• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2000년도 봄 학술발표회 논문집
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• pp.393-398
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• 2000

To use concrete box culverts effectively, precast goods are manufactured at a factory, then linked and anchored with prestressing tendon at a field. However, the corrosion of rebar and prestressing tendon in the box culverts utilizing portland cement concrete is issued when the cracks occur at a underground water level. It has been reported that reported that expansive concrete, compared with portland cement concrete, has many structural advantages such as increasing capacity of watertight, controling initial crack and improving durability due to its property of expansion. During flexure test with RC beam made from expansive concrete, in the case of a constant section of concrete element, the lower steel ratio is, and in the case of a constant steel ratio, the more incremental the section of concrete element, the more incremental the amount of chemical prestress by expansive concrete is. At the segment of the box culverts using expansive concrete, the numbers of crack and its gap is reduced, and ultimate load and initial crack load is much larger than the segment at which expansive concrete is nor used. Also lay-out of tendon with a curvature generate upward force so that deflection is reduced. Through the whole procedure, it could be confirmed that performance precast box culvert by means of using expansive concrete is improved.

• 한국군사과학기술학회지
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• 제15권4호
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• pp.359-365
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• 2012

In the soft recoil system, the recoiling parts are initially accelerated to the forward direction. These parts are returned to original position by the firing with intial acceleration speed. The latch of the soft recoil system keeps the high impact load when the recoil parts were recuperated to the forward direction. In this study, the latch of soft recoil system using the ADAMS program was analyzed. The optimal operation parameters were found that max. angle and expansion length of latch was $50^{\circ}$, 180 mm respectively. Dynamic structural analyses of model cases were performed using finite element model. The max. stress and deflection of latch was 230 MPa and 0.45 mm respectively.

• 한국추진공학회지
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• 제22권6호
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• pp.19-27
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• 2018

본 논문에서는 E-D 노즐 공압 실험 연구의 선행 연구로써, 노즐 압력비에 따라 변화하는 E-D 노즐특성 파악을 위한 해석적 연구가 수행되었다. 설계 변수 중, 핀틀 변곡 각도를 하나의 변수로 하여 서로 다른 세 가지 수치해석 모델을 설계하였다. 노즐 압력비가 낮을 때는 E-D 노즐 내부로 외부 대기가 유입되어 개방 유동장이 형성되었다. 노즐 압력비가 높아짐에 따라 노즐 내부에 재순환 영역이 고립되는 폐쇄 유동장으로 유동 천이가 발생함을 확인하였다. 또한, 전체 노즐 압력비 구간에서 핀틀 변곡 각도가 높은 해석 모델에서 가장 높은 추력 계수가 도출되었다.

• Structural Engineering and Mechanics
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• 제71권5호
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• pp.469-483
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• 2019

In this paper, an improved mathematical model is presented for the bending analysis of doubly curved functionally graded material (FGM) sandwich rhombic conoids. The mathematical model includes expansion of Taylor's series up to the third degree in thickness coordinate and normal curvatures in in-plane displacement fields. The condition of zero-transverse shear strain at upper and lower surface of rhombic conoids is implemented in the present model. The newly introduced feature in the present mathematical model is the simultaneous inclusion of normal curvatures in deformation field and twist curvature in strain-displacement equations. This unique introduction permits the new 2D mathematical model to solve problems of moderately thick and deep doubly curved FGM sandwich rhombic conoids. The distinguishing feature of present shell from the other shells is that maximum transverse deflection does not occur at its center. The proposed new mathematical model is implemented in finite element code written in FORTRAN. The obtained numerical results are compared with the results available in the literature. Once validated, the current model was employed to solve numerous bending problems by varying different parameters like volume fraction indices, skew angles, boundary conditions, thickness scheme, and several geometric parameters.

