• Journal of the Korean Society for Heat Treatment
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• v.17 no.2
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• pp.73-77
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• 2004

The efforts which increase the strength of the auto-body structure and decrease its weight lead to develop a new concept of part production systems, such as Post-Form Strengthening by induction heat treatment. In this study, several cold and hot-rolled sheet steels were used to find out optimum induction heat treatment conditions. After induction heat treatment, strength of heat-treated sheet steels was increased significantly compared with that of as-rolled steels. From these results, auto-body structure which has more light and safe has been made by using this induction hardening method.

• Geotechnical Engineering
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• v.3 no.2
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• pp.41-54
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• 1987

Although natural soil deposits hat.e been consolidated under Ko-stress system, the soil behavior has been predicted in laboratory from the results of tests performed on specimens consolidated under an isotropic stress s).stem. A series of undrained triaxial compression tests are performed on remolded specimens of clay consolidated under both types of stress systems, and the results at.e compared. One dimensional consolidation history induces anisotropy in clalrs, which is called as the stress induced anisotropy. However, if the clays would be reconsolidated under isotropic stress system. the anisotropy of undrained stress비h would be decreased with decrease of overconsolidation ratio. Undrained shear strength of norma]Iy consolidated clay depends on consolidation methods. Both the Rutledge hypothesis and the study of Henkel and Sowa do not agree with the test results obtained in this paper. In addition, a new theory is explained about the relationships between consolidation stresses, water contents and undiained shear strength.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.11a
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• pp.213-216
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• 2005

A numerical analysis was performed for interior connections of continuous flat plate to analyze the effect of design parameters such as column section shape, gravity load and slab span on the behavioral characteristics of the connections. Through the parametric study, the variations of shear stress distribution around the connection were investigated. According to the result of numerical analysis, as the length of the cross section of column in the direction of lateral load increases and gravity load increases, the effective area and the maximum shear strength providing the torsional resistance decrease considerably. And as the slab span loaded with relatively large gravity load increases, the negative moment around the connection increases and therefore the strength of connection against unbalanced moment decreases.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.11a
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• pp.777-780
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• 2005

The paper presents details of an investigation into the effect of sand content upon the strength and shrinkage of mortar. This strategy was to produces more durable strength mortar with less cement. Cement mortars containing $20\;wt.\;\%$ Class F fly ash, and/or $6\;wt.\;\%$ silica fume were prepared at a water/binder ratio of 0.45 and sand/binder ratios of 2.0, 2.5, 2.7, and 3.0. The increase in sand/binder ratio caused a decrease in the mortar flow. However, the sand/binder ratio did not affect the strength development. Drying shrinkage decreased with increasing the sand contents.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.05b
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• pp.513-516
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• 2006

Waste concrete powder(WCP) is a secondary by-product generated while processing waste concrete manufactured to coarse and fine aggregates for concrete. In order to assess the possibility of using WCP as admixture for self-compacting concrete, self-compactability, compressive strength and durability of self-compacting concrete containing waste concrete powder were investigated. Experimental results of this study appeared that in case of SCC mixed with WCP only, self-compactability and compressive strength decreased with increasing mixing ratio of WCP. When Blast-furnace slag(BFS) was added to SCC, self-compactability and compressive strength for a unit amount of cement increased. Also, SCC containing 15% BFS and 15%, 30% and 45% WCP, the dry shrinkage and carbonation depth appeared a tendency to decrease with increasing mixing ratio.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.05b
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• pp.81-84
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• 2006

Currently, natural aggregates of good quality are hard to use because of continuous decrease of internal aggregate resource and regulation of gathering. So, use of crushed sand was being increased. On the other hand, skyscraper projects with 100 stories are being planned within the country and high strength concrete must be used to construct a skyscraper with 100 stories. High strength concrete is necessary to use crushed sand too because we are still unable to secure natural aggregates of good quality. So, This study indicated basic data necessary for mix design of high strength concrete through valuation of concrete property by quality variation of crushed sand.

• International Journal of Concrete Structures and Materials
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• v.10 no.1
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• pp.29-37
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• 2016

The paper presents a research project on the tensile properties of RPC mixed with both steel and polypropylene fibers after exposure to $20-900^{\circ}C$. The direct and the indirect tensile strength (in bending) were measured through tensile experiment on dog-bone specimens and bending experiment on $40{\times}40{\times}160mm$ prisms. RPC microstructure was analyzed using scanning electron microscope. The results indicate that, steel fibers can significantly improve the tensile performance of hybrid fiber-reinforced RPC, whereas polypropylene fibers have no obvious effect on the tensile performance. With increasing temperature, the flexural and axial tensile strength of hybrid fiber-reinforced RPC substantially decrease linearly, which attributes to the deteriorating microstructure. Based on the experimental results, equations are established to express the decay of the flexural and tensile strength with increasing temperature.

• Proceedings of the Korea Concrete Institute Conference
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• 2000.10a
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• pp.641-646
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• 2000

This paper describes an experimental investigation on the influence of concrete cover thickness on tension stiffening behavior. Total 36 direct tension specimens were tested with variation of cover thickness. Three different concrete compressive strengths were also considered. After cracking, as the cover thickness becomes thinner and the concrete strength becomes higher, tensile stiffness is decreased. Thereby an increase in cover thickness results in increase of the tensile cracking load and tension stiffening effect. Also the increase in concrete strength results in sudden decrease in tension stiffening effect. Hence, the cover thickness and concrete strength are proved to be important factors in tension stiffening behavior.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.29 no.3 s.234
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• pp.425-431
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• 2005

The efficiency of complex slurry preparation route for developing the high performance SiC matrix of $RS-SiC_{f}/SiC$ composites has been investigated. The green bodies for RS-SiC materials prior to the infiltration of molten silicon were prepared with various C/SiC complex slurries, which associated with both the sizes of starting SiC particles and the blending conditions of starting SiC and C particles. The characterization of Rs-SiC materials was examined by means of SEM, EDS and three point bending test. Based on the mechanical property-microstructure correlation, the process optimization is also discussed. The flexural strength of Rs-SiC materials greatly depended on the content of residual Si. The decrease of starting SiC particle size in the C/SiC complex slurry was effective for improving the flexural strength of RS-SiC materials.

• Advanced Composite Materials
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• v.16 no.4
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• pp.385-394
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• 2007

In this study, the effect of molding condition on the tensile properties for plain woven hemp fiber reinforced green composite was examined. The tensile properties of the composite were compared with those of the plain woven jute fiber composite fabricated by the same process. Emulsion type biodegradable resin or polypropylene sheet was used as matrix. The composites were processed by the compression molding where the molding temperature and its heating time were changed from 160 to $190^{\circ}C$ and from 15 to 25 min, respectively. The following results were obtained from the experiment. The tensile property of hemp fiber reinforced polypropylene is improved in comparison with polypropylene bulk. The strength of composite is about 2.6 times that of the resin bulk specimen. Hemp fiber is more effective than jute fiber as reinforcement for green composite from the viewpoint of strength. The molding temperature and time are suitable below $180^{\circ}C$ and 20 min for hemp fiber reinforced green composite. Hemp fiber green composite has a tendency to decrease its tensile strength when fiber content is over 50 wt%.