• Journal of the Korea Concrete Institute
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• v.29 no.3
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• pp.237-248
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• 2017

Frequent terror or military attack by explosion, impact, fire accidents have occurred recently. These attacks and incidents raised public concerns and anxiety of potential terrorist attacks on important infrastructures. However, structural behavioral researches on prestressed concrete (PSC) infrastructures such as Prestressed Concrete Containment Vessel (PCCV) and Liquefied Natural Gas (LNG) storage tanks under extreme loading are significantly lacking at this time. Also, researches on possible secondary fire scenarios after terror and bomb explosion has not been performed yet. Therefore, a study on PSC structural behavior from an blast-induced fire scenario was undertaken. To evaluate the blast-fire combined resistance capacity and its protective performance of bi-directional unbonded PSC member, blast-fire tests were carried out on $1,400mm{\times}1,000mm{\times}300mm$ PSC specimens. Blast loading tests were performed by the detonation of 25 kg ANFO explosive charge at 1.0 m standoff distance. Also, fire and blast-fire combined loading were tested using RABT fire loading curve. The test results are discussed in detail in the paper. The results can be used as basic research references for related research areas, which include protective design simulation under blast-fire combined loading.

• The Journal of Korean Academy of Prosthodontics
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• v.25 no.1
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• pp.281-302
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• 1987

의치상 재료 종류에 따라 의치, 점막 및 하악골에 발생되는 변위 및 응력을 연구하기 위하여 컴퓨터를 이용한 수치적 해석인 2차원 유한 요소법을 이용하였다. 2차원 유한 요소 모형으로선 표준 크기의 하악골 및 의치를 고려하여 231개의 사변형 요소 및 268개의 절점으로 분할한 후 각 구성 성분의 물리적 성질인 탄성률 및 프와송비를 대입시켰다. 사용된 의치로서는 일반 합성수지의치, 2mm후경의 탄성재를 의치상 하부에 이장한 합성수지의치, 2mm후경의 탄성재를 치아와 의치상 중앙에 삽입한 합성수지의치 및 0.5mm후경의 금속상의치의 4종류였으며, 하중시에 하악의 고정 부위로선 생체와 동일 조건을 부여하기 위하여 교근, 내측익돌근, 측두근등의 하악 폐구근이 부착되는 하악각 부위 및 하악 근돌기 부위의 16절점을 고정점으로 하였다. 하중 조건으로선 하악 제1대구치의 일점에 10kg의 수직 집중하중, 하악 중절치의 일점에 7kg의 수직 집중하중 및 하악 제 1소구치로 부터 하악 제2대구치까지의 교합면에 10kg의 수직 분산하중을 부여하여 분석한 결과는 다음과 같다. 1. 하중이 의치 교합면위의 가해진 부위에 따라 다양한 의치 회전 및 강하 현상을 보였으며, 탄성재를 이장 및 삽입한 합성 수지 의치의 변위가 일반 합성수지의치 및 금속상 의치의 변위보다 더 컸다. 2. 주응력을 고려할때 점막 부위에는 주로 압축 응력이 작용하였으며 치조제 부위는 압축응력과 인장 응력이 함께 작용하였다. 3. 탄성재를 삽입한 합성수지의치에 최고 등가 응력이 집중되었으며 그 다음은 탄성재를 이장한 합성수지의치, 일반 합성수지의치의 순이였으며 금속상의 경우는 금속을 따라서 높은 등가 응력이 넓게 분산되었다. 4. 의치상 종류에 관계없이 동일 하중 조건하에선 점막에 나타나는 등가 응력의 크기 및 분산양태는 유사하였다. 5. 하악골에서 등가 응력은 의치지지 부위에만 국한되지 않고 넓게 분산 되었으며 의치상 종류 및 하중 조건에 관계없이 치조제 후방 및 하악연의 후방 부위에 특히 높은 등가응력이 집중되었다. 6. 하악 중절치의 일점에 수직 하중을 가한 경우가 다른 하중 조건에 비하여 지지점과의 거리차이로 인하여 하악골에 가장 높은 등가 응력을 유발하였다. 7. 의치상 재료에 따른 하악 골에 발생되는 응력의 크기 및 분산에는 큰 차이가 없으나 금속상의 경우가 교합압을 분산하는데는 효과적이었다.

