• Journal of the Earthquake Engineering Society of Korea
• /
• v.6 no.2
• /
• pp.9-19
• /
• 2002

Steel piers and concrete-filled steel(CFS) piers, in spite of reasonable strength, high ductility, small section, and fast construction, have not been considered as one of alternatives to RC piers even in the highly populated urban area where aseismic safety, limited space and fast construction are indispensably required. This paper, the first of two companion papers for the seismic performance of steel and CFS piers, tests steel and CFS piers under quasi-static cyclic loading to estimate their ductility and strength. Additional details such as rebars and base ribs are added to increase the ductility of a concrete-filled steel pier with minimum additional cost. Also, simplified numerical analyses using nonlinear spring and shell elements are examined for the estimation of the ductility and strength of concrete-filled steel piers and a steel pier. The result shows that concrete-filled steel peirs have higher energy absorption, i.e., ductility and strength than those of steel pier and increasing bonding between in-filled concrete and lower diaphragm, and the improved details of stress concentrated region would be important for the ductility and strength of a pier. Numerical results show that simplified modeling with nonlinear springs and shells has potential to be effective modeling technique to estimate the seismic performance of a concrete-filled steel pier.

• Journal of Korean Association for Spatial Structures
• /
• v.12 no.1
• /
• pp.109-119
• /
• 2012

For membrane structure, there are three main steps in design and construction, which are form finding, statistical load analysis, and cutting patterning. Unlike the first two stages, the step of cutting pattern involves the translation of a double-curved surface in 3D space into a 2D plane with minimal error. For economic reasons, the seam lines of generated cutting patterns rely greatly on the geodesic line. Generally, as searching regions of the seam line are plane elements in the step of shape analysis, the seam line is not a smooth curve, but an irregularly divided straight line. So, it is how we make an irregularly divided straight line a smooth curve that defines the quality of the pattern. Accordingly, in this paper, we analyzed interpolation schemes using spline, and apply these methods to cutting pattern generation on the curved surface. To generate the pattern, three types of spline functions were used, i.e., cubic spline function, B-spline, and least-square spline approximation, and simple model and the catenary-shaped membrane was adopted to examine the result of generation. The result of comparing the approximation curves by the number of elements and the number of extracted nodes of simple model revealed that the seam line for less number of extracted nodes with large number of elements were more efficient, and the least-square spline approximation provided smoother seam line than other methods.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.33 no.2
• /
• pp.95-101
• /
• 2020

The wind turbine blades should be designed to possess a high stiffness and should be fabricated with a light and high strength material because they serve under extreme combination of lift and drag forces, converting kinetic energy of wind into shaft work. The goal of this study is to understand the basic knowledge required to curtail the process time consumed during the construction of small wind turbine blades using carbon fiber reinforced polymer (CFRP) prepeg composites. The configuration of turbine rotor was determined using the QBlade freeware program. The fluid dynamics module simulated the loads exerted by the wind of a specific speed, and the stress analysis module predicted the distributions of equivalent von Mises stress for representing the blade structures. It was suggested to modify the shape of test specimen from ASTM D638 to decrease the variance in measured tensile strengths. Then, a series of experiments were performed to confirm that the bladder compression molded CFRP prepreg can provide sufficient strength to small wind turbine blades and decrease the cure time simultaneously.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.33 no.2
• /
• pp.483-493
• /
• 2013

The high strength materials have been more widely used in a large reinforced concrete structures. It is known that the use of high strength material in RC structures give the benefits of the mechanical and durable properties, but the ductility decreases with an increase in the strength of the materials. In the design of a reinforced concrete beam, both the flexural strength and ductility need to be considered. So, it is necessary to assess accurately the ductility of the beam with high strength materials in order to ensure the ductility requirement in design. In this study, the effects of the material strength on the flexural behavior and curvature ductility factor of reinforcement concrete beam sections with various reinforcement conditions have been evaluated and a newly prediction formula for curvature ductility factor of RC beam has been developed considering the stress of compression reinforcement at ultimate state. The proposed predictions for the curvature ductility factor which is applicable to both singly and doubly reinforced concrete beam are verified by comparisons with other prediction formulas and the proposed formula offers fairly accurate within 9% error and consistent predictions for curvature ductility factor of reinforced concrete beam.

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.19 no.2
• /
• pp.265-281
• /
• 2017

For shallow tunnel constructions, settlement of the ground surface is a main issue. Recent technical developments in shield TBM tunneling technique have enabled a decrease in such settlements based on tunneling with ground deformation controls. For this objective, the tail void grouting is a common practice. Generally surface settlements in a soil of low permeability occur during a tunnel construction but also during a long period after completion of the tunnel. The long-term settlements occur mainly due to consolidation around the tunnel. The consolidation process is caused and determined by the tail void grouting which leads to an excess pore water pressure in the vicinity of the tunnel. Because of this, the grouting pressure has a strong effect on the long-term settlements in the shield tunneling. In order to investigate this effect, a series of coupled hydro-mechanical 3D finite element simulations have been performed. The results show that an increase in grouting pressure reduces the short-term settlements, but in many cases, it doesn't lead to a reduction of the final settlements after the completion of consolidation. Thereby, the existence of a critical grouting pressure is identified, at which the minimal settlements are expected.

