Performance Enhancement of Reinforcing Bars in Concrete with Hooked-End Steel Fibers: A Pull-Out Study

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Bayoumi, Mohammed K. Alkharisi This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6895610/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract This experimental study provides a comprehensive assessment of the bond performance of two deformed steel reinforcing bars with diameters of 8mm, 10mm, and 12mm in two concrete mixes incorporating hooked-end steel fibers. A total of 36 cylindrical pullout specimens were prepared and subjected to rigorous pullout tests. The study meticulously examined the impact of four critical parameters: bar diameter, embedment length (5, 10, and 15 times the bar diameter), concrete strength, and spacing between deformed bars (25mm and 50mm). The influence of these parameters on bond strength was thoroughly evaluated, and failure mechanisms were analyzed. Results indicated that pullout failure was the dominant failure mode for specimens with shorter embedment lengths, while splitting failure prevailed in specimens with the longest embedment lengths. Increasing the embedment length significantly enhanced the ultimate load, toughness, and slip values of the tested specimens. Additionally, specimens with closer bar spacing exhibited superior bonding performance compared to those with wider spacing. Thus, reducing the spacing between reinforcing steel bars in concrete has been proven to improve load transfer efficiency and minimize stress concentrations, leading to higher structural integrity. This practice enhances the bond strength between steel and fiber concrete, resulting in improved resistance to cracking and deformation under applied loads. Civil Engineering Bonding performance bar diameter embedment length strength of concrete spacing between deformed bars pullout test Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 Figure 13 Figure 14 1. Introduction Generally in reinforced concrete structures, an effective bond between the reinforcing steel bars and the concrete is crucial for ensuring optimal structural performance and the efficient transfer of forces. This bond significantly impacts the behavior of reinforced elements, especially when they are subjected to cracking, as it influences the distribution of stresses and the overall response of the structure. An enhanced bond between the concrete and reinforcement not only improves the structural integrity of the material but also increases its ability to withstand various loading conditions and enhances the concrete's strength. As a result, a strong bond is fundamental in achieving the full potential of reinforced concrete under diverse mechanical stresses and environmental conditions. [ 1 – 10 ] The bond strength between reinforcing bars and concrete is essential for ensuring structural integrity and effective force transmission. This bond is primarily influenced by three mechanisms: (1) chemical adhesion between steel bars and surrounding concrete, forming a strong interfacial bond that resists separation under tensile stresses.​ (2) Frictional resistance between steel bars and concrete due to the roughness of the surface of the bars in contact area with the concrete. The asperities on the bar surface interlock with the concrete, enhancing the frictional force that resists relative movement, and (3) bearing of lugs against the concrete (mechanical interlock). This mechanism involves the interlocking of these protrusions with the surrounding concrete, providing resistance to pullout and contributing significantly to the overall bond strength [ 11 – 18 ]. Bond strength is influenced by several factors, including concrete strength, reinforcing bar position, geometry, size, concrete cover thickness, development length, and amount of transverse reinforcement. These factors collectively affect the bond strength and, consequently, the overall performance of reinforced concrete elements [ 19 – 27 ]. However, the failure mode of the bond depends significantly on the degree of confinement, which is provided by transverse reinforcement and adequate concrete cover. In well-confined conditions, such as those found in beam-column joints with sufficient transverse reinforcement, pull-out failure is less likely. Instead, failure modes may include joint shear failure or yielding of the reinforcing bars. Proper detailing of transverse reinforcement is essential to prevent bond failure and ensure the desired performance of RC structures [ 28 – 30 ], while ones with other confinement conditions fail by splitting instead of pulling out. In reality, RC elements in the majority of structures meet confinement conditions in an intermediate between unconfined conditions and well-confined conditions. In such cases, bond failure tends to occur in splitting failure mode. [ 31 – 33 ]. During the construction of structural elements, reinforcing bars are placed frequently in tensioned regions through flexural members which means that the surrounding concrete is cracked due to flexural stresses. Bond-slip mechanism curve comprises several stages according to the mode of failure. For pull out failure, the nonlinear ascending branch is proposed and followed by constant linear stage and simplified linear descending branch while splitting failure, the model is reduced to non-linear ascending branch and simplified linear descending branch. [ 34 – 38 ] During the last decades, bond behavior between reinforcing bars and fiber reinforced concrete has been concerned by many researchers. With the rapid development in the industry, synthetic fibers, i.e. metallic and non-metallic, are widely produced with various shapes and dimensions and added to concrete to enhance its properties and performance. The majority of researchers used pull out test to study the bonding because of its ease and simplicity [ 39 – 43 ]. V. Bilek et al. [ 44 ] studied comparisons of the bond strengths of different types of concretes-alkali activated, ordinary Portland cement based and hybrid cement based concretes. It is concluded that, no significant differences were recorded between the bond strength of alkali activated concrete and ordinary Portland cement, as alkali activated concrete has a significantly higher compressive strength. Hybrid cement concrete showed a much lower bond strength, which is probably the consequence of their lower compressive strengths and tensile splitting strengths. M. M. Kamal et al. [ 45 ] investigated concrete 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. It is observed 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. Eswanth and Dhinakaran [ 46 ] studied experimental and theoretical investigations on the bond strength of normal and high strength concrete. It is concluded that pull out load for normal strength concrete was lower as compared to high strength concrete. Splitting failure occurred for increased embedment lengths whereas Tekle et.al. [ 47 ] discussed bond properties of steel bars with addition fly ash based Geopolymer concrete. It is concluded that pullout load increases with increasing embedment length, but the average bond strength decreases because of the splitting failure mode. Al-Shannag and Charif [ 48 ] studied bond behavior of steel bars embedded in concrete made with natural lightweight aggregates. It is concluded that load slip behavior of deformed steel bars embedded in self-lightweight concrete depends on compressive strength, bar diameter and embedded length. Bond strength of self-lightweight concrete increases with compressive strength and decreases inversely with bar diameter. Extensive researches efforts have been made to examine the bond performance of reinforcing bars embedded in hybrid fiber concrete [ 49 – 51 ]. It was concluded that the combination of a 1% volume fraction of steel fiber with 0.1% volume fraction of polypropylene fibers significantly improve the bond stress for 12mm, 16mm, and 20 mm diameter rebars by about 50%, 46% and 33%, respectively. 2. Research Significance It is clear from the previous review that the bond behavior between two reinforcing bars and fiber reinforced concrete (FRC) still requires further in-depth investigation, as only a limited number of researchers have addressed this topic. This research is considered as a development and extension of the findings presented in reference [ 24 ], where the previous study focused on concrete with a compressive strength of 25 MPa. In the current study, the investigation was carried out using concrete with a higher compressive strength of 35 MPa, and a comparison between the two strength grades was conducted. The main objective of this study was to evaluate the improvement in bond performance between two deformed bars and FRC topping by varying the concrete strength for the topping layer, utilizing the pull-out test method. Two fiber reinforced concrete mixes were used in this study, both selected for their expected ability to provide good bond strength for catenary ties, replicating real-world applications such as in precast concrete beam-column connections, where maximum efficiency and deformability are required to reduce the risk of progressive collapse. The pull-out test setup was modified in this research to investigate the interaction effect between two deformed bars on the bond performance with FRC. Although the stress states developed during pull-out tests in FRC specimens are rarely encountered in practical scenarios, and the bond strengths obtained from these tests may differ significantly from those in actual reinforced concrete structures, the pull-out test remains a widely accepted, economical, and straightforward method for assessing the bond behavior of reinforcing bars. 3. Materials and experimental procedures 3.1 Materials Commercially available local materials were utilized for specimens’ production in this investigation. Materials used to produce concrete comprise two types of Portland cements grade 32.5MPa and 42.5MPa were used in conducting to prediction of compressive strength and water/cement ratio was used in this study equal to 0.50. The fine aggregate was natural siliceous sand with a fineness modulus of 2.8 while the coarse aggregate was crushed stone with a maximum nominal size of 20mm and with the fineness modulus of 2.9. Steel fiber used in this paper was hooked end steel fiber with 0.55mm of diameter and 35mm of length. The steel fiber conforms to ASTM A820 Standards and percentage of steel fiber used in this study was 1%. 3.2 Experimental procedures A series of experiments were conducted to study the bond performance of two-reinforcing steel bars 8mm, 10mm and 12mm diameters (deformed bars) in two concrete mixes. Two-mix proportions were prepared to achieve fiber reinforced concretes. Concrete compressive strength was determined in accordance with ASTM C 39M–03 by using 150mm diameter × 300mm height cylinders. The concrete mix was designed to obtain target strength of at least 25MPa and 35MPa at the age of 28 days. Twelve cylinders were cast to determine the compressive strength of concrete. For each batch, the well-mixed concrete mixture, was poured into moulds to form the cylindrical shape specimens. After being demoulded at the age of one day, all specimens were cured in water at 25°C till the age of testing. The cylinders were tested in direct compression to determine the concrete compressive strength. After testing of cylinders, the mean of compressive strength were 28.63MPa and 42.19MPa, respectively at 28 days. In this study, three different nominal diameters of the embedment reinforcing bars were chosen: 8, 10, and 12mm. The properties of these bars were summarized in Table 1 . The experimental specimens were cast in standard cylindrical molds of 150mm in diameter and 300mm in height. Two-reinforcing deformed bars were partially embedded along the longitudinal axis in the center of the cylinder, using a steel base made in a U-shape and fixed on cylinder sides by two nails. The reinforcing bars were passed through the middle of the base to maintain an embedment length and the same concrete cover from all sides while concrete casting as shown in Fig. 1 (a). Table 1 Characteristics of the tested deformed bars Nominal bar diameter (Ø) Maximum Tensile Force, kN Tensile strength, MPa %Elongation 8 mm 27.02kN 537.84 MPa 23.76% 10mm 39.319kN 500.63MPa 40.57% 12mm 76.024 672.54MPa 10.76% A total of 36 pullout cylindrical specimens were divided into two main groups. Each group contains 18 specimens, the first group discussed the strength of concrete 28.63MPa while the other investigated strength of concrete was 42.19MPa. Four parameters including changes in bar diameter, embedment length, the strength of concrete, and spacing between deformed bars were discussed in this paper to evlaute the effect of these parameters. The effect of bar diameters was tested using 8mm, 10mm, and 12mm diameters bars as illustrated in Fig. 1 (b), while the effect of embedment length (L d ) on the bonding between deformed bars and FRC were investigated in the second parameter as presented in Fig. 1 (c). Embedment length (L d ) were selected in this study were 5, 10, and 15times the bar diameter. For the third parameter, the effect of the compressive strength of concrete ( f c ) on the bond strength between FRC and deformed bars was studied. Two compressive strengths for concrete 28.63MPa and 42.19MPa were used. Finally, the impact of the spacing between deformed bars (S) on the bonding behavior between FRC and bars was examined in the fourth parameter. 