• 한국안전학회지
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• 제21권3호
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• pp.94-100
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• 2006

The goal of this study is to show the way to increase the safety of deteriorated PSC beam bridges by the to-box reinforcing method. This method is to change the open girder section into the closed box section by connecting bottom flanges of neighboring PSC girders with the precast panels embedding PS tendons at the anchor block. The box section is composed of three concrete members with different casting ages, RC slab, PSC beam, precast panel. This different aging requires a time-dependent analysis considering construction sequences. Reliability index and failure probability are produced by the AFOSM reliability analysis. Transversely five schemes and longitudinally two schemes are considered. The full reinforcing scheme, transversely and longitudinally, shows the highest reliability index, but it requires more cost for retrofit. The partial reinforcing scheme 4, 4-1 are recommended in this study as the economically best scheme.

• Computers and Concrete
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• 제5권1호
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• pp.21-36
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• 2008

Steel fiber reinforced concrete is increasingly used day by day in various structural applications. An extensive experimentation was carried out with w/cm ratio ranging from 0.25 to 0.40, and fiber content ranging from zero to1.5 percent by volume with an aspect ratio of 80 and silica fume replacement at 5%, 10% and 15%. The influence of steel fiber content in terms of fiber reinforcing index on the compressive strength of high-performance fiber reinforced concrete (HPFRC) with strength ranging from 45 85 MPa is presented. Based on the test results, equations are proposed using statistical methods to predict 28-day strength of HPFRC effecting the fiber addition in terms of fiber reinforcing index. A strength model proposed by modifying the mix design procedure, can utilize the optimum water content and efficiency factor of pozzolan. To examine the validity of the proposed strength model, the experimental results were compared with the values predicted by the model and the absolute variation obtained was within 5 percent.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2002년도 봄 학술발표회 논문집
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• pp.297-302
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• 2002

This paper investigated the properties of flexural behavior of composite beams (end-Reinforced concrete, center-Steel concrete) according to attaching length of main bars to flange, shear reinforcing length for different types of structure. In the preceding study, structural properties of composite beams were investigated according to shear span to depth ratio, attaching method of main bars and shear reinforcing method. Based on these results, a series of experiments was carried out according to attaching length of main bar ＆ reinforcing length for different types of structure. Consequently, as attaching length of main bar and shear reinforcing length increased, composite beams represented higher strength, ductility index and stress mechanism distributed in connection zone of different types of structure.

• Elastomers and Composites
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• 제55권4호
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• pp.306-313
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• 2020

To investigate the reinforcing effects of functional fillers in nitrile rubber (NBR) materials, high-structure carbon black (HS45), coated calcium carbonate (C-CaCO3), silica (200MP), and multi-walled carbon nanotubes (MWCNTs) were used as functional filler, and carbon black (SRF) as a common filler were used for oil-resistant rubber. The curing and mechanical properties of HS45-, 200MP-, and MWCNT-filled NBR compounds were improved compared to those of the SRF-filled NBR compound. The reinforcing effect also increased with a decrease in the particle size of the fillers. The C-CaCO3-filled NBR compound exhibited no reinforcing effect with increasing filler concentration because of their large primary particle size (2 ㎛). The reinforcing behavior based on 100% modulus of the functional filler based NBR compounds was compared by using several predictive equation models. The reinforcing behavior of the C-CaCO3-filled NBR compound was in accordance with the Smallwood-Einstein equation whereas the 200MP- and MWCNT-filled NBR compounds fitted well with the modified Guth-Gold (m-Guth-Gold) equation. The SRF- and HS45-filled NBR compounds exhibited reinforcing behavior in accordance with the Guth-Gold and m-Guth-Gold equations, respectively, at a low filler content. However, the values of reinforcement parameter (100Mf/100Mu) of the SRF- and HS45-filled NBR compounds were higher than those determined by the predictive equation model at a high filler content. Because the chains of SRF composed of spherical filler particles are similarly changed to rod-like filler particles embedded in a rubber matrix and the reinforcement parameter rapidly increased with a high content of HS45, the higher-structured filler. The reinforcing effectiveness of the functional fillers was numerically evaluated on the basis of the effectiveness index (��SRF/��f) determined by the ratio of the volume fraction of the functional filler (��f) to that of the SRF filler (��SRF) at three unit of reinforcing parameter (100Mf/100Mu). On the basis of their effectiveness index, MWCNT-, 200MP-, and HS45-filled compounds showed higher reinforcing effectiveness of 420%, 70%, and 20% than that of SRF-filled compound, respectively whereas C-CaCO3-filled compound exhibited lower reinforcing effectiveness of -50% than that of SRF-filled compound.

