• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2008년도 추계 학술발표회 제20권2호
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• pp.289-292
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• 2008

본 논문에서는 고장력 철근이 적용된 휨부재의 구조성능과 사용성능에 대하여 실험적으로 연구하였다. 고장력 철근에 관련된 기존 연구결과에 따르면, RC보의 인장철근을 고장력 철근으로 사용할 경우, SD400에 비해 철근의 물량을 경감시킬 수 있는 장점이 있으나, 균열 폭과 처짐이 증가되는 등 부정적인 영향이 있다고 알려졌다. 따라서 본 논문에서는 고장력 철근을 사용함으로써 휨부재의 성능에 미치는 영향을 분석하는 것을 목적으로 하였다. 이에 철근강도를 변수로 SD400, SD600, SD700의 3개 시험체를 제작하여 실험을 수행하였다. 본 연구의 실험 결과, 동일 철근비 사용 시 고장력 철근의 부재 강성이 감소되는 현상을 나타내었으나, 부재의 전체적인 휨내력은 배근된 철근의 강도 및 철근량에 비례하여 나타나는 것을 확인할 수 있었다. 또한, 고장력 철근 사용시 균열갯수 및 최대 균열폭에 큰 변화가 없으므로 사용성 면에서 큰 문제는 없는 것으로 분석되었다.

• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 2005년도 춘계학술대회 논문집
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• pp.405-410
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• 2005

현재 압력이나 가속도를 측정하기 위해 사용되는 반도체 센서 중에서 압저항 센서가 가장 광범위하게 적용되고 있다. 이러한 압저항 센서는 반도체 공정에 의해서 제작되고, 기존의 센서보다 높은 민감도를 가지므로 그 적용성이 매우 높다. 하지만, 압저항 센서를 형성하는 구조물의 형상과 관련된 연구가 국내에서 미비하므로 이에 대한 연구가 요구된다. 본 연구에서는 과도한 압력에 센서를 보호하기 위한 보스(Boss)와 민감도 향상을 위해 사용되는 매스(Seismic Mass)의 기하학적 변화가 민감도에 미치는 영향을 압저항 분포를 통하여 분석하고, 적절한 위치와 크기를 제시하고자 한다.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2004년도 춘계학술발표회
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• pp.968-976
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• 2004

본 논문에서는 여러 가지 입도의 사질토에 폴리프로필렌(polypropylene) 재질의 단섬유(staple fiber)를 중량비 0.3%로 혼합한 섬유혼합도의 거동특성과 보강효과를 평가하였다. 곡류계수는 일정하게 유지하고 균등계수를 변화시켜 성형한 공사체에 공진주시험을 수행하였다. 섬유혼합토의 최대전단탄성계수는 비혼합토에 비해 최대 30%까지 증가하였고, 비선형 영역에서의 전단탄성계수 감소량도 억제되었다. 섬유혼합토의 정규화 전단탄성계수 감소곡선이 Seed와 Idriss의 대표곡선 상한값 쪽으로 이동해, 비혼합토보다 얇은 밴드로 분포하여 섬유의 혼합이 흙의 강성 증가에 효과적임을 증명되었다.

• 콘크리트학회논문집
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• 제17권3호
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• pp.435-444
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• 2005

본 연구에서는 휨모멘트와 축력의 효과가 고려된 변환각 트러스 모델(TATM)을 이용하여 철근콘크리트 기둥의 전단거동을 예측하였다. TATM의 해석결과를 검증하기 위하여 다양한 전단경간비와 축력비를 가지는 총 9개의 철근콘크리트 기둥을 전단 실험하였다. 철근콘크리트 기둥의 곡률, 축변형 및 전단변형을 측정하기 위하여 기둥 옆면 전단위험단면을 중심으로 5개의 변위변환기(LVDT)를 설치하였다. 하중은 최대하중의 $85\%$ 이하로 떨어질 때까지 가력하였으며, 모든 실험체는 휨 철근의 항복이전에 전단파괴 되었다. 기둥의 전단강도와 강성은 축 하중이 증가할수록 증가하는 반면 전단경간비가 증가할수록 감소하였다. TATM으로부터 얻은 전단응력-전단변형률 관계와 전단응력-전단철근변형률 관계는 본 연구에서 수행된 실험결과와 잘 일치하였으며, 기존의 트러스 모델(MCFT, RA-STM, FA-STM)보다 더 우수하였다.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2005년도 추계학술발표대회 논문집
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• pp.179-184
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• 2005

