• Structural Engineering and Mechanics
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• 제32권2호
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• pp.251-267
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• 2009

Reinforced concrete (RC) structures consist of two different materials: concrete and steel bar. The stress transfer behaviour between the two materials through bond plays an important role in the load-carrying capacity of RC structures, especially when they subject to lateral load such as blast and seismic load. Therefore, bond and slip between concrete and reinforcement bar will affect the response of RC structures under such loads. However, in most numerical analyses of blast-induced structural responses, the perfect bond between concrete and steel bar is often assumed. The main reason is that it is very difficult to model bond slip in the commercial finite element software, especially in hydrodynamic codes. In the present study, a one-dimensional slide line contact model in LS-DYNA for modeling sliding of rebar along a string of concrete nodes is creatively used to model the bond slip between concrete and steel bars in RC structures. In order to model the bond slip accurately, a new approach to define the parameters of the one-dimensional slide line model from common pullout test data is proposed. Reliability and accuracy of the proposed approach and the one-dimensional slide line in modelling the bond slip between concrete and steel bar are demonstrated through comparison of numerical results and experimental data. A case study is then carried out to investigate the bond slip effect on numerical analysis of blast-induced responses of a RC column. Parametric studies are also conducted to investigate the effect of bond shear modulus, maximum elastic slip strain, and damage curve exponential coefficient on blast-induced response of RC columns. Finally, recommendations are given for modelling the bond slip in numerical analysis of blast-induced responses of RC columns.

• Proceedings of the Korea Concrete Institute Conference
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• 한국콘크리트학회 2002년도 봄 학술발표회 논문집
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• pp.965-970
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• 2002

The strengthening of concrete structures in situ with externally bonded carbon fiber is increasingly being used for repair and rehabilitation of existing structures. Carbon fiber is attractive for this application due to its good tensile strength, resistances to corrosion, and low weight. Generally bond strength and behavior between concrete and carbon fiber mesh(CFM) is very important, because of the enhanced bond of CFM. Therefore if bond strength is sufficient, it will be expected to enhance reinforcement effect. If insufficient, reinforcement effect can not be enhanced because of bond failure between concrete and CFM. This study is to investigate the bond strength of CFM to the concrete using direct pull-out test and tensile-shear test. The key variables of the experiment are the location of clip, number of clips and thickness of cover mortar. The general results indicate that the clip anchorage technique for increasing bond strength with CFM appear to be effective to maintain the good post-failure behavior.

• Journal of the Korea Concrete Institute
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• 제11권4호
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• pp.129-136
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• 1999

For the prediction of concrete-steel bond ability in reinforced concrete, many countries establish specifications for the pullout test. But these methods hardly to consider many parameters such as strength, shape, diameter and location of steel, concrete restrict condition by loading plate, strength of concrete and cover depth etc, and it is difficult to solve concentration and disturbance of stress. The purpose of this study is to propose a New Ring Test method which can be rational quantity evaluations of bond splitting mechanism. For this purpose, pullout test was carried out to assess the effect of several variables on bond splitting properties between reinforcing bar and concrete. Key variables are concrete compressive strength, concrete cover, bar diameter and rib spacing. Failure mode was examined and maximum bond stress-slip relationships were presented to show the effect of above variables. As the result, it appropriately expressed general characteristics of bond splitting mechanism, and it proved capability for standard test method.

• Structural Engineering and Mechanics
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• 제72권3호
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• pp.305-312
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• 2019

This paper investigates the effect of utilizing vacuum bagging process to enhance the bond behavior between fiber reinforced polymer (FRP) composites and concrete substrate. Sixty specimens were prepared and tested using double-shear bond test. The effect of various parameters such as vacuum, fiber type, and FRP sheet length and width on the bond strength were investigated. The experimental results revealed that utilizing vacuum leads to improve the bond behavior between FRP composites and concrete. Both the ultimate bond forces and the maximum displacements were enhanced when applying the vacuum which leads to reduction in the amount of FRP materials needed to achieve the required bond strength compared with the un-vacuumed specimens. The efficiency of the enhancement in bond behavior due to vacuum highly depends on the fiber type; using carbon fiber showed higher enhancement in the bond strength compared to the glass fiber when vacuum was applied. On the contrary, specimens with glass fiber showed higher enhancement in the maximum slippage compared to specimens with carbon fibers. Utilizing vacuum does not affect the debonding failure modes but lead to increase in the amount of attached concrete on the surface of the debonded FRP sheet.

• Advances in concrete construction
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• 제13권3호
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• pp.265-279
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• 2022

The roughness of substrate concrete interfaces before new concrete placement has a major effect on the interface bond behaviour. However, there are challenges associated with the consistency of the final roughness interface prepared using conventional roughness preparation methods which influences the interface bond performance. In this study, five quantitative interface roughness textures with different roughness tooth angles, depths, and tooth distribution were created to ensure consistency of interface roughness and to evaluate the bond behaviour at a precast and new concrete interface using the splitting tensile test, slant shear test, and double-shear test. In addition, smooth interface specimens and two separate the pitting interface roughness were also utilized. Obtained results indicate that the quantitative roughness has a very limited effect on the interface tensile bond strength if no extra micro-roughness or bonding agent is added at the interface. The roughness method however causes enhanced shear bond strength at the interface. Increased tooth depth improved both the tensile and shear bond strength of the interfaces, while the tooth distribution mainly influenced the shear bond strength. Major failure modes of the test specimens include interface failure, splitting cracks, and sliding failure, and are influenced by the tooth depth and tooth distribution. Furthermore, the interface properties were obtained and presented while a comparison between the different testing methods, in terms of bond strength, was performed.

