• 한국지반공학회논문집
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• 제40권3호
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• pp.65-75
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• 2024

본 연구에서는 여러 영향 인자들이 사질토의 액상화로 인한 침하에 미치는 영향을 확인하기 위해 변형률 제어조건 하에서 반복단순직접전단시험을 수행하였다. 누적 전단 변형률, 상대밀도, 반복 하중의 형태, 시료 준비 방법 등의 다양한 인자들을 선정하였으며, 지진 하중이 발생하였을 때 인자들이 지반 침하에 미치는 영향을 분석하였다. 시험 결과, 누적 전단 변형률이 낮고 상대밀도가 높은 시료에서 더 작은 부피 변형이 발생하였다. 추가적으로 반복하중의 진폭은 부피 변형에 영향을 미쳤으나, 주파수는 시료의 부피 변형에 영향을 미치지 않는다는 사실을 확인할 수 있었다. 시료 준비 방법에 따라서도 액상화에 따른 침하가 다른 양상을 보인다는 사실을 확인하였으며, 이와 같은 결과들은 향후 액상화로 인한 침하 예측을 수행할 때 기초 연구로써 의미가 있을 것으로 기대된다.

• 한국방재학회:학술대회논문집
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• 한국방재학회 2007년도 정기총회 및 학술발표대회
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• pp.546-550
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• 2007

High excess pore water pressure may develop when loose saturated sand is subjected to earthquake excitation, resulting in reduction in the shear strength and stiffness, and ultimately can result in liquefaction. It is very important to accurately assess the level of the pore pressure generation for seismic design and to perform effective stress analysis. A simple numerical 모형 is developed for estimating the development of pore water pressure due to seismic loading. The method only uses two parameters and the length of the accumulated shear strain. The accuracy of the proposed 모형 is verified through a series of laboratory test data. Comparisons show that the modified 모형 is an improvement over existing 모형s.

• 한국지진공학회논문집
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• 제7권5호
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• pp.47-56
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• 2003

본 논문에서는 기존 IWAN 모델을 수정하여 사질토 지반의 반복경화 현상을 나타낼 수 있는 지반의 반복경화모델을 개발하였다. 일반적으로 동적하중을 받는 지반재료는 하중 반복회수에 따라 동적 거동특성이 변화하게 되며 이는 반복 경화 및 연화현상으로 나타난다. 본 논문에서는 등방 경화 또는 등방 연화 거동을 하는 스프링슬라이더 요소를 기존 병렬 IWAN 모델에 추가함으로써 지반의 동적 변형특성 표현이 가능하였다. 등방 경화 거동을 보이는 요소들의 항복 응력은 각각 반복 경화함수에 의하여 증가하도록 정의되었으며, 반복 경화함수는 대칭 한계를 가지는 동적 비틂전단 시험결과로부터 정의되었다. 이렇게 정의된 반복 경화함수는 지반의 동적 변형 특성을 묘사하기 위하여 하나의 독립 변수를 가지게 되며, 사용된 독립변수는 지반의 동적 한계 변형률의 특성을 포함하는 누적전단변형률로 사용되었다. 누적 전단변형률은 반복 전단한계 변형률 이상의 변형률의 누적으로 정의되며, 역재하 및 재재하 곡선에서는 Masing의 법칙을 적용하여 계산될 수 있다. 본 논문에서는 모델의 개발과정을 서술하였고, 모델에 대한 검증은 동반논문인 검증편에 설명하였다.

