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Models used to study the fracture process of concrete are often considered 2D, ignoring the influence of specimen width. However, during the fracture process in pre-cracked concrete beams, the crack length varies along the thickness direction, especially in reinforced concrete. To study the influence of specimen width on reinforced concrete fracture behavior, a 3D numerical method was used to simulate the crack propagation processes of lightly reinforced concrete beams based on Fracture Mechanics. Nonlinear spring elements with different stress-displacement constitutive laws were employed to characterize the softening behavior of concrete and the bond-slip behavior between the steel bars and concrete, respectively. It is assumed that the crack begins to propagate when the maximum stress intensity factor at the crack tip along the beam width reaches the initial fracture toughness of concrete. To verify the validity of the proposed method, the completed crack propagation processes of lightly reinforced concrete three-point bending notched beams were simulated, and the calculated load-crack mouth opening displacement curves showed a reasonable agreement with the experimental data. Moreover, the impact of the 2D reinforced concrete beam model on the crack propagation process was analyzed. The results indicate that at the initial loading stage, the external load P obtained from the 2D model is significantly larger than the result from the presented 3D model. [ABSTRACT FROM AUTHOR]

The bond between reinforced bars and concrete has a significant impact on reinforced concrete structures. Incorporating steel fibers in concrete not only enhances the performance of the concrete but also influences the bond strength of embedded reinforcing bars. In this paper, experiments have been carried out to investigate the influences of different bar diameters, concrete cover and embedment lengths on bond-slip responses between reinforcing bars and steel fiber reinforced concrete (SFRC). Furthermore, pull-out tests with normal concrete were also executed as a comparative group. The bond-slip results of specimens were collected. The impact of embedment length, reinforcing bar diameter, and the existence of steel fibers on the bond behavior of reinforcing bars was comprehensively analyzed. Meanwhile, the results indicate that variations in the ratio of concrete cover to reinforcing bar diameter lead to different effects on the bond behavior of SFRC compared with normal concrete. Different failure modes of specimens were exhibited and discussed. Additionally, a mathematical model for bond strength of bars in SFRC was proposed based on the correction of the bond strength model with normal concrete, which shows good agreement with experimental results.

This study investigates and assesses the bond performance between steel reinforcement and recycled concrete, subject to the confining effect of transverse stirrups post high-temperature exposure. A series of 24 specimen groups was examined, with variations in parameters including transverse stirrup ratios (0 %, 0.24 %, 0.67 %, 1.34 %), recycled concrete aggregate (RCA) replacement ratios (0 %, 50 %, 100 %), and temperatures (300 °C, 500 °C, 700 °C). Central pull tests were administered to discern the impact of each parameter on the bond integrity of steel-reinforced recycled concrete. The results revealed that high temperatures reduced the thickness of the critical cover, altering the failure mode of the specimen. With rising temperatures, the bond strength of steel-reinforced recycled concrete weakened. Nonetheless, an increase in stirrup ratio served to counteract the detrimental effects of high temperatures. In contrast, a higher RCA replacement ratio exacerbated these effects. For example, specimens with a 1.34 % stirrup ratio showed a 30 % decrease in the adverse impacts of high temperature on bond strength compared to those with no stirrups. A comprehensive computational model, devised from experimental data and theoretical analysis, predicts the bond-slip behavior of steel-reinforced recycled concrete, incorporating the constraint coefficient k, temperature T, and replacement ratio r as pivotal parameters. The model’s predictive curve corresponds closely with the experimental findings, effectively capturing the influence of high temperature, lateral restraint, and RCA replacement ratio on the bond performance of steel-reinforced recycled concrete.

Steel-fiber reinforced polymer (FRP) composite bars (SFCBs) can enhance the controllability of damage in concrete structures; thus, studying the interfacial bonding between them is fundamental and a prerequisite for achieving deformation coordination and collaboration. However, research on the interfacial bonding performance between SFCBs and concrete remains inadequate. This study conducted central pullout tests on SFCB-concrete specimens with different concrete strengths (C30, C50, and C70), bar diameters (12, 16 and 20 mm), and hoop reinforcement constraints, analyzing variations in failure modes, bond-slip curves, bond strength, etc. Additionally, finite element simulations were performed using ABAQUS software to further validate the bonding mechanism of SFCB-concrete. The results showed that the failure mode of the specimens was related to the confinement effect on the bars. Insufficient concrete cover and lack of hoop restraint led to splitting failure, whereas pullout failure occurred otherwise. For the specimens with pullout failure, the interfacial damage between the SFCB and concrete was mainly caused by the surface fibers wear of the bar and the shear of the concrete lugs, which indicated that the bond of the SFCB-concrete interface consisted mainly of mechanical interlocking forces. In addition, the variation of concrete strength as well as bar diameter did not affect the bond-slip relationship of SFCB-concrete. However, the bond strength of SFCB-concrete increased with the increase of concrete strength. For example, compared with C30 concrete, when the concrete strength was increased to C70, the bond strength of the specimens under the same conditions was increased to 50–101.6%. In contrast, the bond strength of the specimens decreased by 13.29–28.71% when the bar diameter was increased from 12 to 14 mm. These discoveries serve as valuable references for the implementation of sustainable SFCB-reinforced concrete structures. [ABSTRACT FROM AUTHOR]

Traditional cast-in-place beam–column joints have the defects of high complexity and high construction difficulty, which seriously affect the efficiency and safety of the building construction line, and precast beam–column joints (PBCJs) can greatly improve the construction efficiency and quality. At present, the investigations on the seismic behavior of precast reinforced concrete structures are still mainly focused on experiments, while the numerical simulations for their own characteristics are still relatively lacking. In the present study, the seismic behavior of novel precast beam–column joints with mechanical connections (PBCJs-MCs) is investigated numerically. Based on the available experimental data, fiber models for four PBCJs-MCs are developed. Then, the simulated and experimental seismic behaviors of the prefabricated BCJs are compared and discussed. Finally, the factors influencing the seismic behavior of the PBCJs-MCs are further investigated numerically. The numerical results indicate that the fiber models can consider the effect of the bond–slip relationship of concrete and reinforcement under reciprocating loads. The relative errors of the simulated seismic behavior indexes are about 15%. The bearing capacity and displacement ductility coefficients of the PBCJs-MCs decrease rapidly as the shear-to-span ratio (λ) increases. It is recommended that the optimum λ for PBCJs-MCs is 2.0–2.5. The effect of the axial load ratio on the seismic behavior of PBCJs-MCs can be negligible in the case of the PBCJs-MCs with a moderate value of λ. [ABSTRACT FROM AUTHOR]

