• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2008년도 춘계 학술발표회 제20권1호
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• pp.249-252
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• 2008

이 논문에서는 비부착 CFRP 판으로 긴장된 RC(Reinforced Concrete) 보의 비선형 해석방법을 제시하였다. 하중 재하 시 부재의 단면 내에서 변화하는 재료상태를 정확히 예측하기 위해 철근콘크리트 뼈대는 콘크리트와 보강철근 화이버로 구성된 화이버모델요소로 이상화하였다. 또한 CFRP 판의 비부착 거동을 모사하기 위해 CFRP 판을 뼈대요소의 각 절점에 연결되는 여러 개의 요소로 이상화하되, 연결부에서 슬립이 가능한 것으로 가정하여 슬립으로 인한 CFRP 판의 인장력을 반복적으로 보정함으로써 CFRP 판요소들의 응력이 같도록 하였다. 이 논문에서 제시한 해석방법의 정당성을 검토하기 위해 비부착 CFRP 판으로 긴장된 RC 보의 극한해석을 수행하여 해석결과를 타 연구자의 실험결과와 비교해 본 결과, 두 연구결과가 잘 일치함을 확인하였다.

• Geomechanics and Engineering
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• 제37권3호
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• pp.293-306
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• 2024

Influenced by the alternating effects of dynamic and static pressure during the mining process of close range coal seams, the surrounding rock support of cross mining roadway is difficult and the deformation mechanism is complex, which has become an important problem affecting the safe and efficient production of coal mines. The paper takes the inclined longwall mining of the 10304 working face of Zhongheng coal mine as the engineering background, analyzes the key strata fracture mechanism of the large inclined right-angle trapezoidal mining field, explores the stress distribution characteristics and transmission law of the surrounding rock of the roadway affected by the mining of the inclined coal seam, and proposes a segmented and hierarchical support method for the cross mining roadway affected by the mining of the close range coal seam group. The research results indicate that based on the derived expressions for shear and tensile fracture of key strata, the ultimate pushing distance and ultimate suspended area of a right angle trapezoidal mining area can be calculated and obtained. Within the cross mining section, along the horizontal direction of the coal wall of the working face, the peak shear stress is located near the middle of the boundary. The cracks on the floor of the cross mining roadway gradually develop in an elliptical funnel shape from the shallow to the deep. The dual coupling support system composed of active anchor rod support and passive U-shaped steel shed support proposed in this article achieves effective control of the stability of cross mining roadways, which achieves effective control of floor by coupling active support and preventive passive support to improve the strength of the surrounding rock itself. The research results are of great significance for guiding the layout, support control, and safe mining of cross mining roadways, and to some extent, can further enrich and improve the relevant theories of roof movement and control.

• 한국구조물진단유지관리공학회 논문집
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• 제22권4호
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• pp.100-107
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• 2018

본 연구의 목적은 철근콘크리트 휨 부재에 탄소섬유시트, 유리섬유시트, PET(polyethylene terephthalate) 섬유 등을 이용하여 보강했을 때, 보강재 종류, 보강재 물성, 보강량 등에 따른 보강효과를 파악하는 것이다. 변수별 보강효과를 파악하기 위해 가상의 휨부재를 기준실험체로 선정하여, 기준실험체에 대해 항복단면과 극한단면일 때의 모멘트-곡률 관계를 파악하였다. 보강하지 않은 기준실험체에 보강재 종류, 보강재 물성, 보강량 등 다양한 변수를 적용하여 총 11개의 실험체의 모멘트-곡률 곡선을 비교하였다. 분석 결과, 보강하지 않은 실험체에 비해 보강한 실험체의 휨강도는 높게 나타났다. 그러나 연성에 대해서는 보강하지 않은 기준실험체가 가장 우수한 것으로 나타났다. 변수별 휨 보강효과는 보강량이 많고, 파괴시 재료강도가 높을수록 우수하게 나타났으며, 연성효과는 보강재의 파괴시 변형률이 높을수록 우수한 것으로 나타났다. 손상 전과 손상 후의 보강효과에 대해서는 휨보강 효과와 연성효과 모두 10% 이내로 미미하게 나타나 손상상태에 있더라도 온전한 상태로 해석해도 큰 차이가 없을 것으로 판단된다.

