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    A Review on the Physical Parameters Affecting the Bond Behavior of FRP Bars Embedded in Concrete
    (Mdpi, 2022) Basaran, Bogachan; Kalkan, Ilker; Beycioglu, Ahmet; Kasprzyk, Izabela
    The present study is a detailed literal survey on the bond behavior of FRP (Fiber Reinforced Polymer) reinforcing bars embedded in concrete. There is an urgent need for the accurate assessment of the parameters affecting the FRP-concrete bond and quantification of these effects. A significant majority of the previous studies could not derive precise and comprehensive conclusions on the effects of each of these parameters. The present study aimed at listing all of the physical parameters affecting the concrete-FRP bond, presenting the effects of each of these parameters based on the common opinions of the previous researchers and giving reasonable justifications on these effects. The studies on each of the parameters are presented in detailed tables. Among all listed parameters, the surface texture was established to have the most pronounced effect on the FRP-concrete bond strength. The bond strength values of the bars with coarse sand-coating exceeded the respective values of the fine sand-coated ones. However, increasing the concrete strength was found to result in a greater improvement in bond behavior of fine sand-coated bars due to the penetration of concrete particles into the fine sand-coating layer. The effects of fiber type, bar diameter and concrete compressive strength on the bar bond strength was shown to primarily originate from the relative slip of fibers inside the resin of the bar, also known as the shear lag effect.
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    Analysis of Thermal Environmental Effects on Precast, Prestressed Concrete Bridge Girders: Temperature Differentials and Thermal Deformations
    (Multi-Science Publ Co Ltd, 2012) Lee, Jong-Han; Kalkan, Ilker
    AASHTO specifications provide vertical thermal gradients for the thermal design of precast, prestressed concrete bridge girders. However, the thermal behavior of the girders pertains to not only vertical thermal movement but also lateral thermal movement. Thus, a one-year experimental and analytical study was conducted on a prestressed concrete BT-1600 girder segment to investigate both the vertical and lateral thermal gradients with variations in environmental conditions. The vertical thermal gradients were compared using current AASHTO recommendations. In addition, this study evaluated the lateral thermal gradients, which are not provided in the specifications, to propose a second-order curve. To determine the magnitudes of the thermal gradients in different environmental conditions, this study has developed equations that calculate the maximum vertical and lateral temperature differentials from daily climatic information. Results of the study showed that the predicted temperature differentials provided good agreement with the measured values. Finally, thermal deformations induced by the vertical and lateral thermal gradients were evaluated using an analytical method derived from one-dimensional beam theory.
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    Behavior of Postfabricated RC Beams under Monotonic Transverse Loading
    (Asce-Amer Soc Civil Engineers, 2019) Aykac, Sabahattin; Jamal, Rohullah; Ozbek, Eray; Kalkan, Ilker; Aykac, Bengi
    Postfabricated beams, that is, newly constructed beams in an existing structural system, provide an effective remedial solution to the serviceability and strength problems in an existing floor system and the discontinuities and irregularities in the seismic-force-resisting system of a structure, mostly caused by design and construction errors or intended omissions of certain members. The purpose of this study is to develop new techniques for postfabrication of these beams and connecting the postfabricated beams to the existing columns and slab. In this respect, an experimental study was planned and a total of 16half-scale specimens, including 3 monolithic (slab, columns, and beams cast monolithically) specimens and 13 specimens with postfabricated beams, were tested under monotonic vertical loads. The longitudinal reinforcement ratio of the postfabricated beam and the connection techniques of the postfabricated beam to the surrounding columns and slab constituted the test parameters. The tests indicated that the specimens with postfabricated beams were able to reach the strength and behavior of the monolithic specimens.
