• Journal of the Korean Institute of Gas
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• v.5 no.1
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• pp.1-6
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• 2001

The main objective of this study is to determine if the sources of AE in corroded specimens of aluminum could be identified iron the characteristics of the waveform signals recorded during fatigue loading. Coupons of notched 2024-T3 aluminum with or without corrosion (at the notch) were subjected to fatigue loading and the AE signals were recorded using non-resonant, flat, wide-band transducers. The time history and power spectrum of each individual wave signal recorded during fatigue crack growth were examined and classified according to their special characteristics. Five distinct types of signals were observed regardless of specimen condition. The waveform and power spectra were shown to be dependent on specimen condition. During the initial phase of crack growth, the signals obtained in the as-received specimens are most probably due to transgranular cleavage caused by extrusion and intrusion under fatigue loading. In the corroded specimen the signal are probably generated by intergranular cleavage due to embrittlement of grain boundary neat the pitting tip. The need for additional research to further validate these findings is indicated.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.2 no.2
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• pp.1-5
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• 2001

One of the major advantages of using engineering plastics is ease of part assembly through a locking mechanism known as a snap fit. The typical snap fit involves a short cantilever beam with a projection at the free end. which slides over a one way ramp on the mating part to lock in place. The tightness of the mechanism is determined by the lateral interference of the two sliding members If too small they become loose and can't hold together. while if too large. excessive force can be generated. causing failure of the cantilever beam during the assembly operation. Therefore. the accurate determination of the force-deflection relationship for cantilever beams is a key element in snap fit design. And also. the process of injection molding should be considered when cantilever beam is designed. But it is not easy for novice designers to design them appropriately because of the profound knowledge related to injection molding. In this paper. an intelligent design program has been developed and proposed to improve a conventional empirical design method.

• Composites Research
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• v.12 no.3
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• pp.55-65
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• 1999

In this paper, the thermal buckling and postbuckling behaviour of composite beam with embedded shape memory alloy (SMA) wires are investigated experimentally and analytically. The results of thermal buckling tests on uniformly heated, clamped, composite beam embedded with SMA wire actuators are presented and discussed in consideration of geometric imperfections, slenderness ratio of beam and embedding position of SMA wire actuators. The shape recovery force can reduce the thermal expansion of composite laminated beam, which result in increment of the critical buckling temperature and reduction of the lateral deflection of postbuckling behaviours. It is presented quantitatively on the temperature-load-deflection behaviour records how the shape recovery force affects the thermal buckling. The cross tangential method is suggested to calculate the critical buckling temperature on the temperature-deflection plot. Based on the experimental analysis, the new formula is also proposed to describe the critical buckling temperature of a laminated composite beam with embedded SMA wire actuators.

• Journal of the Korean Institute of Gas
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• v.13 no.4
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• pp.27-32
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• 2009

This paper presents the stress and deformation behaviors using the finite element method as a function of the thickness of the helmets without the bead frames on the top of the shell structure. The helmet that would provide head and neck protections without causing discomfort to the user when it was worn for long periods of time should be manufactured for increasing the safety and impact energy absorption. The FEM computed results show that when the impulsive force is applied on the top surface of a helmet, the maximum stress and strain have been occurred around the position of an applied impact force, which may lead to the initial failure on the top surface of the helmet shell. As the helmet thickness is decreased from 4mm to 2mm, the impact energy absorbing rate is radically increased, and the maximum stress of the helmet is increased over the tensile strength, 54.3MPa of the thermoplastic material. Thus, the top surface of the helmet should be supported by a bead frame and increased thickness of the shell structure.

• Journal of the Korean Society for Nondestructive Testing
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• v.27 no.2
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• pp.157-163
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• 2007

Crack detection technique for concrete structures has been developed in this study. Experimental tests were carried out to detect a surface and internal crack, employing common fiber optic cables and OTDR(optical time domain reflectometry), an optical signal analyzer which is widely used to detect damages at fiber optic cables in the field of optical engineering. While initial concrete crack is ready to occur under cracking force, the occurrence and location of the crack are simultaneously detected to give the same damage to fiber optic cables which have been attached to and/or embedded into concrete in advance. It is obtained through successive tests that the principal factors for crack detection is the covering state of fiber optic cable, and total 4 tests including a preliminary test were conducted and the crack detection technique was verified. The practical usefulness would be expected at crack management and maintenance of concrete structures.

• Journal of Korean Society of Steel Construction
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• v.11 no.1 s.38
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• pp.69-78
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• 1999

When the lateral forces are applied to a frame, columns in the frame are usually accompanied with sidesway. If this sidesway is large, the frame is subjected to buckling and an early yielding of members which reduces the overall frame stiffness. In this study, numerical analysis of frames were conducted to evaluate the ultimate lateral strength of steel moment resisting frames permitted to sidesway under axial and lateral forces, and develope the procedure for determining the limits of column slenderness ratios. In the numerical analysis, the effects of the relative stiffness ratio between beam and column, deterioration of overall frame stiffness, slenderness ratio and loading conditions were considered. The elasto-plastic analysis method in which the $P-{\Delta}$effect is implemented, presented by the author previously, was adopted in the analysis. Incremental lateral forces were applied to the frame under constant axial loads and the generalized inverse is employed for the post-ultimate behavior.

