Bond Slip Research Articles

Development of Mapping Function to Estimate Bond–Slip and Bond Strength of RC Beams Using Genetic Programming

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 Influence of Freeze-Thaw Cycles and Corrosion on Reinforced Concrete and the Relationship between the Evolutions of the Microstructure and Mechanical Properties.

Freeze–thaw cycles (FTCs) and steel bar corrosion (SBC) are the most common service conditions of hydraulic concrete and have significant impacts on its durability. Using pullout and microscopic tests of different FTC and SBC rates, we selected the mass loss rate, ultrasonic velocity, bond strength and bond slip in order to describe the changes in the macro-properties, and also selected the porosity and pore size distribution as micro-parameters in order to explore the influence of FTCs and SBC on the mechanical properties of hydraulic concrete. The results showed that the bond strength decreased as the FTCs increased due to the microstructure damage caused by FTC and SBC, which affects the mechanical properties. A corrosion rate of ≤3% offset the damage caused by 50 FTCs. FTCs and SBC resulted in superimposed damage effects on the concrete. In addition, we established a bond strength damage model based on the joint FTCs and SBC and quantitatively described the degradation law of the macro-mechanical properties. The analysis shows that the influence of FTCs on the bond strength was greater than that of the SBC. These research results can provide a reference and experimental support for the frost-resistant design and durability prediction of hydraulic concrete structures in cold environments.

Experimental investigation of bond–slip behavior of between-anchored steel strips to concrete surface

Experimental investigation of bond–slip behavior of between-anchored steel strips to concrete surface

An Experimental Investigation and Computer Modeling of Direct Tension Pullout Test of Reinforced Concrete Cylinder

Executing the obligation of strengthened concrete is essential in investigating load exchanges from concrete to the inner reinforcing bar. The bond–displacement conduct and extreme pullout quality for pullout samples are essential information related to the durability of RC structures. The slip in the interface is basically due to a contrast in stresses between concrete and reinforcement. This distinction brings about the start of the split in encompassing concrete. This study examined the simple pullout solid 3D cylinder model strengthened by a reinforced steel bar, considered a line element for bond–slip conduct. The non-linear finite element model utilizing ANSYS software was established to concentrate on the concrete and steel reinforcement bond. Material nonlinearity because of cracking, crushing of concrete, and the steel reinforcing bar’s yielding were investigated. Test results showed that: a prediction model for early-age bond stress–slip relationship between steel bars and concrete was proposed based on modeling, which showed good agreement with test results. The precision of this model is explored by contrasting the finite element numerical analysis and that anticipated from test consequences of pullout examples. Immense homogeneity between the model and test results was found. This study could provide more accurate bond properties for structural analysis and design.

Numerical modelling of bond mechanism of ETS FRP bar‒concrete joints with long embedment length

In this study, the bond behaviour between the embedded through-section fibre-reinforced polymer (ETS FRP) bars and concrete is investigated using nonlinear finite element (FE) analysis. The pull-out scheme for the investigation of the interfacial interaction of ETS FRP bars adhesively bonded to concrete is presented. The proposed numerical study also considers the ETS FRP bar‒concrete joints with long bond (embedment) length. First, a trapezoidal bond model describing the bond stress‒slip curves of ETS FRP‒concrete interfaces is adopted. Second, nonlinear FE models incorporating the developed bond model analysing the bond behaviour of the ETS FRP bar‒concrete joints are validated against the pull-out test results. The reliable FE models are then used in a parametric study to investigate the effects of key features, such as the properties of adhesives, FRP bars, and concrete, on the bond performance of the ETS FRP bar‒concrete interfaces. The analyses demonstrate the effectiveness and accuracy of the FE models. Expressions for the maximum bond force and the effective bond (embedment) length are rationally formulated based on the parametric study. • FEM coupled with a bond–slip law for ETS FRP bar-to-concrete joints is proposed. • Proposed FEM can predict bond behaviour between ETS bar and concrete well. • Failure in bonded joints is analysed via cohesive zone using trapezoidal bond model. • Properties of FRP, adhesive and concrete affect ETS bonding performance. • Proposed equations for bond strength and effective bond length are highly accurate.

