Bond-slip Curves Research Articles

Effect of polypropylene and brass‐coated steel fibers on bond behavior of GFRP bars in normal and high‐strength geopolymer concrete

AbstractIn the current study, the effect of two types of fibers, polypropylene (PP) and brass‐coated steel (BS) fibers, on the bond performance of glass fiber‐reinforced polymer bars with geopolymer concrete is investigated. Additionally, the impact of embedment length, bar diameter, and compressive strength of the concrete on the bond behavior was considered. The result shows that inclusion of BS fibers considerably improves the pullout capacity and the curve's initial stiffness, as the BS fibers have a superior tensile strength than PP fibers. In the case of PP specimens, few samples demonstrated a change in failure mode from split to pullout. However, in the case of BS specimens, including those that showed split failure in PP specimens, failed in a pullout fashion. The crack width seen on the exterior concrete surface is considerably reduced with the addition of fibers. To assess the post‐peak response of the bond stress versus slip curves, energy‐based bond toughness parameters were proposed, and the results indicate that the post‐peak response was enhanced by the addition of BS fibers. Increasing the embedment length and bar diameter has a negative impact on the bond characteristics, whereas the concrete strength has the opposite effect. Experimental results compared with analytical models, and Cosenza‐Manfredi‐Realfonzo model outperformed the modified Eligehausen, Popov, and Bertero model. Overall, BS fibers produce superior outcomes.

Comparative bond-slip responses of CFRP tubes in seawater sea sand concrete after epoxy mortar modification

The initial bond stress between carbon fiber reinforced polymer (CFRP) and concrete is low, and installing shear connectors on FRP profiles disrupts the integrity of the material. As a result, sand coating is the preferred method for interface treatment. Epoxy mortar, known for its high bond strength and strong permeability, is used to enhance the roughness of the interface. Push-out tests were carried out on interfaces between seawater sea sand concrete (SWSSC) and CFRP coated with epoxy mortar. The results demonstrated that the epoxy mortar bonded well with SWSSC, with failure primarily occurring at the epoxy mortar-CFRP interface. A few specimens exhibited concrete cohesive failure or interlayer fiber cracking. The application of epoxy mortar limited the extrusion behaviour of the core concrete, as evidenced by the reduced critical slip value at the loading end and the low tensile strain measured on the FRP tube. Bond-slip curves were more likely to show peak values for specimens with rougher interfaces or shorter lengths along the push-out direction. For specimens with CRFP tube diameters of 75mm and 110mm, epoxy mortar coating increased the critical bond stresses at the SWSSC-CFRP interface by more than 43.4% and 67.1%, respectively. The epoxy mortar provided mechanical interlocking, reducing the loss of bond stress caused by insufficient confinement or concrete self-shrinkage from 61.4% to 19.6%. This indicates that the epoxy mortar is an effective material for improving the initial FRP interface. In this study, existing bond-slip relationship models were reviewed, suitable parameters for epoxy mortar-modified interfaces were proposed, and the general applicability of the model was verified.

Bond shear modulus in reinforced concrete at high temperature: General trends from test results

The scanty attention devoted so far to bond shear modulus (secant or tangent slope of the loading branch of the bond-slip curve) limits the ability to numerically model such phenomena as tension stiffening, that controls the stiffness of cracked RC structures even past a fire. To improve the knowledge of bond shear modulus at high temperature, the bond stress-bar slip curves resulting from the tests of eleven selected experimental campaigns spanning a forty-year period are re-examined in this paper. Bond shear modulus is derived as the initial slope of the bond stress-bar slip curves of stressed or unstressed specimens in either hot or residual conditions. The criteria to compare the test results coming from very different experimental campaigns are discussed at length. Bond shear modulus is shown to be a decreasing function of the residual compressive strength of the concrete (at high temperature or past cooling). The envelopes of the test data allow to assess the roles of bar diameter and concrete grade. Trend curves are derived for normal-strength and high-strength/high-performance concretes, as a first necessary step for the formulation of parametric design-oriented laws, that may be useful to model tension stiffening and to describe the distribution of the bond stresses in long anchored bars. A numerical example is also developed and the consistency with EuroCode EC2 is checked.

