• 한국구조물진단유지관리공학회 논문집
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• 제12권6호
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• pp.119-128
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• 2008

본 연구는 중진지역에서의 PC(precast conctete) 보-기둥 접합부의 새로운 모멘트-저항 시스템을 제안하는 것이다. 철근 이음형 접합부에서 연결재는 접합부를 관통하고, U형 하프 PC 보의 하부철근과 비접촉 겹칩이음으로 연결되어 있다. 비접촉 겹침이음에 대한 성능을 파악하기 위하여 실험적 연구와 해석적 연구가 수행되었다. 실험의 주요변수는 겹침길이, 연결재의 크기, 그리고 겹침이음된 연결재의 거리 등이다. 또한, 균열양상, 하중-변위 곡선, 내력 비교, 그리고 연결재의 변형 등에 초점을 맞추어 해석적 연구를 수행하여 실험결과와 비교하였다. 해석과 실험 결과 주요변수인 겹침길이, 연결재의 크기, 연결재의 비접촉 수직 거리등에 따라 강도, 연성, 그리고 접합부 거동에 큰 영향을 주는 것으로 나타났다.

• 한국융합학회논문지
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• 제8권3호
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• pp.185-190
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• 2017

본 논문은 탄소섬유로 구성된 평판형태의 시험편에 굽힘 모멘트가 작용할 때 내부의 섬유구조에서 발생되는 굽힘 응력과 전단응력, 변형에너지에 관한 것이다. CFRP는 무수히 많은 섬유가 다축구조를 형성하고 있어 굽힘조건에서 응력을 효과적으로 분산할 수 있다. 이때 적층각도에 따라 다양한 물성을 보이게 되는데, 섬유의 수평방향인 Stacking angle $0^{\circ}$에서부터 수직방향인 $90^{\circ}$에 이르기까지의 결과에 있어, Stacking angle이 증가함에 따라 등가 응력과 전단응력이 점차 줄어들며 $60^{\circ}$를 기점으로 다시 증가함을 보이고 있다. 본 연구결과를 토대로,적층각도에 따른 평판에서의 굽힘으로 인한 파손특성을 해석적 접근을 통해 고찰하였으며, 본연구는 파손방지와 내구성 향상을 위한 안전설계에 기여할 수 있다고 사료된다. 또한 평판 형상으로서의 디자인적 요소를 융합기술에 접목함으로서 그 미적인 감각을 나타낼 수 있다.

• 대한안전경영과학회지
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• 제19권1호
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• pp.15-25
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• 2017

The findings were summarized as follows. The safety check by manufacturer showed that 6 of 13 companies are over the average occurrence of defects. It was expected that there would be a difference between manufacturing technology capability and production system of each manufacturer. Consequently, manufacturers should institutionally improve and strengthen certification items for the upward standardization of safety certification before factory. Second, the safety check by year showed that the results of this study accord with those of previous studies on defect time. Consequently, manufacturers should classify the 3-year-old equipment for vehicle-mounted MEWP into a special check subject to do a nondestructive test according to proven results, and also reflect the test in a safety test system to do regular preventive activities of equipment defects. Third, the safety check by part showed that the boom and outrigger parts of vehicle-mounted MEWP have the most defects. Stress concentration resulted in defects as the boom part was most frequently operated in the structural parts for a real work. To prevent this, it is suitable to improve the hardness of boom materials. The outrigger part needs improvement in safety devices with materials. As an outrigger supports the overturning moment of equipment, it is most affected by its load based on the operating radius, resulting in fatigue crack.

• Computers and Concrete
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• 제20권4호
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• pp.391-407
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• 2017

Fiber reinforced polymer (FRP) bars have been recently used to reinforce concrete members in flexure due to their high tensile strength and especially in corrosive environments to improve the durability of concrete structures. However, FRPs have a low modulus of elasticity and a linear elastic behavior up to rupture, thus reinforced concrete (RC) components with such materials would exhibit a less ductility in comparison with steel reinforcement at the similar members. There were several studies showed the behavior of concrete beams with the hybrid combination of steel and FRP longitudinal reinforcement by adopting the experimental and numerical programs. The current study presents a numerical and analytical investigation based on the data of previous researches. Three-dimensional (3D) finite element (FE) models of beams by using ANSYS are built and investigated. In addition, this study also discusses on the design methods for hybrid FRP-steel beams in terms of ultimate moment capacity, load-deflection response, crack width, and ductility. The effects of the reinforcement ratio, concrete compressive strength, arrangement of reinforcement, and the length of FRP bars on the mechanical performance of hybrid beams are considered as a parametric study by means of FE method. The results obtained from this study are compared and verified with the experimental and numerical data of the literature. This study provides insight into the mechanical performances of hybrid FRP-steel RC beams, builds the reliable FE models which can be used to predict the structural behavior of hybrid RC beams, offers a rational design method together with an useful database to evaluate the ductility for concrete beams with the combination of FRP and steel reinforcement, and motivates the further development in the future research by applying parametric study.

