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After the anchor is installed, relative slip between the anchor and the surrounding rock will occur in the actual engineering. Based on the proposed nonlinear bond-slip model, a three-dimensional elastoplastic analysis of the strain-softened surrounding rock is performed in this study while considering hydraulic-mechanical coupling. A numerical iterative method of surrounding rock analysis is proposed, which considers the relative slip between the anchor and the surrounding rock. These stresses and displacements of the surrounding rock, as well as the anchor shear stress distribution, can be obtained using the proposed method. Furthermore, the calculation results of the program are compared with the existing field test results and with the calculation results of other methods to verify the accuracy of the proposed method. The results indicate that the calculation results of the proposed method are generally in line with the test results, and the largest slips occurring at the two ends of the anchors. Meanwhile, the proposed method is applied to an actual engineering, and the results agree well with the field data. Finally, the effects of seepage and strain softening of the surrounding rock on the interaction between the surrounding rock and the anchors are investigated by parametric analysis. [ABSTRACT FROM AUTHOR]

Estimating the stress of reinforcing bars and its variations in service conditions can be useful to determine the reserve capacity of structures or to assess the risk of fatigue in the reinforcement. This paper investigates the use crack width measurements to estimate the stress in the bars. In existing structures, crack width formulations can be used to estimate the stress in the reinforcement from crack width measurements, profiting from additional information that can be measured in‐situ, such as the crack spacing. Recent experimental results show that the values of the mean bond stress typically considered in code formulations overestimate the actual bond stresses activated in cracked concrete specimens. This paper presents the results of an experimental program consisting of reinforced concrete ties and beams instrumented with Digital Image Correlation and fiber optical measurements. The results confirm the differences with typically assumed bond stresses. A formulation to estimate the bond stresses in service conditions is derived from the results of the numerical integration of a previously developed local bond–slip relationship. Their pertinence for the estimation of the stress in the reinforcement from the measured crack width is evaluated with satisfactory results for monotonic loading and for the maximum force in cyclic tests. [ABSTRACT FROM AUTHOR]

Extrusion tests were conducted on recycled coarse aggregate concrete with circular steel tubes (RCCST, 100% replacement of recycled coarse aggregate) to investigate the impact of freeze–thaw cycles on bond properties. RCCST samples were subjected to 0, 25, 50, 75, 100, 125 and 150 freeze–thaw cycles and their bond properties were then compared with those of natural coarse aggregate concrete with circular steel tubes (NCCST) after 0, 100 and 150 freeze–thaw cycles. The experimental results indicate that freeze–thaw cycling damages the internal structure of RCCST, causing a significant decrease in interfacial bond strength with an increase in the number of freeze–thaw cycles. Freeze–thaw RCCST exhibits lower peak load and higher peak slip compared to NCCST, with increases of 25.2%, 73.2%, and 70.3% after 0, 100, and 150 freeze–thaw cycles, respectively. Regression analysis was used to derive an exponential equation that describes the relationship between longitudinal strain and strain gauge position. Additionally, a segmented fitting method was employed to obtain an expression for the bond slip of the freeze–thaw RCCST with a circular steel pipe. [ABSTRACT FROM AUTHOR]

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]

Copyright of Chinese Journal of Applied Mechanics is the property of Chinese Journal of Applied Mechanics Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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.

The objective of this research is to evaluate numerically and experimentally the cyclic performance of corroded columns constructed with accelerated bridge construction (ABC) methods. Three column-to-footing specimens were built and tested under quasi-static cyclic loads; one specimen was subjected to corrosion with a target 10% mass loss (moderate corrosion), one was subjected to a target 25% mass loss corrosion (severe corrosion), and one served as the control. For the moderately corroded specimen, the accelerated corrosion method resulted in an actual mass loss of 10.5% in the longitudinal steel bars and 18.4% in the steel spiral; for the severely corroded specimen there was an actual mass loss of 24.1% in the longitudinal steel bars and 39.9% in the steel spiral. Increased corrosion caused reduction in column lateral displacement capacity in the cyclic load experiments; the control, moderately corroded, and severely corroded specimens reached a drift ratio of 9.0%, 7.0%, and 6.0%, respectively. Computational models were developed for the control and corroded specimens. Corrosion effects were considered by reducing the cross-sectional area, yield strength, and modulus of elasticity of steel bars; reduction in concrete compressive strength was included due to concrete cracking and reduction of bond. The computational models include bond-slip, intentional debonding, low-cycle fatigue, and buckling. Global and local response comparisons of the numerical models with experiments are carried out. The numerical models show good agreement with the experimental results regarding load and displacement capacity and hysteretic energy dissipation; they are able to capture the main effect of corrosion, which was a reduction in lateral displacement capacity. The computational models were used in parametric studies to examine the lateral force and displacement capacity for a range of corrosion levels. [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. [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]