Research on the bond performance between glass fiber reinforced polymer (GFRP) bars and Ultra-high performance concrete(UHPC)

In recent years, in order to overcome the problems that steel bars are prone to rust and the ductility of GFRP and ordinary concrete is insufficient, a new type of reinforced concrete structure with good durability and high ductility has been developed by combining glass fiber reinforced polymer (GFRP) bars with ultra-high performance concrete (UHPC). The bond performance between GFRP and UHPC is the guarantee for them to work together and achieve optimal performance, which is worthy of further research. In this paper, pull-out tests were performed on 75 center pull-out samples with a side length of 150 mm, taking into account factors such as GFRP bar diameter, surface treatment type, bond length, and fiber content. The failure modes and bond performance of GFRP bars and UHPC pull-out specimens were investigated. The results indicate that the bond-slip curves of GFRP bars in UHPC and ordinary concrete show similar bond-slip characteristics. Compared with ordinary concrete, UHPC pull-out specimens demonstrate superior mechanical properties, including better bond strength and ductility. The UHPC-GFRP bars and UHPC-steel bars (8 mm and 10 mm) underwent pull-out failure. However, the 12 mm steel bar in UHPC reached its ultimate tensile strength, causing pull-off failure. The bond strength of GFRP bars decreases with the increase of diameter. In addition, with the increase of bond anchorage length, the bond strength decreases. When GFRP bars of the same diameter are anchored in ultra-high-performance concrete, the GFRP bars with ribbed surfaces display superior bond performance compared to those with sandblasted surfaces. Based on the models proposed by previous researchers, this paper proposes a suitable formula for estimating the bond strength between GFRP bars and UHPC. The calculated results are in good agreement with the measured results.

Bond performance and damage assessment of self-sensing steel–fiber composite bar with geopolymer concrete

This study employed a novel steel–fiber composite bar (SFCB) enhanced with Distributed Optical Fiber Sensors (DOFS) technology to reveal the local bonding and damage mechanisms between composite reinforcement and seawater sea sand geopolymer concrete. By embedding DOFS within the steel core of the SFCB reinforcement, the local bond stress between the reinforcement and geopolymer concrete was monitored. The continuous measurement provided by DOFS revealed a non-uniform strain distribution along the length of the SFCB reinforcement and an uneven distribution of bond stress within the bonded section. Based on test results, a modified bond–slip model was utilized to predict the bond–slip relationship between the SFCB reinforcement and the geopolymer concrete, taking into account the influence of surface treatment on the descending branch of the bond–slip curve. Additionally, a damage model was employed to evaluate the extent of damage at the bond interface between the SFCB reinforcement and the geopolymer concrete under different load levels. Finally, the modified bond–slip model was also used to propose the anchorage length for SFCB reinforcements, which was compared with ACI, CSA, and JSCE codes.

Experimental investigation on bond properties of nano-Al2O3 and hydroxypropyl methyl cellulose (HPMC) modified coated steel bar embedded in concrete

In this work, cementitious coatings incorporate nano-Al2O3 (NA) and HPMC were developed applying to the surface of steel bars to enhance bond behavior. A total of 81 pull-out specimens were prepared to evaluated bond properties of different coated steel bars embedded in ordinary performance concrete (OPC), high performance concrete (HPC) and ultra-high-performance concrete (UHPC). The mechanical properties of the cement-based coatings have also been examined. Test results show that flexural and compressive strengths of coating paste exhibited initially increasing and followed by decreasing as NA content increase. Synergistic effect of NA and HPMC results in cement-based coating exhibiting superior mechanical properties. Besides, coating microscopic morphology characterized by scanning electron microscope (SEM) technique revealed that fewer coating defects with NA and HPMC compounding. More importantly, the highest bond strength between coated steel bar and different types concretes was found at 1.0 % NA content in the coatings. Synergistic effect of 1.0 % NA and 0.12 % HPMC improved bond strength of coated steel bar embedded in OPC, HPC and UHPC. It can be obtained from bond-slip curve that, regardless of the HPMC addition to coatings, coated steel bar with 1.0 % NA content shows higher bond stiffness. With both NA and HPMC added, bond stiffness, bond toughness and bond ductility of coated steel bar are superior to those of the coating with NA alone. Moreover, as concrete strength increases, the bond strength, bond stiffness and bond toughness of coated steel bar also increase, respectively.

