• 한국콘크리트학회:학술대회논문집
• /
• 한국콘크리트학회 2002년도 봄 학술발표회 논문집
• /
• pp.227-232
• /
• 2002

This paper describes a calculation of an average crack spacing and the maximum crack width for the high-strength concrete tensile and flexural members. Based on the uniform bond stress distribution of the average steel and concrete strains over the transfer length, the crack spacing and the crack width are proposed to utilize influence of the concrete strength and the cover thickness. This analytical results presented in this paper indicate that the proposed equations can be more effectively estimated the maximum crack width and the average crack spacing of the reinforced concrete flexural and tensile members.

• 한국콘크리트학회:학술대회논문집
• /
• 한국콘크리트학회 2001년도 봄 학술발표회 논문집
• /
• pp.903-908
• /
• 2001

This paper deals with the estimation of the maximum flexural crack widths using minimum crack spacing for reinforced concrete members. The proposed method utilizes the conventional crack and bond-slip theories as well as bonding transfer length and effects of creep and shrinkage between the reinforcement and concrete. An analytical equation for the estimation of the maximum flexural crack width is formulated as a function of mean bond stress. The validity, accuracy and efficiency of the proposed method are established by comparing the analytical results with the experimental data and the major code specifications (e.g., ACI, CEB-FIP Model code, Eurocode 2, etc.). The analytical results of analysis presented in this paper indicate that the proposed method can be effectively estimated the maximum flexural crack width of the reinforced concrete members.

• 한국안전학회지
• /
• 제21권3호
• /
• pp.114-121
• /
• 2006

As one of the serviceability limit states, the prediction and control of crack width in reinforced concrete bridges or PSC bridges are very important for the design of durable structures. However, the current bridge design specifications do not provide quantitative information for the prediction and control of crack width affected by the initiation and propagation of corrosion. Considering life span of concrete bridges, an improved control equation about the crack width affected by time-dependent general corrosion is proposed. The developed corrosion and crack width control models can be used for the design and the maintenance of prestressed and non-prestressed reinforcements by varying time, w/c, cover depth, and geometries of the sections. It can also help the rational criteria for the quantitative management and the prediction of remaining life of concrete structures.

• Advances in concrete construction
• /
• 제10권1호
• /
• pp.21-34
• /
• 2020

Precast deck joints have larger crack width than cast-in-place concrete decks. The initial crack typically occurs at the maximum moment but cracks on precast joints are significant and lead to failure of the deck. The present crack equation is applied to cast-in-place decks, and requires correction to calculate the crack width of precast deck joints. This research aims to study the crack width correction equation of precast decks by performing static tests using high strength and normal strength concrete. Based on experimental results, the bending strength of the structural connections of the current precast deck is satisfied. However it is not suitable to calculate and control the crack width of precast loop connections using the current design equation. A crack width calculation equation is proposed for crack control of precast deck loop joints. Also included in this paper are recommendations to improve the crack control of loop connections.

• 한국콘크리트학회:학술대회논문집
• /
• 한국콘크리트학회 2002년도 봄 학술발표회 논문집
• /
• pp.917-922
• /
• 2002

This paper deals with the estimation of the maximum crack widths considering bond-slip relationships based on experimental data that were tensed by axial force. It is certificated that the concrete stress condition clearly affects the bond-slip relationship. The proposed method utilizes the conventional crack and bond-slip theories as well as the characteristics of deformed reinforcement and size effects. An analytical equation for the estimation of the maximum flexural crack width is formulated as a function of minimum crack length and the coefficient of bond stress effect. The validity, accuracy and efficiency of the proposed method are established by comparing the analytical results with the experimental data and the major specifications (e.g., ACI, CEB-FIP Model code, Turocode 2, JSCE, etc.). The analytical results presented in this paper indicate that the proposed method can be effectively estimated the maximum flexural crack width of reinforced concrete.

• 한국구조물진단유지관리공학회 논문집
• /
• 제23권7호
• /
• pp.9-15
• /
• 2019

본 연구의 목적은 영상 처리 기법의 히스토그램 분석을 이용하여 콘크리트 구조물 표면의 최대 균열 폭을 평가하는 것이다. 이를 위하여 콘크리트 표면 균열에 대한 영상을 촬영하고, 촬영된 영상을 회색 영상 및 이진화 영상으로 변환하였다. 이진화된 영상은 팽창과 침식이 적용된 후 레이블링을 통하여 분리된 객체로 인식된다. 콘크리트 표면은 시간이 경과함에 따라 먼지와 얼룩 등이 발생될 수 있으며, 촬영 조건에 따라 그림자 및 조명 반사가 포함될 수 있다. 또한, 콘크리트 균열은 연속적인 형상으로 발생되는 반면에 잡음은 점의 형태로 나타난다. 이러한 영향을 제거하기 위하여 이진화 과정은 양방향 블러와 적응적 경계를 적용하였으며, 레이블링된 영역에 대하여 면적비를 통한 잡음 제거를 수행하였다. 잡음이 제거된 각각의 균열 객체는 히스토그램 분석을 통하여 x축과 y축에 대한 최대값 및 그 위치가 연산되고, 분리된 객체에 대한 각각의 최대값 위치에서 삼각비를 통하여 균열 폭을 평가하게 된다. 제안된 방법에 의해 평가된 최대 균열 폭은 균열 게이지에 의해 계측된 값과 비교 분석되었다. 본 연구에 의해서 제안된 방법은 콘크리트 표면 영상에 대한 균열 폭 평가에 신뢰성을 향상 시킬 수 있을 것이다.