In order to avoid joint failure of half grouted sleeve connection due to bond-slip, a method of applying the anchor plate in half grouted sleeve is proposed to improve reliability and mechanical properties of half-grouted sleeve connection. Using the ABAQUS software, considering the bond-slip between the steel bar and the grouting material and the plastic damage of the grouting material, a finite element simulation specimen group with different diameters of steel bars and with or without anchor plates is set up, and the specimen group is monotonically carried out by means of displacement loading. The results show that the bond strength between steel bar and grout increases and the elongation displacement of half grouted sleeve connection decreases with the increase of anchorage length of steel bar under the same diameter. Under the same length of anchorage, with the increase of steel bar diameter, the relative slip between steel bar and grouting material increases, and the elongation displacement of half grouted sleeve connection increases. At the same time, the restriction effect is more obvious with additional anchor plate. Adding the anchor plate avoids the pull-out failure mode of steel bar when the anchorage length of steel bar is equal or less than 8d (d is the diameter of steel bar). The bonding action range of steel bar-grout interface without anchor plate connection is limited. The anchor plate plays a bearing role, and the stress of the steel bar on the side away from the load end is significantly reduced. Therefore, the performance of half grouted sleeve connections can be improved by means of anchor plates. [ABSTRACT FROM AUTHOR]

Pull-out tests were conducted to investigate the effects of corrosion of both the longitudinal bars and stirrups on the bond slip behaviour of reinforced concrete specimens. The main experimental variables include concrete strength (26.7 MPa, 37.7 MPa and 45.2 MPa) and expected corrosion loss (0%, 4%, 8% and 12%), with a total of 63 specimens fabricated. The results show that the relative bonding strength of specimens under different concrete strengths gradually decreases with increasing corrosion loss, but the higher the concrete strength is, the faster its degradation rate. The influence of stirrup corrosion on the peak slip can be ignored, but it will further aggravate the degradation of the bonding strength of the specimens. This reduction in bonding strength is linearly related to the stirrup corrosion loss. Based on the experimental results of this work and the achievements of other scholars, a modified relative bonding strength degradation model and a bond–slipbond–slip constitutive model of corroded reinforced concrete are presented by accounting for the influence coefficient of concrete strength. The results show that the constitutive model is in good agreement with the relevant experimental results. [ABSTRACT FROM AUTHOR]

The bond performance of CFRP to concrete plays a vital role in CFRP strengthening on concrete structures. In this paper, an experimental study was carried out to investigate the bond performance of CFRP to concrete with a convex-circular arc interface. The main factors were the curvature of the concrete surface and the bond length and the layers of the CFRP laminate. Based on the experimental results, the failure mode of the bond specimens, the variation of the bond capacity, the CFRP strain, and the bond–slip constitutive model are analyzed. The results showed that most of the specimens failed to peel off the interface concrete, and the bond capacity tended to increase with the increase in bond length when the bond length was within an effective value. When the interface curvature increased to 1/0.8 m, the bond capacity tended to increase due to the CFRP exerting a certain pressure on the concrete surface. The prediction formula of the bond capacity between the CFRP and concrete is proposed considering the influence of the interface curvature. The bond–slip curves are given out based on the finite differential analysis of the strain distribution of CFRP laminates. The accuracy and applicability of the proposed model are verified with a comparison to the test results and other existing models. [ABSTRACT FROM AUTHOR]

Ultra-high-performance concrete (UHPC)-filled duct connection is an innovative solution for joining assembled structures, in which the anchorage performance of the rebar and UHPC filled in bellows plays a critical role in determining the overall connection effectiveness. To establish a reliable anchorage length and a bond–slip relationship between rebar and UHPC within a bellow, a total of 16 specimens were conducted, and pullout tests were carried out. Two parameters were considered, including the diameter ratio (D/d), representing the proportion of the diameter of the bellow D to the diameter of the steel bar d, and anchorage length (L). By analyzing the failure modes, load versus deflection curves, and steel strain data, the influences of the diameter ratio and anchorage length on the anchorage performance were discussed. The test results showed that the failure mode changed from rebar pullout to rebar breakage as the anchorage length increased from 3 d to over 10 d. The reliable anchorage length of the rebar was recommended to be at least 10 d with a diameter ratio (D/d) of 2.4. Moreover, a fitting bond–slip model was proposed based on the experimental bond–slip curves between the rebar and UHPC interface within the bellows with high precision. These findings constitute a crucial basis for the comprehensive stress analysis of assembled structures connected using UHPC grouted in bellows. [ABSTRACT FROM AUTHOR]

By investigating the bond performance between glass-fiber-reinforced polymer (GFRP) bars and concrete, GFRP bars can be better applied to concrete structures as a building material. This paper considered the effects of three different GFRP bar surface treatments, three bonding lengths, corrosive solution, and immersion time on the bonding strength. The test results indicated that the bond strength decreases with the increase in the diameter and bond length. The bonding between GFRP bars and concrete can be improved by treating the surface of the bars in different ways. Compared with the control group, the bond strength of the specimens in the saline solution decreased by 1.3–21.4%, and the bond strength of the specimens in the alkaline solution decreased by 26.5–38.8%. In the corrosive environment, the bond properties are degraded. A bond strength calculation formula considering the surface treatment method of the GFRP bars was proposed. The prediction formula of the bond strength retention rate between the GFRP bar and concrete in the corrosive environment was established. The formula was validated with the available research data and the calculated values agreed well with the test values. The MBPE model and CMR model are modified to establish the bond-slip model of the GFRP bars and concrete in the corrosive environment. The model curve is close to the test curve. This paper provides a theoretical basis for future research on the bond-slip performance of GFRP bars and concrete. [ABSTRACT FROM AUTHOR]

