• Journal of the Korean Society for Railway
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• v.19 no.3
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• pp.341-350
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• 2016

Concrete track on railway bridges should be designed to effectively respond to the movement of the superstructure of the bridge. In the design procedure, shear keys are generally placed on the protection concrete layer (PCL) before casting the concrete track so the shear force due to slip between the concrete track and the bridge super-structure can be transferred. In this paper, a nonlinear structural analysis procedure that considers the construction joint has been developed to predict the shear behavior of a shear key. With the developed analysis procedure, it was possible to predict the shear force-shear slip response at the construction joint in a shear key by considering the friction of concrete surface and the dowel action of the rebars. The analysis results showed good agreement with the test results for 4 specimens.

• Steel and Composite Structures
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• v.27 no.1
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• pp.75-87
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• 2018

This paper presents a new method to compute the shear strength of composited structural B-C-W members. These B-C-W members, defined as concrete-filled steel box beams, columns and shear walls, consist of a slender rectangular steel plate box filled with concrete and inserted steel plates connecting the two long-side steel plates. These structural elements are intended to be used in structural members of super-tall buildings and nuclear safety-related structures. The concrete confined by the steel plate acts to be in a multi-axial stressed state: therefore, its shear strength was calculated on the basis of a concrete's failure criterion model. The shear strength of the steel plates on the long sides of the structural element was computed using the von Mises plastic strength theory without taking into account the buckling of the steel plate. The spacing and strength of the inserted plates to induce plate yielding before buckling was determined using elastic plate theory. Therefore, a predictive method to compute the shear strength of composited structural B-C-W members without considering the shear span ratio was obtained. A coefficient considering the influence of the shear span ratio was introduced into the formula to compute the anti-lateral bearing capacity of composited structural B-C-W members. Comparisons were made between the numerical results and the test results along with this method to predict the anti-lateral bearing capacity of concrete-filled steel box walls. Nonlinear static analysis of concrete-filled steel box walls was also conducted by using ABAQUS and the results agreed well with the experimental data.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.11a
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• pp.919-922
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• 2008

This paper reports the physical and shrinkage properties of concrete using expansive additive(E) and three shrinkage reducing admixtures(SRA1, 2, 3) in order to reduce shrinkage of concrete. For the properties of fresh concrete, the use of SRA1, 2, 3 results in a increase in fluidity and decrease in the dosage of super plasticizer as much as 0.05$\sim$0.1%. And For the properties of hardened concrete, the use of SRA1, 2, 3 results in a decrease in compressive, tensile and flexural strength slightly. For drying shrinkage properties, the use of SRA3 is the most effective for reduction of shrinkage, and the next best way to reduce shrinkage is combination with expansive additive(E) and shrinkage reducing admixture(SRA) or the using of expansive additive(E).

• Journal of the Korea institute for structural maintenance and inspection
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• v.20 no.5
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• pp.1-8
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• 2016

This paper presents an evaluation of engineering properties in TDFA(Tire Derived Fuel Ash)- based concrete in early age. Concrete containing 0.5 of w/b(water to binder) ratio and 20% of FA(Fly Ash) replacement ratio are prepared, and FA content are replaced with TDFA from 3% to 12% for evaluating the effect of TDFA on fresh and hardened concrete properties. With higher than 6% of TDFA replacement ratio, workability is significantly worsened but it is improved with more SP(Super plasticizer) and AE(Air Entrainer) agent. Concrete with 6~12% of TDFA shows reasonable strength development and better resistance to carbonation and chloride attack in spite of early-aged condition. However concrete with 6% TDFA shows poor resistance to freezing and thawing action due to insufficient air content. If air content and workability are obtained, replacement of TDFA to 12% can be used for concrete with FA.

• Composite Materials and Engineering
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• v.3 no.3
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• pp.201-220
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• 2021

In this study, potential of three machine learning techniques i.e., M5P, Support vector machines and Gaussian processes were evaluated to find the best algorithm for the prediction of flexural strength of concrete mix with steel fibre. The study comprises the comparison of results obtained from above-said techniques for given dataset. The dataset consists of 124 observations from past research studies and this dataset is randomly divided into two subsets namely training and testing datasets with (70-30)% proportion by weight. Cement, fine aggregates, coarse aggregates, water, super plasticizer/ high-range water reducer, steel fibre, fibre length and curing days were taken as input parameters whereas flexural strength of the concrete mix was taken as the output parameter. Performance of the techniques was checked by statistic evaluation parameters. Results show that the Gaussian process technique works better than other techniques with its minimum error bandwidth. Statistical analysis shows that the Gaussian process predicts better results with higher coefficient of correlation value (0.9138) and minimum mean absolute error (1.2954) and Root mean square error value (1.9672). Sensitivity analysis proves that steel fibre is the significant parameter among other parameters to predict the flexural strength of concrete mix. According to the shape of the fibre, the mixed type performs better for this data than the hooked shape of the steel fibre, which has a higher CC of 0.9649, which shows that the shape of fibers do effect the flexural strength of the concrete. However, the intricacy of the mixed fibres needs further investigations. For future mixes, the most favorable range for the increase in flexural strength of concrete mix found to be (1-3)%.

