• Tunnel and Underground Space
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• v.15 no.5 s.58
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• pp.344-351
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• 2005

Direct back analysis software is coded based on Simplex method using FLAC as a subroutine. For the verification of the software, 12 different cases are assumed combining various displacements in different measuring locations around a tunnel. The number of displacements for cases varies from 3 to 240. It is verified that the exact elasticity and the primary stress state of rock around a tunnel could be found through iterative calculation regardless of the locations and number of displacements and initial values needed for the direct back analysis.

• Proceedings of the Korean Geotechical Society Conference
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• 2009.09a
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• pp.622-640
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• 2009

원유 비축기지 저장공동과 같이 상하로 긴 형상의 대규모 공동에서 횡방향의 지압이 과도하게 작용하면 천정부의 응력집중과 측벽의 암반 변위가 과도하게 발생하여 저장공동의 불안정 요인이 된다. 특히 지압의 절대 크기가 암반 강도의 일정 비율 이상이 되면 응력 집중에 의한 암반의 취성 파괴를 유발하고, 이러한 현상은 터널 굴착 시 발생하는 파괴음(popping)과, 굴착면에 평행한 형태로 암편이 탈락하는 취성파괴(spalling) 현상을 동반한다. 이 글에서는 대규모 지하저장공동 굴착시 실제 발생한 과지압으로 인한 문제 사례에 대해 소개한다. 저장공동 굴착시 관찰된 암편 및 숏크리트 탈락과 균열 발생 현상을 관찰하고 암반 계측결과 분석을 통해 과지압의 현상을 진단하였다. 과지압 구간의 현재 상태 및 원안 설계안에 대해 연속체 및 불연속체 안정성 해석을 실시하여 문제의 심각성을 평가하였다. 이를 통해 굴착 형상 변경 및 특수 보강 방안을 제안하였으며 제안된 안의 보강효과에 대한 수치해석 평가 결과를 재검토 하였다. 이들 결과를 종합하여 과지압구간 보강안을 도출하였으며 상시 안정성 감시 대책으로 현장 암반의 미소파괴음 계측 방안을 제시하였다.

• Geotechnical Engineering
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• v.13 no.1
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• pp.123-136
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• 1997

By applying the finite element theory which is capable of handling the geometrically altered structure in a successive manner, the linear relationship between incremental displacements and the magnitude of the initial stress field was derived. Based on this relationship, back analysis code having the capability of dealing multi-step excavation problem was built and verified With this back analysis code, the measurements of the incremental displacements in a particular excavation step make it possible to back-calculate the initial stress state. illustrative examples showed the applicability of this code to a practical problem.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.29 no.3
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• pp.219-227
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• 2016

In this study, we have proposed a method of monitoring of bridges under construction in view of the long-term behavior of the prestress concrete bridge of which the Free Cantilever Method is applied. As a method to confirm the ability of the long-term behavior of the concrete box girder, temperature sensors and strain gauges were installed, and the measured data was used to calculate creep coefficient. Moreover, we have measured the stress of the concrete box girder during construction which was applied with creep coefficient and compared with the changes in temperature to analyze the vertical displacement along the segment. In conclusion, monitoring of the FCM bridge during construction in consideration of the long-term behavior can be analyzed efficiently by suing temperature and displacement data without the use of laser displacement meter or laser delfectometer.

• Proceedings of the KSME Conference
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• 2003.04a
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• pp.473-478
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• 2003

This paper presents static and dynamic measurement of the stress and motion characteristics for crawler type excavators. Eight scenarios were prepared for static measurement based on two extreme digging positions, maximum digging reach position and maximum digging force position. The measured items for static motion included stress, cylinder pressure, cylinder stroke and digging force. The measured static stresses showed that asymmetric digging force acting on a bucket induced higher stress level than symmetric one. The measured static pressures and digging forces also agreed with design pressures and design digging forces, respectively. The dynamic measurement was performed for two types of motion, that is, simple reciprocation of each cylinder and actual digging motion. The measured items for dynamic motion were stroke and pressure of each cylinder, stresses on the working device and acceleration on the upper plate of an arm. The measured data showed that the natural frequency of the excavator highly depended on the hydraulic stiffness of cylinders. Digging motion tests revealed that digging motion was closer to static motion rather than dynamic one.

• Journal of the Korean GEO-environmental Society
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• v.8 no.1
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• pp.5-11
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• 2007

Internal stress variation in the face slab concrete induced by reservoir water pressure may affect on the stability of the dam so that the reclamation type of strain gauge is applied for measuring internal stress variation. In this study, internal as well as external stress variation of dam was measured by using strain gauge that was reclaimed to the ${\circ}{\circ}$ dam. In the result, it was confirmed that other measurements by relevant gauges need to be supplemented as the use of strain gauge only is insufficient to evaluate the stability analysis and global behavior of the dam.

• Journal of the Korean Geophysical Society
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• v.7 no.4
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• pp.305-311
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• 2004

Several sensor systems are used to estimate the reinforceing effect of pile in hihg cut slopes, and to find a failure zone in slopes effectively. Inclinometer, extensometer and V/W sensor have shown a great potentiality to serve real time health monitoring of the slope structures. They were embedded or attached to the structures, we conducted field tests and test results have shown great solutions for sensor systems of Civil Engineering Smart Structures. This research is to seek for the relationships among the slope movement and the reinforceing effect of pile, and the strain distribution in a active zone by analyzing the data from the in-situ measurement so that the possible failure zone should be well defined based on the relationships. Also, the relationships between temperature and reinforceing effect of pile, and the strain distribution are estimated in this paper.

• Magazine of the Korea Concrete Institute
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• v.6 no.1
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• pp.89-100
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• 1994

The current test procedure for transfer length, which determine transfer length by measuring concrete strain, has an actual bond stress state in the prestressed pretensioned member : however, it is difficult to determine the bond properties of maximum bond stress and bond stiffness with this method. It is also difficult for design engineer to understand and select a correct safety criterion from the widely distributed results of such a ransfer test alone. An alternative testing procedure is provided here to determine the bond properties without measuring the concrete strain. In this test the bond stress is measured directly by creating a similar boundary condition within the transfer length in a real beam during the transfer of prestressing force. The prestressing force was released step by step by step from the unloading side. The release of force induces a swelling of the strand at the unloading side of concrete block, bonding force in the block, and a bond slip of the strand toward the other side of the block. Two center-hole load cells are used to record the end loads until the point of general bond slip(maximum bond stress). It is suggested that this test procedure be performed with the ordinary transfer test when determining the transfer length in a prestressed, pretensioned concrete beam.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.49 no.8
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• pp.617-626
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• 2021

During supersonic flight of vehicles, the thermal behavior of structures under high-temperature environment is important for thermal-structural design. In this study, full-field thermal deformation and stress concentration of the notched structure was performed using global-local multi-digital image correlation (multi-DIC) systems. This techniques were developed and implemented by multi-DIC systems consists of 2D DIC system and 3D DIC system. The specimen was heated in a heating chamber to achieve the thermal expansion behavior. Then the images of structure's deformation and stress concentration at various temperature were recorded and analyzed by multi-DIC system. Afterward, full-field thermal deformation of the notched structure was determined with DIC technique and stress concentration at the notched structure was calculated by further processing. Finite element analysis of the notched structure is performed in ABAQUS^TM and the results of the experiments show good agreement with those obtained from simulation. The results achieved in this study show the efficiency of the muilti-DIC method in thermal deformation as well as stress concentration of notched structure.

• Journal of the Korean Society for Precision Engineering
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• v.23 no.10
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• pp.30-35
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• 2006