25mm and 50mm spacing between deformed bars were adapted in this parameter as illustrated in Fig. 1 (d). The spacing between these bars was chosen on the basis of what is actually implemented during execution of concrete structures, especially in concrete beams. The details of the selected parameters on the current experimental investigation are listed in Table 2 . 4. Testing procedure Pullout test is the oldest, simplest, and less time-consuming to evaluate bonding performance of deformed bars and FRC concrete. The pullout test of the specimens was carried out by a manually fabricated testing frame as shown in Fig. 2. This test can provide a good comparison between bond stresses and corresponding embedment lengths. A universal testing machine (UTM) with 1000kN capacity was used to conduct pullout tests. Vertical displacements of the tested cylinders were recorded automatically. The maximum load and the mode of failure were monitored during the pullout test. It is worth mentioning that the pullout test was performed with the 28days curing specimens. 4.1 Bond stress calculation Bond stress is stuided as average stress between the surrounding concrete and two-reinforcing bars along the embedment length of two-bars. In this study assumed that the bond stress was uniformly distributed along the embedment length of the bar. Therefore, the bond stress could be calculated by dividing the applied load by the contact area between the reinforcing bars and fiber reinforced concrete. The bond stress was computed using the following equation: $$\:{\tau\:}_{av}=\:\frac{F}{2\pi\:\:d\:{L}_{d}}$$ 1 Where τ av is the bond stress, F = Maximum Pull-out load of two-reinforcing bars, d = Diameter of the bar, L d = Embedment of two-bars length Table 2 Summary of various parameter’s studied in this research Parameter’s Details Change in bar diameter Embedment length (L d ) (mm) Strength of Concrete Spacing between bars 8mm 5d = 40mm Compressive Strength of concrete f c = 28.63MPa Compressive Strength of concrete f c = 42.19MPa Spacing between deformed bars S = 25mm Spacing between deformed bars S = 50mm 10d = 80mm 15d = 120mm 10mm 5d = 50mm 10d = 100mm 15d = 150mm 12mm 5d = 60mm 10d = 120mm 15d = 180mm 5 Experimental Results In this part, four main parameters such as change in bar diameter, embedment lengths, strength of concrete, and spacing between deformed bars with different diameter bars of 8mm, 10mm, and 12mm were experimentally investigated using pullout test. During the test execution, pullout load and the slip of two-reinforcing bars were measured and all observations were recorded. 5.1 Bond–slip response for specimens having a spacing S = 25mm & f c = 28.63MPa The test results which reveal the effect of prementioned parameters on the bond-slip response are discussed in this section and presented in Table 3 . Embedment length and compressive strength are a significant factors influencing bond load and slip relationship. Figure 3 shows tensile pullout bond load-slip relationships for various embedment lengths. From these figures, it is shown that as the slip increases the bond load increases steadily at almost a constant rate until it reaches the ultimate strength then the curve goes down. Two embedment lengths (10d and 15d) showed consistent trends of behavior. Furthermore, it was obvious that the behavior of different diameters of 8mm, 10mm and 12mm was close for the embedment lengths 10d and 15d, while the behavior significantly differed for 5d embaded length. Furhtermore, it was found that the two-bars diameter size was directly proportional to the maximum tensile pullout bond load which is increased with the embedment length and the bond load for cylinders with 12mm of diameter was significnalty higher than the bond load of cylinders with bar of diameter 10mm and 8mm, as presented in Fig. 4 . Table 3 The experimental test results for specimens having a spacing S = 25 mm & f c = = 28.63MPa Diameter Specimen Notation Spacing (mm) L d (mm) Max. Pullout load(kN) Bond Stress (MPa) Slippage at Max. load(mm) Toughness (kN.mm) Mode of failure 8mm A1 25 5d = 40 9.02 4.48 9.28 54.29 PO A2 25 10d = 80 18.65 4.63 10.64 114.74 PO A3 25 15d = 120 30.02 4.97 13.43 219.25 PO 10mm B1 25 5d = 50 15.12 4.81 9.55 75.98 PO B2 25 10d = 100 31.46 5.00 11.36 178.19 PO B3 25 15d = 150 48.19 5.11 14.04 352.65 SP 12mm C1 25 5d = 60 23.73 5.24 10.30 69.51 PO C2 25 10d = 120 56.82 6.28 13.32 402.19 SP C3 25 15d = 180 90.05 6.63 14.39 672.43 SP Note: PO: Pullout failure, SP: Splitting failure For 8mm diameter bar, the results showed that increasing the embedment length from 5d to 10d, bond strength increased by 3.34% whereas increasing the embedment length from 10d to 15d, bond strength increased by 7.33%. When the embedment length was increased from 5d to 10d and from 10d to 15d for diameter 10mm, the bond stress increased by about 4.15% and 1.99%, respectively, while in case of diameter 12mm, the bond stress was increased 19.62% and 5.73% for increasing embedment length from 5d to 10d and 10d to 15d, respectively.overall, It can be observed that pullout load increases with increasing embedment length and bar diameter and where the bond efficiency with the long embedment lengths was high due to increase in the contact surface area between FRC and size of the bar diameter. Generally, toughness is an important indicator of the performance of the specimens under pullout loading. The toughness of this system can be defined as the maximum energy that can be sustained by the system up to the failure point. It can be used as an index for the ductility where higher toughness means higher dispersion of energy and indicate increased bond strength and deformability until the failure happened leading to higher ductility. Toughness can be simply obtained by numerically integrating the area under the bond load versus slip curve. From Table 3 , it was clear that the toughness values were increased with the increase of the embedment length. The increase in embedment length from 5d to 10d and from 10d to 15d, the increase in toughness values were 111.35% and 91%, respectively for diameter 8mm. By contrast, for 10mm diameter, the value of toughness increased by 134.52% and 98% when embedment length increaed from 5d to 10d and 10d to 15d, respectively. For the 12 mm diameter, when the embedment length was changed from 10d to 15d and from 5d to 10d, value of toughness increased by 478.6% and 67.2%, respectively. Moreover, it can be concluded from Table 4 that increasing the embedment length increases the toughness values for the same diameter. Bond Failure Mode In pullout specimens presented in this study, when one of the following occurs, failure is considered to be reached: 1-Two-bars pulled out from the circumference concrete media causing splitting cracks. This mode of failure has occurred in the all of experimental specimens with shorter embedment lengths. 2- Splitting pull-out failure usually happened in the pullout test of two-reinforcing bars with the longest embedment lengths. As the embedment length increase, the splitting failure occurs which restrain the strength embedment to reach the ultimate stage. Also, the mode of failure for this system occurred by pulling the two deformed bars simultaneously, due to the close spacing between the two bars. This means that the two reinforcing bars had the same behavior in resisting the influential loads during the test. The picture of typical failure modes was shown in Fig. 5. 5.2 Bond–slip response for specimens having a spacing S = 50mm & f c = 28.63MPa Table 4 summarizes the experimental results of pullout of specimens having a spacing S = 50mm and f c = 28.63MPa and tensile pullout bond load versus slip diagrams are presented in Fig. 6 . Based on the test results, it was found that in the initial stage, the increasing branches of the diagrams are nearly the same. But with the increase of pullout bond force, the bond-slip relationship curve gradually deviates from the previous stage. After the bond load reached to the peak value, the bond load did not disappear completely but decreased gradually with the increase of slip. In this stage, the mechanical occlusion force decreased, and the friction force weakened gradually due to the ribs of deformed bars, which leads to the rapid increase of slip whereas the embedment length increased, the bond load-slip distribution became increasingly non-uniform, ultimate tensile bond load and bond strength increased, as shown in Fig. 7 . For diameter 8mm, the bond stresses increased 5.01% and 3.87%, when the embedded length increased from 5d to 10d and from 10d to 15d, respectively. Whereas, when the embedment length increased from 5d to 10d and from 10d to 15d, the bond stress increased 5.26% and 3.75%, respectively for diameter 10mm. In case of 12mm diameter, the increase in bond stresses were 24.21% and 6.95% as the embedment length increased from 5d to 10d and from 10d to 15d, respectively. For diameter 8mm, the increase in the toughness 128.02% and 44.38% for increase in embedment length from 5d to 10d and from 10d to 15d, respectively while in the case of 10mm diameter, the increase in toughness were 101.55% and 75.58%, respectively for changed in the embedment length from 5d to 10d and from 10d to 15d and these values were 155.89% and 173.69%, respectively for the diameter of 12mm. It can be noticed that toughness was directly proportional to the value of embedment length, as the increase in the embedment length increases the value of toughness due to the fact that the greater the bond length between two deformed bars and FRC. This indicates the significant contribution of the added steel fibers to maintain the tensile cracks in the concrete due to the pullout loading and hence increased the bond strength and toughness values. Table 4 The experimental test results for specimens having a spacing S = 25mm & f c = 28.63MPa Diameter Specimen Notation Spacing (mm) L d (mm) Max. Pullout load (kN) Bond Stress (MPa) Slippage at Max. load(mm) Toughness (kN.mm) Mode of failure 8mm D1 50 5d = 40 8.43 4.19 7.37 31.55 PO D2 50 10d = 80 17.69 4.39 8.49 71.94 SP D3 50 15d = 120 27.55 4.56 8.15 103.87 SP 10mm H1 50 5d = 50 14.31 4.55 7.92 65.66 PO H2 50 10d = 100 30.15 4.8 9.01 132.34 PO H3 50 15d = 150 46.98 4.98 11.18 232.37 SP 12mm L1 50 5d = 60 21.49 4.75 9.65 83.39 SP L2 50 10d = 120 53.37 5.90 9.51 213.39 PO L3 50 15d = 180 85.69 6.31 12.54 584.03 SP Note: PO: Pullout failure, SP: Splitting failure Bond Failure Mode For specimens of this group, it was noted that pullout failure is the predominant type of failure observed for specimens D1, D2, D3, H1, H2, and L1. It was observed during the test of these specimens that at the beginning of loading, one of the deformed bars slipped before the other nevertheless, cracks appeared around the non-slipped reinforcing bar. However, as the loading rate increased, the other reinforcing slipped, as cracks occurred in FRC around the two reinforcing bars, especially in the region between the two bars. The bars slippage was due to extensive cracks on the surface of FRC cylindrical specimens indicating that the bond loss failure mode is occurred. Splitting failures of the remaining specimens are found in this group. At the start of the slip, one of the reinforcing bars behaved without the other, and with an increase in the tensile pull load rate, two reinforcing bars behaved together. It was noted that both transverse and longitudinal cracks were observed at failure where these cracks were extended on the entire surface of FRC cylinder and also appeared on the outer perimeter along the entire embedded lengths, as can be seen in Fig. 8. 