• 한국안전학회지
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• 제33권4호
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• pp.46-53
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• 2018

This study examined the maximum resistant moment and nonlinear rotational stiffness of wedge joint between the vertical and horizontal members of system supports. To examine the maximum resistant moment and propose the nonlinear rotation stiffness of wedge joint, 6 specimens were tested and additional 3 specimens, where the horizontal member was welded to the vertical member, were tested to compare the moment capacity of wedge joints. The average maximum moment in the tested wedge joint was 1.183 kNm which represented about 70 % of the maximum moment developed in the welded specimens. And, as simulating nonlinear rotational stiffness of the wedge joint, a tri-linear model was suggested. The rotational stiffness was estimated as 23.095 kNm/rad in first stage, 7.945 kNm/rad in second stage, and 3.073 kNm/rad in third stage. For the failure mode, the specimen with the wedge joint showed the failure of joint between vertical and horizontal members. However, the specimen with welded joint represented the yielding of horizontal members.

• 한국안전학회지
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• 제32권3호
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• pp.60-65
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• 2017

This study examined the effect of rotational stiffness of joints between vertical and horizontal members in system supports. In order to prevent repeated disasters of system supports, it is important to examine the accurate behavior of system supports. Among various factors affecting the complex behavior of system supports, this study focused on the stiffness of joints between vertical and horizontal members. The considered joint was modelled by a rotational spring, but the translational displacements were fixed. The stiffness of rotational spring was calculated by utilizing the usable experimental data. In addition, the hinge connection condition, which is generally considered in design and only restrict the translational displacements, was modelled to compare the results. The case with the rotational stiffness in joints showed 3.5 times buckling loads compared to the case without the rotational stiffness. Thus, the structural behavior of the vertical member in system supports was similar to the vertical member with the fixed condition. For the combined stresses of vertical members, the combined stress ratios were reduced 5~6% by considering the rotational stiffness of connecting parts. However, for the horizontal member where showed relatively small stress range, the stresses were increased 2.3~7.6 times by considering the rotational stiffness in connecting parts.

• 한국지반환경공학회 논문집
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• 제21권12호
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• pp.5-10
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• 2020

인천에 위치한 OO 깊은 굴착 현장을 대상으로 굴착에 따른 지반 물성값의 변화를 역해석을 통해 분석하였다. 굴착 단계별로 유한 요소 해석을 통해 예측한 굴착 지지 벽체의 수평방향 변위와 현장에서 지중경사계를 이용하여 계측한 값을 비교하여 지반의 강성을 업데이트하였다. 업데이트한 지반의 강성을 다음 굴착 단계에서 굴착 지지 벽체의 거동 예측에 사용하였다. Hardening Soil 모델을 이용한 유한요소해석 기법을 사용하였으며, 굴착 지지 벽체가 위치하는 지층을 역해석 대상 지층으로 선정하였고, 그 지층의 강성값을 역해석 대상으로 선정하였다. 굴착 초기 단계의 지반의 강성값은 당초 설계에서 사용한 강성값에 비해 큰 것으로 나타났다. 굴착이 진행됨에 따라 재역해석을 통해 산정한 지반의 강성값은 초기에 역해석으로 도출한 값에 비해 감소한 것으로 나타났다. 따라서, 굴착 단계에 따라 적절한 지반의 강성값을 입력해야 유한 요소 해석을 통해 정확한 굴착 지지 벽체의 변형을 산정할 수 있을 것으로 판단한다.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2003년도 추계 학술발표회논문집
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• pp.98-106
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• 2003

To construct pile-supported wharf structures that must support heavy horizontal loads, both vertical piles and batter piles are used. Batter piles are used to secure the bearing capacity against the horizontal loads. However, past case histories have shown that the heads of batter piles are vulnerable because these heads are subjected to excessive axial loads during earthquakes. Therefore, the aseismatic reinforcement method must be developed to prevent batter pile heads from breaking due to excessive seismic loads. Two different connecting methods of either inserting rubber or ball-bearing between batter pile head and upper plate were proposed to improve the aseismatic efficiency. Three large-scale pile head models(rubber type model, ball-bearing type model, and fixed type model) were manufactured and horizontal loading tests were peformed for these models. The results showed that the force-displacement relationship of the fixed type model was linear, but that of the rubber type model and the ball-bearing type model was bilinear. The increase in the horizontal displacement led to the increase in the horizontal stiffness of the rubber type models and the decrease in that of the ball-bearing type model. Compared with the values for fixed type model, the damping ratios of the rubber type model and the ball-bearing type model increased about 33~185％ and 263~269％, respectively.