• The Journal of Korean Academy of Prosthodontics
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• v.50 no.4
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• pp.243-248
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• 2012

Purpose: The purpose of this study is to compare the removal torque between prefabricated and customized implant abutment screw. Materials and methods: Three types of implant system (Osstem, Astra, Zimmer) were used. For each system, prefabricated abutment screw (control group) and customized abutment screw (test group) were used to connect the fixture and the abutment (n = 6). Digital torque gauze was used to control the tightening torque and the screws were tightened under each manufacturer's recommendation. 10 minutes after the connection the same tightening torque was applied, and 5 minutes after the second connection, the removal torque was measured. This procedure was repeated 10 times. In the cyclic loading test, 10 minutes after the first connection to the 6 groups (n = 3), the same tightening torque was applied, and a total of 1,000,000 time loading was applied at 30 degree angle to long axis with 50 N load. Repeated measures of ANOVA test (${\alpha}$=.05) was used as statistics to evaluate the effect of repeated loading number on the removal torque. Independent t-test was used to evaluate the difference in removal torque after cyclic loading. Results: The removal torque significantly decreased as the number of loading repetition increased (P<.05). In the 10 time repetition test, there was no significant difference between the prefabricated and customized implant abutment screw of the 3 implant system (P<.05). Also in the cyclic loading test, there was no significant difference between the prefabricated and customized implant abutment screw of the 3 implant system (P<.05). Conclusion: Within the limitation of this study, there was no significant difference in the removal torque between the prefabricated abutment screw and customized abutment screws.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.31 no.4C
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• pp.127-136
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• 2011

The settlement of a compaction plate resting on the surface of rubble-mound and subjected to a vibrating vertical load can be characterized by a transient amplitude and a plastic settlement. As long as the maximum imposed load does not exceed the bearing capacity of the rubble-mound, plastic settlement will approach an ultimate value and essentially steady-state vibration will ensue. For the settlement behavior by vibro-compaction, most laboratory experiments were conducted on laterally confined samples with loads over the full surface area or on samples placed on a vibrating table. In the field, the loads cover only a small fraction of the surface area. In this study, crushed stones are loaded with the same as field condition. According to the vibro-compaction experiments on crushed stone, it was found that approximately 90% of total settlement occur within 2 minutes and plastic settlement increases with increasing cyclic stress levels including static and dynamic stress. A compaction equation on which the number of load cycles, amplitude of plate, settlement, width of plate, and cyclic stress are related each other is proposed.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.10
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• pp.868-874
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• 2007

Noises from the helicopter rotor model are calculated numerically at various pitch angles. The aerodynamic data are calculated by using prescribed wake model and unsteady panel method. The distribution of aerodynamic loads on the blade surface are obtained from $0^{\circ}$ to $9^{\circ}$ pitch angles with equiangular increments of $1.5^{\circ}$. Although thickness noise is not related to the change of pitch angles, loading noise level increases about 3~4dBA every $1.5^{\circ}$ increment of pitch angle. The additive noise level shows sufficient value to perceive the loudness. From the result of directivity pattern the sound level at the lower region of the blade disc plane is higher than that of the upper region.

• Journal of the Korea Concrete Institute
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• v.19 no.4
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• pp.433-439
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• 2007

The main objective of the paper is to investigate the static behavior of a prestressed concrete (PSC) girder that has been spliced with precast box segments. A 20 m long full-scale spliced PSC girder is fabricated and tested to compare its static performance against a monolithic girder. The monolithic girder has the same geometric and material properties with respect to the spliced girder. This includes infernal strain, deflections, neutral axis position, and crack patterns for both girders. The test also consists of monitoring relative displacements occurring across the joints. Both the horizontal displacement (gap) and vertical displacement (sliding) are measured throughout the loading procedure. All results have been compared to those obtained from the monolithic girder. It has been demonstrated that the spliced girder offers close behavior with respect to the monolithic girder up to the crack load. Both girders exhibits ductile flexural failure rather than abrupt shear failure at joints.