This paper conducts research based on the hollow slab members in the reconstruction and expansion project of expressways, two types of numerical finite element models with and without considering bond-slip relationship of reinforcement and concrete are established, and verified by tests. The distribution characteristics of crack spacing in reinforced concrete beams are studied. The results show that the bond-slip characteristics of reinforced concrete have little effect on the load-deflection characteristics of 8m hollow slab beam. Due to the influence of the bond-slip relationship of reinforced concrete, the load-deflection curve is partially serrated, while without considering the bond-slip relationship of reinforced concrete, the load-deflection curve is smooth. In the numerical model without considering the bond-slip characteristics, almost all damage occurs in the longitudinal direction, and the distribution characteristics of cracks can't be accurately determined. Regardless of whether the bond-slip is considered or not, the macroscopic characteristics of the stress distribution is: smaller near the support and larger at the mid-span. As secondary flexural cracks expand, models with and without consideration of bond-slip characteristics can't calculate crack spacing based on the stress distribution characteristics of the reinforcement. [ABSTRACT FROM AUTHOR]

The bonding characteristics between steel bars and concrete in reinforced concrete (RC) structures are crucial for the prediction of load-bearing capacity for seismic design. Nevertheless, most previous studies on bond-slip performance focus on the bond strength based on the pull-out experiments, it is often overlooked that the effect on the failure modes of RC members and the deformation performance due to the bond characteristics. In this research, the effect of the diameter and its arrangement of the reinforcement of the RC column on the bond failure mode and load-bearing capacity based on the cyclic loading tests and the FE analysis are carried out. In the cyclic loading test, it was found that two RC columns with different diameters and reinforcement arrangements showed distinct load-bearing capacity, deformation performance, and failure mode. Despite those columns having the same longitudinal reinforcement ratios. In addition, by applying an advanced finite element analysis using a bond-slip model that induces splitting failure, we succeeded in reproducing the cyclic deformation behavior and local damage obtained in experiments with high accuracy. The proposed model brings in the advanced prediction of the seismic behavior of RC structures and the enhancement of seismic resistance of social infrastructure facilities to earthquake disasters. [ABSTRACT FROM AUTHOR]

With superior mechanical properties and workability, ultra-high-performance concrete (UHPC) has been utilized extensively in engineering projects. To gain a comprehensive understanding of the bond behavior of UHPC or ultra-high-performance fiber-reinforced concrete (UHPFRC), researchers studied the factors influencing the bond-slip between rebar and UHPC or UHPFRC over the past few years. The literature-proposed ultimate bond strength formulas and the bond-slip constitutive model between rebar and UHPFRC are analyzed and compared. Based on the bond test database of UHPFRC, the results indicate that UHPFRC strength, relative concrete cover thickness, relative bond length, and steel fiber volume content are the primary parameters influencing the ultimate bond strength between rebar and UHPFRC. In the bond-slip constitutive model, the nonlinear ascending and linear descending model is more accurate than other models. This paper concludes by discussing the shortcomings in UHPC or UHPFRC bond research and predicting the future research trend. [ABSTRACT FROM AUTHOR]

Steel-fiber reinforced polymer (FRP) composite bars (SFCBs) can enhance the controllability of damage in concrete structures; thus, studying the interfacial bonding between them is fundamental and a prerequisite for achieving deformation coordination and collaboration. However, research on the interfacial bonding performance between SFCBs and concrete remains inadequate. This study conducted central pullout tests on SFCB-concrete specimens with different concrete strengths (C30, C50, and C70), bar diameters (12, 16 and 20 mm), and hoop reinforcement constraints, analyzing variations in failure modes, bond-slip curves, bond strength, etc. Additionally, finite element simulations were performed using ABAQUS software to further validate the bonding mechanism of SFCB-concrete. The results showed that the failure mode of the specimens was related to the confinement effect on the bars. Insufficient concrete cover and lack of hoop restraint led to splitting failure, whereas pullout failure occurred otherwise. For the specimens with pullout failure, the interfacial damage between the SFCB and concrete was mainly caused by the surface fibers wear of the bar and the shear of the concrete lugs, which indicated that the bond of the SFCB-concrete interface consisted mainly of mechanical interlocking forces. In addition, the variation of concrete strength as well as bar diameter did not affect the bond-slip relationship of SFCB-concrete. However, the bond strength of SFCB-concrete increased with the increase of concrete strength. For example, compared with C30 concrete, when the concrete strength was increased to C70, the bond strength of the specimens under the same conditions was increased to 50–101.6%. In contrast, the bond strength of the specimens decreased by 13.29–28.71% when the bar diameter was increased from 12 to 14 mm. These discoveries serve as valuable references for the implementation of sustainable SFCB-reinforced concrete structures.

Traditional cast-in-place beam–column joints have the defects of high complexity and high construction difficulty, which seriously affect the efficiency and safety of the building construction line, and precast beam–column joints (PBCJs) can greatly improve the construction efficiency and quality. At present, the investigations on the seismic behavior of precast reinforced concrete structures are still mainly focused on experiments, while the numerical simulations for their own characteristics are still relatively lacking. In the present study, the seismic behavior of novel precast beam–column joints with mechanical connections (PBCJs-MCs) is investigated numerically. Based on the available experimental data, fiber models for four PBCJs-MCs are developed. Then, the simulated and experimental seismic behaviors of the prefabricated BCJs are compared and discussed. Finally, the factors influencing the seismic behavior of the PBCJs-MCs are further investigated numerically. The numerical results indicate that the fiber models can consider the effect of the bond–slip relationship of concrete and reinforcement under reciprocating loads. The relative errors of the simulated seismic behavior indexes are about 15%. The bearing capacity and displacement ductility coefficients of the PBCJs-MCs decrease rapidly as the shear-to-span ratio (λ) increases. It is recommended that the optimum λ for PBCJs-MCs is 2.0–2.5. The effect of the axial load ratio on the seismic behavior of PBCJs-MCs can be negligible in the case of the PBCJs-MCs with a moderate value of λ.

Abstract Bond–slip is an important characteristic that determines the stiffness, displacement, and load-bearing capacity of a reinforced concrete (RC) beam. It is essential for performing a precise numerical analysis of the beam. In most cases, bond–slip models can define the bond–slip curve only when there are experimental data. However, many bond test data have been obtained from pull-out tests, and the dominant view is that the bond–slip behavior observed in the pull-out test is quite different from that in an actual RC beam. Therefore, a mapping function that makes it possible to estimate the bond–slip behaviors of beam specimens using those of pull-out specimens was developed in this study. A total of 255 pull-out specimen data and 75 beam specimen data were collected from previous studies, and the importance and influence of each feature of the two groups were analyzed using random forest and K-means clustering. The mapping function was derived using genetic programming, and its accuracy was verified through a comparison with existing models. The proposed model exhibits a high degree of accuracy in estimating bond–slip and bond strength in beam specimens and can provide useful information for understanding the difference in bond–slip behaviors between the two groups.

