• Journal of the Korea institute for structural maintenance and inspection
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• v.12 no.2
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• pp.131-138
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• 2008

Fiber-reinforced polymer (FRP) sheets have been successfully used to retrofit a number of existing concrete buildings and structures because of their excellent properties (high strength, light weight and high durability). Bond characteristics between FRP sheets and concrete should be investigated to ensure an effective retrofitting system. RC structures strengthened with FRP sheets are often subjected to cyclic load (traffic, seismic, temperature, etc.). This research addresses a local bond stress-slip relationship under cyclic loading conditions for the FRP-concrete interface. 18 specimens were prepared with three types of FRP sheets (aramid, carbon, and polyacetal) and two types of sheet layer(one or two). The characteristics of bond stress-slip were verified through experimental results on load-displacement relationship.

• Journal of the Korean Society for Advanced Composite Structures
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• v.7 no.1
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• pp.25-31
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• 2016

Bond stress between cast-in-place ductile fiber reinforced cementitious composites and CFRP plank were experimentally analyzed. As failure shape, the mixture of failure between CFRP plank and epoxy, and failure between concrete and epoxy was shown. In case of RFCON from the suggested simple bond slip relationship, the maximum average bond stress was 5.39MPa, the initial slope was 104.09MPa/mm, and the total slip length was 0.19mm. PPCON showed the maximum average bond stress of 4.31MPa, the initial slope of 126.67MPa/mm, and the total slip length of 0.26mm, while RFCON+ appeared to have 8.71MPa, 137.69MPa/mm, 0.16mm. PPCON+ had 6.19MPa maximum average bond stress, 121.56MPa/mm initial slope, and 0.34mm total slip length. To comprehend the behavior of composite structure of FRP and concrete, local bond slip relation is necessary, and thus a simple relation is suggested to be easily applied on hybrid composite system.

• Journal of the Korean Recycled Construction Resources Institute
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• v.11 no.1
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• pp.39-47
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• 2023

The demand for lightweight and high-strength materials is increasing. However, studies on the bond of concrete and reinforcing bars for high-strength lightweight concrete with a compressive strength of 120 MPa and a unit weight of 20 kN/m³ to structural members are lacking. Therefore, in this paper, 108 specimens of high-strength lightweight concrete with a compressive strength of 120 MPa and a unit weight of about 20 kN/m³ were fabricated, a direct pull-out test was performed, and the bond characteristics were evaluated by comparing the test results with design code. Compared to the decrease in unit weight, the solid bubble shows relatively little reduction in compressive strength and modulus of elasticity. It was f ound to have larger slip and parameter values than concrete with low compressive strength and unit weight.

• Journal of the Korea Concrete Institute
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• v.18 no.5 s.95
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• pp.579-588
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• 2006

In recent years, the availability of high-strength reinforcing and prestressing steels leads us to build economically and efficiently designed concrete structural members. One of critical problems faced to the structural engineers dealing with these types of structural member is controls of crack width that is used as a criterion for the serviceability in the limit state design. Especially, flexural cracking must be controlled to secure the structural safety and to improve the durability as well as serviceability of the load carving members. The proposed method utilizes the results of pure tension test in which tensile loads are applied both side of specimen, done by Ikki. The bond characteristics of deformed reinforcing bar under pure tension is considered by the area of concrete and rib area. The results of proposed method are compared with the test data and the results show that the proposed method can take into account the dimensions, variation of sectional properties, and direction of reinforcing and gives more accurate maximum bond stress and corresponding relative slip than the existing methods. the characteristics of bonding is considered by using dimensionless slip magnitude and effective reinforcement ratio. The validity of the proposed equation is verified by test experimental data.

• Journal of the Korea Concrete Institute
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• v.15 no.1
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• pp.17-24
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• 2003

One of the reasons for brittle failure in reinforced concrete structures subjected to severe earthquake is due to large local bond-slippage of bars resulting in fast bond degradation between reinforcing bars and concrete. This study aims to evaluate effects of bar deformation height on bond performance, specially, bond degradation under cyclic loading. Bond test specimens were constructed with machined bars with high relative rib areas. The degree of confinement by transverse bars is also another key parameters in this bond test. From test results, amounts of energy dissipation are calculated and compared for each parameter. Test results show that bond strength and stiffness drops significantly as cycles increases. The confinement and high relative rib area are effective to delay bond degradation, as the reduction of bond strength of cyclic loading compared to monotonic loading decreased for bars with large confinement and high relative rib areas. The energy dissipation also increases as the degree of confinement and relative rib area increases. However, tested bars with very high rib areas show that the bond may be damaged at relatively small slip because of high stiffness. The study will help to understand the bond degradation mechanism due to bar deformation height under cyclic loading and be useful to develop new deformed bars with high relative rib areas.

