• Steel and Composite Structures
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• 제26권6호
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• pp.705-717
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• 2018

This paper presents a numerical investigation on the mechanical performance of concrete-filled dual steel tubular columns of circular section subjected to concentric axial load. A three-dimensional numerical model is developed and validated against a series of experimental tests. A good agreement is obtained between the experimental and numerical results, both in the peak load value and in the ascending and descending branches of the load-displacement curves. By means of the numerical model, a parametric study is carried out to investigate the influence of the main parameters that determine the axial capacity of double-tube columns, such as the member slenderness, inner and outer steel tube thicknesses and the concrete grade - of both the outer concrete ring and inner core -, including ultra-high strength concrete. A total number of 163 numerical simulations are carried out, by combining the different parameters. Specific indexes are defined (Strength Index, Concrete-Steel Contribution Ratio, Inner Concrete Contribution Ratio) to help rating the relative mechanical performance of dual steel tubular columns as compared to conventional concrete-filled steel tubular columns, and practical design recommendations are subsequently given.

• 대한조선학회지
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• 제26권4호
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• pp.81-93
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• 1989

본(本) 논문(論文)에서는 충돌(衝突)이나 중량물(重量物) 낙하(落下)등에 의한 사고하중(事故荷重)을 받는 해양구조물(海洋構造物)의 원통부재(圓筒部材)에 대한 손상변형거동(損傷變形擧動)을 실용적(實用的)으로 추정(推定)할 수 있는 새로운 손상예측(損傷豫測) 모델을 제안(提案)한다. 본(本) 논문(論文)은 하중속도(荷重速度)가 비교적(比較的) 느리고 준정적(準靜的) 문제(問題)로서 다룰수 있는 경우만을 대상(對象)으로 하고 있다. 본연구(本硏究)에서 취급하는 원통부재(圓筒部材)는 양단단순(兩端單純) 지지(支持)되어 있고 축방향(軸方向)의 변위(變位)는 구속(拘束)되어 있으며, 하중(荷重)은 부재(部材)의 중앙위치(中央位置)에서 횡방향(橫方向)으로 작용(作用)한다고 가정(假定)한다. 지금까지의 연구성과(硏究成果) 및 본(本) 연구(硏究)에서 직접(直接) 수행(遂行)한 실험결과(實驗結果)를 바탕으로 사고하중작용시(事故荷重作用時)의 원통부재(圓筒部材)에 대한 손상변형거동(損傷變形擧動)을 상세(詳細)히 파악(把握)하고, 국부(局部) Dent 손상(損傷) 및 전체적(全體的)인 굽힘 처짐의 상관효과(相關效果)를 고려(考慮)한 하중-손상변형(荷重-損傷變形) 관계식(關係式)을 도출(導出)하였으며, 실제적(實際的)인 원통부재(圓筒部材)에 대한 실험결과(實驗結果)와 본연구(本硏究)에서 제안(提案)한 예측(豫測) 모델에 의한 추정결과(推定結果)는 잘 대응(對應)하고 있다는 것을 확인(確認)하였다. 특(特)히, 이 같은 하중상태하(荷重狀態下)에서의 실제부재(實際部材)의 손상변형거동(損傷變形擧動)에 대하여는 국부(局部) Dent 손상(損傷)과 전체적(全體的)인 굽힘처짐의 상관효과(相關效果)가 매우 크다는 것을 알았으며, 본예측(本豫測) 모델은 이들의 효과(效果)도 잘 나타내고 있다.

