Bond Stress-slip Relationship Research Articles

A 2D generic multi-surface cohesive zone model for simulating FRP-to-concrete mixed-mode debonding failure

This paper proposes a 2D generic multi-surface cohesive zone model to simulate the debonding failure process of FRP-to-concrete joints within the framework of plasticity theory. The model combines a tension cut-off yield surface with a Coulomb friction yield surface, which can accurately predict the coupled mixed-mode debonding behaviour. Non-associated flow rule is adopted by the Coulomb friction yield formulation to reproduce the dilation effect, while the tension cut-off criterion is responsible for simulating the separation in the normal direction between two bonded substrates. Given the potential non-convergence problems caused by the presence of vertex region at the intersections between two yield surfaces, a remedy measure using the implicit backward Euler integration method incorporating Koiter’s rule and coupled independent state variables is applied. The proposed 2D interface model is versatile, and its accuracy has been validated by comparing the predicted results with their test counterparts from literature in different aspects, including the capacities of capturing mixed-mode failure, dilation behaviour, lateral compression effect, FRP deformation, and local bond stress-slip relationship. The model’s good compatibility with the constitutive relationship of CDP (concrete damaged plasticity) is also demonstrated.

Probabilistic modeling of reinforced concrete bond behavior considering failure mode and corrosion

Bond at the rebar-concrete interface plays a critical role in the structural performance of reinforced concrete (RC) structures. This bond behavior is typically described by a bond stress-slip relationship, where there are two critical quantities: bond strength ̶ the maximum shear stress that bond can withstand, and peak slip ̶ the slippage at the interface when the bond strength is reached. It is understood that the bond deteriorates when corrosion is present and behaves differently under two distinct bond failure modes (i.e. splitting and pull-out). Thus, this study aims to develop probabilistic prediction models for bond strength and peak slip under the two bond failure modes considering corrosion. In particular, multivariate nonlinear regression with all-possible subset model selection and symbolic multi-gene regression are adopted for the model development. The results show that the developed models outperform other existing models, and also provide satisfactory flexural behavior predictions when they are applied to RC beams.

Bond Characteristics of a Deformed Steel Bar Embedded in Donut-Type Voided Slab

In reinforced concrete (RC) structures, bond behavior between concrete and deformed steel bar (rebar) has a great effect on the structural behavior of members including voided slabs. According to previous research, bond behavior of a rebar in voided slabs is different from that in general RC slabs by the concrete inner cover formed between rebar and void. However, the bond characteristics of rebar in voided slabs have not been clearly verified yet. This study investigated the bond characteristics of rebar in the donut-type voided slab. Like other voided slabs, the donut-type void-shaper make concrete inner cover formed between rebar and void, and some part of the donut-type voided slab has smaller inner cover thickness than 2.5 db. Furthermore, inner cover thickness changes along the longitudinal rebar due to the shape of void. These were expected to affect the bond behavior of rebar in the donut-type voided slab. In this study, pull-out tests were performed to find out the effect of bond condition by the region due to voids. To this end, the donut-type voided slab was divided into three regions according to the shape of void, such as ‘Insufficient region’, ‘Transition region’, and ‘Sufficient region’. Main variables were inner cover thickness, embedded length, and bond location, which is affected by void shape. Bond characteristics of rebar in the donut-type voided slab were evaluated through comparison of bond stress–slip relationship, maximum bond strength, and bond stress distribution of each region. Test results showed that the average bond stress was found to be 25~50% lower than that of the general RC slab in the region of the inner cover thickness of 2.5 db, which was not satisfied due to void, and the bond stress–slip relationship and the bond stress distribution of the donut-type voided slab was also different from that of the general RC slab according to the type of bond region and inner cover thickness. In addition, the calculation method of bond strength of rebar in donut-type voided slab was proposed, which indicated that the error range between the estimated value and the experimental value was within 5%.

Bond behavior of basalt fiber reinforced polymer bars in seawater sea-sand concrete exposed to daily temperature variations

Application of basalt fibre reinforced polymer (BFRP) bar reinforced seawater sea-sand concrete structures in marine and coastal buildings could bring both environmental and economic benefits. As BFRP bar reinforced seawater sea-sand concrete members are likely to be exposed to temperature variations during their service life, the bond durability between BFRP bar and seawater sea-sand concrete should be well understood. This paper investigated the effects of thermal cycling, such as target temperature (i.e. amplitude of variation) and cycling times, bar diameter and concrete strength on the bonding behavior of BFRP bars in seawater sea-sand concrete by pullout test. It is found that target temperature and cycling times lead to a significant reduction of BFRP bar-to-seawater sea-sand concrete bonding, which is mainly attributed by the degradation of BFRP under thermal cycles. Through the method of scanning electron microscopy, microstructure of BFRP is examined and the bond mechanism considering the effect of temperature variations is clarified. Finally, theoretical model is proposed to predict the bond stress-slip relationship of BFRP bars in seawater sea-sand concrete. Accuracy of the predictions is validated by the experimental results.