• 한국구조물진단유지관리공학회 논문집
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• 제10권2호
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• pp.165-176
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• 2006

본 연구는 볼트의 조임력을 이용한 와이어로프의 휨보강 효과에 대한 실험 및 사례에 대한 것이다. 본 공법은 와이어로프에 볼트와 너트를 이용해 긴장응력을 도입하며, 이 방법은 시공성이 매우 우수하다. 제안된 방법에 대한 휨보강 효과에 대한 검증을 위해 실험을 수행하였다. 콘크리트 압축강도는 24MPa이고 전단스팬비(a/d)가 2.8인 실험체의 주요변수로는 초기 긴장응력과 새들 수량으로 하였다. 실험결과, 무보강 실험체에 비해서 휨내력은 약 160% 증가하였으며, 초기 긴장력에 따라서 균열 및 극한모멘트가 증가하였다. 그러나 새들의 수량은 균열 및 극한모멘트에는 영향을 주지 않았다. 실제 구조물의 보강공사에 적용한 사례를 통해서 제안된 공법은 다른 보강방법보다 매우 경쟁력 있는 방법임을 알 수 있었다.

• International Journal of Naval Architecture and Ocean Engineering
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• 제12권1호
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• pp.755-767
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• 2020

A significant development has been made on a new fatigue damage model applicable to Gaussian wide band stress response spectra using numerical approximation methods such as data processing, time simulation, and regression analysis. So far, most of the alternative approximate models provide slightly underestimated or overestimated damage results compared with the rain-flow counting distribution. A more reliable approximate model that can minimize the damage differences between exact and approximate solutions is required for the practical design of ships and offshore structures. The present paper provides a detailed description of the development process of a new fatigue damage model. Based on the principle of the Gaussian wide band model, this study aims to develop the best approximate fatigue damage model. To obtain highly accurate damage distributions, this study deals with some prominent research findings, i.e., the moment of rain-flow range distribution MRR(n), the special bandwidth parameter μk, the empirical closed form model consisting of four probability density functions, and the correction factor QC. Sequential prerequisite data processes, such as creation of various stress spectra, extraction of stress time history, and the rain-flow counting stress process, are conducted so that these research findings provide much better results. Through comparison studies, the proposed model shows more reliable and accurate damage distributions, very close to those of the rain-flow counting solution. Several significant achievements and findings obtained from this study are suggested. Further work is needed to apply the new developed model to crack growth prediction under a random stress process in view of the engineering critical assessment of offshore structures. The present developed formulation and procedure also need to be extended to non-Gaussian wide band processes.

• Computers and Concrete
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• 제29권4호
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• pp.219-235
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• 2022

Strengthening slender reinforced concrete (RC) columns is a challenge. They are susceptible to overall buckling that induces bending moment and axial compression. This study presents the precise three-dimensional finite element modeling of slender RC columns strengthened with fiber-reinforced polymer (FRP) composites sheets with various patterns under concentric or eccentric compression. The slenderness ratio λ (height/width ratio) of the studied columns ranged from 15 to 35. First, to determine the optimal modeling procedure, nine alternative nonlinear finite element models were presented to simulate the experimental behavior of seven FRP-strengthened slender RC columns under eccentric compression. The models simulated concrete behavior under compression and tension, FRP laminate sheets with different fiber orientations, crack propagation, FRP-concrete interface, and eccentric compression. Then, the validated modeling procedure was applied to simulate 58 FRP-strengthened slender RC columns under compression with minor eccentricity to represent the inevitable geometric imperfections. The simulated columns showed two cross sections (square and rectangular), variable λ values (15, 22, and 35), and four strengthening patterns for FRP sheet layers (hoop H, longitudinal L, partial longitudinal L_w, and longitudinal coupled with hoop LH). For λ=15-22, pattern L showed the highest strengthening effectiveness, pattern L_w showed brittle failure, steel reinforcement bars exhibited compressive yielding, ties exhibited tensile yielding, and concrete failed under compression. For λ>22, pattern L_w outperformed pattern L in terms of the strengthening effectiveness relative to equivalent weight of FRP layers, steel reinforcement bars exhibited crossover tensile strain, and concrete failed under tension. Patterns H and LH (compared with pattern L) showed minor strengthening effectiveness.