The grouted splice sleeve (GSS) connection is considered to be an effective bending moment–resisting connection between precast RC members. This connection type has been used extensively in nonseismic regions. The application of such a connection type in moderate or high seismic regions has been investigated and considered for multistory moment frame buildings and highway bridges. A computational modeling strategy is proposed at local and global levels for developing an appropriate computational model for such a connection type using a recessed GSS connection with intentional debonding. A computational model capable of predicting the structural response under cyclic loading was developed using established material models and a forced-based beam-column element considering low-cycle fatigue of reinforcing bars, bar-slip, intentional debonding of reinforcing bars, and plastic hinge length. The proposed model for recessed GSS connections with intentional debonding was experimentally validated. The proposed model was subsequently used to obtain the seismic response of a three-column bridge bent to near- and far-field earthquakes in terms of the overall maximum drift ratio and the drift ratio at the maximum seismic force. [ABSTRACT FROM AUTHOR]

This study investigated the bonding strength between various cement-based grouting materials (CBGM) and high-strength bolts, the flexural and compressive strength variation of different CBGM with curing age, and the failure characteristics of flexural, compressive and bonding strengths. Moreover, the morphological characteristics of bond-slip curves and their similarities and differences were discussed as well. Based on the mechanical property and safety analysis, a calculation model of the critical anchorage length of high-strength bolt in CBGM was proposed. The results indicate that the flexural and compressive strengths increase with the increase of curing age. The strength growth rate is faster at the initial stage of 3 days, which implies that the CBGM has a significant high-early strength characteristic. Depending on the diameter and type of high-strength bolts employed, the bonding strength of specimens can be divided into two failure forms, i.e., splitting and slipping pull-out. The specimens with threaded bolts easily take place a splitting failure form, but the specimens with plain round bolts tend to be destroyed with a slipping pull-out failure form. The ascending section of bond-slip curve is well fitted with the same stage of CEB-FIP 2010. However, a linear relationship can be employed to characterize the bonding strength between CBGM and high-strength bolt. The bond failure capacity is also linear correlation with the strength of CBGM.

• Corrosion impact on bond-slip response of plain round bars in low-strength concrete. • Direct pullout failure mode for plain round bars under monotonic and cyclic loading. • Mathematical relationship for bond-slip interaction of plain bars in low strength concrete. • Corrosion degradation incorporated into bond strength. • Regression analysis correlating maximum crack width with corrosion level and bond strength. 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. [ABSTRACT FROM AUTHOR]

An experimental study consisting of 22 pull-out tests was carried out to investigate the bond-slip performance and load transfer mechanism between near-surface mounted (NSM) Aluminum Alloy (AA) bars and concrete when the AA bars are inserted into pre-cut grooves on the surface of the host structure and bonded with an appropriate bonding agent. The effects of several design parameters were evaluated including bond length, diameter of AA bars, bar surface treatment, and adhesive type. A digital image correlation (DIC) system was used to measure the slips and surface strain and four failure modes were observed in the tests, being concrete splitting failure, epoxy splitting, debonding at the bar-epoxy interface, and AA bar rupture. Results showed that an increase in bond length could make the failure mode more ductile, while AA bars with rough surfaces exhibited a relatively satisfactory bond-slip behavior when a suitable epoxy was used. Finally, the test data from this study were used to examine three bond-slip models based on fiber reinforced polymers (FRP) for the NSM technique. A new bond-slip model considering the influence of the bar external surface was proposed and validated by the test results from both this study and literature. • The bond behavior and load transfer mechanisms between NSM AA bar and concrete is experimentally investigated. • Four failure modes were revealed: concrete splitting, epoxy splitting, debonding at the bar-epoxy interface, AA bar rupture. • Increasing the bond length increased the pull-out load but decreased the bond strength. • For AA bars, the larger geometric ratio and the rougher surface is, the better bonding performance could develop. • An analytical model considering the effect of bar surface treatments was proposed. [ABSTRACT FROM AUTHOR]

Geopolymer concrete reinforced with Glass fiber-reinforced polymer (GFRP) bar presents a novel, durable, eco-friendly strengthening system with significant promise for practical engineering. To employ this strengthening system, a clear understanding of the bond performance between GFRP bars and geopolymer concrete under bending conditions is essential. Interface behaviors of GFRP bars-geopolymer concrete was investigated using hinged beam tests, considering the following parameters: concrete type(geopolymer and ordinary), concrete strength(C30, C50, C70), surface treatment of bars(shallow thread, spiral wrap ribs, and sandblasted), bar diameters(6 mm, 10 mm, and 16 mm), and bond lengths(2, 4, and 8 times the bar diameter). Results indicate a consistent bond mechanism between geopolymer and ordinary concrete. The bond strength increases with higher concrete strength, and the initial bond stiffness is improved by spiral wrap ribs. Moreover, the mBPE model was used to describe the local bond-slip relationship, and the effects of different parameters on interface shear stress distribution were discussed. The development length of GFRP bars in concrete was evaluated and compared with existing codes. These findings provide valuable references for the performance assessment and optimization of GFRP bar-reinforced geopolymer concrete structures in engineering applications. • GFRP bars-geopolymer concrete bond behavior was investigated using hinged beam tests. • Geopolymer concrete exhibits similar bonding mechanisms to ordinary concrete. • The mBPE model was used to describe the local bond-slip relationship. • Developed stress versus bonded length is compared with existing codes formula. [ABSTRACT FROM AUTHOR]

The bond performance of CFRP to concrete plays a vital role in CFRP strengthening on concrete structures. In this paper, an experimental study was carried out to investigate the bond performance of CFRP to concrete with a convex-circular arc interface. The main factors were the curvature of the concrete surface and the bond length and the layers of the CFRP laminate. Based on the experimental results, the failure mode of the bond specimens, the variation of the bond capacity, the CFRP strain, and the bond–slip constitutive model are analyzed. The results showed that most of the specimens failed to peel off the interface concrete, and the bond capacity tended to increase with the increase in bond length when the bond length was within an effective value. When the interface curvature increased to 1/0.8 m, the bond capacity tended to increase due to the CFRP exerting a certain pressure on the concrete surface. The prediction formula of the bond capacity between the CFRP and concrete is proposed considering the influence of the interface curvature. The bond–slip curves are given out based on the finite differential analysis of the strain distribution of CFRP laminates. The accuracy and applicability of the proposed model are verified with a comparison to the test results and other existing models.