Copyright of Acta Materiae Compositae Sinica is the property of Acta Materiea Compositae Sinica Editorial Department and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Journal of Harbin Institute of Technology. Social Sciences Edition / Haerbin Gongye Daxue Xuebao. Shehui Kexue Ban is the property of Harbin Institute of Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Railway Construction Technology is the property of Railway Construction Technology Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

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]

Recycled steel fiber reinforced concrete is an innovative construction material that offers exceptional mechanical properties and durability. It is considered a sustainable material due to its low carbon footprint and environmental friendly characteristics. This study examines the key influencing factors that affect the behavior of this material, such as the steel fiber volume ratio, recycled aggregate replacement rate, concrete strength grade, anchorage length, and stirrup constraint. The study investigates the bond failure morphology, bond-slip, and bond strength constitutive relationship of steel fiber recycled concrete. The results show that the addition of steel fibers at 0.5%, 1.0%, and 1.5% volume ratios can improve the ultimate bond strength of pull-out specimens by 9.05%, 6.94%, and 5.52%, respectively. The replacement rate of recycled aggregate has minimal effect on the typical bond strength of pull-out specimens. However, the ultimate bond strengths of pull-out specimens with concrete strength grades C45 and C60 have improved compared to those with C30 grade. The specimens with longer anchorage lengths exhibit lower ultimate bond strength, with a reduction of 33.19% and 46.37% for anchorage lengths of 5D and 7D, respectively, compared to those without stirrups. Stirrup restraint of 1 φ 8 and 2 φ 8 improves the ultimate bond strength by 5.29% and 6.90%, respectively. Steel fibers have a significant effect on the behavior of concrete after it cracks, especially during the stable expansion stage, crack instability expansion stage, and failure stage. [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]

The failure of the initial support of the tunnel caused by the synergistic deformation of steel and shotcrete under high‐ground stress is expected to be solved by arranging studs and steel webs to enhance the structure's bearing capacity. Hence, the bond‐slip mechanism of steel shotcrete with or without studs is unclear. This study aims to determine the bond behavior of the interface between the steel and shotcrete composite structure for tunnel support. The findings of push‐out experiments demonstrate that shotcrete on steel flange longitudinal splitting failure is the failure mode of natural bonding specimens. Tensile failure and expansion failure under the effect of studs is the failure mechanisms of stud steel‐sprayed concrete specimens. Furthermore, experimental data and a mathematical model establish the bond‐slip constitutive law of natural bonding and stud specimens. Finally, in addition to providing a theoretical foundation for the research of bond‐slip, the constitutive model put forward in this paper also supports the prevention of initial support failure in tunnel engineering. [ABSTRACT FROM AUTHOR]

This work tackles the issue of identifiability of fracture and bond properties in reinforced concrete. The basis for modeling of fracture is a computational model capable of describing damage and failure mechanisms in concrete, as well as bond‐slip which is a result of degradation of the concrete‐steel interface. The discrete approximation combines ED‐FEM for concrete crack representation in each element and X‐FEM representation of bond‐slip along a particular reinforcement bar. The uncertain model parameters are modeled as random variables and identified via Bayesian inference with the help of observations from tensile tests on concrete tie beams with a single embedded reinforcement bar. We discuss how the choice of observation type affects the parameter identifiability and propose combinations which improve the estimation capabilities and reduce the discrepancy between the computed and observed quantities of interest. [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]