• 수산해양기술연구
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• 제58권3호
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• pp.230-240
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• 2022

In general, a high tension on the anchor and chain is placed when a ship at anchor is subjected to heavy weather. Mariners have to pay attention to whether dragging anchor occurs to keep the safety of the ship at anchorage since it is difficult to maintain the stable motion of ship and it causes collisions with other ships nearby. In this paper, the ship motion against the external forces was shown to obtain the fundamental data about characteristic of holding power due to nature of seabed at anchor, so practical trials were carried out in rocky area and muddy area using a trial ship around coastal area of South Korea. In muddy seabed, holding power showed reasonable tension values depending on the distance from anchor position of continuing swing motions of a ship corresponding to wind force. Meanwhile in rocky seabed, tension values on the chain appeared very high occasionally regardless of the distance from the anchor position and seemed to exceed its holding power to be the breaking strain of the chain although weather was not in a severe condition. Therefore, some of the cables laid on the seabed were presumed to be caught in a crack on the rock. It is assumed that even a small amount of external force may cause the chain to break in a moment in rocky seabed. Additionally, wind and current forces had a somewhat contradictory effect on holding power of the ship between them.

• 한국터널지하공간학회 논문집
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• 제16권3호
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• pp.287-298
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• 2014

본 연구에서는 TBM 터널 SFRC 세그먼트 개발을 위하여 이형철근이 보강되지 않은 SFRC 보의 휨파괴 실험을 통하여 SFRC 배합의 평가를 수행하였다. 압축강도, 강섬유의 형상비와 강섬유 혼입률을 변수로 하여 총 16개의 SFRC 보를 제작하고 휨에 의하여 파괴시까지 실험하였다. 하중-수직변위 분석결과, 큰 형상비의 강섬유를 사용하여도 소형보의 실험(Moon et al, 2013)과 달리 보의 인성거동을 증진시키는 효과는 거의 없는 것으로 나타났다. 극한상태에서 강섬유는 균열폭 7 mm까지 하중을 저항하는 것으로 확인되었다. 또한, 기존의 SFRC 보의 휨강도예측모델과 실험결과를 비교한 결과, SFRC 보의 휨강도를 최대 20배까지 과소평가하고 있는 것으로 나타났다. 그러나, TR No. 63 모델(Concrete Society, 2011)은 다른 모델에 비하여 근사하게 휨강도를 예측하는 것으로 확인되었다. 강섬유의 분포에 대한 분석결과, 소형보에서 보다 실제 규모의 보에서 강섬유의 분산도가 훨씬 개선되는 것을 확인하였다.

• 콘크리트학회논문집
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• 제26권1호
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• pp.87-95
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• 2014

이 연구에서는 강섬유 보강 초고성능 콘크리트 보의 비틀림 거동을 파악하기 위한 실험연구를 수행하였다. 정사각형 단면을 갖는 6개의 초고성능 콘크리트 보 부재에 대해 하중재하실험을 수행하여 비틀림 거동 특성을 분석하였다. 부재의 실험변수는 강섬유 혼입량과 폐쇄 스터럽량이다. 강섬유 혼입량은 1.0% 및 2.0%로 변화하였고, 폐쇄 스터럽량은 0, 0.35% 및 0.70%로 변화하였다. 실험 결과는 강섬유양이 증가할수록 극한비틀림강도가 증가하고, 폐쇄스터럽량이 증가할수록 극한비틀림강도가 증가하는 것을 나타낸다. 또한, 비틀림 강도 예측식을 제안하였으며, 예측식은 콘크리트, 스터럽 및 강섬유의 비틀림 강도 기여분을 각각 고려하였다. 실험 결과를 이용하여 초고강도 콘크리트 보의 비틀림 강도 예측식의 적합성을 평가하고자 하였다. 비틀림강도 실험 결과를 예측값과 비교하였으며, 예측값은 실험 결과에 거의 근접하고 있는 것으로 나타났다. 따라서, 제안식을 이용하여 초고성능 콘크리트의 비틀림 강도를 효과적으로 예측할 수 있다고 판단된다.