• Bulletin of the Korean Mathematical Society
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• v.20 no.2
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• pp.99-103
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• 1983

Internal heat generation is one of the insidious conditions affecting the quality of an industrial product after it is cast, coated, molded, forged or laminated. Frequently, the product is pressed into service before the exothermic chemical reactions in the generic material has been completed. The heat liberated from this continuing chemical reaction or the residual deformation from the rheological activities in the materials must be adequately removed or prevented, or the product may be discolored, warped, weakened or even "ignited" spontaneously. Numerous instances of premature structural failures, product-recalls, and/or system-malfunctions have been recorded in recent history. The Coulee Dam was poured with pre-chilled concrete just to negate this freakish encore. It is well-known that concrete (a non-isotropic conducting medium), for instance, takes 28 days to develop its full strength. During this period of curing it is conceivable that the processes of internal heat generation, heat conduction and heat dissipation take place simultaneously inside the medium.he medium.

• International Journal of High-Rise Buildings
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• v.5 no.3
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• pp.213-220
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• 2016

The "China Zun" tower in Beijing will rise to 528 meters in height and will be the tallest building in Beijing once built. Inspired by an ancient Chinese vessel, the "Zun", the plan dimensions reduce gradually from the bottom of the tower to the waist and then expand again as it rises to form an aesthetically beautiful and unique geometry. To satisfy the structural requirement for seismic and wind resistance, the structure is a dual system composed of a perimeter mega structure made of composite mega columns, mega braces, and belt trusses, and a reinforced-concrete core with steel plate-embedded walls. Advanced parametric design technology is applied to find the most efficient outer-perimeter structure system. The seismic design basically follows a mixed empirical and performance-based methodology that was verified by a shaking table test and other specimen lab tests. The tower is now half-way through its construction.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.11a
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• pp.415-418
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• 2005

Nowadays the three major commercially available of organic chemical admixtures are modified lignosulfonates(LS), sulfonated naphthalene-formaldehyde resins (SNF) and sulfonated melamine-formaldehye (SMF). In this study, various sulfonated melamine-formaldehyde (SMF) superplasticizers were synthesized via four synthetic steps. Hydroxymethylation (Step 1), Sulfonation (Step 2), Polymerization (Step 3) and Neutralization and Stabilization (Step 4). In this synthesis of SMF, reaction conditions such as the mole ratio of melamine to formaldehyde and the amount of acid catalyst were changed. After application of SMF superplasticizer to cement paste and mortar, the physical properties including workability, slump loss, compressive strength were compared.

• Proceedings of the Korea Concrete Institute Conference
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• 1993.10a
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• pp.207-212
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• 1993

When constructing highly precise production plants, for example, super LSI plants or semiconductor plants, it is important to take the necessary control countermeasures into consideration to obtain the working microvibration environment, which is directly related to product precision. Working environment of a clean room means vibration-free and there are only ultra-miro vibration which human cannot sense. In order to provide an place having a vibration-free working environment with only ultra-micro vibration it is necessary to posses a great number of vibration isolation technlogies, wide-ranging and abundant survey and teat data, and a high level of knowledge enabling comprehensive judgments to be made. In this study, experimental modal analysis is used to analyze the dynamic characteristics of double floor for vibration-proofing near apparatus which generate vibration. It is concluded that the double floor system with rubber pad inserted between floor panel and pedestal is good for vibration proof.

• Proceedings of the Korea Concrete Institute Conference
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• 2000.10b
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• pp.1205-1210
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• 2000

In this research we made the mean cement particle size 4 $\mu\textrm{m}$ which can penetrate even minor cracks based on the theory of J.K. Michel who reported particles can penetrate the crack of width up to 3 times of maximum particle size. The cement slurries were produced by adding super plasticizer. The slurries were tested with slurry characterization methods and its rheological properties were characterized. The early hydrated phenomena of ultra fine cement were observed by SEM, XRD and DSC during 24 hours. Mechanical properties of hardened slurry with JIS molds were also tested in 3, 7 and 28 days. The cracked specimens which were repaired with slurries produced various conditions were tested after 3, 7 and 28 days curing in the air and adhesion properties were characterized.