• 한국해양환경ㆍ에너지학회지
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• 제17권1호
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• pp.36-41
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• 2014

부유식 해양구조물은 설계수명동안 파랑에 의한 압축력, 굽힘하중, 전단력 등의 작용으로 인해 좌굴이 발생할 가능성이 높다. 이는 부재의 면내 강성 저하를 유발하여 국부 구조물 뿐만 아니라 전체구조의 최종강도에도 영향을 미치게 된다. 본 연구에서는 부유식 진자형 파력발전장치의 수실부와 감쇠판을 연결하는 원통부재의 최종강도에 대해 조사하였다. 탄성좌굴해석을 통해 얻어진 1차 좌굴모드를 초기처짐으로 가정하여 탄소성대변형해석을 수행하였으며 최종강도 특성을 바탕으로 부유식 파력발전장치의 연결부인 원통부재의 최적설계인자를 도출하였다. 이를 통해, 원통부재의 직경을 크게하거나, 판의 두께를 두껍게 하는 방법과 보강재를 사용하여 단면적을 크게하는 것이 최종강도를 증가시킬 수 있음을 확인하였다.

• Steel and Composite Structures
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• 제18권6호
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• pp.1569-1582
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• 2015

This study explores the lateral deflections of diagonal braces in concentrically-braced earthquake-resisting frames. The performance of this widely-used system is often compromised by the flexural buckling of slender braces in compression. In addition to reducing the compressive resistance, buckling may also cause these members to undergo sizeable lateral deflections which could damage surrounding structural components. Different approaches have been used in the past to predict the mid-length lateral deflections of cyclically loaded steel braces based on their theoretical deformed geometry or by using experimental data. Expressions have been proposed relating the mid-length lateral deflection to the axial displacement ductility of the member. Recent experiments were conducted on hollow and concrete-filled circular hollow section (CHS) braces of different lengths under cyclic loading. Very slender, concrete-filled tubular braces exhibited a highly ductile response, undergoing large axial displacements prior to failure. The presence of concrete infill did not influence the magnitude of lateral deflection in relation to the axial displacement, but did increase the number of cycles endured and the maximum axial displacement achieved. The corresponding lateral deflections exceeded the deflections observed in the majority of the previous experiments that were considered. Consequently, predictive expressions from previous research did not accurately predict the mid-height lateral deflections of these CHS members. Mid-length lateral deflections were found to be influenced by the member non-dimensional slenderness (${\bar{\lambda}}$) and hence a new expression was proposed for the lateral deflection in terms of member slenderness and axial displacement ductility.

• KEPCO Journal on Electric Power and Energy
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• 제5권4호
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• pp.257-262
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• 2019

Lattice steel towers for overhead transmission lines have been replaced by tubular steel poles due to the visual impact of large and complex shape of truss type. Demand for tubular steel poles consisting of a single frame member continues to grow because of its advantages such as visual minimization, architectural appeal and minimal site consumptions. However, there are some constraints on the transportation and construction. As the diameter of tower base has been enlarged, it may exceed minimum height limit required to pass the tunnel in case of land transportation. Also, in a narrow place where it is not easy to secure the installation areas such as mountainous places, there might be some areas wherein it must secure a wide working space so that large vehicles and working cranes will be allowed to enter. In this paper, we presented a vertical separated tubular steel pole, which is a new type of support that can be implemented for general purpose such as mountainous areas or narrow areas to improve the issues raised by breaking away from the conventional design and fabrication methods. Technical approaches for overcoming the limit of the cross-sectional size is to separate and modularize the cross-section of the tubular steel pole designed with a size that cannot be carried or assembled, and to lighten it with a weight capable of being transported and assembled in a narrow space or mountainous area. As a result of this research, it will be possible to enter small and medium sized vehicles in locations where it is restricted to transport by large-sized vehicles. In the case of mountainous areas, it will be possible to divide it into a weight capable of being carried by a helicopter and it will be easy to adjust and fabricate it with individual modules. Furthermore, in order to break away from the traditional construction method, we proposed the equipment that can be applied to the assembly of Tubular Steel Pole without using a large crane in locations where there is no accessible road or in locations wherein large cranes cannot enter. In particular, this paper shows the movable assembling equipment and some methods that are specialized for vertical separated tubular steel pole consisting of members with reduced weight. The proposed assembly equipment is a device for assembling the body of the Tubular Steel Poles. It will be installed inside the support and the modules can be lifted by using the support itself.

