• The Journal of the Korea Contents Association
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• v.15 no.9
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• pp.384-394
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• 2015

The purpose of this study was to evaluate the push-shear bond strength between five commercial zirconia veneering ceramics and zirconia core cylinder, and to investigate the effect of biaxial flexural strength and zirconia liner glass treatments. The biaxial flexural strengths of the veneering ceramics were evaluated by a piston-on-three-ball test. The bond strengths between the Y-TZP cylinder and zirconia veneering ceramics were evaluated using the push-shear bond strength test. The data was analyzed using two-way ANOVA and Scheffe's test. The biaxial flexural strength of Cercon ceram kiss (CE) was higher than those of the other groups. The glass-treated and Triceram zirconia groups showed the highest value and the Creation ZI(CR) showed the lowest. In all groups, the liner glass treatment groups showed significantly higher push-shear bond strength than those without(P<0.05). The liner glass treatments of zirconia can improve the bond strength between the zirconia ceramic core and veneering ceramics.

• Structural Engineering and Mechanics
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• v.72 no.4
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• pp.479-489
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• 2019

The corrosion of reinforcement leads to a gradual decay of structural strength and durability. Several models for crack occurrence prediction and crack width propagation are investigated in this paper. Analytical and experimental models were used to predict the bond strength in the period of corrosion propagation. The manner of flexural strength loss is calculated by application of these models for different scenarios. As a new approach, the variation of the concrete beam neutral axis height has been evaluated, which shows a reduction in the neutral axis height for the scenarios without loss of bond. Alternatively, an increase of the neutral axis height was observed for the scenarios including bond and concrete section loss. The statistical properties of the parameters influencing the strength have been deliberated associated with obtaining the time-dependent bending strength during corrosion propagation, using Monte Carlo (MC) random sampling method. Results showed that the ultimate strain in concrete decreases significantly as a consequence of the bond strength reduction during the corrosion process, when the section reaches to its final limit. Therefore, such sections are likely to show brittle behavior.

• Journal of the Korea institute for structural maintenance and inspection
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• v.1 no.1
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• pp.107-112
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• 1997

A series of reinforced concrete beams was tested to evaluate the flexural performance of the repaired RC beams. The key parameters for this study were the size and location of the patch, and the repair materials, including polymer, polymer-cementitious and cementitious materials. The repaired specimens failed by a typical flexural mode with minor interfacial bond failure. Beams repaired with polymer, polymer-cementitious and cementitious materials recover 100%, 91%, and 97% of the flexural strength respectively, while beams with cement mortar lose approximately 30% of the strength. Compared with the pressure injection techniques the specimens repaired with patching techniques show low flexural strength, with significant interfacial bond failure. Location and size of the repaired part do not affect the recovering performance. Interfacial behavior between repair and strengthening materials is the major influencing factor for the composite structures.

• Journal of the Korea Concrete Institute
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• v.14 no.4
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• pp.549-555
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• 2002

Tensile strength of CFRP (Carbon Fiber Reinforced Polymer) is approximately 10 times higher than that of the steel reinforcement, but the design strength of CFRP is normally limited by unpredictable bond failure between RC and CFRP. Many researches concerned with bond behavior between RC and CFRP have been carried out to prevent the bond failure of RC beam strengthened by CFRP, but the national design code for design bond strength of CFRP has not been constructed. In this study, three beam specimens strengthened by CFRP under the parameters of bonded length were tested to derive the design bond strength of CFRP for the RC flexural members. Each bonded length was calculated based on the bond strength of JCI and CFRP manufacturing company. Also, another two beam specimens strengthened by CFRP were tested to inspect the construction environment effects such as mixing error of epoxy resin, and the amount of epoxy primer. From the test results, it is concluded that the maximum design bond strength of CFRP to RC flexural member is considered to be $\tau$a =8 kgf/㎠.

• Structural Engineering and Mechanics
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• v.78 no.2
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• pp.199-207
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• 2021

In the present paper, an analytical model is proposed to determine the flexural and shear strength of normal and high-strength reinforced concrete beams with longitudinal bars, in the presence of transverse stirrups. The model is based on evaluation of the resistance contribution due to beam and arch actions including interaction with stirrups. For the resistance contribution of the main bars in tension the residual bond adherence of steel bars, including the effect of stirrups and the crack spacing of R.C. beams, is considered. The compressive strength of the compressed arch is also verified by taking into account the biaxial state of stresses. The model was verified on the basis of experimental data available in the literature and it is able to include the following variables in the resistance provision: - geometrical percentage of steel bars; - depth-to-shear span ratio; - resistance of materials; - crack spacing; - tensile stress in main bars; - residual bond resistance including the presence of stirrups;- size effects. Finally, some of the more recent analytical expressions able to predict shear and flexural resistance of concrete beams are mentioned and a comparison is made with experimental data.

