• Computers and Concrete
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• v.14 no.3
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• pp.327-345
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• 2014

This paper presents the application of multi-gene genetic programming (MGP) technique for modeling the bond strength of ribbed steel bars in concrete. In this regard, the experimental data of 264 splice beam tests from different technical papers were used for training, validating and testing the model. Seven basic parameters affecting on the bond strength of steel bars were selected as input parameters. These parameters are diameter, relative rib area and yield strength of steel bar, minimum concrete cover to bar diameter ratio, splice length to bar diameter ratio, concrete compressive strength and transverse reinforcement index. The results show that the proposed MGP model can be alternative approach for predicting the bond strength of ribbed steel bars in concrete. Moreover, the performance of the developed model was compared with the building codes' empirical equations for a complete comparison. The study concludes that the proposed MGP model predicts the bond strength of ribbed steel bars better than the existing building codes' equations. Using the proposed MGP model and building codes' equations, a parametric study was also conducted to investigate the trend of the input variables on the bond strength of ribbed steel bars in concrete.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.05a
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• pp.443-448
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• 2001

This paper presents a bond characteristics of high strength steel reinforced concrete members. High strength steel is what yield strength is higher than that of normal strength steel. So, the amount of flexural steel needed in R.C. members can be decreased. In result, it is expected that the workability and structure quality can improve and man power can minimize. For this purpose, specimens were made and tested with experimental parameters, such as concrete strength, steel diameter and yield strength. The result showed that under same tensile force of steel, in case of substituting normal strength steel with high strength steel, maximum bond stress increased and development length didn't almost change. In addition, the governing equation of bond and bond stress verse slip relationship were derived and compared with test values such as maximum bond stress, slip and bond stiffness.

• Computers and Concrete
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• v.19 no.6
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• pp.625-630
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• 2017

In this paper, 54 pull-out specimens and 36 cubic specimens with different replacement ratios of fly ash in the concrete (i.e., 0%, 20%, 30%, 40%, 50%, 60%) were fabricated to evaluate the bond at the interface between fly ash concrete and steel rebar. The results showed that the general shape of the bond-slip curve between fly ash concrete and steel rebar was similar to that for the normal concrete and steel rebar. The bond strength between fly ash concrete and the steel rebar was closer to each other at the same rebar diameter, irrespective of the fly ash replacement percentage. On the basis of a regression analysis of the experimental data, a revised bond strength mode and bond-slip relationship model were proposed to predict the bond-slip behaviour of high volume fly ash concrete and steel rebar.

• Steel and Composite Structures
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• v.20 no.6
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• pp.1275-1303
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• 2016

Steel plates and carbon-fiber-reinforced polymer (CFRP) laminates or plates bonded to concrete substrates have been widely used for concrete strengthening. However, this technique cause plate debonding, which makes the strengthening system inefficient. The main objective of this study is to enhance the bond strength of externally bonded steel plates and CFRP laminates to the concrete surface by proposing new embedded adhesive and steel connectors. The effects of these new embedded connectors were investigated through the tests on 36 prism specimens. Parameters such as interfacial shear stress, fracture energy and the maximum strains in plates were also determined in this study and compared with the maximum value of debonding stresses using a relevant failure criterion by means of pullout test. The study indicates that the interfacial bond strength between the externally bonded plates and concrete can be increased remarkably by using these connectors. The investigation verifies that steel connectors increase the shear bond strength by 48% compared to 38% for the adhesive connectors. Thus, steel connectors are more effective than adhesive connectors in increasing shear bond strength. Results also show that the use of double connectors significantly increases interfacial shear stress and decrease debonding failure. Finally, a new proposed formula is modified to predict the maximum bond strength of steel plates and CFRP laminates adhesively glued to concrete in the presence of the embedded connectors.

• Nuclear Engineering and Technology
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• v.51 no.4
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• pp.1132-1141
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• 2019

Steel-concrete-steel (SCS) sandwich structures have important advantages over conventional concrete structures, however, bond-slip between the steel plate and concrete may lead to a loss of composite action, resulting in a reduction of stiffness and fatigue life of SCS sandwich structures. Due to the inaccessibility and invisibility of the interface, the interfacial performance monitoring and debonding detection using traditional measurement methods, such as relative displacement between the steel plate and core concrete, have proved challenging. In this work, two methods using piezoelectric transducers are proposed to detect the bond-slip between steel plate and core concrete during the test of the beam. The first one is acoustic emission (AE) method, which can detect the dynamic process of bond-slip. AE signals can be detected when initial micro cracks form and indicate the damage severity, types and locations. The second is electromechanical impedance (EMI) method, which can be used to evaluate the damage due to bond-slip through comparing with the reference data in static state, even if the bond-slip is invisible and suspends. In this work, the experiment is implemented to demonstrate the bond-slip monitoring using above methods. Experimental results and further analysis show the validity and unique advantage of the proposed methods.

