• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 1999년도 가을 학술발표회 논문집
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• pp.135-142
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• 1999

Plate girder bridges for tile Korean high-speed railway are optimally designed. Static and dynamic constraints are all considered. The design variables are the thicknesses and the lengths of the plates that are used to form I-shaped main girders with variable cross-sections. And the objective function is tile steel weight of a main girder. A C++ based design program is developed; this program interfaces with a FORTRAN based optimization program ADS. From the results of optimal design for various span lengths, it is observed that the deck vertical acceleration is one of the most important constraints in a special range of tile span length. Front a parametric study, sensitivity of the optimal design to static as well as dynamic constraints are presented.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2009년도 춘계학술대회 논문집
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• pp.417-420
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• 2009

The hot forming process of a CAM for vessel engine was designed by finite element (FE) simulation and experimental analysis. An aim of process design was to achieve the near-net shaped CAM forgings by hot forging process. Based on the compression test results of the low alloy steel, deformation processing map was generated using the superposition approach between the dynamic materials model (DMM) and flow stability and/or instability criteria. From the processing map, the initial heating temperature was determined as $1200^{\circ}C$. FE analysis was simulated to predict the formation of rolling defects and deformed shape with different forging designs. Optimum process design suggested in this work was made by comparing with the CAM for vessel engine manufactured by actual forging process.

• Steel and Composite Structures
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• 제6권4호
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• pp.335-351
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• 2006

The present paper hopes to elucidate the problem of determining if a given I-shaped cross-section is properly proportioned to accommodate sufficient plastic hinge rotation capacity to facilitate the redistribution of moments in a structural system as needed to accommodate the formation of a collapse mechanism. It might be tempting to believe that application of the limiting flange plate slenderness value for the case of major axis flexure are applicable in this case; since the pervasive belief is that this approach ought to be conservative. However, the present research study indicates that this is not the case and thus more sophisticated analysis techniques are required to better understand this case.

• 한국수소및신에너지학회논문집
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• 제24권1호
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• pp.44-49
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• 2013

Hydrogen penetration into a metal leads to damages and mechanical degradations and its content measurement is of importance. For a precise measurement, a sample preparation procedure must be optimized through a series of studies on sample washing and drying. In this study, two-step washing with organic solvents and thermal soaking in inert gas were tried with a rod-shaped, API X65 steel sample. The samples were machined from a steel plate and then washed in acetone and etyl-alcohol for 5 minute each and dried with compressed air. After then, the samples were thermally soaked in a home-made nitrogen gas chamber during 10 minute at different heat gun temperatures from 100 to $400^{\circ}C$ and corresponding temperature range in the soaking chamber was from 77 to $266^{\circ}C$ according to the temperature calibration. Hydrogen residue in the samples was measured with a hot extraction system after each soaking step; hydrogen residue of $0.70{\pm}0.12$ wppm after the thermal soaking at $77^{\circ}C$ decayed with increase of the soaking temperature. By adopting the heat transfer model, decay behavior of the hydrogen residue was fitted into an exponential decay function of the soaking temperature. Saturated value or lower bound of the hydrogen residue was 0.36 wppm and chamber temperature required to lower the hydrogen residue about 95% of the lower bound was $360^{\circ}C$. Furthermore, a thermal desorption spectroscopy was done for the fully soaked samples at $360^{\circ}C$. Weak hydrogen peak was observed for whole temperature range and it means that hydrogen-related contaminants of the sample surface are steadily removed by heating. In addition, a broad peak found around $400^{\circ}C$ means that parts of the hydrogen residue are irreversibly trapped in the steel microstructure.

• 한국강구조학회 논문집
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• 제27권6호
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• pp.513-523
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• 2015