Experimental and Analytical Investigation of Bond Behavior of Deformed Steel Bar and Ultra-High Performance Concrete

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.

Bond-Slip Relationship between Sand-Coated Polypropylene Coarse Aggregate Concrete and Plain Rebar.

Recycled plastic waste as an aggregate in concrete mixtures is one of the important issues in the construction industry since it allows the reduction of building weight and has beneficial effects on the environment. In addition, the bonding ability of this kind of lightweight concrete to reinforcement is also a prerequisite as a composite material in forming reinforced concrete structures. Therefore, in this study, the bond of plain rebar embedded in artificial lightweight aggregate concrete made from polypropylene plastic waste coated with sand was investigated. A pull-out test of nine group specimens was conducted to study the bond strength of 10 mm, 12 mm, and 16 mm diameter plain rebar embedded in polypropylene plastic waste coarse aggregates lightweight concrete (PWCAC), failure mode, and bond stress–slip relationship. The test results show that the bond–slip relationship and bond strength depend mainly on the bar diameter for PWCAC. Meanwhile, for all PWCAC specimens tested, the pull-out failure modes were observed. A bond equation for PWCAC was formulated by performing a regression analysis on the experimental results and afterward was combined with an existing bond–slip equation for normal concrete to have the bond–slip formulation for the lightweight concrete studied. The comparison between the model and experimental results indicates a close agreement.

Anchorage performance of grouted corrugated duct connection under monotonic loading: Experimental and numerical investigation

The grouted corrugated duct connection (GCDC) has wide applications in column-to-cap beam and column-to-footing joint of precast bridges. The anchorage performance of GCDC has received more attention due to the lack of understanding. In this study, a two-phase experimental program was conducted to investigate the anchorage performance of GCDC. The pull-out tests of 40 specimens in Phase Ⅰ mainly focused on the effects of various factors on anchorage requirement of GCDC, in which factors such as anchorage length, duct-to-rebar diameter ratio were considered. Test results indicate that the failure modes of GCDC and the proposed equivalent bond stiffness are mainly governed by the anchorage length and duct-to-rebar diameter ratio. The anchorage length of 10–15 times rebar diameter and duct-to-rebar diameter ratio of 2.5–3.5 are recommended to ensure bond strength. In Phase Ⅱ, 40 design specimens were pulled out to investigate the bond-slip constitutive relationship of GCDC. The variation law of ultimate bond strength was analyzed with the variation of the anchorage length and duct-to-rebar diameter ratio. Based on experimental results, basic bond stress-slip relationship and bond stress distribution function were obtained through curve fitting, which were in good agreement with test results. Finally, the comprehensive bond-slip constitutive model incorporating location function was developed. The refined finite element model considering bond-slip constitutive relationship was established to investigate and verify the pull-out test results. Therefore, the anchorage requirement recommended can provide reference for the selection of anchorage length duct-to-rebar diameter ratio for engineering application of GCDC. Furthermore, the bond-slip constitutive model developed is the theoretical basis for finite element analysis of GCDC.

Bond stress-slip relationship in concrete-filled square stainless steel tubes

The application of stainless steel tubes in concrete-filled steel tube systems can significantly improve their corrosion resistance in comparison with those that employ carbon steel tubes. In this paper, a series of push-out tests were carried out to investigate the bond stress-slip behavior between stainless steel tubes and concrete. A total of 14 concrete-filled square stainless steel tube specimens were tested, covering two cross-sectional width-thickness ratios (B/t = 30 and 50), two concrete strength (fcu = 44 and 76 MPa), three rib stiffener types (ordinary, saw-shaped and perfobond leister) and two stainless steel grades (austenitic and duplex). The test results indicate that B/t, fcu and stainless steel grade have noticeable influences on the ultimate bond stress (τu) in concrete-filled square stainless steel tube and the addition of rib stiffeners significantly improves the bond behavior. The bond mechanism at different stages of loading and the effect of various parameters on τu are discussed. Based on the test results, an idealized bond stress-slip strain (τ-εS) curve was proposed, where good agreement between the test and the proposed model has been achieved.