In the present study, conceptual design of the main wing for 20 seats WIG{wing in Ground Effect) flight vehicle, which will be a high speed maritime transportation system for the next generation, was performed. The high stiffness and strength Carbon-Epoxy material was used for the major structure and the skin-spar with a foam sandwich structural type was adopted for improvement of lightness and structural stability. As a design procedure for this study, firstly the design load was estimated with maximum flight load, and then flanges of the front and the rear spar from major bending load and the skin structure and the webs of the spars were preliminarily sized using the netting rules and the rule of mixture. In order to investigate the structural safety and stability, stress analysis was performed by Finite Element Codes such as NASTRAN/PA TRAN[6] and NISA II [7]. From the stress analysis results, it was confirmed that the upper skin structure between the front spar and rear spar was very unstable for the buckling. Therefore in order to solve this problem, a middle spar and the foam sandwich structure at the upper skin and the web were added. After design modification, even thought the designed wing weight was a little bit heavier than the target wing weight, the structural safety and stability of the final design feature was confirmed. Moreover, in order to fix the wing structure at the fuselage, the insert bolt type structure with six high strength bolts was adopted for easy assembly and removal.

• The Journal of Korean Physical Therapy
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• 제25권2호
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• pp.56-63
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• 2013

Purpose: This study was conducted in order to examine how an effective rehabilitation exercise program influences the activity of shoulder muscles, and to help the clinical application of a rehabilitation program, for prevention and relief of pain, adhesion, and joint stiffness of patients who undergo rotator cuff repair. Methods: Nine test subjects were placed randomly into each group for a total of 27 subjects and exercise program interventions according to the group were conducted for six weeks, after which maximum voluntary isometric contraction (%MVIC) value was re-measured for supraspinatus muscle, infraspinatus muscle, serratus anterior muscle, and middle deltoid muscle in all groups in order to compare changes in muscle activity before and after the experiment in order to perform comparative analysis of changes in muscle activity between groups, based on which four experimental hypotheses were confirmed. Results: Changes in muscle activity according to %MVIC showed a statistically significant difference (p<0.01) (p<0.001) in all muscles, except the middle deltoid muscle, and post-verification results showed that changes in muscle activity according to %MVIC were greater in test groups I and II, compared with the control group, for the supraspinatus muscle, infraspinatus muscle, and serratus anterior muscle. Conclusion: Therefore, rehabilitation through use of the methods described above should be applied efficiently in clinical settings and more research in development of much more efficient rehabilitation program interventions must be conducted.

• Earthquakes and Structures
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• 제7권4호
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• pp.571-586
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• 2014

This paper presents experimental and numerical study on seismic performance of a super tall steel tower structure. The steel tower, with a height of 388 meters, employs a steel space truss with spiral steel columns to serve as its main lateral load resisting system. Moreover, this space truss was surrounded by the spiral steel columns to form a steel mega system in order to support a 12-story platform building which is located from the height of 230 meters to 263 meters. A 1/40 scaled model for this tower structure was made and tested on shake table under a series of one- and two-dimensional earthquake excitations with gradually increasing acceleration amplitudes. The test model performed elastically up to the seismic excitations representing the earthquakes with a return period of 475 years, and the test model also survived with limited damages under the seismic excitations representing the earthquakes with a return period 2475 years. A finite element model for the prototype structure was further developed and verified. It was noted that the model predictions on dynamic properties and displacement responses agreed reasonably well with test results. The maximum inter-story drift of the tower structure was obtained, and the stress in the steel members was investigated. Results indicated that larger displacement responses were observed for the section from the height of 50 meters to 100 meters in the tower structure. For structural design, applicable measures should be adopted to increase the stiffness and ductility for this section in order to avoid excessive deformations, and to improve the serviceability of the prototype structure.