Bond-slip model of corroded plain round bars in low-strength concrete under cyclic and monotonic loading

The effect of corrosion on the overall behavior of beam-type bond-slip samples constructed from low-strength concrete and plain round bars was examined in this study. First, a set of nominally identical specimens underwent testing under both monotonic and cyclic loading, and subsequently, the bond-slip interaction was assessed for each individual sample. The observed failure mode for plain round bars was direct pullout without concrete splitting apart, characterized by the loss of cohesion between the rebar and the adjacent concrete surface. Then, an analytical relationship was established by fitting a curve to the average experimental data using the method of least squares. Corrosion-degradation in the bond stress was considered by incorporating an exponential component into the equation of the reference bond-slip curve (i.e., null corrosion). Besides, the degradation in bond strength was predicted as a function of corrosion level, which is in the form of an exponential curve. The maximum surface crack width, an easily quantified variable on-site, was correlated with the bond strength of corroded bars. The regression analysis successfully established the optimal relationship between the maximum surface crack width and the corrosion level in an exponential form as well. Notably, the majority of the data in all cases fell within the 95% confidence interval.

Influence of mechanical anchors on bond performance of fiber fabric-steel joints

This study proposes an experimental model for anchor reinforcement and conducts uniaxial static tensile tests. The influence of anchor reinforcement on the failure mode of specimens is revealed. This includes the effects of bond length, number of layers, and types of fiber fabric under anchor reinforcement on the ultimate bearing capacity and bond-slip curve. The results demonstrate that anchors can effectively increase the ultimate bearing capacity of the test specimens. There are differences in bond-slip behavior between the anchors near the free end and the joint end. Higher stresses are experienced near the joint end. The use of anchor reinforcement can significantly enhance the load-bearing capacity of multi-layer carbon fiber specimens. Increasing the number of anchors and reducing the distance between the anchor and the joint end can further improve the stiffness of the specimens. A finite element model is established using ANSYS, which agrees well with the experimental results and parameterized analysis results reveal a linear increase in load-bearing capacity and stiffness with higher anchor bolt preload, achieving an 84.42 % increase at 11kN. Increased preload enhances friction at the carbon fiber-steel interface, reducing deformation. Similarly, expanding anchor width from 9 mm to 39 mm improves load-bearing capacity by 54.28 %, with larger anchors significantly boosting stiffness and bonding performance, which can be used to predict the mechanical properties of fiber fabric-steel reinforced by anchors.

Interface mechanical properties of CFRP-seawater sea sand concrete under simulated seawater immersion

In this study, the interfacial mechanical properties of carbon fiber-reinforced polymer (CFRP) sheet reinforced seawater sea sand concrete (SSSC) in simulated seawater immersion environment were studied. The results present that the interface bearing capacity of CFRP-SSSC decreases significantly after seawater immersion. The decreasing rate increases greatly with the extending of immersion periods. Seawater immersion also affects the failure mode of interface between CFRP and SSSC, which leads to the damaged surface expanding from the base layer of concrete to the junction section of resin and aggregate. The distribution of strain and stress along the bonding direction presents the load transfer from the loading end to the free end. The shear stress peak locates near the loading end and decreased about 15–20 % due to seawater immersion as a result of the deterioration of the interfacial property. The analysis on the microstructure of CFRP-SSSC interface proves that the chemical ions in seawater causes the hydrolyzation of epoxy resin adhesive layer. The CFRP-SSSC interface presents a lower interfacial bonding properties than CFRP reinforced normal concrete (NC). The improvement of strength grade of concrete from C30 to C50 increases the bonding properties of the CFRP about 9–12 % and mitigates the influence of seawater immersion. The obtained bond-slip curve indicates that the seawater immersion decreases the interface ductility. A modified Popovics model is applied to predict the bond-slip curve and presents a high fitting degree.

Experimental study on bond-slip behaviors of CFRP sheet-Q690 high strength steel plate considering the effect of CFRP sheet thickness and bonding length

With the increasing application of carbon fiber reinforced polymer (CFRP) in steel structure engineering, the bond-slip behavior between the two has attracted much attention. Firstly, 18 sets of CFRP sheet-Q690qD high-strength steel double strap shear specimens were fabricated considering the effects of CFRP sheet thicknesses and bond length. Then, static and fatigue tests were conducted on them. Subsequently, based on the 3D-DIC acquisition technology, the bond-slip curves were obtained using the smoothing method and the fitting method respectively Finally, the three key parameters of τmax, s1and sf in the bifurcated model at each working condition were obtained. The experimental results indicated that the bond length was positively correlated with the static load ultimate strength, while the thickness of the CFRP sheet had less effect on the ultimate strength. The fatigue life of the specimen with a bond length of 40 mm under equal stress ratio fatigue loading was much higher than that of the specimens with bond lengths of 60 mm and 80 mm. It was found that the fitting method had better stability and accuracy in fitting the bond-slip curves of CFRP sheet-Q690qD high-strength steel specimens. The accuracy of the fitting maximum bond load was above 80 %, which can provide a relevant basis for the subsequent numerical simulation calculation.

