• Computers and Concrete
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• 제30권1호
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• pp.19-32
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• 2022

This paper presents an investigation into the failure of RC columns under impact loadings. A numerical simulation of 19 identical RC columns subjected to single and repeated impact loadings was performed. A free-falling hammer was dropped at midspan with the same total kinetic energy input but varying mass and momentum. The specimens under the repeated impact test were struck two times at the same location. The colliding index, defined as the impact energy-momentum ratio, was proposed to explain the different impact responses under equal-energy impacts. The increase of colliding index from low to high indicates the transition of the impact response from static to dynamic and failure mode from flexure to shear. This phenomenon was more evident when the column had a greater axial load and was impacted with a high colliding index. The existence of the axial load had an inhibitory effect on the crack development and increased the shear resistance. The second impact changes the failure mode from flexural to brittle shear as found in the specimen with 20% axial load subjected to high a colliding index. Moreover, a deflection prediction equation based on the impact energy and force was limited to the low colliding index impact.

• Structural Engineering and Mechanics
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• 제76권4호
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• pp.465-477
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• 2020

This paper presents an investigation on the dynamic behavior of SRC columns with built-in cross-shaped steels under impact load. Seven 1/2 scaled SRC specimens were subjected to low-speed impact by a gravity drop hammer test system. Three main parameters, including the lateral impact height, the axial compression ratios and the stirrup spacing, were considered in the response analysis of the specimens. The failure mode, deformation, the absorbed energy of columns, as well as impact loads are discussed. The results are mainly characterized by bending-shear failure, meanwhile specimens can maintain an acceptable integrity. More than 33% of the input impact energy is dissipated, which demonstrates its excellent impact resistance. As the impact height increases, the flexural cracks and shear cracks observed on the surface of specimens were denser and wider. The recorded time-history of impact force and mid-span displacement confirmed the three stages of relative movement between the hammer and the column. Additionally, the displacements had a notable delay compared to the rapid changes observed in the measured impact load. The deflection of the mid-span did not exceed 5.90mm while the impact load reached peak value. The impact resistance of the specimen can be improved by proper design for stirrup ratios and increasing the axial load. However, the cracking and spalling of the concrete cover at the impact point was obvious with the increasing in stiffness.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2000년도 추계학술발표대회 논문집
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• pp.67-70
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• 2000

This study was performed to investigate the material behavior of hybrid thermoplastic composites contained glass fiber and calcium carbonate. The composite was prepared with each combination ratio of calcium carbonate, and the content of glass fiber was fixed with 10% by weight. In order to investigate the material behavior for various combination ratio, tension test, flexural test, and impact test were performed. Microscopic observation were conducted to examine the fractured surface of specimen for tension test. And the material behavior of the hybrid thermoplastic composite immersed in salt water with definite time was investigated.

• Advances in concrete construction
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• 제5권6호
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• pp.575-586
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• 2017

The disposal of polythene waste and fly ash is causing serious threat to the environment. Aim of this study is to decrease environmental pollution by using polythene waste and fly ash in concrete. In this study, cement was partially replaced with 0%, 5%, 10%, 15% and 20% fly ash (by weight) and plastic waste was added in shredded form at 0.6% by weight of concrete. The specimens were prepared for the concrete mix of M25 grade and water to cementitious material ratio (w/c) was maintained as 0.45. Fresh concrete property like workability was examined during casting the specimens. Hardened properties were found out by carrying out the experimental work on cubes, cylinders and beams which were cast in laboratory and their behavior under test were observed at 7 & 28 days for compressive strength and at 28 days for density, flexural strength, dynamic modulus of elasticity, abrasion resistance, water permeability and impact resistance. Overall results of this study show that addition of 0.6% (by weight of the concrete) plastic waste with 10% (by weight of cement) replacement of cement by fly ash result an improvement in properties of the concrete than conventional mix.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2002년도 춘계학술발표대회 논문집
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• pp.195-198
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• 2002

Two types of conformal load-bearing antenna structure (CLAS) were designed with microwave composite laminates and Nomex honeycomb cores, to give both structural rigidity and good electrical performance. One is 4$\times$8 array for Synthetic Aperture Radar(SAR) system and the other is $5\times2$ array for wireless LAN system. Design was based on wide bandwidth, high polarization purity, low loss and good structural rigidity. We studied the design, fabrication and structural/electrical performances of the antenna structures. The flexural behavior was observed under a 3-point bending test, an impact test, and a buckling test. Electrical measurements were in good agreement with simulation results and these complex antenna structures have good flexural characteristics. The design of this antenna structure is extended to give a useful guide for sandwich panel manufacturers as well as antenna designers.

• 한국염색가공학회지
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• 제28권4호
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• pp.246-252
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• 2016

In comparison to metal alloys, braided composite features a high impact resistance and crash energy absorption potential, and also it still remained competitive stiffness and strength properties. Braiding angle is one of the most important parameters which affect the mechanical behaviors of braided composite. This paper presents transverse low velocity impact failure behavior analysis on the carbon 3D triaxial braided composite tube with the braiding angle of $20^{\circ}$, $50^{\circ}$ and $80^{\circ}$. The flexural behaviour of 3D triaxial braided composite tube under bending loads was studied by conducting quasistatic three point bending test. Also, the low velocity impact responses of the braided composite tubes were also tested to obtain load-displacement curves and energy absorption. Consequently, the increase of the braided angle, the peak load also increases owing to the bigger bending stiffness.

