• 한국강구조학회 논문집
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• 제19권2호
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• pp.139-146
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• 2007

국내 LRFD 도로교설계규정의 휨에 대한 재료 저항계수 정립 시 기초 통계자료로 활용하기 위하여 국산 강재를 적용한 강합성 플레이트 거더 단면의 정모멘트 및 부모멘트 하 휨저항강도를 통계적으로 분석하였다. 최근 국내에서 생산된 16,000여 표본의 구조용 강재와 철근에 대한 항복강도와 인장강도 등의 기계적 특성을 통계적으로 분석하여, 공칭강도에 대한 편심계수(bias factor)와 변동계수(coefficient of variation)를 구하였다. 이들 국산 강재와 철근을 적용하여 정 부모멘트를 받는 도로교 강합성 플레이트 거더교 대표단면에 대한 재료 비선형 소성해석을 수행하였으며, 해석결과로부터 모멘트-곡률 곡선을 구하고 단면의 휨저항강도를 산정하였다. 공칭휨강도와 극한휨저항강도를 비교하고 대표적 강합성 단면에 대한 편심계수와 변동계수 통계치를 제시하였다.

• Wind and Structures
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• 제29권5호
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• pp.339-359
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• 2019

Pre-stressed concrete poles are among the supporting systems used to support transmission lines. It is essential to protect transmission line systems from harsh environmental attacks such as downburst wind events. Typically, these poles are designed to resist synoptic wind loading as current codes do not address high wind events in the form of downbursts. In the current study, the behavior of guyed pre-stressed concrete Transmission lines is studied under downburst loads. To the best of the authors' knowledge, this study is the first investigation to assess the behaviour of guyed pre-stressed concrete poles under downburst events. Due to the localized nature of those events, identifying the critical locations and parameters leading to peak forces on the poles is a challenging task. To overcome this challenge, an in-house built numerical model is developed incorporating the following: (1) a three-dimensional downburst wind field previously developed and validated using computational fluid dynamics simulations; (2) a computationally efficient analytical technique previously developed and validated to predict the non-linear behaviour of the conductors including the effects of the pretension force, sagging, insulator's stiffness and the non-uniform distribution of wind loads, and (3) a non-linear finite element model utilized to simulate the structural behaviour of the guyed pre-stressed concrete pole considering material nonlinearity. A parametric study is conducted by varying the downbursts locations relative to the guyed pole while considering three different span values. The results of this parametric study are utilized to identify critical downburst configurations leading to peak straining actions on the pole and the guys. This is followed by comparing the obtained critical load cases to new load cases proposed to ASCE-74 loading committee. A non-linear failure analysis is then conducted for the three considered guyed pre-stressed concrete transmission line systems to determine the downburst jet velocity at which the pole systems fail.

• 한국방재학회 논문집
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• 제11권1호
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• pp.7-13
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• 2011

지진에 대한 장대 교량의 정확한 반응 해석은 지진 방재에 있어서 중요한 역할을 한다. 본 논문은 비동기 다지지점 지진입력에 의한 교량의 반응을 진동수 영역방법과 시간 영역방법으로 해석하였으며 그 결과를 동기 입력 결과와 비교하였다. 시간영역방법에서는 선형모드 중첩 법으로 최대반응 값을 계산하였다. 진동수영역방법에서는 선형랜덤진동 이론을 사용하여 교량 성능에 영향을 미치는 모드와 다지지점 지진입력의 상호상관관계를 고려한 반응의 제곱평균근(RMS값)을 계산하였다. 교량 성능 반응 중, 변위 및 부재의 내력에 대한 시간 영역해석 결과와 진동수영역 해석 결과로부터 최대반응 값과 RMS값의 비로 정의된 최대반응 계수의 실용적인 값과 계산 방법을 요약하였다. 신뢰 있는 최대 반응계수가 있으면, 교량의 성능기반설계에서 구체적인 임의의 입력을 고려한 시간영역방법보다 결과의 일반성 및 수치적인 장점을 갖은 진동수영역방법이 더 효율적이다.

• Structural Engineering and Mechanics
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• 제68권5호
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• pp.603-619
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• 2018

In this research, an effective computational technique is carried out for nonlinear and post-buckling analyses of cracked imperfect composite plates. The laminated plates are assumed to be moderately thick so that the analysis can be carried out based on the first-order shear deformation theory. Geometric non-linearity is introduced in the way of von-Karman assumptions for the strain-displacement equations. The Ritz technique is applied using Legendre polynomials for the primary variable approximations. The crack is modeled by partitioning the entire domain of the plates into several sub-plates and therefore the plate decomposition technique is implemented in this research. The penalty technique is used for imposing the interface continuity between the sub-plates. Different out-of-plane essential boundary conditions such as clamp, simply support or free conditions will be assumed in this research by defining the relevant displacement functions. For in-plane boundary conditions, lateral expansions of the unloaded edges are completely free while the loaded edges are assumed to move straight but restricted to move laterally. With the formulation presented here, the plates can be subjected to biaxial compressive loads, therefore a sensitivity analysis is performed with respect to the applied load direction, along the parallel or perpendicular to the crack axis. The integrals of potential energy are numerically computed using Gauss-Lobatto quadrature formulas to get adequate accuracy. Then, the obtained non-linear system of equations is solved by the Newton-Raphson method. Finally, the results are presented to show the influence of crack length, various locations of crack, load direction, boundary conditions and different values of initial imperfection on nonlinear and post-buckling behavior of laminates.