• Steel and Composite Structures
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• v.38 no.3
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• pp.241-255
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• 2021

In order to study the interfacial bond-slip behavior of steel reinforced recycled concrete (SRRC) under cyclic loading, thirteen specimens were designed and tested under cyclic loading and one under monotonic loading. The test results indicated that the average bond strength of SRRC decreased with the increasing replacement ratio of recycled concrete, whereas the bond strength increased with an increase in the concrete cover thickness, the volumetric stirrup ratio, and the strength of recycled concrete. The ultimate bond strength of the cyclically-loaded specimen was significantly (41%) lower than that of the companion monotonically-loaded specimen. The cyclic phenomena also showed that SRRC specimens went through the nonslip phase, initial slip phase, failure phase, bond strength degradation phase and residual phase, with all specimens exhibiting basically the same shape of the bond-slip curve. Additionally, the paper presents the equations that were developed to calculate the characteristic bond strength of SRRC, which were verified based on experimental results.

• International Journal of Concrete Structures and Materials
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• v.5 no.1
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• pp.65-73
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• 2011

Corrosion of steel bars embedded in concrete admixed with 0%, 2% and 4% calcium nitrite (CN), having compressive strengths of 20 and 46 MPa was investigated. Reinforced concrete specimens were immersed in 3% NaCl solutions for 1, 7 and 15 days where 0.4A external current was applied to accelerate the chemical reactions. Corrosion rate was measured by retrieving electrochemical data via potentiodynamic polarization technique. Pull-out tests of reinforced concrete specimens were then conducted to assess the corroded steel-concrete bond characteristics. Experimental results showed that corrosion rate of steel bars and steel-concrete bond strength were dependent on concrete strength, amount of CN added and accelerated corrosion period. As concrete strength increased from 20 to 46 MPa, corrosion rate of embedded steel decreased. The addition of 2% CN to concrete of 20 MPa was not effective in retarding corrosion of steel at long time of exposure. However, the combination of higher strength concrete and 2% or 4% CN appear to be a desirable approach to reduce the effect of chloride-induced corrosion of steel reinforcement. After 1 day of corrosion acceleration, specimens without CN showed higher bond strength in both concrete mixes than those with CN. After 7 and 15 days of exposure, the higher concentration of CN, the higher bond strength in both concrete mixes achieved, except for the concrete specimen of 20 MPa compressive strength with 2% CN that recorded the highest deterioration in bond strength at 15 days of exposure.

• Computers and Concrete
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• v.8 no.4
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• pp.465-472
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• 2011

This paper investigates bond behavior of structural lightweight concrete (SLWC) and ordinary concrete (OC) comparatively using bending test called Standard Belgium Hinged Beam Test (SBHBT). For this purpose the experiments were carried out as three series on 36 beam specimens (12 specimens of SLWC and OC with $20{\phi}$ development length, 12 specimens of SLWC with $25{\phi}$ development length). For each series bond behavior of steel rebars with 8, 10, 12, 14 mm diameters were tested. The results indicate that bond strength of SLWC is considerable lower than OC and $20{\phi}$ development length is insufficient for steel rebars with 12 mm and 14 mm diameters. Therefore development length of SLWC was extended to $25{\phi}$, even if 8 and 10 mm steel rebars provided acceptable bond strength. In this way, bond strength between SLWC and 8 and 10 mm steel rebars was developed. In addition, adequate bond behavior was achieved for 12 mm rebar but the beam in which 14 mm rebar used exceeded their bearing capacity by shear forces before yield stress. This result shows that SBHBT is more convenient for small sized steel rebars.

• KCI Concrete Journal
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• v.13 no.2
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• pp.67-74
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• 2001

In this study, a numerical model for the simulation of reinforced concrete columns subject to cyclic loading is presented. The model consists of three separate models representing concrete, reinforcing steel bars and bond-slip between a reinforcing bar and ambient concrete. The concrete model is represented by the plane stress plastic-damage model and quadrilateral finite elements. The nonlinear steel bar model embedded in truss elements is used for longitudinal and transverse reinforcing bars. Bond-slip mechanism between a reinforcing bar and ambient concrete is discretized using connection elements in which the hysteretic bond-slip link model defines the bond stress and slip displacement relation. The three models are connected in finite element mesh to represent a reinforced concrete structure. From the numerical simulation, it is shown that the proposed model effectively and realistically represents the overall cyclic behavior of a reinforced concrete column. The present plastic-damage concrete model is observed to work appropriately with the steel bar and bond-slip link models in representing the complicated localization behavior.

• Computers and Concrete
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• v.23 no.3
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• pp.155-160
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• 2019

The use of recycled aggregate concrete for the purpose of environmental and resource conservation has gained increasing interest in construction engineering. Nevertheless, few studies have reported on the bonding performance of the bars in recycled aggregate concrete after exposed to high temperatures. In this paper, 72 pull-out specimens and 36 cubic specimens with different recycled coarse aggregate content (i.e., 0%, 50%,100%) were cast to evaluate the bond behavior between recycled aggregate concrete and steel bar after various temperatures ($20^{\circ}C$, $200^{\circ}C$, $400^{\circ}C$, $600^{\circ}C$). The results show that the recycled aggregate concrete pull-out specimens exhibited similar bond stress-slip curves at both ambient and high temperature. The bond strength declined gradually with the increase of the temperature. On the basis of a regression analysis of the experimental data, a revised bond strength mode and peak slip ratios relationship model were proposed to predict the post-heating bond-slip behavior between recycled aggregate concrete and steel bar.