• Computers and Concrete
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• v.22 no.3
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• pp.279-289
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• 2018

Shear walls are one of the important structural elements for bearing loads imposed on buildings due to winds and earthquakes. Composite shear walls with high lateral resistance, and high energy dissipation capacity are considered as a lateral load system in such buildings. In this paper, a composite shear wall consisting of steel faceplates, infill concrete and tie bars which tied steel faceplates together, and concrete filled steel tubular (CFST) as boundary columns, was modeled numerically. Test results were compared with the existing experimental results in order to validate the proposed numerical model. Then, the effects of some parameters on the behavior of the composite shear wall were studied; so, the diameter and spacing of tie bars, thickness and compressive strength of infill concrete, thickness of steel faceplates, and the effect of strengthening the bottom region of the wall were considered. The seismic behavior of the modeled composite shear wall was evaluated in terms of stiffness, ductility, lateral strength, and energy dissipation capacity. The results of the study showed that the diameter of tie bars had a trivial effect on the performance of the composite shear wall, but increasing the tie bars spacing decreased ductility. Studying the effect of infill concrete thickness, concrete compressive strength, and thickness of steel faceplates also showed that the main role of infill concrete was to prevent buckling of steel faceplates. Also, by strengthening the bottom region of the wall, as long as the strengthened part did not provide a support performance for the upper part, the behavior of the composite shear wall was improved; otherwise, ductility of the wall could be reduced severely.

• International Journal of Highway Engineering
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• v.20 no.2
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• pp.9-17
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• 2018

PURPOSES : The frequency and severity of natural disasters such as torrential rain or typhoons have become increasingly significant worldwide. Events such as summer typhoons and localized torrential downpour can cause severe damages to a residential area and road networks, resulting in serious harm to the daily lives of people, especially in rural areas by isolating residents from road networks. An immediate and emergency repair technology for the collapsed road networks is urgently needed. This study introduces a new technology to repair road bases or slopes. METHODS : The development of new technology for emergency and permanent repair consists of first, packing of cement paste-coated gravel, second, combining appropriate equipment, and third, conducting a field applicability test. In this research, the compressive strength of cement pastecoated gravel, gravel-netting concrete properties, and packing efficiency were determined, and a full scale field mock-up test was carried out. RESULTS : The compressive strength of the cement paste-coated gravel concrete satisfied the required limit for road base of 5 MPa after 7 days. With appropriate netting materials and packing size, gravel-netting concrete was successful up to a slope of 1:1.5. The full scale field mock-up test showed efficiency in the field and penetration resistance performance. CONCLUSIONS : The new technology of emergency and permanent repair for damaged road bases and slopes, introduced in this study, showed satisfactory performance. The technology is expected to be applied in the field when construction procedures and quality specifications are made.

• Journal of the Korea Concrete Institute
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• v.28 no.2
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• pp.223-234
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• 2016

In this study, direct tension test for hybrid steel fiber reinforced ultra-high performance concrete (UHPC) containing two different steel fibers with a length of 16 and 19 mm was performed to investigate the fracture behavior of UHPC. Test results showed that crack strength and tensile strength, and fracture energy increased with increasing the fiber volume ratio. Based on the test results, the peak cohesive stress at the crack tip, tensile strength, and fracture energy depending on the fiber volume ratio were proposed. The proposed tensile strength of UHPC was suggested as a function of the fiber volume ratio and compressive strength. The peak cohesive stress at the crack tip and fracture energy were also proposed as a function of the tensile strength. The predicted values were relatively agree well with the test results. Thus, the proposed equations is expected to be applicable to UHPC with a compressive strength of 140~170 MPa and a fiber volume ratio of less than 2%.

• KIEAE Journal
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• v.13 no.4
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• pp.103-112
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• 2013

The Federal Democratic Republic of Nepal(Nepal) is one of the poorest country in the world. People in Nepal are having lots of housing problems including the lack of housing provision. Even Habitat for Humanity Nepal (HfH_Nepal) has developed various programs to diffuse ecological housing, still there are many problems due to financial and technological shortage. The purpose of this study is to verify the effects of suggestion of performance improvement for HfH_Nepal eco house with introduction of the housing situation and efforts to provide sustainable housing by HfH_Nepal in Terai plain. Ideas on CGI sheet roof with poor insulation, double panel bamboo wall and adobe brick wall which can overcome structural and waterproof flaws of the thin single panel bamboo wall. The experiment result shows that both ideas adapted to adobe brick house reduces daily temperature range 50.8% and humidity adjust effect. For the effective provision of adobe brick house, compressive strength was tested for the bricks made with locally available fiber materials. Brick with jute displayed 41.1% betterment than plain brick with closest packing condition while coconut and straw showed 25.1% and 7.9% improvement respectively. Technical and economic problems brought up during the building and experiment process were listed and countermeasures established. This kinds of building prototype houses and experiments can improve the living conditions of people in developing countries with little supplement of resources. Furthermore, consideration of locally available and affordable material can help the social and ecological sustainability in the world.

