• Structural Engineering and Mechanics
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• 제77권1호
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• pp.89-102
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• 2021

Rapid construction of prefabricated bridges requires minimizing the field work of precast members and ensuring structural stability and constructability. In this study, we conducted experimental and analytical investigations of transverse joints of prefabricated T-girder bridge superstructures to verify the flexural performance and serviceability. In addition, we conducted parametric studies to identify the joint parameters. The results showed that both the segmented and continuous specimens satisfied the ultimate flexural strength criterion, and the segmented specimen exhibited unified behavior, with the flexural strength corresponding to that of the continuous specimen. The segmented specimens exhibited elastic behavior under service load conditions, and the maximum crack width satisfied the acceptance criteria. The reliability of the finite element model of the joint was verified, and parametric analysis of the convexity of the joint section and the compressive strength of the filler concrete showed that the minimum deflection and crack width occurred at a specific angle. As the strength of the filler concrete increased, the deflection and crack width decreased. However, we confirmed that the reduction in the crack width was hardly observed above a specific strength. Therefore, a design suitable for prefabricated bridges and accelerated construction can be achieved by improving the joint specifications based on the required criteria.

• 콘크리트학회논문집
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• 제24권1호
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• pp.15-23
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• 2012

이 논문은 철근콘크리트 구조부재의 사용성능 검증을 위한 균열폭과 처짐을 산정할 수 있는 새로운 계산 방법을 제안하고 이를 자동으로 계산할 수 있는 프로그램을 개발한 것이다. 이를 위하여 콘크리트의 재료특성을 포물-사각형 응력-변형률 곡선으로 반영한 철근응력과 피복두께의 영향을 반영한 인장증강 계수를 이용한 곡률을 계산할 수 있는 수치 모델링을 실시하였다. 이와 함께 균열폭과 처짐을 계산하는데 필요한 인장증강효과와 유효인장단면적은 균열이 발생한 휨부재 단면의 인장영역을 인장 현재로 이상화하여 정의하였다. 그리고 수정된 인장증강 계수를 이용하여 유효곡률을 계산하였다. 제안된 균열폭과 처짐 산정 방법을 이용하여 여러 연구자들이 수행한 실험 자료를 계산한 결과, 현행 설계기준들의 규정보다 실험값을 비교적 정확하게 예측하는 것으로 나타났다.

• 콘크리트학회논문집
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• 제26권3호
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• pp.299-306
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• 2014

콘크리트 구조물의 철근 부식 문제를 해결하기 위하여 코팅철근이 사용된다. 에폭시 코팅 철근에 비해 아연코팅철근의 콘크리트 보의 휨 거동 영향에 대한 자료는 거의 없는 실정이다. 이 연구의 목적은 아연코팅철근이 콘크리트 보의 휨 거동에 미치는 영향을 파악하는 데 있다. 아연코팅철근을 사용한 부재와 일반철근을 사용한 부재의 구조실험을 통하여 휨 거동 특성을 비교하였다. 실험변수로써 철근의 아연코팅 유무, 사용 철근비와 피복 두께를 고려하였다. 아연코팅철근 콘크리트 보의 균열패턴, 균열폭, 처짐 및 변형률 특성을 파악하였다. 아연코팅철근 콘크리트 보의 휨강도는 일반철근 콘크리트 보의 휨강도와 거의 차이가 나지 않는다. 철근표면의 아연코팅은 처짐, 균열폭 비교 결과에도 뚜렷한 영향을 미치지 않는다. 또한, 아연코팅철근 보와 일반철근 보의 하중-변형률 곡선은 비슷한 결과를 나타낸다. 따라서, 전반적으로 아연코팅철근의 사용은 일반철근을 사용할 때에 비해 콘크리트 보의 휨 거동에 악영향을 미치지는 않는 것으로 나타난다.

• International Journal of Precision Engineering and Manufacturing
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• 제7권1호
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• pp.24-29
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• 2006

In this paper, the effect of open crack on the dynamic behavior of simply supported Timoshenko beam with a moving mass was studied. The influences of the depth and the position of the crack on the beam were studied on the dynamic behavior of the simply supported beam system by numerical methods. The equation of motion is derived by using Lagrange's equation. The crack section is represented by a local flexibility matrix connecting two undamaged beam segments. The crack is modeled as a rotational spring. This flexibility matrix defines the relationship between the displacements and forces on the crack section and is derived by applying fundamental fracture mechanics theory. As the depth of the crack increases, the mid-span deflection of the Timoshenko beam with a moving mass is increased.

