• Structural Engineering and Mechanics
• /
• v.53 no.1
• /
• pp.41-55
• /
• 2015

In this paper, a model for the evaluation of shear strength of fibre reinforced polymer (FRP)-reinforced concrete beams is given. The survey of literature indicates that the FRP reinforced beams tested with shear span to depth ratio less than or equal to 1.0 is limited. In this study, eight concrete beams reinforced with GFRP rebars without stirrups are cast and tested over shear span to depth ratio of 0.5 and 1.75. The concrete compressive strength is varied from 40.6 to 65.3 MPa. The longitudinal reinforcement ratio is varied from 1.16 to 1.75. The experimental shear strength and load-deflection response of the beams are determined and reported in this paper. A model is proposed for the prediction of shear strength of beams reinforced with FRP bars. The proposed model accounts for compressive strength of concrete, modulus of FRP rebar, longitudinal reinforcement ratio, shear span to depth ratio and size effect of beams. The shear strength of FRP reinforced concrete beams predicted using the proposed model is found to be in better agreement with the corresponding test data when compared with the shear strength predicted using the eleven models published in the literature. Design example of FRP reinforced concrete beam is also given in the appendix.

• Journal of the Korean Society of Environmental Restoration Technology
• /
• v.10 no.1
• /
• pp.82-90
• /
• 2007

In order to analyse the strength problems for an unsaturated soil, it is required to examine closely the characteristics of the parameters of shear strength which was changed with the metric suction and void ratio. To this ends, a triaxial compression test was conducted on the three samples-granular soil, cohesive soil and silty soil. The specimen was made by pressing the static pressure on the mold filled soil and was controled the void ratio with the different compaction ratio. And the test was performed by using the modified apparatus of the triaxial compression tester. The range of matric suction was 0-90 kPa.The measured results for the deviator stress and parameters of shear strength were analysed with the void ratio and the compaction ratio, and they were examined closely the characteristics of the strength for an unsaturated soil.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2001.05a
• /
• pp.947-952
• /
• 2001

The prediction model is proposed to estimate the variation of compressive strength of fly ash concrete with aging. After analyzing the experimental result with the model, the regression results are presented according to fly ash replacement content and water/cement ratio. Based on the regression results, the influence of fly ash replacement content and water/cement ratio on apparent activation energy was investigated. According to the analysis, the model provides a good estimate of compressive strength development of fly ash concrete with aging. As the fly ash replacement content increases, the limiting relative compressive strength and initial apparent activation energy become greater. The concrete with water/cement ratio smaller than 0.40 shows that the limiting relative compressive strength and apparent activation energy are nearly constant according to water/cement ratio. But, the concrete with water/cement ratio greater than 0.40 has the increasing limiting relative compressive strength and apparent activation energy with increasing water/cement ratio.

• Journal of the Korea Concrete Institute
• /
• v.17 no.5 s.89
• /
• pp.843-852
• /
• 2005

Presently, test results and stress-strain models for poorly confined high-strength columns, more specifically for columns with a tie volumetric ratio smaller than $2.0\%$, are scarce. This paper presents test results loaded in axial direction for square reinforced concrete columns confined by various volumetric ratio lateral ties including low-volumetric ratio. Test variables include concrete compressive strength, tie yield strength, tie arrangement type, and tie volumetric ratio. Local strains measured using strain gages bonded to an acryl rod. For square RC columns confined by lateral ties, the confinement effect was efficiently improved by changing tie arrangement type from Type-A to Type-B. A method to compute the stress in lateral ties at the concrete peak strength and a new stress-strain model for the confined concrete are proposed. Over a wide range of confinement parameters, the model shows good agreement with stress-strain relationships established experimentally.

• Journal of the Korean Society of Safety
• /
• v.36 no.4
• /
• pp.29-36
• /
• 2021

The allowable strength based on experiments and the design allowable strength calculated using the design criteria were compared, which suggested a ratio between the allowable strengths for the reused vertical members of the system scaffolding and system support. By investigating a total of 421 certification reports for reused vertical members, the experimental allowable strengths were collected. Using design criteria such as the road bridge design and KDS 14 30 10, the design allowable strengths were calculated for various slenderness ratios. For the system scaffolding, the average ratio between the experimental and design allowable strengths was calculated to be 0.880 by assuming a normal distribution for all specimens. However, by analyzing the strength ratio according to the slenderness ratio, the lowest average strength ratio was found to be at least 0.844. Therefore, it is reasonable to assume that the allowable strength of the reused vertical members was 80-84% of the design allowable strength. In addition, assuming the allowable strength to be 85% of the design allowable strength is a possible method for reused vertical members of system supports.

