• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.2A
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• pp.187-196
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• 2008

The punching shear strength of RC slabs is estimated analytically by the simple truss model. To avoid intrinsic difficulties in punching shear analysis of reinforced concrete slabs, the slabs were divided into three sub-structures as the punching cone and the remaining parts. The strength of the punching cone was evaluated by the stiffness of inclined strut. The stiffness of springs which control lateral displacement of the roller supports consists of the steel reinforcement which passed through the punching cone. Initial angle of struts was determined by curve fitting method of the experimental data with variable reinforcement ratio in order to compensate for uncertainties in the slab's punching shear, the simplification errors and the stiffness of the remaining sub-structures. The validity of computed punching shear strength by simple truss model was shown by comparing with experimental results. The punching shear strength, which was determined by snap-through critical load of shallow truss, can be used effectively to examine punching shear strength of RC slabs.

• The korean journal of orthodontics
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• v.22 no.2 s.37
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• pp.327-343
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• 1992

Metal brackets and ceramic brackets were bonded to natural teeth, porcelain crowns and gold crowns After stored in artificial saliva solution for 72 hours at $37^{\circ}C$, the shear bond strengths were measured by Instron and compared with them, the bonding sites and bracket bases were examined by scanning electron microscope and light optical stereomicroscope. The results were as follows: 1. The shear bond strengths of the group which metal brackets were bonded to natural teeth and the groups which ceramic brackets were bonded to natural teeth and porcelain crowns were comparable to each other, the shear bond strength of the group which metal brackets were bonded to gold crowns was significantly low. 2. The bond failed predominantly at the bracket base/adhesive interface with the bulk of adhesive remaining on enamel in the group which metal brackets were bonded to natural teeth. 3. The bond failed consistently at the crown/adhesive interface with all of adhesive remaining on the bracket babes in the group which metal brackets were bonded to gold crowns. 4. The bond failed at the enamel or crown/adhesive interface with the bulk of adhesive remaining on the bracket bases in the groups which cramic brackets were bonded to natural teeth and porcelain crowns. 5. The shear bond strengths of the groups which ceramic brackets were bonded to porcelain crowns were not affected by etching time.

• Structural Engineering and Mechanics
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• v.36 no.1
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• pp.1-18
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• 2010

A total of 28 wall panels were cast and tested under uniformly distributed axial load in one-way in-plane action to study the effect of slenderness ratio (SR) and aspect ratio (AR) on the ultimate load. Two concrete formulations, normal concrete (NC) and self compacting concrete (SCC), were used for the casting of wall panels. Out of 28 wall panels, 12 were made of NC and the remaining 16 panels were of SCC. All the 12 NC panels and 12 out of 16 SCC panels were used to study the influence of SR and the remaining 4 SCC panels were tested to study the effect of AR on the ultimate load. A brief review of studies available in literature on the strength and behaviour of reinforced concrete (RC) wall panels is presented. Load-deformation response was recorded and analyzed. The ultimate load of SCC wall panels decreases non-linearly with the increase in SR and decreases linearly with increasing values of AR. Based on this study a method is proposed to predict the ultimate load of reinforced SCC wall panels. The modified method includes the effect of SR, AR and concrete strength.

• Steel and Composite Structures
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• v.12 no.5
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• pp.379-393
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• 2012

Many steel bridge infrastructures in the world are getting older, and a large number of these structures are in need of maintenance, rehabilitation or replacement. Most of them are subjected to corrosion due to exposure to aggressive environmental conditions and inadequate maintenance, causing reduction of their carrying capacities. In order to have an adequate bridge management, it is of paramount importance to develop an efficient, accurate and rapid condition assessment method which can be used to make reliable decisions affecting the cost and safety. Therefore, a simple and accurate method of calculating remaining yield and tensile strength by using a concept of representative effective thickness with correlation of initial thickness and maximum corroded depth is proposed in this study, based on the results of many tensile coupon tests of corroded plates obtained from a steel plate girder with severe corrosion, used for about 100 years. Furthermore, a strength reduction diagram which will be very useful for bridge inspection engineers to make rational decisions about the maintenance management of aged steel bridge infrastructures is presented.