• Proceedings of the Korea Inteligent Information System Society Conference
• /
• 2000.11a
• /
• pp.257-266
• /
• 2000

산업 및 가정용 기기들이 점차 복잡해짐에 따라 다양한 공학 분야의 해석 기술을 동시에 고려하면서 이들 원리를 적용한 최적의 설계를 결정하는 방법론의 필요성이 대두되고 있다. 다분야통합최적설계 또는 MDO(Multidisciplinary Design Optimization)라 일컫는 새로운 기술은 이러한 필요에 대응하는 기술로서 국내외적으로 활발한 연구가 진행되고 있다. 이러한 MDO 기술을 구현하는 소프트웨어와 하드웨어 복합 체계를 MDO 프레임웍(framework)이라 한다. 일반적으로 프레임웍이란 실제 응용프로그램의 용도에 맞는 주문제작(customization)이 가능한 일종의 전단계 프로그램이라 할 수 있다 MDO 프레임웍은 설계 및 해석 도구들간의 인터페이스를 제공하고, 이들 도구들이 사용하는 설계 데이터를 효율적으로 공유할 수 있도록 지원하여, 설계 작업을 정의, 실행, 관리하는 역할을 한다. 이러한 MDO 프레임웍은 설계 작업을 통합적으로 관리하고 자동화하여 설계 도구간의 데이터 전달과 변환에 소묘되는 설계자의 부담을 경감시키며 다분야 전문가가 참여하는 공통 작업 환경을 제공함으로써 설계 효율성을 증진시킨다. 본 논문에서는 이러한 효용을 달성하기 위한 MDO 프레임웍(framework)을 제시하고 프레임웍 설계의 논리적 근저와 타당성을 밝힌다. 본 논문에서 제안하는 다분야 통합 최적화를 위한 분산형 지능 시스템인 DisMDO는 사용자가 GUI를 동해서 편리하게 다분야통합최적화 문제를 해결할 수 있도록 지원하며, 제공되는 스크립트 언어를 동해서도 이를 정의할 수 있도록 지원하여 일괄처리도 가능하도록 한다. 또한, 집중화된 데이터베이스를 관리하여 다분야 전문가들이 공통의 데이터를 안전하게 공유할 수 있도록 지원하며, 외부에서 제공되는 해석 도구나 최적화 모듈을 손쉽게 프레임웍에 통합시킬 수 있도록 하는 인터페이스 제작기(factory) 기능을 제공한다.ackscattering spectroscopy, X-ray diffraction, secondary electron microscopy, atomic force microscoy, $\alpha$-step, Raman scattering spectroscopu, Fourier transform infrared spectroscopy 및 micro hardness tester를 이용하여 기판 bias 전압이 DLC 박막의 특성에 미치는 영향을 조사하였다. 분석결과 본 연구에서 제작된 DLC 박막은 탄소와 수소만으로 구성되어 있으며, 비정질 상태임을 알 수 있었다. 기판 bias 전압의 증가에 따라 박막의 두께가 감소됨을 알 수 있었고, -150V에서는 박막이 거의 만들어지지 않았으며, -200V에서는 기판 표면이 식각되었다. 이것은 기판 bias 전압과 ECR 플라즈마에 의한 이온충돌 효과 때문으로 판단되며, 150V 이하에서는 증착되는 양보다 re-sputtering 되는 양이 더 많을 것으로 생각된다. 기판 bias 전압을 증가시킬수록 플라즈마에 의한 이온충돌 현상이 두드러져 탄소와 결합하고 있던 수소원자들이 떨어져 나가는 탈수소화 (dehydrogenation) 현상을 확인할 수 있었으며, 이것은 C-H 결합에너지가 C-C 결합이나 C=C 결합보다 약하여 수소 원자가 비교적 해리가 잘되므로 이러한 현상이 일어난다고 판단된다. 결합이 끊어진 탄소 원자들은 다른 탄소원자들과 결합하여 3차원적 cross-link를 형성시켜 나가면서 내부 압축응력을 증가시키는 것으로 알려져 있으며, hardness 시험 결과로 이것을 확인할 수 있었다. 그리고 표면거칠기는 기판 bias 전압을 증가시킬수록 더 smooth 해짐을 확인하였다.인하였다.을 알 수 있었다. 즉 계면에서의 반응에 의해 편석되는 Ga에 의해 박막의 strain이 이완되면, pinhole 등의 박막결함

