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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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Korea Concrete Institute
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Volume & Issues
Volume 21, Issue 6 - Dec 2009
Volume 21, Issue 5 - Oct 2009
Volume 21, Issue 4 - Aug 2009
Volume 21, Issue 3 - Jun 2009
Volume 21, Issue 2 - Apr 2009
Volume 21, Issue 1 - Feb 2009
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Estimation of Local Strain Distribution of Shear-Compressive Failure Type Beam Using Digital Image Processing Technology
Kwon, Yong-Gil ; Han, Sang-Hoon ; Hong, Ki-Nam ;
Journal of the Korea Concrete Institute, volume 21, issue 2, 2009, Pages 121~127
DOI : 10.4334/JKCI.2009.21.2.121
The failure behavior of RC structure was exceedingly affected by the size and the local strain distribution of the failure zone due to the strain localization behavior on the tension softening materials. However, it is very difficult to quantify and assess the local strain occurring in the failure zone by the conventional test method. In this study, image processing technology, which is available to measure the strain up to the complete failure of RC structures, was used to estimate the local strain distribution and the size of failure zone. In order to verify the reliability and validity for the image processing technology, the strain transition acquired by the image processing technology was compared with strain values measured by the concrete gauge on the uniaxial compressive specimens. Based on the verification of image processing technology for the uniaxial compressive specimens, the size and the local strain distribution of the failure zone of deep beam was measured using the image processing technology. With the results of test, the principal tensile/compressive strain contours were drawn. Using the strain contours, the size of the failure zone and the local strain distribution on the failure of the deep beam was evaluated. The results of strain contour showed that image processing technology is available to assess the failure behavior of deep beam and obtain the local strain values on the domain of the post-peak failure comparatively.
An Experimental Study on Retrofit Effect of Shear Wall with Opening Using Steel Bar or Steel Plate
Choi, Youn-Cheul ; Bae, Baek-Il ; Choi, Chang-Sik ; Choi, Hyun-Ki ;
Journal of the Korea Concrete Institute, volume 21, issue 2, 2009, Pages 129~138
DOI : 10.4334/JKCI.2009.21.2.129
Recently, for more demands of the economical benefits and environmental conservation, many engineers prefer to choose remodeling. Artificial openings are often unavoidable to make house wider, which will degrade wall strength and stiffness by losing effective wall section that may cause the weakening of system capacity. In these cases the damaged shear walls need to be retrofitted by additional materials or members. In this research, four specimens were tested to investigate the capacity of the damaged wall and the retrofitted wall. The artificially damaged wall was prestressed by tendons to improve the shear capacity of the wall, and the other walls were retrofitted by adding steel plate at the surface for the same purpose. Consequently, these retrofitted walls had improved capacity and stiffness in both shear and flexure. Especially, the wall with steel plate showed ductile behavior after ultimate load and the prestressed wall had greater stiffness than the unstrengthened prototype wall.
Long-Term Behavior of CFRP Strips under Sustained Loads
You, Young-Chan ; Choi, Ki-Sun ; Kim, Keung-Hwan ;
Journal of the Korea Concrete Institute, volume 21, issue 2, 2009, Pages 139~146
DOI : 10.4334/JKCI.2009.21.2.139
Experimental study was performed to evaluate the long-term behavior of CFRP (carbon fiber reinforced polymer) strips under sustained loads including prestressing force in strengthening RC members with post-tensioned CFRP strips. Two types of CFRP strip such as unidirectional CFRP strip and hybrid CFRP strip which is composed of carbon fiber and steel plate were considered. Also two types of loading scheme were included in this study. Direct sustained loading test had been carried out to estimate the creep deformation and relaxation of CFRP strips including slip deformation at both mechanical anchorages for over 700 days. Also, flexural sustained loading test had been conducted to estimate the initial prestress losses on clamping the CFRP strips at jacking anchorages for over 90 days. From the sustained loading tests, it was observed that stress losses of unidirectional CFRP strips due to the creep deformation and relaxation of material itself and slip deformation at mechanical anchorage were ignorable. On the other hand, significant stress losses caused by the yielding of steel embedded in CFRP strips were found in case of hybrid CFRP strips due to the initial jacking force over steel yielding stress. Also, initial prestress losses during setting of CFRP strips on mechanical anchorage were about 10% of intial jacking force, which must be considered in the design.