Effect of Time-Dependent Bond Slip on Delayed Failure of Reinforced Concrete Frames

Effect of Time-Dependent Bond Slip on Delayed Failure of Reinforced Concrete Frames

Study on bond behaviour of stainless steel reinforced concrete

The stainless steel rebar (SSR) and concrete are mainly bonded to transfer force and coordinate deformation. Therefore, it is necessary to study the bond behavior of stainless steel reinforced concrete. In this paper, the reinforced concrete specimens of carbon steel rebar (CSR), austenitic stainless steel rebar(ASSR) and duplex stainless steel rebar (DSSR) are made by taking concrete strength, steel rebar diameter, anchorage length, thickness of concrete cover and stirrup ratio as test parameters. Through the pull-out test, the failure phenomenon, bond stress-slip curve, ultimate load and ultimate bond strength of three kinds of reinforced concrete specimens are compared. The influence regularity of different factors on the bond behavior of SSR concrete is studied.. The bond strength formulas of ASSR and DSSR concrete are obtained by data fitting. The test results show that: (1) Both CSR concrete specimens and ASSR concrete specimens are mainly damaged by steel pulling out; (2) The failure mode of DSSR concrete specimens is mainly concrete splitting failure; (3) The change of concrete strength has the greatest influence on bond slip of DSSR concrete, followed by CSR concrete, and finally ASSR concrete; (4) CSR concrete has the best bond slip performance, followed by DSSR concrete, and finally ASSR concrete; (5) The recommended design value and calculation formula of anchorage length of ASSR and DSSR are given.

Durability of CFRP-Steel Double-Lap Joints under Cyclic Freeze-Thaw/Wet-Dry Conditions.

The usage of carbon fiber–reinforced polymer (CFRP) to strengthen cracked steel structures can effectively improve its bear capacity, so it has been extensively used in recent years. The degradation of interfacial bonding is one of the most important factors affecting the durability of CFRP–steel structures under a freeze–thaw(F–T)/wet–dry (W–D) environment. In this study, epoxy resin adhesive (ERA) dog-bone specimens and CFRP–steel double-lap joints (bonded joints) were prepared. F–T/W–D cycles experiment and tensile tests of the ERA specimens and the bonded joints were also performed. Under F–T/W–D cycles, the main properties of the ERA specimens and the bonded joints were examined. Results indicated that fracture failure occurred in all ERA specimens. The hybrid failure modes of fiber peeling on the surface of CFRP plate and the bonded interface peeling between the CFRP plate and ERA layer primarily occurred in the bonded joints. The failure of both of them can be considered to be brittle, which was unaffected by the F–T/W–D cycles. With increased F–T/W–D cycles, the ultimate load and tensile strength of the ERA specimens initially increased and then decreased, whereas the elastic modulus initially increased and then remained unchanged. The ultimate load of the bonded joints decreased gradually. Based on the relationship between the interfacial bond-slip parameters and the number of F–T/W–D cycles, the bond–slip model of the bonded joints was established. The proposed relationship was validated by comparing with the experimental bond-slip relationships and the predicted relationships under the F–T/W–D cycles.

Numerical Simulation of Lap-Spliced Ultra-High-Performance Concrete Beam Based on Bond–Slip

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.

Analytical and Numerical Modeling of the Pullout Behavior between High-Strength Stainless Steel Wire Mesh and ECC.

Bond behavior is a key factor in the engineering application of composite material. This study focuses on the constitutive model of the bond behavior between high-strength stainless steel strand mesh and Engineered Cementitious Composites (ECC). In this paper, the effects of strand diameter, bond length and transverse steel strand spacing on bond behavior were studied based on 51 direct pullout tests. Experimental results showed that the high-strength stainless steel strand mesh provided specimens an excellent ductility. Based on the experimental data, the existing bond–slip model was revised using the theory of damage mechanics, which fully considered the influence of the steel strand diameter on the initial tangent stiffness of the bond–slip curve. The results of the model verification analysis show that errors are within 10% for most parameters of the bond–slip model proposed, especially in the ascending section, the errors are within 5%, indicating that the calculated results using the revised model are in good agreement with the test results. In addition, the revised model was applied to the finite element analysis by using the software ABAQUS to simulate the pullout test, in which the spring-2 nonlinear spring element was used to stimulate the bond behavior between steel strand meshes and ECC. The simulation results show that the numerical analysis fits the experimental result well, which further verifies the accuracy of the model and the feasibility and applicability of the numerical analysis method.

