• Journal of Welding and Joining
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• 제28권5호
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• pp.51-57
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• 2010

Brittle microstructure created in a heat affected zone (HAZ) during the welding of low alloy steel can be eliminated by post-weld heat treatment (PWHT). If the PWHT is not possible during a repair welding, the controlled bead depositions of multi-pass welding should be applied to obtain tempering effect on the HAZ without PWHT. In order to anticipate and control the tempering effect during the temper bead welding, the definition of temperature curve obtained from the analytical solution was suggested in this research. Because the analytical solution for heat flow is expressed as a mathematical equation of weld parameters, it may be effective in anticipating the effect of each weld parameter on the tempering in HAZ during the successive bead depositions. The reheating effect by the successive bead layer on the brittle coarse grained HAZ formed by earlier bead deposition was estimated by comparing the overlapped distance between the temperature curves in the HAZ. Three layered weld specimens of SA508 base metal with A52 filler were prepared by controlling heat input ratio between layers. The tempering effect anticipated by using the overlapped distance between the temperature curves was verified by measuring the micro-hardness distribution in the HAZ of prepared specimens. The temperature curve obtained from analytical solution was expected as a good tool to find optimal temper bead welding conditions.

• 기술사
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• 제16권3호
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• pp.5-23
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• 1983

On the Seoul Metropolitan Subway Construction of No. 3, 4 Line, the total length is 57 Km and it is now undergoing almost 55％ progress. The working method is classified into Open Cut of 70% and the rest of 30% tunnelling method in the 48 job site. Above tunnelling method is execute by American Steel Support System and the rest of 10 job site carried out by New Austria Tunnelling Method. This paper describes Blasting Standardizations works on the above Tunnelling ' Open Cut Method under big slogan, first safety, second execution. As a superintendent, I strived standardization of works with Better powder, Better Drills ' Better Pattern. Geological structure of Seoul area is composed by Jurassic Granite and also the above rockgroup are over burden by Alluviums as a Unconformity. First of all, I carried out the standard amount of powder and burden through experimental standard blasting by each powder as following Blasting works in the subway construction is surrounding shop Building, under pass the city river and also under pass highest building basement floor. I made allowable Blasting Vibration Value by West-Germany Vornorm DIN 4150, Teil 3 and should measure each blasting works as fellows all of powder is used basically Low-Gravity and Low Velocity such as Slurry, Ammonium Nitrate ' Finex I, II. for Smooth Blasting Instead of Gelatin Dynamite. Electric Detonation Cap is used basically M/S Delay Cup instead of Electric delay ' Simultaneous cap. I applied following formula V=KW3/4 $D^{-2}$ V=Particle Velocity (Cm/sec) K=Ginh Huh's Value W=Delay Charge (Kg) D=Distance(m) In the Open Cut, within 1m distance from H-pile I made to use the Concrete breaker, as following V=7W/$^{0.5}$V/$^{-1.75}$ On the Concentrate Building area, I advise to use Light class drill ø36m Bit and advance 1.1m per round blasting the three boom jumbo drill over ø45mm used only suburb of city.e Light class drill ø36m Bit and advance 1.1m per round blasting the three boom jumbo drill over ø45mm used only suburb of city.

• 한국지반환경공학회 논문집
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• 제11권2호
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• pp.43-52
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• 2010

쉴드공법은 막장을 굴착함과 동시에 원통형 강재를 지반속에 추진시켜 터널을 축조하는 공법이다. 1818년 마크 브루넬이 런던의 템즈강 하저 굴착공사에 처음 사용한 이래 지반조건에 따른 다양한 쉴드 TBM이 개발되어 도로, 지하철, 전력구, 상하수도 등에 널리 활용되고 있다. 막장상태를 수시로 관찰하며 지반변화에 빠르게 대처할 수 있는 NATM 공법과 달리, 쉴드 공법은 굴진이 시작되면 장비 교체가 거의 불가능하다. 따라서 지반조사 및 실내시험 결과에 따라 적절한 장비를 설계하고, 막장상태에 따라 압입깊이, 커터헤드 회전속도 등을 효율적으로 관리하여 장비의 성능을 최대한 활용하여 굴착공사를 수행해야 한다. 본 연구에서는 분당선 한강하저터널의 지반조건을 NTNU, $Q_{TBM}$, 합경도, KICT-SNU 등의 모델에 적용하여 굴진성능을 예측하고, 실시공 굴진자료와 비교 분석하여 예측모델의 적용성을 검토하였으며, 한강하저터널 하행선의 굴진성능 저하원인을 분석하였다.

• 대한건축학회논문집:구조계
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• 제33권12호
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• pp.37-44
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• 2017

Due to structural characteristics, construction costs and duration of a modular system would be saved by minimizing the schedule on the job site. As such, it is crucial to develop a connection that can guarantee stiffness while allowing for simple assembling. Particularly, the mid- to high-rise construction of the modular system necessitates the securing of the structural stability and seismic performance of multi-unit frames and connections, and thus, the stiffness of unit-assembled structures needs to be re-evaluated and designed. However, evaluating a frame consisting of slender members and reinforcing materials is a complicated process. Therefore, the present study aims to examine the structural characteristics of a modular unit connection based a method for reinforcing connection brackets and hinges while minimizing the loss of the cross section. Toward this end, the study modeled the beam-to-column connection of a modular system with the proposed connection, and produced a specimen which was used to perform a cycling loading test. The study compared the initial stiffness, the attributes of the hysteretic behavior, and the maximum flexural moment, and observed whether the model acquired the seismic performance, compared to the flexural strength of the steel moment frame connection that is required by the Korean Building Code. The test results showed that the proposed connection produced a similar initial stiffness value to that of the theoretical equation, and its maximum strength exceeded the theoretical strength. Furthermore, the model with a larger ceiling bracket showed higher seismic performance, which was further increased by the reinforcement of the plate.

