• Earthquakes and Structures
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• 제10권5호
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• pp.1143-1179
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• 2016

Offshore wind turbines are considered as a fundamental part to develop substantial, alternative energy sources. In this highly flexible structures, monopiles are usually used as support foundations. Since the monopiles are large diameter (3.5 to 7 m) deep foundations, they result in extremely stiff short monopiles where the slenderness (length to diameter) may range between 5 and 10. Consequently, their elastic deformation patterns under lateral loading differ from those of small diameter monopiles usually employed for supporting structures in offshore oil and gas industry. For this reason, design recommendations (API and DNV) are not appropriate for designing foundations for offshore wind turbine structures as they have been established on the basis of full-scale load tests on long, slender and flexible piles. Furthermore, as these facilities are very sensitive to rotations and dynamic changes in the soil-pile system, the accurate prediction of monopile head displacement and rotation constitutes a design criterion of paramount importance. In this paper, the Fourier Series Aided Finite Element Method (FSAFEM) is employed for the determination of static impedance functions of monopiles for OWT subjected to horizontal force and/or to an overturning moment, where a non-homogeneous soil profile has been considered. On the basis of an extensive parametric study, and in order to address the problem of head stiffness of short monopiles, approximate analytical formulae are obtained for lateral stiffness $K_L$, rotational stiffness $K_R$ and cross coupling stiffness $K_{LR}$ for both rough and smooth interfaces. Theses expressions which depend only on the values of the monopile slenderness $L/D_p$ rather than the relative soil/monopile rigidity $E_p/E_s$ usually found in the offshore platforms designing codes (DNV code for example) have been incorporated in the expressions of the OWT natural frequency of four wind farm sites. Excellent agreement has been found between the computed and the measured natural frequencies.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 1994년도 가을 학술발표회 논문집
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• pp.113-120
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• 1994

Large Concrete Panel Structures behave quite differently from frame or monolithic shear wall structures because of the weakness of Joint in stiffness and strength. The joint experiences large deformation such as shear-slip in vertical and horizontal joint and rocking and crushing in horizontal joint because of localized stress concentration, but the wall panels behave elastically under cyclic loads. In order to describe the nonlinear behavior of the joint in the analysis of PC structures, different analysis technique from that of RC structures is needed. In this paper, for analysis of large concrete panel subassemblage subjected to cyclic loads, the wall panels are idealized by elastic finite elements, and the joints by nonlinear spring elements with various load-deflection relationship. The analytical results are compared with the experimental results on the strength, stiffness, energy dissipation and lateral drift, and the effectiveness of this computer analysis modelling technique is checked.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1998년도 봄 학술발표회논문집(II)
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• pp.481-486
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• 1998

In this paper, elastic and inelastic behavior of exterior joint of moment-resisting R.C frame with non-seismic detail subjected to reversed cyclic lateral load such as earthquake excitations was investigated. 1/2-scals subassemblage exterior beam-column joint including slab was manufactured based on similitude law. Then, pseudo static test under the displacement control was performed. The results of 1)crack pattern and failure mode, 2)degradation stiffness and strength, energy dissipation capacity from load-displacement hysteresis curve, 3)strain of steel were analysed.

• 대한토목학회논문집
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• 제13권1호
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• pp.1-12
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• 1993

가상변수(假想變數)의 원리(原理)를 이용하여 공간박벽(空間薄璧) 및 뼈대구조물(構造物)의 비틂 및 횡좌굴해석(橫挫掘解析)을 수행하기 위한 접선강도(接線剛度)매트릭스들이 유도(誘導)된다. 구속(拘束)된 비틂을 고려하는 경우와 무시하는 경우 각각에 대하여, 탄성(彈性) 및 기하적(幾何的)인 강도(剛度)매트릭스들이 얻어지며 이때 축방향(軸方向) 변위(變位), 횡방향(橫方向) 처짐들, 그리고 비틂회전각에 대하여 적절한 Hermitian 다항식들을 형상함수(形狀函數)로 사용된다. 수치해석예제(數値解析例題)들을 통하여 본 연구(硏究)에서 제시한 이론(理論)의 정당성(正當性)을 입증(立證)한다.

• Advances in Computational Design
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• 제5권1호
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• pp.35-54
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• 2020

One of the prevailing structural systems in high-rise buildings is the core-wall system. On the other hand, the existence of one or more underground stories causes the perimeter below-grade walls with the diaphragm of grade level to constitute of a very stiff box. In this case or a similar situation, during the lateral response of a tall building, underground perimeter walls and diaphragms that provide an increased lateral resistance relative to the core wall may introduce a prying action in the core that is called backstay effect. In this case, a rather great force is generated at the diaphragm of the grade-level, acting in a reverse direction to the lateral force on the core-wall system, and thus typically causes a reverse internal shear. In this research, in addition to review of the results of the preceding studies, an improved relationship is proposed for prediction of backstay force. The new proposed relationship takes into account the effect of foundation flexibility and is presented in a non-dimensional form. Furthermore, a specific range of the backstay force to lateral load ratio has been determined. And finally, it is shown that although all suggested formulas are valid in the elastic domain, yet with some changes in the initial considerations, they can be applied to some certain non-linear problems as well.