• Structural Engineering and Mechanics
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• 제76권6호
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• pp.765-779
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• 2020

This article presents a nonclassical size dependent model based on the modified couple stress theory to study and analyze the bending behavior of perforated microbeams under different loading patterns. Modified equivalent material and geometrical parameters for perforated beam are presented. The modified couple stress theory with one material length scale parameter is adopted to incorporate the microstructure effect into the governing equations of perforated beam structure. The governing equilibrium equations of the perforated Timoshenko as well as the perforated Euler Bernoulli are developed based on the potential energy minimization principle. The Poisson's effect is included in the governing equilibrium equations. Regular square perforation configuration is considered. Based on Fourier series expansion, closed forms for the bending deflection and the rotational displacements are obtained for simply supported perforated microbeams. The proposed methodology is validated and compared with the available results in the literature and an excellent agreement is detected. Numerical results demonstrated the applicability of the proposed methodology to investigate the bending behavior of regularly squared perforated beams incorporating microstructure effect under different excitation patterns. The obtained results are significantly important for the design and production of perforated microbeam structures.

• Structural Engineering and Mechanics
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• 제83권6호
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• pp.757-770
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• 2022

In this paper, the vibration of a moderately thick plate to a moving mass is investigated. Pasternak foundation with a variable subgrade modulus is considered to tackle the shortcomings of Winkler model, and an analytical-numerical solution is proposed based on the eigenfunction expansion method. Parametric studies by using both CPT (Classical Plate Theory) and FSDT (First-Order Shear Deformation Plate Theory) are carried out, and, the differences between them are also highlighted. The obtained results reveal that utilizing FSDT without considering the rotary inertia leads to a smaller deflection in comparison with CPT pertaining to a thin plate, while it demonstrates a greater response for plates of higher thicknesses. Moreover, it is shown that CPT is unable to properly capture the variation of the plate thickness, thereby diminishing the accuracy as the thickness increases. The outcomes also indicate that the presence of a foundation contributes more to the dynamic response of thin plates in comparison to moderately thick plates. Furthermore, the findings suggest that the performance of the moving force approach for a moderately thick plate, in contrast to a thin plate, appears to be acceptable and it even provides a much better estimation in the presence of a foundation.

• Structural Engineering and Mechanics
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• 제82권1호
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• pp.31-40
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• 2022

In structural engineering, the material properties of the structures such as elastic modulus, shear modulus, density, and size may not be deterministic and may vary at different locations. The dynamic response analysis of such structures may need to consider these properties as stochastic. This paper introduces a stochastic finite element method (SFEM) approach to analyze moving loads problems. Firstly, Karhunen-Loéve expansion (KLE) is applied for expressing the stochastic field of material properties. Then the mathematical expression of the random field is substituted into the finite element model to formulate the corresponding random matrix. Finally, the statistical moment of the dynamic response is calculated by the point estimation method (PEM). The accuracy and efficiency of the dynamic response obtained from the KLE-PEM are demonstrated by the example of a moving load passing through a simply supported Euler-Bernoulli beam, in which the material properties (including elastic modulus and density) are considered as random fields. The results from the KLE-PEM are compared with those from the Monte Carlo simulation. The results demonstrate that the proposed method of KLE-PEM has high accuracy and efficiency. By using the proposed SFEM, the random vertical deflection of a high-speed railway (HSR) bridge is analyzed by considering the random fields of material properties under the moving load of a train.

• Nuclear Engineering and Technology
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• 제27권6호
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• pp.811-824
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• 1995