• Structural Engineering and Mechanics
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• 제83권6호
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• pp.709-727
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• 2022

Fastening systems have a significant role in the response of railway slab track systems. Although experimental tests indicate nonlinear behavior of fastening systems, they have been simulated as a linear spring-dashpot element in the available literature. In this paper, the influence of the nonlinear behavior of fastening systems on the slab track response was investigated. In this regard, a nonlinear model of vehicle/slab track interaction, including two commonly used fastening systems (i.e., RFFS and RWFS), was developed. The time history of excitation frequency of the fastening system was derived using the short time Fourier transform. The model was validated, using the results of a comprehensive field test carried out in this study. The frequency response of the track was studied to evaluate the effect of excitation frequency on the railway track response. The results obtained from the model were compared with those of the conventional linear model of vehicle/slab track interaction. The effects of vehicle speed, axle load, pad stiffness, fastening preload on the difference between the outputs obtained from the linear and nonlinear models were investigated through a parametric study. It was shown that the difference between the results obtained from linear and nonlinear models is up to 38 and 18 percent for RWFS and RFFS, respectively. Based on the outcomes obtained, a nonlinear to linear correction factor as a function of vehicle speed, vehicle axle load, pad stiffness and preload was derived. It was shown that consideration of the correction factor compensates the errors caused by the assumption of linear behavior for the fastening systems in the currently used vehicle track interaction models.

• International Journal of Computer Science & Network Security
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• 제21권12호
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• pp.309-315
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• 2021

The purpose of the article is to analyze the functioning of economic systems in the context of the development of their potential in a circular economy. It is determined that the functioning of economic systems to ensure their sustainability should meet modern challenges and provide for the formation of competitive institutional architecture, the introduction of structural and regulatory innovations, the transition to an innovative model of development. The specific principles of functioning of economic systems include openness, nonlinearity, multivectority, dynamism, emergence, uncertainty about the development of economic processes. It is substantiated that the linear nature of development and equilibrium are not dominant in the functioning of economic systems, and increasing the level of economic efficiency should go hand in hand with minimizing the activities of enterprises, which necessitates the use of circular economy. The main prerequisites for the transition to a circular economy are analyzed. It is determined that the basic concept of the circular economy involves the development of a system of production and consumption, which is based on processing, reuse, repair, product sharing, change of consumption patterns and new business models and systems. The main elements of the circular economy include: a closed cycle, the use of renewable energy sources, systems thinking. The correlation of the principles of sustainable development and the peculiarities of the application of the circular economy is analyzed. It is determined that the circular economy contrasts with the traditional linear economic model, which is based on the model of "take-do-consume-throw away". The advantages and disadvantages due to the use of the principles of circular economy are given. Based on the study, steps are identified to accelerate the transition from a linear economy to a circular economy.

• Structural Engineering and Mechanics
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• 제87권6호
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• pp.529-540
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• 2023

A novel laminated-hybrid-composite-beam (LHCB) of glass-epoxy infused with flyash and graphene is constructed for this study. The conventional mixture-rule and constitutive-relationship are modified to incorporate filler and lamina orientation. Eringen's non-local-theory is used to include the filler effect. Hamilton's principle based on fifth-order-layer-wise-shear-deformation-theory is applied to formulate the equation of motion. The analogous shear-spring-models for LHCB with multiple-cracks are employed in finite-element-analysis (FEA). Modal-experimentations are conducted (B&K-analyser) and the findings are compared with theoretical and FEA results. In terms of dimensionless relative-natural-frequencies (RNF), the dynamic-response in cantilevered support is investigated for various relative-crack-severities (RCSs) and relative-crack-positions (RCPs). The increase of RCS increases local-flexibility in LHCB thus reductions in RNFs are observed. RCP is found to play an important role, cracks present near the end-support cause an abrupt drop in RNFs. Further, multiple cracks are observed to enhance the nonlinearity of LHCB strength. Introduction of the first to third crack in an intact LHCB results drop of RNFs by 8%, 10%, and 11.5% correspondingly. Also, it is demonstrated that the RNF varies because of the lamina-orientation, and filler addition. For 0° lamina-orientation the RNF is maximum. Similarly, it is studied that the addition of graphene reduces weight and increases the stiffness of LHCB in contrast to the addition of flyash. Additionally, the response of LHCB to moving mass is accessed by appropriately modifying the numerical programs, and it is noted that the successive introduction of the first to ninth crack results in an approximately 40% to 120% increase in the dynamic-amplitude-ratio.

