• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.397-402
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• 2003

Fracture resistance curves for concerned materials are required in order to perform elastic-plastic fracture mechanical analyses. Fracture resistance curve is built with J-integral values and crack extension values. The objective of this paper is to apply the load ratio method to the measurement of the crack length for the real scale pipe specimen. For these, the fracture test using the real scale pipe specimen and finite element analyses were performed. A 4-point bending jig was manufactured for the pipe test and the direct current potential drop method and the load ratio method was used to measure the crack extension and the length for the real scale pipe test. Finite element analyses about the compliance of the pipe specimen were executed for applying the load ratio method according to the crack length.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2008년도 춘계 학술발표회 초청강연 및 논문집
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• pp.1454-1465
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• 2008

• 한국철도학회:학술대회논문집
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• 한국철도학회 2011년도 정기총회 및 추계학술대회 논문집
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• pp.3208-3213
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• 2011

It has regarded an attempt to design and construct more safe structures as challenges such as fate. In order to operate public facilities safely, It can be taken how to improve the resistance to applied load by increasing the cross-section of structural members or by installing reinforcement. But inevitably such a way is accompanied by an increase of construction cost or maintenance cost. To make a cost-effective construction, Reliability-based decision analysis which can judge the adequacy of investment is suggested using statistical data of the load, resistance and the maintenance cost.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1990년도 추계학술대회 논문집 학회본부
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• pp.184-187
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• 1990

This paper presents the self-matched line pulse generator and the concerned principles on its operation and characteristics are mentioned. The circuit consists of a charged transmission line and a high speed switch, and it generates a square wave pulse with the very fast rise time. The generated waveform depends on the load resistance. As the load resistance is infinite, a single rectangular wave pulse is generated and its efficiency is nearly unity.

• 한국지반공학회논문집
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• 제21권5호
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• pp.187-196
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• 2005

풍화 및 절리가 발달한 암반에 근입된 말뚝의 허용지지력 결정에는 침하량이 매우 중요한 인자가 되며, 설계단계에서 말뚝두부의 침하량을 예측하기 위해서는 말뚝의 하중전이기구에 대한 이해가 필수적이다. 따라서 본 연구에서는 풍화된 암반에 근입된 현장타설말뚝의 하중전이기구에 대한 연구를 수행하였다. 이를 위해 직경 1m의 총 5본의 현장 타설말뚝을 풍화된 편마암 부지에 시공하구 재하시험 및 하중전이 계측을 수행하여 말뚝의 축방향 지지거동을 분석하였다. 암반상태를 정량적으로 파악하기 위하여 재하시험 부지의 암반에 대한 엄밀한 현장/실내시험을 수행하고, 이를 토대로 암반상태가 말뚝의 하중전이기구에 미치는 영향을 분석하였다. 하중전이 계측을 통해 얻은 주면하중전이 (f-w) 곡선은 풍화상태가 상대적으로 양호한(MW) 연암의 경우, 수 mm의 변위에서 항복에 도달하며, 이후 변위에 따른 지지하중의 증가율이 급격히 둔화되는 경향을 보였다. 반면 풍화암/풍화토에 근입된 말뚝의 f-w 곡선은 뚜렷한 항복점을 보이지 않으며, 상대적으로 큰(>15m) 변위까지 주면하중이 쌍곡선 형태로 증가하였다. 선단하중전이(q-w) 곡선은 암반상태에 관계없이 선단변위 (q-w)까지는 선형적인 거동을 보였다.

• Geomechanics and Engineering
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• 제23권6호
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• pp.523-533
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• 2020

The current study focuses on the effect of the end shape of steel pipe piles on installation effort and bearing resistance using the pressing method of installation under dense ground conditions. The effect of pile rotation on the installation effort and bearing resistance is also investigated. The model steel piles with a flat end, cone end and cutting-edge end were used in this study. The test results indicated that cone end pile with the pressing method of installation required the least installation effort (load) and showed higher ultimate resistance than flat and cutting-edge end piles. However, pressing and rotation during cutting-edge end pile installation considerably reduces the installation effort (load and torque) if pile penetration in one rotation equal to the cutting-edge depth. Inclusion of rotation during pile installation reduces the ultimate bearing resistance. However, if penetration of the cutting-edge end pile equal to the cutting-edge depth in one rotation, the reduction in ultimate resistance can be minimized. In comparing the cone and cutting-edge end piles installed with pressing and rotation, the least installation effort is observed in the cutting-edge end pile installed with penetration rate equal to the cutting-edge depth per rotation.

