• International Journal of Highway Engineering
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• v.13 no.1
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• pp.157-168
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• 2011

Recently, the cases of freeze-thaw distress on concrete pavement in domestic have been reported periodically. Hereupon, the necessity to establish the standard of spacing factor came to the fore. The test method for analyzing spacing factor is provided in the standard of ASTM C 457. Since researchers tend to judge study results subjectively, the results should be revised throughly. Image analysis program for determining the characteristics of air-void system on hardened concrete identify air void through the difference of a color. The pixel intensity values used in this program have a significant effect on the analysis results. This study compared the automated void count by varying pixel intensity values with the manual void count in order to determine the optimum range of pixel intensity values. Also, this study analyzed the air-void characteristics on eight kinds of concrete mixtures. In this study, it was confirmed that the variation of void counted manually was around 10% from the results of round robin test, and that the optimum range of pixel intensity values is around 80~90. And it was also confirmed that air content (as a whole) was increased generally and spacing factor was decreased by increasing air-entrainer content. But some concrete mixtures showed a tendency that air content was constant and spacing factor was decreased by increasing air-entrainer content. This causes the air entrained by air-entrainer has more influence on spacing factor than air content. Also, the deviation of spacing factor by cutting position of concrete specimen was about 30~100${\mu}m$ because of the limit of 2-D image analysis. The additional study about variation of spacing factor by cutting position of concrete specimen will be performed later.

• Journal of the Korea Concrete Institute
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• v.16 no.4 s.82
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• pp.493-500
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• 2004

FREP(Fiber Reinforced Epoxy Panel) are used for strengthening the damaged RC beams due to its good tensile strength, low weight, resistance to corrosion, and easy applicability. This study sets up structure equation for FREP bending reinforcement before and during the usage of RC beam. It finds the difference and finds the mechanical characteristics of rip-off failure that is caused by stress concentration in reinforcement material cutting part to estimate the performance of bending reinforcement. The result of this research can be summarized as two main consequences. The main failure of FREP reinforced concrete beam is rip-off failure and it evaluated rip-off failure of RC reinforcing bean based on the test and analytical conditions of this study. It found that stress was concentrated due to rapid change of bending rigidity in reinforced cutting part as a result of excessive reinforcement thickness of FREP. It resulted in rip-off failure. It means that it should evaluate the rip-off failure when designing reinforcement. It analyzed the reinforcement effect according to reinforced period for FREP. It found that reinforcement effect of P-Type that was reinforced during the usage decreased compared to I-Type that was reinforced before the usage. So when reinforcing a existing structure that is being used, it should consider the stress that is produced due to the fixed load.

• The Journal of Engineering Geology
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• v.26 no.1
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• pp.51-61
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• 2016

New building methods are needed to aid increased inner-city redevelopment and industrial construction. A particular area of improvement is the efficient use of cut slopes, with the minimization of associated problems. A retaining wall of precast panels can resist the horizontal earth pressure by increasing the shear strength of the ground and reinforcing it through contact with the panels. Precast panels allow quick construction and avoid the problem of concrete deterioration. Other problems to be solved include the digging of borrow pits, the disposal of material cut from the slope, and degradation of the landscape caused by the exposed concrete retaining wall.This study suggest the methods of improvement of an existing precast panel wall system by changing the appearance of the panels to that of natural rock and improving the process of adhering the panel to a vertical slope. The panels were tested in the laboratory and in the field. The laboratory test verified their specific strength and behavior, and the field test assessed the panels' ground adherence at a vertical cutting. Reinforcement of the cutting slope was also measured and compared with the results of 3D numerical analysis. The results of laboratory test, identified that the shear bar increase the punching resistance of panel. And as a results of test construction, identified the construct ability and field applicability of the panel wall system adhered to in-situ ground. In addition to that, extended measurement and numerical analysis, identified the long-term stability of panel wall system adhered to in-situ ground.

• Explosives and Blasting
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• v.31 no.1
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• pp.49-54
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• 2013

External charges with four different kinds of tamping materials are tested to determine the effect of tamping on the blasting of steel components and concrete blocks. The tamping materials used are tamping cap, urethane foam, sand bag and mud. As a result, the tamping cap, urethane foam, and sand bag show no significant effect of tamping. But the mud tamping shows that the charge amount can be reduced by more than 20% in completely cutting the structural components. In addition, it is found from the test that the standard equation for calculating the proper charge is rather conservative, which means the equation overestimates the necessary charge for the blasting.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.20 no.3
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• pp.247-253
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• 2007

Determination of crack depth in filed using the self-calibrating surface wane transmission measurement and the cutting frequency in the transmission function (TRF) is very difficult due to variations of the measurement conditions. In this study, it is proposed to use the measured full TRF as a feature for crack depth assessment. A Principal component analysis (PCA) is employed to generate a basis of the measured TRFs for various crack cases. The measured TRFs are represented by their projections onto the most significant principal components. Then artificial neural networks (NNs) using the PCA-compressed TRFs is applied to assess the crack in concrete. Experimental study is carried out for five different crack cases to investigate the effectiveness of the proposed method. Results reveal that the proposed method can be effectively used for the crack depth assessment of concrete structures.