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    Behaviour of brick infill walls strengthened with expanded steel plates
    (Springer, 2016) Cumhur, Alper; Altundal, Adil; Kalkan, Ilker; Aykac, Sabahattin
    The present study was dedicated to investigate an effective, economical and convenient method for strengthening brick infill walls, i.e. the use of externally-bonded expanded steel plates. A total of 30 plastered wall assemblies were tested under monotonic diagonal loading to investigate the contribution of these plates to the load capacities, ductilities and rigidities of brick walls. The plate thickness, bolt spacing and location of the plates in the wall were the parameters of the test program. The experiments indicated that application of the plates on the outermost fine plaster layer significantly improves the diagonal load-deflection behaviour of infill walls and reducing the bolt spacing provides the strengthened walls with higher load capacity values. An analytical expression was developed for estimating the diagonal load capacities of plated brick walls. The analytical load estimates were found to be in close agreement with the experimental values.
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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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    Deflections of reinforced concrete beams with transverse openings of different geometries
    (Techno-Press, 2021) Kalkan, Ilker; Ceylan, Ece; Kartal, Saruhan; Baran, Mehmet
    The present study pertains to the in-plane bending deflections of reinforced concrete beams with multiple regular transverse openings along the beam length. The total deflections in the beam were obtained from bending deflections and the additional deflections from the Vierendeel panel action. The accuracy of the deflection estimates from the proposed formula were observed to depend on the opening geometry. Among different geometries, the presence of rectangular and parallelogram web openings resulted in the experimental deflections to deviate more considerably from the analytical values due to the stress concentrations around the corners of the openings. Consequently, a multiplier was incorporated into the deflection formula to account for the opening geometry. The new revised formula was found to generate analytical load-deflection curves in close agreement with the experimental ones and service-load deflections close to the FEA values of beams with varying amount of tension reinforcement. The diagonal reinforcement around the openings and the short stirrups in the posts and chords increased the accuracy of the analytical deflection estimates by reducing the undesired additional deformations in the beam due to the poorer integrity of the posts and chords around the openings.
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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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    Discussion on "Seismic capacity of masonry infilled RC frame strengthening with expanded metal ferrocement" by A. Leeanansaksiri, P. Panyakapo, A. Ruangrassamee [Eng. Struct. 159 (2018) 110-127]
    (Elsevier Sci Ltd, 2018) Aykac, Sabahattin; Ozbek, Eray; Kalkan, Ilker; Aykac, Bengi
    A discussion on the paper by Leeanansaksiri et al. (2018) is presented. In the paper, strengthening of the masonry infill walls using ferrocement reinforced with standard expanded steel plates (EMS) was investigated experimentally. A bare frame without infill wall, a frame with a plain (unstrengthened) infill wall and a frame with a strengthened infill wall were tested under reversed cyclic lateral loading. The type of EMS to be used for strengthening was decided based on compressive strength tests on plain (unstrengthened) and strengthened masonry prisms and monotonic diagonal loading tests on wall panels. The results of the prism and panel tests were also used to determine the parameters of the analytical hysteric models, which closely estimated the experimental results of the frame tests. While the paper reached important conclusions related to the proposed strengthening technique, the authors of this discussion felt obliged to present their significant findings on the issues, raised in the paper for further research to increase the efficiency of the proposed technique. Furthermore, this discussion summarizes the findings of the authors on the strategies to investigate the efficiency of an infill wall strengthening technique.
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    Effect of shrinkage restraint on deflections of reinforced self-compacting concrete beams
    (Korean Society Of Civil Engineers-Ksce, 2013) Kalkan, Ilker; Lee, Jong-Han
    This paper presents the results of a study aimed at investigating the effects of restrained shrinkage on the in-plane deflection behavior of reinforced beams cast with self-compacting concrete. The load-deflection data from the tests on two sets of heavily-reinforced concrete beams were analyzed. The first set of beams was made with self-compacting concrete while conventionally vibrated concrete with shrinkage reducing admixture was used in the second set. It was found out that the first set underwent shrinkage cracking at early ages and this cracking caused the member responses of the beams to be closer to the fully-cracked response at the initial stages of loading. The second set of beams was found to have initial responses approximate to the uncracked response and the maximum shrinkage restraint stresses were calculated to be in the order of 20-40% of the modulus of rupture of concrete. The maximum shrinkage-induced restraint stress expressions of the AS 3600-2001, AS 3600-2009, EC2, and CSA A23.3-04 codes were found to underestimate the restraint stresses developed in the first set, yet the estimates from code solutions were in closer agreement with the experimental values in the second set.