• 소성∙가공
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• 제32권1호
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• pp.35-40
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• 2023

In the case of a wire with a very fine diameter during the multi-stage drawing process, the heterogeneity of the deformation in the radial direction tends to develop strongly as the amount of deformation is accumulated. It is known that the heterogeneity of deformation in the radial direction of the wire is closely related to the process parameters during the multi-stage drawing process. In this study, finite element analysis (FEA) was used to theoretically examine the effect of friction between the surface of the wire and the drawing die during the multi-stage drawing process of Cu-0.2wt%Mg alloy on the deformation heterogeneity developed in the radial direction of the wire. The distribution of effective strain, radial strain, circumferential strain, and shear strain developed in the radial direction of the wire during the multi-stage drawing process was analyzed while changing the friction coefficient, and the results were analyzed and compared for each path and position. The FEA results revealed that the shear strain developed in the radial direction of the wire during the multi-stage drawing process of Cu-0.2wt%Mg alloy showed the most non-uniform distribution and was also severely affected by the friction coefficient.

• 한국구조물진단유지관리공학회 논문집
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• 제25권6호
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• pp.103-110
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• 2021

유연한 고무재료와 강재 보강판을 적층으로 구성한 탄성받침은 우수한 수직강성과 유연한 횡강성으로 교량의 내진보강용으로 널리 사용되고 있다. 무엇보다 시공이 간단하고 비용이 높지 않다는 장점을 지니고 있다. 고무재료의 한 종류인 합성고무는 천연고무에 비해 노화에 대한 저항성이 크지만 이 역시 다양한 열화요인으로 성능이 저하된다. 내진설계기준 및 내진성능평가요령에서는 이러한 노화의 특성을 반영하고 있지 않지만 관련 연구가 축적되면 이를 반영하는 것이 합리적이다. 합성고무를 대상으로 노화촉진시간과 노출시간을 변수로 하여 노화촉진시험을 수행하여 전단특성의 변화를 분석하였다. 노화가 진행될수록 최대전단응력과 전단변형율은 감소한다. 또한 동일한 전단변형률에서 전단강성이 크게 증가한다.

• Geomechanics and Engineering
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• 제12권4호
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• pp.611-626
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• 2017

The research reported herein is concerned with the model testing of piles socketed in soft rock which was simulated by cement, plaster, sand, water and concrete hardening accelerator. Model tests on a single pile socketed in simulated soft rock under axial cyclic loading were conducted and the bearing capacity and accumulated deformation characteristics under different static, and cyclic loads were studied by using a device which combined oneself-designed test apparatus with a dynamic triaxial system. The accumulated deformation of the pile head, and the axial force, were measured by LVDT and strain gauges, respectively. Test results show that the static load ratio (SLR), cyclic load ratio (CLR), and the number of cycles affect the accumulated deformation, cyclic secant modulus of pile head, and ultimate bearing capacity. The accumulated deformation increases with increasing numbers of cycles, however, its rate of growth decreases and is asymptotic to zero. The cyclic secant modulus of pile head increases and then decreases with the growth in the number of cycles, and finally remains stable after 50 cycles. The ultimate bearing capacity of the pile is increased by about 30% because of the cyclic loading thereon, and the axial force is changed due to the applied cyclic shear stress. According to the test results, the development of accumulated settlement is analysed. Finally, an empirical formula for accumulated settlement, considering the effects of the number of cycles, the static load ratio, the cyclic load ratio and the uniaxial compressive strength, is proposed which can be used for feasibility studies or preliminary design of pile foundations on soft rock subjected to cyclic loading.

• 한국구조물진단유지관리공학회 논문집
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• 제8권2호
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• pp.195-204
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• 2004

본 연구에서는 약액주입 사질고결토에 대해 일정재하크리프시험과 반복재하크리프시험을 실시하여 점 탄소성 거동 규명과 크리프예측을 수행하였다. 일정재하크리프 시험결과 총 변형률은 탄성, 소성 그리고 점탄성변형률로 구분되었으며 이러한 변형률은 응력의 증가에 비례하여 증가하였고 회복된 변형률은 제하시간에 무관함을 알았다. 일정재하크리프시험 예측결과 일반화된 모델과 지수함수모델은 시험결과와 잘 일치하였다. 반복재하크리프시험에서 순간회복변형률은 반복횟수에 무관하였고 누적소성 변형률은 반복횟수에 따라 증가하였으며 응력레벨에 비례함을 알 수 있었다. 반복재하크리프시험의 예측결과 첫 사이클에서는 잘 일치하였으나 반복횟수가 증가함에 따라 약간의 오차가 발생되었다.