5.3 Bond–slip response for specimens having a spacing S = 25mm & f c = 42.19MPa Table 5 illustrates the experimental results of the tested specimens and Fig. 9 shows the tensile pullout bond load–slip relationship for specimens of this group. Table 5 The experimental test results for specimens having a spacing S= 25mm & f c = 42.19MPa Diameter Specimen Notation Spacing (mm) L d (mm) Max. Pullout load (kN) Bond Stress (MPa) Slippage at Max. load (mm) Toughness (kN.mm) Mode of failure 8mm O1 25 5d = 40 10.91 5.43 6.24 37.36 PO O2 25 10d = 80 22.57 5.61 10.01 131.9 PO O3 25 15d = 120 36.20 6.00 10.5 212.04 PO 10mm P1 25 5d = 50 19.24 6.13 6.69 53.08 PO P2 25 10d = 100 40.78 6.49 10.89 201.65 PO P3 25 15d = 150 63.52 6.74 10.95 377.16 PO 12mm Q1 25 5d = 60 29.51 6.52 9.05 124.86 PO Q2 25 10d = 120 65.76 7.27 11.80 359.55 SP Q3 25 15d = 180 103.52 7.63 14.31 465.66 SP Note: PO: Pullout failure, SP: Splitting failure According to the results of this group, it was observed that by increasing the diameter of the deformed bar and embedment length, the bond strength increased. For diameter 8mm, the results of the experiment showed that by increasing the embedment length from 5d to 10d, bond strength increased by 3.31% and increasing the embedment length from 10d to 15d, bond strength increased by 6.95%. When the embedment length was increased from 5d to 10d and from 10d to 15d for diameter of 10mm, the bond strength increased by about 5.87% and 3.85%, respectively, while in the case of diameter of 12mm, the bond strength increased 11.5% and 4.9% for increasing embedment length from 5d to 10d and from 10d to 15d, respectively. Figure 10 shows the effect of embedment length on the ultimate tensile bond load. Also, it was clear that toughness values increased with the increase of the embedment length. In the case of the increase in embedment length from 5d to 10d and from 10d to 15d, the increase in toughness values was 253.05% and 60.75%, respectively for diameter of 8mm. However, in the case of 10mm diameter, the value of toughness increased 279.89% and 87.04% for the embedment length chenged from 5d to 10d and from 10d to 15d, respectively. For the 12 mm of diameter, value of toughness increased 187.96% and 29.51%, when the embedment length varied from 10d to 15d and from 5d to 10d, respectively. Bond Failure Mode Bond failure on the deformed bar depended on the embedment length and strength of the concrete where pullout failure and splitting failure occurred. Pullout failure was occured for all embedded lengths with diameters 8mm, 10mm, and for embedded length 5d for diameter of 12mm, while splitting failure was occurred for diameter of 12mm with embedment lengths of 10d and 15d. In pullout failure, two deformed bars were pulled out simultaneously without any cracking in the FRC concrete for diameter 8mm and for 5d for diameter 10mm, due to the close spacing between the two bars while for 10d and 15d for diameter 10 mm, cracking occurred in the region between bars and on the outer perimeter of the cylinder. This means that the two reinforcing bars had the same behavior in resisting the influential loads during the test. On the other hand, splitting failure usually occurred in the pullout test of deformed bars with the longest embedment lengths for diameter 12 (10d and 15d). The cracking of surrounding FRC concrete would occur under the action of the radial component of the squeeze force of the steel deformed rib on the concrete, and when this force exceeded the tensile strength of concrete, the concrete cover layer would be split and this cracking extended to the outer circumference of the cylinder over the entire of embedment lengths. The appearance of the tested cylinders after the pullout test is shown in Fig. 11. 5.4 Bond–slip response for specimens having a spacing S = 50mm & f c = 42.19MPa Table 6 summarizes the test results of maximum pullout load, bond stress, maximum slippage and toughness values and Fig. 12 demonstrates tensile pullout bond load versus slip relationships for diameters 8mm, 10mm, and 12mm for various embedment lengths with 50mm spacing between the reinforcing bars. Table 6 The experimental test results for specimens having a spacing S = 50mm & f c = 35MPa Diameter Specimen Notation Spacing (mm) L d (mm) Max. Pullout load (kN) Bond Stress (MPa) Slippage at Max. load (mm) Toughness (kN.mm) Mode of failure 8mm R1 50 5d = 40 10.10 5.02 8.38 44.37 SP R2 50 10d = 80 20.93 5.20 10.19 97.44 SP R3 50 15d = 120 34.57 5.73 11.38 214.44 SP 10mm V1 50 5d = 50 18.87 6.01 9.01 80.23 SP V2 50 10d = 100 40.08 6.38 12.98 271.19 SP V3 50 15d = 150 60.97 6.47 12.72 359.89 SP 12mm X1 50 5d = 60 27.21 6.01 9.71 104.34 SP X2 50 10d = 120 61.32 6.78 12.75 345.19 SP X3 50 15d = 180 100.86 7.43 13.23 680.83 SP Note: SP: Splitting failure From the previous comparisons, as mentioned previously, as the embedment length increased, the bond load-slip distribution in the bonded section became increasingly non-uniform. The ultimate tensile bond load increased with the increase of embedment length, as shown in Fig. 13 . Also, it is shown that the bond stress was directly proportional to the value of embedment length, as the increase in the embedment length increases the value of bonding stress due to the fact that the greater the bond length between two reinforcing bars and FRC concrete, the more serious non-uniformity of the bond stress occurred. For diameter of 8mm, the bond stresses were 3.58% and 10.19%, when the increase of the embedment length from 5d to 10d and from 10d to 15d, respectively. However, when the embedment length varied from 5d to 10d and from 10d to 15d, the bond stress increased 6.15% and 1.41%, respectively for diameter 10mm while in the case of 12mm diameter, the increase in bond stresses were 12.81% and 9.5% for the increase in the embedment length from 5d to 10d and from 10d to 15d, respectively. For diameter 8mm, the increase in toughness were 119.6% and 120.07% for increase in embedment length from 5d to 10d and from 10d to 15d, respectively while in the case of diameter 10mm, the increase in toughness was 238.01% and 32.7%, respectively for change the embedment length from 5d to 10d and from 10d to 15d and these values were 230.83% and 97.23%, respectively for diameter 12mm. It seems that the increase of the depth of embedment length plays an important role in the resistance of bonding between reinforcing two-bars and FRC concrete. Bond Failure Mode In this group, splitting failure mode was the predominant type of failure of the tested specimens. At the start of the slip, one of the reinforcing bars behaved without the other, and with an increase in the tensile pull load rate, two reinforcing bars behaved together. It was characterized by the splitting of the FRC concrete specimen in a brittle mode of failure. Both transverse and longitudinal cracks were observed at failure where the crush of the FRC concrete surrounding deformed bars was observed. These cracks were extended on the entire surface of FRC cylinder and also appeared on the outer perimeter along the entire embedment lengths. Modes of failure for specimens of this group can be seen in Fig. 14. 6. Conclusions Pull-out tests were conducted in this study to evaluate the bond performance between two deformed reinforcing bars embedded in fiber-reinforced concrete (FRC). Based on the results obtained from the experimental investigation, the following conclusions can be drawn: An increase in the embedment length of reinforcing bars led to higher ultimate load capacity, improved toughness, and greater slip values. For larger bar diameters, increasing embedment length resulted in bond behavior that was more significantly influenced by splitting cracks, whereas specimens with smaller bar diameters and shorter embedment lengths predominantly experienced pull-out failure. Specimens with reduced spacing between the deformed bars exhibited higher bond strength compared to those with greater spacing. Bond strength was found to increase with the compressive strength of the fiber-reinforced concrete for bars of the same diameter, attributed to improved interaction within the interfacial transition zone between concrete components. For concrete compressive strengths of f c = 28.63MPa and f c = 42.19MPa with spacing S = 25mm, pull-out failure was commonly observed in specimens with shorter embedment lengths, while splitting failure was more frequent in specimens with longer embedment lengths. In specimens with 50mm spacing between bars and a concrete strength of f c = 28.63MPa, splitting failure was the dominant failure mode. At the onset of slip, one deformed bar initially displaced independently. However, as the applied tensile load increased, both bars began to act together. Declarations Conflict of Interests The author declares that there is no conflict of interests regarding the publication of this paper. Data Availability Statement The data presented in this study are available on request from the author. Funding This research received no external funding. Authors Contributions Conceptualization, E.A.B.; methodology, E.A.B., and M. K. Kh.; formal analysis, E.A.B., and M. K. Kh.; resources, M. K. Kh.; data curation, E.A.B., and M. K. Kh.; writing—original draft preparation, E.A.B., writing—review and editing, E.A.B., and M. K. Kh.; funding acquisition, M. K. Kh.; All authors have read and agreed to the published version of the manuscript. References G. Xing, C. 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various embedment lengths (Spacing = 50mm)\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-6895610/v1/cd0fc236b10d830bf9b218ce.png"},{"id":84920104,"identity":"8f7fa004-f607-4a6c-ae08-66adc9546b00","added_by":"auto","created_at":"2025-06-18 19:35:53","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":38861,"visible":true,"origin":"","legend":"\u003cp\u003eTensile Pullout bond load-slip relationships for various embedment lengths (Spacing =25mm)\u003c/p\u003e","description":"","filename":"9.png","url":"https://assets-eu.researchsquare.com/files/rs-6895610/v1/6d5451dbb64c60777328146c.png"},{"id":84920132,"identity":"8ab30d54-4d0b-4d89-a43c-b601f7125b46","added_by":"auto","created_at":"2025-06-18 19:35:54","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":27642,"visible":true,"origin":"","legend":"\u003cp\u003eEffect of embedment length on ultimate tensile bond load (Spacing =25mm)\u003c/p\u003e","description":"","filename":"10.png","url":"https://assets-eu.researchsquare.com/files/rs-6895610/v1/83f980c13e86a9898c9e4ed7.png"},{"id":84921441,"identity":"b0857cff-3049-4763-be55-d764c33019dc","added_by":"auto","created_at":"2025-06-18 19:51:53","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":296096,"visible":true,"origin":"","legend":"\u003cp\u003eSpecimen failure mechanism for various embedment lengths(spacing = 25mm)\u003c/p\u003e","description":"","filename":"11.png","url":"https://assets-eu.researchsquare.com/files/rs-6895610/v1/26df02db96d6d0a43333450a.png"},{"id":84920110,"identity":"a8f279f8-6731-4d7c-be0f-ae5696d9da25","added_by":"auto","created_at":"2025-06-18 19:35:53","extension":"png","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":40099,"visible":true,"origin":"","legend":"\u003cp\u003eTensile Pullout bond load-slip relationships for various embedment lengths (Spacing =50mm)\u003c/p\u003e","description":"","filename":"12.png","url":"https://assets-eu.researchsquare.com/files/rs-6895610/v1/97bd0ffd8ee5506082fd2234.png"},{"id":84920102,"identity":"fb445ba2-9595-4695-a887-8b6853d035fd","added_by":"auto","created_at":"2025-06-18 19:35:53","extension":"png","order_by":13,"title":"Figure 13","display":"","copyAsset":false,"role":"figure","size":28902,"visible":true,"origin":"","legend":"\u003cp\u003eEffect of embedment length on ultimate tensile bond load (Spacing =50mm)\u003c/p\u003e","description":"","filename":"13.png","url":"https://assets-eu.researchsquare.com/files/rs-6895610/v1/4bceba2088afe423ece3624a.png"},{"id":84921141,"identity":"e9393089-10a3-4b61-9b68-7cc5ed85ea06","added_by":"auto","created_at":"2025-06-18 19:43:54","extension":"png","order_by":14,"title":"Figure 14","display":"","copyAsset":false,"role":"figure","size":331173,"visible":true,"origin":"","legend":"\u003cp\u003eSpecimen failure mechanism for various embedment lengths (spacing = 50mm)\u003c/p\u003e","description":"","filename":"14.png","url":"https://assets-eu.researchsquare.com/files/rs-6895610/v1/b4a71f2ed4ab7768575eb353.png"},{"id":84922112,"identity":"5fa2227d-a440-4f60-91e4-65ca19e8feef","added_by":"auto","created_at":"2025-06-18 20:08:01","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":3238132,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6895610/v1/c0a6939d-b384-41e7-94cb-690adf76296d.pdf"},{"id":84920089,"identity":"2bd581a8-107e-494f-b5b5-d60a11a7c4ab","added_by":"auto","created_at":"2025-06-18 19:35:53","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":31902,"visible":true,"origin":"","legend":"\u003cp\u003eHighlights\u003c/p\u003e","description":"","filename":"Highlights.docx","url":"https://assets-eu.researchsquare.com/files/rs-6895610/v1/d65d22ba06cfc37bff794c87.docx"}],"financialInterests":"The authors declare no competing interests.","formattedTitle":"\u003cp\u003e\u003cstrong\u003ePerformance Enhancement of Reinforcing Bars in Concrete with Hooked-End Steel Fibers: A Pull-Out Study\u003c/strong\u003e\u003c/p\u003e","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eGenerally in reinforced concrete structures, an effective bond between the reinforcing steel bars and the concrete is crucial for ensuring optimal structural performance and the efficient transfer of forces. This bond significantly impacts the behavior of reinforced elements, especially when they are subjected to cracking, as it influences the distribution of stresses and the overall response of the structure. An enhanced bond between the concrete and reinforcement not only improves the structural integrity of the material but also increases its ability to withstand various loading conditions and enhances the concrete's strength. As a result, a strong bond is fundamental in achieving the full potential of reinforced concrete under diverse mechanical stresses and environmental conditions. [\u003cspan additionalcitationids=\"CR2 CR3 CR4 CR5 CR6 CR7 CR8 CR9\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]\u003c/p\u003e \u003cp\u003eThe bond strength between reinforcing bars and concrete is essential for ensuring structural integrity and effective force transmission. This bond is primarily influenced by three mechanisms: (1) chemical adhesion between steel bars and surrounding concrete, forming a strong interfacial bond that resists separation under tensile stresses.