• Journal of Power System Engineering
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• v.17 no.4
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• pp.103-108
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• 2013

This study was investigated the effect of austenitizing treatment the microstructure and mechanical properties in modified 440A steel, and the results were as follows. The amount of remaining carbide decreases with increasing the austenitizing treatment temperature, and all carbide is completely dissolved at $1250^{\circ}C$. The amount of remaining carbide decreases with increasing the austenitizing treatment time, but the carbide remains insoluble up to 120 minutes at $1050^{\circ}C$. The strength and hardness gradually decrease with increasing the austenitizing treatment temperature and is significantly lower at $1250^{\circ}C$, while the elongation and the impact value rapidly increase. The strength and hardness rapidly decrease, the elongation and impact value rapidly insrease with increasing the austenitizing treatment time and exhibit no change at above 120 minutes. The austenitizing treatment modified 440A steel is required for temperature of above $1050^{\circ}C$ and time of above 60 minutes.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.05b
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• pp.37-40
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• 2005

Recently, in order to reduce the spalling of high strength concrete under fire, the addition of organic fibres to high strength concrete has been investigated. In this study, the effect of thermal characteristic of organic fibres on the spalling of high strength concrete was experimantally investigated. Two types of fibre, polypropylene(PP) and polyvinyl alcohol(PVA) fibres, were selected, and the strength level of concrete was correnponding to the design strength of 80MPa. As a result, it appears that when the remaining ratios(by weight) of fibre at 300$^{circ}C$ and 350$^{circ}C$ are less than 80$\%$ and 50$\%$, respectively, the spalling of high strength concrete is prevented.

• Proceedings of the KSME Conference
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• 2000.11a
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• pp.193-198
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• 2000

The small punch test have been developed to evaluate the material strength of the power plant components. This small punch test specimen is very small than the conventional strength test specimens. Korea Electric Power Research Institute (KEPRI) have been applying this test to assess accurately the life of thermal power plant and enhancing the reliability. The small punch test for gas turbine blades is under development. It's possible to compare the relative strength among the same materials having different operation histories. In this paper, the strength reductions of gas turbine materials are investigated by the small punch tests. All materials shows the almost same strength and deformation with the allowable deviation. At the same test temperature, the damaged material has the maximum load value. The strength reduction is not shown in this small punch test results.

• Proceedings of the Korea Concrete Institute Conference
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• 2002.10a
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• pp.155-160
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• 2002

This study is performed to analyze of reinforced concrete beams under fire and to calculate remaining strength. The analysis is based on the assumption that plane section remains plane after bending due to load and non-linear temperature increases. Finite difference method is used to find temperature field in a section. The residual strength is attained considering the effect of temperature rise on the mechanical properties of concrete, self-equilibrium stress and reduced section. Further research in much needed on the material models of concrete since it governs temperature distribution and theoretical results.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.05b
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• pp.17-20
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• 2006

Recently, in order to reduce the spalling of high strength concrete under fire, the addition of organic fibres to high strength concrete has been investigated. In this study, the effect of fiber length and specimen size on the spalling and temperature distribution in high strength concrete specimen was experimentally investigated. Three HSC specimens measuring $305{\times}305mm$, $500{\times}500mm$ and $700{\times}700mm$ with the fiber were prepared. The fiber length was 6mm and 10mm. As a result, it appears that when the remaining ratios(by weight) of fibre at $300^{\circ}C$ and $350^{\circ}C$ are less than 80% and 50%, respectively, the spalling of high strength concrete is prevented.

• Journal of the Korean Society for Heat Treatment
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• v.26 no.3
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• pp.120-125
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• 2013

In this study, the effect of tempering treatment on the mechanical properties in modified 440A steel has been investigated. The amount of remaining carbide decreased with increasing the austenitizing treatment temperature, and all carbides were completely dissolved at $1250^{\circ}C$. The amount of remaining carbide decreased with increasing the time of austenitizing, but the carbide remained insoluble up to 120 minutes at $1050^{\circ}C$. With increasing the tempering temperature, tensile strength decreased, and elongation increased slowly, while hardness rapidly decreased, and impact value unchanged and then rapidly increased over $500^{\circ}C$. The strength and hardness slowly decreased, while the elongation and impact absorbed energy increased with increasing the tempering time. $Cr_{23}C_6$ type carbide was precipitated and sharp decrease of elongation and toughness by tempering did not appear.