• Tunnel and Underground Space
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• v.13 no.5
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• pp.362-372
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• 2003

Since the occurrence of Portland cement, a great number of concrete structures were constructed. But the concrete structures have their own life times, which inevitably demand repairing treatments, especially on their surface parts. Currently many various methods have been developed and are being applied fer this purpose. In this study, a newly developed method using pneumatic chipping machine and anchor pin was adopted far repair of old concrete structure and the mechanical characteristics of cementing plane between existing and new concrete were tested. Comparing the removal methods for the decrepit part of existing concrete using pneumatic chipping machine and hydraulic breaker, the peak cohesion was higher when using chipping machine at the cementing plane. On the other hand, the residual cohesion was higher for the case of breaker. Step shaped chipping on the cementing plane was effective in increasing peak cohesion, which results 14% increase in the case of 30 mm step height and 22% in 50 mm height when compared with planar chipping plane. The use of anchor pin increased the residual cohesion, which restricted shear slip on the cementing plane after peak shear stress and the tensile strength of 32% compared with that of non-anchored case. According to the combined effect of step shaped chipping of 30 mm and anchor pin with an interval of 15 cm, the peak cohesion reached up to 77% and the residual cohesion showed 180% of the ones of the fresh concrete, respectively.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.32 no.4D
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• pp.377-386
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• 2012

Crack sealing has been widely used in the pavement maintenance due to its advantage of repairing the cracks at the preliminary stages. However, it has been analyzed that the crack sealing work process is dangerous and labor intensive. Moreover, quality and productivity of crack sealing work are highly depended on labor experience and skills. Therefore, various crack sealing machines have been researched but revealed many limitations in practical application. This research analyses conventional crack sealing work process and previously developed crack sealing machines in order to develop an automated pavement crack sealing machine which can be practically and widely applied in the construction fields. This paper develops the previously proposed conceptual design by drawing detailed designs and fabricating the hardware(manipulator and end-effector) of the automated pavement crack sealing machine. The crack sealing machine suggested in this paper overcomes limitations of existing crack sealing machines and designed to meet the domestic road conditions and regulations. It is expected that automating the conventional crack sealing method contributes to the improvement of quality, economy and reduce accidents.

• Journal of the Korea institute for structural maintenance and inspection
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• v.19 no.2
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• pp.170-178
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• 2015

In this study, it was developed eco-friendly alkali-activated slag fiber reinforced concrete using ground granulated blast furnace slag, alkali activator (water glass, sodium hydroxides), and steel fiber. Eight reinforced concrete beam using alkali-activated slag concrete were constructed and tested under monotonic loading. The major variables were mixture ratio of alkali activator, mixed/without of steel fiber. Experimental programs were carried out to improve and evaluate the flexural performance of such test specimens, such as the load-displacement, the failure mode, the maximum load carrying capacity, and ductility capacity. All the specimens were modeled in scale-down size. The reinforced concrete beams using the eco-friendly alkali-activated slag fiber reinforced concrete was failed by the flexure or flexure-shear in general. In addition, the maximum strength increased with the adding the mol of sodium hydroxide, and the specimen reinforced the steel fiber showed the value of maximum strength which is increased by 15.8% through 25.9%. It is thought that eco-friendly alkali-activated slag fiber reinforced concrete can be used with construction material and product to replace normal concrete. If there is applied to structures such as precast concrete member and production of 2nd concrete product, it could be improved the productivity and reduction of construction duration etc.

• Journal of the Korea Concrete Institute
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• v.18 no.2 s.92
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• pp.257-266
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• 2006

Flat-plate building systems are utilized extensively for construction of apartments, hotels and office buildings because of short construction period, low floor-to-floor height and flexibility in plan design. Recently, to increase lateral seismic resistance of flat-plate building systems, wall-columns are used frequently. Therefore, to estimate strength of flat-plate column connection accurately, the effect of column section shape on the behavior of flat-plate column connection should be considered properly, In the present study, a numerical analysis was performed for interior connections of continuous flat-plate to analyze the effect of column section shape. For the purpose, a computer program for nonlinear FE analysis was developed, and the validity was verified. Through the parametric study, the variations of shear stress distribution around the connection were investigated. According to the result of numerical analysis, as the length of the cross section of column in the direction of lateral load increases, the effective area and the maximum shear strength providing the torsional resistance decrease considerably. Therefore, these effects should be considered properly to estimate the strength of flat-plate connection accurately.

