• Steel and Composite Structures
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• 제28권2호
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• pp.233-250
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• 2018

Back-to-back built-up cold-formed steel un-lipped channel sections are used in cold-formed steel structures; such as trusses, wall frames and portal frames. In such built-up columns, intermediate fasteners resist the buckling of individual channel-sections. No experimental tests or finite element analyses have been reported in the literature for back-to-back built-up cold-formed steel un-lipped channel sections and specially investigated the effect of screw spacing on axial strength of such columns. The issue is addressed in this paper. The results of 95 finite element analyses are presented covering stub to slender columns. The finite element model is validated against the experimental tests recently conducted by authors for back-to-back built-up cold-formed steel lipped channel sections. The verified finite element model is then used for the purposes of a parametric study to investigate the effect of screw spacing on axial strength of back-to-back built-up cold-formed steel un-lipped channel sections. Results are compared against the built-up lipped channel sections and it is shown that the axial strength of un-lipped built-up sections are 31% lesser on average than the built-up lipped channel sections. It was also found that the American Iron and Steel Institute (AISI) and the Australian and New Zealand Standards were over-conservative by around 15% for built-up columns failed through overall buckling, however AISI and AS/NZS were un-conservative by around 8% for built-up columns mainly failed by local buckling.

• Journal of the Korean Wood Science and Technology
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• 제35권6호
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• pp.118-125
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• 2007

경골목조건축공법에서 개구부의 헤더로 많이 사용되는 조립보에 대한 설계자료를 구하기 위하여 $2{\times}6$ ($38{\times}140 mm$), $2{\times}8$ ($38{\times}184 mm$), $2{\times}10$ ($38{\times}235 mm$) 및 $2{\times}12$ ($38{\times}286 mm$) 부재를 3개 겹쳐서 휨 시험편을 제작하였다. 이들에 대한 휨 시험을 통하여 조립보에 대한 허용응력을 구하고 허용응력에 근거하여 여러 가지 하중 조건에 대한 경간표를 작성하였다. 조립보에 대한 휨 시험 결과로부터 10 mm의 처짐이 발생할 때의 휨응력을 조립보 헤더의 휨강도로 산정하였다. 조립보에 대한 경간표는 외벽에서 헤더가 사용되는 위치에 따른 5가지 하중조건과 내벽에서 헤더가 사용되는 위치에 따른 2가지 하중조건을 고려하여 작성할 수 있는 것으로 생각된다. 총 7가지 하중 조건에 있어서 외벽에 사용되는 헤더에 대한 5가지 하중조건에서는 고정하중, 활화중 및 적설하중이 포함되었으며 내벽에 사용되는 헤더에 대한 2가지 하중조건에서는 고정하중과 활하중이 포함되었다.

• Steel and Composite Structures
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• 제31권6호
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• pp.601-615
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• 2019

In cold-formed steel (CFS) structures, such as trusses, wall frames and columns, the use of back-to-back built-up CFS angle sections are becoming increasingly popular. In such an arrangement, intermediate fasteners are required at discrete points along the length, preventing the angle-sections from buckling independently. Limited research is available in the literature on the axial strength of back-to-back built-up CFS angle sections. The issue is addressed herein. This paper presents the results of 16 experimental tests, conducted on back-to-back built-up CFS screw fastened angle sections under axial compression. A nonlinear finite element model is then described, which includes material non-linearity, geometric imperfections and explicit modelling of the intermediate fasteners. The finite element model was validated against the experimental test results. The validated finite element model was then used for the purpose of a parametric study comprising 66 models. The effect of fastener spacing on axial strength was investigated. Four different cross-sections and two different thicknesses were analyzed in the parametric study, varying the slenderness ratio of the built-up columns from 20 to 120. Axial strengths obtained from the experimental tests and finite element analysis were used to assess the performance of the current design guidelines as per the Direct Strength Method (DSM); obtained comparison showed that the DSM is over-conservative by 13% on average. This paper has therefore proposed improved design rules for the DSM and verified their accuracy against the finite element and test results of back-to-back built-up CFS angle sections under axial compression.

