직접인장 모드에 의한 신·구콘크리트의 부착강도 특성 분석

이봉학,홍창우,김동호,김성환 강원대학교 부설 석재복합신소재 제품연구센터 2002 석재연 논문집 Vol.7 No.-

본 연구에서는 부착 특성평가를 위하여 코어깊이, 덧씌우기 두께, 기존 콘크리트와 덧씌우기 재료의 탄성계수비, Steel Disk의 두께를 변화하여 유한요소해석을 실시하였다. 이때 부착면에 발생한 응력의 특성을 비교하여 응력집중계수를 산출하여 최적의 직접인장시험 기준을 마련하고자 하였다. 제안된 실험 방법의 검증을 위하여 보통콘크리트와 초속경 라텍스 개질 콘크리트를 사용하여 실내실험을 실시하였다. 이 두 재료의 부착강도특성을 분석하기 위해서 보통콘크리트와 라텍스 개질 콘크리트로 구성된 복합콘크리트 슬래브를 제작하여 직접인발실험(Pull-out test)을 실시하였다. 주요 실험변수로써 코어직경, 코어깊이, 부착면의 수분상태에 따른 초속경 라텍스 개질 콘크리트의 부착강도 특성을 분석하였다. Significant improvements in the bond strength between new and existing concretes can be achieved through the modification of the new concrete by latex modification. But, no test method has been adopted as a standard to measure the bond strength between the concretes used to repair and the substrate being repaired. The performance of old and the new concretes construction depends upon bond strength between old and the new concretes. Current adhesive strength measurement method ignores the effect of stress concentration by shape of specimens. Therefore, this research calculated stress concentration coefficient using finite element analysis and direction tensile strength test (pull-off test). The result showed that the minimum required core depth was 2.5㎝. Elastic modulus and overlay thickness did not affect to stress concentration.

초속경 라텍스개질 콘크리트의 균열 억제방안

이봉학,최판길 江原大學校 産業技術硏究所 2008 産業技術硏究 Vol.28 No.A

An increase in the amount of cracking in repaired concrete bridge decks using VES-LMC(Very Early Strength - Latex Modified Concrete ; below VES-LMC) has been noticed by Yun et a1(1). Literature indicates that indeed many concrete bridge decks develop transverse cracking, most developing at early ages(3~7 days), many right after construction. The purpose of this study was to establish prevention of map, transverse and longitudinal cracking in VES-LMC and to provide a control methods for minimizing the occurrence of cracks. The proposed prevention against map and transverse cracking was verified by field ayplications. VES cement was modified, the unit cement contents was reduced into 360kg/m^(3) from 390kg/m^(3), the maximum size of coarse aggregate was increase into 19mm from 13mm, wire mesh and steel fibers were incorporated in concrete mixture. A series of variable combinations were attempted. As a results, the proposed prevention against map and transverse cracking was verified because no crack were occurred until 90 days after overlay.

축하중과 첨가질량이 작용하는 적층복합판의 진동해석

이봉학,김경진,원치문,성기태 江原大學校 産業技術硏究所 1995 産業技術硏究 Vol.15 No.-

A method of calculating the natural frequency corresponding to the first mode of vibration of beams and tower structures, with irregular cross-sections and with arbitrary boundary conditions was developed and reported by D. H. Kim in 1974. IN this paper, hte result of application of this method to the laminated plates with axial forces and with attached point mass/masses is presented. Both N? and N? forces are considered. The solution for the laminated plates with arbitrary boundary conditions and irregular section can be obtained by simply obtaining the deflection influence coefficients by any method. The effect of neglecting the mass of the plates on the natural frequency, as the ratio of the point mass/masses to the plate mass increases, is thoroughly studied. The influence of N? and N? is also carefully investigated.

산업폐기물인 제강 슬래그쇄석을 이용한 콘크리트의 강도특성

이봉학,김태경 江原大學校 産業技術硏究所 1996 産業技術硏究 Vol.16 No.-

An experimental study os performed to examine the feasibility of using wastes steel furnace slagh construction mtaterials and its utility as a replacement for teh natural resources to prevent the economic loss was investigated. A half factorial exprements was performed with the variables of W/C ratio, S/A, Coarse aggrigate /Slag ratio and slump as apreliminary study for optimum mix design of concrete strength. The substitute of waste Slag up to 100% has little influence, saying that it can substitute the coarse asggregate without damaging th econcrete properties.

