• Steel and Composite Structures
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• 제20권5호
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• pp.1023-1042
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• 2016

Based on Hamilton's principle, the flexural vibration differential equations and boundary conditions of the steel-concrete composite beam (SCCB) with comprehensive consideration of the influences of the shear deformation, interface slip and longitudinal inertia of motion were derived. The analytical natural frequencies of flexural vibration were compared with available results previously observed by the experiments, the results calculated by the FE model and the other similar beam theories available in the open literatures. The comparison results showed that, the calculation results of the analytical and Timoshenko models had a good agreement with the results of the experimental test and FE model. Finally, the influences of shear deformation and interface slip on the flexural natural frequencies of the SCCB were discussed. The shear deformation effect increases with the increase of the mode orders of flexural natural vibration, and the flexural natural frequencies of the higher mode orders ignoring the influence of shear deformations effect would be overestimated. The interface slip effect decrease with the increase of the mode orders of flexural natural vibration, and the influence of the interface slip effect on flexural natural frequencies of the low mode orders is significant. The influence of the degree of shear connection on shear deformation effect is insignificant, and the low order modes of flexural natural vibration are mainly composed of the rotational displacement of cross sections.

• 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.

• 한국구조물진단유지관리공학회 논문집
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• 제22권2호
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• pp.26-33
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• 2018

본 논문은 SIFCON으로 제작된 휨부재의 휨거동에 대한 실험적 해석적 연구결과를 제시한다. 우선, 12개의 SIFCON 보에 대한 휨 실험을 실시하고 휨거동을 평가하였다. 실험변수로는 강섬유 종류, 인장철근 유 무, 단면의 높이를 고려하였다. Type-A 강섬유보다 뽐힘저항성이 우수한 Type-B 강섬유를 사용한 시험체는 전단파괴가 발생하지 않고 휨파괴 거동을 보였으며, 강섬유 형상비는 인장철근을 사용하지 않는 SIFCON 보의 거동에 큰 영향을 주었으나 인장철근을 갖는 SIFCON 보의 거동에 대해서는 그 영향이 매우 미미하게 나타났다. 추가적으로 본연구에서는 SIFCON에 대한 휨강도 예측식을 제시하였다. 휨강도 예측값에 대한 실험값의 비의 평균과 표준편차가 각각 1.02와 0.04로 나타나 휨강도 예측식은 SIFCON 보의 설계 및 성능 평가에 유용하게 사용될 수 있을 것으로 생각된다.

• 한국지반신소재학회논문집
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• 제16권1호
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• pp.19-29
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• 2017

시멘트-점토-모래 혼합토의 휨성능 개선을 위하여 합성섬유를 이용해서 보강한 섬유보강토에 대한 휨성능 시험을 실시하였다. 시멘트, 모래, 그리고 섬유가 혼합토의 휨성능에 미치는 영향을 평가하기 위하여 시멘트량(15%, 20%, 25%), 모래함량(0%, 10%, 20%), 섬유의 종류(PP, PVA)와 길이(6mm, 12mm), 섬유혼입량(0.5%, 1.0%, 1.5%)을 조합하여 시험편을 제작하였다. 본 연구의 결과 시멘트 개량토를 섬유를 이용해서 보강하면 휨강도와 휨인성이 개선되는 효과를 확인할 수 있었다. 휨성능 시험 결과에 대한 다중선형회귀분석 결과 시멘트량과 모래함량은 휨강도에 영향을 미치는 주요 인자인 것으로 나타났고, 반면에 섬유혼입량은 균열발생 후의 거동에 영향을 미치는 주요 인자인 것으로 나타났다.

• 콘크리트학회논문집
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• 제12권2호
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• pp.89-98
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• 2000

The mechanical properties of specialty cellulose fiber reinforced concrete and the contribution of specialty cellulose fiber to drying shrinkage crack reduction potential of concrete and theirs evaluation are presented in this paper. The effects of differing fiber volume fraction(0.03%, 0.06%, 0.08%, 0.1%, 0.15%, 0.2%) were studied. The results of tests of the specialty cellulose fiber reinforced concrete were compared with plain and polypropylene fiber reinforced concrete. Flexural performance(flexural strength and flexural toughness) test results indicated that specialty cellulose fiber reinforcement showed an ability to increase the flexural performance of normal- and high- strength concrete(as compared to plain and polypropylene fiber reinforced concrete). Optimum specialty cellulose fiber reinforced concrete were obtianed using 0.08% fiber volume fraction. Drying shrinkage cracking test results confirmed specialty cellulose fibers are effective in reducing the drying shrinkage cracking of normal and high-strength concrete(as compared to popylene fiber reinforced concrete).