Abstract Corrosion-induced bond degradation of deformed steel rebar in concrete is experimentally investigated with acoustic emission (AE) and 3D laser scan technique. Concrete specimens were fabricated and subjected to direct pullout test after being corroded to different levels. The number and width of cracks present during the corrosion tests and the pull-out tests were recorded. The energy released during the pullout tests were captured with AE probes, and the frequency characteristics was analyzed. After pullout tests, the surface morphology of corroded steel rebars was determined with a 3D laser scanner. A modified bond deterioration model was proposed and the parameters associated with the model were analyzed. Results indicated that two types of AE signals were acquired during pullout tests: concrete cracking in high frequency range of 35 ~ 41 kHz and steel-concrete friction in low frequency range of 3 ~ 15 kHz. The bond strength and the bond-slip characteristics depend upon the level of corrosion as well as the number and width of cracks. The reduction factor of the bond-slip model exponentially decreases as a function of the average cross-sectional area loss and linearly decreases with an increase of the rib area loss.

The detection of bond-slip between the reinforcing bar (RB) and concrete is of great importance to ensure the safety of reinforced concrete (RC) structures. The techniques to monitor the connection between the RB and concrete are in constant development, with special focus on the ones with straightforward operation and simple non-intrusive implementation. In this work, a simple configuration is developed using 10 optical fiber sensors, allowing different sections of the same RC structure to be monitored. Since the RB may suffer different strains along its length, the location of the sensors is critical to provide an early warning about any displacement. Bragg gratings were inscribed in both silica and polymer optical fibers and these devices worked as displacement sensors by monitoring the strain variations on the fibers. The results showed that these sensors can be easily implemented in a civil construction environment, and due to the small dimensions, they can be a non-intrusive technique when multiple sensors are implemented in the same RC structure. [ABSTRACT FROM AUTHOR]

The bonding performance between a basalt fiber-reinforced composite material (BFRP) grid and an engineering cementitious composite (ECC) is the basis that affects the synergy between the two. However, the research on the bonding behavior between the FRP grid and ECC is limited; in particular, the theoretical study on the bond–slip intrinsic relationship model and a reliable anchorage length calculation equation is lacking. To study the bond–slip relationship between the BFRP grid and ECC material, we considered the parameters of BFRP grid thickness, anchorage length, ECC substrate protective layer thickness, and grid surface treatment, and conducted center pull-out tests on eight sets of specimens. By analyzing the characteristics of the bond–slip curve of the specimen, a bond–slip constitutive model between the BFRP grid and ECC was established. Combining the principle of equivalent strain energy, the calculation formula of the basic anchorage length of the BFRP grid in the ECC matrix was derived. Research shows that the bonding performance between the BFRP grid and ECC improves with the increase in the grid anchoring length, grid thickness, and ECC layer strength. Sand sticking on the surface of the BFRP grid can enhance the bonding force between the two. The established bond–slip constitutive model curve is in good agreement with the test curve. The bond–slip relationship between the BFRP grid and ECC can be described by the first two stages in the BPE model. The derived formula for calculating the basic anchorage length of the BFRP mesh in the ECC matrix is computationally verified to be reliable in prediction. [ABSTRACT FROM AUTHOR]

Reinforced concrete (RC) columns may be damaged under earthquakes or wind loads, which will severely affect their bearing capacity. Current damage evaluation methods are mainly based on displacement measurement, which makes evaluating local structural damage difficult. Therefore, this study proposes an RC column structural monitoring and evaluation method based on a distributed self-sensing basalt fiber reinforced polymer (BFRP) bar with optical fiber sensors inside. First, the self-sensing BFRP bar is introduced, including the sensing principle, inner structure, and basic sensing performance. It is found that the strain sensing coefficient of the proposed self-sensing BFRP bar presents only 2.2 % difference from that of the bare optical fiber sensor, meaning the BFRP package take no negative effect on the strain sensitivity. Second, the analytical methods of curvature and displacement are established based on the strain distribution measurement, in which the influence of bond-slip on parameter calculations is mainly considered. Finally, the proposed method was well verified by the loading tests of one RC column with self-sensing BFRP bars. Among the results, the absolute displacement measurement error increase with the development of structure damage, which can be even up to several mm after the steel yielding. However, the relative displacement measurement error can be still controlled within 20 % until the structure failure of the RC column. Considering the additional long-term performance of the proposed self-sensing BFRP bar, the proposed method is expected to implement long-term monitoring of RC columns.

Ultra-high-performance concrete (UHPC)-filled duct connection is an innovative solution for joining assembled structures, in which the anchorage performance of the rebar and UHPC filled in bellows plays a critical role in determining the overall connection effectiveness. To establish a reliable anchorage length and a bond–slip relationship between rebar and UHPC within a bellow, a total of 16 specimens were conducted, and pullout tests were carried out. Two parameters were considered, including the diameter ratio (D/d), representing the proportion of the diameter of the bellow D to the diameter of the steel bar d, and anchorage length (L). By analyzing the failure modes, load versus deflection curves, and steel strain data, the influences of the diameter ratio and anchorage length on the anchorage performance were discussed. The test results showed that the failure mode changed from rebar pullout to rebar breakage as the anchorage length increased from 3 d to over 10 d. The reliable anchorage length of the rebar was recommended to be at least 10 d with a diameter ratio (D/d) of 2.4. Moreover, a fitting bond–slip model was proposed based on the experimental bond–slip curves between the rebar and UHPC interface within the bellows with high precision. These findings constitute a crucial basis for the comprehensive stress analysis of assembled structures connected using UHPC grouted in bellows.

By investigating the bond performance between glass-fiber-reinforced polymer (GFRP) bars and concrete, GFRP bars can be better applied to concrete structures as a building material. This paper considered the effects of three different GFRP bar surface treatments, three bonding lengths, corrosive solution, and immersion time on the bonding strength. The test results indicated that the bond strength decreases with the increase in the diameter and bond length. The bonding between GFRP bars and concrete can be improved by treating the surface of the bars in different ways. Compared with the control group, the bond strength of the specimens in the saline solution decreased by 1.3–21.4%, and the bond strength of the specimens in the alkaline solution decreased by 26.5–38.8%. In the corrosive environment, the bond properties are degraded. A bond strength calculation formula considering the surface treatment method of the GFRP bars was proposed. The prediction formula of the bond strength retention rate between the GFRP bar and concrete in the corrosive environment was established. The formula was validated with the available research data and the calculated values agreed well with the test values. The MBPE model and CMR model are modified to establish the bond-slip model of the GFRP bars and concrete in the corrosive environment. The model curve is close to the test curve. This paper provides a theoretical basis for future research on the bond-slip performance of GFRP bars and concrete.