• 한국정밀공학회지
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• 제22권1호
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• pp.143-151
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• 2005

This paper study the effect of open cracks on the dynamic behavior of simply supported Timoshenko beam with a moving mass. The influences of the depth and the position of the crack in the beam have been studied on the dynamic behavior of the simply supported beam system by numerical method. Using Lagrange's equation derives the equation of motion. The crack section is represented by a local flexibility matrix connecting two undamaged beam segments i.e. the crack is modeled as a rotational spring. This flexibility matrix defines the relationship between the displacements and forces on the crack section and is derived by the applying fundamental fracture mechanics theory. As the depth of the crack is increased the mid-span deflection of the Timoshenko beam with the moving mass is increased. And the effects of depth and position of crack on dynamic behavior of simply supported beam with moving mass are discussed.

• 대한기계학회논문집
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• 제12권6호
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• pp.1343-1349
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• 1988

In this study, it is investigated for the effects of stress ratio and grain size on fatigue crack growth behavior and crack closure, in ferrite-martensite dual phase steels. The results obtained are as follows ; .DELTA. $K_{th}$ is independent of the ferrite grain size, but decreases with increasing stress ratio. The relation between .DELTA. $K_{th}$ and stress ratio R is as follows : .DELTA. $K_{th}$ =15.1(1-0.95R). But (.DELTA. $K_{eff}$)$_{th}$ in terms of crack closure is approximately 2.5 MPa.root.m. Also, variation of the degree of crack deflection to crack tip opening displacement at the minimum load is considered as a parameter of crack closure.e.e.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2000년도 가을 학술발표회논문집(I)
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• pp.733-738
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• 2000

It is difficult to obtain accurate fracture toughness values by RILEM committees proposed three point bend test(TPB) because the shape of load-deflection curve is irregular and final crack propagation occurs after some slow stable cracking. However, for disk test, fracture toughness is easily obtained from crack initial load. We examined the cracked high strength concrete disk and the experimental results were compared with the results by finite element analysis(FEA). Also we compared experimental fracture locus with theoretical fracture locus.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2005년도 춘계학술대회논문집
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• pp.707-710
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• 2005

In this paper, we studied about the dynamic behavior of a cracked rotating cantilever beam. The influences of a rotating angular velocity, the crack depth and the crack position on the dynamic behavior of a cracked cantilever beam have been studied by the numerical method. The cracked cantilever beam is modeled by the Euler-Bernoulli beam theory. The crack is assumed to be in the first mode of fracture and to be always opened during the vibrations. The lateral tip displacement and the axial tip deflection of a rotating cantilever beam is more sensitive to the rotating angular velocity than the depth and position of crack. Totally, as the crack depth is increased, the natural frequency of a rotating cantilever beam is decreased in the first and second mode of vibration.

• 한국농공학회논문집
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• 제49권6호
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• pp.47-54
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• 2007

This paper is on the research of the special character of the dynamic response according to a design of the clamped reinforced concrete slab. In this study, the 20-node solid element has been used to analyze the dynamic characteristics of RC slabs with clamped edges. The elasto-visco plastic model for material non-linearity and the smeared crack model have been adopted in the finite element formulation. The design factor, which affect the dynamic response of the reinforced concrete slab, are the steel layer thickness, steel layer depth, steel layout method, steel layout angle and the slab thickness and span ratio. The main purpose of this study was to find out the dynamic response of the reinforced concrete slab according to above variables. The reduction of deflection/thickness ratio appeared less than 2% when the slab thickness between 20 and 21cm. It is desirable that the slab thickness must be above 20-21cm. The reduction ratio of deflection is appeared greatly when the value of the span/thickness ratio is between 25 and 30. In conclusion, the steel layer depth and thickness had a little effect on deflection of the dynamic response, but had no effect on the steel layout angle.

• Carbon letters
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• 제7권1호
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• pp.19-26
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• 2006

Three point bending tests of single edge notched beam (SENB) specimens were carried out to evaluate the fracture behavior of the fine-grain isotropic nuclear grade graphite, IG-11. To measure the crack initiation point and the subsequent crack growth, the direct current potential drop (DCPD) method and a traveling microscope were used. The effects of test variables like initial crack length, specimen thickness, notch type and loading rate on the measured fracture toughness, $K_Q$, were investigated. Based on the test results, the ranges of the test variables to measure the reliable fracture toughness value were proposed. During the crack growth, the rising R-curve behavior was observed in IG-11 graphite when the superficial crack length measured on the specimen surface was used. The increase of crack growth resistance was discussed in terms of crack bridging, crack meandering, crack branching, microcracking and crack deflection, which increase the surface energy and friction force.