균열발생 후 철근부식을 고려한 철근콘크리트 인장부재의 균열거동

Abstract

철근콘크리트 구조물은 내구성이 매우 우수하고 반영구적이기 때문에 건설재료의 가장 큰 부분을 차지하고 있다. 그러나 인장을 받는 철근콘크리트조에 균열이 발생하고 오랜 시간이 경과하게 되면 열화현상이 일어나게 되고 그 중 가장 심각한 것이 철근의 부식으로 이는 주로 외부로부터 콘크리트 내부로 부식인자들이 침투하여 철근이 부식하기 때문에 발생된다. 그러나 우리나라의 경우 균열발생 후 철근이 부식된 구조물에 대한 균열거동 연구가 거의 이루어지고 있지 않은 실정이다. 균열폭에 대한 현행 설계기준 규정11)-14)이나 여러 연구자들의 제안식15)-17)은 콘크리트 내 철근이 부식되지 않았을 경우에만 적용가능하며 균열 후 부식이 발생했을 때의 균열폭 산정에 대한 식은 찾아보기 어렵다. 따라서 본 연구에서는 균열이 발생된 구조물의 철근부식정도에 따른 구조물의 거동을 알아보기 위해 균열요소 수치해석 모델을 구축하고 기존 연구자들의 재료적 관점에서 수행된 철근부식에 관한 실험결과(철근부식속도, 부착강도감소율, 부식면적율)를 해석모델에 적용가능토록 변환하였다.; A structure life is different with a various condition. Currently, it is common knowledge that a life of the reinforced concrete structure in our country is from ten to twenty year short and from forty to fifty year generally. Recently, a long-term life of the structure is demanded by a environmental necessity such as a reduction on use of resources and energy. In case of the long-term life structure, it must be took into account for steel corrosion by a concrete crack in usability and safety of the structure. Because of the uncertain factors like concrete nonlinear behavior and discontinuity as well as a secondary crack in member, the estimate of a crack dimension is difficult but it is the important matter on an usability assessment of the reinforce concrete structure. Consequently, it should be predicted that a crack behavior under service load. In respect of a crack width, from 0.1mm to 0.4mm of the crack allowance value is ruled by the various countries of the world with circumstance condition of the structure. Therefore, it must be predicted that crack behavior which is affected by a crack width tension stiffening effect, stress change in member considering steel corrosion. In this study, to understand the structure behavior as degree of steel corrosion for a cracked structure, it was set up the numerical analysis model with a crack element. And, it was converted to apply to analysis models that the experiment result related to steel corrosion performed from the viewpoint of the material. First, the short term model was expanded into a long term model considering a time course variation of the material, creep and drying shrinkage of the concrete, the bond creep as well as affection of the steel corrosion. Here, as a influence of a corrosion, it was considered that reduction of bond strength and a steel section and a lengthening of the rusted steel. It was applied for the consideration like this after changing results of a material experiment with the structural view. According to this course, it predicts the crack behavior of a tensile member at the reinforced concrete such as crack width and tension stiffening under effect of steel corrosion with a environment condition and a service period of structure after a crack. This paper is divided into six chapters; Chapter1, Introduction; Chapter 2, Crack theory of reinforce concrete tensile member; Chapter 3, Modeling of crack element; Chapter 4, a long term corrosion bond model; Chapter 5, Model simulation; Chapter 6, Conclusion. The following summarized the content of each chapter. Chapter 1 describes the background, purpose, content, and the limits of the research. Chapter 2 presents crack theory of a tensile member on the reinforce concrete and a crack width model by each regulation. Chapter 3 introduces to modeling of the crack differential element and relation of between bond stress and slip. Chapter 4 explains a long term corrosion bond model applied this study. Chapter 5 presents simulation results performed by a short term bond model, a long term bond model, and a long term corrosion bond model. Chapter 6 suggests the next assignment through results of this study. The following present the conclusions of this paper. 1) The short term bond model was expanded into a long term corrosion bond model considering a time course variation of the material, creep and drying shrinkage of the concrete, the bond creep as well as affection of the steel corrosion. 2) As taking advantage of a long term corrosion bond model, it can be predicted that the crack behavior such as a steel stress and the bond stress and a slip change on a crack plane by corrosion rate from initial steel corrosion. 3) By the simulation on a long term corrosion bond model, it was predicted that a crack width with the elapse of time for the cracked structure in carbonation environment. Under the service load, the crack width after twenty years from initial steel corrosion increased normally about 137% by contrast to it before corrosion. 4) In this paper, it was applied for the quantified steel corrosion speed by an environment. But, it was not considered a reduction of the corrosion speed with the effect of corrosion residual products created by the corrosion in the structure. Thus, a research including this matter need to hereafter.