• Structural Engineering and Mechanics
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• 제9권4호
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• pp.365-374
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• 2000

The structural behavior of connections between concrete-filled rectangular tubular column (CFRT column) and steel beam has been studied in this paper through sub-assemblage loading tests. It is found that the sub-assemblages exhibit ductile restoring force characteristics under seismic loading. A formula for the prediction of the yield strength of each member in the connection is proposed by using the yield line theory under the assumption of a simple stress transfer mechanism. It is shown that the proposed formula can produce a reasonable prediction while providing a basis for further investigation.

• 소성∙가공
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• 제17권7호
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• pp.481-485
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• 2008

The subframe type rear suspension consisting of a side member and a front/rear cross member is widely used in a medium car and full car. In the small car case, the beam of tubular type without independent suspension system is used to reduce manufacturing cost. In this study, a subframe type rear suspension by hydroforming has been developed. In designing suspension, a driving stability and durability should be considered as an important factor for the performance improvement, respectively. Thus, we focus on increasing the stiffness of suspension and decreasing the maximum stress affecting a durability cycle life. Several optimization design techniques such as shape, size, and topology optimization are implemented to meet these requirements. The shapes of rear suspension obtained from optimization are formed by using hydroforming process. Through commercial software based on the finite element, the superiority of this design method is demonstrated.

• 한국산학기술학회논문지
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• 제15권3호
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• pp.1764-1769
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• 2014

본 논문에서는 기존의 단일대형강관 타워의 일부를 복수의 강관으로 대체한 멀티기둥-단일대형강관 하이브리드형식 풍력타워의 적용성을 평가하기 위하여 연결부의 성능을 수치해석적으로 평가하였다. 연결부의 형태는 멀티기둥의 단일대형강관 단부 관통 여부, 멀티기둥 하단부 날개 보강재의 유무 및 단일대형강관 내부 가로보 배치형식으로 구분하였다. 해석은 응력집중을 평가하기 위한 선형탄성해석과 극한강도을 평가하기 위한 재료 및 기하비선형 해석이 수행되었다. 수직력과 수평력에 대한 구조성능 분석 결과, 가로보 배치형식과 날개 보강재는 타워 구조계의 극한강도에 민감하게 영향을 주는 것으로 확인되었다.

• 대한조선학회논문집
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• 제41권6호
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• pp.48-55
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• 2004

Loads on offshore structures are largely transferred to the bracing members in the form of axial forces. The detrimental effects of imperfections on compressive strength are well recognized. Damage in the members of offshore structures would significantly affect the compressive behavior of the members. As a result, such damages may also affect the ability of the structure to withstand the functional and environmental loads. It is important to be able to assess the residual strength of damaged members quickly and accurately. This will help operators to make the decision whether the member has to be repaired or not. In this study, a series of calculation is performed to study the effects of different parameters on the behavior of such damaged members under axial load. And the results of analysis are compared with those of experiment.

• 국제초고층학회논문집
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• 제3권3호
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• pp.215-221
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• 2014

Ultra-high strength concrete and high tensile steel are becoming very attractive materials for high-rise buildings because of the need to reduce member size and structural self-weight. However, limited test data and design guidelines are available to support the applications of high strength materials for building constructions. This paper presents significant findings from comprehensive experimental investigations on the behaviour of tubular columns in-filled with ultra-high strength concrete at ambient and elevated temperatures. A series of tests was conducted to investigate the basic mechanical properties of the high strength materials, and structural behaviour of stub columns under concentric compression, beams under moment and slender beam-columns under concentric and eccentric compression. High tensile steel with yield strength up to 780 MPa and ultra-high strength concrete with compressive cylinder strength up to 180 MPa were used to construct the test specimens. The test results were compared with the predictions using a modified Eurocode 4 approach. In addition, more than 2000 test data samples collected from literature on concrete filled steel tubes with normal and high strength materials were also analysed to formulate the design guide for implementation in practice.