• Journal of Korean Society of Steel Construction
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• v.17 no.2 s.75
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• pp.217-225
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• 2005

The purpose of this study is to investigate the behavior of H-shape column base plates subjected to axial loads and moments. In this study, the behavior of H-shape column base plates is investigated using finite element analysis method and an analytical modelingof the base plates is obtained. The variations of six test specimens include ratiosof axial load, sizes of anchor bolts, and thicknesses of base plates. The experimental results are compared with the results from the finite element analyses and those of the analytical modeling. Bearing pressures of base plates from the finite element analyses are compared with those that are assumed in the design of the base plates. From the results of the research, it is observed that the initial stiffness and yield strengths in the analytical study are very similar to the experimental results. And bearing pressures are concentrated under column section with thin base plates.

• Journal of Korean Society of Steel Construction
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• v.18 no.4
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• pp.491-502
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• 2006

This paper summarizes full-scale test results on CFT column-to- flat plate connections has gained wide acceptance subjected to gravity loading. CFT construction has gained wide acceptance in a relatively short time in domestic building construction practice due to its various structural and construction advantages. However, efficient details for CFT column to flat plate connections have not been proposed yet. Based on the strategies that maximize economical field construction, several connecting schemes were proposed and tested. Test results showed strength and connection stiffness exceeding those of R/C flat p late counterparts. A semi-analytical procedure is presented to model the behavior of CFT column-to-flat plate connections. The five parameters to model elastic to post-punching catenary action range are calibrated based on the limited test data of t to progressive collapse prevention design is also illustrated.

• Journal of Korean Society of Steel Construction
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• v.22 no.6
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• pp.599-608
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• 2010

Steel trusses that act compositely with concrete slabs have proven to be an economical system for long-span floors. The composite action is generally achieved by providing shear connections between the steel top chord and the concrete topping. The composite sections have greater stiffness than the sum of the individual stiffnesses of the slab and truss. Therefore, steel trusses that act compositely with concrete slabs can carry larger loads and are stifferand less prone to transient vibration. During the tests that were performed in this study, the crack pattern and deflection of the beam of the composte truss were investigated. The test results were compared with the results for the noncomposite trusses.

• 한국방재학회:학술대회논문집
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• 2011.02a
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• pp.165-165
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• 2011

내진 설계규정이 적용되기 이전에 시공되어 사용 중인 교량의 경우 지진 발생시 교각의 파괴 또는 구조적 피해는 교량 전체 시스템의 붕괴를 초래하므로 지진하중에 대하여 피해를 최소화해야 한다. 이를 위해 내진설계규정이 적용되기 이전의 교량 또는 지진취약지역으로 분류된 곳의 교량, 사회적 중요도가 높은 교량에 대해 교각의 내진성능보강을 실시하고 있다. 2007년 말 국토해양부가 관리하고 있는 11,940개 교량 중 지진 발생시 피해가 우려되는 1,342개(일반국도 682개, 고속국도 600개) 교량에 대해 2006년부터 내진보강이 착수되었고 2009년에는 확대 추진하여 일반국도 80개교, 고속국도 100개교에 대한 보강을 실시하였다. 이와 같이 확대 추진되고 있는 정책에 반해, 내진보강 기술 및 제품이 부족하고 새로운 내진보강재 개발이 불가피해지고 있는 것이 현실이다. 소성영역에서의 횡방향 철근은 지진 시 종방향 철근의 좌굴과 콘크리트의 압축강도저하를 방지하며, 전단보강철근으로도 중요한 역할을 하여 교각의 전단강도를 증가시킨다. 그러나 이러한 횡방향 철근은 초기 설계에 의한 시공이 종료된 후 기존의 성능을 증가시키기 위하여 철근량을 증가하거나 단면의 변화를 주기에는 매우 어려운 일이다. 따라서 내진성능을 위한 단면력 증가를 위하여 다양한 재료의 보강재와 형식이 사용되고 있다. 본 연구에서는 원형교각 모델의 구조해석을 이용해 내진성능평가를 선행한 후 실험체를 제작, Helical Bar를 보강하여 준정적 실험을 통해 내진보강성능을 평가하였다. 압축설계강도 $f_{ck}=240kgf/cm^2$를 기준으로 교량등급 2등교인 일반적인 도로교의 1/4축소모형을 설계, 기초부는 $1,200{\times}600{\times}600$ (mm)으로 철근과 콘크리트로 구성하였으며, 기둥부는 직경 400mm, 높이 1,250mm 크기의 철근콘크리트 원형 교각 실험체를 제작하였다. 제작된 실험체는 총 3개로, 분류는 무보강 일반 실험체, Helical Bar 직경에 따른 분류, 보강간격에 따른 분류로 나누어진다.