• Journal of the Korea Concrete Institute
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• v.24 no.4
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• pp.445-452
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• 2012

In this study, experimental research was carried out to evaluate the structural performance of the reinforced concrete beam using strengthening materials (embedded FRP rod, metal fittings) in existing reinforced concrete buildings. Seven reinforced concrete beams comprised of retrofitted embedded FRP rod (BCR series), embedded FRP rod with metal fittings (BCR-AC series), and standard specimen (BSS) were constructed and tested under monotonic loading. Design parameters of test specimens were amount of embedded FRP rod and metal fittings. The test results showed that the maximum load carrying capacity of specimens with embedded FRP rod (BCR series) and embedded FRP rod with metal fittings (BCR-AC series) increased by 21~55% and 21~63%, respectively, in comparison with the standard specimen BSS. BCR series test specimens failed by the adhesion slip and concrete cover separation. BCR-AC series test specimens failed by the adhesion slip due to the confining effect of metal fittings.

• Proceedings of the Korea Concrete Institute Conference
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• 2008.04a
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• pp.249-252
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• 2008

A study for the nonlinear analysis method of RC(Reinforced Concrete) beams with unbonded prestressing CFRP plate is presented. The cross-section of RC beam element is idealized as an assemblage of concrete and reinforcing steel fibers in order to account for varied material properties within the cross-section of the element. The unbonded CFRP plate is modeled as a series of the CFRP plate segments each of which is linked to the RC beam element, but slips without any resistance to simulate the unbonded behavior of the CFRP plate. The stress of each CFRP plate segment is redistributed iteratively using the force equilibrium relationship at each common node until it reaches at the same stress level. To evaluate the validity of the proposed analysis method, the results of ultimate analysis of the reinforced concrete beams with unbonded prestressing CFRP plates are compared with the experimental results obtained from other investigators. The proposed analysis method is found to predict ultimate behaviors of these beams fairly well.

• Journal of the Korea institute for structural maintenance and inspection
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• v.14 no.3
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• pp.100-107
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• 2010

This study evaluates the bond behavior of reinforced concrete (RC) beams using recycled coarse aggregates. A total of four specimens were cast and tested. The test parameter was the type of coarse aggregates, that is, natural and recycled coarse aggregates, and the absorption ratio of recycled coarse aggregate. The recycled coarse aggregates with absorption ratios of 3% and 6% were used in this test. The specimens were simply supported and were subjected to a concentrated load. A test method proposed by Ichinose was adopted to estimate effectively the bond properties of specimens. From the experimental results, it was found that there was no difference of bond characteristics according to the absorption ratio of recycled coarse aggregates.

• Journal of the Korea Concrete Institute
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• v.16 no.1 s.79
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• pp.10-17
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• 2004

Shear tests were performed on four ends of full scale U-type beams which were designed by optimum process for the depth with a live load of 4903Pa. The ratio of width to depth of full scale 10.5 m-span, composite U-type beams with topping concrete was greater than 2. Following conclusions were obtained from the evaluation on the shear performance of these precast prestressed beams. 1) Those composite U-type beams performed homogeneously up to the failure load, and conformed to ACI Strength design methods in shear and flexural behaviors. 2) The anchorage requirements on development length of strand In the ACI Provisions preyed to be a standard to determine a failure pattern within the limited test results of the shallow U-type beams. 3) Those all shear crackings developed from the end of the beams did not lead to anchorage failure. However, initiated strand slip may leads the bond failure by increasing the size of diagonal shear crackings. 4) The flexural mild reinforcement around the vertical center of beam section was effective for developments of a ductile failure.

• Journal of the Korea Concrete Institute
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• v.21 no.6
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• pp.773-780
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• 2009

Experiments on steel-concrete interface are performed to investigate and determine the mechanical roles and properties of interface parameters. The intrinsic different nature of bonded and unbonded interfaces are addressed based on the experimental observations that were obtained from two types of tests considering bonded and unbonded interfaces. The unbonded tests are performed for the specimens that are in unbonded when the initially bonded specimens are tested first. Four cases of lateral confinements including pure slip, and low and medium levels of lateral pressure are taken into account to investigate the effects of lateral confinements on interface behavior. It is shown that the maximum shear strengths, the levels of residual strengths and the Mode II fracture energy release rates are linearly related to the confinement levels. Based on the experimental evidences obtained from this study, the values of interface parameters required in a steel-concrete interface constitutive model will be presented in the companion paper.