• Computers and Concrete
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• 제15권2호
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• pp.231-257
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• 2015

This paper discusses the spatial variability of the carbonation depth caused by the mesoscopic structure of the concrete and the influence of the spatial variability on the thickness of the concrete cover. To conduct the research, a method to generate the random aggregate structure (RAS) based on polygonal particles and a simplified numerical model of the concrete carbonation at meso-scale are firstly developed. Based on the method and model, the effect of the aggregate properties including shape, content and gradation on the spatial variability of the carbonation depth is comprehensively studied. The results show that a larger degree of the spatial variability will be obtained by using (1) the aggregates with a larger aspect ratio; (2) a larger aggregate content; (3) the gradation which has more large particles. The proper sample size and model size used in the analysis are also studied. Finally, a case study is conducted to demonstrate the influence of the spatial variability of the carbonation depth on the proper thickness of the concrete cover. The research in this paper not only provides suggestions on how to decrease the spatial variability, but also proposes the method to consider the effect of the spatial variability in designing the thickness of the concrete cover.

• 콘크리트학회논문집
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• 제11권6호
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• pp.35-46
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• 1999

The steel fiber reinforced concrete may affect substantially to the tension stiffening at post cracking behavior. Even if several tension stiffening models exist, they are for plain and normal strength concrete. Thus, the development of tension stiffening models for steel fibrous high strength RC members are necessary at this time when steel fiber reinforced and high strength concretes are common in use. This paper presents tension stiffening effects from experimental results on direct tension members with the main variables such as concrete strength, concrete cover depth, steel fiber quantity and aspect ratio. The comparison of existing models against experimental results indicated that linear reduced model closely estimated the test results at normal strength level but overestimated at high strength level. Discontinuity stress reduced model underestimated at both strength levels. These existing models were not valid enough in applying at steel fibrous high strength concrete because they couldn't consider the concrete strength nor section area. Thus, new tension stiffening models for high strength and steel fiber reinforced concrete were proposed from the analysis of experimental results, considering concrete strength, rebar diameter, concrete cover depth, and steel fiber reinforcement.

• Smart Structures and Systems
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• 제17권4호
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• pp.577-591
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• 2016

In this study, the transfer length of 2400 MPa, seven-wire high-strength steel strands with a 15.2 mm diameter in pretensioned prestressed concrete (PSC) beams utilizing high strength concrete over 58 MPa at prestress release was evaluated experimentally. 32 specimens, which have the variables of concrete compressive strength, concrete cover depth, and the number of PS strands, were fabricated and corresponding transfer lengths were measured. The strands were released gradually by slowly reducing the pressure in the hydraulic stressing rams. The measured results of transfer length showed that the transfer length decreased as the concrete compressive strength and concrete cover depth increased. The number of strands had a very small effect, and the effect varied with both the concrete cover depth and concrete strength. The results were compared to current design codes and transfer lengths predicted by other researchers. The comparison results showed that the current transfer length prediction models in design codes may be conservatively used for 2400 MPa high-strength strands in high-strength concrete beams exceeding 58 MPa at prestress release.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2010년도 춘계 학술논문 발표대회 1부
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• pp.5-7
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• 2010

Corrosion sensors were devised to develop a system whereby the depth of chloride permeation from concrete surfaces can be monitored in cover concrete of reinforced concrete structures. For making sensor which is similar to rebar author uses Screen printer machines, Ag paste and Fe powder. Appropriate portion of Ag and Fe is over 1:2. The resistance of sensors increased as the degree of corrosion increased. And according to cover depth author suggests sensor system which has a demanded cover depth. It was therefore confirmed that the corrosion sensor can monitor chloride permeation by change of resistance.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2006년도 추계 학술발표회 논문집
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• pp.597-600
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• 2006

In this study, field survey of carbonation for RC column in city is carried out and carbonation behavior in sound, joint, and cracked concrete is also analyzed. Futhermore, probability of durability failure with time is calculated through considering probability variables such as concrete cover depth and carbonation depth which are obtained from field survey. The probability of durability failure in cracked concrete with considering crack width and time is also calculated and service life is predicted based on intended failure probability in domestic specification. Through this study, it is known that service life in a RC column is evaluated differently for local conditions and each service life is rapidly decreased with decrease in cover depth and increase in crack width.

• 한국화재소방학회논문지
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• 제25권1호
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• pp.78-84
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• 2011

최근 콘크리트 내화 연구는 대부분 고강도 콘크리트의 내화성능 확보에 많은 초점이 맞추어져 있다. 그러나 국내의 콘크리트 수요를 살펴보면 40MPa 이하의 일반강도 콘크리트의 수요가 전체 콘크리트 수요량의 대부분을 차지한다. 따라서 고강도 콘크리트의 내화성능에 대한 연구뿐만 아니라 일반콘크리트의 내화성능에 관한 연구도 필요하다. 본 연구에서는 40MPa 콘크리트 기둥을 대상으로 콘크리트 피복 두께와 단면크기를 변수로하여 내화성능을 평가하였으며, 연구 결과 단면크기가 커질수록, 피복두께가 두꺼워질수록 내화성능은 향상되는 것으로 나타났다.

