• Journal of the Korean GEO-environmental Society
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• v.14 no.1
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• pp.33-42
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• 2013

In this paper, a series of monotonic undrained shear tests were carried out on four kinds of sand-fine mixtures with various fines content. Two kinds of sands (Silica sand V3, V6) and fines (Iwakuni natural clay, Tottori silt) were mixed together in various proportions, while paying attention to the void ratio expressed in terms of sand structure $(F_c{\leq}F_{cth})$. The undrained shear strength of mixtures below the threshold fines content was observed so that as the plastic fines content increases, maximum deviator stress ratio decrease for dense samples while an increase is noted for loose samples. For non-plastic fines, the increase in the amount of fines leads to an increase in density of the soil, which results in an increase in strength. Then, the monotonic shear strength of the mixtures was estimated using the concept of granular void ratio. It was found that the shear strength of mixtures is greatly dependent on the skeleton structure of sand particles.

• Macromolecular Research
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• v.12 no.5
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• pp.540-543
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• 2004

Surface treatment using an excimer pulse laser beam has been conducted in order to increase the adhesive strength of vulcanized rubber. The adhesive strength increased with increasing the number of irradiation time with laser pulses and reached to 1,500 N/m after 100 cycles of irradiation. Increased in energy density was directly proportional to the improvement of the adhesive strength. Maximum value of the adhesive strength of 1,500 N/m obtained at the energy density of 176 mJ/$\textrm{cm}^2$. We conclude that an increased energy density improves in both the surface area and adhesive strength.

• Journal of Welding and Joining
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• v.18 no.6
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• pp.83-88
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• 2000

Variation of welded-joint hardness and tensile strength of a accelerated-cooled fine-grained ferritic-pearlitic steel with heat input was investigated. In a weld heat-affected zone, a softened zone was formed and it had lower hardness than that of a base metal. While the width of a softened zone increased continuously with an increase of heat input up to 100kJ/cm. the minimum hardness in a softned zone was almost constant after a continuos decrease up to 60KJ/cm. Because of a softened zone, the welded-joint was fractured in the HAZ and its maximum reduction of tensile strength was about 20%. Measured welded-joint tensile strength and calculated minimum tensile strength in a welded-joint was almost same, which means that the plastic restraint of a softened zone did not occur in this experiment. It is believed that as a softened zone width-to-specimen thickness ratio is as high as 2~6 in this experiment, the plastic restraint effect does not occur. Theoretical analysis shows that the plastic restraint effect occurs only when the ratio is below 0.5.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.05a
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• pp.259-262
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• 2005

Numerous studies showed that safety and serviceability of many concrete infrastructures and buildings built in 1970's have capacity less than their design capacities and thereby require immediate retrofitting. Currently, these aged concrete structure are being repaired using many repair and strengthening methods developed in the past. Therefore, in this study, a repairing and strengthening method for retrofitting high strength concrete columns that can effectively improve the performance of high strength concrete columns is developed. The square high strength concrete column's cross-sectional shape is modified to octagonal shape by attaching precast members on the surface of the column. Then, the octagonal column surface is wrapped using Carbon Fiber Sheets (CFS). The method allowed the maximum usage of confinement effect of externally wrapped CFS, which resulted in improved strength and ductility of repaired high strength concrete columns.

• Proceedings of the Korean Geotechical Society Conference
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• 2009.09a
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• pp.511-518
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• 2009

In this study, by the consideration of in situ curing conditions, cemented sand with cement ratio less than 20% is prepared by air dry condition and then wetted. A series of unconfined compression tests are carried out to evaluate the effect of wetting on the strength of cemented soils. Strength of air dry cured specimen drops to maximum 30% after wetting at the end of curing period when cement ratio is low. However, regardless of cement ratio, strength of repetitively wetted specimens during curing increases as the number of wetting increases. The results of this study can predict the strength variation of cemented sand depending on wetting conditions in the field, which can guarantee the safety of geotechnical structures such as dam.

