• Journal of the Korea institute for structural maintenance and inspection
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• v.16 no.1
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• pp.78-88
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• 2012

Although structural concrete is well known for its good economic efficiency, it has limits of structural performance due to the low tensile strength, for which new structural members utilizing various concrete composite materials have been developed. Steel Fiber-Reinforced Concrete(SFRC) has great tensile strength, which is the one of the excellent composite material to complement the weakness of concrete, and it is also considered as a good alternative to prevent the explosive failure of high strength concrete under fire. Also, prestressed concrete members are of great advantages to long span structures and have greater shear strength compared to conventional reinforced concrete members. In this research, thus, a total of 22 direct shear test specimens were fabricated and tested to understand the shear behavior of Steel Fiber-Reinforced Prestressed Concrete(SFR-PSC) members, in which SFRC members combined with prestressing method. Based on the test results, the constitutive equations of shear behavior at crack interfaces were proposed, which provided good estimation on the shear behavior of the SFR-PSC direct shear test specimens.

• Journal of the Korea Concrete Institute
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• v.27 no.4
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• pp.399-409
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• 2015

Recently, the use of composite construction method using precast (PC) and cast-in-place (CIP) concrete is increased in modular construction. For PC members, pre-tensioning is used to improve efficiency of the structural performance. However, current design codes do not clearly define shear strength of prestressed PC-CIP composite members. In this study, 22 specimens were tested to evaluate shear strength of prestressed composite members with vertical shear reinforcement. The test variables were the area ratio of high-strength (60 MPa) to low-strength concrete (24 MPa), prestressing force of strands, shear span-to-depth ratio(a/d), and vertical shear reinforcement ratio. The test results showed the prestressing force did not completely restrain diagonal cracking of non-prestressed concrete in the web. Thus, the effect of prestress force was not insignificant in the effect for monolithic beams. The vertical shear strength and horizontal shear strength of the composite beams were compared with the strength predictions of KCI design method.

• Proceedings of the Korea Concrete Institute Conference
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• 1995.10a
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• pp.246-251
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• 1995

To reduce the size of structural members high strength concrete has recently been utilized for structrue such as ultra-high-rise buildings and prestressed concrete bridges in North America. and its compressive strength has gone up to 1300kgf/$\textrm{cm}^2$. In Japan, research on high-strength concrete has been undertaken on a large scale by the national enterprise so-called New RC Project, and this project purposed to develop the design compressive sstength of 1200kgf/$\textrm{cm}^2$. Considering these circumstance. the aim of this aim of this experimental study is to develop ultra-high-strength concrete with compressive stength over 2300kgf/$\textrm{cm}^2$ with domestic current materials. There are so many factors which influence on manufacturing of ultrahigh-strength concrete. The experimental factors selected in this study are mixing methods, curing methods, water-binder ratio, maximum size of coarse aggregate, and the replacement proportion of cement by silica fume. The results of this expermental study show that it is possible to develop the ultra-high-strength concrete with compressive strength over 2300kgf/$\textrm{cm}^2$.

• International Journal of Concrete Structures and Materials
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• v.10 no.3
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• pp.257-269
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• 2016

Early-strength-concrete (ESC) made of Type I cement with a high Blaine value of $500m^2/kg$ reaches approximately 60 % of its compressive strength in 1 day at ambient temperature. Based on the 210 compressive test results, a generalized rateconstant material model was presented to predict the development of compressive strengths of ESC at different equivalent ages (9, 12, 18, 24, 36, 100 and 168 h) and maximum temperatures (20, 30, 40, 50 and $60^{\circ}C$) for design compressive strengths of 30, 40 and 50 MPa. The developed material model was used to find optimum curing regimes for precast prestressed members with ESC. The results indicated that depending on design compressive strength, conservatively 25-40 % savings could be realized for a total curing duration of 18 h with the maximum temperature of $60^{\circ}C$, compared with those observed in a typical curing regime for concrete with Type I cement.

• Proceedings of the Korea Concrete Institute Conference
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• 2010.05a
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• pp.23-24
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• 2010

In this research, the comparison and analysis of domestic prestressed concrete bridges were performed with major variations of superstructure type, and span lengths using the 'current status of roadbridge and tunnel' informations provided by MLTM and STATISTICS KOREA. As a result of analysis, steel box girder bridges with 50~100m span length represent about 76% of bridges, but prestressed concrete bridges represent a relatively smaller percentage. In order to replace steel box girder bridges with prestressed concrete bridges, it is necessary to develop prestressed concrete bridges with high-strength tendons and concrete.

