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REFERENCE LINKING PLATFORM OF KOREA S&T JOURNALS
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Journal of the Korea Concrete Institute
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Journal DOI :
Korea Concrete Institute
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Volume & Issues
Volume 23, Issue 6 - Dec 2011
Volume 23, Issue 5 - Oct 2011
Volume 23, Issue 4 - Aug 2011
Volume 23, Issue 3 - Jun 2011
Volume 23, Issue 2 - Apr 2011
Volume 23, Issue 1 - Feb 2011
Selecting the target year
Development of Actual Measurement Spacing Factor Using Spacing Data of Air Void in Concrete
Lee, Jin-Bum ; Jeon, Sung-Il ; Kwon, Soo-Ahn ; An, Ji-Hwan ;
Journal of the Korea Concrete Institute, volume 23, issue 6, 2011, Pages 701~709
DOI : 10.4334/JKCI.2011.23.6.701
One of the typical evaluation models of concrete air-void system is spacing factor (SF), which was suggested by Power. Power Spacing Factor (PSF) has a disadvantage of the result being different from the actual case due to the existence of entrapped air, because PSF uses average single spacing factor. Therefore, the Actual Measurement Spacing Factor (AMSF) using actually measured data of air void spacing was developed from this study. PSF and AMSF were compared and evaluated in this study by using the image analysis test result of concrete mixture. This study results showed that PSF and AMSF are generally similar, but AMSF had a larger value when PSF was greater than
. The results indicated a possibility of PSF giving false measurement estimation where the measurement is less than the actual value in the concrete mixture containing less air. Also, in the result of PSF and AMSF analysis according to the existence of entrapped air, AMSF showed a larger value in the analysis without entrapped air. But PSF showed a smaller value in the analysis without entrapped air, which was different from the actual case. Because PSF used average single spacing factor, it tended to give a false result. The study results showed that AMSF gave more accurate analysis results.
Behavior of Steel Fiber-Reinforced Concrete Exterior Connections under Cyclic Loads
Kwon, Woo-Hyun ; Kim, Woo-Suk ; Kang, Thomas H.K. ; Hong, Sung-Gul ; Kwak, Yoon-Keun ;
Journal of the Korea Concrete Institute, volume 23, issue 6, 2011, Pages 711~722
DOI : 10.4334/JKCI.2011.23.6.711
Beam-column gravity or Intermediate Moment frames subjected to unexpected large displacements are vulnerable when no seismic details are provided, which is typical. Conversely, economic efficiency of those frames is decreased if unnecessary special detailing is applied as the beam and column size becomes quite large and steel congestion is caused by joint transverse reinforcement in beam-column connections. Moderate seismic design is used in Korea for beam-column connections of buildings with structural walls, which are to be destroyed when the unexpected large earthquake occurs. Nonetheless, performance of such beamcolumn connections may be substantially improved by the addition of steel fibers. This study was conducted to investigate the effect of steel fibers in reinforced concrete exterior beam-column connections and possibility for the replacement of some joint transverse reinforcement. Ten half-scale beam-column connections with non-seismic details were tested under cyclic loads with two cycles at each drift up to 19 cycles. Main test parameters used were the volume ratio of steel fibers (0%, 1%, 1.5%) and joint transverse reinforcement amount. The test results show that maximum capacity, energy dissipation capacity, shear strength and bond condition are improved with the application of steel fibers to substitute transverse reinforcement of beam-column connections. Furthermore, several shear strength equations for exterior connections were examined, including the proposed equation for steel fiber-reinforced concrete exterior connections with non-seismic details.
Evaluation on Mechanical Properties of High Strength Light-Weight Concrete with Elevated Temperature and loading
Kim, Gyu-Yong ; Kim, Young-Sun ; Choe, Gyeong-Cheol ; Park, Hyun-Gil ; Lee, Tae-Gyu ;
Journal of the Korea Concrete Institute, volume 23, issue 6, 2011, Pages 723~730
DOI : 10.4334/JKCI.2011.23.6.723
It is very important to experimentally evaluate concrete behavior at elevated temperature because aggregates make up approximately 80 percent of volume in concrete. In this study, an experiment to evaluate mechanical properties of normal weight and light weight concrete of 60 MPa was conducted. Based on loading level of 0, 20 and 40 percent, the tests of 28 days compressive strength, elastic modulus, thermal strain, total strain, and transient creep using
cylindrical specimens at elevated temperature were performed. Then, the results were compared with CEB (Committes Euro-international du Beton) model code. The results showed that thermal strain of light weight concrete was smaller than normal weight concrete. Also, the results showed that compressive strength of light concrete at
was higher than normal weight concrete and CEB code, similar to that obtained at ambient temperature. Transient creep developed from loading at a critical temperature of
caused the concrete strains to change from expansion to compression. The transient creep test result showed that internal force was high when the ratio of shrinkage between concrete and aggregate was more influential than thermal expansion.
