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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 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
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Indeterminate Strut-Tie Model and Load Distribution Ratio of Continuous RC Deep Beams (I) Proposal of Model ＆ Load Distribution Ratio
Kim, Byung-Hun ; Chae, Hyun-Soo ; Yun, Young-Mook ;
Journal of the Korea Concrete Institute, volume 23, issue 1, 2011, Pages 3~12
DOI : 10.4334/JKCI.2011.23.1.003
The structural behavior of continuous reinforced concrete deep beams is mainly controlled by the mechanical relationships associated with the shear span-to-effective depth ratio, flexural reinforcement ratio, load and support conditions, and material properties. In this study, a simple indeterminate strut-tie model which reflects characteristics of the complicated structural behavior of the continuous deep beams is presented. In addition, the reaction and load distribution ratios defined as the fraction of load carried by an exterior support of continuous deep beam and the fraction of load transferred by a vertical truss mechanism, respectively, are proposed to help structural designers for the analysis and design of continuous reinforced concrete deep beams by using the strut-tie model approaches of current design codes. In the determination of the load distribution ratio, a concept of balanced shear reinforcement ratio requiring a simultaneous failure of inclined concrete strut and vertical steel tie is introduced to ensure a ductile shear failure of reinforced concrete deep beams, and the primary design variables including the shear span-to-effective depth ratio, flexural reinforcement ratio, and concrete compressive strength are implemented after thorough parametric numerical analyses. In the companion paper, the validity of the presented model and load distribution ratio was examined by applying them in the evaluation of the ultimate strength of multiple continuous reinforced concrete deep beams, which were tested to failure.
Indeterminate Strut-Tie Model and Load Distribution Ratio of Continuous RC Deep Beams (II) Validity Evaluation
Chae, Hyun-Soo ; Kim, Byung-Hun ; Yun, Young-Mook ;
Journal of the Korea Concrete Institute, volume 23, issue 1, 2011, Pages 13~22
DOI : 10.4334/JKCI.2011.23.1.013
In this study, ultimate strengths of 51 continuous reinforced concrete deep beams were evaluated by the ACI 318M-08's strut-tie model approach implemented with the presented indeterminate strut-tie model and load distribution ratio of the companion paper. The ultimate strengths of the continuous deep beams were also estimated by the shear equations derived based on experimental results, conventional design codes based on experimental and theoretical shear strength models, and current strut-tie model design codes. The validity of the presented strut-tie model and load distribution ratio was examined through the comparison of the strength analysis results classified according to the primary design variables of shear span-to-effective depth ratio, flexural reinforcement ratio, and concrete compressive strength. The present study results of ultimate strengths obtained using the indeterminate strut-tie model and load distribution ratio of the continuous deep beams agree fairly well with those obtained using other approaches. In addition, the present approach reflected the effect of the primary design variables on the ultimate strengths of the continuous deep beams consistently and accurately. Therefore, the present study will help structural designers to conduct rational and practical strut-tie model designs of continuous deep beams.
Properties on the Freeze-Thaw of Concrete Subjected to Seawater Attack
Park, Kwang-Pil ; Kim, Seong-Soo ; Lee, Seung-Tae ; Kim, Jong-Pil ; Jung, Ho-Seop ;
Journal of the Korea Concrete Institute, volume 23, issue 1, 2011, Pages 23~30
DOI : 10.4334/JKCI.2011.23.1.023
In this study, deterioration degrees of concrete were investigated at laboratory under seawater attack and cycling freeze-thaw, which are major durability performance deterioration factors of concrete. Deteriorations of mixed concrete using Portland & blended cement were examined by instrumental analysis of changes in relative dynamic modulus of elasticity and compressive strength. After 520 cycles of freeze-thaw, relative dynamic modulus of elasticity and compressive strength of concrete mixed with normal Portland and LHC over 75% showed relatively low resistance of approximately 44% of those values of SRC. Concrete replaced with 50% fine powder of blast furnace slag showed the most excellent freeze-thaw resistance among the tested blended cement concrete.
