• Journal of Korean Society of Steel Construction
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• v.20 no.1
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• pp.43-53
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• 2008

Because the torque control method, which is also caled the clamping method in domestic construction sites, is affected by a variation of the torque coefficient, quality control of the torque coefficient is essential. This study was focused to evaluate the effects of several environmental factors and errors when installing bolts while tightening high-strength bolts. Conditioning environmental parameters include wet, rusty and exposure-to-air-only conditions. In addition, because of errors in workability such as instalation of two washers, upset washers are selected. During the tests, torque, torque coefficient, tension and angle of nut rotation were obtained using a bolt testing machine. Test specimens of four types of bolts (High-Strength Hexagon bolt on KS B 1010, Torque Shear Bolt on KS B 2819, High-Strength Hexagon bolt coated with zinc, and ASTM 490 bolt) were recomended. Based on test results, the tightening characteristics subjected to environmental parameters were investigated and compared with the results in normal condition.

• Journal of The Korean Society of Agricultural Engineers
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• v.49 no.1
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• pp.45-54
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• 2007

This study was performed to evaluate strength and watertightness properties of EVA modified high strength concrete in order to improve durability of concrete used in agricultural water utilization facilities that are in constant contact with water. Materials used were cement, coarse and fine aggregates, silica fume, EVA and AE water reducing agent. Tests for the slump, compressive and flexural strengths, absorption ratio and permeability coefficient according to curing condition (water and water+dry curing) and content ratio of EVA were performed. The slump results of EVA modified high strength concrete similarly showed in the content ratio of EVA powder less than 4% and decreased in the content ratio of EVA powder more than 6% compared to that of concrete without EVA powder. The compressive strength of EVA modified high strength concrete decreased with increasing the content ratio of EVA powder. The flexural strength of EVA modified high strength concrete increased with increasing the content ratio of EVA powder in the content ratio of EVA powder ratio less than 4% and had similar or slightly decreased in the content ratio of EVA powder more than 6% compared to that of concrete without EVA powder. The absorption ratio and permeability coefficient of EVA modified high strength concrete decreased with increasing the content ratio of EVA powder in the content ratio of EVA powder less than 4% and slightly increased in the content ratio of EVA powder more than 6%.

• Proceedings of the KIEE Conference
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• 1999.07d
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• pp.1901-1903
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• 1999

To investigate invar alloy as a core material for increased capacity over-head transmission line which have high strength and low thermal expansion coefficient, hardness and thermal expansion coefficient of Fe-Ni-Co alloy have been studied. It is necessary that invar alloy have low thermal expansion coefficient and high strength for increased capacity over-head transmission line. In this paper. we tried to find out the effect of Ni and Co which has ferromagnetic properties and high saturation magnetization. It was found that Ni decrease thermal expansion coefficient and hardness, Co decrease thermal expansion coefficient but increase hardness in Fe-xNi-Co system. In Fe-(29-x)Ni-Co system, the material has no low thermal expansion properties substituting Co instead of Ni in concentration range of $1\sim7$%Co.

• Journal of Korean Society of Steel Construction
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• v.18 no.2
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• pp.181-189
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• 2006

This study analyzes the effects of the curvature friction coefficient, the wobble friction coefficient, and the increased strength of concrete, reinforced tendon on optimum de signs by using the optimum-design program, to minimize the cost of a PSC box girder bridge using the full staging method. The objective of this study is to find a proper tendon for the friction coefficient, and thereafter, to indicate the direction of the study development about tendons and to indicate the direction of a study on the increased strength of used materials. This program used the SUMT procedure and Kavlie's extended-penalty function to allow infeasible design points in the process. Powel's direct method was used in searching design points, and the gradient approximate method was used to reduce the design hours.

• Journal of the Korean Society for Nondestructive Testing
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• v.11 no.2
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• pp.22-31
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• 1991

Various types of ultrasonic techniques have been used for the estimation of compressive strength of concrete structures. However, conventional ultrasonic velocity method using only longitudial wave cannot be determined the compressive strength of concrete structures with accuracy. In this paper, by using the introduction of multiple parameter, e. g. velocity of shear wave, velocity of longitudinal wave, attenuation coefficient of shear wave, attenuation coefficient of longitudinal wave, combination condition, age and preservation method, multiple regression analysis method was applied to the determination of compressive strength of concrete structures. The experimental results show that velocity of shear wave can be estimated compressive strength of concrete with more accuracy compared with the velocity of longitudinal wave, accuracy of estimated error range of compressive strength of concrete structures can be enhanced within the range of ${\pm}$10% approximately.

