• Steel and Composite Structures
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• 제52권2호
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• pp.135-143
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• 2024

Once the foundation displacement of the transmission tower occurs, additional stress will be generated on the tower members, which will affect the seismic response of transmission tower-line systems (TTLSs). Furthermore, existing research has shown that the reciprocating slippage of joints needs to be considered in the seismic analysis. The hysteretic behavior of joints is obtained by model tests or numerical simulations, which leads to the low modeling efficiency of TTLSs. Therefore, this paper first utilized numerical simulation and model tests to construct a BP neural network for predicting the skeleton curve of joints, and then a numerical model for a TTLS considering the bolt slippage was established. Then, the seismic response of the TTLS under foundation displacement was studied, and the member stress changes and the failed member distribution of the tower were analyzed. The influence of foundation displacement on the seismic performance were discussed. The results showed that the trained BP neural network could accurately predict the hysteresis performance of joints. The slippage could offset part of the additional stress caused by foundation settlement and reduce the stress of some members when the TTLS with foundation settlement was under earthquakes. The failure members were mainly distributed at the diagonal members of the tower leg adjacent to the foundation settlement and that of the tower body. To accurately analyze the seismic performance of TTLSs, the influence of foundation displacement and the joint effect should be considered, and the BP neural network can be used to improve modeling efficiency.

• Earthquakes and Structures
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• 제12권4호
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• pp.397-407
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• 2017

To estimate the structural seismic demand, some methods are based on an equivalent linear system such as the Capacity Spectrum Method, the N2 method and the Equivalent Linearization method. Another category, widely investigated, is based on displacement correction such as the Displacement Coefficient Method and the Coefficient Method. Its basic concept consists in converting the elastic linear displacement of an equivalent Single Degree of Freedom system (SDOF) into a corresponding inelastic displacement. It relies on adequate modifying or reduction coefficient such as the inelastic deformation ratio which is usually developed for systems with known ductility factors ($C_{\mu}$) and ($C_R$) for known yield-strength reduction factor. The present paper proposes a rational approach which estimates this inelastic deformation ratio for SDOF bilinear systems by rigorous nonlinear analysis. It proposes a new inelastic deformation ratio which unifies and combines both $C_{\mu}$ and $C_R$ effects. It is defined by the ratio between the inelastic and elastic maximum lateral displacement demands. Three options are investigated in order to express the inelastic response spectra in terms of: ductility demand, yield strength reduction factor, and inelastic deformation ratio which depends on the period, the post-to-preyield stiffness ratio, the yield strength and the peak ground acceleration. This new inelastic deformation ratio ($C_{\eta}$) is describes the response spectra and is related to the capacity curve (pushover curve): normalized yield strength coefficient (${\eta}$), post-to-preyield stiffness ratio (${\alpha}$), natural period (T), peak ductility factor (${\mu}$), and the yield strength reduction factor ($R_y$). For illustrative purposes, instantaneous ductility demand and yield strength reduction factor for a SDOF system subject to various recorded motions (El-Centro 1940 (N/S), Boumerdes: Algeria 2003). The method accuracy is investigated and compared to classical formulations, for various hysteretic models and values of the normalized yield strength coefficient (${\eta}$), post-to-preyield stiffness ratio (${\alpha}$), and natural period (T). Though the ductility demand and yield strength reduction factor differ greatly for some given T and ${\eta}$ ranges, they remain take close when ${\eta}>1$, whereas they are equal to 1 for periods $T{\geq}1s$.