• Restorative Dentistry and Endodontics
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• 제42권3호
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• pp.216-223
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• 2017

Objectives: The aim of this study was to compare the mechanical properties of various nickel-titanium (NiTi) files with similar tapers and cross-sectional areas depending on whether they were surface-treated. Materials and Methods: Three NiTi file systems with a similar convex triangular cross-section and the same ISO #25 tip size were selected for this study: G6 (G6), ProTaper Universal (PTU), and Dia-PT (DPT). To test torsional resistance, 5 mm of the straightened file's tip was fixed between polycarbonate blocks (n = 15/group) and continuous clockwise rotation until fracture was conducted using a customized device. To evaluate cyclic fatigue resistance, files were rotated in an artificial curved canal until fracture in a dynamic mode (n = 15/group). The torsional data were analyzed using 1-way analysis of variance and the Tukey post-hoc comparison test, while the cyclic fatigue data were analyzed using the Mann-Whitney U test at a significance level of 95%. Results: PTU showed significantly greater toughness, followed by DPT and G6 (p < 0.05). G6 showed the lowest resistance in ultimate torsional strength, while it showed a higher fracture angle than the other files (p < 0.05). In the cyclic fatigue test, DPT showed a significantly higher number of cycles to failure than PTU or G6 (p < 0.05). Conclusions: Within the limitations of this study, it can be concluded that the torsional resistance of NiTi files was affected by the cross-sectional area, while the cyclic fatigue resistance of NiTi files was influenced by the surface treatment.

• 한국농공학회지
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• 제31권2호
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• pp.125-134
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• 1989

This study was conducted to investigate the flexural behaviour of sandwich constructions with cement concrete core and polymer concrete facings. Six different cross-sectional shapes using epoxy based polymer concrete facings were investigated. Some of the results from the static tests are given including the load-deflection responses, load-strain relationships, ultimate moment, and mode of failure. From the. results the following conclusions can be made. 1. The various strengths of polymer concrete were very high compared to the strengths for portland cement concrete, while modulus of elasticity assumed an aspect of contrast. 2. The thickness of core and facing exerted a great influence on the deflection and ultimate strenght of polymer concrete sandwich constructions. 3. The variation shape of deflection and strain depend on loading were a very close approximation to the straight line. The ultimate strain of polymer concrete at the end of tensile side were ranged from 625x10-6 to 766x10-6 and these values increased in proportion to the decrease of thickness of core and facings. 4. The ultimate moments of polymer sandwich constructions were 3 to 4 times that of cement concrete constructions which was transformed same section. It should he noted that polymer concrete have an effect on the reinforcement of weak constructions. 5. Further tests are neede to investigate the shear strain of constructions, and thermal expansion, shrinkage and creep of cement and polymer concrete which were composite materials of sandwich constructions.

• 한국강구조학회 논문집
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• 제18권2호
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• pp.137-146
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• 2006

본 연구에서는 단재하경로 구조로 인식되는 강합성 2-거더교에서 가로보의 제원 및 배치 간격에 따른 여유도 평가를 위한 해석적인 연구를 수행하였다. 이를 위해 수평브레이싱은 생략하고 수직브레이싱은 I-단면 가로보로 적용한 40+50+40m의 2차로 연속교를 대상으로 하였다. 본 교량에 대해 정상 상태 및 한 개 거더에 심각한 균열을 가정한 손상 상태로 구분하고 가로보의 제원과 배치 간격을 변수로 하여 재료 및 기하비선형 해석을 수행하였다. 해석으로부터 구해진 각 경우에 대한 내하력을 토대로 정상 상태 및 손상 상태 교량의 여유도를 평가하였다. 평가 결과, 정상 상태 및 손상 상태 모두 가로보의 제원과 배치 간격에 따른 여유도 차이는 거의 없었다.