• Structural Engineering and Mechanics
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• 제76권3호
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• pp.279-291
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• 2020

The seismic design of conventional frame structures is meant to enhance plastic deformations at beam ends and prevent yielding in columns. To this end, columns are made stronger than beams. Yet yielding in columns cannot be avoided with the column-to-beam strength ratios (about 1.3) prescribed by seismic codes. Preventing plastic deformations in columns calls for ratios close to 4, which is not feasible for economic reasons. Furthermore, material properties and the rearrangement of geometric shapes inevitably make the distribution of damage among stories uneven. Damage in the i-th story can be characterized as the accumulated plastic strain energy (W_pi) normalized by the product of the story shear force (Q_yi) and drift (δ_yi) at yielding. Past studies showed that the distribution of the plastic strain energy dissipation demand, W_pi/ΣW_pj, can be evaluated from the deviation of Q_yi with respect to an "optimum value" that would make the ratio W_pi/(Q_yiδ_yi) -i.e. the damage- equal in all stories. This paper investigates how the soil type and ductility demand affect the optimum lateral strength distribution. New optimum lateral strength distributions are put forth and compared with others proposed in the literature.

• 한국해양공학회지
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• 제25권3호
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• pp.53-65
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• 2011

This is the third of several companion papers dealing with the derivation of material constants for ductile failure criteria under hydrostatic stress. It was observed that the ultimate engineering stresses and elongations at fracture from tensile tests for round specimens with various notch radii tended to increase and decrease, respectively, because of the stress triaxiality. The engineering stress curves from tests are compared with numerical simulation results, and it is proved that the curves from the two approaches very closely coincide. Failure strains are obtained from the equivalent plastic strain histories from numerical simulations at the time when the experimental engineering stress drops suddenly. After introducing the new concept of average stress triaxiality and accumulated average strain energy, the material constants of the Johnson-Cook failure criterion for critical energies of 100%, 50%, and 15% are presented. The experimental results obtained for EH-36 steel were in relatively good agreement with the 100% critical energy, whereas the literature states that aluminum fits with a 15% critical energy. Therefore, it is expected that a unified failure criterion for critical energy, which is available for most kinds of ductile materials, can be provided according to the used materials.

• Advances in materials Research
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• 제3권3호
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• pp.163-174
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• 2014

In this study, fatigue properties and crack growth characteristics of a polycarbonate (PC) were examined during cyclic loading at various mean stress (${\sigma}_{amp}$) and stress amplitude (${\sigma}_{mean}$) conditions. Different S vs. N and da/dN vs. ${\Delta}K$ relations were obtained depending on the loading condition. The higher fatigue strength and the higher resistance of crack growth are seen for the PC samples cyclically loaded at the higher mean stress and lower stress amplitude due to the low crack driving force. Non-linear S - N relationship was detected in the examination of the fatigue properties with changing the mean stress. This is attributed to the different crack growth rate (longer fatigue life): the sample loaded at the high mean stress with lower stress amplitude. Even if the higher stress amplitude, the low fatigue properties are obtained for the sample loaded at the higher mean stress. This was due to the accumulated strain energy to the sample, where severe plastic deformation occurs instead of crack growth (plasticity-induced crack closure). Shear bands and discontinuous crack growth band (DGB) are observed clearly on the fracture surfaces of the sample cyclically loaded at the high stress amplitude, where the lower the ${\sigma}_{mean}$, the narrower the shear band and DGB. On the other hand, final fracture occurred instantly immediately after the short crack growth occurs in the PC sample loaded at the high mean with the low ${\sigma}_{amp}$, i.e., tear fracture, in which the shear bands and DGB are not seen clearly.