Cracking is an inherent characteristic of a reinforced-concrete (RC) element subjected to tension or bending. The crack width growth with loading depends on the rebar-concrete bond behavior. RC bridges are designed under strict requirements to ensure their proper long lifetime performance. Limiting the crack widths improves the performance and safety of bridges that are exposed to harsh climatic and environmental effects and enhances bridge service life-cycle expectancy. This paper presents an extended one-dimensional formulation for analyzing RC elements subjected to tensile loads and solves the one-dimensional tension stiffening problem. The extended bond-slip model analyses the entire range of loading, following cracks growth up to their maximum allowed width, employing a bi-linear bond-slip relationship. The analytical solution refers to the early loading stage where the first bond-slip segment governs the entire element and a closed form solution is obtained, followed by the higher loading stage where two different bond-slip relationships govern two complementary segments of the element. Analytical expressions for the stresses, strains, and displacements in concrete, steel, and interface are developed. Cracking is followed until rebar yielding. Validation of the model with available test results shows good agreement that is superior to the commonly used linear bond-slip model. [ABSTRACT FROM AUTHOR]

Bond–slip is an important characteristic that determines the stiffness, displacement, and load-bearing capacity of a reinforced concrete (RC) beam. It is essential for performing a precise numerical analysis of the beam. In most cases, bond–slip models can define the bond–slip curve only when there are experimental data. However, many bond test data have been obtained from pull-out tests, and the dominant view is that the bond–slip behavior observed in the pull-out test is quite different from that in an actual RC beam. Therefore, a mapping function that makes it possible to estimate the bond–slip behaviors of beam specimens using those of pull-out specimens was developed in this study. A total of 255 pull-out specimen data and 75 beam specimen data were collected from previous studies, and the importance and influence of each feature of the two groups were analyzed using random forest and K-means clustering. The mapping function was derived using genetic programming, and its accuracy was verified through a comparison with existing models. The proposed model exhibits a high degree of accuracy in estimating bond–slip and bond strength in beam specimens and can provide useful information for understanding the difference in bond–slip behaviors between the two groups. [ABSTRACT FROM AUTHOR]

In this paper, 3D finite element simulations were conducted for lap-spliced ultra-high-performance concrete (UHPC) beams using ABAQUS software. Based on the concrete damaged plasticity (CDP) model, the plastic damage factor was introduced to simulate the material properties of UHPC. The nonlinear characteristics of the steel bar and UHPC were considered, and the bond–slip constitutive relationship was selected to evaluate the bond–slip between the lap-spliced steel bar and UHPC. The simulated load–deflection curve, peak load, bond strength, and failure mode were in good agreement with the experimental results. The verified finite element model was used to analyze the parameters of the lap-spliced UHPC beam. The effects of lap-spliced steel bar diameter, stirrup spacing of non-lap segment, and shear span ratio on the mechanical properties and bond properties of the lap-spliced UHPC beam were studied. This study can provide a reference for the future simulation and design of lap-spliced UHPC beams. [ABSTRACT FROM AUTHOR]

In this study, a full-scale test on the bending performance of concrete sandwich laminated floor slabs with integrated thermal and sound insulation was carried out, and the effects of different reinforcement ratios on the bending performance of concrete sandwich laminated floor slabs were investigated as well as the variation law of the failure modes, characteristic loads, load-mid span deflection, load-rebar strain curves, and anti-slip performance. The results indicate that the concrete sandwich laminated floor slabs present typical bending failure characteristics. According to bending failure characteristics, the damage process can be divided into three stages, i.e., elasticity, cracking, and failure. The bearing capacity significantly increases with the increase in reinforcement ratio. The normal service, yield, and ultimate loads of bearing capacity of the floor slabs with a larger reinforcement ratio increase by 54.55%, 52.94%, and 46.46%, respectively. Moreover, the mid-span deflection decreases significantly with the increase in reinforcement ratio, and the cracking expansion is also delayed. Before cracking, the prefabricated layer and laminated layer can realize load bearing together, and the floor slab is in a state of complete interaction. When the floor slabs reach the ultimate state, the superimposed surface produces a sliding effect, and the floor slab is in a state of partial interaction. The finite element analysis software ABAQUS (with the version number of ABAQUS 2020, the chief creator of David Hibbitt, and the sourced location of the United States) was used to perform nonlinear numerical simulation. The test results accord well with the simulation results, which verifies the correctness of the finite element model. Based on finite element simulation, the influence of post-cast concrete strength on the ultimate load can be ignored. [ABSTRACT FROM AUTHOR]

Due to the limited properties of coral aggregate concrete, it is worth exploring its expanded applications in island construction by reinforcing it with carbon fiber and stainless steel rebar. Moreover, given the complexity of stress states in frame joints, studying the bond behavior of stainless steel rebar and carbon fiber reinforced coral concrete is critical. This study used lateral constraint to simulate the stress state of the joints. The results showed that increasing fibers content could enhance bond strength by 14.5 %. Furthermore, bond strength significantly increased with the increase of lateral constraint, although the growth rate first increased and then decreased, peaking at 20.68 %. Because the lateral constraint and the bond direction were not in the same plane, a spatial theoretical bond strength model was proposed to predict the characteristic bond values in four distinct states. Finally, a damage constitutive model was established to predict the bond-slip relationship based on damage theory. The research presents valuable insights into using coral concrete in marine structure frame joints, serving as a basis for future studies. • The bond failure patterns under various lateral constraints were observed. • The bond strength was analyzed in the presence of lateral constraints and CFs. • A spatial theoretical bond strength model under lateral pressure was established. • The bond-slip trend was predicted by a modified damage constitutive model. [ABSTRACT FROM AUTHOR]

