• Computers and Concrete
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• v.15 no.2
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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.

• Journal of the Korea Concrete Institute
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• v.11 no.6
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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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• 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.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2010.05a
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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.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.11a
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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.

• Fire Science and Engineering
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• v.25 no.1
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• pp.78-84
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• 2011

Recent researches of the fire resistance in concrete focus on how to secure relevant functions in the high strength concrete. However, the demand of normal strength concrete less than 40 MPa takes most of the total concrete demand. Therefore, fire resistance study needs to cover not only high strength concretes but also normal strength concretes. This study evaluated the fire resistance performance of 40 MPa concrete columns, taking the concrete covering thickness and the size of section as variables. Consequently, the fire resistance performance improved as the section size and the covering thickness became larger.

• Journal of the Korea institute for structural maintenance and inspection
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• v.12 no.2
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• pp.49-58
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• 2008

Generally, steel corrosion occurs in concrete structures due to carbonation in down-town area and underground site and it propagates to degradation of structural performance. In general diagnosis and inspection, only carbonation depth in sound concrete is evaluated but unsound concrete such as joint and cracked area may occur easily in a concrete member due to construction process. In this study, field survey of carbonation for RC columns in down-town area is performed and carbonation depth in joint and cracked concrete including sound area is measured. Probability of durable failure with time is calculated through probability variables such as concrete cover depth and carbonation depth which are obtained from field survey. In addition, service life of the structures is predicted based on the intended probability of durable failure in domestic concrete specification. It is evaluated that in a RC column, various service life is predicted due to local condition and it is rapidly decreased with insufficient cover depth and growth of crack width. It is also evaluated that obtaining cover depth and quality of concrete is very important because the probability of durable failure is closely related with C.O.V. of cover depth.

• Journal of the Korean Recycled Construction Resources Institute
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• v.11 no.1
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• pp.79-88
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• 2023

In this study, a development of the rust formation arising from steel corrosion was modelled to quantify the structural impact in steel reinforced concrete. The interfacial gap, cover depth and diameter of steel rebar were taken for variables in modelling. It was found that the interfacial gap was the most influencing on the structural limit at steel corrosion, followed by steel diameter and cover depth. At 75 mm of cover depth with 20 mm of the steel diameter, the rust amount to reach cracking accounted for 16.95-27.69 ㎛ to 1-10 ㎛ of the interfacial gap. It was found that there was no risk of cracking and structural limit until the rust was formed within the interfacial gap. With a further formation of rust, the concrete section was successively behaved to yielding, cracking and failure. Additionally, the interfacial gap was the most dominant parameter for the rust amount to reach the cracking of concrete at the interfacial zone, whilst the cover depth had a marginal effect on cracking but had a crucial influence on the rust to failure.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2006.05a
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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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• v.6 no.1
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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.