​ (2) Frictional resistance between steel bars and concrete due to the roughness of the surface of the bars in contact area with the concrete. The asperities on the bar surface interlock with the concrete, enhancing the frictional force that resists relative movement, and (3) bearing of lugs against the concrete (mechanical interlock). This mechanism involves the interlocking of these protrusions with the surrounding concrete, providing resistance to pullout and contributing significantly to the overall bond strength [\u003cspan additionalcitationids=\"CR12 CR13 CR14 CR15 CR16 CR17\" citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. Bond strength is influenced by several factors, including concrete strength, reinforcing bar position, geometry, size, concrete cover thickness, development length, and amount of transverse reinforcement. These factors collectively affect the bond strength and, consequently, the overall performance of reinforced concrete elements [\u003cspan additionalcitationids=\"CR20 CR21 CR22 CR23 CR24 CR25 CR26\" citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]. However, the failure mode of the bond depends significantly on the degree of confinement, which is provided by transverse reinforcement and adequate concrete cover. In well-confined conditions, such as those found in beam-column joints with sufficient transverse reinforcement, pull-out failure is less likely. Instead, failure modes may include joint shear failure or yielding of the reinforcing bars. Proper detailing of transverse reinforcement is essential to prevent bond failure and ensure the desired performance of RC structures [\u003cspan additionalcitationids=\"CR29\" citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e], while ones with other confinement conditions fail by splitting instead of pulling out. In reality, RC elements in the majority of structures meet confinement conditions in an intermediate between unconfined conditions and well-confined conditions. In such cases, bond failure tends to occur in splitting failure mode. [\u003cspan additionalcitationids=\"CR32\" citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e]. During the construction of structural elements, reinforcing bars are placed frequently in tensioned regions through flexural members which means that the surrounding concrete is cracked due to flexural stresses. Bond-slip mechanism curve comprises several stages according to the mode of failure. For pull out failure, the nonlinear ascending branch is proposed and followed by constant linear stage and simplified linear descending branch while splitting failure, the model is reduced to non-linear ascending branch and simplified linear descending branch. [\u003cspan additionalcitationids=\"CR35 CR36 CR37\" citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e]\u003c/p\u003e \u003cp\u003eDuring the last decades, bond behavior between reinforcing bars and fiber reinforced concrete has been concerned by many researchers. With the rapid development in the industry, synthetic fibers, i.e. metallic and non-metallic, are widely produced with various shapes and dimensions and added to concrete to enhance its properties and performance. The majority of researchers used pull out test to study the bonding because of its ease and simplicity [\u003cspan additionalcitationids=\"CR40 CR41 CR42\" citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eV. Bilek et al. [\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e] studied comparisons of the bond strengths of different types of concretes-alkali activated, ordinary Portland cement based and hybrid cement based concretes. It is concluded that, no significant differences were recorded between the bond strength of alkali activated concrete and ordinary Portland cement, as alkali activated concrete has a significantly higher compressive strength. Hybrid cement concrete showed a much lower bond strength, which is probably the consequence of their lower compressive strengths and tensile splitting strengths. M. M. Kamal et al. [\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e] investigated concrete 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. It is observed 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.\u003c/p\u003e \u003cp\u003eEswanth and Dhinakaran [\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e] studied experimental and theoretical investigations on the bond strength of normal and high strength concrete. It is concluded that pull out load for normal strength concrete was lower as compared to high strength concrete. Splitting failure occurred for increased embedment lengths whereas Tekle et.al. [\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e] discussed bond properties of steel bars with addition fly ash based Geopolymer concrete. It is concluded that pullout load increases with increasing embedment length, but the average bond strength decreases because of the splitting failure mode. Al-Shannag and Charif [\u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e] studied bond behavior of steel bars embedded in concrete made with natural lightweight aggregates. It is concluded that load slip behavior of deformed steel bars embedded in self-lightweight concrete depends on compressive strength, bar diameter and embedded length. Bond strength of self-lightweight concrete increases with compressive strength and decreases inversely with bar diameter. Extensive researches efforts have been made to examine the bond performance of reinforcing bars embedded in hybrid fiber concrete [\u003cspan additionalcitationids=\"CR50\" citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e51\u003c/span\u003e]. It was concluded that the combination of a 1% volume fraction of steel fiber with 0.1% volume fraction of polypropylene fibers significantly improve the bond stress for 12mm, 16mm, and 20 mm diameter rebars by about 50%, 46% and 33%, respectively.\u003c/p\u003e"},{"header":"2. Research Significance","content":"\u003cp\u003eIt is clear from the previous review that the bond behavior between two reinforcing bars and fiber reinforced concrete (FRC) still requires further in-depth investigation, as only a limited number of researchers have addressed this topic. This research is considered as a development and extension of the findings presented in reference [\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e], where the previous study focused on concrete with a compressive strength of 25 MPa. In the current study, the investigation was carried out using concrete with a higher compressive strength of 35 MPa, and a comparison between the two strength grades was conducted. The main objective of this study was to evaluate the improvement in bond performance between two deformed bars and FRC topping by varying the concrete strength for the topping layer, utilizing the pull-out test method. Two fiber reinforced concrete mixes were used in this study, both selected for their expected ability to provide good bond strength for catenary ties, replicating real-world applications such as in precast concrete beam-column connections, where maximum efficiency and deformability are required to reduce the risk of progressive collapse. The pull-out test setup was modified in this research to investigate the interaction effect between two deformed bars on the bond performance with FRC. Although the stress states developed during pull-out tests in FRC specimens are rarely encountered in practical scenarios, and the bond strengths obtained from these tests may differ significantly from those in actual reinforced concrete structures, the pull-out test remains a widely accepted, economical, and straightforward method for assessing the bond behavior of reinforcing bars.\u003c/p\u003e"},{"header":"3. Materials and experimental procedures","content":"\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Materials\u003c/h2\u003e \u003cp\u003eCommercially available local materials were utilized for specimens\u0026rsquo; production in this investigation. Materials used to produce concrete comprise two types of Portland cements grade 32.5MPa and 42.5MPa were used in conducting to prediction of compressive strength and water/cement ratio was used in this study equal to 0.50. The fine aggregate was natural siliceous sand with a fineness modulus of 2.8 while the coarse aggregate was crushed stone with a maximum nominal size of 20mm and with the fineness modulus of 2.9. Steel fiber used in this paper was hooked end steel fiber with 0.55mm of diameter and 35mm of length. The steel fiber conforms to ASTM A820 Standards and percentage of steel fiber used in this study was 1%.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e3.2 Experimental procedures\u003c/h2\u003e \u003cp\u003eA series of experiments were conducted to study the bond performance of two-reinforcing steel bars 8mm, 10mm and 12mm diameters (deformed bars) in two concrete mixes. Two-mix proportions were prepared to achieve fiber reinforced concretes. Concrete compressive strength was determined in accordance with ASTM C 39M\u0026ndash;03 by using 150mm diameter \u0026times; 300mm height cylinders. The concrete mix was designed to obtain target strength of at least 25MPa and 35MPa at the age of 28 days. Twelve cylinders were cast to determine the compressive strength of concrete. For each batch, the well-mixed concrete mixture, was poured into moulds to form the cylindrical shape specimens. After being demoulded at the age of one day, all specimens were cured in water at 25\u0026deg;C till the age of testing. The cylinders were tested in direct compression to determine the concrete compressive strength. After testing of cylinders, the mean of compressive strength were 28.63MPa and 42.19MPa, respectively at 28 days.\u003c/p\u003e \u003cp\u003eIn this study, three different nominal diameters of the embedment reinforcing bars were chosen: 8, 10, and 12mm. The properties of these bars were summarized in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. The experimental specimens were cast in standard cylindrical molds of 150mm in diameter and 300mm in height. Two-reinforcing deformed bars were partially embedded along the longitudinal axis in the center of the cylinder, using a steel base made in a U-shape and fixed on cylinder sides by two nails. The reinforcing bars were passed through the middle of the base to maintain an embedment length and the same concrete cover from all sides while concrete casting as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e (a).\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eCharacteristics of the tested deformed bars\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"4\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eNominal bar diameter (\u0026Oslash;)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eMaximum Tensile Force, kN\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eTensile strength, MPa\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003e%Elongation\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e8 mm\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e27.02kN\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e537.84 MPa\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e23.76%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e10mm\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e39.319kN\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e500.63MPa\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e40.57%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e12mm\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e76.024\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e672.54MPa\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e10.76%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eA total of 36 pullout cylindrical specimens were divided into two main groups. Each group contains 18 specimens, the first group discussed the strength of concrete 28.63MPa while the other investigated strength of concrete was 42.19MPa. Four parameters including changes in bar diameter, embedment length, the strength of concrete, and spacing between deformed bars were discussed in this paper to evlaute the effect of these parameters. The effect of bar diameters was tested using 8mm, 10mm, and 12mm diameters bars as illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e (b), while the effect of embedment length (L\u003csub\u003ed\u003c/sub\u003e) on the bonding between deformed bars and FRC were investigated in the second parameter as presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e (c). Embedment length (L\u003csub\u003ed\u003c/sub\u003e) were selected in this study were 5, 10, and 15times the bar diameter.