The study of interfacial behaviour between ribbed steel rebars and concrete is a subject that has been widely studied. However, the definition of the bond stress distribution throughout the embedded length of the steel rebar is still controversial due to the difficulty of experimentally obtaining such distribution for a fixed load magnitude. It is also undeniable its relevancy for the better understanding and model reinforced concrete (RC) structures. So, the definition of the local behaviour between the ribbed steel rebar and concrete is critical to correctly simulate the adherence between both materials. In this matter, the local bond-slip models recommended in codes seem to satisfy some researchers while others suggest prudence in using them. Therefore, only choosing the correct bond-slip relationship may lead to exact interpretations and conclusions of the structural behaviour of a concrete structure but with the existing different bond-slip types, researchers can be misled inadvertently. This work aims to clarify some of these aspects by numerically simulating several pull-out tests under different conditions and checking their influence (or not) on real-scale specimens. After the validation of the numerical model through a proposed new bond-slip relationship, other parameters were studied also. Although the type of the bond-slip relationship influences the detachment of the steel rebar from the concrete, the yielding of the former material was found to be the main parameter that masks the differences in the behaviour of real-scale RC structures when different types of bond-slip relationships were considered in the numerical simulations. [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 numerical evaluation of the shear strength of Steel-Fiber Reinforced Concrete (SFRC) beams without coarse aggregate using data from previous research has been performed in MIDAS FEA. The SFRC beams are modeled by using the total strain crack model with Thorenfeldt for compression behavior and brittle tension behavior. Modified bond stress-slip functions proposed by fib have been used to model the bond between concrete and reinforcement. From the finite element analysis, the cracking pattern and the maximum load at failure of SFRC beams without coarse aggregate have been similar to the test results. As the longitudinal reinforcement ratio increases above 3%, the finite element analysis starts to give overestimated maximum load. The highest ratio of maximum load from analysis and test results equal to 136% has been obtained from 7.82% reinforcement. It is also observed that the influence of longitudinal reinforcement ratio on the shear strength of SFRC without coarse aggregate is lower compared to normal-strength concrete predicted by ACI 318-19. Further studies on bond stress-slip relationship of SFRC without coarse aggregate are needed. [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 seeks to identify bond strength and bond-slip behavior of deformed reinforcing bars under high sustained loads. ASTM A944 beam-end test specimens were subjected to sustained load levels ranging from 71 to 100% of their ultimate capacity. The sustained loading tests were conducted until bond failure or at least 20 days. Three of the specimens failed under sustained load at load levels as low as 80% of the control specimens. Subsequent loading of the specimens that survived the high sustained load showed that the residual ultimate capacity was not reduced by the application of sustained load. The slip creep under sustained load was on average 124% of the initial slip, and over 45% of the slip creep occurred in the first day. The effects of concrete cover depth and bond length were examined. With the available data, a simple time-dependent model for determining the bond-slip under high sustained loading was suggested. [ABSTRACT FROM AUTHOR]

The bond strength between materials is the basis of the cooperative work of composite structures. This study aims to investigate the bonding performance of push-out tests conducted on self-compacting rubberized concrete-filled steel tubes (SCRCFST). The rubber content, particle size, interface bonding length, and water–cement ratio were varied to evaluate their impact on bond strength. The failure mode and failure mechanism were analyzed. The bond damage and energy consumption capacity were investigated. Moreover, this study reveals the characteristics of the stress–slip curve and derives the characteristic equations from reviewing the different points. Test results indicate that rubber particles enhance the energy dissipation capacity of specimens after reaching ultimate bond strength. Furthermore, bond strength decreases with the increase of rubber particles size and water–cement ratio, while the bonding length is barely impacted. It is worth noting that the bonding strength increases slightly at 10% rubber content. The main contribution of this work is to fill the gap in the bonding performance of SCRCFST and guide engineering utilization. Seventeen cylindrical specimens of SCRCFST performed a push-out test by monotonous loading. Bond damage degree and energy dissipation capacity were investigated. Increasing rubber-related parameters negatively affected the bond properties of the structure. Bond strength equations were proposed. [ABSTRACT FROM AUTHOR]

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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]