• Journal of the Korea institute for structural maintenance and inspection
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• v.26 no.4
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• pp.40-47
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• 2022

The present study aimed to examine the effectiveness of different techniques for controlling the diagonal cracks at the corners of openings on the strength, deformation, and crack propagation in reinforced concrete walls. The crack control strip proposed in this study, the conventional diagonal steel reinforcing bars, and stress-dispersion curved plates were investigated for controlling the diagonal cracks at the opening corners. An additional crack self-healing function was also considered for the crack control strip. To evaluate the volume change ratio and crack width propagation around the opening, downsized wall specimens with a opening were tested under the diagonal shear force at the opening corner. Test result showed that the proposed crack control strip was more effective in reducing the volume change and controlling the crack width around the opening when compared to the conventional previous methods. The crack control strip with crack healing feature displayed the superior performance in improving the strength of the wall and reducing the crack width while healing cracks occurred in the previous tests.

• Explosives and Blasting
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• v.19 no.4
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• pp.5-10
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• 2001

발파시 공벽 주변에서 방사상으로 발생하는 무수한 균열들을 제어하고 일정한 방향으로 절단면을 형성하기 위해서 split tube를 이용한 발파 방법에 대한 현장 실험을 실시하였다. 현장 실험결과 절단면을 발달시키고자 하는 방향으로 제어할 수 있었다. 계산에 의한 발파압력과 제어된 균열면의 길이를 비교하였다. 현장 벤치 벽면에서 에멀젼 계열 폭약의 발파 압력이 700㎫이상일 경우 균열을 원하는 방향으루 제어할 수 있었을 뿐만 아니라, 공경의 30배까지 균열이 전파되었다.

• Journal of the Korea Concrete Institute
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• v.24 no.4
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• pp.381-390
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• 2012

The KCI Building Code (2003 and 2007) provisions to control flexural cracking in beams and one-way slabs are discussed for related researches and the development of the provisions. Based on the basic ideas over the development of current provisions, possible problems with cracking control are identified and discussed for the remedies to fix the problems. Simple and clear equations to control flexural cracking in beams and one-way slabs are presented. The presented equations would avoid any conflicts with other provisions for the spacing of reinforcement.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.5
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• pp.98-105
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• 2018

Cracks in RC members occurred as a result of material and structural factors. The crack width and a crack location are very difficult to examine. A direct crack control method and indirect crack control method to control a crack are presented in the KHBDC (LSD) and KSCDC (2012). In the KSCDC text, cracks are controlled by steel spacing indirectly under a service load. On the other hand, in the KSCDC appendix, cracks are controlled by a crack width directly under a sustained load. In particular, the loading state considered is different. On the other hand, cracks are controlled under a combination of service load and an effective elastic modulus is used in KHBDC. Therefore, in this study, an effective elastic modulus that can reflect the ratio of the sustained load and live load was applied, and a maximum steel spacing was calculated through a design crack width. A variable interpretation was carried out, and a rational crack control method was assessed. As a result, a steel spacing through the design crack width in the KSCDC was smaller than that from the design crack width in the KHBDC, which leads to a conservative design. In addition, the maximum steel spacing suggested in this study has a consistency eliminating the difference between direct crack control and indirect crack control.

• Journal of the Korea Concrete Institute
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• v.23 no.4
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• pp.471-478
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• 2011

For a practical simplicity in designing of reinforced concrete structures, the indirect crack controlling method of limiting bar spacing is adopted in KCI structural design provisions. In addition, a direct method for evaluating crack width is also provided in the appendix of the code. But there may be some mismatched results between these two crack controlling methods. In this study, limit values of maximum bar spacing calculated from KCI provisions, KCI appendix, and Frosch's equation are examined as concrete strength, cross-section height, and concrete cover are varied, and the differences are analyzed. From the results, it becomes clear that the differences between maximum bar spacing calculated from KCI code text provisions and those from KCI code appendix provisions are too significant to be neglected. Therefore, rational crack models are suggested in order to get rid of the discrepancy between the direct and indirect control methods.