CANDU 핵연료봉의 휨 열적 휨 멘트와 수력학적 견인력 및 기계적 하중에 기인하는 휨 모멘트에 의하여 일어난다. 여기서, 연료봉 휨은 연료봉 축방향 중심선으로부터의 측면 처짐으로 정의한다. 본 논문에서는 연료봉 축방향 중심선에 대한 비대칭 온도불포에 의해 핵연료 피복관 자체와 피복관과 소결체의 상호작용 부위에서 발생하는 열적 휨만을 취급한다. 이를 위해 1).소결체와 피복관사이의 기계적 상호작용을 무시한 조건에서의 핵연료 피복관의 휨과 2) 소결체와 피복관의 온도 변화에 기인하여 발생하는 소결체와 피복관 사이의 기계적 상호작용을 고려한 조건에서의 연료봉 휨을 혼합 고려하고, 각각에서 피복관의 비대칭 온도분포가 (i) 냉각재의 불완전한 혼합에 따른 비균질 냉각재 온도, (ii) 핵연료 피복관과 냉각재 사이의 비균질한 열전달 계수, (iii) 핵연료내 반경 방향으로의 중성자속 감쇄에 의한 비대칭 열 발생 등의 복합적효과에 의해 발생되는 것으로 고려하여 피복관의 대칭온도 분포까지 포함 할 수 있는 열적 휨의 일반적 해석 공식을 제시하였다. 본 휨 공식에 사용되는 모든 변수에 대한 민감도 분석을 통해, 핵연료봉 길이, 피복관 내경, 냉각재 평균 온도 및 변화 인자, 소결체 -피복관 기계적 상호 작용 인자, 중성자속 감쇄 인자, 핵연료 열팽창 계수, 피복관-냉각재 열전도 계수 등의 변화가 피복관 두께, 피복관-냉각재 열전달 계수, 피복관 열팽창 계수, 핵연료-피복관 열전달 계수 등의 변화보다 핵연료봉의 열적 휨에 상대적으로 더욱 영향을 미치는 것으로 밝혀졌다.

• 한국추진공학회지
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• 제20권3호
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• pp.87-95
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• 2016

본 논문에서는 E-D 노즐을 설계하여 고도 보정에 대한 효과와 Throttling에 대한 가능성 연구를 수행하였다. 고도 보정에 대한 효과를 확인하기 위하여 연소실 압력을 일정하게 유지하며, 총 3가지(해수면, 고도 10 km, 고도 16 km)의 외부 대기환경 조건을 이용하여 해석적 연구를 수행하였다. 그 결과 고도가 상승할수록 유효 노즐 출구 면적 역시 점점 증가하였으며 이로 인하여 추력도 증가하였다. 또한 Throttling에 대한 가능성을 파악하기 위하여 핀틀의 위치를 연소실 쪽으로 후진시켜 노즐 목 면적을 작게 모델링하여 해석적 연구를 수행하였다. 일반적인 핀틀 추력기와 동일하게 노즐 목 면적이 줄어들수록 연소실 압력이 상승하며 추력 역시 증가하였다.

• 한국농공학회지
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• 제40권5호
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• pp.68-79
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• 1998

In the years, the concern about high-strength concrete which is new material has been heightened as a result of active research and development. Recently, as the building structure has been being bigger, higher, longer and more specialized, the demand of material with high-strength concrete for building has been increasing. The demand of high -strength concrete is expected to increase with expansion of usage about the complex concrete structures such as bridge structure as well as nuclear plants, underground structures, hydraulic structures and arctic area sturctures. In this research, silica-fume was used as an admixture in order to get a high-strength concrete. Water/binder ration was limited no more than 18 percent and the amount of unit cement was increased. In this study, a number of trial in concrete mix was carried out to get optimal mix design, and the target slump with $10{\pm}2cm$ was set for in-situ construction. High-strength concrete with cylinder strength of 1,200kgf/$cm^2$ in the 28-days was produced and tested. The static test was carried out to measure the ultimate load, the initial load of flexural and diagonal cracking, crack patterns, fracture modes. The load versus strain and load versus deflection relations were obtained form the static test. The test results were compared with the shear strengths predicted by the equations of ACI code 318-89 and orther researchers. Based on the test results, shear strength equation of reinforced concrete beam using high strength concrete was proposed. Form an evaluation of the results of this experimental investigation, it was concluded that shear strength after diagonal tention cracking diminished with the increase in compressive strength for beams.