Redistribution of Negative Moments in Beams Subjected to Lateral Load
Eom, Tae-Sung ;
Journal of the Korea Concrete Institute, volume 23, issue 6, 2011, Pages 731~740
DOI : 10.4334/JKCI.2011.23.6.731
Provisions for the redistribution of negative moments in KCI 2007 and ACI 318-08 use a method for continuous flexural members subjected to uniformly-distributed gravity load. Moment redistributions and plastic rotations in beams of reinforced concrete moment frames subjected to lateral load differ from those in continuous flexural members due to gravity load. In the present study, a quantitative relationship between the moment redistribution and plastic rotation is established for beams subjected to both lateral and gravity loads. Based on the relationship, a design method for the redistribution of negative moments is proposed based on a plastic rotation capacity. The percentage change in negative moments in the beam was defined as a function of the tensile strain of re-bars at the section of maximum negative moment, which is determined by a section analysis at an ultimate state using KCI 2007 and ACI 318-08. Span, reinforcement ratio, cracked section stiffness, and strain-hardening behavior substantially affected the moment redistribution. Design guidelines and examples for the redistribution of the factored negative moments determined by elastic theory for beams under lateral load are presented.
Comparison on Characteristics of Concrete Autogenous Shrinkage according to Strength Level, Development Rate and Curing Condition
Yang, Eun-Ik ; Shin, Jung-Ho ; Choi, Yoon-Suk ; Kim, Myung-Yu ; Lee, Kwang-Myong ;
Journal of the Korea Concrete Institute, volume 23, issue 6, 2011, Pages 741~747
DOI : 10.4334/JKCI.2011.23.6.741
In this study, autogenous shrinkage strain and prediction models of concrete specimens were compared with strength level and development rate. Also, concrete autogeneous shrinkage under various curing conditions was investigated. The results showed that autogeneous shrinkage increased as concrete strength increased. However, when the concrete strength was almost identical, the initial autogeneous shrinkage of OPC was larger than BFS, but the final autogeneous shrinkage of BFS was larger than OPC. Early wet curing reduced autogeneous shrinkage strain. Especially, when the early wet curing was applied for more than 24 hours, final autogeneous shrinkage was significantly reduced. The results showed that the existing EC2 models do not reflect concrete properties properly. Therefore, the revised model was proposed to better predict autogeneous shrinkage.
The Combined Effect of Concrete Environment and High Temperature on Interlaminar Shear Strength of FRP Reinforcement
Moon, Do-Young ; Oh, Hong-Seob ;
Journal of the Korea Concrete Institute, volume 23, issue 6, 2011, Pages 749~756
DOI : 10.4334/JKCI.2011.23.6.749
Most experimental studies on durability of FRP reinforcements subjected to high temperature have focused on the effect of high temperature only on tensile properties. But FRP reinforcement used in newly constructed concrete structure is first degraded by moisture and alkaline environment of concrete. When the structure is subjected to fire, the degraded FRP reinforcement is exposed to high temperature. Therefore, the effects of concrete environment and high temperature should be simultaneously considered for evaluation of FRP reinforcement damaged by fire. In this study, FRP reinforcements submerged in simulated solutions of pH 12.3 and 7 for extended period of time were subjected to temperatures of
to be examined. In order to investigate the effect of the high temperature, interlaminar shear strengths were measured and compared to those of control ones. The experimental results demonstrated that the combined effect of concrete environment and high temperature on properties of FRP reinforcement was more significant than the effect of high temperature or concrete environment solely.