The amount of research on the external bonding of Carbon Fiber Reinforced Polymers (CFRP) to degraded structures has increased recently. The adhesive is the weakest element of the joint and the bonding of the adherends is critical for the efficiency of the joint. Therefore, the influence of multiple debonding defects on CFRP-to-steel joints has still not been correctly quantified nor fully understood. For this reason, the current work proposes a new numerical strategy that allows for studying the influence of multiple debonding defects when a brittle and ductile adhesive is used. A new nonlinear bond-slip relationship is used and four different ratios between the debonded and the bonded area (η) are assumed: 0%, 25%, 50%, and 75%. The proposed model is based on the Finite Difference Method (FDM) and validation is carried out with a commercial Finite Element Method (FEM) package. The load-slip curves allowed for observing that the proposed FDM and the FEM are consistent and both revealed degradation of the load capacity of the joints with the increase of η. Moreover, by adopting a displacement control at the CFRP-free end, a snap-through and snap-back phenomenon are observed in the specimens with a localized debonding defect. [ABSTRACT FROM AUTHOR]

The bonding characteristics between steel bars and concrete in reinforced concrete (RC) structures are crucial for the prediction of load-bearing capacity for seismic design. Nevertheless, most previous studies on bond-slip performance focus on the bond strength based on the pull-out experiments, it is often overlooked that the effect on the failure modes of RC members and the deformation performance due to the bond characteristics. In this research, the effect of the diameter and its arrangement of the reinforcement of the RC column on the bond failure mode and load-bearing capacity based on the cyclic loading tests and the FE analysis are carried out. In the cyclic loading test, it was found that two RC columns with different diameters and reinforcement arrangements showed distinct load-bearing capacity, deformation performance, and failure mode. Despite those columns having the same longitudinal reinforcement ratios. In addition, by applying an advanced finite element analysis using a bond-slip model that induces splitting failure, we succeeded in reproducing the cyclic deformation behavior and local damage obtained in experiments with high accuracy. The proposed model brings in the advanced prediction of the seismic behavior of RC structures and the enhancement of seismic resistance of social infrastructure facilities to earthquake disasters.

With superior mechanical properties and workability, ultra-high-performance concrete (UHPC) has been utilized extensively in engineering projects. To gain a comprehensive understanding of the bond behavior of UHPC or ultra-high-performance fiber-reinforced concrete (UHPFRC), researchers studied the factors influencing the bond-slip between rebar and UHPC or UHPFRC over the past few years. The literature-proposed ultimate bond strength formulas and the bond-slip constitutive model between rebar and UHPFRC are analyzed and compared. Based on the bond test database of UHPFRC, the results indicate that UHPFRC strength, relative concrete cover thickness, relative bond length, and steel fiber volume content are the primary parameters influencing the ultimate bond strength between rebar and UHPFRC. In the bond-slip constitutive model, the nonlinear ascending and linear descending model is more accurate than other models. This paper concludes by discussing the shortcomings in UHPC or UHPFRC bond research and predicting the future research trend.

The nonuniformity of stress and strain analysis is an important consideration that describes the bond behavior between concrete and externally bonded fiber reinforced polymer (FRP) laminates. The interfacial stress transfer between FRP and concrete generates a longitudinal strain gradient in the longitudinal (or FRP fiber) direction. Most of the available studies in this area have focused on nonuniformity in the longitudinal direction. In this paper, the nonuniformity in the FRP width direction is investigated by studying the strain distribution using digital image correlation (DIC) full-field optical techniques. In the direction along the FRP width, there is an area in the middle that has consistent strain and stress, while the edge regions have strain and stress gradients. During the complete debonding process, the width of the central area is found to be insignificantly affected by the concrete strength but significantly affected by the FRP stiffness. The fracture characteristics below the central region are purely Mode II fracture. However, the complex curved cracks and high in-plane shear strains at the interface near the FRP edge regions show a mixed mode with Modes II and III. This boundary effect results in a significant difference in the bond–slip characteristics of FRP along the width direction. The maximum bond stress of the central region is higher than that of the edge region. However, for FRP with higher stiffness, the inhomogeneity of the stress distribution is weakened. Moreover, it is reasonable to find that calculating the sum of the bearing capacity of the single FRP strips along the width direction is close to the experimental bond strength. Based on the research findings in this study, it is qualitatively recommended that the width factor model in calculating FRP-concrete bond strength should include the significant effect of FRP stiffness. • The stress and deformation nonuniformities in the FRP width direction are initially investigated. • The width of the central stable portion increases with increasing FRP stiffness but is insensitive to the concrete strength. • By dividing the FRP into multiple strips with different bond–slip curves, the sum load matches well with the experimental peak load. • A new rational and accurate width factor model considering the FRP stiffness effect is necessary to be developed. [ABSTRACT FROM AUTHOR]

This paper presents a comprehensive investigation of the bond characteristics of steel bar reinforced geopolymer concrete (GPC). The ASTM A944 beam end tests were conducted on GPC beams reinforced with plain or ribbed bars. The bond–slip curves and the bond strength of GPC beams were obtained. The relationship between the bond stress and relative slip in plain and ribbed bar reinforced GPC has been represented by empirical formulae. The bond testing results were compared with those of corresponding ordinary Portland cement concrete (OPC) using statistical hypothesis tests. The results of hypothesis testing showed that GPC was significantly superior to OPC in terms of bond capability with plain bars and bond stiffness with ribbed bars. The statistical analysis indicated that the bond–slip relations derived for OPC are inapplicable to GPC; thus, new bond–slip relations are suggested to estimate the development of bond stress and relative slip between GPC and steel bars. [ABSTRACT FROM AUTHOR]

Ultra-high performance concrete (UHPC) has been demonstrated to be a realistic alternative to less maintenance and significantly longer service life due to its better mechanical properties and low permeability. The bond performance of the deformed steel bar embedded in UHPC is critically important for the safety of the UHPC structures. This paper conducted an experimental investigation on the bond behavior of deformed steel bars and UHPC. The impacts of loading method, UHPC strength, steel fiber type and content, rebar diameter, and cover thickness were studied. The testing results revealed that the specimens failed in three modes: pull-out, splitting + pull-out, and cone failure. The main factors affecting the bond strength are UHPC compressive strength, cover thickness, and fiber characteristics. The peak slip of rebar-UHPC increases with cover thickness and rebar diameter. Finally, an analytical model of the bond stress-slip relationship between the UHPC and deformed steel bar is obtained, which is in suitable agreement with the test results. [ABSTRACT FROM AUTHOR]