Performance Evaluation of Artificial Lightweight Aggregate Mortar Manufactured with Waste Glass
Kim, Seong-Soo ; Lee, Jeong-Bae ; Nam, Ba-Reum ; Park, Kwang-Pil ;
Journal of the Korea Concrete Institute, volume 21, issue 2, 2009, Pages 147~152
DOI : 10.4334/JKCI.2009.21.2.147
The compressive strength test, bulk density and mortar absorption ratio were carried out to utilize the data as the basic sources for the lightweight mortar and the lightweight concrete, through the study on the physical characteristics of the artificial lightweight aggregate (ALA) made of waste glasses, which was developed for the first time in the country. On the basis of these experiments, the density and the unit volume weight of the ALA showed the value less than 50% of the common aggregate due to the independent pore structure, and the mortar that contains ALA had no big difference from the Control mortar in the test of the absorption ratio. It is judged that this happens based on the internal independent pore structure of the ALA. In case of the mortar containing ALA, there was a tendency of declination in the compressive strength and the bending strength as the mixing rate is increasing, but all mortar showed more than 70% of the Control mortar compressive strength except for the La50 mortar. Hereafter, it is judged that according to the control of the mixing ratio of mineral admixing agent, water and cement, it will realize the equal strength to the control mortar, and the long term edurance is needed to be considered together.
Steel Probing in Concrete Using Steel Corrosion Surface Measurement Method Modeling
Rhim, Hong-Chul ; Ma, Hyang-Hwa ; Lee, Suk-Yong ; Lee, Kun-Woo ; Oh, Jin-Won ;
Journal of the Korea Concrete Institute, volume 21, issue 2, 2009, Pages 153~158
DOI : 10.4334/JKCI.2009.21.2.153
Using non-invasive surface measurement method, the corrosion state of steel embedded inside concrete can be measured by placing four electrodes on the surface of concrete. Modeling of such measurements can provide valuable information as how interfacial impedance between corroded steel and surrounding concrete results in measured impedance on the concrete surface. In this paper, the modeling of surface measurement technique is used for the determination of the sensitivity of the measurements with respect to steel bar size embedded inside concrete and cover thickness. Modeling results indicated that steel bar sizes varied from D10 to D35 could be identified. Concrete cover thickness changes from 0.02 m to 0.1 m was also distinguished using the modeling scheme. The results confirm this modeling technique is capable of determining steel bar sizes and cover thickness, as well as simulating corrosion responses.
An Experimental Study on Uniaxial Compressive Behavior of RC Circular Columns Laterally Confined with Prestressing Aramid Fiber Strap
Han, Sang-Hoon ; Hong, Ki-Nam ; Lee, Jae-Bum ;
Journal of the Korea Concrete Institute, volume 21, issue 2, 2009, Pages 159~168
DOI : 10.4334/JKCI.2009.21.2.159
In this study, strength, stiffness and confinement effect with stress-strain and stress-volumetric strain curves for improved uniaxial compressive behavior of RC circular columns laterally confined with prestressing aramid fiber strap were experimentally investigated. The test variables were the specimens with or without axial reinforcing bar and the number and spacing of strap, prestressing level, the types of reinforcing fiber (CFS, GFS). As a result, the failure type of the columns was very stable and strength increase rate was about 73% comparison with the general RC columns. Moreover, the strain increase rate is very small and the axial displacement confinement effect was very effective compared with existry methods (CFS, GFS), the initial and final lateral confinement effect was excellent.
Modified Equation for Ductility Demand Based Confining Reinforcement Amount of RC Bridge Columns
Lee, Jae-Hoon ; Son, Hyeok-Soo ;
Journal of the Korea Concrete Institute, volume 21, issue 2, 2009, Pages 169~178
DOI : 10.4334/JKCI.2009.21.2.169
An equation for calculating confining reinforcement amount of RC bridge columns, specified in the current bridge design codes, has been made to provide additional load-carrying strength for concentrically loaded columns. The additional load-carrying strength will be equal to or slightly greater than the resistant strength of a column against axial load, which is lost because the cover concrete spalls off. The equation considers concrete compressive strength, yield strength of transverse reinforcement, and the section area ratio as major variables. Among those variables, the section area ratio between the gross section and the core section, varying by cover thickness, is a variable which considers the strength in the compression-controlled region. Therefore, the cross section ratio does not have a large effect in the aspect of ductile behavior of the tension-controlled region, which is governed by bending moment rather than axial force. However, the equation of the design codes for calculating confining reinforcement amount does not directly consider ductile behavior, which is an important factor for the seismic behavior of bridge columns. Consequently, if the size of section is relatively small or if the section area ratio becomes excessively large due to the cover thickness increased for durability, too large an amount of confining reinforcement will be required possibly deteriorating the constructability and economy. Against this backdrop, in this study, comparison and analysis were performed to understand how the cover thickness influences the equation for calculating the amount of confining reinforcement. An equation for calculating the amount of confining reinforcement was also modified for reasonable seismic design and the safety. In addition, appropriateness of the modified equation was examined based on the results of various test results performed at home and abroad.