• 한국지진공학회논문집
• /
• 제19권2호
• /
• pp.75-83
• /
• 2015

The purpose of this study is to improve the previous damage evaluation model for RC members which is proposed by Igarashi[1] in 2010.The previous model was not confirmed by enough data of damage such as, residual crack length, width and area for exfoliation of concrete, etc. In addition, validation of the model is still insufficient. Therefore, experiment of a real-scale RC structure and experiment of RC columns using the high-strength concrete were conducted to gather the data of damage in RC members. The investigation has been conducted gathering the data not only additional experiments data but also existing data for modification of damage evaluation model. It has been investigated on changing damage in RC due to axial force ratio, shear reinforcement and shear span ratio. As a result, several problems were founded in the previous model, such as, hinge length($l_p$), spacing of flexural crack($S_{av,f}$), total width of flexural cracks regulated by maximum width of flexural crack($n_f$) and total width of shear cracks regulated by maximum width of shear crack($n_s$). New model is proposed and evaluated the damage properly.

• 한국산학기술학회논문지
• /
• 제19권5호
• /
• pp.98-105
• /
• 2018

철근 콘크리트 부재에서 균열은 구조적 요인 뿐만 아니라 재료적 인자에 의해서도 발생한다. 이러한 균열의 크기와 발생 위치를 파악하는 것은 매우 어렵다. 도로교설계기준(한계상태설계법)과 콘크리트구조기준(2012)에서는 균열을 제어하기 위해 직접균열제어 방법과 간접균열제어 방법을 제시하였다. 콘크리트구조기준 본문에서는 사용하중 하에서 철근 간격을 사용하여 간접적으로 균열을 제어한다. 이에 반해, 콘크리트구조기준 부록에서는 지속하중 하에서 균열폭을 통해 직접적으로 균열을 제어한다. 즉, 균열 제어를 위해 고려하는 하중 상태가 상이하다. 그러나 도로교설계기준에서는 사용하중조합에서 균열을 제어하고, 유효탄성계수를 사용하고 있다. 따라서 이 연구에서는 고정 하중과 활하중의 비율을 반영할 수 있는 유효탄성계수를 적용한 설계 균열폭으로부터 최대철근간격을 산정하였다. 그리고 변수 해석을 수행하여 합리적인 균열 검증 방법에 대하여 모색하였다. 해석 결과 콘크리트구조기준으로부터 유도된 철근 간격은 도로교설계기준으로부터 유도된 값보다 작아 보수적인 설계를 유도하였다. 또한, 이 연구에서 제시한 최대철근간격은 직접균열제어와 간접균열제어 사이의 차이를 제거하여 해석의 일관성을 확보할 수 있는 것으로 판단된다.

• International Journal of Concrete Structures and Materials
• /
• 제10권4호
• /
• pp.407-424
• /
• 2016

This study tests ten full-size simple-supported beam specimens with the high-strength reinforcing steel bars (SD685 and SD785) using the four-point loading. The measured compressive strength of the concrete is in the range of 70-100 MPa. The main variable considered in the study is the shear-span to depth ratio. Based on the experimental data that include maximum shear crack width, residual shear crack width, angle of the main crack and shear drift ratio, a simplified equation are proposed to predict the shear deformation of the high-strength reinforced concrete (HSRC) beam member. Besides the post-earthquake damage assessment, these results can also be used to build the performance-based design for HSRC structures. And using the allowable shear stress at the peak maximum shear crack width of 0.4 and 1.0 mm to suggest the design formulas that can ensure service-ability (long-term loading) and reparability (short-term loading) for shear-critical HSRC beam members.

• 동력기계공학회지
• /
• 제19권1호
• /
• pp.45-49
• /
• 2015

This study focuses on the crack-healing behavior and bending strength of SiC ceramics with sintering additives of $SiO_2$colloid. Optimized crack-healing condition was found to be 1hr at an atmosphere of 1373 K. The maximum crack size that can be healed at the optimized condition was a semi-elliptical surface crack of $450{\mu}m$ in diameter. After heat treatment at the optimum temperature in air, the crack morphology almost entirely disappeared and the strength recovered to the value of the smooth specimens at room temperature for the investigated crack sizes up to $450{\mu}m$. The crack with width $1.4{\mu}m$ can be completely heal the surface crack.