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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 22, Issue 6 - Dec 2010
Volume 22, Issue 5 - Oct 2010
Volume 22, Issue 4 - Aug 2010
Volume 22, Issue 3 - Jun 2010
Volume 22, Issue 2 - Apr 2010
Volume 22, Issue 1 - Feb 2010
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An Experimental Study on Mechanical Properties of Ultra-High Strength Powder Concrete
Jo, Byung-Wan ; Yoon, Kwang-Won ; Park, Jung-Hoon ; Kim, Heoun ;
Journal of the Korea Concrete Institute, volume 22, issue 3, 2010, Pages 287~295
DOI : 10.4334/JKCI.2010.22.3.287
In this study, ordinary Portland cement was used and the air void was minimized by using minute quartz as the filler. In addition, steel fibers were used to mitigate the brittle failure problem associated with high strength concrete. This study is in progress to make an Ultra-high strength powdered concrete (UHSPC) which has compressive strength over 300 MPa. To increase the strength of concrete, we have compared and analyzed the compressive strengths of the concretes with different mix proportions and curing conditions by selecting quartz sand, dolomite, bauxite, ferro silicon which have diameters less than 0.6 mm and can increase the bond strength of the transition zone. Ultra-high strength powdered concrete, which is different from conventional concrete, is highly influenced by the materials in the mix. In the study, the highest compressive strength of the powdered concrete was obtained when it is prepared with ferro silicon, followed in order by Bauxite, Dolomite, and Quartz sand. The amount of ferro silicon, when the highest strength was obtained, was 110%, of the weight of the cement. SEM analysis of the UHSPC showed that significant formation of C-S-H and Tobermorite due to high temperature and pressure curing. Production of Ultrahigh strength powdered concrete which has 28-day compressive strength upto 341MPa has been successfully achieved by the following factors; steel fiber reinforcement, fine particled aggregates, and the filling powder to minimize the void space, and the reactive materials.
Performance Evaluation of Encased-Concrete Bridge Plate(Deep Corrugated Steel Plate) Member
Sim, Jong-Sung ; Park, Cheol-Woo ; Kim, Tae-Soo ; Lee, Hyoung-Ho ; Kang, Tae-Sung ;
Journal of the Korea Concrete Institute, volume 22, issue 3, 2010, Pages 297~303
DOI : 10.4334/JKCI.2010.22.3.297
The current encased-concrete deep corrugated steel plate has an arch type plate structure, which is a compressive strength-dominant structure that has a small moment due to its arch shape. Therefore, it increases the strength against compression by adding reinforcements to make concrete-filling spaces for increasing the compressive strength and forming cross sections that contain reinforced concrete. In this study, the safety factor of the new-concept encased-concrete bridge plate member was evaluated by comparing the compressive strength obtained from the compressive tests, flexural tests and the design compressive strength determined by using the Canadian Highway Bridge Design Code (CHBDC, 2003), which is a design standard for the encased-concrete bridge plate structures. The results of the safety factor evaluation using the design compressive strength and the test results showed that the safety factor was well above the appropriate value 2.0, which could be adjudged very conservative. If the safety factor based on this study results is considered and applied to the design, economical construction will be possible due to the reduced cross section and construction cost.
Evaluation of Durability Characteristics of High Performance Shotcrete Using Fly Ash
Park, Cheol-Woo ; Lee, Hyeon-Gi ; Kang, Tae-Sung ;
Journal of the Korea Concrete Institute, volume 22, issue 3, 2010, Pages 305~311
DOI : 10.4334/JKCI.2010.22.3.305
The industrial by-product market has increased at a geometric rate worldwide with the rapid economic growth. At present time, conventional disposal methods of industrial by-products in Korea including landfill, incineration and storage already have reached their limits. In this study, the industrial by-products such as fly ash and silicafume were used as mineral admixtures, which are commonly added to concrete mix to inhance the economic efficiency, long-term strength and durability of concrete, to determine the optimized mix proportion of high performance shotcrete. Through the series of tests (compressive strength test, accelerated chloride ion penetration test, measurement of chloride diffusion coefficient). The results of the study showed that the proposed mix proportions satisfied the requirements of domestic as well as international guidelines for shotcrete, with a higher durability than the existing shotcrete.