\u003c/p\u003e \u003cp\u003eFor the third parameter, the effect of the compressive strength of concrete (\u003cem\u003ef\u003c/em\u003e\u003csub\u003e\u003cem\u003ec\u003c/em\u003e\u003c/sub\u003e) on the bond strength between FRC and deformed bars was studied. Two compressive strengths for concrete 28.63MPa and 42.19MPa were used. Finally, the impact of the spacing between deformed bars (S) on the bonding behavior between FRC and bars was examined in the fourth parameter. 25mm and 50mm spacing between deformed bars were adapted in this parameter as illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e (d). The spacing between these bars was chosen on the basis of what is actually implemented during execution of concrete structures, especially in concrete beams. The details of the selected parameters on the current experimental investigation are listed in Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e.\u003c/p\u003e \u003c/div\u003e"},{"header":"4. Testing procedure","content":"\u003cp\u003ePullout test is the oldest, simplest, and less time-consuming to evaluate bonding performance of deformed bars and FRC concrete. The pullout test of the specimens was carried out by a manually fabricated testing frame as shown in Fig.\u0026nbsp;2. This test can provide a good comparison between bond stresses and corresponding embedment lengths. A universal testing machine (UTM) with 1000kN capacity was used to conduct pullout tests. Vertical displacements of the tested cylinders were recorded automatically. The maximum load and the mode of failure were monitored during the pullout test. It is worth mentioning that the pullout test was performed with the 28days curing specimens.\u003c/p\u003e \u003cdiv id=\"Sec7\" class=\"Section2\"\u003e \u003ch2\u003e4.1 Bond stress calculation\u003c/h2\u003e \u003cp\u003eBond stress is stuided as average stress between the surrounding concrete and two-reinforcing bars along the embedment length of two-bars. In this study assumed that the bond stress was uniformly distributed along the embedment length of the bar. Therefore, the bond stress could be calculated by dividing the applied load by the contact area between the reinforcing bars and fiber reinforced concrete. The bond stress was computed using the following equation:\u003cdiv id=\"Equ1\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ1\" name=\"EquationSource\"\u003e\n$$\\:{\\tau\\:}_{av}=\\:\\frac{F}{2\\pi\\:\\:d\\:{L}_{d}}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e1\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eWhere τ\u003csub\u003eav\u003c/sub\u003e is the bond stress, F\u0026thinsp;=\u0026thinsp;Maximum Pull-out load of two-reinforcing bars, d\u0026thinsp;=\u0026thinsp;Diameter of the bar, L\u003csub\u003ed\u003c/sub\u003e = Embedment of two-bars length\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eSummary of various parameter\u0026rsquo;s studied in this research\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"6\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colspan=\"6\" nameend=\"c6\" namest=\"c1\"\u003e \u003cp\u003eParameter\u0026rsquo;s Details\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eChange in bar diameter\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eEmbedment length (L\u003csub\u003ed\u003c/sub\u003e) (mm)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c4\" namest=\"c3\"\u003e \u003cp\u003eStrength of Concrete\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colspan=\"2\" nameend=\"c6\" namest=\"c5\"\u003e \u003cp\u003eSpacing between bars\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003e8mm\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e5d\u0026thinsp;=\u0026thinsp;40mm\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\" morerows=\"8\" rowspan=\"9\"\u003e \u003cp\u003eCompressive Strength of concrete\u003c/p\u003e \u003cp\u003e\u003cem\u003ef\u003c/em\u003e\u003csub\u003e\u003cem\u003ec\u003c/em\u003e\u003c/sub\u003e = 28.63MPa\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\" morerows=\"8\" rowspan=\"9\"\u003e \u003cp\u003eCompressive Strength of concrete\u003c/p\u003e \u003cp\u003e\u003cem\u003ef\u003c/em\u003e\u003csub\u003e\u003cem\u003ec\u003c/em\u003e\u003c/sub\u003e = 42.19MPa\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\" morerows=\"8\" rowspan=\"9\"\u003e \u003cp\u003eSpacing between deformed bars\u003c/p\u003e \u003cp\u003eS\u0026thinsp;=\u0026thinsp;25mm\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\" morerows=\"8\" rowspan=\"9\"\u003e \u003cp\u003eSpacing between deformed bars\u003c/p\u003e \u003cp\u003eS\u0026thinsp;=\u0026thinsp;50mm\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e10d\u0026thinsp;=\u0026thinsp;80mm\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e15d\u0026thinsp;=\u0026thinsp;120mm\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003e10mm\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e5d\u0026thinsp;=\u0026thinsp;50mm\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e10d\u0026thinsp;=\u0026thinsp;100mm\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e15d\u0026thinsp;=\u0026thinsp;150mm\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003e12mm\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e5d\u0026thinsp;=\u0026thinsp;60mm\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e10d\u0026thinsp;=\u0026thinsp;120mm\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e15d\u0026thinsp;=\u0026thinsp;180mm\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"5 Experimental Results","content":"\u003cp\u003eIn this part, four main parameters such as change in bar diameter, embedment lengths, strength of concrete, and spacing between deformed bars with different diameter bars of 8mm, 10mm, and 12mm were experimentally investigated using pullout test. During the test execution, pullout load and the slip of two-reinforcing bars were measured and all observations were recorded.\u003c/p\u003e \u003cdiv id=\"Sec9\" class=\"Section2\"\u003e \u003ch2\u003e5.1 Bond\u0026ndash;slip response for specimens having a spacing S\u0026thinsp;=\u0026thinsp;25mm \u0026amp; \u003cem\u003ef\u003c/em\u003e\u003csub\u003e\u003cem\u003ec\u003c/em\u003e\u003c/sub\u003e = 28.63MPa\u003c/h2\u003e \u003cp\u003eThe test results which reveal the effect of prementioned parameters on the bond-slip response are discussed in this section and presented in Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e. Embedment length and compressive strength are a significant factors influencing bond load and slip relationship. Figure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e3\u003c/span\u003e shows tensile pullout bond load-slip relationships for various embedment lengths.\u003c/p\u003e \u003cp\u003eFrom these figures, it is shown that as the slip increases the bond load increases steadily at almost a constant rate until it reaches the ultimate strength then the curve goes down. Two embedment lengths (10d and 15d) showed consistent trends of behavior. Furthermore, it was obvious that the behavior of different diameters of 8mm, 10mm and 12mm was close for the embedment lengths 10d and 15d, while the behavior significantly differed for 5d embaded length. Furhtermore, it was found that the two-bars diameter size was directly proportional to the maximum tensile pullout bond load which is increased with the embedment length and the bond load for cylinders with 12mm of diameter was significnalty higher than the bond load of cylinders with bar of diameter 10mm and 8mm, as presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e4\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eThe experimental test results for specimens having a spacing S\u0026thinsp;=\u0026thinsp;25 mm \u0026amp; \u003cem\u003ef\u003c/em\u003e\u003csub\u003e\u003cem\u003ec\u003c/em\u003e\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;=\u0026thinsp;28.63MPa\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"9\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eDiameter\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSpecimen Notation\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSpacing (mm)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eL\u003csub\u003ed\u003c/sub\u003e (mm)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eMax. Pullout load(kN)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eBond Stress (MPa)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eSlippage at Max. load(mm)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003eToughness (kN.mm)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c9\"\u003e \u003cp\u003eMode of failure\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003e8mm\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eA1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e5d\u0026thinsp;=\u0026thinsp;40\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e9.02\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e4.48\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e9.28\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e54.29\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003ePO\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eA2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e10d\u0026thinsp;=\u0026thinsp;80\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e18.65\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e4.63\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e10.64\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e114.74\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003ePO\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eA3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e15d\u0026thinsp;=\u0026thinsp;120\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e30.02\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e4.97\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e13.43\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e219.25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003ePO\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003e10mm\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eB1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e5d\u0026thinsp;=\u0026thinsp;50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e15.12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e4.81\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e9.55\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e75.98\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003ePO\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eB2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e10d\u0026thinsp;=\u0026thinsp;100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e31.46\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e5.00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e11.36\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e178.19\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003ePO\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eB3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e15d\u0026thinsp;=\u0026thinsp;150\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e48.19\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e5.11\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e14.04\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e352.65\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003eSP\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003e12mm\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eC1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e5d\u0026thinsp;=\u0026thinsp;60\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e23.73\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e5.24\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e10.30\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e69.51\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003ePO\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eC2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e10d\u0026thinsp;=\u0026thinsp;120\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e56.82\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e6.28\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e13.32\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e402.19\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003eSP\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eC3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e15d\u0026thinsp;=\u0026thinsp;180\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e90.05\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e6.63\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e14.39\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e672.43\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003eSP\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"9\"\u003eNote: PO: Pullout failure, SP: Splitting failure\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eFor 8mm diameter bar, the results showed that increasing the embedment length from 5d to 10d, bond strength increased by 3.34% whereas increasing the embedment length from 10d to 15d, bond strength increased by 7.33%. When the embedment length was increased from 5d to 10d and from 10d to 15d for diameter 10mm, the bond stress increased by about 4.15% and 1.99%, respectively, while in case of diameter 12mm, the bond stress was increased 19.62% and 5.73% for increasing embedment length from 5d to 10d and 10d to 15d, respectively.overall, It can be observed that pullout load increases with increasing embedment length and bar diameter and where the bond efficiency with the long embedment lengths was high due to increase in the contact surface area between FRC and size of the bar diameter.