Flexural and Punching Behaviors of Concrete Strengthening with FRP Sheets and Steel Fibers under Low-Velocity Impact Loading
Min, Kyung-Hwan ; Shin, Hyun-Oh ; Yoo, Doo-Yeol ; Yoon, Young-Soo ;
Journal of the Korea Concrete Institute, volume 23, issue 1, 2011, Pages 31~38
DOI : 10.4334/JKCI.2011.23.1.031
In this study, in order to observe the behaviors of fiber reinforced polymer (FRP) strengthened and steel fiber reinforced concrete specimens for impact and static loads, flexural and punching tests were performed. For the one-way flexural and two-way punching tests, concrete specimens with the dimensions of
mm were fabricated, respectively. The steel fiber reinforced concrete specimens showed much enhanced resistance on two-way punching of static and impact loads. In addition the FRP strengthening system provided the outstanding performance under a punching load. Because of a large tensile strength and toughness of ultra high performance concrete (UHPC), the UHPC specimens retrofitted with FRP showed marginally enhanced strength and energy dissipating capacity.
Effect of Partial Prestressing Ratio and Effective Prestress on the Flexural Behavior of Prestressed Lightweight Concrete Beams
Yang, Keun-Hyeok ; Moon, Ju-Hyun ; Byun, Hang-Yong ;
Journal of the Korea Concrete Institute, volume 23, issue 1, 2011, Pages 39~48
DOI : 10.4334/JKCI.2011.23.1.039
The present investigation evaluates the flexural behavior of pre-tensioned lightweight concrete beams under two-point symmetrical concentrated loads according to the variation of the partial prestressing ratio and the effective prestress of prestressing strands. The designed compressive strength of the lightweight concrete with a dry density of 1,770
was 35 MPa. The deformed bar with a yield strength of 383 MPa and three-wire mono-strands with tensile strength of 2,040 MPa were used for longitudinal tensile reinforcement and prestressing steel reinforcement, respectively. According to the test results, the flexural capacity of pre-tensioned lightweight concrete beams increased with the increase of the partial prestressing ratio and was marginally influenced by the effective prestress of strands. With the same reinforcing index, the normalized flexural capacity of pre-tensioned lightweight concrete beams was similar to that of pre-tensioned normal-weight concrete beams tested by Harajli and Naaman and Bennett. On the other hand, the displacement ductility ratio of pre-tensioned lightweight concrete beams increased with the decrease of the partial prestressing ratio and with the increase of the effective prestress of strands. The load-displacement relationship of pre-tensioned lightweight concrete beam specimens can be suitably predicted by the developed non-linear two-dimensional analysis procedure. In addition, the flexural cracking moment and flexural capacity of pre-tensioned lightweight concrete beams can be conservatively evaluated using the elasticity theorem and the approach specified in ACI 318-08, respectively.
Characteristics of Alkali-Silica Reaction according to Types and Substitution Ratios of Mineral Admixtures in Korea
Kim, Seong-Kwon ; Hong, Seung-Ho ; Hur, In ; Yun, Kyong-Ku ;
Journal of the Korea Concrete Institute, volume 23, issue 1, 2011, Pages 49~55
DOI : 10.4334/JKCI.2011.23.1.049
The distresses of alkali-silica reaction (ASR) was recently reported at highway cement concrete pavement in Korea, which showed typical cracking and spalling patterns of ARS. Korea is was no longer safe zone against ASR, needding to find a control methodology against ASR. The purpose of this research was to provide a control methodology against ASR using mineral admixtures through a series of laboratory test program. Laboratory works included the accelerated mortar bar test (AMBT) by ASTM C 1260 regulation with five types of aggregate and three types of mineral admixtures (fly ash, ground granulated blast-furnace slag and silica fume). The result of ASTM C 1260 test for five types of aggregates without mineral admixtures showed that Siltstone and Mudstone were found to be "reactive." Tuff and Andesite-1 were found to be "possiblely reactive." In case of concrete mixed with 10, 20, and 30% fly ash, all specimens except Mudstone mixed with 10% FA were found to be "non-reactive". In cases of concrete mixed with 30, 40, and 50% ground granulated blast-furnace slag and 5, 7.5, and 10% silica fume, all specimens were found to be "non-reactive." These results could be selectively applied in constructions in Korea.
Combined Design Method for Shear and Torsional Moment
Min, Chang-Shik ;
Journal of the Korea Concrete Institute, volume 23, issue 1, 2011, Pages 57~65
DOI : 10.4334/JKCI.2011.23.1.057
Both shear and torsional moments apply shear stresses on cross-section of a member, which need to be considered in the design. But in the current Korean Building Code, the design equations for shear and torsional moments are expressed in terms of the sectional strength with different units, causing figures to be drawn separately in two axes. If the design equations are expressed in terms of stresses, then the stresses of shear and torsional moments can be added, allowing figures to be drawn in one axis for easy recognition of the design procedure and the final design results. Moreover, the current code's design equations for shear and torsional moments are considered separately with the intention of summing the area of stirrups with respect to unit length for shear moment (
) and torsional moment (
). Since the size or type of vertical stirrups are predetermined in the design process, the design equations are expressed in terms of the spacing of stirrups rather than the
terms, clarifying various design steps and a design process.