• Earthquakes and Structures
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• v.26 no.1
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• pp.49-58
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• 2024

The purpose of this study was to develop a system capable of restoring the seismic performance of a precast concrete (PC) connection damaged by an earthquake. The developed PC connection consists of a top-and-seat angle, post-tensioning (PT) tendons, and U-shaped steel. The PC beam can be replaced by cutting the PT tendons in the event of damage. In addition, the seismic performance of the developed PC beam-column connection was evaluated experimentally. A PC beam-column connection specimen was fabricated, and a quasistatic cyclic loading test was conducted to a maximum drift ratio of 2.3%. Subsequently, the PC beam was replaced by a new PC beam, and the repaired PC connection was loaded to a maximum drift ratio of 5.1%. The structural performance of the repaired PC connection was then compared with that of the original PC connection. The difference in the load at the drift ratio of 2.3% between the original and the repaired PC specimens was only 0.2%. The residual drift ratio in the repaired PC specimen did not exceed 1.0% at the 2.0 % drift ratio cycles, which satisfies the life safety performance level specified in ACI 374.2R-13. When the developed PC connection system is used, structural performance can be restored by rapidly replacing the damaged elements.

• Proceedings of the Korean Radioactive Waste Society Conference
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• 2004.02a
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• pp.96-105
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• 2004

The decommissioning project of the KRR 1 & 2 was started in January 1997. The actual decommissioning activity was started at the RI production facility and was finished at the end of 2002. The dismantling works of all components including the reactor structure of the KRR-2 was started in January, 2003 and will be carried out for 2 years till the end of 2004. The project schedule is estimated to delay for 4∼5 months beyond the original plan because of delaying on the cutting of thermal column nose and removal of the graphite bricks, but it may be caught up during the removal working of concrete from biological shielding structure. This paper summarizes the general status of the KRR 1 & 2 and decommissioning activities.

• Journal of the Korean Society for Railway
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• v.9 no.2 s.33
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• pp.174-179
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• 2006

Recently, the crossing tunnel has been constructed frequently to connect the separated area by highway and railroad. The construction of crossing tunnel must be progressed while maintaining the existing traffic of the highway as well as railroad. There are many cross funnelling methods such as NTR, TRCM, Messer Shield, Front Jacking, and Pipe Roof Method. The advantages of adopting RPS(Roof Panel Shield) method in crossing tunnel construction with comparing other existing cross funnelling methods are needed a little volume of concrete and easy to change the direction of cutting shoe during the construction of pipe roof, The 3-dimensional numerical analysis of RPS to consider the arching effect was performed for the application in the crossing tunnel under railroad. The earth pressure distribution and settlement were predicted when the RPS method was applied during the excavation for crossing railroad tunnel construction.

• 제어로봇시스템학회:학술대회논문집
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• 1992.10a
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• pp.67-70
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• 1992

1930년 스웨덴에서 개발에 성공, 네덜란드에서 더욱 발전시킨 ALC(Autoclaved Light-weignt Concrete의 약칭) 는 가볍고, 견고하고, 그리고 시공이 간편한 경제적인 요건들을 충족시키는 건축자재로 세계적으로 널리 사용되고 있으며 , 국내에서는 불과 수년 전부터 연구 개발되고 있는 실정이다. ALC 란 시멘트와 규사, 생석회등 무기질 원료를 고온,고압으로 증기 양생시킨 경량의 기포 콘크리트 제품을 통칭한 것이다. ALC공정은 bulk ALC를 생산하는 batch공정과 이 bulk ALC에 대한 처리 공정으로 크게 나눌 수가 있으며 여기에서는 bulk ALC 처리 공정을 side shield treatment, anti-corrosion treatment, curing grate transferer, cutting station, curing car transportation, autoclave traveling platform, 및 packing 의 공정으로 세분하여 각 공정개요 소개 및 PLC(Programmable Logic Controller의 약칭)를 이용한 제어 system에 대하여 설명하고자 한다.

• Proceedings of the Korean Institute of Building Construction Conference
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• v.y2004m10
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• pp.39-44
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• 2004

A heat and room temperature construction method of asphalt have been mainly applying to rooftop waterproofing in concrete structure, and the rest construction method are sheet, membrane and mortar waterproofing construction method. In particular, joint method in sheet waterproof method is as overlap joint which on being reinforced with fiber and tape, have been applying for job site to mechanical fix using protection disk and anchorage and metal ironwork on the end of sheet. These construction method cause cutting off joint of sheet as behavior of structure according to repairs of sheet itself and thermal conduct, outdoor air environment. In conclusion, we analyzed and examined the application of various sheets and piece ashes about superior 'I' joint which divide from one and the other sheet and progressed about joint construction method of fixing method for overlap.