• Structural Engineering and Mechanics
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• v.75 no.1
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• pp.123-131
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• 2020

The bond performance of glass fibre reinforced polymer (GFRP) bars and that of steel bars embedded in Alkali Activated Cement (AAC) concrete are analysed and compared using pull-out specimens. The bond failure modes, the average bond strength and the free end bond stress-slip curves are used for comparison. Tepfers' concrete ring model is used to further analyse the splitting failure in ribbed steel bar and GFRP bar specimens. The angle the bond forces make with the bar axis was calculated and used for comparing bond behaviour of ribbed steel bar and GFRP bars in AAC concrete. The results showed that bond failure mode plays a significant role in the comparison of the average bond stress of the specimens at failure. In case of pull-out failure mode, specimens with ribbed steel bars showed a higher bond strength while specimens with GFRP bars showed a higher bond stress in case of splitting failure mode. Comparison of the bond stress-slip curves of ribbed steel bars and GFRP bars depicted that the constant bond stress region at the peak is much smaller in case of GFRP bars than ribbed steel bars indicating a basic bond mechanism difference in GFRP and ribbed steel bars.

• 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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• 2003.11a
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• pp.239-243
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• 2003

A reducing bearing angle theory for bond of ribbed reinforcing bars to concrete is proposed to simulate experimental observation. Analytical expressions to determine bond strength for splitting and pullout failure are derived, where the bearing angle is a key variable. As bearing angle is reduced, splitting strength decreases and shearing strength increases. The proposed reducing bearing angle theory is effective to simulate damage of the deformed bar-concrete interface and understand bond mechanism of ribbed reinforcing steel in concrete structures.

• Structural Engineering and Mechanics
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• v.84 no.5
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• pp.651-664
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• 2022

A precise prediction of the ultimate bond strength between rebar and surrounding concrete plays a major role in structural design, as it effects the load-carrying capacity and serviceability of a member significantly. In the present study, Gaussian models are employed for modelling bond strength of ribbed steel bars embedded in concrete. Gaussian models offer a non-parametric method based on Bayesian framework which is powerful, versatile, robust and accurate. Five different Gaussian models are explored in this paper-Gaussian Process (GP), Variational Heteroscedastic Gaussian Process (VHGP), Warped Gaussian Process (WGP), Sparse Spectrum Gaussian Process (SSGP), and Twin Gaussian Process (TGP). The effectiveness of the models is also evaluated in comparison to the numerous design formulae provided by the codes. The predictions from the Gaussian models are found to be closer to the experiments than those predicted using the design equations provided in various codes. The sensitivity of the models to various parameters, input feature space and sampling is also presented. It is found that GP, VHGP and SSGP are effective in prediction of the bond strength. For large data set, GP, VHGP, WGP and TGP can be computationally expensive. In such cases, SSGP can be utilized.

• Structural Engineering and Mechanics
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• v.53 no.2
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• pp.311-324
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• 2015

The purpose of this study was to investigate experimentally the fatigue performance of reinforced concrete (RC) beams with hot-rolled ribbed fine-grained steel bars of yielding strength 500MPa (HRBF500). Three rectangular and three T-section RC beams with HRBF500 bars were constructed and tested under static and constant-amplitude cyclic loading. Prior to the application of repeated loading, all beams were initially cracked under static loading. The major test variables were the steel ratio, cross-sectional shape and stress range. The stress evolution of HRBF500 bars, the information about crack growth and the deflection developments of test beams were presented and analyzed. Rapid increases in deflections and tension steel stress occured in the early stages of fatigue loading, and were followed by a relatively stable period. Test results indicate that, the concrete beams reinforced with appropriate amount of HRBF500 bars can survive 2.5 million cycles of constant-amplitude cyclic loading with no apparent signs of damage, on condition that the initial extreme tensile stress in HRBF500 steel bars was controlled less than 150 MPa. It was also found that, the initial extreme tension steel stress, stress range, and steel ratio were the main factors that affected the fatigue properties of RC beams with HRBF500 bars, whose effects on fatigue properties were fully discussed in this paper, while the cross-sectional shape had no significant influence in fatigue properties. The results provide important guidance for the fatigue design of concrete beams reinforced with HRBF500 steel bars.

• Proceedings of the Korea Concrete Institute Conference
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• 2000.04a
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• pp.545-550
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• 2000

Bond between reinforcing bars and the surrounding concrete is supposed to safely transfer load in the design process of reinforced concrete structures. Bar with high relative rib area will be studied further not only static load but also dynamic loading conditions to sustain better performance of bond for reinforced concrete structures under earthquake. To determine the bond behavior of high ribbed bars in beam and column joints under repeated loads, 31 pullout specimens were tested. Bond strength increases as relative rib area increases. Also the effect of relative rib area on bond is larger in cyclic loading than in monotonic loading.

• Advances in concrete construction
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• v.2 no.1
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• pp.1-11
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• 2014

This paper demonstrates an experimental study to evaluate the effects of environmental exposures on the bond between ribbed Glass Fiber Reinforced Polymer (GFRP) reinforcing bars and concrete. The equation recommended by ACI 440-1R-06, for the bond stress,was evaluated in this study. A total of 16 pullout samples, 12with GFRP bars and 4with steel bars, were exposed to two different harsh environments for different periods of time. The exposed harsh environments included direct sun exposure and cyclic splash zone sea water. The variation in the shear (bond) strengths before and after exposure was considered as a measure of the durability of the bond between GFRP bars and concrete.Experimental results showed there is no significant difference of the bond strength between 60 and 90 days of exposures.It also showed that the empirical equation of the bond stress calculated by ACI 440-IR-06 is very conservative.

• 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.

• Structural Engineering and Mechanics
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• v.77 no.1
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• pp.75-87
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• 2021

The present study pertains to the introduction of two new types of grip adaptor for universal testing machines, namely Polyvinyl Chloride (PVC) and Polyoxymethylene (POM) grip adaptors, and their application to tension testing of FRP bars with different fiber and surface finish types. The tabs are connected to the FRP bar sample with the help of mechanical anchors, i.e. bolts. These new adaptors offer vital superiorities over the existing end tab designs (anchors with filling material or mechanical anchorage), including the reduction in the time and labor for production, reusability and the mild nature, i.e. low hardness of the tab material, which retards and even prevents peeling and crushing in the gripping regions of an FRP sample. The methods were successfully applied to FRP bars with different types of fiber (CFRP, GFRP and BFRP) and different types of surface texture (ribbed, wrapped, sand-coated and wound). The test results indicated that the both types of end caps prevented slip of the bar, crushing and peeling in the gripping zone. The mechanical properties from the material tests with the new caps were in perfect agreement with the ones from the material tests with steel tubular caps.

• Journal of the Korea Concrete Institute
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• v.13 no.3
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• pp.244-250
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• 2001

One of the reasons for brittle failure in reinforced concrete structures subjected to severe earthquake is due to large slip between reinforcing steel and concrete. This study aims to evaluate effects of deformation patterns of ribbed reinforcing bars on bond under cyclic loading. Bond test specimens were constructed with machined bars to test the newly developed reinforcing bars with high relative rib areas. The degree of confinement is also another key parameter in this bond test. From the test results under monotonic and cyclic loading, bond strength and stiffness were evaluated. Bond strength and bond stiffness increase as relative rib areas under cyclic loading for specimens highly confined by transverse reinforcement. The increase rates of the bond performance under cyclic loading are larger than those of specimens under monotonic loading. The developed bars with high relative rib areas will contribute for better bond performance for reinforced concrete structures subjected to severe seismic loadings.