.85 mm, TRcM 구간 천단침하 1.32 mm 발생하는 것으로 나타났으며, 복합거동 해석결과 지표침하 1.2 mm, TRcM 구간 최대 천단침하 1.72 mm으로 나타나 지하수위 저하에 의해 추가 변위가 발생하나 침하량이 크지 않아 안정성에는 영향이 없는 것으로 분석되었다.