Comparative analysis of different types of damage indexes of coastal bridges based on time-varying seismic fragility

When bridge is constructed in a seismic-prone area, different damage index analysis methods will cause errors in seismic performance evaluation of bridge. Focusing on time-varying chloride erosion, time-varying bond–slip, and time-varying damage indexes, this paper presents a methodology to carry out fragility analysis of bridge under earthquake, which can incorporate the various existing analytical methods of damage index of pier in a coastal environment. First, the mechanical properties of concrete and steel in the entire life cycle considering chloride erosion and the repair of damaged concrete of piers are introduced. Then, ground motion input, fragility analysis method, and time-varying attenuation analysis of the varies exiting damage indexes of piers are constructed. After that, a methodology to carry out the fragility analysis of bridges under earthquake is proposed. According to the proposed flowchart of the computational procedure, using a coastal bridge as an example to investigate the seismic performance of bridges. Results show that fragility analysis based on security is significantly more conserved than economy-based methods. The maximum difference between them appears on the side with smaller seismic intensity when damage degree is small, while it appears on the side with larger seismic intensity when damage degree is large.

Bond performance of GFRP bars embedded in steel‐PVA hybrid fiber concrete subjected to repeated loading

AbstractThe bond performance of glass fiber‐reinforced polymer (GFRP) bars embedded in steel fiber–PVA hybrid fiber concrete plays an important role in their integration. In the present work, hybrid fiber concrete in different volume ratios of hybrid fibers with GFRP was investigated. Pullout tests with two amplitude regimes were conducted on hybrid fiber concrete specimens integrated with GFRP bars to investigate its ultimate bond strength, bond–slip curve, energy dissipation characteristics, and bond stiffness. The results indicate that when the total fiber volume ratio was fixed at 0.9%, the bond strength between the GFRP bars and hybrid fiber concrete increased gradually as the steel fiber volume increased, and the energy consumption increased gradually during the pullout. The slip corresponding to the ultimate bond strength under variable‐amplitude repeated loading is in good agreement with the experimental results under monotonic loading. The specimen P1S8 (0.1% PVA, 0.8% steel fiber) hybrid exhibited sufficient energy dissipation capacity and deformation capacity under repeated loads, and the bond stiffness is relatively higher and more stable during the loading and unloading stages.

Tensile Experiments and Numerical Analysis of Textile-Reinforced Lightweight Engineered Cementitious Composites.

Despite many cases of textile-reinforced engineered cementitious composites (TR-ECCs) for repairing and strengthening concrete structures in the literature, research on lightweight engineered cementitious composites (LECC) combined with large rupture strain (LRS) textile and the effect of textile arrangement on tensile properties is still lacking. Therefore, this paper develops textile-reinforced lightweight engineered cementitious composites (TR-LECCs) with high strain characteristics through reinforcement ratio, arrangement form, and textile type. The study revealed that, by combining an LRS polypropylene (PP) textile and LECC, TR-LECCs with an ultimate strain of more than 8.0% (3–4 times that of traditional TR-ECCs) could be developed, and the PP textile’s utilization rate seemed insensitive to the enhancement rate. The basalt fiber-reinforced polymer (BFRP) textile without epoxy resin coating had no noticeable reinforcement effect because of bond slip; in contrast, the BFRP grid with epoxy resin coating had an apparent improvement in bond performance with the matrix and a better reinforcement effect. The finite element method (FEM) verified that a concentrated arrangement increased the stress concentration in the TR-LECC, as well as the stress value. In contrast, a multilayer arrangement enabled uniform distribution of the stress value and revealed that the weft yarn could help the warp yarn to bear additional tensile loads.