• 한국방재학회 논문집
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• 제7권4호
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• pp.13-18
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• 2007

본 연구에서는 구조물의 내구성 설계 시에 영향을 미치는 설계인자들에 대한 고찰을 하고, 내구성 설계에 사용되고 있는 기준에 대한 국내외 문헌연구를 수행하였으며, 국내기준을 가지고 지하 구조물 단면을 대상으로 내구성 설계를 수행하였다. 국내 지하구조물의 내구설계 지침에 따른 결과는 사용 철근의 직경을 작게 하고 간격을 좁힐수록 구조물의 내구성에 유리한 것으로 나타났으며, 환경지수 제한치를 상회하는 내구지수를 가지기 위해서는 최소한 6.6cm의 피복을 가져야 하며, 내구지수와 내구지수 증분치 변화의 최대 철근피복은 12cm인 것으로 나타났다. 별도의 제한규정이 없는 경우, 철근피복의 최소치와 최대치 사이에서 중성화로 인한 내구연한은 철근피복에 비례하였다.

• Computers and Concrete
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• 제22권5호
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• pp.481-492
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• 2018

In this paper, a new hybrid fiber system (NHFS) is investigated for the application of slab. The steel fiber, polyvinyl alcohol (PVA) fiber and calcium carbonate ($CaCO_3$) whisker is added to form NHFS. The four-point bending test is carried out on the flexural properties of slab with plain, steel fiber, traditional hybrid fiber system (THFS) and NHFS reinforced cementitious composites. The flexural behavior is evaluated by ASTM C1018-97, JCI-SF4 and post-crack strength (PCS) technique. The evaluation parameters of flexural toughness such as toughness index (TI), equivalent flexural strength (EFS) and PCS are determined. The size of slab specimens is $15mm(thickness){\times}50mm(width){\times}200mm(length)$. The results show that adding $CaCO_3$ whisker to THFS can significantly improve the flexural strength, TI, EFS, PCS of the slab. The empirical relation between reinforcing index ($RI_v$) and flexural parameters show that flexural parameters of slabs increase first and then decrease; which indicates that optimum $RI_v$ values can be helpful in the considering the mix design of steel-PVA fibers-$CaCO_3$ whisker composites for achieving the desired flexural-related properties. The scanning electron microscopy is performed to observe the micro-morphological characteristics of the fracture surface, which proved the positive hybrid effect among the different fibers in cementitious composites. The NHFS can arrest the generation and propagation of the crack from micro to macro level.

• Computers and Concrete
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• 제11권2호
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• pp.149-167
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• 2013

The complete stress-strain behavior of steel fiber reinforced concrete in compression is needed for the analysis and design of structures. An experimental investigation was carried out to generate the complete stress-strain curve of high-performance steel fiber reinforced concrete (HPSFRC) with a strength range of 52-80 MPa. The variation in concrete strength was achieved by varying the water-to-cementitious materials ratio of 0.40-0.25 and steel fiber content (Vf = 0.5, 1.0 and 1.5% with l/d = 80 and 55) in terms of fiber reinforcing parameter, at 10% silica fume replacement. The effects of these parameters on the shape of stress-strain curves are presented. Based on the test data, a simple model is proposed to generate the complete stress-strain relationship for HPSFRC. The proposed model has been found to give good correlation with the stress-strain curves generated experimentally. Inclusion of fibers into HPC improved the ductility considerably. Equations to quantify the effect of fibers on compressive strength, strain at peak stress and toughness of concrete in terms of fiber reinforcing index are also proposed, which predicted the test data quite accurately. Compressive strength prediction model was validated with the strength data of earlier researchers with an absolute variation of 2.1%.