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    Effect of the GFRP wrapping on the shear and bending Behavior of RC beams with GFRP encasement
    (Techno-Press, 2022) Ozkilic, Yasin Onuralp; Gemi, Lokman; Madenci, Emrah; Aksoylu, Ceyhun; Kalkan, Ilker
    The need for establishing the contribution of pultruded FRP encasements and additional FRP wraps around these encasements to the shear strength and load-deflection behavior of reinforced concrete beams is the main motivation of the present study. This paper primarily focuses on the effect of additional wrapping around the composite beam on the flexural and shear behavior of the pultruded GFRP (Glass Fiber Reinforced Polymer) beams infilled with reinforced concrete, taking into account different types of failure according to av/H ratio (arch action, shear-tension, shear-compression and pure bending). For this purpose, nine hybrid beams with variable shear span-to-depth ratio (av/H) were tested. Hybrid beams with 500 mm, 1000 mm, and 1500 mm lengths and cross-sections of 150x100 mm and 100x100 mm were tested under three-point and four-point loading. Based on the testing load-displacement relationship, ductility ratio, energy dissipation capacity of the beams were evaluated with comprehensive macro damage analysis on pultruded GFRP profile and GFRP wrapping. The GFRP wraps were established to have a major contribution to the composite beam ductility (90-125%) and strength (40-75%) in all ranges of beam behavior (shear-dominated or dominated by the coupling of shear and flexure). The composite beams with wraps were showns to reach ductilities and strength values of their counterparts with much greater beam depth.
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    Effects of fly ash column treatment of HP clayey soils on seismic behavior of R/C structures
    (Techno-Press, 2021) Toprak, Baran; Bas, Selcuk; Kalkan, Ilker
    The behavior of soil directly affects not only its stability condition but also structural response of structural systems. High-plasticity clay soil (CH) is vulnerable to volumetric swelling leading to different settlements in structural systems. Hence, it becomes indispensable to propose practical solutions to reducing this effect. In the present study, structural response of R/C frame buildings, resting on high plasticity clayey soils strengthened through the coal fly ash column technique, to earthquake motion is investigated. For this aim, the swelling behavior of high plasticity clay soil (CH) is identified with in-situ experimental tests on the regions with high swelling potential in the city of Kirikkale, Turkey. In order to reduce the swelling potential of the investigated regions, the coal fly ash column technique was implemented to the reference soil specimen with high swelling percentage of 15.6%. Experimental results obtained from the strengthened soil specimens were compared to those from the reference specimen. This comparison revealed that the coal fly ash column approach has a considerable effect on improving the swelling behavior of the high plasticity clay soil. The decrease in the volumetric swelling value is also thought to directly improve the response of a building structure settled on high plasticity clay soil. The improvement in the seismic response of existing R/C structures located in the regions with high swelling potential was identified by adopting the increased allowable bearing pressure value of the improved soil in the analyses. Based on the comparative study, structural earthquake response of R/C frame systems was investigated on the basis of the engineering parameters, including the base-shear force, base overturning moment, base axial force and settlement of foundation. The percent changes in these values showed that the base axial force and settlement of foundation were improved with the help of this strengthening application.