스팬방향으로의 吹出이 날개의 空力特性에 미치는 影響

李奉俊,金學奉 한국항공대학교 1982 論文集 Vol.20 No.-

유체의 흐름속에 놓인 날개의 상하면에는 壓力差가 생기고 자유흐름과 結合하여 날개Rmx 주위에는 trailing vortex라는 나선형 흐름이 생긴다. 이 날개끝 (과)流를 抑制하여 誘導抗力을 減少시키는 장치에는 여러가지가 있다. 實驗에 依하면 날개끝 次出이 날개의 揚ㆍ抗特性向上에 效果가 있음이 發見되었다. 本 論文에서는 이러한 次出인 境遇에 對하여 새로운 조건을 주고 V.L.M(Vortex Lattice Method)을 利用하여 날개의 揚ㆍ抗係數에 對한 數値解를 구하였다. 數値解와 잘 一致하는 傾向을 보였다. A wing moving through afluid induces a differential pressure field between the upper and lower surfaces. The resultant spanwise movement of fluid cmobined with the free stream velocity generates a helical movement of fluid about the wingtip called trailing vortex. A number of devices have been employed in an attempt to reduce the induced drag by controlling the trailing vortex. The experimental results showed that the wing tip blowing was more effective to increase aerodynamic characteristics of a wing. In this paper, a new numerical analysis was conducted by using vortex lattice method on the effect of a wing tip blowing on the lifyt and drag characteristics of a wing. The numerically predicted results agree closely with experimental data.

부순모래를 사용한 고강도 콘크리트의 배합설계에 관한 연구

이봉학,김동호,홍창우,이주형 江原大學校 産業技術硏究所 2001 産業技術硏究 Vol.21 No.A

The amount used of aggregates for concrete is increasing rapidly since the mid-1980s in Korea. The natural gravels from river are already displaced with crushed stone, and use of crushed sand as a substitute of natural river sands, also, is getting increased day by day. This paper is presented for mixture of high strength concrete using crushed sands. Mixing design of concretes alee various water-cement ratios(w/c) such as 25%, 40%, 55% and different replacement radio of crushed sands to natural sands such as 0%, 20%, 40%, 60%. As a results, it has been shown that compressive strength of concretes with w/c lower than 40% and 25% is higher than 400 kgf/cm2 and 600 kgf/cm2 respectively.

강섬유 보강 콘크리트의 인장강성 및 피로파괴특성

이봉학,윤경구,홍창우,김동호 강원대학교 부설 석재복합신소재 제품연구센터 2000 석재연 논문집 Vol.5 No.-

콘크리트의 취성적 성질을 개선하고 부재의 인성을 증가시킨 강섬유보강 콘크리트는 건설분야에 활용할 가치가 크다. 그러나 설계규준이나 해석방법이 정비되지 못한 현 실정에서 거동 특성을 규명하고 이에 유효하고 타당한 해석모델을 제시하는 것이 요구된다. 본 논문에서는 강섬유보강 콘크리트의 강도특성실험, 직접인장실험 및 피로실험을 수행하여 이에 대한 역학적 특성을 고찰하고 거동특성을 규명함으로서 설계와 해석의 기초 자료로 활용하고자 하였다. This study is conducted on the test to find tension stiffening, flexural fatigue characteristics and mechanical properties of steel fiber reinforced concrete. Experimental investigation is examined accord to hooked type fiber contents(0, 0.4 , 0.7, 1.0%), fiber aspect ratio(60.83). The principal results obtain through this study are as follows; steel fiber reinforced concrete is increased completely tensile & flex strength properties compared with normal concrete. The tension stiffening and fatigue life tend considerably increase with fiber contents, fiber aspect ratio.

