• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2000년도 가을 학술발표회 논문집(II)
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• pp.873-878
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• 2000

Tension stiffening effects of reinforced concrete member with large diameter bar, mainly used at reactor building of nuclear power plant, are studied by uniaxial structural tests. Bond length and stress of steel bar, size of steel bar, and compressive strength of concrete are evaluated to tension stiffening by uniaxial tests. Problems and solution during the uniaxial test are suggested. The prevent splitting cracks, concrete cover-to-bar diameter ratio $c/d_{b}$ is kept 2.6~2.8. Because the bond length is increased as the size of steel bar, the specimen length of the D35 steel bar is required at least 2.0 m. The specimen length must be decided with bond length as well as concrete cover-to-bar diameter ratio to prevent splitting crack.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1996년도 가을 학술발표회 논문집
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• pp.127-132
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• 1996

Recently in the country a corrosion of steel is accelerated due to using of sea sand including salts, and critical problem on the durability of concrete structure is occured. Thus a control of steel corrosion is very important in the stability of structure. Coated steel is in use with a method of steps of steel corrosion in U.S,A. Japan etc, and as well in domestic case the manufactured coating steel of three types is on the market. Those are Epoxy coated steel, Zinc-strength, concrete specimen size, bar diameter, which can affect bond characteristics between steel and concrete in order to know their relative bond characteristics.

• Advances in concrete construction
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• 제1권4호
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• pp.273-288
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• 2013

The main objective of this research was to evaluate the potentials of self-compacting concrete (SCC) mixes to develop bond strength. The investigated mixes incorporated relatively high contents of dolomite powder replacing Portland cement. Either silica fume or fly ash was used along with the dolomite powder in some mixes. Seven mixes were proportioned and cast without vibration in long beams with 10 mm and 16 mm steel dowels fixed vertically along the flowing path. The beams were then broken into discrete test specimens. A push-put configuration was adopted for conducting the bond test. The variation of the ultimate bond strength along the flowing path for the different mixes was evaluated. The steel-concrete bond adequacy was evaluated based on normalized bond strength. The results showed that the bond strength was reduced due to Portland cement replacement with dolomite powder. The addition of either silica fume or fly ash positively hindered further degradation as the dolomite powder content increased. However, all SCC mixes containing up to 30% dolomite powder still yielded bond strengths that were adequate for design purpose. The test results demonstrated inconsistent normalized bond strength in the case of the larger diameter compared to the smaller one.

• Structural Engineering and Mechanics
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• 제3권4호
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• pp.299-312
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• 1995

A new reinforcing steel model which is embedded inside a concrete element and also accounts for the effect of bond-slip is developed. Unlike the classical bond-link or bond-zone element using double nodes, the proposed model is considering the bond-slip effect without taking double nodes by incorporation of the equivalent steel stiffness. After calculation of nodal displacements, the deformation of steel at each node can be found through the back-substitution technique from the first to the final steel element using a governing equation constructed based on the equilibrium at each node of steel and the compatibility condition between steel and concrete. This model results in significant savings in the number of nodes needed to account for the effect of bond-slip, in particular, when the model is used for three dimensional finite element problems. Moreover a new nonlinear solution scheme is developed in connection with this model. Finally, correlation studies between analytical and experimental results and several parameter studies are conducted with the objective to establish the validity of the proposed model.

• Computers and Concrete
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• 제29권3호
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• pp.145-159
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• 2022

In this study, the extreme learning machine and deep learning models were devised to estimate the bond strength of corroded reinforcement in concrete. The six inputs and one output were used in this study. The compressive strength, concrete cover, bond length, steel type, diameter of steel bar, and corrosion level were selected as the input variables. The results of bond strength were used as the output variable. Moreover, the Analysis of variance (Anova) was used to find the effect of input variables on the bond strength of corroded reinforcement in concrete. The prediction results were compared to the experimental results and each other. The extreme learning machine and the deep learning models estimated the bond strength by 99.81% and 99.99% accuracy, respectively. This study found that the deep learning model can be estimated the bond strength of corroded reinforcement with higher accuracy than the extreme learning machine model. The Anova results found that the corrosion level was found to be the input variable that most affects the bond strength of corroded reinforcement in concrete.

