• 한국기계가공학회지
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• 제10권6호
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• pp.63-69
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• 2011

This study analyzes stress, fatigue and vibration on main rotor and body of helicopter. The maximum stress is shown on adjoint part between body and main rotor at the lower position of main rotor. As the maximum displacement amplitude is happened at 4000Hz, there is no resonance and the state of helicopter becomes safe at hovering without the abnormal air current and the disabled rotor. Among the cases of nonuniform fatigue loads, 'SAE bracket history' with the severest change of load becomes most unstable but 'Sample history' becomes most stable. In case of 'Sample History' with the average stress of 0MPa to $-10^5MPa$ and the amplitude stress of 0MPa to $8.539{\times}10^5MPa$, the possibility of maximum damage becomes 3%. This stress state can be shown with 5 times more than the damage possibility of 'SAE bracket history' or 'SAE transmission'. The structural result of this study by using the analysis of vibration and fatigue can be effectively utilized for safe and durable design of helicopter.

• Steel and Composite Structures
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• 제20권3호
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• pp.719-729
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• 2016

There are great needs of simple but reliable mechanical nonlinear behavior analysis and performance evaluation method for frames constructed by steel and concrete composite beams or columns when the structures subjected extreme loads, such as earthquake loads. This paper describes an approach of simplified macro-modelling for composite frames consisting of steel-concrete composite beams and CFST columns, and presents the performance evaluation procedure based on the pushover nonlinear analysis results. A four-story two-bay composite frame underground is selected as a study case. The establishment of the macro-model of the composite frame is guided by the characterization of nonlinear behaviors of composite structural members. Pushover analysis is conducted to obtain the lateral force versus top displacement curve of the overall structure. The identification method of damage degree of composite frames has been proposed. The damage evolution and development of this composite frame in case study has been analyzed. The failure mode of this composite frame is estimated as that the bottom CFST columns damage substantially resulting in the failure of the bottom story. Finally, the seismic performance of the composite frame with high strength steel is analyzed and compared with the frame with ordinary strength steel, and the result shows that the employment of high strength steel in the steel tube of CFST columns and steel beam of composite beams benefits the lateral resistance and elasticity resuming performance of composite frames.

• 한국지진공학회논문집
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• 제25권6호
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• pp.251-259
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• 2021

Current seismic fragility functions for buildings were developed by defining damage state threshold based on story drift concerning foreign references and using the capacity spectrum method based on spectral displacement. In this study, insufficient details and dependence on the core location of piloti-type buildings were not reflected in the fragility function because it was developed before the Pohang earthquake. In order to develop an improved one for piloti-type buildings, several types of core were selected, damage state threshold was determined based on the capacity of structural members, and three-dimensional analyses were utilized. As a result, seismic fragility functions based on spectral acceleration were developed for various core locations and different shear strengths of the column stirrup. The fragility of piloti-type buildings significantly varied according to core location, an additional single wall, and whether the contribution of column stirrup was included or not. To estimate fragility more reasonably, it is necessary to prepare the parameters to reflect actual state well.

• Structural Engineering and Mechanics
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• 제72권2호
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• pp.191-201
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• 2019

Finite element analysis is one of the most used tools for studying femoral neck fracture. Nerveless, consensus concerning either the choice of material characteristics, damage law and /or geometric models (linear on nonlinear) remains unreached. In this work, we propose a numerical quasi-brittle damage model to describe the behavior of the proximal femur associated with two methods to evaluate the Young modulus. Eight proximal femur finite elements models were constructed from CT scan data (4 donors: 3 women; 1 man). The numerical computations showed a good agreement between the numerical curves (load - displacement) and the experimental ones. A very encouraging result is obtained when a comparison is made between the computed fracture loads and the experimental ones ($R^2=0.825$, Relative error =6.49%). All specific numerical computation provided very fair qualitative matches with the fracture patterns for the sideway fall simulation. Finally, the comparative study based on 32 simulations adopting linear and nonlinear meshing led to the conclusion that the quantitatively results are improved when a nonlinear mesh is used.