• 한국해양공학회지
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• 제22권2호
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• pp.85-90
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• 2008

Ships in bad weather conditions are likely to be subjected to accidental loads, such as high bending moment, collision, and grounding. Once she has damage to her hull, her ultimate strength will be reduced. This paper discusses an investigation of the effect of collision damage on the ultimate strength of a ship structure by performing a series of collapse tests. For the experiment, five box-girder models with stiffeners were prepared with a cross section of $720mm\;{\times}\;720mm$ and a length of 900mm. Of the five, one had no damage and four had an ellipse shaped damage area that represented the shape of the bulbous bow of a colliding ship. The amount of damage size was different between models. Among the damaged models, the damage in three of them was made by cutting the plate and stiffener, and in one by pressing to represent collision damage. Experiments were carried out under a pure bending load and the applied load and displacements were recorded. The ultimate strength was reduced as the damage size increased, as expected. The one with the largest amount of damage had damage to 30% of the depth, and its ultimate strength was reduced by 19% compared to the undamaged one. The pressed one has higher ultimate strength than those that were cut. This might be due to the fact that the plate around the pressed damage area contributes to the ultimate strength, whereas the cut one has no plate to contribute.

• Structural Engineering and Mechanics
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• 제81권4호
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• pp.493-502
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• 2022

Shear lag phenomenon has long been considered in numerous structural codes; however, the AISC provisions have now no longer proposed any unique equation to calculate the shear lag ratio in bolted connections for angles in general. It is noticeable that, however, codes used in this case are largely conservative and need to be amended. A parametric study consisting of 27 angle sections with equal legs and different with bolted connections was performed to investigate the effects of shear lag on the ultimate tensile capacity of angle members. The main parameters were: steel grade, connection length and eccentricity from the center of the plate, as well as the number of rows of bolts parallel to the applied force. The test results were compared with the predictions of the classical 1-x/l law proposed by Mons and Chesen to investigate its application to quantify the effect of shear lag. A parametric study was performed using valid FE models that cover a wide range of parameters. Finally, based on the numerical results, design considerations were proposed to quantify the effect of shear lag on the ultimate tensile capacity of the tensile members.

• 한국구조물진단유지관리공학회 논문집
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• 제19권6호
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• pp.1-9
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• 2015

횡방향철근은 기둥의 소성힌지구간에 충분한 구속효과, 축방향철근의 좌굴방지와 연성거동을 확보하기 위해 적용된다. 기둥에서 사각형 후프 띠철근과 보강 띠철근의 조립 및 배근방법은 시공이 까다롭고 많은 횡방향철근량이 요구된다. 본 논문에서, 이러한 문제점들을 해결하기 위하여 장방형 단면과 플레어 기둥의 횡구속을 위한 장방형 후프 띠철근을 사용한 새로운 횡구속 방법이 제안되었다. 개발된 장방형 후프 띠철근 상세는 장방형 단면과 플레어 기둥의 시공성과 경제성을 향상시켜줄 수 있는 하나의 대안으로서 적용 가능한 것으로 판단된다. 본 연구의 최종목적은 철근콘크리트 교각의 시공성 향상을 위한 장방형 후프 띠철근 상세의 제시와 실험적 기초자료의 제공과 함께 하중단계별 성능 및 손상평가를 위한 정량적 수치와 경향을 제공하기 위한 것이며, 극한변위, 극한드리프트비율, 변위연성도, 응답수정계수, 등가점성감쇠비, 잔류변형지수, 유효강성 등의 주요 내진성능평가 변수들에 대한 분석결과를 나타내었다.

• Structural Engineering and Mechanics
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• 제51권5호
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• pp.847-866
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• 2014

This paper describes a formulation to predict optimum post-tensioning forces and cable dimensioning for self-anchored cable-stayed suspension bridges. The analysis is developed with respect to both dead and live load configurations, taking into account design constrains concerning serviceability and ultimate limit states. In particular, under dead loads, the analysis is developed with the purpose to calculate the post-tensioning cable forces to achieve minimum deflections for both girder and pylons. Moreover, under live loads, for each cable elements, the lowest required cross-section area is determined, which verifies prescriptions, under ultimate or serviceability limit states, on maximum allowable stresses and bridge deflections. The final configuration is obtained by means of an iterative procedure, which leads to a progressive definition of the stay, hanger and main cable characteristics, concerning both post-tensioning cable stresses and cross-sections. The design procedure is developed in the framework of a FE modeling, by using a refined formulation of the bridge components, taking into account of geometric nonlinearities involved in the bridge components. The results demonstrate that the proposed method can be easily utilized to predict the cable dimensioning also in the framework of long span bridge structures, in which typically more complexities are expected in view of the large number of variables involved in the design analysis.