• Proceedings of the Korea Concrete Institute Conference
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• 1998.04b
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• pp.421-426
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• 1998

Current code provisions for the development of positive moment reinforcement is reviewed and criticized in this paper. Both the flexural bond and development length concepts are neccesary to consider anchorage requirement of reinforcement at beam ends. The curent design codes show unconservatism for the detailing of reinforcement at the beam ends. This study proposes a new design formula for the development of positive moment reinforcement.

• Computers and Concrete
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• v.2 no.1
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• pp.1-18
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• 2005

This paper presents a study on the effects of localized steel-concrete bond degradation on the flexural behaviour of RC beams. A finite element analysis is undertaken to complete the experimental analysis. The first part deals with an experimental study on beams where bond was removed by using plastic tube at different locations and for various lengths. The flexural behaviour was studied at global scale (load-deflection) and local scale (moment-curvature). The second part, a numerical study using a simplified special finite element (rust element) modelling the rust layer occurring between reinforcement and concrete with corrosion was conducted in order to find the relation between the degree of corrosion and the degradation of the steel-concrete bond. The computed value of the corrosion degree corresponding to the total degradation of bond has been used in a second time to model the tests, in order to evaluate the influence of the loss of bond, the steel cross section reduction, and the combination of both. The results enable to evaluate the influence of the different corrosion effects on the flexural behaviour, according to the length and the location of the corroded zone.

• Structural Engineering and Mechanics
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• v.5 no.4
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• pp.339-353
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• 1997

Fiber reinforced plastic (FRP) rods provide certain benefits over steel as concrete reinforcement, such as corrosion resistance, magnetic and electrical insulation, light weight, and high strength. FRP composites can be combined with a steel core to form hybrid reinforcing rods that take advantage of properties of both materials. The objective of this study was to characterize the bond behavior of hybrid FRP rods made with braided epoxy-impregnated aramid or poly-vinyl alcohol FRP skins. Eleven rod types were tested using two concrete strengths. Specific topics examined were bond strength, slip, and type of failure in concentric pull-out tests from concrete cubes. From analysis of identical pull-out tests on both hybrid and steel rods, information on relative bond strength and behavior were obtained. It is concluded that strength is similar but slip in hybrid rods is much higher. Hybrid rods failed either by pull-out or splitting the concrete block (with or without yielding of the steel core). Experimental data showed consistency with similar test results presented in the literature.

• Journal of the Korea Concrete Institute
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• v.22 no.4
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• pp.527-534
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• 2010

This study presents a simple method to improve the bond performance of reinforced concrete (RC) beams having high-strength shear reinforcement. In general, the yield strength and the ratio of shear reinforcements are the main parameters governing the shear capacity of RC beams. The yield strength of shear reinforcement, however, has little influence on the bond capacity of RC beams. Therefore, a sudden bond failure of the members with high-strength shear reinforcement can occur before flexural failure. To estimate the structural performance of the proposed method, four RC beams were cast and tested. The main test parameters were the yield strength, ratio, and reinforcing types of shear reinforcements. The experimental results indicated that the proposed method was able to effectively improve the bond performance of RC beams with high-strength shear reinforcement.

• Proceedings of the Korea Concrete Institute Conference
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• 1998.04b
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• pp.653-660
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• 1998

Bond strength of reinforcing bar to high-performance concrete using belite cement is explored using beam end test specimen. The key parameters for the bond test are slump of concrete, top bar effect, and strength of concrete in addition to concrete covers. Specimen failed in the typical brittle bond failure splitting the concrete cover as the wedging action. The test results show that the specimens with belire cement concrete show higher bond strength than those with portland cement concrete. Bond strength of the top bar is less than bond strength of bottom bar, but the top bar factor satisfies the modification factor for top reinforcement. The results also show that the bond strength is function of the square root of concrete compressive strength and cover thickness. The recently developed high-strength and high-slump concrete with belite cement performs well in terms of bond strength to reinforcing steel.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.05a
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• pp.478-481
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• 2004