• Wind and Structures
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• 제38권1호
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• pp.43-58
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• 2024

To ensure the flutter stability of three-tower suspension bridges under skew wind, by using the computational procedure of 3D refined flutter analysis of long-span bridges under skew wind, in which structural nonlinearity, the static wind action(also known as the aerostatic effect) and the full-mode coupling effect etc., are fully considered, the flutter stability of a three-tower suspension bridge-the Taizhou Bridge over the Yangtze River in completion and during the deck erection is numerically investigated under the constant uniform skew wind, and the influences of skew wind and aerostatic effects on the flutter stability of the bridge under the service and construction conditions are assessed. The results show that the flutter critical wind speeds of three-tower suspension bridge under service and construction conditions fluctuate with the increase of wind yaw angle instead of a monotonous cosine rule as the decomposition method proposed, and reach the minimum mostly in the case of skew wind. Both the skew wind and aerostatic effects significantly reduce the flutter stability of three-tower suspension bridge under the service and construction conditions, and the combined skew wind and aerostatic effects further deteriorate the flutter stability. Both the skew wind and aerostatic effects do not change the evolution of flutter stability of the bridge during the deck erection, and compared to the service condition, they lead to a greater decrease of flutter critical wind speed of the bridge during deck erection, and the influence of the combined skew wind and aerostatic effects is more prominent. Therefore, the skew wind and aerostatic effects must be considered accurately in the flutter analysis of three-tower suspension bridges.

• 한국철도학회논문집
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• 제15권4호
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• pp.413-421
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• 2012

하이브리드 실험은 구조물의 거동을 수치해석 모델과 물리적 부분구조 모델로 나누어 동시에 수행되는 실험법으로써 본 논문에서는 지진하중에 의한 1경간 2층 강 뼈대 구조에 대한 하이브리드 시험을 수행하였다. 1층 기둥 1개소를 물리적 부분구조모형으로 선택하고, 한 개의 액추에이터를 이용해 수평방향으로 변위를 가하여 수치해석과 하이브리드 실험결과 사이의 거동추이를 분석하였다. 입력 지진데이터로는 El Centro를 사용하였으며, OpenSees를 이용하여 강구조물의 선형 또는 비선형 거동을 비교 분석하였다. 그 결과, 선형해석은 수치해석과 하이브리드 응답형상이 매우 잘 일치하였으며, 비선형 해석은 재료 비선형성에 의한 영구변형의 차이는 발생하였으나 최대변위 및 전체응답형상은 매우 유사하였다. 또한, 하이브리드 실험 소요시간은 실제 가진 시간에 약 9.6%의 속도로 현재 국내에서 수행된 실험 중 가장 실시간에 근접한 실험이라 할 수 있다. 따라서, 본 하이브리드 실험은 구조물의 동적 거동을 예측하는데 적절하게 활용될 수 있으며, 공간적, 경제적 제약이 있는 진동대 실험을 대체할 수 있으리라 판단된다.

• 한국전산구조공학회논문집
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• 제24권6호
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• pp.715-722
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• 2011

본 논문에서는 항공기 충돌에 의한 원전 격납건물의 거동을 병렬해석을 통해 수행하였다. 지금까지의 원전 격납건물에 대한 항공기 충돌관련 연구는 항공기의 경우, Riera의 충격하중-시간함수를 이상화하여 대상 구조체의 일정영역에 대해 충격하중으로 적용하는 방법을 사용해 왔고 충돌대상 구조체의 경우, 단순 철근콘크리트 벽체나 빌딩에 머물러 왔다. 하지만 본 논문에서는 항공기(Boeing-767, http://www.boeing.com)와 가상의 원전 격납건물을 실제와 유사하게 모델링하여 해석을 수행하였으며, 항공기모델은 충돌평가 가이드인 NEI 07-13(2009)에서 허용하는 Riera의 식에 따른 충돌하중이력곡선과 비교하는 방법으로 검증되었다. 또한, 일반적으로 고속 충돌해석은 짧은 시간동안 두 개 이상의 물체가 접촉하고 동적 대변형을 일으키는 비선형성이 강한 문제로 많은 계산시간이 요구되기 때문에 이를 효과적으로 다루기 위해서는 단일 CPU만으로는 한계가 있다. 따라서 본 논문에서는 해석의 효율성을 향상시키기 위해 자체 구축한 리눅스 클러스터 시스템을 이용하여 Message-Passing MIMD 형태의 병렬해석을 수행하였고 병렬성능에 대한 평가를 위해 무근콘크리트(Plain Concrete, PC), 철근콘크리트(Reinforced Concrete, RC), 내부 Liner Plate를 부착한 철근콘크리트(RC with Containment Liner Plate, CLP), SC구조(Steel-Plate Concrete, SC)등 4가지 경우에 대한 수치해석 효율성이 비교 검토되었다.