• Journal of the Earthquake Engineering Society of Korea
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• v.20 no.6
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• pp.361-368
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• 2016

Coupling beams serve as primary source of energy dissipation in coupled shear wall systems during large earthquakes. However, the overestimation of the shear strength of diagonally reinforced coupling beams may be adverse effect on the seismic performance of coupled shear wall systems. In order to force coupling beams to properly work during earthquakes, coupling beams should be designed with accurate shear strength equations. The objective of this study is to propose the accurate shear strength equation for slender diagonally reinforced coupling beams. For this purpose, experimental tests were conducted using three diagonally reinforced coupling specimens with different amount of transverse reinforcement under reversed cyclic loads to evaluate the hysteretic behavior of the specimens. The test results show that transverse reinforcement of slender diagonally reinforced coupling beam affects the maximum strength and drift ratio.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2002.04a
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• pp.61-68
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• 2002

Tubular members have been applied in a wide range of frame structures including offshore structures. For the efficient load flow in tubular-member structures, the joints of tubular members are usually reinforced using internal ring stiffener for the steel tubular joint having a large diameter. The objective of this paper is to numerically assess the behavior of X-joints with an internal ring stiffener, and to evaluate the reinforcement effect of a ring stiffener, and to establish the strength formulae. Nonlinear finite element analysis is used to compute the static strength of axially loaded tubular joints. From the numerical results, internal ring stiffener is found to be efficient in improving static strength of tubular X-joints. Maximum strength ratios are calculated as 1.5~3.5, and the effective dimensions of ring stiffener are found. Regression analyses are performed considering practical size of ring stiffener and strength estimation formulae are proposed.

• Steel and Composite Structures
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• v.14 no.5
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• pp.473-491
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• 2013

The primary objectives of this paper are to describe the buckling patterns and to determine the squash load of steel plate-concrete (SC) walls. The major variables in this study were the width-thickness (B/t) ratio and yield strength of surface steel plates. Six SC walls were tested, and the results include the maximum strength, buckling pattern of steel plates, strength of headed studs, and behavior of headed studs. Based on the test results, the effects of the B/t ratio on the compressive strength are also discussed. The paper also presents recommended effective length coefficients and discusses the effects of varying the yield strength of the steel plate, and the effects of headed studs on the performance of SC structures based on the test results and analysis.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.10
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• pp.2165-2171
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• 2002

Poly-butylene-terephalate(PBT) can be impact-modified by blending with ABS material. The effects of compatibilizers and ABS content on the mechanical properties of PBT/ABS blend were examined in this study. EPDM-g-GMA and polycarbonate(PC) were used as a compatibilizer. As the GMA content in EPDM-g-GMA increased, the tensile strength of PBT/ABS blend increased and the impact strength decreased. With increasing the EPDM-g-GMA content in PBT/ABS blend, the tensile strength and impact strength decreased. With PC compatibilizer, the particle size of ABS in PBT/ABS blend became smaller than that of the blend without compatibilizer and the particles were more evenly dispersed in matrix. The maximum impact strength of the PBT/ABS blend was observed in the range of 20~30% ABS content.

• Journal of Surface Science and Engineering
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• v.36 no.6
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• pp.475-479
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• 2003

In this study, to investigate the effects of 2-step shot peening at the surface of spring steel, tests are conducted on spring steel and shot peened specimens. Various tests are accomplished to evaluate mechanical properties influenced by shot peening process, and fatigue tests are also performed to evaluate the improvement of fatigue strength. And then the residual stresses are examined. The mechanical properties of material did not change so much by shot peening. However, the fatigue strength of notched specimen remarkably increased. In the case of 1-step shot peening, fatigue strength increased by about 20％ than unpeened specimen. Especially, in the case of 2-step shot peening, fatigue strength increased by about 40％, because the residual compressive stress at surface was higher than that of 1-step shot peened specimen. The fatigue strength and life are closely related to the value and position of maximum compressive residual stress by shot peening.