In this study, the influence of graphene oxide nanoparticles on the bond-slip behavior of fiber and fly-ash-based geopolymer paste was examined. Geopolymer paste incorporating a graphene oxide nanoparticle solution was cast in half briquetted specimens and embedded with a fiber. Three types of fiber were used: steel, polypropylene, and basalt. The pullout test was performed at two distinct speeds: 1 mm/s and 3 mm/s. The results showed that the addition of graphene oxide increased the compressive strength of the geopolymer by about 7%. The bond-slip responses of fibers embedded in the geopolymer mixed with graphene oxide exhibited higher peak stress and toughness compared to those embedded in a normal geopolymer. Each fiber type also showed a different mode of failure. Both steel and polypropylene fibers showed full bond-slip responses due to their high ductility. Basalt fiber, on the other hand, because of its brittleness, failed by fiber fracture mode and showed no slip in pullout responses. Both bond strength and toughness were found to be rate-sensitive. The sensitivity was higher in the graphene oxide/geopolymer than in the conventional geopolymer. [ABSTRACT FROM AUTHOR]

Reliable and robust numerical modeling of RC columns under lateral load is commonly performed using one-dimensional elements. Although the strain is assumed to vary linearly through the section, bond-slip and buckling of reinforcing bars at the joints/connections contribute substantially to the column response. This paper presents a three-dimensional (3-D) fiber-based model with explicit representation of the bond-slip that occurs at the column-footing interface for cast-in-place columns and at the interface between bars and mechanical couplers for precast columns with grouted sleeve (GS) connections. The model contains beam elements with fiber sections for concrete, beam elements for longitudinal steel bars and sleeves, and spring elements for interfacial bond-slip behavior. The novelty is that the model can be achieved using existing software implementations, retains the efficiency of fiber-based elements under cyclic loading, and parameters are calibrated based on component-level testing, unlike other resultant or hybrid models that require arbitrary backbone and cyclic property specification. An extensive experimental program was conducted to investigate the behavior of GS couplers and calibrate the bond-slip models. Four large-scale RC columns were then used to verify the proposed model by comparing the measured load-displacement, energy dissipation, curvature, and failure mode with the numerical responses. [ABSTRACT FROM AUTHOR]

Crack width is a major performance criterion in reinforced-concrete structures, in general, and is of utmost importance in ensuring bridge performance, in particular. A reliable theory-based method is required to assess crack widths and gain insight into their dependence on material, geometry, and loading parameters. A new, exact analytical method is proposed for a one-dimensional reinforced concrete element based on equilibrium, constitutive, and kinematic relationships, accounting for the geometrical and material behavior of the concrete and reinforcement. A linear interfacial bond stress slip is assumed to represents the small slips associated with the limited allowed crack width. Closed-form expressions have been developed and a wealth of information can be calculated immediately, such as the cracking load levels, the crack width dependence on the load level, the expected number of cracks, and the cracks spacing. The entire nonlinear force-displacement relationship of a cracked reinforced-concrete element may be depicted, demonstrating the tension-stiffening behavior that depends on the variations in the crack width throughout the loading history. Comparisons of the model with experimental data demonstrate very good agreement. [ABSTRACT FROM AUTHOR]

The concrete-GFRP composite beams have received extensive attention in civil engineering. However, the ambiguity of the fracture, debonding of the interface, and the GFRP profile limit the precise design of the composite beam. This article presents a comprehensive numerical study for the structural performance of composite pultruded GFRP beams to provide a better understanding of the mechanism of interfacial debonding and GFRP matrix fracture. The failure and delamination process of pultruded GFRP for anisotropy of materials is modeled using the Hashin criteria. The bond–slip behavior between the concrete slab and the top flange of the GFRP I-beam is simulated by the bilinear cohesive interface element. The availability and accuracy of the finite element model are verified by comparison with the four-point bending test results of the pure GFRP I-beam and composite beams as well. Based on the proposed comprehensive finite element model, the effects of the strength, thickness, and width of the concrete slab and the shear-span ratio of the beam on the structural behavior of the composite beam are studied. According to the parametric analysis, the excessive high strength of concrete, the width, and/or thickness of the concrete slab would lead to shear failure of the slab rather than significantly increasing the ultimate load of the composite beam. When having a small shear-span ratio, the matrix fracture and delamination will occur in the web of the GFRP profile. In addition, the height of the I-profile web has a significant effect on the stress and strain distribution of the composite beam. These parametric analyses could provide the numerical basis for the design of the GFRP composite beams.

Fiber-optic sensing (FOS) provides distributed strain measurement that can enhance both structural health monitoring (SHM) and laboratory testing capabilities. In particular, optical frequency domain reflectometry (OFDR) provides strain or temperature measurements every millimeter over tens of meters of fiber, with a high sampling rate. For RC applications with embedded fiber-optic cables, the sensitivity of the fibers and their ability to measure and survive cracking are both important considerations. In this study, tests were conducted on six RC specimens to investigate the effectiveness of using OFDR strain sensing to evaluate the cracking behavior of concrete and the deformation of steel reinforcing bars. Six types of fiber-optic cables with very different structures, sensitivity, and survivability were tested. Fibers were placed in the concrete and in grooves in the reinforcing bars. A new deconvolution method was developed; using the method, crack widths were accurately measured up to the target load levels using both the more sensitive fiber-optic cables and cables with reduced sensitivity but better survivability. OFDR strain sensing, combined with new methods of data processing, was shown to be capable of detecting distributed microcracking and providing reliable crack widths. The OFDR technique was also used to reveal the location-dependent bond-slip relationships between the concrete and rebar at early stages. [ABSTRACT FROM AUTHOR]

The detection of bond-slip between the reinforcing bar (RB) and concrete is of great importance to ensure the safety of reinforced concrete (RC) structures. The techniques to monitor the connection between the RB and concrete are in constant development, with special focus on the ones with straightforward operation and simple non-intrusive implementation. In this work, a simple configuration is developed using 10 optical fiber sensors, allowing different sections of the same RC structure to be monitored. Since the RB may suffer different strains along its length, the location of the sensors is critical to provide an early warning about any displacement. Bragg gratings were inscribed in both silica and polymer optical fibers and these devices worked as displacement sensors by monitoring the strain variations on the fibers. The results showed that these sensors can be easily implemented in a civil construction environment, and due to the small dimensions, they can be a non-intrusive technique when multiple sensors are implemented in the same RC structure.