• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1999년도 봄 학술발표회 논문집(I)
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• pp.393-398
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• 1999

The main objective of this project is to define the ultimate bond performance of domestic prestressing strands in the precast prestensioned concrete beams. Eight specimens from four different companies were fabricated and tested in this study. Four-point loading tests were performed on the beams of domestic strands with an arbitrary anchorage length. The research has shown, that all seven specimens except one failed in bond are capable of developing their full flexural capacity and the strands within them are fully anchored even with the sudden transfer of frame cutting. Following results are summarized from the tests conducted. 1) All of the specimens are tested at an embedment lengths much shorter than those required by the ACI code, failed in flexure except one failed in bond. 2) It seems that the beam depth can not be an effective variable to estimate the bond length within these sections and length of specimens on this tests. 3) The development length with the stirrup space which are considered for correction factors in the equations of Russel and Paulsgrove, is fully accurate to determine the required length for the beam tested in this research.

• 전기학회논문지
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• 제58권4호
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• pp.788-794
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• 2009

To assess the condition of stator insulation, nondestructive tests were performed on twenty five coil groups and twenty six motors. The stator windings has nominal ratings of 6.6kV and are classified into five coil groups ;one group with healthy insulation and four groups with four different types of artificial defects. After completing nondestructive tests, the AC voltage applied to the stator windings was gradually increasing until insulation failure in order to obtain the breakdown voltage. No.1, No.2 and No.6 of 6.6kV motors failed near rated voltage of 14kV, 8.7kV and 14kV, respectively. The breakdown voltage of three motors was lower that expected for good quality coils(14.2kV) in 6.6kV motors. No.3 and No.6 of 4.16kV motors failed near rated voltage of 5.6kV and 4.2kV, respectively. Almost all of failures were located in a line-end coil at the exit from the core slot. The breakdown voltages and the types of defects showed strong relation to the stator insulation tests such as in the case of AC current, dissipation factor(tan${\delta}$) and partial discharge magnitude.

• 한국산학기술학회논문지
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• 제7권3호
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• pp.393-397
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• 2006

신제품에 대한 개발 주기가 짧아지고 있는 현시점에서 제품의 수명을 예측하고 평가하기 위한 방법으로 가속 수명시험과 시험을 통해 관측된 고장 데이터의 분석에 대한 관심이 증대되고 있다. 이에 따라 가속 수명시험을 위한 시험 조건과 고장 데이터의 정확한 분석을 위한 고장 데이터의 최적 분포 결정 방법에 대한 관심 또한 증대되고 있다. 따라서 본 논문에서는 고장 데이터를 기반으로 신뢰성 예측을 할 때 사용하는 분포 함수 결정을 위한 방법으로 관측된 고장 데이터만의 분포를 고려하는 Anderson-Darling 방법과 관측된 고장 데이터의 수명-스트레스 관계식을 적용하여 고장 데이터의 분포를 결정하는 Likelihood Function 방법을 비교한다. 두 가지 방식을 비교한 결과 각 방식에 의해 선택되는 최적분포가 다르며, 따라서 각 방식에 의해 선택된 최적 분포에 의해서 예측되는 수명도 다름을 알 수 있다.

• 한국산학기술학회논문지
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• 제13권11호
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• pp.5572-5577
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• 2012

사면파괴가 발생한 사면의 하부 연약지반에 대한 현장원치시험결과와 실내시험결과 그리고 강도 추정식에 의한 결과를 상호 비교분석해 보았다. 사면 하부연약지반에 대한 콘관입시험결과와 현장베인시험결과의 비교를 통해 결정된 연약지반의 콘계수값은 12였다. 콘관입시험자료로부터 콘계수 추정식을 적용하여 구한 연약지반의 비배수강도는 현장베인시험에 의한 그것보다 보수적인 값을 주었다. 압밀시험결과를 이용한 추정식을 통해 연약지반의 비배수강도를 추정하고 현장베인시험에 의한 비배수강도와 비교해 보았다. 세 가지 방법을 통한 추정결과에 따르면 Jamiolkowsky 방법에 의한 결과가 시험을 통해 구한 결과에 가장 근접하였으며 현장베인시험에 의한 비배수강도에 비해 0.88~1.23 범위의 값을 보였다.

• Steel and Composite Structures
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• 제33권1호
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• pp.37-66
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• 2019