Fracture characteristics and stress transfer length of CFRP-concrete bond under field conditioning

To estimate the actual durability of CFRP-concrete bond, an investigation into bond behavior of the interface between CFRP and concrete under field conditioning (FC) in a subtropical area is presented. Single lap-shear tests were conducted on CFRP-concrete specimens subjected to FC for up to 360 days. Bond slip law and fracture characteristics were evaluated using a generalized approach based on the experimental load-displacement curves. The results show that the local bond strength decreased by 30% in the initial 90 days and a 10% recovery appeared after additional 270 days, while the interfacial fracture energy showed a 30% increase after 360 days. Analytical modeling incorporating the evaluated bond slip law was performed and the effect of FC on the stress transfer was revealed. The effective bond length increased by 50% throughout FC. Besides, it can be found that an electromechanical impedance method (EMI) via the use of PZTs was able to monitor the CFRP-concrete interface during single lap-shear tests, and the monitoring results can indicate the bond deterioration.

Simulation Study on Mechanical Characteristics of Rock Bolt in Rock Mass with Bedding Separation Based on the Nonlinear Bond Slip Relationship

The mechanical equation on the mechanical characteristics of rock bolt in rock mass with bedding separation is established, based on the bond slip relationship of anchoring interface by the load transfer method. The validity of the numerical simulation is verified by the analytical solution of mechanical equation, when the bond slip relationship is linear. Further, the nonlinear bond slip relationship of anchoring interface is input into Flac3D by FISH. The mechanical characteristics of rock bolt are studied with the single and multiple bedding separation by numerical simulation. The results show that the axial force and the interfacial shear stress distribution curves on both sides are symmetrically distributed with the single bedding separation in rock mass, when the bedding separation is located in the center of the anchoring segment. When the bedding separation positions are not located in the center of the anchoring segment, the bedding separation value at different positions versus the axial force curves shows a single peak distribution. The axial force of rock bolt is mainly controlled by the side with the shorter anchoring length. Compared with the single bedding separation in rock mass, the additional stress of rock bolt occurred by the multiple bedding separation will superimpose each other. This paper leads to a better understanding for the load transfer mechanism for grouted rock bolt systems in rock mass with bedding separation and provides a reference for scientific support design and evaluation method.

Improved Meta-learning Neural Network for the Prediction of the Historical Reinforced Concrete Bond–Slip Model Using Few Test Specimens

The bond–slip model plays an important role in the structural analysis of reinforced concrete structures. However, many factors affect the bond–slip behavior, which means that a large number of tests are required to establish an accurate bond–slip model. This paper aims to establish a data-driven method for the prediction of the bond–slip model of historical reinforced concrete with few test specimens and many features. Therefore, a new Mahalanobis-Meta-learning Net algorithm was proposed, which can be used to solve the implicit regression problem in few-shot learning. Compared with the existing algorithms, the Mahalanobis-Meta-learning Net achieves fast convergence, accurate prediction and good generalization without performing a large number of tests. The algorithm was applied to the prediction task of the bond–slip model of square rebar-reinforced concrete. First, the first large pretraining database for the bond–slip model, BondSlipNet, was established containing 558 samples from the existing literature. The BondSlipNet database can be used to provide a priori knowledge for learning. Then, another database, named SRRC-Net, was obtained by 16 groups of pull-out tests with square rebar. The SRRC-Net database can be used to provide the posteriori knowledge. Finally, based on the databases, the algorithm not only successfully predicted the bond–slip model of square rebar-reinforced concrete, but also that of the other 23 types of reinforced concrete. The research results can provide a scientific basis for the conservation of square rebar-reinforced concrete structures and can contribute to the bond–slip model prediction of the other types of reinforced concrete structures.

Estimation of Bond Strength and Effective Bond Length for the Double Strap Joint between Carbon Fiber Reinforced Polymer (CFRP) Plate and Corroded Steel Plate.