• 한국건설순환자원학회논문집
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• 제10권4호
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• pp.523-530
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• 2022

해수의 흐름이 존재하는 방조제 제체 보강공사 시 가장 큰 문제는 재료의 유출로, 콘크리트의 중력식 타설은 원활히 공극을 채우기 어렵고 굳지 않은 콘크리트의 시멘트는 해수에 분산될 확률이 높기 때문에 경화 후 품질의 신뢰성이 저하될 뿐만 아니라, 인근 환경에 악역향을 끼칠 수 있다. 이에 주입이 가능한 겔형태의 주입재가 필요하다, 본 연구에서는 급결성을 띠는 전기로환원슬래그 및 고로슬래그를 활용하여 초기 강도와 해수 침지에 따른 내구성 향상 효과를 평가하였다, 실험 결과 실리카계 약액과의 반응을 통해 흐름성을 갖는 겔형태의 주입재 제조가 가능하였으며 겔의 흐름성은 배합에 따라 105~143 mm 수준으로 현장모사 시험을 통해 외부 유출 없이 공극을 채울 수 있어 현장 적용성을 확인하였다.

• 한국건축시공학회지
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• 제23권2호
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• pp.113-121
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• 2023

본 연구에서는 부산물(석분 슬러지, 고로슬래그, 제강슬래그, 폐콘크리트 슬러지, 바텀애시) 5종과 클링커 내 중금속 분석을 위한 레이져 유도 플라즈마 분광법(LIBS) 적용성과 재현성 검토를 실험적으로 수행하였다. 클링커를 포함한 6종의 부산물 시료에 대한 ICP-MS, XRF, LIBS 분석 결과, 정량적 분석에서 ICP와 XRF의 차이가 확인되었으나, LIBS 분석은 표준분석과 일치하지 않고 시료의 정성적인 분석만 가능하였다. LIBS를 통한 정량적 분석을 위하여 Cd, Pb, Hg에 대하여 LIBS 분석 파장(Cd - 214.44nm, Pb - 405.78nm, Hg - 253.65nm)을 설정하였고, 농도별(1~1000ppm) 용액에 함침하여 건조시킨 멤브레인 표면에 레이져를 조사한 결과, 스펙트럼 강도와 농도 사이의 상관관계를 확인할 수 있었다.

• Advances in concrete construction
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• 제2권1호
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• pp.1-11
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• 2014

This paper demonstrates an experimental study to evaluate the effects of environmental exposures on the bond between ribbed Glass Fiber Reinforced Polymer (GFRP) reinforcing bars and concrete. The equation recommended by ACI 440-1R-06, for the bond stress,was evaluated in this study. A total of 16 pullout samples, 12with GFRP bars and 4with steel bars, were exposed to two different harsh environments for different periods of time. The exposed harsh environments included direct sun exposure and cyclic splash zone sea water. The variation in the shear (bond) strengths before and after exposure was considered as a measure of the durability of the bond between GFRP bars and concrete.Experimental results showed there is no significant difference of the bond strength between 60 and 90 days of exposures.It also showed that the empirical equation of the bond stress calculated by ACI 440-IR-06 is very conservative.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 1999년도 봄 학술발표회 논문집
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• pp.209-216
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• 1999

Prefabricated piles used for construction of highway bridges are most of steel pipe piles and few of prestressed concrete piles. Its installation and inspection are less controllable and have much uncertainty due to changes in subsoil and groundwater conditions. However, most of these piles have been controlled using outdated pile driving formula such as Hiley's formula which models just the energy conservation due to its simple applicability in the field. This formula results in overstriking or sometimes understocking due to buckling of pile head. Engineers cannot ensure by the formula whether pile is installed properly. To compensate the drawbacks of excising pile formula, parameters in Hiley's formula and 55 formula are reviewed. Final sets used in pile formula and PDA test results(E.O.I.D) are measured during pile driving along the depth. These measured results along the depth were compared with each other and with N values, so that relations between the each result could be inferred. Also the factor of safety which can be used for pile driving formula are suggested.

• Advances in concrete construction
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• 제10권1호
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• pp.21-34
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• 2020

Precast deck joints have larger crack width than cast-in-place concrete decks. The initial crack typically occurs at the maximum moment but cracks on precast joints are significant and lead to failure of the deck. The present crack equation is applied to cast-in-place decks, and requires correction to calculate the crack width of precast deck joints. This research aims to study the crack width correction equation of precast decks by performing static tests using high strength and normal strength concrete. Based on experimental results, the bending strength of the structural connections of the current precast deck is satisfied. However it is not suitable to calculate and control the crack width of precast loop connections using the current design equation. A crack width calculation equation is proposed for crack control of precast deck loop joints. Also included in this paper are recommendations to improve the crack control of loop connections.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1999년도 학회창립 10주년 기념 1999년도 가을 학술발표회 논문집
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• pp.693-696
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• 1999

Reinforced concrete is, in general, known as high durability construction material under normal environments due to strong alkalinity of cement. It is , however, well known that moderate or minor cracks in reinforced concrete should be most serious causes to deteriorate the durability of RC structures. Furthermore, chloride contents penetrating through unexpected cracks in reinforced concrete bridges get to weaken corrosion resistance of reinforcement steel in concrete and than to accelerate the deterioration of concrete durability. The objective of this experimental research is 1) to evaluate the effect of various corrosion protection system for reinforced concrete specimens with moderate or minor cracks which are exposed to cyclic wet and dry seawater, and then 2) to develop effective corrosion protection system for reinforced concrete bridges under the exposure of various detrimental environments such as seawater, deicing and etc.