Durability of High Early Strength Concrete Using Fine Particles Cement
Kim, Yong-Jic ; Park, Sang-Joon ; Kim, Kyoung-Min ;
Journal of the Korea Concrete Institute, volume 23, issue 6, 2011, Pages 757~763
DOI : 10.4334/JKCI.2011.23.6.757
In order to secure the effective high early age strength of the concrete, the study was carried out with a goal of functional improvement of cement. This study was carried out as a follow up for the previous study, which analyzed the high early age strength and durability of concrete mixed with fine particle cement (FC) during cement production. The experimental results showed that the target range for each mix was satisfied at fresh state of concrete. Also, when mixed with fine particles cement, the setting time improved. Additionally, compressive strength and heat of hydration increased and remained same, respectively. Especially, the durability remained same even when mixed with fine particle cement.
A Stress-Strain Relationship of Alkali-Activated Slag Concrete
Yang, Keun-Hyeok ; Song, Jin-Kyu ; Lee, Kyong-Hun ;
Journal of the Korea Concrete Institute, volume 23, issue 6, 2011, Pages 765~772
DOI : 10.4334/JKCI.2011.23.6.765
The present study summarizes a series of compressive tests on concrete cylinder in order to examine the stressstrain relationship of alkali-activated (AA) slag concrete. The compressive strength and unit weight of concrete tested ranged from 8.6 MPa to 42.2 MPa and from
, respectively. A mathematical equation representing the complete stress-strain curve was developed based on test results recorded from 34 concrete specimens. The modulus of elasticity, strain at peak stress, slopes of ascending and descending branches of stress-strain curves were generalized as a function of compressive strength and unit weight of concrete. The mean and standard deviation of the coefficient of variance between measured and predicted curves were 6.9% and 2.6%, respectively. This indicates that the stress-strain relationship of AA slag concrete is represented properly with more accuracy in the proposed model than in some other available models for ordinary portland cement (OPC) concrete.
A Study on the Thermal Crack Control of the In-Ground LNG Storage Tank as Super Massive Structures
Kwon, Yeong-Ho ;
Journal of the Korea Concrete Institute, volume 23, issue 6, 2011, Pages 773~780
DOI : 10.4334/JKCI.2011.23.6.773
In this study, thermal stress analysis are carried out considering material properties, curing condition, ambient temperature, and casting date of the mass concrete placed in bottom slab and side wall of the in-ground type LNG tank as a super massive structure. Also, based on the numerical results, cracking possibility is predicted and counter measures to prevent the cracking are proposed. For the tasks, two optimum mix proportions were selected. From the results of the thermal stress analysis, the through crack index of 1.2 was satisfied for separately caste concrete lots except for the bottom slab caste in 2 separate sequences. For the double caste bottom slab, it is necessary introduce counter measures such as pre-cooling prior to the site construction. Also, another crack preventive measure is to lower the initial casting temperature by
or less to satisfy 1.2 through crack index criterion. In the
caste bottom slab, the surface crack index was over 1.2. Therefore, the surface cracks can be controlled by implementing the curing conditions proposed in this study. Since the side wall's surface crack index was over 1.0, it is safe to assume that the counter preventive measures can control width and number of cracks.
Strengthening Effect of Reinforced Concrete Beams Strengthened with NSM CFRP Reinforcements and Various Reinforcement Details
Jung, Woo-Tai ; Park, Young-Hwan ; Park, Jong-Sup ; Kim, Chul-Young ;
Journal of the Korea Concrete Institute, volume 23, issue 6, 2011, Pages 781~790
DOI : 10.4334/JKCI.2011.23.6.781
This paper contains the experimental results on strengthening effect of RC beams strengthened with NSM CFRP reinforcement and various strengthening details. A total of 14 beams have been tested to analyze strengthening effects of NSMR with various reinforcement details. Variables were cross-sectional shape of CFRP reinforcements, strengthening areas, grooves the number and location etc. Test results revealed that failure modes of NSMR showed two types. One was bond failure at interface between concrete and filler and the other was CFRP rupture. Also, failure mode of specimens with two grooves occurred premature bond failure because of superposition of failure surfaces at concrete around grooves. failure mode of MI specimens considered the equivalent section have changed bond failure to CFRP rupture and CFRP efficiency has improved 83% to 100%.