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    Effects of the location and size of web openings on shear behavior of clamped-clamped reinforced concrete beams
    (Techno-Press, 2024) Aksoylu, Ceyhun; Ozkilic, Yasin Onuralp; Hakeem, Ibrahim Y.; Kalkan, Ilker
    The present study pertains to the effects of variations in the location and size of drilled web openings on the behavior of fixed -fixed reinforced concrete (RC) beams. For this purpose, a reference bending beam with a transverse opening in each half span was tested to failure. Later, the same beam was modeled and analyzed with the help of finite element software using ABAQUS. Upon achieving close agreement between the experimental and numerical results, the location and size of the web opening were altered to uncover the effects of these factors on the shear strength and load -deflection behavior of RC beams. The experimental failure mode of the tested beam and the numerical results were also verified by theoretical calculations. In numerical analysis, when compared to the reference (D0) specimen, if the distance of the opening center from the support is 0 or h or 2h, reduction in load -bearing capacity of 1.5%-22.8% or 2.0%-11.3% or is 4.1%-40.7%. In other words, both the numerical analyses and theoretical calculations indicated that the beam behavior shifted from shear -controlled to flexure -controlled as the openings approached the supports. Furthermore, the deformation capacities, energy absorption values, and the ductilities of the beams with different opening diameters also increased with the decreasing distance of the opening from supports. Web compression failure was shown to be the predominant mode of failure of beams with large diameters due to the lack of sufficient material in the diagonal compression strut of the beam. The present study indicated that transverse openings with diameters, not exceeding about 1/3 of the entire beam depth, do not cause the premature shear failure of RC beams. Finally, shear damage should be prevented by placing special reinforcements in the areas where such gaps are opened.
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    Effects of the sole or combined use of chemical admixtures on properties of self-compacting concrete
    (Springernature, 2021) Sevim, Ozer; Kalkan, Ilker; Demir, Ilhami; Akgungor, Ali Payidar
    Chemical additives are very important in determining the behavioral characteristics of self-compacting concrete. For this reason, determining the building materials that make up the chemical structure of self-compacting concrete and the interactions of these materials is of great importance. The present study pertains to the effects of the use of different chemical admixtures (high-range water-reducing, i.e., superplasticizer, hydration accelerating, air-entraining, shrinkage reducing, and hydration heat reducing admixtures) on the fresh and hardened properties of self-compacting concrete. The influence of using a single one or a hybrid combination of the air-entraining, hydration-accelerating, heat-reducing, and shrinkage-reducing admixtures on the mechanical properties of fresh and hardened SCC was investigated through a set of tests. For this purpose, sixteen different SCC mixtures with different combinations of chemical additives were prepared and tested. The properties of fresh concrete were examined as well as the compressive and tensile strengths of the mixtures. SCC mixtures with shrinkage-reducing admixtures were evaluated in terms of shrinkage development. The effect of the use of admixtures was found to be more pronounced on the early-age concrete strength. The use of any type of additive in addition to the shrinkage-reducing admixture increased the speed of flow of fresh concrete.
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    Effects of the use of the surface spectrum of a specific region on seismic performances of R/C structures
    (Springer, 2018) Sonmezer, Y. Bulent; Kalkan, Ilker; Bas, Selcuk; Akbas, S. Oguzhan
    The present study pertains to the estimation of the significance of the use of the local acceleration spectrum of a region rather than the design spectra based on the linear time-history analyses of real structures in the region. The study was realized in three stages: (1) development of the target spectrum of the bedrock level accounting for the possible devastative earthquake, the distance of the region to the main fault and the earthquake magnitude; (2) establishment of the surface (local) spectrum of the region based on the bedrock spectrum and soil profile; and (3) the linear time-history analyses of the existing R/C building structures from the studied region using earthquake records that were produced by spectral matching according to the site-depended local spectrum and the design spectra of the seismic code. For this objective, the city of Kirikkale, located in mid-Anatolia, was adopted as the study region owing to the high seismic risk of the region and the presence of abundant poorly designed and poorly or non-engineered structures. The analyses indicated that the use of the local spectrum instead of the code design spectra is rather crucial in R/C structures with irregular story plans. In addition, structures with high eccentricity were obtained to be rather affected from earthquake motions compared to those with regular story plan. The use of the code design spectra provides closer and more conservative base shear, base overturning moment and lateral displacement estimates in R/C structures with regular story plans.