• Journal of Welding and Joining
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• 제24권6호
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• pp.39-43
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• 2006

A ferritic stainless steel, STS430, and a galvanized steel for case and frame of electronic goods are welded by resistance spot welding and resistance projection welding methods. In this study, resistance spot welding has been performed to investigate the weldability of dissimilar materials such as a ferritic stainless steel and a galvanized steel. Tensile load of the spot weld without heat treatment was 196 kN and brittle fracture occurred at interface between STS430 and nugget due to the high hardness, 380 Hv, in nugget. It was found that the hardness of as-welded nugget increased with higher cooling rate during resistance spot welding by comparing with GTA weld of same materials. Heat treatment by applying second current made nugget softened. Tensile load of heat treated weld increased and reached to 303 kN and fracture occurred at base metal, a galvanized steel.

• Steel and Composite Structures
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• 제15권1호
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• pp.103-130
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• 2013

Fire performance and fire safety of high-rise buildings have become major concerns after the disasters of World Trade Center in the U.S. in 2001 and Windsor tower in Spain in 2005. Performance based design (PBD) approaches have been considered as a better method for fire resistance design of structures because it is capable of incorporating test results of most recent fire resistance technologies. However, there is a difficulty to evaluate fireproof performance of large structures, which have multiple structural members such as columns, slabs, and walls. The difficulty is mainly due to the limitation in the testing equipment, such as size of furnace that can be used to carry out fire tests with existing criteria like ISO 834, BS 476, and KS F 2257. In the present research, a large scale calorie meter (10 MW) was used to conduct three full scale fire tests on medical modular blocks. Average fire load of 13.99 $kg/m^2$ was used in the first test. In the second test, the weighting coefficient of 3.5 (the fire load of 50 $kg/m^2$) was used to simulate the worst fire scenario. The flashover of the medical modular block occurred at 62 minutes in the first test and 12 minutes in the second test. The heat resistance capacity of the external wall, the temperatures and deformations of the structural members satisfied the requirements of fire resistance performance of 90 minutes burning period. The total heat loads and the heat values for each test are calculated by theoretical equations. The duration of burning was predicted. The predicted results were compared with the test results, and they agree quite well.

• 대한금속재료학회지
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• 제49권12호
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• pp.967-976
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• 2011

Conventional fracture tests of resistance spot welds have been performed without consideration of the paint baking process in the automobile manufacturing line. The aim of this paper is to investigate the effect of the paint baking process on load carrying capacity and fracture mode for resistance spot welded 590 dual phase (DP), 780DP, 980DP, 590 transformation in duced plasticity (TRIP), 780TRIP and 1180 complex phase (CP) steels. With paint baking after resistance spot welding, the l-shape tensile test (LTT) and nano-indentation test were conducted on the as-welded and paint baked samples. Paint baking increased the load-carrying capacity of the resistance spot welded samples and improved the fracture appearance from partial interfacial fracture (PIF) to button fracture (BF). Improvement in fracture appearance after LTT is observed on weldments of 780 MPa grade TRIP steels, especially in the low welding current range with paint baking conditions. The higher carbon contents (or carbon equivalent) are attributed to the low weldability of the resistance spot welding of high strength steels. Improvement of the fracture mode and load carrying ability has been achieved with ferrite hardening and carbide formation during the paint baking process. The average nano-indentation hardness profile for each weld zone shows hardening of the base metal and softening of the heat affected zone (HAZ) and the weld metal, which proves that microstructural changes occur during low temperature heat treatment.

• 한국건설순환자원학회논문집
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• 제8권3호
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• pp.349-355
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• 2020

이 연구의 목적은 섬유의 혼입량과 종류에 따른 고강도 섬유보강 복합재료의 정적하중에서의 압축강도 및 인장거동과 비상체 하중 하에서의 충격 저항성을 조사하고자 한다. 이를 위하여 3가지 배합을 설계하였고, 압축강도, 직접인장, 그리고 고속 비상체 충돌 실험을 수행하였다. 실험결과 섬유의 혼입량은 압축강도에 비하여 인장강도에 큰 영향을 미치며, 하이브리드 섬유 사용으로 인장변형성능이 향상되는 것으로 나타났다. 강섬유의 혼입량은 충격 저항성에 큰 영향을 미치는 것으로 나타났다. 하이브리드 섬유를 사용하면 충격 저항성이 더욱 향상되는 것으로 나타났다. 다만, 단일 섬유 사용에 비하여 실험체별성능 차이가 크게 발생하는 것으로 나타났다.