• 콘크리트학회지
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• 제2권2호
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• pp.73-80
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• 1990

지진이나 충격과 같은 강한 동적반복하중을 받을 경우 철근콘크리트 부재의 거동을 예측하는 현재의 해석기법은 변형율속도의 영향을 고려하고 있지 않으며, 휨거동 만을 이상화하고 있어 예측치와 실험치 사이에 커다란 오차를 수반하고 있다는 문제점이 있다. 따라서, 본 연구에서는 변형율속도의 변화에 따른 부재의 휨강도 및 전단강도를 예측 할 수 있는 기법과 부재거동의 구성요소인 휨변형과 전단변형을 몇 개의 이력변수를 사용하여 이상화한 구조해석 모델을 접목함으로써 강한 동적반복하중에서도 실제와 거의 일치하는 구조거동을 예측 할 수 있는 소프트웨어를 완성하였으며, 그를 이용한 비교결과는 비교적 만족스러웠다.

• Structural Engineering and Mechanics
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• 제87권2호
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• pp.151-164
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• 2023

The latest earthquake's costly repairs and economic disruption were brought on by excessive residual drift. Self-centering systems are one of the most efficient ways in the current generation of seismic resistance system to get rid of and reduce residual drift. The mechanics and behavior of the self-centering system in response to seismic forces were impacted by a number of important factors. The amount of post-tensioning (PT) force, which is often employed for the standing posture after an earthquake, is the first important component. The energy dissipater element is another one that has a significant impact on how the self-centering system behaves. Using the damper as a replaceable and affordable tool and fuse in self-centering frames has been recommended to boost energy absorption and dampening of structural systems during earthquakes. In this research, the self-centering steel moment frame connections are equipped with cushion flexural dampers (CFDs) as an energy dissipator system to increase energy absorption, post-yielding stiffness, and ease replacement after an earthquake. Also, it has been carefully considered how to reduce permanent deformations in the self-centering steel moment frames exposed to seismic loads while maintaining adequate stiffness, strength, and ductility. After confirming the FE model's findings with an earlier experimental PT connection, the behavior of the self-centering connection using CFD has been surveyed in this study. The FE modeling takes into account strands preloading as well as geometric and material nonlinearities. In addition to contact and sliding phenomena, gap opening and closing actions are included in the models. According to the findings, self-centering moment-resisting frames (SF-MRF) combined with CFD enhance post-yielding stiffness and energy absorption with the least amount of permeant deformation in a certain CFD thickness. The obtained findings demonstrate that the effective energy dissipation ratio (β), is increased to 0.25% while also lowering the residual drift to less than 0.5%. Also, this enhancement in the self-centering connection with CFD's seismic performance was attained with a respectable moment capacity to beam plastic moment capacity ratio.

• 한국구조물진단유지관리공학회 논문집
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• 제23권4호
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• pp.86-95
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• 2019

탄소섬유는 경량이면서 높은 기계적 특성 때문에 우주항공, 선박, 자동차, 토목 및 건축과 같은 산업분야에서 그 어느 때 보다 더 광범위하게 적용되고 있다. 본 연구는 섬유혼입률 및 섬유길이 변화에 따른 탄소섬유 보강시멘트 복합재료( CFRC)의 역학적 특성과 휨 거동을 분석하였으며, 또한 자연 낙하시험에 의한 모르타르 시편에 대한 내충격성을 비교, 검토하였다. 더불어, 탄소섬유(CF)의 혼입률은 0.5%, 1.0%, 2.0% 및 3.0%로 변화를 주었으며, 각각의 섬유길이는 6 mm와 12 mm를 사용 하였다. 실험결과, 플로우 값은 탄소섬유의 뭉침현상으로 인해 유동성 측면에서 매우 불리하였으며, 단위용적질량은 다소 감소하였다. 특히, 압축강도는 탄소섬유 혼입량이 증가함에 따라 감소하는 것으로 나타내었다. 반면 휨 강도는 섬유 길이가 12 mm이고 2% 혼입한 것이 가장 높은 휨 강도를 보였다. 내충격성 시험결과, 보통 모르타르 시편은 완전파괴까지의 낙하횟수가 2~3회 정도 걸리지만 반면 CFRC 시편은 섬유혼입량이 증가함에 따라 다소 차이가 있지만, 섬유길이가 12 mm이고 섬유혼입량 2% 인 경우 충격에 대한 저항성이 가장 높았다.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2000년도 추계학술발표대회 논문집
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• pp.88-91
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• 2000

흑연분말, 카본블랙, 탄소섬유분말을 첨가제로 한 저밀도 2-D 탄소/탄소 복합재의 밀도 및 기 기공도에 피치는 영향과 ILSS, 굽힘강도 및 충격에너지와 같은 기계적 물성과의 상관관계에 대하여 연구하였다. 흑연분말을 약 9 vol.% 첨가한 경우 가장 큰 ILSS값과 굽힘강도 및 충격에너지 흡수 거동을 나타내었는데, 특히 흑연의 함량이 증가함에 따라 puncture mode로의 충격 거동을 나타내 띠 많은 충격에너지를 흡수하였고, 인성이 상당히 증가하였다 카본블랙이 첨가된 경우에는, 약 3 vol.%에서 ILSS 값이 증가하였으나 큰 개선을 보이지 못하였으며, 굽힘강도는 감소하였다. 탄소섬유분말의 첨가량이 증가함에 따라 층간분리에 의해 밀도가 현저히 감소하여 ILSS 및 굽힘강도의 감소를 보였다.