In this paper, we examine the development of the estimation models of bond strength and effective bond length for a double strap joint between carbon fiber reinforced polymer (CFRP) plate and corroded steel plate. The experimental study on the bond behavior between CFRP plate and corroded steel plate is summarized first and the analytical interfacial bond–slip model for CFRP plate externally bonded to corroded steel plate is proposed. Based on the theoretical stress analysis for the CFRP plate–corroded steel plate double-lap joint, the piecewise expressions of the interfacial shear stress and the normal peel stress of the interface between CFRP plate and corroded steel plate were established. The estimation models of the bond strength and the effective bond length for the double strap joint between the CFRP plate and the corroded steel plate were consequently developed on the basis of interfacial stress distribution equations and the stress boundary conditions. The comparison between the predicted and experimental results indicated that the proposed models could be adopted to predict the bond strength and effective bond length for the CFRP plates externally bonded to corroded steel substrates with reasonable accuracy. The proposed estimation models are expected to provide meaningful references and essential data for the reliable application of CFRP strengthening system to the performance improvement of corroded steel structures.

Bond Behavior of Steel Cords Embedded in Inorganic Mortars.

This paper investigates the bond behavior of steel cords embedded in inorganic matrices. A series of pull-out tests were carried out on individual galvanized steel cords embedded in either a cementitious or lime-based mortar matrix and the corresponding bond-slip relationships were derived. The quality of bond between cord and mortar was found to be critically affected by the workability of the mortar and its ability to create adequate composite action along the entire embedment length of the cord. The more workable lime-based mortar was found to guarantee a better interaction with the steel cord, in terms of initial bond stiffness, maximum bond strength, and post-peak behavior. The experimentally derived bond–slip relationships were subsequently integrated in a 3D non-linear finite element framework and used to determine the constitutive relationship of a surface-based cohesive contact between cord and mortar. The cohesive bond behavior was used to conduct a series of parametric studies on cords embedded in a lime-based mortar and examine the stress development within specimens with cords of different embedment lengths and subjected to different loading conditions (i.e., pull-out and direct tension). The active ‘Stress Transfer Zone’ was found to be about 125 mm, while an ‘Effective Transfer Radius’ of approximately 3.5–4 mm was identified. The numerical investigation implemented in this paper enabled one to study key interaction properties of steel reinforced grouts and can assist the design of more effective strengthening solutions.

Bond behavior of recycled coarse aggregate concrete with rebar after freeze–thaw cycles: Finite element nonlinear analysis

Abstract In this article, the bond performance of recycled coarse aggregate concrete with rebar after freeze–thaw cycles is analyzed by the ABAQUS finite element method. The result shows that the finite element simulation value of the ultimate bond strength of recycled aggregate concrete specimens is in good agreement with the experimental value, while the agreement between the finite element simulation value of the peak bond slip of recycled aggregate concrete specimens and the experimental value is low; the bond strength between rebar and recycled aggregate concrete increased with the increase of concrete strength and concrete cover depth; the calculation formula for the bond strength between recycled aggregate concrete specimens with different concrete strengths and different concrete cover depth after freeze and thaw cycles are obtained.

Experimental and numerical investigation of bond behavior between geopolymer based ultra-high-performance concrete and steel bars

In this study, a total of twenty groups of specimens were tested to investigate bond behavior between the geopolymer based ultra-high-performance concrete (G-UHPC) and steel bars. The failure modes and bond stress-slip relationships were analyzed and discussed in detail. Subsequently, a detailed 3D numerical model was developed and validated against the experimental findings. The validated numerical model was then employed to perform parametric studies to evaluate the effects of steel strength, bond length, and protective layer thickness on the bond behavior between G-UHPC and the steel bar. It was revealed that the bond strength between the steel bar and G-UHPC was enhanced upon increasing the steel bar strength and protective layer thickness, along with reducing the steel bar diameter. The bond slip decreased with an increase in the steel fiber length and volume fraction. Further, the protective layer thickness exhibited an insignificant effect on the linear ascending stage of the bond stress-slip relationships, but positively impacted the maximum bond strength of the specimen. Finally, a bond stress-slip constitutive model was proposed to precisely predict the bond behavior between G-UHPC and the steel bars.