A Study on the Optimization of the Mix Proportions of High Strength Concrete Fire-Resistant Reinforcement Using Orthogonal Array Table
Lee, Mun-Hwan ;
Journal of the Korea Concrete Institute, volume 21, issue 2, 2009, Pages 179~186
DOI : 10.4334/JKCI.2009.21.2.179
The peculiarity pointed out for high strength concrete is the occurrence of spalling during a fire. Recently, there are many efforts such as development of all types of spalling reducing materials and other innovative materials in various fields. Need is now to examine the adequate mixing proportions of these materials. This study intended to derive experimentally and statistically mix proportions that can represent the basic quality requirements as well as the optimal effects on the fire-resistance for 4 types of functional materials that are metakaolin, waste tire chip, polypropylene fiber and steel fiber. Here, the tests were planned through an optimal test method using an orthogonal array table with 4 parameters and 3 levels. The statistical analysis adopted the response surface analysis method. Results verified mutual complementary contribution between the materials when using a combination of the functional materials selected as parameters for the strengthening of the fire-resistance of 80 MPa-class high strength concrete. Besides, the optimal conditions of the fire-resistance strengthening materials derived through response surface analysis were a volumetric replacement of silica fume by 80% of metakaolin, a volumetric replacement of fine aggregates by 3% of tire waste chip, and an addition of 0.2% of the whole volume by polypropylene fiber without mixing of steel fiber. In such cases, the basic characteristics as well as the fire-resistant characteristics of high strength concrete were also satisfied.
Fragility Analysis Method Based on Seismic Performance of Bridge Structure considering Earthquake Frequencies
Lee, Dae-Hyoung ; Chung, Young-Soo ; Yang, Dong-Wook ;
Journal of the Korea Concrete Institute, volume 21, issue 2, 2009, Pages 187~197
DOI : 10.4334/JKCI.2009.21.2.187
This paper presents a systematic approach for estimating fragility curves and damage probability matrices for different frequencies. Fragility curves and damage probability indicate the probabilities that a structure will sustain different degrees of damage at different ground motion levels. The seismic damages are to achieved by probabilistic evaluation because of uncertainty of earthquakes. In contrast to previous approaches, this paper presents a method that is based on nonlinear dynamic analysis of the structure using empirical data. This paper presents the probability of damage as a function of peak ground acceleration and estimates the probability of five damage levels for prestressed concrete (PSC) bridge pier subjected to given ground acceleration. At each level, 100 artificial earthquake motions were generated in terms of soil conditions, and nonlinear time domain analyses was performed for the damage states of PSC bridge pier structures. These damage states are described by displacement ductility resulting from seismic performance based on existing research results. Using the damage states and ground motion parameters, five fragility curves for PSC bridge pier with five types of dominant frequencies were constructed assuming a log-normal distribution. The effect of dominant frequences was found to be significant on fragility curves.
An Experimental Study on Characteristics of Averaged Electromagnetic Properties considering Moisture Changes in Cement Mortar
Kwon, Seung-Jun ; Maria, Q. Feng ; Na, Ung-Jin ;
Journal of the Korea Concrete Institute, volume 21, issue 2, 2009, Pages 199~207
DOI : 10.4334/JKCI.2009.21.2.199
Many researches on electromagnetic (EM) properties like dielectric constant and conductivity are performed since they can be characterized in nonmetallic cement-based material such as mortar and concrete. However, they are much affected by the moisture so that the behaviors of EM properties are to be clearly understood. In this paper, measurements for saturation and EM properties are performed for cement mortar specimens with five different water to cement (W/C) ratios including basic tests like compressive strength and porosity measurement. Every saturated specimens are exposed to room condition and the changes in EM properties caused by decreasing saturation are analyzed. In the saturated condition, higher measurement of EM properties are evaluated in the specimens with higher porosity, however this relationship is adversely changed with drying process. Since the pores without filled water causes the decreases in EM properties, the measurements show stable and linear increment with the lower W/C ratios. Furthermore, the increasing ratios of EM measurements with W/C ratio are shown with saturation and the relationships between them are derived through regression analysis.