Tension Stiffening Effect Considering Cover Thickness in Reinforced Concrete Tension Members
Lee, Gi-Yeol ; Kim, Min-Joong ; Kim, Woo ; Lee, Hwa-Min ;
Journal of the Korea Concrete Institute, volume 23, issue 6, 2011, Pages 791~797
DOI : 10.4334/JKCI.2011.23.6.791
This paper presents the test results of 12 direct tensile specimens to investigate the effect of cover thickness on the tension stiffening behavior in axially loaded reinforced concrete tensile members. Six concrete cover thickness ratios are selected as a main experimental parameter. The results showed that, as cover thickness became thinner, more extensive split cracking along the reinforcement occurred and transverse crack spacing became smaller, making the effective tensile stiffness of thin specimens at the stabilized cracking stage to be much smaller than that of thick specimens. This observation is not implemented in the current design provisions, in which the significant reduction of tension stiffening effect can be achieved by applying thinner cover thickness. Based on the present results, a modified tension stiffening factor is proposed to account for the effect of the cover thickness.
The Suggestion of Testing Method for Analysis of Tensile Strength of Multi-Directional GFRP Plate
Sim, Jong-Sung ; Kwon, Hyuck-Woo ; Lee, Hyoung-Ho ; Kim, Hyun-Joong ;
Journal of the Korea Concrete Institute, volume 23, issue 6, 2011, Pages 799~808
DOI : 10.4334/JKCI.2011.23.6.799
In this study, a standardized test method to analyze tensile properties of multi-directional GFRP plate was proposed. Presently, tensile strength test of FRP composite reinforced with isotropic and orthotropic fiber is standardized according to ISO standard. Also, even though many studies were performed on test method to analyze the dynamic properties, the properties of tensile strength for multi-directional GFRP plate were not clearly identified. Currently, the domestic test method in accordance with ASTM, which is applicable to unidirectional FRP plate, gave tensile test results greater than actual properties. Thus, in this study, GFRP tensile test was conducted using the method found to be commonly applicable to all standards based on literature review of domestic and international references. Then, anchorage length experiments were performed using the proposed tension test method to evaluate validity of the method. Finally, optimal anchorage length was estimated from the numerical analysis to propose the standardized tensile strength method for GFRP multi-directional composite evaluation.
Bond Properties of GFRP Rebar in Fiber Reinforced Concrete (Engineered Cementitious Composite)
Choi, Yun-Cheul ; Park, Keum-Sung ; Choi, Chang-Sik ; Choi, Hyun-Ki ;
Journal of the Korea Concrete Institute, volume 23, issue 6, 2011, Pages 809~815
DOI : 10.4334/JKCI.2011.23.6.809
An experimental investigations on the bond-slip properties of the steel and Glass Fiber Reinforced Polymer(GFRP) bars in engineered cementitious composite (ECC) with Polyvinyl Alcohol (PVA) fibers are presented. Total of 8 beam specimens prepared according to the Rilem procedures with 2% of PVA and PE fiber volume percentage and steel and GFRP reinforcements significantly changed the failure mechanism and slightly improved bond strength. The main objective of the tests was to evaluate the load versus displacement and load versus slip behaviors and the bond strength for the following parameters: concrete type (normal and fiber concrete) and bar diameter (10 and 13 mm). The study results showed that ordinary concrete and ECC specimens showed similar behavior for steel reinforced specimen. However, GFRP reinforced specimen showed different behavior that the steel specimen. The code analytical results showed more accuracy compared to the experimental results as expected in conservative code provisions. Based on the obtained results, it is safe to conclude that the new parameters need to be adopted to ensure safe usage of ECC for construction applications.
A Study on the Performance Improvement and Long-Term Strength Properties of Eco-cement Concrete
Park, Kwang-Min ; Lee, Gun-Cheol ;
Journal of the Korea Concrete Institute, volume 23, issue 6, 2011, Pages 817~826
DOI : 10.4334/JKCI.2011.23.6.817
Concrete using eco-cement has a problem with long-term strength development. However, currently, a long-term strength development mechanism is not confirmed, resulting in a lack of application of eco-cement in construction fields. In this study, the curing humidity influence on development in long-term strength of concrete using eco-cement and the relationship between strength and pore structure were examined. The results showed that wet cured eco-cement with a high water/cement ratio showed serious long-term strength reduction due to non-reduction of pore volume (pore size over 10 nm) in mortar caste with eco-cement. Also, the study results on improvement of long-term strength of eco-cement by partial replacement with ordinary portland cement and finely-ground fly ash showed that both of these alternatives improved long-term strength of concrete caste with eco-cement due to gradual refinement of their micro-structure.