• Structural Engineering and Mechanics
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• 제74권5호
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• pp.635-655
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• 2020

The sag effect of long stay cables is one of the key factors restricting further increase in the span of cable-stayed bridges. Based on the formerly proposed concept of long stay cables lifted by an auxiliary suspension cable in cross-strait cable-stayed bridges, corresponding static approximate calculations and analytical theory based on catenary and parabolic cable configurations are established. Taking a main span 1400 m cable-stayed bridge as the research object, three typical lifting conditions and the whole process of auxiliary cable lifting are analyzed and discussed. The results show that the sag effect is effectively reduced. The support efficiency is only improved when the cables are lifted above the original cable chord. Reduction of the horizontal component force of the cable is limited. The equivalent elastic modulus and the vertical support stiffness of the lifted cables are significantly increased with increased horizontal projection length and not sensitive to the change of the lifting point position. The scheme of lifting the cable to the chord midpoint is more economical because of the less steel required for the auxiliary suspension cable, but its effect on improving the vertical support efficiency is limited. The support efficiency is better when the cable is lifted to the cable end tangential to the original cable chord, but the lifting force and the cross-sectional area of the auxiliary suspension cable are doubled. The approximate calculation results of the lifted cables are very close to the numerical analysis results, which verifies the applicability of the approximation method proposed in this study. The results of parabolic approximation calculations are approximately equal to that of catenary cable geometry. As the parabolic approximation analysis theory of lifted cables is more convenient in mathematical processing, it is feasible to use parabolic approximation analysis theory as the analytical method for the conceptual design of lifted cables of super-long span cable-stayed bridges.

• 한국공간구조학회논문집
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• 제12권3호
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• pp.71-78
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• 2012

공간구조물은 높이-경간비 또는 개각과 같은 아치의 형상비에 따라 상이한 동적거동특성을 나타내며, 이러한 공간구조물은 지진의 영향을 직접적으로 받는 하부구조의 강성 및 그 접합부에 따라 상이한 지진응답특성을 나타낸다. 따라서 본 연구에서는 수직진동모드와 수평진동모드의 영향이 다른 단층아치구조에 하부기둥의 강성과 접합부에 따른 지진응답특성을 분석하고자 한다. 하부기둥의 영향으로 단층아치구조는 수직방향 응답이 더 많은 영향을 받으며, 기둥의 접합부 회전강성에 있어서는 활절을 제외하고는 큰 영향이 없는 것으로 나타난다.

• Structural Engineering and Mechanics
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• 제77권6호
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• pp.819-830
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• 2021

To evaluate the performance of concrete load bearing walls in a structure under horizontal loads after being exposed to real fire, two steps were followed. In the first step, an experimental study was performed on the thermo-mechanical properties of concrete after heating to temperatures of 200-1000℃ with the purpose of determining the residual mechanical properties after cooling. The temperature was increased in line with natural fire curve in an electric furnace. The peak temperature was maintained for a period of 1.5 hour and then allowed to cool gradually in air at room temperature. All specimens were made from calcareous aggregate to be used for determining the residual properties: compressive strength, static and dynamic elasticity modulus by means of UPV test, including the mass loss. The concrete residual compressive strength and elastic modulus values were compared with those calculated from Eurocode and other analytical models from other studies, and were found to be satisfactory. In the second step, experimental analysis results were then implemented into structural numerical analysis to predict the post-fire load-bearing capacity response of the walls under vertical and horizontal loads. The parameters considered in this analysis were the effective height, the thickness of the wall, various support conditions and the residual strength of concrete. The results indicate that fire damage does not significantly affect the lateral capacity and stiffness of reinforced walls for temperature fires up to 400℃.

• 한국압력기기공학회 논문집
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• 제16권1호
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• pp.30-36
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• 2020

In SMART, the flow mixing header assembly (FMHA) is used to mix the coolant flowing into the reactor core to maintain a uniform temperature. The FMHA is designed to have enough stiffness so the resonance with reactor internal structures does not occurs during the pipe break and the seismic accidents. Since the gap between the FMHA and the core support barrel assembly is very narrow compared with the diameter of FMHA, the hydrodynamic mass effect acting on the FMHA is not negligible. Therefore the hydrodynamic mass characteristics on the FMHA are investigated to consider the fluid and structure interaction effects. The result of modal analysis for the dry and underwater conditions, the natural frequency of primary vibration mode for the horizontal direction is reduced from 136.67 Hz to 43.76 Hz. Also the result of frequency response spectrum seismic analysis for the dry and underwater conditions, the maximum equivalent stress are increased from 13.89 MPa to 40.23 MPa. Therefore, reactor internal structures located in underwater condition shall consider carefully the hydrodynamic mass effects even though they have sufficient stiffness required for performing its functions under the dry condition.

• 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.

• Wind and Structures
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• 제7권3호
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• pp.203-214
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• 2004

This paper describes a method for developing a multi-degree-of freedom aero-elasto-plastic model of a base-isolated mid-rise building. The horizontal stiffness of isolators is modeled by several tension springs and the vertical support is performed by air pressure from a compressor. A lead damper and a steel damper are modeled by a U-shaped lead line and an aluminum line. With this model, the frequency ratio of torsional vibration to sway vibration, and plastic displacements of isolation materials can be changed easily when needed. The results of isolation material tests and free vibration tests show that this model provides the object performance. The peak displacement factors are about 4.5 regardless of wind speed in wind tunnel tests, but their gust response factor decreases with increment of wind speed.