• Journal of Korean Society of Transportation
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• v.22 no.5
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• pp.75-87
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• 2004

Along the seashore regions in Korea, though strong winds with very large strength are frequently witnessed, no system which can provide appropriate speed information for driving vehicle has been introduced. The driving against strong winds could be very dangerous because of the high possibility of accidents such as rollover and collision. These accidents usually resulted from driver's forced driving try even in difficult situation for steering vehicle, and sometimes overspeed without consideration of wind impact to the vehicles. To reduce accident caused by strong winds, it is important to inform drivers of appropriate driving speeds by perceiving strong winds. By setting up WIS at the main points where strong winds frequently appear and using the variable message sign(VMS) connected to the on-line whether information system, it tis possible to provide desired speed information, which can maintain vehicles' tractive force and maximum running resistance. The case study is conducted on the case of Mokpo-Big-Bridge, which is under construction at Mokpo city. The result show that in case the annual average direction of wind is South and the wind speed is over 8m/hr, the desired speed, which is required in order for vehicles running to South direction to maintain the marginal driving power, is 60km/hr. In addition, for the case of a typhoon such as Memi generated in 2003 year, if wind speed had been 18m/sec in Mokpo city at that time, the running resistance at the speed of 40km/hr is calculated as 1131N. This resistance can not be overcome at the 4th gear(1054N) level, therefore, the gear of vehicles should be reduced down to the 3rd level. In this case, the appropriate speed is 40km/h, and at this point the biggest difference between running resistance and tractive force is generated.

• Proceedings of the Korea Water Resources Association Conference
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• 2006.05a
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• pp.254-258
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• 2006

경제발전 과정에서 급격한 도시화로 인해 건기의 하천 수량은 줄어들고, 비점오염 발생량은 증가하였으며 심지어 하천이 복개되고 직강화되어 홍수 피해 및 수질오염은 더욱 증가하고 있다. 다행히 최근 소득수준의 증가와 여가시간이 확대됨에 따라, 그 동안의 도시화와 산업화로 인한 오염된 하천을 다시 복원하려는 운동이 활발하게 진행되고 있다. 안양천은 이 같은 하천 중 가장 대표적인 하천 중 하나이다. 본 연구에서는 다속성선택법(CE: choice experiments)을 적용하여 안양천이 어떠한 속성을 갖고 있으며 각각의 속성에 대해 안양천 유역주민들의 사회적인 경험과 인식, 그리고 각 속성의 수준간의 상쇄관계(trade-off)를 고려함으로써 소비자선호에 근거한 한계가치(marginal value)를 추정하였다. 2차례에 걸친 예비조사를 통해 안양천이 가진속성을 홍수피해위험, 가뭄시 하천유량, 수질등급, 하천형태로 설정하였고 설문지 작성을 위해 개별 속성들간의 직교성(orthogonality)을 보장해 주는 주효과 직교설계(orthogonal main effects design) 방법을 이용하였다. 작성된 설문지를 이용해 안양천 유역 10개 지자체 거주민을 대상으로 설문조사를 실시하였고 설문조사 결과를 통해 추정된 각 속성에 대한 가구당 매월 한계지불의사액은 하류구간의 잠재적 홍수피해(PFD가 0.5)가 보통일 경우는 1,764.8원/월, 낮을(PFD가 0.5이하) 경우는 1,783.8원/월, 가뭄시 하천수가 목표유지유량보다 는 작지만 매말라 있지 않은 경우에는 1,496.8원/월, 가뭄시 하천수가 목표유지유량 이상 유지될 경우에는 2,274.9원/월, 수질 등급 3등급일 경우 1,721.5원/월, 수질 등급 2등급일 경우 1,764.4원/월, 하천둔치를 체육공원과 산책로를 조성할 경우 2,078.1원/월, 하천둔치를 자연친화형 하천으로 보존할 경우 2,441.7원/월으로 분석되었다. 또한 추정된 가구당 매월 한계지불의사액을 통해 각 지자체별 정책대안의 기대효과에 대한 편익을 추정하였다. 각 기대효과는 치수, 수량확보, 수질, 생태로서 각각의 기대효과에 대해 가장 높은 편익을 나타내는 것은 부천시의 하수처리장 건설로서 이는 매년 926.8억원의 편익이 발생되며 그 다음으로는 부천의 하수관거정비(역곡)로서 이는 매년 601.5억원의 편익이 발생하는 것으로 추정되었다.