H형강 철골 모멘트 골조에서는 기둥의 강축 방향 용접 모멘트접합부를 활용하는 것이 구조적으로 가장 이상적이다. 하지만, 모멘트 골조가 직교하는 경우, 기둥의 약축 방향으로도 용접 모멘트접합부를 사용해야 한다. 국내에서는 특히 강축 및 약축 방향 모두를 용접 모멘트접합부를 자주 사용하는 관행이 있다. 대표적인 연성내진상세인 RBS(reduced beam section, 보단면감소)접합부의 경우 국내외적으로 강축접합 위주로 실험연구가 진행되어 약축 RBS 용접모멘트접합부에 대한 실험자료가 매우 희소하다. 본 연구에서는 RBS를 도입한 약축 용접 모멘트접합부의 내진성능을 실험적으로 고찰하였다. Gilton-Uang (2002)의 선행연구를 참고하여 보 플랜지는 연속판과 맞댐용접하고 웨브는 전단이음판과 C-형 필릿용접부로 설계하여 실험을 수행하였다. 보에 사용된 강재가 내진용 강재가 아닌 일반 SS400 강재임에도 불구하고 3% 이상의 소성회전각을 발휘하였다. 제한된 결과이긴 하지만, 전단이음판과 보 웨브 사이의 C-형 필릿용접부 설계에서 보 웨브에 작용하는 휨모멘트와 전단력의 편심의 영향을 구체적으로 고찰할 필요가 있는 것으로 판단된다. 본 실험결과를 토대로 전단이음판 부근의 보 웨브 파단을 방지할 수 있는 C-형 필릿용접 형상 및 설계방안을 제안하였다. 보 플랜지와 연속판의 완전용입 용접부는 맞댄이음(butt joint) 형식이 되어 국부좌굴에 취약하고 이로 인해 피로파괴가 발생하는 경향이 있으므로 용접작업에 지장이 없는 범위에서 용접접근공(스켈럽)의 크기를 최소화할 필요가 있다. RBS형상, 스틱아웃, 트림, 연속판 두께 증가 등과 같이 이미 검증된 약축 모멘트 용접접합부의 내진상세들은 따르는 것이 바람직하다.

• 한국분말재료학회지
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• 제24권3호
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• pp.202-209
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• 2017

A cold-work tool steel powder is used to fabricate 3-dimensional objects by selective laser melting using a high-pressure gas atomization process. The spherical powder particles form continuous carbide networks among the austenite matrix and its decomposition products. The carbides comprise Nb-rich MC and Mo-rich $M_2C$. In the SLM process, the process parameters such as the laser power (90 W), layer thickness ($25{\mu}m$), and hatch spacing ($80{\mu}m$) are kept fixed, while the scan speed is changed from 50 mm/s to 4000 mm/s. At a low scan speed of 50 mm/s, spherical cavities develop due to over melting, while they are substantially reduced on increasing the speed to 2000 mm/s. The carbide network spacing decreases with increasing speed. At an excessively high speed of 4000 mm/s, long and irregularly shaped cavities are developed due to incomplete melting. The influence of the scan pattern is examined, for which $1{\times}1 mm^2$ blocks constituting a processing layer are irradiated in a random sequence. This island-type pattern exhibits the same effect as that of a low scan speed. Post processing of an object using hot isostatic pressing leads to a great reduction in the porosity but causes coarsening of the microstructure.

• Structural Engineering and Mechanics
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• 제83권4호
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• pp.415-433
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• 2022

Eighteen (18) (120×300×2200 mm) beams were prepared and tested to evaluate the shear strength of Glass Fiber Reinforced Concrete (GFRC) beams with no shear reinforcement, and evaluate the effectiveness of various innovative strengthening systems to increase the shear capacity of the GFRC beams. The test variables are the amount of discrete glass fiber (0.0, 0.6, and 1.2% by volume of concrete) and the type of longitudinal reinforcement bars (steel or GFRP), the strengthening systems (externally bonded (EB) sheet, side near-surface mounted (SNSM) bars, or the two together), strengthening material (GFRP or steel) links, different configurations of NSM GFRP bars (side bonded links, full wrapped stirrups, side C-shaped stirrups, and side bent bars), link spacing, link inclination angle, and the number of bent bars. The experimental results showed that adding the discrete glass fiber to the concrete by 0.6%, and 1.2% enhanced the shear strength by 18.5% and 28%, respectively in addition to enhancing the ductility. The results testified the efficiency of different strengthening systems, where it is enhanced the shear capacity by a ratio of 28.4% to 120%, and that is a significant improvement. Providing SNSM bent bars with strips as a new strengthening technique exhibited better shear performance in terms of crack propagation, and improved shear capacity and ductility compared to other strengthening techniques. Based on the experimental shear behavior, an analytical study, which allows the estimation of the shear capacity of the strengthened beams, was proposed, the results of the experimental and analytical study were comparable by a ratio of 0.91 to 1.15.