Shear Strength Prediction of FRP RC Baem without Shear Reinforcements
Lee, Jae-Hoon ; Shin, Sung-Jin ;
Journal of the Korea Concrete Institute, volume 22, issue 3, 2010, Pages 313~324
DOI : 10.4334/JKCI.2010.22.3.313
There are many problems in application of FRP reinforcing bars as shear reinforcement, since bending of FRP bars is not a feasible process on construction site. Even though FRP bars can be manufactured in bent shape, they have lower strength at bent location. However, there are no serious problems to use FRP bars as flexural reinforcement. Plates or slabs like bridge decks, in general, do not need shear reinforcements. These types of members with FRP flexural reinforcement have lower shear strength than those with conventional steel flexural reinforcement. However, reliable process or equation for shear strength estimation of FRP reinforced concrete without shear reinforcement are not established, yet. In this study, predicted shear strength obtained from available design equations and assessment equations are compared with 211 experimental results. The results showed that among the current design codes, the Architectural Institute of Japan (AIJ) and the Institution of Structural Engineers (ISE) provided the best estimation. ACI 440.1R-06 provided conservative results with degree of dispersion similar to that of ISE. In addition, regression analysis on the collected experimental results was conducted to develop regression models. As a result, a new reliable shear strength equation was proposed.
Structural Capacity Evaluation of Hybrid Precast Concrete Beam-Column Connections Subjected to Cyclic Loading
Choi, Hyun-Ki ; Yoo, Chang-Hee ; Choi, Yun-Cheul ; Choi, Chang-Sik ;
Journal of the Korea Concrete Institute, volume 22, issue 3, 2010, Pages 325~333
DOI : 10.4334/JKCI.2010.22.3.325
In this study, new moment-resisting precast concrete beam-column joint made up of hybrid steel concrete was developed and tested. This beam-column joint is proposed for use in moderate seismic regions. It has square hollow tubular section in concrete column and connecting plate in precast U-beam. The steel elements in column and beam members were connected using bolt. Furthermore, in order to prevent the premature failure of concrete in hybrid steel-concrete connection, ECC(engineered cementitious composite) was used. An experimental study was carried out investigating the joint behavior subjected to reversed cyclic loading and constant axial compressive load. Two precast beam-column joint specimens and monolithic reinforced concrete joint specimen were tested. The variables for interior joints were cast-in-situ concrete area and transverse reinforcement within the joint. Tests were carried out under displacement controlled reverse cyclic load with a constant axial load. Joint performance is evaluated on the basis of connection strength, stiffness, energy dissipation, and displacement capacity. The test results showed that significant differences in structural behavior between the two types of connection because of different bonding characteristics between steel and concrete; steel and ECC. The proposed joint detail can induce to move the plastic hinge out of the ECC and steel plate. And proposed precast connection showed better performance than the monolithic connection by providing sufficient moment-resisting behavior suitable for applications in moderate seismic regions.
Concrete Mixture Design for RC Structures under Carbonation - Application of Genetic Algorithm Technique to Mixture Conditions
Lee, Sung-Chil ; Maria, Q. Feng ; Kwon, Sung-Jun ;
Journal of the Korea Concrete Institute, volume 22, issue 3, 2010, Pages 335~343
DOI : 10.4334/JKCI.2010.22.3.335
Steel corrosion in reinforced concrete (RC) structures is a critical problem to structural safety and many researches are being actively conducted on developing methods to maintain the required performance of the RC structures during their intended service lives. In this study, concrete mixture proportioning technique through genetic algorithm (GA) for RC structures under carbonation, which is considered to be serious in underground site and big cities, is investigated. For this, mixture proportions and diffusion coefficients of
from the previous researches were analyzed and fitness function for
diffusion coefficient was derived through regression analysis. This function based on the 12 experimental results consisted of 5 variables including water-cement ratio (W/C), cement content, sand percentage, coarse aggregate content per unit volume of concrete in unit, and relative humidity. Through genetic algorithm (GA) technique, simulated mixture proportions were proposed for 3 cases of verification and they showed reasonable results with less than relative error of 10%. Finally, assuming intended service life, different exposure conditions, design parameters, intended
diffusion coefficients, and cement contents were determined and related mixture proportions were simulated. This proposed technique is capable of suggesting reasonable mix proportions and can be modified based on experimental data which consider various mixing components like mineral admixtures.