• Earthquakes and Structures
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• 제10권5호
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• pp.1111-1123
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• 2016

To study seismic performance of steel frame-bent structure, one specimen with one-tenth scale, three-bay, and five-story was tested under reversed cyclic lateral load. The entire loading process and failure mode were observed, and the seismic performance indexes including hysteretic loops, skeleton curve, ductility, load bearing capacity, drift ratio, energy dissipation capacity and stiffness degradation were analyzed. The results show that the steel frame-bent structure has good seismic performance. And the ductility and the energy dissipation capacity were good, the hysteresis loops were in spindle shape, which shape were full and had larger area. The ultimate elastic-plastic drift ratio is larger than the limit value specified by seismic code, showing the high capacity of collapse resistance. It can be helpful to design this kind of structure in high-risk seismic zone.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1999년도 봄 학술발표회 논문집(I)
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• pp.529-536
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• 1999

The objective of the research stated herein is to observe th elastic and inelastic behaviors and ultimate capacity of 1 : 5 scale 3-story reinforced concrete frame. Pushover tests were performed to 1:5 scale 3-story reinforced concrete frames without and with infilled masonry. To simulate the earthquake effect, the lateral force distribution was maintained to be an inverted triangle by using the whiffle tree. From the results of tests, the relations between the total lateral load and the roof drift, the distribution of column shears, the relation between story shear and story drift, and the angular rotations at the critical portions of structures were obtained. The effects of infilled masonry are investigated with regards to the stiffness, strength, and ductility of structures. Final collapse modes of structures with and without infilled masonry are compared.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1996년도 봄 학술발표회 논문집
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• pp.317-322
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• 1996

The objective of this study is to investigate the characteristics of elastic and inelasitc behavior of ductile moment-resisting reinforced concrete frame subhected to reversed lateral loading such as eqrthquake excitations. For this purpose, a 2-bay 2-story R.C. plane frame with seismic detail was designed and one 1/2.5-scale subassemblage was manufactured according to the required similitude law. Then the reversed load test under the displacement control was performed statically to this subassemblage. Finally the results of this test were analysed regarding to (1) the design load vs actual strength, (2) degradation in stiffness and strength, (3) failure mode or main plastic mechanism in energy dissipation, (4) local deformations.

• Earthquakes and Structures
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• 제16권1호
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• pp.97-107
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• 2019

The frame structures investigated in this paper is composed of Concrete encased columns with L-shaped steel section and steel beams. The seismic behavior of this structural system is studied through experimental and numerical studies. A 2-bay, 3-story and 1/3 scaled frame specimen is tested under constant axial loading and cyclic lateral loading applied on the column top. The load-displacement hysteretic loops, ductility, energy dissipation, stiffness and strength degradation are investigated. A typical failure mode is observed in the test, and the experimental results show that this type of framed structure exhibit a high strength with good ductility and energy dissipation capacity. Furthermore, finite element analysis software Perform-3D was conducted to simulate the behavior of the frame. The calculating results agreed with the test ones well. Further analysis is conducted to investigate the effects of parameters including concrete strength, column axial compressive force and steel ratio on the seismic performance indexes, such as the elastic stiffness, the maximum strength, the ductility coefficient, the strength and stiffness degradation, and the equivalent viscous damping ratio. It can be concluded that with the axial compression ratio increasing, the load carrying capacity and ductility decreased. The load carrying capacity and ductility increased when increasing the steel ratio. Increasing the concrete grade can improve the ultimate bearing capacity of the structure, but the ductility of structure decreases slightly.

• 대한토목학회논문집
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• 제13권1호
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• pp.13-24
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• 1993

가상(假想)일의 원리(原理)를 이용하여 강절(剛節)-힌지단(端)을 갖는 평면(平面)뼈대요소(要素)와 비대칭(非對稱) 박벽단면(薄壁斷面)을 갖는 공간(空間)뼈대요소(要素)의 접선강도(接線剛度)매트릭스가 유도된다. 양단(兩端) 구속(拘束)된 비틂을 무시하는 경우, 구속(拘束)된 비틂을 고려하는 경우, 그리고 왼쪽단은 구속(拘束)된 비틂을 고려하고 오른쪽단은 구속(拘束)된 비틂을 무시하는 경우 각각에 대하여 박벽공간(薄壁空間)뼈대요소(要素)의 탄성(彈性) 및 기하적(幾何的)인 강도(剛度)매트릭스를 산정한다. 이때, 휨을 받는 평면(平面)보의 처짐함수를 적절히 선택하여 공간(空間)뼈대요소(要素)의 세방향처짐과 비틂회전각에 대한 형상함수(形狀函數)로 사용한다. 공간(空間)뼈대 구조물(構造物)과 원형(圓形)아아치의 횡좌굴(橫挫屈)문제를 해석(解析)하여 본(本) 연구(硏究)에 의한 해석결과(解析結果)들과 엄밀해(嚴密解) 또는 다른 문헌(文獻)의 결과(結果)들과 비교(比較) 분석(分析)하여 본(本) 연구(硏究)에서 제시한 이론(理論)의 정당성(正當性)을 입증(立證)한다.