The Effect of Steel-Fiber Contents on the Compressive Stress-Strain Relation of Ultra High Performance Cementitious Composites (UHPCC)
Kang, Su-Tae ; Ryu, Gum-Sung ;
Journal of the Korea Concrete Institute, volume 23, issue 1, 2011, Pages 67~75
DOI : 10.4334/JKCI.2011.23.1.067
The effect of steel-fiber contents on the compressive behavior of ultra high performance cementitious composites (UHPCC) was studied to propose a compressive behavior model for UHPCC. The experiments considered fiber contents of 0~5 vol.% and the results indicated that compressive strength and corresponding strain as well as elastic modulus were improved as the fiber contents increased. Compared to the previous study results obtained from concrete with compressive strength of 100MPa or less, the reinforcement effect on strength showed similar tendency, while the effect on the strain and elastic modulus were much less. Strength, strain, and elastic modulus according to the fiber contents were presented as a linear function of fiber reinforcement index (RI). Fiber reinforcement in UHPCC had no influence on the shape of compressive behavioral curve. Considering its effect on compressive strength, strain, and elastic modulus, a compressive stress-strain relation for UHPCC was proposed.
Stress Relaxation Coefficient Method for Concrete Creep Analysis of Composite Sections
Yon, Jung-Heum ; Kyung, Tae-Hyun ; Kim, Da-Na ;
Journal of the Korea Concrete Institute, volume 23, issue 1, 2011, Pages 77~86
DOI : 10.4334/JKCI.2011.23.1.077
The concrete creep deformation of a hybrid composite section can cause additional deformation of the composite section and the stress relaxation of pre-compressive stress on the concrete section due to partial restraint of the deformation. In this study, the stress relaxation coefficient method (SRCM) is derived for simple analysis of complicate hybrid or composite sections for engineering purpose. Also, an equation of the stress relaxation coefficient (SRC) required for the SRCM is proposed. The SRCM is derived with the parameters of a creep coefficient, section and loading properties using the same method as the constant-creep step-by-step method (CC-SSM). The errors of the SRCM is improved by using the proposed SRC equation than the average SRC's which were estimated from the CC-SSM. The root mean square error (RMSE) of the SRCM with the proposed SRC equation for concrete with creep coefficient less than 3 was less than 1.2% to the creep deformation at the free condition and was 3.3% for the 99% reliability. The proposed SRC equation reflects the internal restraint of composite sections, and the effective modulus of elasticity computed with the proposed SRC can be used effectively to estimate the rigidity of a composite section in a numerical analysis which can be applied in analysis of the external restrain effect of boundary conditions.
Indirect Crack Controling Method Affected by Variation of Material Characteristics in Reinforced Concrete Flexural Members
Choi, Seung-Won ; Kim, Woo ;
Journal of the Korea Concrete Institute, volume 23, issue 1, 2011, Pages 87~98
DOI : 10.4334/JKCI.2011.23.1.087
Crack formations are inevitable in reinforced concrete structures. To estimate crack widths, empirical formulae are used widely and indirect crack controling methods of limiting bar spacing and bar diameter are also used due to their simplicity. In EC2, the characteristic crack width is calculated by multiplying maximum crack spacing and average strain. In this study, limit values of maximum bar spacing and bar diameter are examined as the material characteristics are varied. Two models of tension stiffening effect and maximum crack spacing and their effects are evaluated. The obtained results are compared with the values obtained using KCI method. The results showed that a significant difference is found when two tension stiffening effect are employed, and an under-estimation is found when 2nd order tension stiffening effect and maximum crack spacing limit from Part II were implemented. Therefore, a rational indirect crack control method attained using the tension stiffening effect of 2nd order form is needed. Also, a consistency in serviceabiliy analysis in flexural members needs to be secured. In order to achieve these goals, two crack controling models are suggested.