• Journal of the wind engineering institute of Korea
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• v.22 no.4
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• pp.171-177
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• 2018

In order to investigate the cause of damage of the offshore meteorological tower, the measured wind speed data were analyzed, the dynamic displacement due to fluctuating wind load and wave load was calculated, and the fatigue was examined for vortex-induced vibration. It was confirmed from the results that the vibration lasting for four hours occurred in the meteorological tower when the maximum wind speeds for 10 minutes were compared for both the vane anemometer and ultrasonic anemometer. The effect of the gust wind on the dynamic response of the meteorological tower was greater than the wave. However, the combined forces acting on the meteorological tower was much lower than the design force even though the wind and wave loads were simultaneously applied. The vortex-induced vibration seemed to be cause of the fatigue failure in the connecting bolts. The destruction of the offshore meteorological tower was considered to be a vortex-induced vibration, not a fluctuating fluid flows.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.45 no.10
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• pp.898-906
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• 2017

This paper discusses the efficient high fidelity calculation of external thermal loads of a spacecraft on its orbit. Thermal loads to a spacecraft consist of three major components, direct solar radiation, earth reflection of solar rays, and earth irradiation. With the assumption that both earth reflection and earth emission are diffuse, thermal loads from earth surface divided into pieces of segments to satellite surfaces are individually calculated and summed over. By using analytical integration of both reflected and emitted heat load by earth, high rate of numerical convergence is achieved and the results are even exactly calculated in special cases. Moreover, KD tree ray tracing is employed in the calculation of thermal load to determine whether the radiated ray is obstructed or not by satellite structure.

• Journal of the Korean Geotechnical Society
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• v.17 no.5
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• pp.115-128
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• 2001

본 논문에서는 반복하중이나 지진하중을 받는 지반-구조물 시스템의 설계에 필수적인 변수인 전단탄성계수와 감쇠비에 대한 연구를 국내에 존재하는 비점성토 지반에 대하여 수행하였다. 국내 퇴적토지반 및 풍화토지반에서 채취된 자연시료와 입도분포를 조정하여 제작한 시료를 포함하여 총 60개의 시료에 대하여 20kPa에서 500kPa의 구속응력 범위에서 공진주 시험을 수행하고, 이를 조립질 사질토, 실트 및 실트질 모래, 풍화토의 3개의 그룹으로 나누어 결과를 정리하였다. 저변형률 영역의 변형특성인 최대전단탄성계수와 최소감쇠비에 대하여 구속응력의 영향을 확인하였다. 최대전단탄성계수를 예측하는 경험식을 3개의 그룹별로 제안하였다. 최소감쇠비는 구속응력에 따른 분포영역을 제시하였다. 세립분이 적은 조립질 사질토의 경우, 비선형 변형특성이 구속응력의 영향을 뚜렷이 받고 있어 이를 주요한 변수로 고려하여 대표곡선과 분포영역을 제안하였다. 구속응력의 영향을 적게 받는 실트 및 실트질 모래와 풍화토는 구속응력에 관계없이 대표곡선과 분포영역을 제안하였다. 제안된 각 시료의 대표곡선과 기존의 Vucetic-Dobry와 Seed-Idriss가 제안한 곡선과 비교하였다. 본 논문의 연구결과는 국내지반의 비점성토 지반에 대한 지진해석이나 동하중을 받는 시스템의 해석시 유용하게 사용될 것으로 판단된다.

• Journal of Korean Society of Disaster and Security
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• v.7 no.1
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• pp.43-50
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• 2014

Based on the reliability theory, the risk assessment of steel beams is performed by the determination of failure probability. In the calculation, bending, shearing and combined (bending + shearing) modes are examined. The resistance and the loads on the beam are assumed to be normal distribution. To investigate the failure probability changes, total load applied at the mid span of beam is divided into 1 to 1 and 1 to 2 ratio and then these divided loads are placed on the trisected points on beam. The change of boundary conditions at beam ends are also included in the investigation. It shows that failure is governed by the combined mode for the present beams and the second order bound analysis of failure probability is not crucial. On the whole failure probability decreases with increasing end restraints at the beam ends with some exception.