• 한국강구조학회 논문집
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• 제22권6호
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• pp.589-597
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• 2010

강구조물의 점검시 피로균열이 발견되는 경우에는 보수 보강 시행의 결정과 구조물의 점검주기 결정을 위한 균열의 현재 상태평가와 앞으로의 균열진행 정도에 대한 정량적인 예측이 요구된다. 피로균열에 대한 손상도 평가는 파괴역학 파라미터를 이용한 균열진전속도와 취성파단의 여부 결정이 대표적인 방법으로 파괴역학에 관한 전문적인 지식과 함께 수치해석 프로그램의 활용능력이 필요하다. 이에, 본 연구에서는 피로손상도 평가 방법에 관한 다양성을 확보하고, 파괴역학에 대한 전문적인 지식이 없는 기술자가 피로균열에 의한 강구조물의 손상도를 간편하게 평가 할 수 있는 방법을 개발하기 위한 첫 단계로, 관통균열 시험편을 이용한 균열진전시험을 실시하였다. 그리고 피로균열 표면으로부터 측정된 COD(Crack Opening Displacement)의 크기와 측정위치를 이용하여, 균열진전속도를 추정하기 위한 파라미터를 도출하고, 그 타당성을 분석하였다. 그리고 관통균열이 있는 시험편의 형상, 응력범위, 그리고 응력비에 상관없이 COD를 이용하여 피로균열진전속도를 추정할 수 있는 방법을 제시하였다.

• 한국구조물진단유지관리공학회 논문집
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• 제15권2호
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• pp.179-188
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• 2011

강부재의 피로가 주요원인이 되어 구조물이 붕괴되거나 교체되는 사례를 찾아보기 어렵다. 이처럼 사실상 피로에 대해서는 손상을 허용하고 있지만, 발견되는 피로균열에 대한 직접적인 상태평가는 이루어지지 않고 있다. 피로균열에 대한 진전 비진전성의 판단 및 균열진전속도의 평가가 이루어져야만, 합리적인 보수 보강 공법의 선정과 시행시기가 결정될 수 있을 것이다. 본 연구에서는 측정되는 COD(Crack Opening Displacement)를 통한 피로균열진전속도 평가법을 검토하기 위하여, 2종류의 관통 균열 시험편과 면외거셋 용접이음 시험편의 균열진전시험을 실시하였다. 그리고 실용적인 COD의 측정을 위해 변형률 게이지를 이용하는 방법에 대해 검토하였다. 그 결과, COD 측정을 통한 균열진전속도의 합리적인 평가법을 제안하였고, 변형률 게이지를 이용한 성공적인 COD 측정을 실험적으로 증명하였다.

• 복식문화연구
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• 제22권2호
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• pp.290-299
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• 2014

This research sought to analyze the characteristics of breast movement at the treadmill activity levels. It also examined the effect of wearing a sports bra in reducing breast displacement. The subjects for the data collection were females in their 20s (n=2) with C-cup size breast. The experimental conditions were three different moving speeds (4 km/h, jogging: 7 km/h, and sprinting: 10 km/h) and two types of sports bras. Three dimensional breast displacement was measured. The displacement of the right nipple point was measured with a 3D motion analyzer. The results show that the breasts were greatly displaced from the walking speed (4 km/h) when subjects did not wear any bra. Whereas their breast displacement distance decreased remarkably when they wore sports bras. The nipple point moved 42~44 mm in the vertical direction at walking speed with naked condition. But it was reduced by 80% after wearing sports bras. When subjects running (7 km/h, 10 km/h) without any bra, the nipple point moved 122~141 mm. However it was reduced by 60~70% when they wore sports bras. The apartment time (time delay) between at the highest point of the upper body and the nipple was 0.25 seconds at the running speeds (7 km/h, 10 km/h) without wearing any bra. After wearing sports bras, the time delay was cut to 0.06~0.12 seconds. These results implies that without wearing any bra the skin surrounding the breasts might be seriously pulled at running activity. The functional sports bra suppress breast movement. It might prevent the sagging of breasts by preventing the damage of the Cooper's ligaments.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2008년도 춘계 학술발표회 제20권1호
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• pp.73-76
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• 2008