• Journal of the Korea Concrete Institute
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• 제24권4호
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• pp.415-422
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• 2012

This paper analyzed seventy eight previous test results to evaluate bond strength of Near Surface-Mounted (NSM) FRP and prediction formulas previously proposed by researchers. The results showed that the most reliable bond strength prediction was the one proposed by Seracino, who considered the shape coefficient (ratio of width-thickness) and stiffness of FRP. However, the equation tended to underestimate the bond strength, especially serious when FRP bond length was relatively short, because the equation did not consider the effect of bond length. Based on the analysis of previous test results, the relation between bond length and bond strength and the group effect due to close proximity of FRPs were determined. Based on the findings, the Seracino's formula was modified and it's applicability was evaluated. The result showed that the suggested formula can be used effectively to predict the bond strength of NSM FRP.

• Bulletin of the Korean Chemical Society
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• 제12권2호
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• pp.182-188
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• 1991

The reactions of aniline with benzyl and phenacyl compounds are studied by the AM1 method. Two types of modeling were adopted: Cation-neutral, in which a proton is attached to the leaving group F and anion-neutral model, in which aniline was replaced by phenoxide with Cl as the leaving group. The cation-neutral model represented the reactvery well, reproducing the various solution-phase experimental results. In the benzyl system, the ${\pi}$-electrons of the two rings (X-ring in the nucleophile and Y-ring in the substrate) interact conjugatively in the transition state (TS) resulting in a bond contraction of the $C_{\alpha}-C_{Y1}$ bond (benzylic effect), whereas in the phenacyl system the ${\pi}$ electrons of the X-ring delocalizes more efficiently into the carbonyl group than into the Y-ring (resonance shunt effect) with a bond contraction of the $C_{\alpha}-C_{\beta}$ bond. The bond contraction in the benzylic effect was substantially greater than that in the resonance shunt effect. The TS was rather loose for benzyl while it was tighter for phenacyl system. Various bond length changes with substituents in the TS were, however, found to be irregular.

• The Journal of Asian Finance, Economics and Business
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• 제7권11호
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• pp.23-31
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• 2020

This paper investigates the impact of monetary policy independence shock on bond yield by allowing for heterogeneous coefficients in the model based on panel data for 19 developing countries using quarterly data from 1991 to 2016. First, we estimate the model using conventional panel VAR estimation with the assumption of homogeneous coefficients across countries. Second, by performing Chow and Roy-Zellner tests to check the homogeneity assumption, we find that the assumption does not hold in the model. Third, we apply a mean-group estimation for panel VAR as a solution for heterogeneity panel model. The results reveal that central bank independence is effective in reducing bond yield with the maximum at period 6 after the shock. Shock one standard deviation bond yield has a negative effect on consumption and investment. We determine that central bank independence has a contradictory effect on real activity; a negative effect on consumption but a positive influence on investment for the first two years after the shock. Additionally, we split our sample into three groups to make the subgroups pool. Our empirical result shows that monetary policy independence shock reduces bond yield. Meanwhile, the response of economic activity to bond yield varies for all three groups.

• Proceedings of the Korea Concrete Institute Conference
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• 한국콘크리트학회 2005년도 추계 학술발표회 제17권2호
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• pp.65-68
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• 2005

An analytical procedure to analyze reinforced concrete (RC) frame subject to cyclic as well as monotonic loadings is proposed on the basis of the layered section method. In contrast to the classical nonlinear approaches adopting the perfect bond assumption, the bond-slip effect along the reinforcing bar is quantified with the force equilibrium and compatibility condition at the post-cracking stage and its contribution is implemented into the reinforcing. The advantage of the proposed analytical procedure, therefore, will be on the consideration of the bond-slip effect while using the classical layered section method without additional consideration such as taking the double nodes. Through correlation studies between experimental data and analytical results, it is verified that the proposed analytical procedure can effectively simulate the cracking behavior of RC beams, columns and Frame accompanying the stiffness degradation caused by the bond-slip.

• Structural Engineering and Mechanics
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• 제73권4호
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• pp.437-445
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• 2020

The microstructure and mechanical properties of concrete will degrade significantly at high temperatures, thus affecting the bond strength between reinforcing steel and surrounding concrete in reinforced concrete members. In this study, the effect of individual and hybrid fiber on the local bond-slip behavior of lightweight aggregate concrete (LWAC) after exposure to elevated temperatures was experimentally investigated. Tests were conducted on local pullout specimens (150 mm cubes) with a reinforcing bar embedded in the center section. The embedment lengths of the pullout specimens were 4.2 times the bar diameter. The parameters investigated included concrete type (control group: ordinary LWAC; experimental group: fiber reinforced LWAC), concrete strength, fiber type, and targeted temperature. The test results showed that for medium-strength LWACs exposed to high temperatures, the use of only steel fibers did not significantly increase the residual bond strength. Moreover, the addition of individual and hybrid fiber had little effect on the residual bond strength of the high-strength LWAC after exposure to a temperature of 800℃.