Optimum Mix Proportion of the High Strength and Self Compacting Concrete Used Above-Ground LNG Storage Tank
Kwon, Yeong-Ho ;
Journal of the Korea Concrete Institute, volume 23, issue 1, 2011, Pages 99~107
DOI : 10.4334/JKCI.2011.23.1.099
This study is to performed to find the optimum mix proportion of the high strength and self compacting concrete for the above-ground LNG storage tank construction and field application. If LNG storage tank wall thicknesscan be reduced, the construction cost and quality can be improved by using self-compacting high strength concrete with compressive strength 60~80 MPa. For this purpose, low heat cement (Type IV) and class F fly ash are used in concrete mix to control hydration heat, flowability, and viscosity. Mix design variables of unit water, fly ash replacement ratio, water-binder ratio, and fine aggregate ratio are selected and tested for material properties and manufacturing cost of the concrete. Also, fly ash replacement ratio is considered using confined water ratio test. The test results showed that the optimum mix proportion of the self-compacting high strength concrete characteristics are as follows. 1) In case of the concrete with specified compressive strength of 60 MPa, the optimum mix proportion is fly ash replacement ratio of 20% and water- binder ratio of 27~30%. 2) In case of the concrete with the strength of 80 MPa, the optimum mix proportion is fly ash replacement ratio of 10% and water-binder ratio 25%. But unit water and fine aggregate ratio are 165
, respectively, regardless of the traget concrete compressive strength range. Also, test results showed that concrete manufacturing cost of 60 MPa and 80 MPa concrete require additional costs of 14~22% and 33%, respectively, compared to the manufacturing cost of 40 MPa concrete. Therefore, application of the self-compacting high strength concrete has proven to be economical in the perspective of the material cost, quality control, and site management.
Crack Control of Flexure-Dominant Reinforced Concrete Beams Repaired with Strain-Hardening Cement Composite (SHCC) Materials
Cha, Jun-Ho ; Park, Wan-Shin ; Lee, Young-Oh ; Kim, Sun-Woo ; Yun, Hyun-Do ;
Journal of the Korea Concrete Institute, volume 23, issue 1, 2011, Pages 109~120
DOI : 10.4334/JKCI.2011.23.1.109
This paper presents an experimental study results on the crack control of flexure-dominant reinforced concrete beams repaired with strain-hardening cement composite (SHCC). Five RC beams were fabricated and tested until failure. One unrepaired RC beam was a control specimen (CBN) and remaining four speciemens were repaired with SHCC materials. The test parameters included two types of SHCC matrix ductility and two types of repair method (patching and layering). Test results demonstrated that RC beams repaired with SHCC showed no concrete crushing or spalling until final failure, but numerous hair cracks were observed. The control specimen CBN failed due to crushing. It is important to note that SHCC matrix can improve crack-damage mitigation and flexural behavior of RC beams such as flexural strength, post peak ductility, and energy dissipation capacity. In the perspective of crack width, crack widths in RC beams repaired with SHCC had far smaller crack width than the control specimen CBN under the same deflection. Especially, the specimens repaired with SHCC of PVA0.75%+PE0.75% showed a high durability and ductility. The crack width indicates the residual capacity of the beam since SHCC matrix can delay residual capacity degradation of the RC beams.
Characteristics of Natural Loess (Hwangtoh) Paste Subjected to Geopolymerization
Kim, Baek-Joong ; Choi, Hee-Bok ; Kang, Kyung-In ; Yi, Chong-Ku ;
Journal of the Korea Concrete Institute, volume 23, issue 1, 2011, Pages 121~127
DOI : 10.4334/JKCI.2011.23.1.121
In this study, possible use of indigenous natural loess (Hwangtoh) as a new binding material via geopolymerization process is examined. Hwangtoh pastes with four different mix proportions of varying alkali liquid concentrations (6 M, 8 M) and the constituents of the binder as well as the alkali liquid at a constant liquid-to-binder ratio of 0.55 were prepared. Analysis of the natural loess (Hwangtoh) paste was carried out as follows : 1) Measurement of compressive strength and weight of cubic specimens versus curing time; 2) Analysis by X-ray diffraction (XRD) and scanning electron microscope (SEM) about reaction product; 3) Porosity analysis of hardened Hwangtoh paste. The result showed that it is possible to prepare Hwangtoh paste with 29.1 MPa at the age of 7 day by using alkali solution (made as 1 : 4.5 the mass ratio of liquefied
and NaOH solution and applying the curing temperature of
). Compressive strength development with respect to the degree of moisture evaporation from the paste seems to be independent of curing temperature. Therefore, it seems that higher early strength of the paste specimens cured at higher temperature can be attributed to both higher rate of reaction and moisture evaporation.