\u003c/p\u003e \u003cp\u003eGenerally, toughness is an important indicator of the performance of the specimens under pullout loading. The toughness of this system can be defined as the maximum energy that can be sustained by the system up to the failure point. It can be used as an index for the ductility where higher toughness means higher dispersion of energy and indicate increased bond strength and deformability until the failure happened leading to higher ductility. Toughness can be simply obtained by numerically integrating the area under the bond load versus slip curve. From Table \u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e, it was clear that the toughness values were increased with the increase of the embedment length. The increase in embedment length from 5d to 10d and from 10d to 15d, the increase in toughness values were 111.35% and 91%, respectively for diameter 8mm. By contrast, for 10mm diameter, the value of toughness increased by 134.52% and 98% when embedment length increaed from 5d to 10d and 10d to 15d, respectively. For the 12 mm diameter, when the embedment length was changed from 10d to 15d and from 5d to 10d, value of toughness increased by 478.6% and 67.2%, respectively. Moreover, it can be concluded from Table \u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e that increasing the embedment length increases the toughness values for the same diameter.\u003c/p\u003e \u003cp\u003e \u003cb\u003eBond Failure Mode\u003c/b\u003e \u003c/p\u003e \u003cp\u003eIn pullout specimens presented in this study, when one of the following occurs, failure is considered to be reached:\u003c/p\u003e \u003cp\u003e1-Two-bars pulled out from the circumference concrete media causing splitting cracks. This mode of failure has occurred in the all of experimental specimens with shorter embedment lengths.\u003c/p\u003e \u003cp\u003e2- Splitting pull-out failure usually happened in the pullout test of two-reinforcing bars with the longest embedment lengths. As the embedment length increase, the splitting failure occurs which restrain the strength embedment to reach the ultimate stage. Also, the mode of failure for this system occurred by pulling the two deformed bars simultaneously, due to the close spacing between the two bars. This means that the two reinforcing bars had the same behavior in resisting the influential loads during the test. The picture of typical failure modes was shown in Fig.\u0026nbsp;5.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section2\"\u003e \u003ch2\u003e5.2 Bond\u0026ndash;slip response for specimens having a spacing S\u0026thinsp;=\u0026thinsp;50mm \u0026amp; \u003cem\u003ef\u003c/em\u003e\u003csub\u003e\u003cem\u003ec\u003c/em\u003e\u003c/sub\u003e = 28.63MPa\u003c/h2\u003e \u003cp\u003eTable\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e summarizes the experimental results of pullout of specimens having a spacing S\u0026thinsp;=\u0026thinsp;50mm and \u003cem\u003ef\u003c/em\u003e\u003csub\u003e\u003cem\u003ec\u003c/em\u003e\u003c/sub\u003e = 28.63MPa and tensile pullout bond load versus slip diagrams are presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e6\u003c/span\u003e. Based on the test results, it was found that in the initial stage, the increasing branches of the diagrams are nearly the same. But with the increase of pullout bond force, the bond-slip relationship curve gradually deviates from the previous stage. After the bond load reached to the peak value, the bond load did not disappear completely but decreased gradually with the increase of slip. In this stage, the mechanical occlusion force decreased, and the friction force weakened gradually due to the ribs of deformed bars, which leads to the rapid increase of slip whereas the embedment length increased, the bond load-slip distribution became increasingly non-uniform, ultimate tensile bond load and bond strength increased, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e7\u003c/span\u003e.\u003c/p\u003e \u003cp\u003eFor diameter 8mm, the bond stresses increased 5.01% and 3.87%, when the embedded length increased from 5d to 10d and from 10d to 15d, respectively. Whereas, when the embedment length increased from 5d to 10d and from 10d to 15d, the bond stress increased 5.26% and 3.75%, respectively for diameter 10mm. In case of 12mm diameter, the increase in bond stresses were 24.21% and 6.95% as the embedment length increased from 5d to 10d and from 10d to 15d, respectively. For diameter 8mm, the increase in the toughness 128.02% and 44.38% for increase in embedment length from 5d to 10d and from 10d to 15d, respectively while in the case of 10mm diameter, the increase in toughness were 101.55% and 75.58%, respectively for changed in the embedment length from 5d to 10d and from 10d to 15d and these values were 155.89% and 173.69%, respectively for the diameter of 12mm. It can be noticed that toughness was directly proportional to the value of embedment length, as the increase in the embedment length increases the value of toughness due to the fact that the greater the bond length between two deformed bars and FRC. This indicates the significant contribution of the added steel fibers to maintain the tensile cracks in the concrete due to the pullout loading and hence increased the bond strength and toughness values.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab4\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eThe experimental test results for specimens having a spacing S\u0026thinsp;=\u0026thinsp;25mm \u0026amp; \u003cem\u003ef\u003c/em\u003e\u003csub\u003e\u003cem\u003ec\u003c/em\u003e\u003c/sub\u003e = 28.63MPa\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"9\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eDiameter\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSpecimen Notation\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSpacing (mm)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eL\u003csub\u003ed\u003c/sub\u003e (mm)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eMax. Pullout load (kN)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eBond Stress (MPa)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eSlippage at Max. load(mm)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003eToughness (kN.mm)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c9\"\u003e \u003cp\u003eMode of failure\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003e8mm\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eD1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e5d\u0026thinsp;=\u0026thinsp;40\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e8.43\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e4.19\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e7.37\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e31.55\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003ePO\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eD2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e10d\u0026thinsp;=\u0026thinsp;80\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e17.69\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e4.39\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e8.49\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e71.94\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003eSP\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eD3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e15d\u0026thinsp;=\u0026thinsp;120\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e27.55\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e4.56\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e8.15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e103.87\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003eSP\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003e10mm\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eH1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e5d\u0026thinsp;=\u0026thinsp;50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e14.31\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e4.55\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e7.92\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e65.66\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003ePO\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eH2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e10d\u0026thinsp;=\u0026thinsp;100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e30.15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e4.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e9.01\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e132.34\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003ePO\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eH3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e15d\u0026thinsp;=\u0026thinsp;150\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e46.98\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e4.98\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e11.18\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e232.37\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003eSP\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003e12mm\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eL1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e5d\u0026thinsp;=\u0026thinsp;60\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e21.49\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e4.75\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e9.65\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e83.39\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003eSP\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eL2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e10d\u0026thinsp;=\u0026thinsp;120\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e53.37\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e5.90\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e9.51\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e213.39\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003ePO\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eL3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e15d\u0026thinsp;=\u0026thinsp;180\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e85.69\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e6.31\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e12.54\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e584.03\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003eSP\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"9\"\u003eNote: PO: Pullout failure, SP: Splitting failure\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cb\u003eBond Failure Mode\u003c/b\u003e \u003c/p\u003e \u003cp\u003eFor specimens of this group, it was noted that pullout failure is the predominant type of failure observed for specimens D1, D2, D3, H1, H2, and L1. It was observed during the test of these specimens that at the beginning of loading, one of the deformed bars slipped before the other nevertheless, cracks appeared around the non-slipped reinforcing bar. However, as the loading rate increased, the other reinforcing slipped, as cracks occurred in FRC around the two reinforcing bars, especially in the region between the two bars. The bars slippage was due to extensive cracks on the surface of FRC cylindrical specimens indicating that the bond loss failure mode is occurred.