• Steel and Composite Structures
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• 제33권6호
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• pp.793-803
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• 2019

Concrete-filled steel tubular (CFST) beam-columns are widely used owing to their good performance. They have high strength, ductility, large energy absorption capacity and low costs. Externally stiffened CFST beam-columns are not used widely due to insufficient design equations that consider all parameters affecting their behavior. Therefore, effect of various parameters (global, local slenderness ratio and adding hoop stiffeners) on the behavior of CFST columns is studied. An experimental study that includes twenty seven specimens is conducted to determine the effect of those parameters. Load capacities, vertical deflections, vertical strains and horizontal strains are all recorded for every specimen. Ratio between outer diameter (D) of pipes and thickness (t) is chosen to avoid local buckling according to different limits set by codes for the maximum D/t ratio. The study includes two loading methods on composite sections: steel only and steel with concrete. The case of loading on steel only, occurs in the connection zone, while the other load case occurs in steel beam connecting externally with the steel column wall. Two failure mechanisms of CFST columns are observed: yielding and global buckling. At early loading stages, steel wall in composite specimens dilated more than concrete so no full bond was achieved which weakened strength and stiffness of specimens. Adding stiffeners to the specimens increases the ultimate load by up to 25% due to redistribution of stresses between stiffener and steel column wall. Finally, design equations previously prepared are verified and found to be only applicable for medium and long columns.

• Smart Structures and Systems
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• 제25권5호
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• pp.515-530
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• 2020

A new type of pure torsional yielding damper made from steel pipe is proposed and introduced. The damper uses a special mechanism to apply force and therefore applies pure torsion in the damper. Uniform distribution of the shear stress caused by pure torsion resulting in widespread yielding along pipe and consequently dissipating a large amount of energy. The behavior of the damper is investigated analytically and the governing relations are derived. To examine the performance of the proposed damper, four types of the damper are experimentally tested. The results of the tests show the behavior of the system as stable and satisfactory. The behavior characteristics include initial stiffness, yielding load, yielding deformation, and dissipated energy in a cycle of hysteretic behavior. The tests results were compared with the numerical analysis and the derived analytical relations outputs. The comparison shows an acceptable and precise approximation by the analytical outputs for estimation of the proposed damper behavior. Therefore, the relations may be applied to design the braced frame system equipped by the pure torsional yielding damper. An analytical model based on analytical relationships was developed and verified. This model can be used to simulate cyclic behavior of the proposed damper in the dynamic analysis of the structures equipped with the proposed damper. A numerical study was conducted on the performance of an assumed frame with/without proposed damper. Dynamic analysis of the assumed frames for seven earthquake records demonstrate that, equipping moment-resisting frames with the proposed dampers decreases the maximum story drift of these frames with an average reduction of about 50%.

• 한국지진공학회논문집
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• 제5권6호
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• pp.47-54
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• 2001

가새형 소성 감쇠기는 에너지 소산 이력거동을 통해 강한 지진하중을 받는 구조물의 구조적 손상을 방지하거나 감소시킨다. 본 연구에서는 성능수준 만족을 위한 가새형 소성 금비기의 직접적인 설계 방법을 개발하였다. 많은 해석 시간이 요구되는 비선형 동적 시간이력해석 대신 비선형 정적해석법인 능력스펙트럼법을 이용하여 주어진 성능을 만족하기 위하여 필요한 유효 감쇠비를 구한 후 이를 이용하여 가새형 소성 감쇠기의 크기를 구하였다. 각 설계변수의 영향을 파악하기 위하여 단자유도계에서 구조물의 주기, 요구되는 탄성강도에 대한 항복강도의 비, 항목 후 강성비, 가새형 소성 감쇠기의 항복응력 등을 변수로 하여 해석을 수행하였다. 본 연구를 통해 제안된 방법을 5층과 10층 건물에 적용하여 검증하였다. 시간이력해석 결과, 제안된 방법에 따라 설계된 가새형 소성 감쇠기를 설치한 예제 구조물의 최대응답은 주어진 목표변위와 잘 일치하였다.