지진에 의한 피해는 지진이 가지는 불확실성으로 인하여 확률적으로 예측하여야 한다. 취약도 분석은 교량구조물의 피해를 지반가속도에 따른 확률로 나타내고 주어진 지진파에 대한 손상확률의 단계를 추정할 수 있다. 본 연구에서는 프리스트레스트 콘크리트 교량에 대한 수치적 시뮬레이션에 의한 취약도 곡선을 산출하기위해 해석적 연구를 수행하였다. 이를 위해 지반조건에 따라 각각 100개의 인공지 진파를 생성하고 비선형 시간이력해석을 수행하였다. 손상단계는 기존의 실험결과에 기초한 성능기반에 따라 정의하였으며 RC 교각의 지진거동을 변위연성도로 나타내었다. 손상단계 및 지반가속도를 이용하여 PSC교량의 지반조건에 따른 손상곡선을 도출하여 비교분석하였다. 연구결과에 따르면 지반조건 및 구속철근량에 따른 손상확률의 차이를 확인할 수 있다.

• 한국방재학회 논문집
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• 제5권4호
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• pp.95-105
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• 2005

우리나라는 비교적 안정된 판 내부에 존재한다. 하지만, 1976년 안전지대로 평가된 중국 탕산지역의 대규모 지진이 발생한 것처럼 우리나라도 지진에 대해 안전한 지역이라고 단언할 수는 없다. 게다가, 지진학자들도 국내에서 중규모 이상의 지진발생 가능성이 높다고 지적하고 있다. 이러한, 지진은 자체를 예방할 수 없기 때문에 내진설계에 대한 연구와 지진재해 관리체계에 대한 연구가 전반적으로 이루어지고 있다. 그러나, 지진발생 시 초기 대응이나 수습과정에 대한 연구는 미비한 상태이며, 지진피해 평가시스템 구축을 위한 극소수의 연구가 진행되고 있는 실정이다. 따라서, 본 연구는 국내실정을 고려한 지진피해 평가시스템 구축을 위한 기초자료를 제시함을 목적으로 한다. 이를 위하여 강남구 비내진 철근콘크리트 아파트를 표준형 건축물로 선정하여 지진피해를 예측하고, 취약도 함수의 도출과 층간변위에 따른 피해평가를 행하여 HAZUS 프로그램 취약도 함수 적용결과와 비교 분석한다.

• International Journal of Precision Engineering and Manufacturing
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• 제3권2호
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• pp.95-101
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• 2002

The propagation rate(da/dt) prediction parameter and the microstructure properties of creep crack in domestic 3.3NiCrMov steel were investigated at 550$\^{C}$ by using 0.5" CT specimen under constant load(4090N) and constant Ct(300∼4000N/mhr) condition that was maintained during crack growth of 1mm distance. C＊ usually increased with crack length though load was reduced in order to maintain constant Ct value as crack growth and considerably showed the scatter band, but Ct depended on load line displacement rate and represented a good relation with da/dt. At constant toad and Ct region, crack growth slope was 0.900 and 0.844 each, in the other hand C＊ slope was 0.480. Fully coalesced area(FCA) ahead of crack tip was increased as Ct value increase to the critical value, and after that value FCA decreased. The average diameter ditribution of cavity in FCA showed the greatest value about 1.5 ㎛ when Ct=2000N/mhr. The increasing of Ct in FCA view point enlarged the size of damage area and the size reached to maximum 800 ㎛ when Ct=2000N/mhr.