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    Comparison of different FRP reinforcement-concrete bond test methods according to parameters affecting this bond
    (Gazi Univ, Fac Engineering Architecture, 2021) Basaran, Bogachan; Kalkan, Ilker
    There are many test methods in the international testing standards for the evaluation of FRP reinforcement-concrete bond. However, differences in test conditions of these methods affect FRP reinforcement-concrete bond. Therefore, even in the tests with identical test parameters, different bond strength values are attained due to experimental differences. In this study, the factors affecting FRP reinforcement-concrete bond were determined individually for four different test methods (hinged beam, beam-end, spliced beam and pullout tests) by using the gauss process regression (GPR) method. Accordingly, eight parameters affecting the bond strength, namely the diameter, fiber type, surface texture, embedment length, location in concrete and clear cover of reinforcement, the concrete compressive strength and the presence and degree of confining by means of transverse reinforcement were adopted as test parameters. In this way, the effects of each variable on bond strength were investigated for each test method and the methods were compared in terms of each parameter. The analyses on the four methods for identical test parameters depicted that there were differences in bond strength values as great as four times from one test method to another. The average bond strength values from the hinged beam tests were about 31, 3 and 146 % higher than the respective values from the pullout tests, beam-end tests and spliced beam tests, respectively. The degree of influence of each parameter on bond strength was established to depend on the test method and the same parameter was found to even have opposite effects on bond strength in different test methods.
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    Development length and bond strength equations for FRP bars embedded in concrete
    (ELSEVIER SCI LTD, 2020) Basaran, Bogachan; Kalkan, Ilker
    The present study pertains to the linear multiple regression analyses on a database of 185 hinged-beam experiments on FRP bars. The database was compiled from 51 tests conducted within the scope of the present study and 134 tests conducted by previous researchers. Bond strength and development length equations, taking different types of FRP bars and surface finishes into account, were developed and the estimates from the proposed equations were compared to the estimates from the respective equations of various international FRP-reinforced concrete codes. The proposed equations, addressing all kinds of FRP bars and surface finishes, were shown to be in much closer agreement with the experimental results compared to all previous equations according to different statistical evaluation criteria, i.e. the Coefficient of Determination, Root Mean Square Error and Mean Absolute Percentage Error. The code equations were established to yield to exteremely over-conservative and non-economical results in all types of FRP bars with different surface textures.
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    Effects of Waste Powder, Fine and Coarse Marble Aggregates on Concrete Compressive Strength
    (Mdpi, 2022) Basaran, Bogachan; Kalkan, Ilker; Aksoylu, Ceyhun; Ozkilic, Yasin Onuralp; Sabri, Mohanad Muayad Sabri
    The use of marble wastes in concrete mixtures, causing air and water pollution, has been promoted in the academic and practical spheres of the construction industry. Although the effects of various forms (powder, fine, coarse and mixed) of this waste on the concrete compressive strength has been subject to a decent number of studies in the literature, the difficulties in reaching specific conclusions on the effect of each test parameter constitute a major restraint for the proliferation of the use of marble wastes in the concrete industry. Most of these studies are far from underscoring all of the parameters affecting the concrete compressive strength. Due to the urgent need in the literature for comprehensive studies on concrete mixtures with marble wastes, the results of the axial compression tests on a total of 429 concrete mixtures with marble aggregates were compiled by paying special attention to reporting all test variables (form and content of marble wastes, water-cement ratio, cement content, proportion of coarse and fine aggregates in all aggregates) affecting the concrete strength. In this context, multivariate regression analyses were carried out on the existing test results. These regression analyses yielded to relationships between the change in concrete compressive strength and the test parameters for each and every form of marble waste (powder, fine and coarse aggregate). The study indicated that independent from the form of marble wastes (as powder, fine aggregate or coarse aggregate), aggregate replacements of up to 50% can yield to significant changes in the concrete compressive strength. In addition, the analytical estimates from the developed equations exhibited a high correlation (a least r value of 0.91) with the experimental results from the previous studies, yielding to rather low error values (RMSE value is 5.06 MPa at max). For this reason, the developed equations can consistently predict the changes in concrete compressive strength with varying amounts and forms of the marble aggregates as well as the other test variables.
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    Estimation of the FRP-concrete bond strength with code formulations and machine learning algorithms
    (Elsevier Sci Ltd, 2021) Basaran, Bogachan; Kalkan, Ilker; Bergil, Erhan; Erdal, Erdal
    The present study pertains to the bond strength and development length of FRP bars embedded in concrete. The experimental results in the literature were compared to the analytical estimates from the equations of different international codes and machine learning techniques, i.e. Gaussian Process Regression, Artificial Neural Networks, Support Vector Machines Regression, Regression Tree and Multiple Linear Regression. The comparison was realized for four different experimental methods, i.e. hinged beam, beam-end, spliced beam and pullout, to specify the analytical equation or method with the highest agreement with the test results for each method. GPR method was found to provide the highest accuracy with a mean value of 0.95 and a standard deviation of 0.14 for the predicted-to-experimental bond strength ratio. Based on coefficient of determination, Root Mean Square Error and Mean Absolute Percentage Error statistical criteria, GRP method was followed by ANN, MLR and SVMR based on the agreement with the experimental results. Among the code equations, the bond strength equation of the ACI 440.1R-15 code resulted in highest agreement with experimental results, but the predicted values remained on the over-conservative side. The other code formulations were established to yield to estimates, nearly constant for varying test parameters and highly conservative.
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    Investigation on variables affecting bond strength between FRP reinforcing bar and concrete by modified hinged beam tests
    (ELSEVIER SCI LTD, 2020) Basaran, Bogachan; Kalkan, Ilker
    Abstract The bond strength between FRP reinforcement and concrete significantly affects the load bearing capacity and deformation ability of an FRP reinforced concrete member subjected to bending. There are numerous parameters affecting this bond. In the past, however, studies of FRP rebar-concrete bond strength have considered only one or more of the basalt, glass and carbon FRP reinforcement types, and generally only one or a limited number of surface properties. Since all variables affecting this bond were not set forth, experiments were not conducted on the basis of keeping other test variables constant to examine the effect of a single parameter. In this study, in order to conduct a proper experimental study on concrete-FRP bond by isolating a single parameter in the related tests, 90 hinged beam tests were carried out under transverse loading. The effects of reinforcement fiber type (basalt, glass, carbon), reinforcement surface property (ribbed, wrapped, wounded, sand coated), distance between rebars, bottom and side concrete cover, reinforcement diameter, reinforcement embedment length, presence of stirrups, concrete compressive strength on FRP -concrete bond strength were investigated. Experiments conducted within the scope of this study showed that the effects of concrete compressive strength and concrete cover (bottom and side) on this bond are limited. Moreover, the bond strength values of rebars with mechanical interlocking load-bearing mechanism were found to be higher than the respective values of the ones with friction mechanism. Finally, an increase in the modulus of elasticity of FRP resulted in an increase in bond strength and the presence of stirrups in the beams reduced the bond strength.
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    PVC and POM gripping mechanisms for tension testing of FRP bars
    (Techno-Press, 2021) Basaran, Bogachan; Yaka, Harun; Kalkan, Ilker
    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.