• Proceedings of the Korean Institute of Building Construction Conference
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• 2011.05a
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• pp.73-75
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• 2011

In this study, prediction of later-age compressive strength of ultra-high strength concrete, based on the accelerated strength of concrete cured in 50, 60℃ warm water was investigated. W/B of 32, 23.5, 19% 3 levels were examined. And the specimens were cured in 50, 60℃ warm water. The results showed reliable accuracy by regression relation between 28day strength cured by standard curing method and accelerated strength of the concrete cured in warm water. And the specimens cured in 50, 60℃ showed more high strength development. So 60℃ curing could be considered in order to reduce the measurement error. As a result, the feasibility of 50, 60℃ warm water curing method at high strength level was confirmed.

• Magazine of the Korea Concrete Institute
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• v.8 no.5
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• pp.156-162
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• 1996

The purpose of this study is to find experimentally bond properties of deformed bars in high strength concwtc. Bond properties of deformed bars in high strength concrete are tested i n tensile stress state. Eighty beam-end specimens are used for this experiment. Concrete compressive strength is used as main experimental variable, in addition a few variables affecting bond properties are used : bond length, cover thickness and bar diameter. The principal results obtained from this study are as follows ; - Bond strength is not proportionate to bond length in high strength concrete. The rate of bond strength increase followed by bond length rapidly diminish according to concrete strength increase. The reason is analyzed in FEM analysis that bond stress is not uniformly distributed in high strength concrete and concentrate on loading area. - Bond strength is linearly proportionate to cover thickness without regard to concrete strength. Especially the rate of strength increase is gradually increased by concrete strength.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.05a
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• pp.443-448
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• 2001

This paper presents a bond characteristics of high strength steel reinforced concrete members. High strength steel is what yield strength is higher than that of normal strength steel. So, the amount of flexural steel needed in R.C. members can be decreased. In result, it is expected that the workability and structure quality can improve and man power can minimize. For this purpose, specimens were made and tested with experimental parameters, such as concrete strength, steel diameter and yield strength. The result showed that under same tensile force of steel, in case of substituting normal strength steel with high strength steel, maximum bond stress increased and development length didn't almost change. In addition, the governing equation of bond and bond stress verse slip relationship were derived and compared with test values such as maximum bond stress, slip and bond stiffness.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.05b
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• pp.609-612
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• 2006

The quality of the concrete compression strength can be determined after the passage of 28 days, but if any defect is found the quality of concrete after that length of time, there can be serious problems in dismantling and repair. Thus, in response to the use of concrete using non sintering cement (NSC), the present study purposed to propose a method of managing the strength of high strength concrete using NSC in comparison with high strength concrete using ordinary Portland cement (OPC) through early strength estimation using microwave, which enables the quick estimation of the strength of high strength concrete using NSC.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.10a
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• pp.307-310
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• 2009

Nowadays, the usage of high strength steel has been growing in automobile industry mainly as structural parts since for its lightweight and high strength properties the oil crisis happened. Owing to poor formability, complex-shaped high-strength steel components are invariably produced through hot press forming. The high-strength steel sheets are in so me instances used with an Al-Si-coating with a view to prevent scaling of components during hot press forming. How ever, friction and fracture characteristics of Al-Si-coated high-strength steel during hot press forming process have not yet been investigated. In this paper, the formed parts which were formed in hot bending process were investigated by using EDS. SEM and nano indenter in order to analysis the coating layer behavior.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2015.11a
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• pp.162-163
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• 2015

Thermal deformation behavior of high-strength concrete (HSC) exposed to fire is different from that of normal strength concrete (NSC). In case of ultra-high-strength concrete (UHSC), it is well known that thermal deformation behavior is greater than HSC. With increasing research of UHSC in buildings, it is necessary to understand the performance of UHSC at elevated temperatures considering loading condition. Therefore, evaluation on properties of thermal strain behavior properties of ultra high strength concrete by loading and high temperature was conducted.

• 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.

• Proceedings of the Korea Concrete Institute Conference
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• 2009.05a
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• pp.249-250
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• 2009

Recently, the interest on self-compacting concrete (SCC) without any mechanical vibration is increasing as the demand for high-strength and high surface quality of precast element increased. In this work, precast beam element with 7m length was manufactured using high-strength SCC with design strength of 60MPa, resulting in high-strength and high surface quality was obtained from the precast beam cast by high-strength SCC.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2007.10a
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• pp.300-301
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• 2007

In this study, it is investigated that sheet characteristics of high strength steel sheets and effect of springback. High strength steel sheets has got attention in automobile industry of high strength and high formability. Springback is a common phenomenon in sheet metal forming, caused by the elastic recovery of the internal stresses after removal of the tooling. However, the information in deformation behavior of high strength steel sheets, including bending and sheet characteristics and springback, is not enough until now. In this research, the V-bending experiment and analysis have been done to obtain the information of springback of high strength steel sheets. Tensile test for high strength steel sheets was done to got tensile properties of elastic modulus and flow stress of the material. It analyzed springback according to the sheet characteristics with using roll-forming model. FE-Simulation used DEFORM-$3D^{TM}$.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2015.05a
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• pp.73-74
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• 2015

As this study is one related to ultra high strength concrete using crushed coarse limestone aggregates among the series of experiments for improving the economic inefficiency of the ultra high strength concretes used for high rise structures, it has analyzed the flowability of ultra high strength concrete according to the variation of blended fine aggregates. As a result of analyzing the characteristics of fresh concrete, it is determined that the application of ultra high strength concrete would be difficult in case of a mix using blended fine aggregates as lower flowability than the mix using limestone crushed fine aggregate only was shown in all mixes using blended fine aggregates.