Meso-scale Study of Bond Behavior between Ribbed Steel Rebar and Fiber-reinforced Cementitious Composite Considering Rebar Rib Geometry

This study aims to develop a meso-scale finite element approach to investigate the pull-out behavior of ribbed steel rebar and fiber-reinforced cement composites. We considered separately the three phases of steel fibers, cement composite matrix, and rebar within the meso-scale finite element model. A random distribution of fibers was generated in the matrix based on the geometric characteristics of the fibers and their volume fraction. By employing the interfacial transition zone (ITZ) model, the interaction between rebar and fibers with cement composite was simulated. Experimental pull-out tests were conducted to determine the parameters of the model. A meso-scale finite element model was validated and the effect of rebar diameter and fiber volume fraction on the bond behavior of rebar with fiber-reinforced cement composites was examined. In accordance with the experimental results, the bond-slip curve obtained with the meso-scale finite element model can be divided into five areas: non-slip, slight slip, splitting, decreasing, and residual. Additionally, it can be observed that fiber-free cement composites fail by splitting, whereas specimens containing fibers fail by sliding. This numerical model is therefore able to predict and estimate the influence of a variety of parameters on the pull-out response between fiber-reinforced cement composite and ribbed bar and failure mechanisms without the need for expensive and time-consuming testing.

Corrosion effects on bond strength in reinforced concrete with fly ash

Reinforcing steel bars provides additional strength and ductility to concrete by forming a strong bond with the concrete matrix. Corrosion of steel bars can significantly reduce the bonding effect between the steel bar and concrete, which can compromise the structural integrity and durability of reinforced concrete structures. An experimental investigation was performed to examine the influence of fly ash (FA) and corrosion on concrete–steel bond behavior. The accelerated corrosion method was employed to obtain the desired level of corrosion. The FA content, corrosion percentage, and presence of stirrups were considered significant factors influencing bond behavior. The bond–slip curves and bond toughness were used to discuss bond behaviors. The findings indicated that mild corrosion (below 2.5%) can enhance concrete–steel bond performance, and the addition of 20% FA leads to higher ultimate bond strength (τu ), significantly mitigating the decrease in bond strength caused by severe rebar corrosion. Also, this study analyzed the influence of stirrups on the bond strength of FA concrete and had a nearly insignificant effect compared to regular concrete. The results and discussions of the present study carry significant importance in the establishment of a bond–slip constitutive model under multifactor coupling conditions. Furthermore, it offers valuable insights into the design of engineering structures.

Numerical analysis of the effect of bar anchorage length on bond behavior in pull-out test

This paper presents a numerical simulations of a pull-out test conducted using ABAQUS software. The purpose of the simulations was to evaluate the effect of anchorage length on the bond behavior of ribbed bars in this test, based on the experiments performed. The interaction at the bar-concrete interface was modeled using a contact cohesive surface and calibrated bond-slip curves obtained from experiments. Material models were defined using mechanical parameters obtained from in-house tests on concrete and steel. The analysis shows that the bond behavior is significantly influenced by the anchorage length. Numerical simulation results demonstrate excellent convergence with laboratory tests, both in terms of the bond-slip curve and material behavior

Bond performance of marine concrete with nano-particles to steel bars under the action of both Cl− erosion and freeze-thaw cycles