• 한국정보과학회논문지:소프트웨어및응용
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• 제29권1_2호
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• pp.65-79
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• 2002

객체지향 프레임웍은 다수의 응용 소프트웨어의 개발에 반복적으로 재사용되므로 철저한 시험이 요구될 뿐만 아니라 재사용 시 확장된 프레임웍에 대해서도 추가적인 시험이 필요하다. 그런데 프레임웍은 개조, 합성된 확장 부위의 시험에 대한 제어와 관찰을 어렵게 하는 성질을 갖고 있다. 본 논문에서는 프레임웍을 개조, 확장하여 응용 프로그램을 구현할 때 발생할 수 있는 오류들이 시험을 통하여 효율적으로 발견될 수 있도록 프레임웍의 가변 부위에 테스터 컴포넌트들을 BIT(Built-in Test)로 내장하는 방법을 기술한다. 프레임웍에 이와 같이 내장된 테스터 컴포넌트들은 프레임웍의 시험 시 제어와 관찰을 용이하게 하여 프레임웍의 시험성을 높여준다. 여기서 제안된 방법으로 설계된 테스터 컴포넌트들은 시험대상 프레임웍의 확장 부위에 프레임웍 코드의 변경이나 간섭 효과가 없게 부착할 수 있고 필요에 따라 동적으로 탈착할 수 있다.

• Structural Engineering and Mechanics
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• 제70권4호
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• pp.499-511
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• 2019

In this study, the axial compressive behavior of novel quadruple C-channel built-up cold-formed steel columns with different slenderness ratio was investigated, using the experimental and numerical analysis. The axial compressive capacity and failure modes of the columns were obtained and analyzed. The finite element models considering the geometry, material and contact nonlinearity were developed to simulate and analyze the structural behavior of the columns further. There was a great correlation between the numerical analyses and test results, which indicated that the finite element model was reasonable and accurate. Then influence of, slenderness ratio, flange width-to-thickness ratio and screw spacing on the mechanical behavior of the columns were studied, respectively. The tests and numerical results show that due to small slenderness ratio, the failure modes of the specimens are generally local buckling and distortional buckling. The axial compressive strength and stiffness of the quadruple C-channel built-up cold-formed steel columns decrease with the increase of maximum slenderness ratio. When the screw spacing is ranging from 150mm to 450mm, the axial compressive strength and stiffness of the quadruple C-channel built-up cold-formed steel columns change little. The axial compressive capacity of quadruple C-channel built-up cold-formed steel columns increases with the decrease of flange width-thickness ratio. A modified effective length factor is proposed to quantify the axial compressive capacity of the quadruple C-channel built-up cold-formed steel columns with U-shaped track in the ends.

• Wind and Structures
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• 제22권4호
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• pp.503-524
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• 2016

The suitability of Computational Fluid Dynamics (CFD) simulations on the built environment for the purpose of estimating average roughness characteristics and for studying wind flow patterns within the environment is assessed. Urban models of various levels of complexity are considered including an empty domain, array of obstacles arranged in regular and staggered manners, in-homogeneous roughness with multiple patches, a semi-idealized built environment, and finally a real built environment. For each of the test cases, we conducted CFD simulations using RANS turbulence closure and validated the results against appropriate methods: existing empirical formulas for the homogeneous roughness case, empirical wind speed models for the in-homogeneous roughness case, and wind tunnel tests for the semi-idealized built environment case. In general, results obtained from the CFD simulations show good agreement with the corresponding validation methods, thereby, giving further evidence to the suitability of CFD simulations for built environment studies consisting of wide-ranging roughness. This work also provides a comprehensive overview of roughness modeling in CFD-from the simplest approach of modeling roughness implicitly through wall functions to the most elaborate approach of modeling roughness explicitly for the sake of accurate wind flow simulations within the built environment.

• Steel and Composite Structures
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• 제45권6호
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• pp.907-929
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• 2022

Compression experiments were conducted to investigate the compressive behavior of built-up open-section columns consisting of four cold-formed steel channels (BOCCFSs) of different lengths, thicknesses, and cross-section sizes (OB90 and OB140). The load-displacement curves, failure modes, and maximum compression strength values were analyzed in detail. The tests showed that the failure modes of the OB90 specimens transformed from a large deformation concentration induced by local buckling to flexural buckling with the increase in the slenderness ratio. The failure modes of all OB140 specimens were deformation concentration, except for one long specimen, whose failure mode was flexural buckling. When the slenderness ratios of the specimens were less than 55, the failure modes were controlled by local buckling. Finite element models were built using ABAQUS software and validated to further analyze the mechanical behavior of the BOCCFSs. A parametric study was conducted and used to explore a wide design space. The numerical analysis results showed that when the screw spacing was between 150 mm and 450 mm, the difference in the maximum compression strength values of the specimens was less than 4%. The applicability and effectiveness of the design methods in Chinese GB50018-2002 and AISI-S100-2016 for calculating the compression strength values of the BOCCFSs were evaluated. The prediction methods based on the assumptions produced predictions of the strength that were between 33% to 10% conservative as compared to the tests and the finite element analysis.