• Nuclear Engineering and Technology
• /
• v.27 no.4
• /
• pp.453-462
• /
• 1995

In connection with the safe storage of high level nuclear waste, effect of $H_2O$$_2$ on the corrosion behavior of 304L stainless steel was examined. Open circuit potentials and polarization curves were measured with and without $H_2O$$_2$. The experimental results show that $H_2O$$_2$ increased corrosion potential and decreased pitting potential. The passive range, therefore, decreased as $H_2O$$_2$ concentration increased, indicating that pitting resistance was decreased by the existence of $H_2O$$_2$ in the electrolyte. These effect of $H_2O$$_2$ on corrosion of 304L stainless steel are considered to be similar to those of ${\gamma}$-irradiation. To compare the effects of $H_2O$$_2$ with those of $O_2$, cathodic and anodic polarization curves ore made in three types of electrolyte such as aerated, deaerated, and stirred electrolyte. The experimental results show that the effects of $H_2O$$_2$ on the corrosion behavior were tory similar to those of $O_2$ such as increase of corrosion potential, decrease of pitting resistance, and increase of repassivation potential. In acid and alkaline media, the corrosion potential shifts by $H_2O$$_2$ were restricted by the large current density of proton reduction and by the le Chatelier's principle respectively.y.

• Journal of the Korean GEO-environmental Society
• /
• v.15 no.2
• /
• pp.5-15
• /
• 2014

Target reliability index in the limit state design indicated the safety margin and it is important to determine the partial factor. To determine the target reliability index which is needed in the limit state design, the six design and construction case histories of gravel compaction piles (GCP) were investigated. The limit state functions were defined by bulging failure for the major failure mode of GCP. The reliability analysis were performed using the first order reliability method (FORM) and the reliability index was calculated for each ultimate bearing capacity formulation. The reliability index of GCP tended to be penportional to the safety factor of allowable stress design and average value was ${\beta}$=2.30. Reliability level that was assessed by reliability analysis and target reliability index for existing structure foundations were compared and analyzed. As a result, The GCP was required a relatively low level of safety compared with deep and shallow foundations and the currd t reliability level were similar to the target reliability in the reinforced earth retaining-wall and soil-nailing. Therefore the target reliability index of GCP suggested as ${\beta}_T$=2.33 by various literatures together with the computed reliability level in this study.

• Journal of the Geological Society of Korea
• /
• v.54 no.6
• /
• pp.615-630
• /
• 2018

Basin analysis is a research field to understand the formation and evolution of sedimentary basins. This task requires various geoscientific datasets as well as numerical and graphical modelling techniques to synthesize results dimensionally in time and space. For basin analysis and modelling in a comprehensive workflow, BasinVis 1.0 was released as a MATLAB-based program in 2016, and recently the software has been extended to BasinVis 2.0, with new functions and revised user-interface. As a case study, this work analyses the southern Vienna Basin and visualizes the sedimentation setting and subsidence evolution to introduce the basin modelling functions of BasinVis 2.0. This is a preliminary study for a basin-scale modelling of the Vienna Basin, together with our previous studies using BasinVis 1.0. In the study area, during the late Early Miocene, sedimentation and subsidence are significant along strike-slip and en-echelon listric normal faults. From the Middle Miocene onwards, however, subsidence decreases abruptly over the area and this situation continues until the Late Miocene. This is related to the development of the pull-apart system and corresponds to the episodic tectonic subsidence in strike-slip basins. The subsidence of the Middle Miocene is confined mainly to areas along the strike-slip faults, while, from the late Middle Miocene, the depocenter shifts to a depression along the N-S trending listric normal faults. This corresponds to the regional paleostress regime transitioning from NE-SW trending transtension to E-W trending extension. This study applies various functions and techniques to this case study, and the modelled results demonstrate that BasinVis 2.0 is effective and applicable to the basin modelling.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.34 no.5
• /
• pp.263-270
• /
• 2021

In this study, a reliability-based design optimization of a 130-m class fixed-type offshore platform, to be installed in the North Sea, was carried out, while considering environmental, material, and manufacturing uncertainties to enhance its structural safety and economic aspects. For the reliability analysis, and reliability-based design optimization of the structural integrity, unity check values (defined as the ratio between working and allowable stress, for axial, bending, and shear stresses), of the members of the offshore platform were considered as constraints. Weight of the supporting jacket structure was minimized to reduce the manufacturing cost of the offshore platform. Statistical characteristics of uncertainties were defined based on observed and measured data references. Reliability analysis and reliability-based design optimization of a jacket-type offshore structure were computationally burdensome due to the large number of members; therefore, we suggested a method for variable screening, based on the importance of their output responses, to reduce the dimension of the problem. Furthermore, a deterministic design optimization was carried out prior to the reliability-based design optimization, to improve overall computational efficiency. Finally, the optimal design obtained was compared with the conventional rule-based offshore platform design in terms of safety and cost.