Shear Strength Model for Interior Flat Plate-Column Connections
Choi, Kyoung-Kyu ; Park, Hong-Gun ;
Journal of the Korea Concrete Institute, volume 22, issue 3, 2010, Pages 345~356
DOI : 10.4334/JKCI.2010.22.3.345
An alternative design method for interior flat plate-column connections subjected to punching shear and unbalanced moment was developed. Since the slab-column connections are severely damaged by flexural cracking before punching shear failure, punching shear was assumed to be resisted mainly by the compression zone of the slab critical section. Considering the interaction with the flexural moment of the slab, the punching shear strength of the compression zone was evaluated based on the material failure criteria of concrete subjected to multiple stresses. The punching shear strength was also used to evaluate the unbalanced moment capacity of the slab-column connections. For verification, the proposed strength model was applied to existing test specimens subjected to direct punching shear or combined punching shear and unbalanced moment. The results showed that the proposed method predicted the strengths of the test specimens better than current design methods in ACI 318 and Eurocode 2.
Hysteretic Behavior of R/C Shear Wall with Various Lateral Reinforcements in Boundary Columns for Cyclic Lateral Load
Seo, Soo-Yeon ; Oh, Tae-Gun ; Kim, Kyeong-Tae ; Yoon, Seong-Joe ;
Journal of the Korea Concrete Institute, volume 22, issue 3, 2010, Pages 357~366
DOI : 10.4334/JKCI.2010.22.3.357
This paper presents experimental results about shear wall with various lateral reinforcement details in boundary elements. The research objective is to study the structural behavior of shear wall with boundary column confined by rectangular spiral hoops and headed cross ties developed to improve workability in the fabrication of boundary columns. These two details can be fabricated in a factory and put together on-site after being delivered so that the construction work may be reduced. Main parameters in the experimental study were the types of hoop and cross tie: rectangular spiral hoop and headed cross tie vs. standard hoop and cross tie with hook. Four half scaled shear wall specimens with babel shape were made and tested by applying horizontal cyclic load under constant axial force, 10% of nominal compressive strength of concrete. Based on the test result, it was shown that the shear wall with rectangular spiral hoop and headed cross tie in boundary columns has structural capacity compatible with conventional shear wall. The specimen SW-Hh which has bigger hoop bar and higher volumetric ratio of transverse reinforcements than other showed improved energy dissipating characteristic but it presented a rapid reduction of strength after peak point. The results indicates that, it is necessary to consider volumetric ratio of transverse reinforcements as well as hoop space in designing of shear wall with boundary columns for improved strength and ductility.
Punching Shear Strength of the Void Transfer Plate
Han, Sang-Whan ; Park, Jin-Ah ; Kim, Jun-Sam ; Im, Ju-Hyeuk ; Park, Young-Mi ;
Journal of the Korea Concrete Institute, volume 22, issue 3, 2010, Pages 367~374
DOI : 10.4334/JKCI.2010.22.3.367
The transfer slab system is a structural system that transfers the loads from the upper shear wall structure to the lower columns. This is a costly system due to a very thick slab, and the relatively high cost can be mitigated by introducing voids in the slab. However, this system of flat plate containing voids is vulnerable to brittle failure caused by punching shear in vicinity of slab-column connection. Thus, the punching shear capacity of the void system is very important. However, the current code doesn`t provide a clear design provision for the strength of slabs with a void section. In this study, experimental study was conducted to investigate the punching shear strength of the void slab system. The shear strength of the specimens was predicted by current code and previous researches. In result, the punching shear strength of the void system is determined as the least value calculated at critical section located a distance d/2 from the face of the column and the center of the void section using the effective area at critical section.
Physical Properties of Cement Blended Finex-Slag Powder
Lee, Keun-Jae ; Byun, Seung-Ho ; Choi, Hyun-Kook ; Song, Jong-Taek ;
Journal of the Korea Concrete Institute, volume 22, issue 3, 2010, Pages 375~380
DOI : 10.4334/JKCI.2010.22.3.375
In this study, physical properties of cement blended with Finex-slag powder(OPC-FS) were investigated by the measurement of flowability, compressive strength, hydration heat, and
content. In addition, those properties of the cement blended with blast furnace slag(OPC-BFS) were also measured for comparison. It was found that OPC-FS and OPC-BFS showed similar trend in the rheological properties. In the blended cement pastes with the
Blaine value the flowability of OPCFS was better than that of OPC-BFS. The initial 3 day mortar compressive strength and the hydration heat of paste of OPC-FS was a bit higher, compared with OPC-BFS. Accordingly
produced in the cement hydration was decreased very rapidly.