Offshore structures serve in harsh environment here the combined effects of freeze-thaw cycles and Cl− erosion severely degrade the bond performance between steel bars and concrete, significantly reducing the structures' service life. This paper investigates the bond performance of marine concrete with nano-particles to steel bars under the simultaneous influence of Cl− erosion and freeze-thaw cycles. The bond-slip (τ-s) curves are derived from pull-out tests, in order to reveal the mechanism of nano-particles to improve the bond performance of reinforced concrete under the action of both Cl− erosion and freeze-thaw cycles, the microstructure of the bond interface between steel bar and concrete is examined using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and mercury impression test (MIP). The test results show that adding nano-SiO2 and nano-TiO2 enhance the cracking bond strength (τs), ultimate bond strength (τu), ultimate slip value (Su), and residual bond strength (τr) of reinforced concrete. The optimal content for both nano-SiO2 and nano-TiO2 are 2 %, with nano-SiO2 showing superior effect. When Cl− erosion and the number of freeze-thaw cycles are certain (N = 100), the τu values of NSC20 and NTC20 are increased by 26.25 % and 16.68 %, and the Su values are increased by 25.30 % and 22.89 %, respectively, compared with PC. The results of the SEM and EDS analyses indicate that nano-particles promote C–S–H gel formation, reduce porosity and optimize concrete's pore structure, enhance shear strength at the bonding surface, reduce Cl− content at the interface, slow down the corrosion of the steel bars. Thus, the addition of nano-particles significantly improves the bond performance of reinforced concrete under the action of both Cl− erosion and freeze-thaw cycles, which is vital for enhancing the load-bearing capacity and seismic performance of engineering structures.

Bond properties of GFRP bar embedded in marine concrete subjected to sustained loads

In this work, a total of 20 beam type concrete specimens were prepared to investigate bond behavior of glass fiber reinforced polymer (GFRP) bar embedded in marine concrete. The influence of sustained loads (load level: 0.25, 0.45 and 0.65 ultimate load (Pu)) and stirrup on bond properties was investigated. After sustained load period, flexural bond test was conducted to determine bond stress and slip. Test results indicate that bond strength of GFRP bars shows decreased trend with increasing sustained loading. Compared with specimen not subjected to sustained load, bond strength significantly decreased under 0.25, 0.45 and 0.65 Pu. Also, sustained load deteriorates the bond stiffness and bond toughness. What’ s more, differences in failure modes and bond strength of steel bar and GFRP bars in flexural bonding tests were analyzed and compared. All GFRP bar specimens subjected to sustained load exhibit bars pull-out failure. In contrast to steel bar, the influence of stirrups on GFRP bar-marine concrete bond strength is relatively limited (specimens with stirrups exhibited only 1.8 % increase over specimens without stirrups), due to GFRP bars lower rib heights and weaker mechanical interlocking with concrete. Characterization of different stages of bond-slip curves of GFRP bar beam specimen subjected to sustained loads was carried out and bond-slip curves of GFRP shows two peaks. According bond strength and slip test data, bond stress-slip mathematical relationship model between GFRP bar and marine concrete under sustained load has been fitted.

Experimental study on bond behavior between wet lay-up CFRP and corroded steel plates

Corrosion of steel in marine environments is a major safety concern for marine steel structures throughout their service lives. Strengthening these corrosion-damaged structures with carbon fiber-reinforced polymer (CFRP) shows great potential for extending their service lives. However, the bond behavior between CFRP and corroded steel, especially the influence from adhesive properties and corrosion degree, has not been fully understood. This paper therefore presents the results of a comprehensive experimental study on the bond behavior between wet lay-up CFRP and corroded Q355B steel plates. Tensile tests on double-lap CFRP-to-steel joint specimens with different bonded lengths, adhesives and corrosion durations were then conducted. The failure modes, load-displacement curves, strain and local shear stress distributions, effective bond lengths, and bond-slip relationships of the test joint specimens were investigated in detail. The result showed that the influence of corrosion on the CFRP-to-steel bond performance varied depending on the failure modes resulting from the material properties of adhesives. However, corrosion has insignificant influence on the general patterns of load-displacement curves, strain distribution, local shear stress distribution, local bond-slip curves with same adhesives. When failure occurred in the adhesive or the steel-adhesive interface, the corrosion tended to have a more accentuated effect on the bond performance.

Analysis of Bonding Properties of Corroded Reinforcement Concrete

In order to investigate the degradation of bonding properties between corroded steel bars and concrete, this study employs the half-beam method to conduct bond-slip tests between corroded steel bars and concrete after impressed-current accelerated corrosion of the steel bars in concrete. The effects of steel corrosion rate, steel bar diameter, steel bar strength grade, and concrete strength grade on the bonding properties between concrete and corroded steel bars were analyzed. The influence of different corrosion rates on specimens’ bonding strength and bond-slip curves was determined, and a constitutive relationship for bond-slip between corroded steel bars and concrete was proposed. The results indicate that the ultimate bonding strength of corroded reinforced concrete specimens decreases with increasing corrosion rate. Additionally, an increase in corrosive crack width leads to a linear decrease in bonding strength. Evaluating the decline in adhesive properties through rust expansion crack width in engineering applications is feasible. Furthermore, a bond-slip constitutive relationship between corroded steel bars and concrete was established using relative bond stress and relative slip values, which aligned well with the experimental findings.