• The Journal of Korean Academy of Prosthodontics
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• v.41 no.4
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• pp.476-492
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• 2003

Purpose : The purpose of this study was to compare HEMA and TEGDMA as diluents for the composite resin. Material and methods : Eight kinds of experimental light curable composite resins were prepared and used. Concentrations of monomer and filler were same for all experimental composites, except, the diluent's ratios to the monomer. The ratio of diluents to Bis-GMA were 15%, 20%, 25%, and 30%, and two kinds of diluents were used, so total experimental groups were eight including one control group of 25% TEGDMA. Results : Depth of cure, flexural strength, shear bond strength to bovine enamel, shear bond strength to bovine dentin, water absorption and solubility of composites in water were measured. Sample size for each groups were 10. Arithmetic means were used as each groups representative values, and regression test for two diluents and low concentrations, Duncan's multiple range test, and Two-way ANOVA test were done for kinds of diluents and its concentrations at level of 0.05. Conclusion : Following results were obtained ; 1. There were not significant differences in effects of HEMA and TEGDMA to depth of cure, flexural strength of composites and shear bond strength to bovine enamel (p>0.05). 2. Increase of the concentrations of the diluents made the depth of cure (p<0.001) and flexural strength (p<0.05) a little higher. 3. Shear bond strength to dentin was higher on HEMA containing composites than TEGDMA containing composites (p<0.001). 4. Water absorption was higher on HEMA containing composites than TEGDMA containing composites (p<0.01).

• Computers and Concrete
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• v.6 no.3
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• pp.235-252
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• 2009

Due to the reduction of bond strength resulting from the high corrosion level of reinforcing bars, influence of this reduction on flexural capacity of reinforced concrete (RC) beam should be considered. An extreme case is considered, where bond strength is complete lost and/or the tensile steel are exposed due to heavy corrosion over a fraction of the beam length. A compatibility condition of deformations of the RC beam with partially unbonded length is proposed. Flexural capacity of this kind of RC beam is predicted by combining the proposed compatibility condition of deformations with equilibrium condition of forces. Comparison between the model's predictions with the experimental results published in the literature shows the practicability of the proposed model. Finally, influence of some parameters on the flexural capacity of RC beam with partially unbonded length is discussed. It is concluded that the flexural capacity of the beam may not be influenced by the completely loss of bond of the whole beam span as long as the tensile steel can yield; whether or not the reduction of the flexural capacity of the beam resulting from the loss of bond over certain length may occur depends on the detailed parameters of the given beam.

• The Journal of Korean Academy of Prosthodontics
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• v.38 no.4
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• pp.500-509
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• 2000

In general, the three major oral functions of edentulous patients-mastication, phonation, esthetics-can be rehabilitated by the complete dentures, and both the resin based complete denture and the metal based complete denture are commonly used by many clinicians today. For the sake of many advantages such as the excellent thermal conductivity, low volumetric change, high strength, low risk of fracture and the better patient's adaptation, the metal based complete dentures are indicated to the several cases. But, there are common failures of these type of dentures mainly by the fracture or the debonding between the resin structures and the metal frameworks which is caused by the discrepancies of the flexural strength and the coefficient of thermal expansion. This is aggravated by the water contamination of the interface when exposed to the oral environment and results in the failure of complete denture treatment. So, the purpose of this study is to compare the bond strength and the fracture patterns of the gold alloy based and the Co-Cr alloy based complete dentures using the PMMA resins and the 4-META adhesive resins. The results of this study were as follows. 1. Both to the PMMA resin and the 4-META resin, the flexural bond strength of gold alloy is lower than that of Co-Cr alloy(P<0.05) 2. To the Co-Cr alloy, the bond strength of the 4-META resin is significantly higher than that of PMMA resin(P<0.05). 3. The flexural strength of the group with the mechanical retention form is significantly higher than that of the group without retention form(P<0.05). 4. Comparing with the other groups, the fracture patterns of the group 3 are quite different from the group 1,2,5.

• Journal of the Korea institute for structural maintenance and inspection
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• v.3 no.3
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• pp.203-211
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• 1999

This study is to examine the feasibility of carbon fiber sheet(CFS), a kind of fiber reinforced plastic(FRP), for a repair and reinforcement of R/C beams. The flexural strength of R/C beams, that were preloaded and then the cracks were repaired, maintains that of the uncracked R/C beams. The flexural strength of R/C beams increases with the reinforcement of CFS. In order to practically apply the repair and reinforcement method, further research is needed for the distribution, amount, and bond of CFS. In this study, an experiment was conducted for R/C beams reinforced with CFS, for various wrapping method and amounts of CFS. Experimental results showed the wrapping method increasing the bond area and amount of CFS layer caused the increase in the strength of the beams. It is found that the strength of CFS should be used as 70% of the maximum strength in retrofitting reinforced concrete beams in evaluating flexural capacity on the basis of ultimate strength design method.

• International Journal of Highway Engineering
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• v.3 no.3 s.9
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• pp.135-146
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• 2001

This study focused on the investigation of compressive and flexural strengths development, and bond strength of latex modified concrete in order to validate the feasibility of application into concrete bridge deck overlay. Pull-out bond test was used for evaluating the bond strength of latex modified concrete to substrate. The main experimental variables were latex-cement ratio, surface preparation and moisture levels. The compressive strength of latex modified concrete decreased slightly and the flexural strength increased as the latex content increased from 5% to 20%. This might be due to the flexibility latex filled in voids and interconnections of hydrated cement and aggregates by a film of latex particles, respectively. In general, increasing the amount of latex will produce concrete with increased tensile and flexural strength and lower modulus of elasticity. Significant improvements in bond strength between new and existing concrete were achieved through the modification of the new concrete bridge deck overlay by latex polymers. The effect of surface preparation on bond of latex modified concrete to conventional concrete were significant at the conditions by sand paper and wire brush. A better bond could be achieved by rough surface rather than smooth. The saturated condition of surface is the most appropriate moisture level among the considered followed by dry condition and wet condition.