• 한국건축시공학회지
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• 제13권5호
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• pp.434-440
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• 2013

최근 건축은 정형의 건축물의 외관과 설계 범위를 벗어난 비정형의 설계, 시각화, 3차원 모델 구현이 이루어지고 있다. 일반 정형건축물과는 달리 비정형건축물의 지붕과 외벽은 디자인 중심의 외벽시스템과 배수, 방수의 성능을 지닌 지붕마감시스템으로 설계되고 시공되었다. 그러나 비정형 건축물은 외벽과 지붕의 구분이 없어지고 외피로의 개념으로 통합된다. 또한 건축설계의 디자인 트렌드가 정형에서 비정형의 자유로운 형태로 급변하고 있어 각종 현상설계 및 턴키 등 설계경기의 당선을 위하여 비정형의 건축물이 자주 등장하고 있다. 기존 비정형 건축구조물의 곡면외피를 시공하기 위해서는 스틸 각파이프나 C형강으로 비정형 형태를 만들고 거기에 외장을 시공한다. 그러나 이는 공사 기간 지연과 높은 공사비용이 소요되는 문제점이 있다. 제작, 설치, 검측 후 비정형 패널의 부착 오류, 줄눈의 불일치, 곡면의 직선 시공 등의 오류가 매우 빈번히 발생하고 있다. 이에 본 연구는 3차원 좌표제어 기술의 하나인 CNC Twisted Tube 공법을 적용한 구조체의 시공과정을 면밀히 검토하여 3차원 좌표제어 기술로 비정형 건축물의 구현 방안을 제시한다.

• Steel and Composite Structures
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• 제27권3호
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• pp.337-353
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• 2018

In previous weak-axis moment connection tests, brittle fracture always initiated near the edge of the beam flange groove weld due to force flow towards the stiffer column flanges, which is the opposite pattern as strong-axis moment connections. As part of the China NSFC (51278061) study, this paper tested two full-scale novel weak-axis reduced beam section moment connections, including one exterior frame connection specimen SJ-1 under beam end monotonic loading and one interior frame joint specimen SJ-2 under column top cyclic loading. Test results showed that these two specimens were able to satisfy the demands of FEMA-267 (1995) or ANSI/AISC 341-10 (2010) without experiencing brittle fracture. A parametric analysis using the finite element software ABAQUS was carried out to better understand the cyclic performance of the novel weak-axis reduced beam section moment connections, and the influence of the distance between skin plate and reduced beam section, a, the length of the reduced beam section, b, and the cutting depth of the reduced beam section, c, on the cyclic performance was analyzed. It was found that increasing three parametric values reasonably is beneficial to forming beam plastic hinges, and increasing the parameter a is conducive to reducing stress concentration of beam flange groove welds while increasing the parameters b and c can only reduce the peak stress of beam flange groove welds. The rules recommended by FEMA350 (2000) are suitable for designing the proposed weak-axis RBS moment connection, and a proven calculation formulation is given to determine the thickness of skin plate, the key components in the proposed weak-axis connections. Based on the experimental and numerical results, a design procedure for the proposed weak-axis RBS moment connections was developed.

• 한국진공학회지
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• 제7권1호
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• pp.1-4
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• 1998

이온 펌프의 중심에 네그(Non-Evaporable Getters)가 삽입된 새로운 조합 펌프를 사용하여 극고진공 시스템을 구현하였다. 진공 용기는 터보 분자 펌프만으로도 극고진공에 성공하였던, $450^{\circ}C$에서 잘 산화된 304 스테인레스 스틸 쳄버를 사용하였다. 시스템의 압력은 Leybold사의 EXG(Extractor Gauge)로 측정하였으나, 본 실험에서의 최고 진공도는 이미 그 게이지의 측정 한계인 1~$2\times10^{-12}$torr범위를 훨씬 지나 게이지 지시가 $-0\times10^{-12}$torr를 읽교 있는 극고진공에 도달해 있었다. 이는 효과적인 네그 활성화로 수소 가스에 대한 배기 속도 를 크게 향상시켜준 결과라 볼 수 있다. 또한 본 실험은 극고진공 표면 분석 장치의 실현 가능성을 시사해주는 것으로, 앞으로의 초미세 표면 과학에 있어서 새로운 장을 열어줄 것 으로 기대된다.