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    The effects of vertical earthquake motion on an R/C structure
    (Techno-Press, 2016) Bas, Selcuk; Kalkan, Ilker
    The present study investigated the earthquake behavior of R/C structures considering the vertical earthquake motion with the help of a comparative study. For this aim, the linear time-history analyses of a high-rise R/C structure designed according to TSC-2007 requirements were conducted including and excluding the vertical earthquake motion. Earthquake records used in the analyses were selected based on the ratio of vertical peak acceleration to horizontal peak acceleration (V/H). The frequency-domain analyses of the earthquake records were also performed to compare the dominant frequency of the records with that of the structure. Based on the results obtained from the time-history analyses under the earthquake loading with (H+V) and without the vertical earthquake motion (H), the value of the overturning moment and the top-story vertical displacement were found to relatively increase when considering the vertical earthquake motion. The base shear force was also affected by this motion; however, its increase was lower compared to the overturning moment and the top-story vertical displacement. The other two parameters, the top-story lateral displacement and the top-story rotation angle, barely changed under H and H+V loading cases. Modal damping ratios and their variations in horizontal and vertical directions were also estimated using response acceleration records. No significant change in the horizontal damping ratio was observed whereas the vertical modal damping ratio noticeably increased under H+V loading. The results obtained from this study indicate that the desired structural earthquake performance cannot be provided under H+V loading due to the excessive increase in the overturning moment, and that the vertical damping ratio should be estimated considering the vertical earthquake motion.
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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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    Experimental and Analytical Investigation of Lateral-Torsional Buckling of RC Beams with Geometric Imperfections
    (Trans Tech Publications Ltd, 2014) Lee, Jong-Han; Kalkan, Ilker
    The design of reinforced concrete beams has usually focused on the ultimate flexural capacity and disregarded the lateral stability of the beams. However, the development of high-strength concrete and the implementation of new construction techniques increase the use of longer and deeper concrete beams, which makes the lateral instability a primary concern of failure in concrete bridges. In particular, the lateral stability should be more taken into consideration in the construction and erection phases due to inadequate lateral supports. Thus, an experimental study was carried out to evaluate the lateral torsional buckling of reinforced concrete beams with initial geometric imperfections. The lateral flexural and torsional rigidity expressions, which could account for the flexural, torsional, and shrinkage cracking of concrete, the contribution of longitudinal and shear reinforcement, and the nonlinearity of materials, were proposed for rectangular reinforced concrete beams. Finally, this study proposed an analytical formula to estimate the buckling loads of initially imperfect reinforced concrete beams. The estimates of the study showed close agreement with the experimental values.
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    Flexural Behavior and Strength of Reinforced Concrete Beams with Multiple Transverse Openings
    (Amer Concrete Inst, 2014) Aykac, Bengi; Aykac, Sabahattin; Kalkan, Ilker; Dundar, Berk; Can, Husnu
    Reported are the results of experiments on 10 rectangular reinforced concrete (RC) beams with and without multiple web openings. The effects of opening geometry, the-use of longitudinal stirrups in the posts between the openings, the use of diagonal reinforcement around openings, and the longitudinal reinforcement ratio on the flexural behavior of RC beams with openings were investigated. The stirrups in the posts were shown to have a significant contribution to the ductility of an RC beam with openings if no diagonal reinforcement is used. For the same reinforcement details, RC beams with circular openings were found to have higher load capacities and ductilities than beams with rectangular openings. The experiments indicated that the posts between the openings need to be prevented from undergoing shear failure to avoid Vierendeel truss action and allow a beam to develop its ductility and bending capacity.
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    Flexural behavior of RC beams with regular square or circular web openings
    (Elsevier Sci Ltd, 2013) Aykac, Bengi; Kalkan, Ilker; Aykac, Sabahattin; Egriboz, Yusuf Emre
    This paper presents a study aimed at investigating the influence of multiple web openings along the length of an RC beam on its flexural behavior. A total of nine rectangular beams were tested. Diagonal reinforcement around openings effectively prevented premature failure of some specimens due to Vierendeel action, the expected failure mode according to bending moment-axial force interaction diagrams. Longitudinal rebars and full-depth stirrups adjacent to openings and short stirrups in the chords prevented beam-type and frame-type shear failures. The length of the plastic failure mechanism increased in the presence of multiple openings compared to beams with a single opening. (C) 2013 Elsevier Ltd. All rights reserved.