\u003c/p\u003e \u003cp\u003eSplitting failures of the remaining specimens are found in this group. At the start of the slip, one of the reinforcing bars behaved without the other, and with an increase in the tensile pull load rate, two reinforcing bars behaved together. It was noted that both transverse and longitudinal cracks were observed at failure where these cracks were extended on the entire surface of FRC cylinder and also appeared on the outer perimeter along the entire embedded lengths, as can be seen in Fig.\u0026nbsp;8.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section2\"\u003e \u003ch2\u003e5.3 Bond\u0026ndash;slip response for specimens having a spacing S\u0026thinsp;=\u0026thinsp;25mm \u0026amp; \u003cem\u003ef\u003c/em\u003e\u003csub\u003e\u003cem\u003ec\u003c/em\u003e\u003c/sub\u003e = 42.19MPa\u003c/h2\u003e \u003cp\u003eTable\u0026nbsp;\u003cspan refid=\"Tab5\" class=\"InternalRef\"\u003e5\u003c/span\u003e illustrates the experimental results of the tested specimens and Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e9\u003c/span\u003e shows the tensile pullout bond load\u0026ndash;slip relationship for specimens of this group.\u003c/p\u003e\u003cp\u003e\u003cstrong\u003eTable 5\u003c/strong\u003e The experimental test results for specimens having a spacing S= 25mm \u0026amp; \u003cem\u003ef\u003csub\u003ec\u003c/sub\u003e\u003c/em\u003e = 42.19MPa\u003c/p\u003e\u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"No\" id=\"Taba\" border=\"1\"\u003e \u003ccolgroup cols=\"9\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eDiameter\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSpecimen Notation\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSpacing (mm)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eL\u003csub\u003ed\u003c/sub\u003e (mm)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eMax. Pullout load (kN)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eBond Stress (MPa)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eSlippage at Max. load (mm)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003eToughness (kN.mm)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c9\"\u003e \u003cp\u003eMode of failure\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003e8mm\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eO1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e5d\u0026thinsp;=\u0026thinsp;40\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e10.91\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e5.43\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e6.24\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e37.36\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003ePO\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eO2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e10d\u0026thinsp;=\u0026thinsp;80\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e22.57\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e5.61\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e10.01\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e131.9\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003ePO\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eO3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e15d\u0026thinsp;=\u0026thinsp;120\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e36.20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e6.00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e10.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e212.04\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003ePO\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003e10mm\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eP1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e5d\u0026thinsp;=\u0026thinsp;50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e19.24\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e6.13\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e6.69\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e53.08\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003ePO\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eP2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e10d\u0026thinsp;=\u0026thinsp;100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e40.78\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e6.49\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e10.89\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e201.65\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003ePO\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eP3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e15d\u0026thinsp;=\u0026thinsp;150\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e63.52\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e6.74\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e10.95\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e377.16\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003ePO\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003e12mm\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eQ1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e5d\u0026thinsp;=\u0026thinsp;60\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e29.51\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e6.52\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e9.05\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e124.86\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003ePO\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eQ2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e10d\u0026thinsp;=\u0026thinsp;120\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e65.76\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e7.27\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e11.80\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e359.55\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003eSP\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eQ3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e15d\u0026thinsp;=\u0026thinsp;180\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e103.52\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e7.63\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e14.31\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e465.66\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003eSP\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"9\"\u003eNote: PO: Pullout failure, SP: Splitting failure\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eAccording to the results of this group, it was observed that by increasing the diameter of the deformed bar and embedment length, the bond strength increased. For diameter 8mm, the results of the experiment showed that by increasing the embedment length from 5d to 10d, bond strength increased by 3.31% and increasing the embedment length from 10d to 15d, bond strength increased by 6.95%. When the embedment length was increased from 5d to 10d and from 10d to 15d for diameter of 10mm, the bond strength increased by about 5.87% and 3.85%, respectively, while in the case of diameter of 12mm, the bond strength increased 11.5% and 4.9% for increasing embedment length from 5d to 10d and from 10d to 15d, respectively. Figure\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e10\u003c/span\u003e shows the effect of embedment length on the ultimate tensile bond load. Also, it was clear that toughness values increased with the increase of the embedment length. In the case of the increase in embedment length from 5d to 10d and from 10d to 15d, the increase in toughness values was 253.05% and 60.75%, respectively for diameter of 8mm. However, in the case of 10mm diameter, the value of toughness increased 279.89% and 87.04% for the embedment length chenged from 5d to 10d and from 10d to 15d, respectively. For the 12 mm of diameter, value of toughness increased 187.96% and 29.51%, when the embedment length varied from 10d to 15d and from 5d to 10d, respectively.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cb\u003eBond Failure Mode\u003c/b\u003e \u003c/p\u003e \u003cp\u003eBond failure on the deformed bar depended on the embedment length and strength of the concrete where pullout failure and splitting failure occurred. Pullout failure was occured for all embedded lengths with diameters 8mm, 10mm, and for embedded length 5d for diameter of 12mm, while splitting failure was occurred for diameter of 12mm with embedment lengths of 10d and 15d. In pullout failure, two deformed bars were pulled out simultaneously without any cracking in the FRC concrete for diameter 8mm and for 5d for diameter 10mm, due to the close spacing between the two bars while for 10d and 15d for diameter 10 mm, cracking occurred in the region between bars and on the outer perimeter of the cylinder. This means that the two reinforcing bars had the same behavior in resisting the influential loads during the test. On the other hand, splitting failure usually occurred in the pullout test of deformed bars with the longest embedment lengths for diameter 12 (10d and 15d). The cracking of surrounding FRC concrete would occur under the action of the radial component of the squeeze force of the steel deformed rib on the concrete, and when this force exceeded the tensile strength of concrete, the concrete cover layer would be split and this cracking extended to the outer circumference of the cylinder over the entire of embedment lengths. The appearance of the tested cylinders after the pullout test is shown in Fig.\u0026nbsp;11.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section2\"\u003e \u003ch2\u003e5.4 Bond\u0026ndash;slip response for specimens having a spacing S\u0026thinsp;=\u0026thinsp;50mm \u0026amp; \u003cem\u003ef\u003c/em\u003e\u003csub\u003e\u003cem\u003ec\u003c/em\u003e\u003c/sub\u003e = 42.19MPa\u003c/h2\u003e \u003cp\u003eTable\u0026nbsp;\u003cspan refid=\"Tab6\" class=\"InternalRef\"\u003e6\u003c/span\u003e summarizes the test results of maximum pullout load, bond stress, maximum slippage and toughness values and Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e12\u003c/span\u003e demonstrates tensile pullout bond load versus slip relationships for diameters 8mm, 10mm, and 12mm for various embedment lengths with 50mm spacing between the reinforcing bars.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab6\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 6\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eThe experimental test results for specimens having a spacing S\u0026thinsp;=\u0026thinsp;50mm \u0026amp; \u003cem\u003ef\u003c/em\u003e\u003csub\u003e\u003cem\u003ec\u003c/em\u003e\u003c/sub\u003e = 35MPa\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"9\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eDiameter\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSpecimen Notation\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eSpacing (mm)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eL\u003csub\u003ed\u003c/sub\u003e (mm)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eMax. Pullout load (kN)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eBond Stress (MPa)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eSlippage at Max. load (mm)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003eToughness (kN.mm)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c9\"\u003e \u003cp\u003eMode of