An experimental investigation on the relationship between corrosion of reinforcement and bond strength in pull-out test specimen has been conducted to establish the allowable limit of rust of reinforcement in the construction field. The reinforcing bars used in this study were rusted before embedded in pull-out test specimen. The first component of this experiment is to make reinforcing bar rust electrically based on Faraday's theory to be 2, 4, 6, 8 and $10\%$ of reinforcing bar weight. For estimation of the amount of rust by weight, Clarke's solution and shot blasting were adopted and compared. Parameters also include 24 and 45MPa of concrete compressive strengths and diameter of reinforcing bar (16, 19 and 25mm). Pull-out tests were carried out according to KS F 2441 and ASTM C 234. Results show that up to $2\%$ of rust increases the bond strength regardless of concrete strength and diameter of reinforcing bar. As expected, the bond strength increases as compressive strength of concrete increases and the diameter of bar decreases.

• Proceedings of the Korea Concrete Institute Conference
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• 2005.11a
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• pp.189-192
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• 2005

Glass fiber reinforced polymer (GFRP) bars gain increasingly more attention as a reinforcing option for concrete because of their corrosion resistance and non-magnetism. GFRP reinforcement for concrete does not have the same shape as steel reinforcement. Therefore, the bond performance of FRP bars, unlike that of steel, is dependent on their design, manufacture and mechanical properties. This paper studied the effect of high strength concrete on the bond strength of GFRP bars. Twenty-nine specimens having different compressive strength of concrete were tested in order to examine the bond behavior of GFRP bars.

• Structural Engineering and Mechanics
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• v.5 no.5
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• pp.663-677
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• 1997

Bond-slip behavior between reinforcement and concrete under push-pull cyclic loadings is numerically investigated based on a reinforcement model proposed in this paper. The equivalent reinforcing steel model considering the bond-slip effect without taking double nodes is derived through the equilibrium at each node of steel and the compatibility condition between steel and concrete. Besides a specific transformation algorithm is composed to transfer the forces and displacements from the nodes of the steel element to the nodes of the concrete element. This model first results in an effective use in the case of complex steel arrangements where the steel elements cross the sides of the concrete elements and second turns the impossibility into a possibility in consideration of the bond-slip effect in three dimensional finite element analysis. Finally, the correlation studies between numerical and experimental results under the continuously repeated large deformation stages demonstrate the validity of developed reinforcing steel model and adopted algorithms.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.5A
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• pp.511-518
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• 2009

This study was intended to compare and evaluate the adhesion of High flowing Self-compacting Concrete (HSCC), Conventional Concrete (CC) and deformed bar based on concrete strength 3 (30, 50 and 70 MPa), among the factors affecting the bond strength between concrete and rebar, after fabricating the specimen by modifying the rebar position at Horizontal reinforcement at bottom position (HB), horizontal reinforcement at top position (HT) and vertical reinforcement type (V). As a result of measuring bond strength of HB/HT rebar to evaluate the factor of the rebar at top position, the bond strength of HB/HT rebar at 50 and 70 MPa was 1.3 or less and at 30 MPa, HSCC and CC appeared to be 1.2 and 2,1, respectively. Thus, when designing the anchorage length according to the concrete structure design standard (2007) at HSCC 30, 50 and 70 MPa, it would be desirable to reduce the correction factor of anchorage length of the horizontal reinforcement at top position, which is suggested for the reinforcement at top position, to less than 1.3 of CC.

• Journal of the Korea Concrete Institute
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• v.16 no.5 s.83
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• pp.719-724
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• 2004

The ribs of deformed bars can split the cover concrete by wedging action or shear off the concrete in front of the ribs. As slip of deformed bars increases, the rib face angle is flattened by the crushed concrete wedge, which reduces the rib face angle to a smaller bearing angle. The roles of bearing angle are explored to simulate this observation. Analytical expressions to determine bond strength for splitting and pullout failure are derived, where the bearing angle is a key variable. As the bearing angle is reduced, splitting strength decreases and shearing strength increases. When splitting strength becomes larger than shearing strength, the concrete key is supposed to be sheared off and the bearing angle is reduced with decreasing the splitting strength. As bars slip, bearing angle decreases continually so that splitting bond strength is maintained to be less than shearing bond strength. The bearing angle is found to play a key role in controlling the bond failure and determination of bond strength of ribbed reinforcing steel in concrete structures.