• Journal of the Korea Concrete Institute
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• v.28 no.3
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• pp.357-363
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• 2016

To solve the exhaustion problem of natural aggregate which were create the high value in construction and environmental industry, recycled aggregates have considerable benefits than other materials. However, even though many researches have been conducted with recycled aggregates, building structures with recycled aggregated are rarely constructed because it has lower quality than natural aggregates have. In this study, mechanical and strain properties of recycled aggregates concrete containing steel fibers have been reviewed in order to complement performance of recycled aggregates concrete. As results, recycled aggregates concrete showed lower compressive strength and elastic modulus than plain concrete. But, recycled aggregates concrete containing steel fibers showed equivalent performance with plain concrete. In review of drying shrinkage and creep coefficient, recycled aggregates concrete containing steel fibers showed similar behavior with plain concrete in the range of 0.5 Vol.% fiber content rate by internal restraint effect, moisture transport restraint effect and strength enhancement effect of steel fiber. Therefore, it is considered that mixing steel fibers with concrete is the effective method as a active application plan for recycled aggregates.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2005.11a
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• pp.169-172
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• 2005

A flywheel system is an electromechanical energy storage device that stores energy by rotating a rotor. The rotating part, supported by magnetic bearings, consists of the metallic shaft, composite rims of fiber-reinforced materials, and a hub that connects the rotor to the shaft. The delamination in the fiber wound composite rotor often lowered the performance of the flywheel energy storage system. In this work, an advanced hybrid composite rotor with a split hub was designed to both overcome the delamination problem in composite rim and prevent separation between composite rim and metallic shaft within all range of rotational speed. It was analyzed using a three-dimensional finite clement method. In order to demonstrate the predominant perfom1ance of the hybrid composite rotor with a split hub, a high spin test was performed up to 40,000 rpm. Four radial strains and another four circumferential strains were measured using a wireless telemetry system. These measured strains were in excellent agreement with the FE analysis. Most importantly, the radial strains were reduced using the hybrid composite rotor with a split hub, and all of them were compressive. As a conclusion, a compressive pressure on the inner surface of the proposed flywheel rotor was achieved, and it can lower the radial stresses within the composite rotor, enhancing the performance of the flywheel rotor.

• Journal of the Korea Institute of Building Construction
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• v.9 no.6
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• pp.175-181
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• 2009

In this research, experiments were conducted to find out whether polycarboxylate could be used as a crude steel admixture for practical work, depending on the change in the replacement level of the compound mixed into polycarboxylate. Its fluidity was satisfactory, its airspace was a bit smaller than the KS standard, and its unit volume weight was proven to meet the standard. The amount of bleeding was smallest in B2, and in terms of the solidification time, the first and the last solidification was faster in A1, B1, and C1. With regard to the compressive strength in early days as acharacteristic of hardened concrete, all addition rates of 7-day C2 displayed the highest strength value, among which the addition rate of 1.3% had the biggest strength performance tendency. The seal strength also showed the strength performance rate which was about one tenth as big as that of the compressive strength. The length change rate resulting from dryness and contraction was proven to be good, and once the appropriate AE air entraining agent is used, it is evaluated to be a very useful and practical compound out in the field.

• Journal of the Korean Recycled Construction Resources Institute
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• v.2 no.1
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• pp.10-18
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• 2014

This study carried out to evaluate the hydration heat analysis and fundamental characteristics such as air content, slump, compressive strength and dry shrinkage according to concrete with premixed cement, ternary concrete and OPC concrete for using concrete with premixed cement. The results of experiment are founded that concrete with premixed cement have sufficient performances such as workability, compressive strength and dry shrinkage. Also, the results of hydration heat analysis are founded that concrete with premixed cement have more performance than ternary concrete and OPC concrete at a point of view for the quality control such as thermal crack reducing and economic benefit. Therefore, it is desirable that concrete with premixed cement should be used to rise durability performance and convenience of maintenance.

• Journal of the Korean Recycled Construction Resources Institute
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• v.1 no.1
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• pp.26-34
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• 2013

Durability performance in RC structures varies significantly with changes in cover depth and mix proportions. GGBFS (Ground Granulated Blast Furnace Slag) is very effective mineral admixture and widely used for an improved resistance to chloride attack. In this paper, characteristics such as porosity, compressive strength, and diffusion coefficient are evaluated in GGBFS concrete with 30~70% of replacement ratio and $4,000{\sim}8,000cm^2/g$ of fineness. Through the tests, more dense pore structure, higher compressive strength, and lower diffusion coefficient are obtained in GGBFS concrete, which are evaluated to be more dependent on replacement ratio than fineness. With increasing curing period from 3 to 91 days, porosity decreases to 77.47% and strength increases to 373% in GGBFS concrete. Chloride diffusion coefficient in GGBFS concrete decreases to 64.4% compared with that in OPC concrete, which shows significant improvement of durability performance.

• Composites Research
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• v.25 no.4
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• pp.110-116
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• 2012

Recently, the development and field applications of Ternary Blended Cement(TBC), where blast furnace slag and fly ash are recycled in Ordinary Portland Cement(OPC) in order to obtain improvements in the durability and heat of hydration reduction performance in large scale civil structures, have been increasing. Also, there are continuing efforts by construction companies to reduce the construction time with the aim of reducing construction costs. Therefore, there is a need to improve the performance of TBC, which has a relatively slow early strength development. In order to improve the early strength of TBC mortar, the compressive strength, SO3 content, and SEM analysis was determined in this study on mortar with the fineness and content of blast furnace slag and anhydrite regulated. As a result, to secure the early strength of TBC mortar, using blast furnace slag with a fineness of approximately $4,200cm^2/g$, adding 3.5% anhydrite with a fineness of approximately $10,000cm^2/g$, and managing the $SO_3$ content to roughly 3.72% was found to provide the most outstanding early strength properties.