• Steel and Composite Structures
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• 제42권4호
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• pp.513-538
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• 2022

This paper reports on experiments addressing the buckling and collapse behavior of an innovative built-up cold-formed steel (CFS) columns. The built-up column consists of four individual CFS lipped channels, two of them placed back-to-back at the web using two self-drilling screw fasteners at specified spacing along the column length, while the other two channels were connected flange-to-flange using one self-drilling screw fastener at specified spacing along the column length. In total, 12 experimental tests are reported, covering a wide range of column lengths from stub to slender columns. The initial geometric imperfections and material properties were determined for all test specimens. The effect of screw spacing, load-versus axial shortening behaviour and buckling modes for different lengths and screw spacing were investigated. Nonlinear finite element (FE) models were also developed, which included material nonlinearities and initial geometric imperfections. The FE models were validated against the experimental results, both in terms of axial capacity and failure modes of built-up CFS columns. Furthermore, using the validated FE models, a parametric study was conducted which comprises 324 models to investigate the effect of screw fastener spacing, thicknesses and wide range of lengths on axial capacity of back-to-back and flange-to-flange built-up CFS channel sections. Using both the experimental and FE results, it is shown that design in accordance with the American Iron and Steel Institute (AISI) and Australia/New Zealand (AS/NZS) standards is slightly conservative by 6% on average, while determining the axial capacity of back-to-back and flange-to-flange built-up CFS channel sections.

• 대한임베디드공학회논문지
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• 제5권4호
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• pp.217-224
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• 2010

Nowadays, people perform their tasks anywhere anytime using their mobile devices. For this reason, data synchronization (DS) between mobile devices and a central server has become one of the most essential technologies in mobile environments. Currently, several mobile DS protocols are proposed and used. However, the existing DS protocols cannot guarantee interoperability between them. To solve the problem, an embedded DS gateway has been developed in our previous study. The gateway runs on a Windows Mobile-based emulator. It converts data on a mobile device into common data specified by OMA DS standard protocol and vice versa. The embedded gateway has been built to support the OMA DS standard protocol. In order to verify that the embedded gateway conforms to the OMA DS standard protocol, two kinds of OMA conformance tests have to be conducted - interoperability test with an OMA DS-based server and conformance test with SCTS (SyncML Conformance Test Suit). In this paper, some parts of the gateway previously built are modified and the modified gateway is installed on a Windows Mobile-based smart phone. And the interoperability test and the conformance test with the SCTS are conducted. The results of the tests show that the embedded DS gateway operates properly on the Windows Mobile-based smart phone and that the gateway passes the tests, verifying its conformity to the OMA DS standard protocol. In addition, DS performance tests show that DS delay times between a real smart phone and a DS server increase gently as the number of DS data increases. In other words, the embedded DS gateway built in this paper can be used for a real smart phone at a reasonable performance cost.

• 대한전자공학회논문지SD
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• 제40권8호
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• pp.610-618
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• 2003

테스터를 사용하는 테스트 방법이 매우 비싸고 동작속도에서의 테스트가 어려운 상황에서 BIST의 출현 은 이러한 난점을 해결하는 좋은 방법이다. 하지만, 이러한 BIST에도 해결해야 할 문제점들이 많다. 의사 무작위 테스트시 패턴 카운터와 비트 카운터의 역할이 단순히 카운팅만 하는데 한정되어 있으므로 이들 카운터를 패턴을 생성하는 역할에도 이용함으로써 BIST의 효율을 증대시키고자 한다. 새로운 BIST 구조는 LFSR이 아닌 카운터로 패턴을 생성하고 LFSR로 이의 동작을 무작위하게 또는 의도적으로 조정함으로써 다른 테스트 성능의 저하 없이 테스트 하드웨어를 축소하는 방법을 제안한다. 결정 테스트를 위한 하드웨어가 너무 크게 되는 단점을 해결하고자 본 논문에서의 실험은 실험결과에서 의사 무작위 테스트와 결정 테스트의 성능을 고장검출을, 테스트 시간과 하드웨어 관련 인자들로 표현한다.