• Steel and Composite Structures
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• v.2 no.4
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• pp.247-258
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• 2002

The high-temperature material properties of steel are very important to the fire resistance analysis of high-strength bolt connections. This paper reports on the results of the experimental studies on the high-temperature properties of 20 MnTiB steel which is widely used in high-strength bolts, and the friction coefficient of 16Mn steel plates at elevated temperature which is a necessary parameter for bolted frictional connection analysis. The test data includes yield strength, limit strength, modulus of elasticity, elongation and expansion coefficient of 20MnTiB steel at elevated temperature, and the friction coefficients between two 16Mn steel plates under elevated temperatures and after cooling. Based on the data from the tests, the mathematical models for predicting the mechanical properties of 20MnTiB steel and friction coefficients of 16Mn steel plates have been established.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.10 no.4
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• pp.38-43
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• 2011

Industrial reducer is in general use to Deck Crane. High-precision and high-efficient reducer is minimized the power-loss and energy-loss of a machine. So it contribute the price reduction and life extension. Reducer is usually using the Planetary gear reducer. Planetary gear reducer is composed the sun gear, planet gear, internal gear and casing. Industrial reducer's wear and breakage have a short-life. To solve this problem, it is using the profile-shifted-gear or tooth modification. This study was carried out the effect of addendum modification coefficient on tooth fillet bending strength to planetary reducer. Tooth fillet bending stress is calculate. And all parameter were expressed the function of addendum modification coefficient. And then stress concentration factor of tooth fillet curve was express the function of addendum modification coefficient using comparison between theory and finite element analysis.

• Geomechanics and Engineering
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• v.14 no.1
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• pp.29-42
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• 2018

This paper presents the results of an empirical study in which square rock-like blocks containing two parallel pre-existing rough non-persistent joints were subjected to uniaxial compression load. The main purpose of this study was to investigate uniaxial compressive strength and deformation modulus of jointed specimens. Response Surface Method (RSM) was utilized to design experiments and investigate the effect of four joint parameters, namely joint roughness coefficient (JRC), bridge length (L), bridge angle (${\gamma}$), and joint inclination (${\theta}$). The interaction of these parameters on the uniaxial compressive strength (UCS) and deformation modulus of the blocks was investigated as well. The results indicated that an increase in joint roughness coefficient, bridge length and bridge angle increased compressive strength and deformation modulus. Moreover, increasing joint inclination decreased the two mechanical properties. The concept of 'interlocking cracks' which are mixed mode (shear-tensile cracks) was introduced. This type of cracks can happen in higher level of JRC. Initiation and propagation of this type of cracks reduces mechanical properties of sample before reaching its peak strength. The results of the Response Surface Methodology showed that the mutual interaction of the joint parameters had a significant influence on the compressive strength and deformation modulus.

• Advances in concrete construction
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• v.5 no.4
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• pp.359-375
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• 2017

This paper presents a study of the properties and behavior of self-compacting concretes (SCC) in the hot climate. The effect of curing environment and the initial water curing period on the properties and behavior of SCC such as compressive strength, ultrasonic pulse velocity (UPV) and sorptivity of the SCC specimens were investigated. Three Water/Binder (W/B) ratios (0.32, 0.38 and 0.44) have been used to obtain three ranges of compressive strength. Five curing methods have been applied on the SCC by varying the duration and the conservation condition of SCC. The results obtained on the compressive strength show that the period of initial water curing of seven days followed by maturation in the hot climate is better in comparison with the four other curing methods. The coefficient of sorptivity is influenced by W/B ratio and the curing methods. It is also shown that the sorptivity coefficient of SCC specimens is very sensitive to the curing condition. The SCC specimens cured in water present a low coefficient of sorptivity regardless of the ratio W/B. Furthermore, the results show that there is a good correlation between ultrasonic pulse velocity and the compressive strength.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2009.05b
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• pp.73-76
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• 2009

Autogenous shrinkage of high-strength mass concrete is affected high temperature history. So to evaluate autogenous shrinkage of high-strength mass concrete accurately, thermal expansion in it should be removed. In this study, compensated autogenous shrinkage was calculated after gathering thermal expansion coefficient at early age experimentally. As a result of the study. Autogenous shrinkage of mass specimen (300 ${\times}$ 300 ${\times}$ 300mm) was remarkably higher than it of standard specimen (100 ${\times}$ 100 ${\times}$ 400mm). So it was found that compensation on thermal expansion should in evaluating autogenous shrinkage of high-strength mass concrete. And this study shows results on opc and similar own contraction, if used retarder.