failure\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003e8mm\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eR1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e5d\u0026thinsp;=\u0026thinsp;40\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e10.10\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e5.02\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e8.38\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e44.37\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003eSP\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eR2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e10d\u0026thinsp;=\u0026thinsp;80\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e20.93\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e5.20\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e10.19\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e97.44\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003eSP\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eR3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e15d\u0026thinsp;=\u0026thinsp;120\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e34.57\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e5.73\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e11.38\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e214.44\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003eSP\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003e10mm\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eV1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e5d\u0026thinsp;=\u0026thinsp;50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e18.87\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e6.01\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e9.01\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e80.23\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003eSP\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eV2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e10d\u0026thinsp;=\u0026thinsp;100\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e40.08\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e6.38\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e12.98\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e271.19\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003eSP\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eV3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e15d\u0026thinsp;=\u0026thinsp;150\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e60.97\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e6.47\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e12.72\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e359.89\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003eSP\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\" morerows=\"2\" rowspan=\"3\"\u003e \u003cp\u003e12mm\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eX1\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e5d\u0026thinsp;=\u0026thinsp;60\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e27.21\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e6.01\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e9.71\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e104.34\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003eSP\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eX2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e10d\u0026thinsp;=\u0026thinsp;120\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e61.32\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e6.78\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e12.75\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e345.19\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003eSP\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eX3\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e15d\u0026thinsp;=\u0026thinsp;180\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e100.86\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e7.43\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e13.23\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e680.83\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003eSP\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003ctfoot\u003e \u003ctr\u003e\u003ctd colspan=\"9\"\u003eNote: SP: Splitting failure\u003c/td\u003e\u003c/tr\u003e \u003c/tfoot\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFrom the previous comparisons, as mentioned previously, as the embedment length increased, the bond load-slip distribution in the bonded section became increasingly non-uniform. The ultimate tensile bond load increased with the increase of embedment length, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e13\u003c/span\u003e. Also, it is shown that the bond stress was directly proportional to the value of embedment length, as the increase in the embedment length increases the value of bonding stress due to the fact that the greater the bond length between two reinforcing bars and FRC concrete, the more serious non-uniformity of the bond stress occurred. For diameter of 8mm, the bond stresses were 3.58% and 10.19%, when the increase of the embedment length from 5d to 10d and from 10d to 15d, respectively. However, when the embedment length varied from 5d to 10d and from 10d to 15d, the bond stress increased 6.15% and 1.41%, respectively for diameter 10mm while in the case of 12mm diameter, the increase in bond stresses were 12.81% and 9.5% for the increase in the embedment length from 5d to 10d and from 10d to 15d, respectively.\u003c/p\u003e \u003cp\u003eFor diameter 8mm, the increase in toughness were 119.6% and 120.07% for increase in embedment length from 5d to 10d and from 10d to 15d, respectively while in the case of diameter 10mm, the increase in toughness was 238.01% and 32.7%, respectively for change the embedment length from 5d to 10d and from 10d to 15d and these values were 230.83% and 97.23%, respectively for diameter 12mm. It seems that the increase of the depth of embedment length plays an important role in the resistance of bonding between reinforcing two-bars and FRC concrete.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003e \u003cb\u003eBond Failure Mode\u003c/b\u003e \u003c/p\u003e \u003cp\u003eIn this group, splitting failure mode was the predominant type of failure of the tested specimens. At the start of the slip, one of the reinforcing bars behaved without the other, and with an increase in the tensile pull load rate, two reinforcing bars behaved together. It was characterized by the splitting of the FRC concrete specimen in a brittle mode of failure. Both transverse and longitudinal cracks were observed at failure where the crush of the FRC concrete surrounding deformed bars was observed. These cracks were extended on the entire surface of FRC cylinder and also appeared on the outer perimeter along the entire embedment lengths. Modes of failure for specimens of this group can be seen in Fig.\u0026nbsp;14.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"6. Conclusions","content":"\u003cp\u003ePull-out tests were conducted in this study to evaluate the bond performance between two deformed reinforcing bars embedded in fiber-reinforced concrete (FRC). Based on the results obtained from the experimental investigation, the following conclusions can be drawn:\u003c/p\u003e \u003cp\u003e \u003cul\u003e \u003cli\u003e \u003cp\u003eAn increase in the embedment length of reinforcing bars led to higher ultimate load capacity, improved toughness, and greater slip values.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eFor larger bar diameters, increasing embedment length resulted in bond behavior that was more significantly influenced by splitting cracks, whereas specimens with smaller bar diameters and shorter embedment lengths predominantly experienced pull-out failure.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eSpecimens with reduced spacing between the deformed bars exhibited higher bond strength compared to those with greater spacing.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eBond strength was found to increase with the compressive strength of the fiber-reinforced concrete for bars of the same diameter, attributed to improved interaction within the interfacial transition zone between concrete components.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eFor concrete compressive strengths of \u003cem\u003ef\u003c/em\u003e\u003csub\u003e\u003cem\u003ec\u003c/em\u003e\u003c/sub\u003e = 28.63MPa and \u003cem\u003ef\u003c/em\u003e\u003csub\u003e\u003cem\u003ec\u003c/em\u003e\u003c/sub\u003e = 42.19MPa with spacing S\u0026thinsp;=\u0026thinsp;25mm, pull-out failure was commonly observed in specimens with shorter embedment lengths, while splitting failure was more frequent in specimens with longer embedment lengths.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eIn specimens with 50mm spacing between bars and a concrete strength of \u003cem\u003ef\u003c/em\u003e\u003csub\u003e\u003cem\u003ec\u003c/em\u003e\u003c/sub\u003e = 28.63MPa, splitting failure was the dominant failure mode. At the onset of slip, one deformed bar initially displaced independently. However, as the applied tensile load increased, both bars began to act together.\u003c/p\u003e \u003c/li\u003e \u003c/ul\u003e \u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eConflict of Interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe author declares that there is no conflict of interests regarding the publication of this paper.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData Availability Statement \u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe data presented in this study are available on request from the author.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis research received no external funding.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthors Contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eConceptualization, E.A.B.; methodology, E.A.B., and M. K. Kh.; formal analysis, E.A.B., and M. K. Kh.; resources, M. K. Kh.; data curation, E.A.B., and M. K. Kh.; writing\u0026mdash;original draft preparation, E.A.B., writing\u0026mdash;review and editing, E.A.B., and M. K. Kh.; funding acquisition, M. K. Kh.; All authors have read and agreed to the published version of the manuscript.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eG. Xing, C. Zhou, Tao Wu, B. Liu, \u0026quot;Experimental Study on Bond Behavior between Plain Reinforcing Bars and Concrete\u0026quot;, Advances in Materials Science and Engineering, vol. 2015, Article ID 604280, 9 pages, 2015. https://doi.org/10.1155/2015/604280\u003c/li\u003e\n\u003cli\u003eACI Committee 408R-03, \u0026ldquo;Bond and Development of Straight Reinforcing Bars in Tension\u0026rdquo;, American Concrete Institute, Farmington Hills, Mich., 2003, 1.111. https://standards.globalspec.com/std/1526591/aci-408r\u003c/li\u003e\n\u003cli\u003eA. M. Diab, H. E. Elyamany, M. A. 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Sureshbabu, \u0026ldquo;Bond-slip Behavior of Geopolymer Concrete after Exposure to Elevated Temperatures\u0026rdquo;, Jordan Journal of Civil Engineering, vol. 15(4), 2021, PP:570-585. https://jjce.just.edu.jo/issues/paper.php?p=6034.pdf\u003c/li\u003e\n\u003cli\u003eMujalli M.A., Dirar, S., Mushtaha, E., Hussien, A., Maksoud, A. \u0026ldquo;Evaluation of the Tensile Characteristics and Bond Behaviour of Steel Fibre-Reinforced Concrete: An Overview\u0026rdquo;, Fibers Journal, vol. 10(104), 2022. https://doi.org/10.3390/fib10120104\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":true,"highlight":"","institution":"Department of Civil Engineering, College of Engineering, Qassim University, Buraidah 52571, KSA","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Bonding performance, bar diameter, embedment length, strength of concrete, spacing between deformed bars, pullout test","lastPublishedDoi":"10.21203/rs.3.rs-6895610/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6895610/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThis experimental study provides a comprehensive assessment of the bond performance of two deformed steel reinforcing bars with diameters of 8mm, 10mm, and 12mm in two concrete mixes incorporating hooked-end steel fibers. A total of 36 cylindrical pullout specimens were prepared and subjected to rigorous pullout tests. The study meticulously examined the impact of four critical parameters: bar diameter, embedment length (5, 10, and 15 times the bar diameter), concrete strength, and spacing between deformed bars (25mm and 50mm). The influence of these parameters on bond strength was thoroughly evaluated, and failure mechanisms were analyzed. Results indicated that pullout failure was the dominant failure mode for specimens with shorter embedment lengths, while splitting failure prevailed in specimens with the longest embedment lengths. Increasing the embedment length significantly enhanced the ultimate load, toughness, and slip values of the tested specimens. Additionally, specimens with closer bar spacing exhibited superior bonding performance compared to those with wider spacing. Thus, reducing the spacing between reinforcing steel bars in concrete has been proven to improve load transfer efficiency and minimize stress concentrations, leading to higher structural integrity. This practice enhances the bond strength between steel and fiber concrete, resulting in improved resistance to cracking and deformation under applied loads.\u003c/p\u003e","manuscriptTitle":"Performance Enhancement of Reinforcing Bars in Concrete with Hooked-End Steel Fibers: A Pull-Out Study","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-06-18 19:35:48","doi":"10.21203/rs.3.rs-6895610/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"4597ab99-f1c3-44ef-aa7a-8dce95852643","owner":[],"postedDate":"June 18th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":50056624,"name":"Civil Engineering"}],"tags":[],"updatedAt":"2025-06-18T19:35:48+00:00","versionOfRecord":[],"versionCreatedAt":"2025-06-18 19:35:48","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-6895610","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6895610","identity":"rs-6895610","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}