In cold-formed steel structures, such as trusses, wall frames and portal frames, the use of back-to-back built-up cold-formed stainless-steel lipped channels as compression members are becoming increasingly popular. The advantages of using stainless-steel as structural members are corrosion resistance and durability, compared with carbon steel. The AISI/ASCE Standard, SEI/ASCE-8-02 and AS/NZS do not include the design of stainless-steel built-up channels and very few experimental tests or finite element analyses have been reported in the literature for such back-to back cold-formed stainless-steel channels. Current guidance by the American Iron and Steel Institute (AISI) and the Australian and New Zealand (gAS/NZS) standards for built-up carbon steel sections only describe a modified slenderness approach, to consider the spacing of the intermediate fasteners. Thus, this paper presents a numerical investigation on the behavior of back-to-back cold-formed stainless-steel built-up lipped channels. Three different grades of stainless steel i.e., duplex EN1.4462, ferritic EN1.4003 and austenitic EN1.4404 have been considered. Effect of screw spacing on the axial strength of such built-up channels was investigated. As expected, most of the short and intermediate columns failed by either local-global or local-distortional buckling interactions, whereas the long columns, failed by global buckling. All three grades of stainless-steel stub columns failed by local buckling. A comprehensive parametric study was then carried out covering a wide range of slenderness and different cross-sectional geometries to assess the performance of the current design guidelines by AISI and AS/NZS. In total, 647 finite element models were analyzed. From the results of the parametric study, it was found that the AISI & AS/NZS are conservative by around 10 to 20% for cold-formed stainless-steel built-up lipped channels failed through overall buckling, irrespective of the stainless-steel grades. However, the AISI and AS/NZS can be un-conservative by around 6% for all three grades of stainless-steel built-up channels, which failed by local buckling.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2008년도 Techno-Fair 및 추계학술대회 논문집 전기물성,응용부문
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• pp.93-94
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• 2008

Diagnostic tests were performed in three high voltage motors. These tests included insulation resistance, polarization index, ac current, dissipation factor($tan{\delta}$) and partial discharge magnitude. The rewind of motor stator insulation at rated voltage is assessed by the results of these tests. After completing the diagnostic tests, the stator windings of motors were subjected to gradually increasing ac voltage, until the insulation punctured. NO.1 and No.2 motors failed near rated voltage of 14.0 kV, respectively. These motors are lower that expected for good quality coils in 6.6 kV class motors. The breakdown voltage of No.3 motor was 15.0 kV.

• Steel and Composite Structures
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• 제28권4호
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• pp.449-460
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• 2018

This paper reports the experimental results of three through bolt beam-column connections under pure shear forces using modified push-out tests. The investigated specimens include extended end-plates and six through-bolts connecting square concrete-filled steel tubular column (S-CFST) to steel beams. The main goal of this study is to investigate if and how the mechanical shear connectors, such as steel angles and stud bolts, contribute to the shear transfer mechanisms in the steel-concrete interface of the composite column. The contribution of shear studs and steel angles to improve the shear resistance of steel-concrete interface in through-bolt connections was investigated using tests. The results showed that their contribution is not significant when the beam-column connection is included in the push-out tests. The specimens failed by pure shear of the long bolts, and the ultimate load can be predicted using the shear resistance of the bolts under shear forces. The predicted values of load allowed obtaining a good agreement with the tests results.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2010년도 하계학술대회 논문집
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• pp.124-124
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• 2010

Diagnostic tests were performed on six high voltage motors. These tests included ac current, dissipation factor(tan6) and partial discharge(PD) magnitude. The rewind of motor stator insulation at rated voltage is assessed by the results of these tests. After completing the diagnostic tests, the stator windings of motors were subjected to gradually increasing ac voltage, until the insulation punctured. No. 1 and No.2 motors(4.16 kV) failed near rated voltage of 12.3 kV and 14.2 kV, respectively. The breakdown voltage of No.3 and No.4 motors(6.6 kV) was 17.6 kV and 17.8 kV, respectively. These motors are higher that expected for good quality coils in 6.6 kV class motors.

• Corrosion Science and Technology
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• 제4권5호
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• pp.211-216
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• 2005

Failure analysis of the latch ram ball and the C-ram ball with the trade name AFBMA Gr. 50 Colmonoy No. 6, has been performed to identify the root cause of the failure. The study required the extraction of the both failed and normal balls from the nuclear fuel exchanger. Microstructures of both balls were examined after polishing and etching. Breaking tests of both the ball revealed similarity in cleavage surfaces. Fracture surfaces of both failed ball and normal ball after breaking test were examined with SEM and EDX. Microstructure of the ball revealed an austenite phase with coarse Cr rich precipitate. Indented marks observed on the surface of the failed ball are believed to be produced by overloading. In the light of the afore mentioned observations and studies, the failure mechanism of the ball in nuclear fuel exchanger seem to be caused by impact or mechanical overloading on ball.

• International Journal of Naval Architecture and Ocean Engineering
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• 제10권3호
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• pp.403-412
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• 2018

Medium-scale tests were conducted to measure and observe the strength and failure behavior of freshwater ice rubble. A custom box measuring $3.05m{\times}0.94m{\times}0.94m$, with Plexiglas walls was built so that failure mechanisms could be observed. Ice rubble beams of nominal thickness 50 cm were produced by placing randomly sized ice pieces into the box filled with water at its freezing temperature. After the specified consolidation time, ranging between 0.2 and 70.5 h, the ice rubble beam was deformed by pushing a platen vertically downwards though the center of the beam until failure. For consolidation times less than 4 h, the ice beam failed progressively and tended to fail by shearing on macroscopic scale. At times greater than 4 h the beam failed by bending. The change in failure behaviour has been attributed to the degree of bonding between ice blocks.