• Magazine of the Korea Concrete Institute
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• v.14 no.2
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• pp.52-60
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• 2002

지하철 구조물과 같은 매스 콘크리트 구조물을 시공할 때 온도 측정을 하는 경우는 많으나 이는 내외부 온도차를 적정한 수준으로 유지하여 균열 발생을 제어하기 위한 수단일 뿐 균열폭을 일정한도 내로 제어할 수 있는 조치는 아니다. 매스 콘크리트 구조물에서 균열폭을 제한 값 이하로 하기 위해서는 적절한 양의 철근을 배치하여야 한다. 또한 시공 이음 등을 작은 간격으로 설치하는 것은 구속도를 완화시키고 온도응력이나 균열폭을 저감시켜 균열 제어상 매우 효과적인 수단이 될 수 있다. 그러나 시공 이음, 균열 유발 줄눈 등의 이음간 간격을 좁히면 내하력 수밀성, 내구성 등에 악영향을 미칠 가능성이 높고, 타설 회수가 많아져 동일한 공정이 반복 투입되므로 시공 속도의 저하 및 공사비 상승 등의 단점이 나타날 수 있다.(중략)

• Journal of the Korea Concrete Institute
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• v.23 no.1
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• pp.87-98
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• 2011

Crack formations are inevitable in reinforced concrete structures. To estimate crack widths, empirical formulae are used widely and indirect crack controling methods of limiting bar spacing and bar diameter are also used due to their simplicity. In EC2, the characteristic crack width is calculated by multiplying maximum crack spacing and average strain. In this study, limit values of maximum bar spacing and bar diameter are examined as the material characteristics are varied. Two models of tension stiffening effect and maximum crack spacing and their effects are evaluated. The obtained results are compared with the values obtained using KCI method. The results showed that a significant difference is found when two tension stiffening effect are employed, and an under-estimation is found when 2nd order tension stiffening effect and maximum crack spacing limit from Part II were implemented. Therefore, a rational indirect crack control method attained using the tension stiffening effect of 2nd order form is needed. Also, a consistency in serviceabiliy analysis in flexural members needs to be secured. In order to achieve these goals, two crack controling models are suggested.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.19 no.1 s.71
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• pp.15-25
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• 2006

The researches on the early-aged concrete hydration process and the techniques for the early-aged concrete crack control mainly have been focused and developed on the massive concretes in both experimental and numerical studies. However, those researches for relatively thin members such as the upper slab of the reinforced concrete rahmen bridge have nearly been attempted. In this study, a designing technique for crack controlling in the thin members of the early-aged reinforced concrete rahmen bridges based on measured temperature history, strength revelation model and sinkage model is proposed. A method of calculating the reinforcing bar area for crack controlling is also proposed and it is found that the distributing bars under the design loads become the main reinforcing bars in the temperature stress analysis of the early-aged reinforced concrete rahmen bridges. It is shown that the proposed analysis technique is able to use the design of crack control for the early-aged reinforced concrete rahmen bridge.

• Tunnel and Underground Space
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• v.20 no.4
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• pp.299-307
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• 2010

The model experiments, which employ a charge hole and guide hole, are simulated to examine the effect of the guide hole on the crack propagation control in blasting. Crack patterns resulted from the analysis models, which consider the distance between the charge hole and guide hole, were compared. From the simulation analysis for the model experiments, it was revealed that all the guide holes used in this study were effective for controlling the crack propagation in blasting.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.12 no.2
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• pp.201-214
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• 1999

이 연구는 2경간 연속 PSC-Beam 교량의 경간 내측 지지점의 바닥판에서 발생할 수 있는 균열의 제어에 관한 내용을 다루고 있다. PSC-Beam 교량은 주형인 PSC-Beam을 거치시킨후 바닥판을 현장타설 콘크리트로 시공된다. 이로 인하여 주형 콘크리트와 바닥판 콘크리트의 시간의존적 거동차이, 주형의 연속화에 따른 거동 등에 의하여 부모멘트가 가장 크게 걸리는 지점부에서 균열이 쉽게 발생된다. 따라서 이 논문에서는 2경간 연속 PSC-Beam 교량의 연속화에 따른 거동을 수치적 방법으로 해석하여 지점부 바닥판의 균열거동이 예측되었다. 이를 위하여 해석모델에는 콘크리트의 시간의존적 현상인 크리프와 건조수축이 고려되었으며, 2경간 연속 PSC-Beam 교량의 거동에 영향을 나타내는 여러 가지 인자가 고려되어 해석되었다. 끝으로 콘크리트의 모델식을 이용하여 지점부 균열을 억제하기 위한 현장에서 관리가능한 방안이 수치적으로 제안되었다.