• 콘크리트학회지
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• 제11권2호
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• pp.209-220
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• 1999

터널의 숏크리트 라이닝이나 포장 콘크리트 보강용으로 요접철망(wire mesh)을 대신해서 강섬유가 사용되고 있다. 본 연구에서는 강섬유 보강으로 인한 인성평가 대상 구조물을 slab panel 구조($60{\times}60{\times}10$cm)로 하고, 강섬유 혼입률은 콘크리트 용적의 0.5% ~ 2%로 다양화하였다. 이 때 사용한 강섬유는 Dramix ZC type으로 직경은 0.8mm, 길이는 60mm이다. 강섬유 효과의 상대평가를 위한 용접철망(wire mesh)보강은 상면, 하면, 상하면 보강으로 하였다. 이들 실험 결과를 각국의 인성 평가 방법으로 비교 검토한 결과 슬래브(slab) 시험체 적용을 위한 EFNARC의 방법은 25mm의 처짐까지 측정하는 것이 너무 큰 것으로 평가되었고, 보의 휨인성 평가법을 적용하여 검토한 결과에서는 Johnston(II)방법에 의한 $I_{5.5}$ 가장 적절하였으며, JCI-SF4방법에서 지간의 1/150까지 측정하는 것은 너무 작았다. 또한 강섬유로 용접철망(wire mesh)을 효과적으로 대치할 수 있음을 알 수 있었고, 인성효과에 유용한 강섬유 혼입량은 0.5% ~ 1%범위에 있는 것으로 나타났다.

• 한국구조물진단유지관리공학회 논문집
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• 제12권3호
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• pp.101-109
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• 2008

본 연구에서는 마이크로 입자들로 구성된 매트릭스의 강섬유 보강 시멘트 복합체에서 강섬유가 압축강도에 미치는 영향을 규명하고자 하였으며, 강섬유의 섬유혼입률과 섬유형상비에 따른 영향을 파악하고 혼입률과 형상비를 동시에 고려한 변수인 섬유보강지수(RI)에 따른 압축강도의 변화를 살펴보았다. 실험결과에 따르면 마이크로 입자로 구성된 매트릭스의 강섬유보강 복합체에서는 섬유보강지수가 증가에 따라 압축강도가 선형적으로 증가하였다. 이와 같은 결과로부터 섬유보강지수와 압축강도와의 관계를 나타내는 모델식을 제안하였다.

• 콘크리트학회논문집
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• 제22권5호
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• pp.651-658
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• 2010

콘크리트의 슬럼프와 역학적특성에 대한 마이크로 섬유와 매크로 섬유의 영향을 파악하기 위하여 강섬유와 PVA 섬유로 하이브리드 보강된 콘크리트 16배합과 무보강 콘크리트 1배합을 실험하였다. 주요 변수는 강섬유와 PVA 섬유의 체적비 및 길이이다. 하이브리드 섬유보강 콘크리트의 역학적특성들은 섬유보강지수에 따라 분석되었으며, 강섬유 또는 PVA 섬유만으로 보강된 콘크리트와 비교하였다. 하이브리드 섬유보강 콘크리트의 슬럼프는 섬유 체적비와 형상비 증가와 함께 감소하였으며, 할렬인장강도, 파괴계수, 탄성계수 및 휨 인성지수는 섬유보강지수의 증가와 함께 증가하였다. 단일 섬유보강 콘크리트의 섬유체적비에 비해 낮은 체적비를 갖는 하이브리드 섬유보강 콘크리트의 파괴계수와 휨인성지수는 단일 섬유보강 콘크리트에 비해 높았다. 하이브리드 섬유보강 콘크리트의 휨 인성 향상을 위해서는 30 mm와 60 mm 길이의 강섬유를 함께 사용하는 것보다는 60 mm 강섬유만을 사용하는 것이 효율적이었다.