• 한국터널지하공간학회 논문집
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• 제4권3호
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• pp.175-184
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• 2002

일반적으로 터널 굴착시 지보재의 설치시기에 대한 예측을 위하여서는 지반반응곡선 (Ground reaction curve)을 활용하고 있다. 이 지반반응곡선은 굴착에 따른 지반의 변위 특성을 나타내며, 일반적으로 원형단면이고 등방상태 (K = 1.0)로 가정하여 단순화시킨 Closed Form Solution을 통해서 구해진다. 그러나, 원형단면이 아니고, 비등방 응력상태인 실질적인 현장조건을 고려해 본다면, 이 지반반응특성 예측식을 현장조건에 적용함에 있어서 어떠한 한계점을 갖는지에 대하여 규명할 필요가 있다. 이를 위해, 본 논문에서는 굴착단면 형상에 따른 측벽에서의 초기탄성변위 및 임계지보압의 변화 특성에 대하여 연구하였다. 터널굴착 형상은 단면의 높이 (b)와 폭 (a)의 비, 즉 굴착형상 계수 S (=b/a)값이 1.0, 0.8, 0.6, 0.4로 변화하도록 하였으며, 각각의 굴착형상마다 초기등방응력을 5~30 MPa사이에서 변화시켜가면서 수치해석을 통해 지반반응곡선을 얻었다. 수치해석을 통해 얻어진 측벽에서의 지반반응곡선을 분석하여 그에 따른 특성을 제시하였다. 검토결과 지반의 자립성을 평가하는데 있어서 Closed form solution의 사용에는 한계가 있는 것으로 판단된다.

• 한국지반공학회논문집
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• 제21권3호
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• pp.87-98
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• 2005

지하수위 아래에 터널이 굴착되면, 지하수가 터널내로 유입되면서 터널 단면에 침투력이 작용하게 된다. 지반반응 곡선은 내압과 터널 내공단면의 변위 관계로 정의되기 때문에 이러한 침투력의 영향을 크게 받게 된다. 본 연구에서는 건조상태 및 침투력을 고려할 경우의 지반반응곡선의 이론식을 각각 유도하였다. 또한, 유도된 이론식은 수치해석을 통하여 검증되었다. 다양한 지하수위 조건에서의 지보계 설치를 고려하여 지보재특성곡선과 함께 지반반응곡선을 연구하였다. 결국, 본 연구에서 유도된 지반반응곡선의 이론식은 합리적인 설계를 위한 적절한 지보계 설치시기 및 지보재 강성 등을 결정하는데 이용될 수 있다.

• 대한기계학회논문집A
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• 제36권11호
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• pp.1479-1485
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• 2012

철도차량 곡선구간 주행 시 곡선주행성능을 향상시키기 위한 능동형 철도차량 개발 분야에서 곡선구간을 실시간으로 인식하기 위한 기술 확보는 매우 중요하다. 그러나 고가의 전용 검측차량을 이용하거나 여러 가지 센서를 복합적으로 이용하는 기존의 곡률반경 추정방법은 실차에 적용하기에는 실용성이 미흡하다. 따라서 본 논문에서는 실차에 적용이 용이하고 경제적인 곡률반경 추정방법을 제안하였다. 새로운 방법은 철도차량 곡선구간 주행 시 발행하는 차체와 대차간의 상대변위를 측정하여 곡률반경을 실시간으로 추정할 수 있는 방법이다. 본 제안 방법의 타당성을 검토하기 위하여 모사해석 및 실차시험을 수행하였으며 그 결과, 제안한 곡률반경 추정방법의 타당성을 확인하였다.

• 한국지반공학회논문집
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• 제34권7호
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• pp.51-58
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• 2018

본 연구에서는 하중 조건에 따른 지반-말뚝 상호작용 시스템의 거동 차이를 분석하기 위해 일련의 원심모형 실험을 수행하였다. 정적 하중 조건의 경우, 말뚝 직경의 50% 수준까지 변위제어를 통해 하중을 재하하였으며, 지진 하중 조건의 경우 0.1g~0.4g 수준으로 1Hz 정현파를 가진하였다. 실험 결과로부터 얻은 정적 및 동적 p-y 곡선을 API p-y 곡선과 비교한 결과, API p-y 곡선과 정적 하중조건에서의 실험 p-y 곡선은 최대 지반반력 값이 20% 이내의 오차를 보인 반면, 동적 하중 조건에서의 실험 p-y 곡선과는 최대 지반반력 값이 5배 이상 차이가 발생하였다. 이는 등가정적 해석에서 기존 API p-y 곡선을 적용할 경우 비선형 영역에서 지반 반력을 크게 과소평가하며 보수적 설계를 야기할 수 있음을 의미한다.