• 한국구조물진단유지관리공학회 논문집
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• 제12권2호
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• pp.49-58
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• 2008

대도시 및 지하구조물에서 주로 발생하는 탄산화는 사용기간의 증가에 따라 철근부식이 발생하며, 이러한 철근부식은 구조물의 성능저하로 진전된다. 하나의 RC 구조물이라 하더라도, 콘크리트 시공에 의해 건전부뿐 아니라 시공이음부 또는 균열부와 같은 취약부가 발생하기가 쉽지만, 진단시에는 일반적으로 건전부만을 대상으로 탄산화 거동을 분석하고 있다. 본 연구에서는 대도시에서 사용중인 고가교의 RC 교각을 대상으로 하여 건전부, 균열부, 시공이음부 콘크리트의 탄산화 실태조사를 수행하였다. 조사된 탄산화 깊이와 측정된 피복두께를 확률변수로 하여, 사용기간에 따라 증가하는 내구적 파괴확률을 도출하였다. 한편 국내 시방서에서 제시하는 목표파괴확률을 기준으로 대상구조물의 내구수명을 평가하였다. 동일한 기둥부재라 하더라도 건전부, 균열부, 시공이음부 콘크리트에 따라 도출된 내구수명은 각각 다르게 평가되었으며, 피복두께가 작고 균열폭이 큰 경우에서는 매우 빠르게 감소함을 알 수 있었다. 피복두께의 변동계수에 따라서도 내구적 파괴확률의 변화가 크므로 적절한 시공과 품질확보가 중요함을 알 수 있다.

• 한국건설순환자원학회논문집
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• 제11권1호
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• pp.79-88
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• 2023

본 연구에서는 철근 부식에 의한 콘크리트 단면의 구조적 거동을 정량화하기 위해 철근 표면에 형성되는 녹을 모델링했으며, 변수로는 철근과 콘크리트 사이의 계면 공극, 피복두께, 철근 직경을 취했다. 철근 부식시 구조적 한계에 가장 큰 영향을 미치는 인자는 계면의 공극크기였으며, 철근 직경, 피복두께 순으로 나타났다. 피복두께 75 mm, 철근직경 20 mm의 콘크리트 단면에서 계면의 공극이 1 ㎛에서 10 ㎛로 증가되면, 균열을 유발시키는 철근 부식량은 16.95 ㎛에서 27.69 ㎛로 크게 증가 되었다. 또한 철근 표면에 형성된 녹이 계면의 공극을 다 채우기 전까지 콘크리트 단면에는 손상이 발생되지 않았으며, 계면공극 범위를 넘어서는 양의 녹이 철근 표면에 형성된 후 콘크리트 단면은 항복, 균열 및 파단 상태에 이르렀다.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2006년도 춘계학술논문 발표대회 제6권1호
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• pp.163-166
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• 2006

The purpose of the research is to assess the accuracy of steel bar detector among other nondestructive testing equipment. The result of previous research shows that the average errors of rebar detector are 14.7% for the cover depth, 2.3% for the rebar spacing, and 11% for the rebar diameter. But this experiment was performed at the laboratory and the mortar was used for covering the steel bars instead of concrete. In situ condition can be different from the laboratory's so the outcomes do not correspond with those of laboratory. This research was performed at the buildings to be reconstructed. Nondestructive and destructive testing can be performed side by side since the building if to be destroyed. Steel bar detector was operated on the beam and the column and concrete cover of those members was removed for the actual measurement of rebar depth, spacing, and diameter finally, presumed value can be directly compared with actual data.

• Computers and Concrete
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• 제6권1호
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• pp.79-93
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• 2009

In the present paper, a methodology has been presented for the reliability assessment of concrete barriers that lie at a certain depth in the soil, and a missile (a rigid projectile) impacts the top of the soil cover normally, and subsequently after penetrating the soil cover completely it hits the barrier with certain striking velocity. For this purpose, using expressions available in the literature, striking velocity of missile at any depth of soil has been derived and then expressions for the depths of penetration in crater and tunnel region of concrete barrier have been deduced. These depths of penetration have been employed for the derivation of limit state functions. Using the derived limit state functions reliability assessment of underground concrete barrier has then been carried out through First Order Reliability Method (FORM). To study the influence of various random variables on barrier reliability, sensitivity analysis has also been carried out. In addition, a number of parametric studies is conducted to obtain the results of practical interest.