A Study on the Seismic Response of a Non-earthquake Resistant RC Frame Using Inelastic Dynamic Analyses
Jeong, Seong-Hoon ; Lee, Kwang-Ho ; Lee, Soo-Kueon ;
Journal of the Korea Concrete Institute, volume 22, issue 3, 2010, Pages 381~388
DOI : 10.4334/JKCI.2010.22.3.381
In this study, characteristics of the seismic response of the non-earthquake resistant reinforced concrete (RC) frame were identified. The test building is designed to withstand only gravity loads and not in compliance with modern seismic codes. Smooth bars were utilized for the reinforcement. Members are provided with minimal amount of stirrups to withstand low levels of shear forces and the core concrete is virtually not confined. Columns are slender and more flexible than beams, and beam-column connections were built without stirrups. Through the modeling of an example RC frame, the feasibility of the fiber elementbased 3D nonlinear analysis method was investigated. Since the torsion is governed by the fundamental mode shape of the structure under dynamic loading, pushover analysis cannot predict torsional response accurately. Hence, dynamic response history analysis is a more appropriate analysis method to estimate the response of an asymmetric building. The latter method was shown to be accurate in representing global responses by the comparison of the analytical and experimental results. Analytical models without rigid links provided a good estimation of reduced stiffness and strength of the test structure due to bond-slip, by forming plastic hinges closer to the column ends. However, the absence of a proper model to represent the bond-slip poased the limitations on the current inelastic analysis schemes for the seismic analysis of buildings especially for those with round steel reinforcements. Thus, development of the appropriate bond-slip model is in need to achieve more accurate analysis.
Models for Hydration Heat Development and Mechanical Properties of Ultra High Performance Concrete
Cha, Soo-Won ; Kim, Ki-Hyun ; Kim, Sung-Wook ; Park, Jung-Jun ; Bae, Sung-Geun ;
Journal of the Korea Concrete Institute, volume 22, issue 3, 2010, Pages 389~397
DOI : 10.4334/JKCI.2010.22.3.389
Concrete has excellent mechanical properties, high durability, and economical advantages over other construction materials. Nevertheless, it is not an easy task to apply concrete to long span bridges. That`s because concrete has a low strength to weight ratio. Ultra high performance concrete (UHPC) has a very high strength and hence it allows use of relatively small section for the same design load. Thus UHPC is a promising material to be utilized in the construction of long span bridges. However, there is a possibility of crack generation during the curing process due to the high binder ratio of UHPC and a consequent large amount of hydration heat. In this study, adiabatic temperature rise and mechanical properties were modeled for the stress analysis due to hydration heat. Adiabatic temperature rise curve of UHPC was modeled superposing 2-parameter model and S-shaped function, and the Arrhenius constant was determined using the concept of equivalent time. The results are verified by the mock-up test measuring the temperature development due to the hydration of UHPC. In addition, models for mechanical properties such as elastic modulus, tensile strength and compressive strength were developed based on the test results from conventional load test and ultrasonic pulse velocity measurement.
Effect of Freeze-Thaw Cycles after Cracking Damage on the Flexural Behavior of Reinforced Concrete Beams
Kim, Sun-Woo ; Choi, Ki-Bong ; Yun, Hyun-Do ;
Journal of the Korea Concrete Institute, volume 22, issue 3, 2010, Pages 399~407
DOI : 10.4334/JKCI.2010.22.3.399
The flexural behaviors of two types of beam members exposed to freeze-thaw cycles were evaluated. This study aims to examine the effect of freeze-thaw cycles on the behavior characteristics of reinforced concrete (RC) beams. For the purpose, a part of the beam specimens were damaged until yielding of tension reinforcement was reached, before they were exposed to 150 and 300 cycles of freeze-thaw. Cyclic tests, as well as monotonic tests, were conducted to evaluate the stiffness degradation characteristics when same cycle is repeated. The material tests showed that relative dynamic modulus of concrete exposed to 300 cycles of freeze-thaw moderately decreased to 86.8% of normal concrete, indicating that concrete used in this study has good durability against freeze and thaw damage. The results of monotonic tests showed reduction of flexural strength, ductility and stiffness of the beam specimens exposed to freeze-thaw cycles compared with those of the control speciments. In particular, BDF13 specimens, which had been subjected to artificial cracking damage, did not showed enough flexural strength to satisfy nominal moment required by current concrete structure design code. In the monotonic tests results, BF75 specimens exposed to freeze-thaw cycles showed 10% or more cyclic stiffness degradation. Therefore, it was thought that deformation of concrete in compression have to be considered in design process of members under cyclic load, such as seismic device.