• Advances in concrete construction
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• 제1권1호
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• pp.103-119
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• 2013

The applicability of limit analysis methods in design and assessment of concrete structures generally requires a certain plastic deformation capacity. The latter is primarily provided by the ductility of the reinforcement, being additionally affected by the bond properties between reinforcing steel and concrete since they provoke strain localization in the reinforcement at cracks. The bond strength of reinforcing bars is not only governed by concrete quality, but also by construction details such as bar ribbing, bar spacing or concrete cover thickness. For new concrete structures, a potentially unfavorable impact on bond strength can easily be anticipated through appropriate code rules on construction details. In existing structures, these requirements may not be necessarily satisfied, consequently requiring additional considerations. This two-part paper investigates in a theoretical study the impacts of the most frequently encountered construction details which may not satisfy design code requirements on bond strength, steel strain localization and plastic deformation capacity of cracked structural concrete. The first part introduces basic considerations on bond, strain localization and plastic deformation capacity as well as the fundamentals of the Tension Chord Model underlying the further investigations. It also analyzes the impacts of the hardening behavior of reinforcing steel and concrete quality. The second part discusses the impacts of construction details (bar ribbing, bar spacing, and concrete cover thickness) and of additional structure-specific features such as bar diameter and crack spacing.

• Steel and Composite Structures
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• 제19권1호
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• pp.21-41
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• 2015

Push-out tests have been conducted on 18 rectangular concrete-filled steel tubular (CFST) columns with the aim of studying the bond behaviour between the steel tube and the concrete infill. The obtained load-slip response and the distribution of the interface bond stress along the member length and around the cross-section for various load levels, as derived from measured axial strain gradients in the steel tube, are reported. Concrete compressive strength, interface length, cross-sectional dimensions and different interface conditions were varied to assess their effect on the ultimate bond stress. The test results indicate that lubricating the steel-concrete interface always had a significant adverse effect on the interface bond strength. Among the other variables considered, concrete compressive strength and cross-section size were found to have a pronounced effect on the bond strength of non-lubricated specimens for the range of cross-section geometries considered, which is not reflected in the European structural design code for composite structures, EN 1994-1-1 (2004). Finally, based on nonlinear regression of the test data generated in the present study, supplemented by additional data obtained from the literature, an empirical equation has been proposed for predicting the average ultimate bond strength for SHS and RHS filled with normal strength concrete.

• Steel and Composite Structures
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• 제33권6호
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• pp.823-836
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• 2019

Spiral welded tubes (SWTs) are fabricated by helically bending a steel plate and welding the resulting abutting edges. The cost-effectiveness of concrete-filled steel tube (CFST) columns can be enhanced by utilising such SWTs rather than the more conventional longitudinal seam welded tubes. Even though the steel-concrete interface bond strength of such concrete-filled spiral-welded steel tubes (CF-SWSTs) is an important consideration in relation to ensuring composite behaviour of such elements, especially at connections, it has not been investigated in detail to date. CF-SWSTs warrant separate consideration of their bond behaviour to CFSTs of other tube types due to the distinct weld seam geometry and fabrication induced surface imperfection patterns of SWTs. To address this research gap, axial push-out tests on forty CF-SWSTs were carried out where the effects of tube material, outside diameter (D), outside diameter to wall thickness (D/t), length of the steel-concrete interface (L) and concrete strength grade (f'_c) were investigated. D, D/t and L/D values in the range 102-305 mm, 51-152.5 and 1.8-5.9 were considered while two nominal concrete grades, 20 MPa and 50 MPa, were used for the tests. The test results showed that the push-out bond strengths of CF-SWSTs of both mild-steel and stainless-steel were either similar to or greater than those of comparable CFSTs of other tube types. The bond strengths obtained experimentally for the tested CF-SWSTs, irrespective of the tube material type, were found to be well predicted by the guidelines contained in AISC-360.

• 콘크리트학회논문집
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• 제11권6호
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• pp.129-135
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• 1999

Reinforced concrete structures are constructed under the basic assumption of perfect bonding between steel and concrete. The corrosion of steel in the reinforced concrete beams results in the excessive cracks and gradual deterioration of concrete. This paper are concerned about the slip characteristics of reinforced concrete between steel and concrete. The accelerated test by external power supply was conducted with the three corrosion rates in the laboratory. As a result, it was obtained as follows: (1) the yield strength of steel was reduced according to corrosion states. (2) the equivalent steel area should be considered for detailed analysis. (3) According to the use of corroded steel or not, slip amounts between concrete and steel in test beams increased as the corrosion rate increased. These results can be explained from the bond loss between concrete and steel in test beams.

• 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.