Bond properties between corroded steel bars and recycled aggregate concrete after high-temperature exposure

Increasingly used reinforced recycled aggregate concrete (RAC) structures may suffer from steel corrosion and high-temperature exposure. The bond behaviors between corroded steel bars and RAC after high-temperature exposure are important in the high-temperature/fire damage assessment of aging RAC structures. In this study, pull-out tests were carried out on specimens of corroded steel and natural aggregate concrete (NAC) or RAC after high-temperature exposure. The specimens were exposed to 20, 100, 200, 300, 400, 500, 600, 700 and 800 °C with steel bar in the specimens corroded with corrosion ratios of 0.00 %, 1.05 %, 3.07 %, 5.34 %, 7.50 %. The failure modes, bond-slip curves and bond strength were studied. Effects of corrosion/temperature on bond strength and their difference when using different aggregates (RAC and NAC) were analyzed. The test results indicated that the bond strength of most specimens decreased with increasing high-temperature exposure, and the bond strength degradation of NAC was slightly higher than that of RAC. The bond strength first increased and then decreased as the corrosion ratio increased, and the bond strength of NAC is higher than that of RAC under high corrosion conditions. The failure modes and bond strength also varied with and without stirrups. A bond-slip constitutive model of corroded steel bar and RAC without stirrups after high temperature was established introducing temperature and corrosion influence coefficients.

Bond Properties of CFRP Externally Bonded Reinforcement on Groove in Concrete

Externally bonded reinforcement on groove (EBROG) is a significant reinforcement technology proposed by researchers to enhance the bond properties of reinforced concrete structural members. To understand the influence of groove size on concrete specimens of different strength, a total of 60 concrete specimens with 4 different strengths were cast with the single shear test in this paper, among which 48 EBROG specimens and 12 specimens with externally bonded reinforcement method (EBR) were used as the control group. The failure modes and failure mechanisms of specimens with various sizes and reinforcement methods were analyzed. Additionally, the test results of ultimate load, load–displacement curves, and bond-slip curves for specimens with different groove sizes were compared. The effectiveness of EBROG method in enhancing the ultimate load capacity at the bond interface of the specimens is proved. Furthermore, in situations where the volume of the groove was kept constant, the specimens with lower concrete strength and deeper groove exhibited superior bond properties. Also, the influence of groove width on bond properties was better than that of groove depth. Finally, the test results in this paper were compared with the prediction of the existing EBR and EBROG models to evaluate the performance of different models, and based on the original model, a prediction model for EBROG method in the groove region with higher accuracy was proposed.

Bond behavior and modeling of steel-FRP composite bars in engineered cementitious composites

The combination of the steel-FRP composite bar (SFCB) and engineered cementitious composite (ECC) holds favorable applications in terms of durable resilient structures. However, a clear understanding of the interfacial bond performance of this novel combination is currently lacking. Therefore, the bond behavior and mechanism of the SFCB-ECC interface were investigated through direct pullout tests. A total of 48 cube specimens were fabricated, with the test variables including bar type, bar diameter, embedment length, and matrix type. The experimental results indicated that the bond failure mode of SFCBs and FRP bars differed from that of deformed steel bars, attributed to the damage of resin-rich ribs in relatively high-strength ECC. The bond-slip curves revealed both the fundamental differences and similarities among steel bars, SFCBs, and FRP bars. The Poisson effect and shear lag effect increased with a decrease in bar stiffness and an increase in diameter. The combined impact of the interaction between the bar stiffness and diameter resulted in varying bond strengths for steel bars, SFCBs, and GFRP bars, despite their similar surface geometries. A theoretical model for the bond strength at the SFCB-ECC interface was derived using the thick-walled cylinder principle and subsequently validated with test data. Finally, a unified empirical model framework for predicting the bond strength of various bar-matrix combinations was proposed based on the theoretical model. The accuracy of this method was evaluated using a collected database.