Similitude Law on Material Non-linearity for Seismic Performance Evaluation of RC Columns
Lee, Do-Keun ; Cho, Jae-Yeol ;
Journal of the Korea Concrete Institute, volume 22, issue 3, 2010, Pages 409~417
DOI : 10.4334/JKCI.2010.22.3.409
This paper discusses a series of experiments including material improvement in order to ensure quality of grouting for the post-tensioned structure. In prestressed concrete, grouting refers to the construction procedure of filling empty space of duct enclosing with strands using cementitious material, To date, adequate quality control of the grouting has not been established in Korea because the relationship between the grouting and durability of post-tensioned structure is not well-recognized. The Korean standard does not consider the important material characteristic, wick effect, which is caused by strands in the ducts and current standard testing method unlikely quantify reasonable material segregation. As a result, the grout material, which meets the current material standards, may exhibit excessive bleeding water or shrinkage during construction. In this study, international codes and standards related to grouting were surveyed. The ratio of constituents and novel admixtures were suggested to meet equivalently with these standards. Performance of this enhanced grout was compared to common domestic grout using the international standard testing method. A series of mock-up specimens considering geometry of PC beam was constructed and grout flow pattern was observed as the grout was injected. It was observed that the grouting performance was highly influenced by material properties and filling characteristic can be varied depending on geometry of ducts.
Study on Material Segregation of Grout and Filling Characteristic of Grouting for Post-Tensioned Concrete Beam
Lee, Jun-Ki ; Choi, Joon-Ho ; Yoon, Jeong-Seob ; Cho, In-Sung ;
Journal of the Korea Concrete Institute, volume 22, issue 3, 2010, Pages 419~426
DOI : 10.4334/JKCI.2010.22.3.419
This paper discusses a series of experiments including material improvement in order to ensure quality of grouting for the post-tensioned structure. In presstressed concrete, grouting refers to the construction procedure of filling empty space of duct enclosing the prestress tendons using cementitious material, To date, adequate quality control of the grouting has not been established in Korea because the relationship between the grouting and durability of post-tensioned structure is not well-recognized. The Korean standard does not consider the important material characteristic, wick effect, which is caused by tendons in the ducts, and furthermore current standard testing method does not quantify reasonable material segregation. As a result, the grout material, which satisfies the current material standards, may well exhibit excessive bleeding of water or shrinkage during construction. In this study, international codes and standards related to grouting were surveyed. The mix proportions of the constituents and novel admixtures were suggested to meet equivalently with these standards. Performance of this enhanced grout was compared with common domestic grouts using the international standard testing method. A series of mock-up specimens considering geometry of PC beam was constructed and grout flow pattern was observed as the grout was injected. It was observed that the grouting performance was highly influenced by material properties and filling characteristic can be varied depending on geometry of ducts.
Variation of Bilinear Stress-Crack Opening Relation for Tensile Cracking of Concrete at Early Ages
Kwon, Seung-Hee ; Choi, Kang ; Lee, Yun ; Park, Hong-Yong ;
Journal of the Korea Concrete Institute, volume 22, issue 3, 2010, Pages 427~435
DOI : 10.4334/JKCI.2010.22.3.427
One of the most vulnerable properties in concrete is tensile cracking, which usually happens at early ages due to hydration heat and shrinkage. In order to accurately predict the early age cracking, it needs to find out how stress-crack opening relation is varying over time. In this study, inverse analyses were performed with the existing experimental data for wedge-splitting tests, and the parameters of the softening curve for the stress-crack opening relation were determined from the best fits of the measured load-CMOD curves. Based on the optimized softening curve, variation of fracture energy over time was first examined, and a model for the stress-crack opening relation at early ages was suggested considering the found feature of the fracture energy. The model was verified by comparisons of the peak loads, CMODs at peak loads, and fracture energies obtained from the experiments and the inverse analysis.