• Structural Engineering and Mechanics
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• v.63 no.1
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• pp.55-64
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• 2017

The paper concerns concrete carbonation, the phenomena that occurs in every type of climate, especially in urban-industrial areas. In European Standards, including Eurocode (EC) for concrete structures the demanded durability of construction located in the conditions of the carbonation threat is mainly assured by the selection of suitable thickness of reinforcement cover. According to EC0 and EC2, the thickness of the cover in the particular class of exposure depends on the structural class/category and concrete compressive strength class which is determined by cement content and water-cement ratio (thus the quantitative composition) but it is not differentiated for various cements, nor additives (i.e., qualitative composition), nor technological types of concrete. As a consequence the selected thickness of concrete cover is in fact a far estimation - sometimes too exaggerated (too safe or too risky). The paper presents the elaborated "self-terminated carbonation model" that includes abovementioned factors and enables to indicate the maximal possible depth of carbonation. This is possible because presented model is a hyperbolic function of carbonation depth in time (the other models published in the literature use the parabolic function that theoretically assume the infinite increase of carbonation depth value). The paper discusses the presented model in comparison to other models published in the literature, moreover it contains the algorithm of concrete cover design with use of the model as well as an example of calculation of the cover thickness.

• Proceedings of the Korea Concrete Institute Conference
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• 1999.04a
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• pp.653-658
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• 1999

Bond between reinforcing bars and the surrounding concrete is supposed to safely transfer load in the design process of reinforced concrete structures. Bond failure of reinforcing bars generally take place by splitting of concrete cover as bond force between concrete and reinforcing bars exceeds the resistance by the confinement of the concrete cover and transverse reinforcement. Confinement, concrete cover and transverse reinforcement, on bond are the key factor of current provision to determine development length of reinforcing bars to concrete. In this study, previous available data are analyzed with respect to the current provisions for development and splice of reinforcement. From this study, the new provision for the design are proposed, which will be efficient and effective with some specific limit value.

• International Journal of Concrete Structures and Materials
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• v.3 no.2
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• pp.103-110
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• 2009

Concrete carbonation is a cause of problems in concrete structures, so it needs to be estimated. And concrete cover is designed to protect structures from this damaging. Usually the cover thickness is considered based on the limit states design codes in which the important target is the reliability safety index. However, it is not clear that whether the safety index determined is optimal or not with respect to the cost. The codes are mainly proceeded quantitatively (i.e. making a safe structure) while the economic aspects are only considered qualitatively. So the reliability-based design considering life cycle cost (LCC) is called for, and here the focus is on the advanced analysis solution to optimize the reliability safety regarding LCC.

• Computers and Concrete
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• v.3 no.2_3
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• pp.145-161
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• 2006

This article involves architecting prototype-fuzzy expert system for designing the nominal cover thickness by means of fuzzy inference for quantitatively representing the environment affecting factor to reinforced concrete in chloride-induced corrosion environment. In this work, nominal cover thickness to reinforcement in concrete was determined by the sum of minimum cover thickness and tolerance to that defined from skill level, constructability and the significance of member. Several variables defining the quality of concrete and environment affecting factor (EAF) including relative humidity, temperature, cyclic wet and dry, and the distance from coast were treated as fuzzy variables. To qualify EAF the environment conditions of cycle degree of wet-dry, relative humidity, distance from coast and temperature were used as input variables. To determine the nominal cover thickness a qualified EAF, concrete grade, and watercement ratio were used. The membership functions of each fuzzy variable were generated from the engineering knowledge and intuition based on some references as well as some international codes of practice.

• International Journal of Concrete Structures and Materials
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• v.18 no.1E
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• pp.49-54
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• 2006

Confinement is major contribution to bond strength between reinforcement steel bars and concrete. Cover thickness, bar spacing and transverse reinforcement are the key confinement factors of current provisions for the development and splices of reinforcement. However, current provisions are still too complicated to determine the values of the confinement, which need to be well delineated in the process of design. In this study, an experimental work using beam-end and splice specimens was performed to examine the effect of concrete cover on bond strength. The results of this experiment and previously available data are analyzed to identify the effects of confinement on bond strength. From this reevaluation, new provisions for the development and splices of reinforcement are proposed. The provisions suggest some limitations in the confinement index. The new provisions will allow the engineers to use a simple and yet satisfactory and appropriate method or a precise approach for design to determine the values of confinement on the calculation of development and splice lengths.