• The Journal of Engineering Geology
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• v.21 no.3
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• pp.239-246
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• 2011

Upon encountering weathering soil at a construction site, it may be necessary to change the design and construction plans for geotechnical structures. When weathering soil is exposed to air, the weathering process proceeds rapidly, resulting in significant damage to geotechnical structures, particle defects, and an increase in moisture sensitivity. The management of weathering-soil compaction is challenging. Because the engineering properties of weathering-soils vary regionally, it is important to report the result of research into the regional characteristics of such soils. At two locations of granite gneiss in the Gansung area of Gangwon-do, geological studies were performed at 22 and 8 sites, respectively. At each site, test samples were collected for analysis by XRD and to measure particle size, consistency, and compaction. To evaluate the suitability of the material for road subgrade, we examined the interrelationship between CBR value and the uniformity coefficient, the 200 sieve passing ratio and the aggregate ${\geq}$ 2 mm) content. We found that for the weathered granite soil, aggregate sized > 2 mm has a significant effect on the CBR value. In addition, the mixing of aggregate sized > 2 mm with sub-quality soil improves the soil condition.

• Journal of the Korea Concrete Institute
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• v.17 no.5 s.89
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• pp.769-774
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• 2005

Fluosilicic acid(H2SiF6) is recovered as an aqueous solution which absorbs $SiF_4$ produced from the manufacturing of industrial-graded H3PO4 or HF. Generally, fluosilicates are the salts produced by the reaction of H2SiF6 and metal salts. Addition of fluosilicates to cement endows odd properties through unique chemical reaction with the fresh and hardened cement. This study was performed to know mechanical properties and watertightness using fluosilicates based composite made from fluosilicates and other compounds. Mix proportions for experiments were modulated at 0.45 of water to cement ratio and $0.0-2.0\%$ of adding ratio of fluosilicates based composite. Evaluation for mechanical properties of concrete was conducted to know fresh state of concrete, hardening state of concrete, and watertightness. Evaluation for watertightness of concrete was carried out permeability, absorption test and porosity analysis. In addition. Scanning Electron Microscopy(SEM) and Energy Dispersive X-Ray(EDX) used for investigating micro-structure and atomic component distributed in hardened concrete. It is ascertained that characteristics of mechanical properties and watertightness was more improved than non-added because of packing role of fluosilicates based composite and pozzolanic reaction of soluble $SiO_2$. Also, concrete added fluosilicates based composite had a tendency to delay setting time and only $0.5\%$ addition of fluosilicates based composite delayed 150 minutes compared with non-added.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.11
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• pp.870-877
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• 2020

A suction bucket foundation, especially useful at depths of more than 20m, is a method of construction. The method first places an empty upturned bucket at the target site. Then, the bucket is installed by sucking water or air into it to create negative pressure. For stability, it is crucial to secure the verticality of the bucket. However, inclination by the bucket may occur due to sea-bottom conditions. In general, a repeated intrusion-pulling method is used for securing verticality. However, it takes a long time to complete the job. In this paper, we propose a real-time suction bucket verticality monitoring system. Specifically, the system consists of a sensor unit that collects raw verticality data, a controller that processes the data and wirelessly transmits the information, and a display unit that shows verticality information of a circular steel pipe. The system is implemented using an inclination sensor and an embedded controller. Experimental results show that the proposed system can efficiently measure roll/pitch information with a 0.028% margin of error. Furthermore, we show that the system properly operates in a suction bucket-based model experiment.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.7
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• pp.38-45
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• 2020

A magnetically levitating capsule train, which runs inside the sub-vacuum tube, can reach ultra-fast speeds by dramatically reducing the aerodynamic drag and friction. The capsule train uses the superconductor electrodynamic suspension (SC-EDS) method for levitation. The SC-EDS method has advantages, such as a large levitation gap and free of gap control, which could reduce the infra-construction cost. On the other hand, disadvantages, such as the large variation of the levitation-guidance gap and small damping characteristics in levitation-guidance force, could degrade the running stability and ride comfort of the capsule train. In this study, a dynamic analytical model of a capsule train based on the SC-EDS was developed to analyze the running dynamic characteristics. First, as important factors in the capsule train dynamics, the levitation and guidance stiffness in the SC-EDS system were derived, which depend non-linearly on the velocity and gap variation. A 3D dynamic analysis model for capsule trains was developed based on the derived stiffness. Through the developed model, the effects of the different running speeds on the ride comfort were analyzed. The effects of a disturbance from infrastructure, such as the curve radius, tube sag, and connection joint difference, on the running stability of the capsule train, were also analyzed.