• 한국세라믹학회지
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• 제52권1호
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• pp.61-65
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• 2015

The effect of Sr addition on the flexural strength of bulk SiOC ceramics was investigated in polymer-derived SiOC ceramics prepared by conventional hot pressing. Crack-free, dense SiOC discs with a 30 mm diameter were successfully fabricated from commercially available polysiloxane with 1 mol% strontium isopropoxide derived Sr as an additive. Agglomerates formed after the pyrolysis of polysiloxane led to the formation of domain-like structures. The flexural strength of bulk SiOC was strongly dependent on the domain size formed and Sr addition. Both the minimization of the agglomerate size in the starting powders by milling after pyrolysis and the addition of Sr, which reinforces the SiOC structure, are efficient ways to improve the flexural strength of bulk SiOC ceramics. The typical flexural strength of bulk Sr-doped SiOC ceramics fabricated from submicron-sized SiOC powders was ~209 MPa.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 1999년도 추계학술발표대회 논문집
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• pp.95-100
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• 1999

A FEA(finite element analysis model) was proposed to study stress and strain distributions in thick composites with fiber waviness and initial curvature under flexural loading. Three types of model with initial curvature were considered in this study: flat, concave and concave models. In the analysis, both material and geometrical nonlinearities were incorporated. Four point flexural tests were conducted on the flat specimens to obtain the flexural behavior of thick composites experimentally. It was concluded that the predictions from the models were in good agreement with the experimental results. It was shown that the stress and strain distributions as well as nonlinear flexural behaviors of thick composites were significantly affected by the fiber waviness and initial curvature.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2003년도 봄 학술발표회 논문집
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• pp.421-426
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• 2003

For the replacement of deteriorated concrete decks or wider-span slab, composite slab could be very attactive due to higher stiffness and strength. Based on the previous research, a modified I-beam composite hollow slab was suggested. In order to investigate the static flexural behavior of the proposed composite slab and to suggest its flexural design method, experiments were performed. Judging from the tests, a composite slab with I-beam having a semi-circle hole showed better structural performance. The effect of web details on the flexural stiffness was negligible. Flexural stiffness, ultimate strength, and ductility of the composite slabs were significantly greater than the RC slab due to composite action. While the failure of the RC slab was punching shear failure, the composite hollow slab showed flexural cracking and failure by yielding of the I-beams and crushing of concrete. Therefore, the current one-way design concept is appropriate for the design of I-beam composite hollow slab.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2003년도 봄 학술발표회 논문집
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• pp.567-572
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• 2003

An experimental work is presented to evaluate the retrofit method for improving the flexural capacity of shear walls. Fives shear wall specimens are designed and retrofitted by using carbon fiber materials such as rod, sheet and plate. Cyclic horizontal loads are applied to the specimens under constant axial load, $0.1f_{ck}A_g$. Test result shows that specimens with additional flexural reinforcement have the increased initial stiffness and deformation capacity. However, the strength is not improved as much as expected. This is because that the flexural reinforcement is pulled out from the foundation at the latter half of cycles. In order to maximize the flexural retrofit, therefore, it is required to study the anchorage behavior of the flexural reinforcement for retrofit.

• 대한치과기공학회지
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• 제30권2호
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• pp.65-69
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• 2008

Recently, zirconia is widely used in the field of dental ceramics thanks to the proliferation of CAD/CAM systems. Accordingly, different types of zirconia block are being solid in the market. However, there are no precise, objective standards for properties of zirconia. This study concerns the flexural strength of zirconia ceramic for CAD/CAM block. The test specimens used for this study were ZirBlank(Acucera), ZirBlank shade(Acucera), VITA, Cercon(Densply) and Cerasys. The test results suggest that ZirBlank shade block shows the highest flexural strength and density among the zirconia blocks tested. Its flexural strength was $971{\pm}58MPa$ and its density was 99.89%. On the other hand, Cerasys block shows the lowest flexural strength of $576{\pm}36MPa$ and the lowest density of 94.85%. Given all, the density of the specimens is found to be directly proportional to strength and inversely to grain size.