• Journal of the Society of Disaster Information
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• v.11 no.2
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• pp.253-261
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• 2015

Deterioration of reinforced concrete structures in corrosive environment is tend to be accelerated due to ingress of aggressive ion such as chloride ion. Chloride-induced corrosion is affected by various factors such as cover concrete qualities, width of existing cracks, and cover depth of concrete. However, the allowable crack width of RC structure in design code does not consider the concrete material properties and conditions of construction except the cover depth. In this paper, an equation for allowable crack width is proposed to consider the cover concrete quality, crack width, and cover depth. Crack width, cover depth, and water-cement ratio of concrete are selected as influencing factors on corrosion of reinforcement for rapid chloride tests. From test results, the relationships between the factors and corrosion are derived. Finally, the equation for allowable crack width is derived in terms of concrete compressive strength and cover depth. The presented equation is verified by comparative calculations with design code variables.

• Journal of the Korea Concrete Institute
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• v.17 no.1 s.85
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• pp.157-166
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• 2005

This article involves architecting prototype-fuzzy expert system for designing the nominal cover thickness by means of fuzzy inference for quantitatively representing the environment affecting factor to reinforced concrete in chloride-induced corrosion environment. In this work, nominal cover thickness to reinforcement in concrete was determined by the sum of minimum cover thickness and tolerance to that defined from skill level, constructability and the significance of member. Several variables defining the quality of concrete and environment affecting factor (EAF) including relative humidity, temperature, cyclic wet and dry, and the distance from coast were treated as fuzzy variables. To qualify EAF the environment conditions of cycle degree of wet-dry, relative humidity, distance from coast and temperature were used as input variables. To determine the nominal cover thickness a qualified EAF, concrete grade, and water-cement ratio were used. The membership functions of each fuzzy variable were generated from the engineering knowledge and intuition based on some references as well as some international codes of practice.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.05a
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• pp.345-350
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• 2001

Reinforced concrete is, in general, known as a high durability material due to a strong alkalinity of cement. Probable concrete cracks could incur steel corrosion of RC structures and then could easily deteriorate the concrete durability, which can be fully secured by a systematic quality control for the construction of concrete structures. For the corrosion protection of reinforcing steels in concrete, however, current design specifications of concrete cover depth do not in-depth consider the effect of the cracks as well as the chloride content of RC structures. Therefore, appropriate provisions for concrete cover depth should be coded by considering the influence of concrete cracks on the corrosion of reinforcing steels. The objective of this research is to investigate pertinent cover depth, which can prohibit rebar corrosion, on the basis of experimental corrosion measurements of reinforcing steels on crack characteristics such as the width, depth and frequency of concrete cracks.

• Structural Engineering and Mechanics
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• v.36 no.4
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• pp.447-461
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• 2010

Fiber reinforced polymer (FRP) bars have been widely used as reinforcement for concrete structures. However, under elevated temperatures, the difference between the transverse coefficients of thermal expansion of FRP rebars and concrete may cause the splitting cracks of the concrete cover. As a result, the bonding of FRP-reinforced concrete may not sustain its function to transfer load between the FRP rebar and the surrounding concrete. The current study investigates the cracking resistance of FRP reinforced concrete against the thermal expansion based on a mechanical model that accounts for the tensile softening behavior of concrete. To evaluate the efficacy of the proposed model, the critical temperature increments at which the splitting failure of the concrete cover occurs and the internal crack radii estimated are compared with the results obtained from the previous studies. Simplified equations for estimating the critical temperature increments and the minimum concrete cover required to prevent concrete splitting failure for a designated temperature increment are also derived for design purpose.

• Smart Structures and Systems
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• v.17 no.4
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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.