교량 바닥판 보수공사에서 발생하는 콘크리트 폐수처리 방안

이봉학,최판길,김정기 江原大學校 産業技術硏究所 2008 産業技術硏究 Vol.28 No.A

As of 2003, construction waste has been produced at the level of 130,614.8 tons/day, in which the amount of waste concrete was 92,639.1 tons/day and accounted for about 66.4% of the amount of construction waste. Waste concrete is mainly produced in construction work and civil engineering work. Especially, road surface crushing method using a large amount of water requires thorough management of concrete wastewater. The aim of this study was to analyze water pollution due to concrete wastewater generated in repair of bridge deck using road surface crushing equipment and to suggest reasonable countermeasures for solve the problem. In this study, it was surveyed current conditions of produced concrete wastewater in bridge deck repair, analyzed physical features of concrete wastewater, expected effects of water pollution on inflow rivers if it is not treated, established treatment plan of water pollution by categories, and calculated capacity of each treatment process and required amount of necessary chemicals. As a result of sampling wastewater generated in field sites and testing it at a lab scale, it was revealed that the original wastewater was produced in removing concrete from bridge deck slabs using surface crushing equipment whose pH was 12.53, CODMn was 12.910mg/L, SS was 547.0mg/L, and other heavy metals were included in extremely small quantities.

시멘트 종류에 따른 SB 라텍스 개질 콘크리트의 강도 및 투수특성

이봉학,홍창우,이주형,김동호 江原大學校 産業技術硏究所 2001 産業技術硏究 Vol.21 No.B

This study focused on the investigation of strength development and permeability of LMC(Latex Modified Concrete) and RSLM(Rapid-Setting Cement Latex Modified Concrete) as the latex content cement types and s/c ratio changed. The compressive strength of latex modified concrete decreased slightly and the flexural strength increased quitely at 15% of latex content. This may be due to the flexibility of latex filled in voids and interconnections of hydrated cement and aggregates by a film of latex particles, respectively. The permeability test results showed that the permeability of LMC was considerably lower than that of conventional concrete. Results of chloride permeability test, for RSLMC indicated very low at an early age caused by the early formation of needle-shape ettringites and latex film.

유한요소해석과 실험검증을 통한 콘크리트 직접인발 시험방법 개발

이봉학,김동호,김성환,김현오 강원대학교 부설 석재복합신소재 제품연구센터 2003 석재연 논문집 Vol.8 No.-

시험편 형상에 의해 발생되는 불규칙한 응력 분포의 하나인 응력집중은 정확한 부착강도 측정을 위하여 최소화해야한다. 이 논문은 pull-off 시험에 영향을 주는 주요 인자들인, 코어 천공 깊이, 강판의 강성, 탄성계수 비, 덧씌우기 두께에 대하여 논의 하고자 한다. 콘크리트 계면에서 위의 변수에 의한 응력 집중의 영향을 평가하기 위하여 유한 요소 해석을 수행하였고, 유한 요소 해석을 통해, 현장 적용을 위한 뛰어난 콘크리트 pull-off 부착강도 시험 방법을 제안하였다. 유한 요소 해석으로부터 제안된 방법은 실험을 통해 검증하였다. 또한 pull-off 시험 방법과 휨 시험 방법과 니플 파이프 직접 인장 시험 방법에 의한 실험을 실시하고 그 결과를 비교하였을 때 표준편차의 관점에서 좋은 결과를 보임을 알 수 있었다. The stress concentration, which is one of non-uniform stress distribution and arises from specimen geometry, should be minimized in order to measure the bond strength correctly. This study discusses the main relevant issues effecting to core pull-off test, namely, core drilling depth stiffness of steel disk, modulus ratio, overlay thickness and length of between cores and edges. Finite element analysis is carried out in order to investigate the effects of those above into the stress concentration at concrete interface. From a series of finite element analysis, a fine concrete pull-off bond strength test method is proposed for field application. The proposed method from finite element analysis is evaluated from a series of experiments. The test results show that the repeatability of the core pull off test are comparable and relatively good in terms of standard deviation, compared from those of flexural beam test method and nipple pipe direct tensile test method.