• Journal of the Korea Institute of Building Construction
• /
• v.8 no.5
• /
• pp.59-65
• /
• 2008

In the evaluation method of KS on the activity factor of fly ash, same amount of cement should be replaced with fly ash. Therefore, contradictory effects on concrete strength exist, i. e. strength decease due to low content of cement and strength increase of strength due to filling-pore-function of fly ash. European Committee for Standardization (CEN) specifies the method 1 to 4. adding fly ash without reducing the content of cement, for the evaluation method on activity factor of fly ash. This study investigates the applicability of the method 2 of CEN to mix design of concrete. The followings are derived ; There is a key ratio of f)y ash mixing which enhances the incremental ratio of mixing water to improve fluidity of mortar. The incremental ratio of mixing water is maximized about 11% ratio of fly ash mixing. Compressive strength most slightly increases at that ratio of fly ash mixing. Activity factor of fly ash increases as water-cement ratio becomes low and contents of fly ash becomes high. Moreover, quality of fly ash and condition of mix design affect the applicable amount of fly ash and available range of water-cement ratio. However, this method has some problems for practical purpose because activity factors of fly ash for some cases are over 1.0. Further research should be conducted to develop more useful method of evaluating activity factor of fly ash.

• Journal of the Korea Concrete Institute
• /
• v.26 no.5
• /
• pp.591-598
• /
• 2014

In this study, the relationship between compressive strength and water-cement ratio according to water reducing ratio was evaluated, concrete mix was prepared according to 3 level of water reducing ratio (0%, 8% and 16%) and 3 level of water-cement ratio (40%, 45% and 50%). In addition, concrete mix was carried out repetition test of three times in order to secure the reliability. As a result, compressive strength according to water reducing ratio was shown that difference of strength was about 20% occurred, effect of compressive strength according to water reducing ratio was found more than the water-cement ratio. Therefore, reflected the effect of water reducing ratio, relationship equation between new compressive strength and water-cement ratio was proposed.

• Journal of the Korea Institute of Building Construction
• /
• v.7 no.4
• /
• pp.145-151
• /
• 2007

In this paper, tests are carried out in order to investigate the strength development of concrete under various binder types, W/B and curing temperature ranged from $5{\sim}20^{\circ}C$. Fly ash and blast furnace slag were incorporated by as much as 30%, respectively. Strength development of concrete are estimated using Logistic model and strength ratio of concrete at 28days to that at early age are also investigated. According to experimental results, it is found that good agreements are obtained between measured values and calculated ones using logistic model below $20^{\circ}C$. Strength ratio of concrete at 28days to that at early age increases in case W/B decreases and curing temperature increases. Tables and graphs for strength ratio of concrete are provided in this paper. It is capable of obtaining and predicting the periods to attain design strength by considering increment factor of strength easily with the table and graphs presented in this paper. This paper presents the reference data to decide removal time of form, time to reach target strength and strength inspection of remicon whether the test specimens meet the specified criteria of compressive strength. Multi regression models with respect to the relationship between 7days compressive strength and 28 days compressive strength depending on W/B and admixture types are presented.

• Journal of The Korean Society of Agricultural Engineers
• /
• v.48 no.1
• /
• pp.51-60
• /
• 2006

This study was conducted to investigate experimentally the drying shrinkage and the strength properties of redispersible SBR and PAE powder-modified mortars. Polymer-cement ratio, content of shrinkage-reducing agent and antifoamer content were manipulated as the experimental variables. The peculiarity of this study is to obtain a high early-age strength by using the portland cement and alumina cement with the ratio of 8 : 2. Until 7 days of age, the drying shrinkage remarkably increased up to $1\~2\times10^{-4}$, while it tended to decrease as the ratio of polymer to cement ratio and the content of shrinkage-reducing agent increased. Polymer-cement ratio was effective in improving the flexural, tensile and adhesive strengths: As the ratio increased, the strengths correspondingly increased. The flexural strength was in the range of $7\~11$ MPa, the tensile strength was $3.5\~5$ MPa and the adhesive strength was $1.2\~3.9$ MPa. On the other hand, the compressive strength tended to decrease as the polymer-cement ratio increased, and it was in the range of $23\~39$ MPa. All strengths, flexural, tensile, adhesive and compressive strengths, decreased as the content of powder shrinkage-reducing agent increased. It turned out that the polymer-cement ratio influenced more on the behavior of drying shrinkage and the properties of strength than the powder shrinkage-reducing agent did.

• Proceedings of the Korea Concrete Institute Conference
• /
• 1991.10a
• /
• pp.129-134
• /
• 1991

The effects of water-cement ratio, age, and admixture such as fly ash, silica fume on the bond strength between aggregate and mortar were investigated. As the result, with increasing of water-cement ratio, the bond strength was slightly decreased while the compressive strengths of mortar and concrete were seriously decreased. The rate of strength gain of bond strength was not decreased with increasing of water-cement ratio while that of compressive strength was gradually decreased.