• Geomechanics and Engineering
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• 제28권1호
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• pp.11-23
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• 2022

The response of pile foundations under lateral loads are usually analyzed using beam-on-nonlinear-Winkler-foundation (BNWF) model framework employing various forms of empirically derived p-y curves and p-multipliers. In practice, the p-y curve presented by the American Petroleum Institute (API) is most often utilized for piles in granular soils, although its shortcomings are recognized. The objective of this study is to evaluate the performance of the BNWF model and to quantify the error in the estimated pile response compared to a rigorous numerical model. BNWF analyses are performed using three sets of p-y curves to evaluate reliability of the procedure. The BNWF model outputs are compared with results of 3D nonlinear finite element (FE) analysis, which are validated via field load test measurements. The BNWF model using API p-y curve produces higher load-displacement curve and peak bending moment compared with the results of the FE model, because empirical p-y curve overestimates the stiffness and underestimates ultimate resistance up to a depth equivalent to four times the pile diameter. The BNWF model overestimates the peak bending moment by approximately 20-30% using both the API and Reese curves. The p-multipliers are revealed to be sensitive on the p-y curve used as input. These results highlight a need to develop updated p-y curves and p-multipliers for improved prediction of the pile response under lateral loading.

• Interaction and multiscale mechanics
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• 제6권4호
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• pp.339-356
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• 2013

This paper investigates the optimized parameters of Tuned Mass Dampers (TMDs) for vibration control of high-rise structures including Soil Structure Interaction (SSI). The Artificial Bee Colony (ABC) method is employed for optimization. The TMD Mass, damping coefficient and spring stiffness are assumed as the design variables of the controller; and the objective is set as the reduction of both the maximum displacement and acceleration of the building. The time domain analysis based on Newmark method is employed to obtain the displacement, velocity and acceleration of different stories and TMD in response to 6 types of far field earthquakes. The optimized mass, frequency and damping ratio are then formulated for different soil types; and employed for the design of TMD for the 40 and 15 story buildings and 10 different earthquakes, and well results are achieved. This study leads the researchers to the better understanding and designing of TMDs as passive controllers for the mitigation of earthquake oscillations.

• Advanced Composite Materials
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• 제18권1호
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• pp.21-42
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• 2009

The vibration characteristics of post-buckled laminated composite doubly curved shells are investigated. The finite element method is used for the analysis of post-buckling and free vibration of post-buckled laminated shells. The geometric non-linear finite element model includes the general non-linear terms in the strain-displacement relationships. The shell geometry used in the present formulation is derived using an orthogonal curvilinear coordinate system. Based on the principle of virtual work the non-linear finite element equations are derived. Arc-length method is implemented to capture the load-displacement equilibrium curve. The vibration characteristics of post-buckled shell are performed using tangent stiffness obtained from the converged deflection. The code is first validated and then employed to generate numerical results. Parametric studies are performed to analyze the snapping and vibration characteristics. The relationship between loads and fundamental frequencies and between loads and the corresponding displacements are determined for various parameters such as thickness ratio and shallowness.

• 한국산업안전학회:학술대회논문집
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• 한국안전학회 1998년도 춘계 학술논문발표회 논문집
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• pp.89-97
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• 1998

In this study, under large scale yielding conditions crack propagation is found to governed by parameters based on the J-integral or on the crack opening displacement. But initiation of crack propagation of ductile material seems to be controlled by just on parameter that is the strain. The relationship between the critical value of J-integral and the local fracture strain in uniaxial tensile test in the region of maximum reduction in area. Therefore, the fundamental theorectical equation by the proposed elastic-plastic fracture toughness and the local fracture strain has a merit. in comparison with the ASTM method, which can measure by using the load-displacement curve and the specimens in tenslie test.