• Computers and Concrete
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• v.22 no.1
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• pp.71-81
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• 2018

Introduction of prestressed concrete slabs based on post-tensioned (PT) method aids in constructing larger spans, more useful floor height, and reduces the total weight of the building. In the present paper, for the first time, simulation of 32 two-way PT slab-edge column connections is performed and verified by some existing experimental results which show good consistency. Finite element method is used to assess the performance of bonded and unbonded slab-column connections and the impact of different parameters on these connections. Parameters such as strand bonding conditions, presence or absence of a shear cap in the area of slab-column connection and the changes of concrete compressive strength are implied in the modeling. The results indicate that the addition of a shear cap increases the flexural capacity, further increases the shear strength and converts the failure mode of connections from shear rigidity to flexural ductility. Besides, the reduction of concrete compressive strength decreases the flexural capacity, further reduces the shear strength of connections and converts the failure mode of connections from flexural ductility to shear rigidity. Comparing the effect of high concrete compressive strengths versus the addition of a shear cap, shows that the latter increases the shear capacity more significantly.

• Proceedings of the Korea Concrete Institute Conference
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• 1994.10a
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• pp.171-174
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• 1994

To reduce the size of structural members, high strength concrete has recently been utilized for structure such as ultra-high-rise buildings and prestressed concrete bridges in North America, and its compressive strength has gone up to 1300kg/$\textrm{cm}^2$. In Japan, research on high-strength concrete has been undertaken on a large scale by the national enterprise so-called New RC Project. And high-strength concrete with a design compressive strength over 450kg/$\textrm{cm}^2$ has recently been employed for high rised reinforced concrete building. As a result of the serious land availability situation of metropolitan areas in the world, buildings will become taller, and even higher strengths will be required. In the future, the utilization of high-strength concrete will spread widely through the development of new structural concepts, application of steels of a higher yield stress, silica fume, and other new materials. Considering these circumstance, the aim of this experimental study is to develop ultra-high-strength concrete with compressive strength over 1800kg/$\textrm{cm}^2$ with domestic current materials. There are so many factors which influence the manufacturing of ultra-high-strength concrete. The experimental factors selected in this study are mixing methods, curing methods, water-binder ratio, maximum size of coarse by silica fume. The results of this experimental study show that it is possible to develop the ultra-high-strength concrete with compressive strength over 1700kg/$\textrm{cm}^2$ at 28days, 1800kg/$\textrm{cm}^2$ at 56 days.

• Journal of the Korea Concrete Institute
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• v.17 no.6 s.90
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• pp.963-974
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• 2005

This paper presented four shear test results from experimental tests of two large prestressed concrete beams cast with high strength concrete. In particular, this experiment investigated the effects of draped strands on shear behavior of these full-scaled beams. This study indicated that the use of draped strands increased the ultimate shear capacity as well as the web-shear cracking load. The test results also showed that draped strands reduced strand slip at ends of beams, which represented that these strands were effective to relieve the anchorage stresses. The test results were compared to predictions by two major codes; ACI 318-02 Building Code and AASHTO LRFD(2002). The shear design provisions in these codes provided conservative results on the shear strengths of all test specimens with reasonable margins of safety, and these provisions were particularly more conservative for test specimens having draped strands.

• Journal of the Korean Society of Hazard Mitigation
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• v.8 no.2
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• pp.51-58
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• 2008

This study is to investigate the ultimate shear load of prestressed girder made of Ultra High Performance Fiber Reinforced Concrete (UHPFRC). Nine girders were tested until failure in shear. An analytical model to predict the ultimate shear load was formulated based on the Two Bounds Theory. A fiber reinforcing model was constituted based on the random assumption of steel fiber uniform distribution. The predicted values were compared with the conventional predictions and the test results. The proposed equations for computing the ultimate shear strength can be used for the ultimate failure status analysis, which could also be utilized for numerical limit analysis of prestressed UHPFRC girder. The established fiber reinforcing theoretical model can also be a reference for micro-mechanics analysis of UHPFRC.

• Proceedings of the Korea Concrete Institute Conference
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• 1994.10a
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• pp.167-170
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• 1994

To reduce the size of structural members, high strength concrete has recently been utilized for structure such as ultra-high-rise buildings and prestressed concrete bridges in North America, and its compressive strength has gone up to 1300kg/$\textrm{cm}^2$. In Japan, research on high-strength concrete has been undertaken on a large scale by the national enterprise so-called New RC Project. And high-strength concrete with a design compressive strength over 450kg/$\textrm{cm}^2$ has recently been employed for high rised reinforced concrete building. As a result of the serious land availability situation of metropolitan areas in the world, buildings will become taller, and even higher strengths will be required. In the future, the utilization of high-strength concrete will spread widely through the development of new structural concepts, application of steels of a higher yield stress, silica fume, and other new materials. Considering these circumstance, the aim of this experimental study is to develop ultra-high-strength concrete with compressive strength over 1800kg/$\textrm{cm}^2$ with domestic current materials. There are so many factors which influence the manufacturing of ultra-high-strength concrete. The experimental factors selected in this study are mixing methods, curing methods, water-binder ratio, maximum size of coarse by silica fume. The results of this experimental study show that it is possible to develop the ultra-high-strength concrete with compressive strength over 1700kg/$\textrm{cm}^2$ at 28days, 1800kg/$\textrm{cm}^2$ at 56 days.