Local Bond Stress-Slip Model of High-Strength Stainless Steel Wire Ropes in ECC

Engineered cementitious composites (ECC) reinforced with high-strength stainless steel wire ropes (HSSSWR) is a new composite that has attracted much attention. Comprehensive understanding of the local bond stress-slip relationship of HSSSWR in ECC is a significant aspect to popularize the application of this new composite. In this research, the local bond stress-slip relationship between HSSSWR and ECC was investigated experimentally and theoretically, considering the influences of bond lengths, nominal diameters of HSSSWR and compressive strength of ECC. In order to accurately predict the bond stress and slip at different positions along the embedded length, a local bond stress-slip model was proposed for HSSSWR-ECC interface, and the model parameters were determined based on the pull-out test results and microsegment analysis of HSSSWR in ECC by using a nested iteration procedure. Furthermore, the three-dimension (3D) nonlinear finite element (FE) modeling method by using the proposed model was used to predict the bond-slip performance of HSSSWR in ECC. Finally, the global load-slip relationships calculated by using the iterative procedure and the 3D FE modeling method were compared with test results, which validated the acceptability of the developed local bond stress-slip model and the FE modeling method.

3D meso-scale modelling of the bonding failure between corroded ribbed steel bar and concrete

Subjected to a corrosive environment, the macroscopic behavior of reinforced concrete structures is closely related to the bond property between rebar and concrete. For assessing the material performance and evaluating the nonlinear bond behavior of the interface between corroded ribbed rebar and concrete, and finally revealing the meso-mechanical failure mechanism of the reinforced concrete structure, we propose a 3D mesoscopic model in the current paper. The following elements that may influence the macroscopic behavior of the reinforced concrete are considered in the model: (1) the friction resistance and the mechanical interaction between corroded ribbed rebar, rust and concrete (2) the surface characteristic of threaded ribbed bar. The proposed mesoscopic model allows us to assess the influences of corrosion on the bond performance of corroded reinforced concrete through a two-stage analysis: after considering the expansive behavior of the reinforced concrete in the model, we apply a pull-out force on the corroded rebar to evaluate the bond-slip behavior between the corroded rebar and concrete. For validating our model, we compare the failure patterns and corroded bond stress-slip curves calculated by the model and obtained by experimental means and found a good consistency between them. Finally, a modified model was developed to describe the corroded bond stress-slip relationship. It has been found that when relative slip is applied, the concrete continues to crack along pre-existing cracks caused by corrosion products until the concrete splitting failure accorded. With the increase of corrosion level, the shape of the bond stress-slip curve is similar with a significantly degradation of the bond strength and peak slip, especially at small corrosion levels. Through comparing the proposed modified formula with the existing test data, one can find that the proposed modified formula can effectively characterize the corroded bond stress-slip relationship between deformed rebar and concrete.

Bond behavior of recycled aggregate concrete-filled steel tube after elevated temperatures

This paper experimentally investigated the interfacial bond behavior of recycled aggregate concrete-filled steel tubes (RACFST) after different temperatures (i.e., 20 °C, 200 °C, 400 °C, 600 °C). A total of 40 specimens (twenty circular columns and twenty square columns) were tested by means of push-out to study the effect of the following parameters: (a) experienced temperature (T), (b) mass replacement percentage of recycled coarse aggregate (γ) and (c) cross-section shape. The influences and mechanism of above parameters on bond behavior were discussed. The test results indicate that T and γ had different influences on bond behavior and interfacial damage resistance. The interfacial failure process of the square specimen was non-uniform compared with that of the circular specimen and its overall failure process was more brittle. The bond behavior and interfacial damage resistance of the circular specimen were generally stronger than those of the square specimen. Besides, applicability of several existing prediction formulas for bond strength was evaluated. Lastly, more accurate prediction formulas for bond strength and analytical models for bond stress-slip relationships were proposed.

Mesoscale modelling of bond performance between deformed steel bar and concrete subjected to dynamic loads

The good bond property is the base for rebar and concrete to work together, influencing the mechanical behaviour of reinforced concrete structures. To investigate the bond-slip performance between deformed steel bars and concrete under dynamic loadings, a three-dimensional meso-scale numerical model was established, considering the inherent heterogeneity of concrete and explicitly modelling the surface characteristics of the rebar. The interaction between the rebar and concrete was implemented by the surface-to-surface contact strategy. The strain rate effect of materials was also taken into account. The rationality and accuracy of the proposed model were verified by the good consistency between the simulation and available test results in terms of failure pattern and bond stress-slip curves. With the help of the meso-scale model, the bond-slip behaviour under various loading rates was simulated and analysed. Finally, a simplified model to describe the dynamic bond stress-slip relationship was developed. It has been found that due to the propagation of stress waves, the cracking process of the specimen varies with the strain rate while the final failure pattern is similar, exhibiting splitting type failure. Thus, a considerable part of pull-out loading was resisted by the inertia of the system at the initial stage. With the increase of strain rate, the shape of the dynamic bond stress-slip curves is similar with a significantly increased bond strength and reduced slip, especially at high strain rates. The ratio between the residual and peak bond stress is approximately constant, irrespective of strain rate. The proposed simplified model is able to effectively characterize the dynamic bond stress-slip relationship between the deformed rebar and concrete.

Experimental study on Bond stress-Slip relationship of Corroded small diameter Reinforcing bars

Experimental study on Bond stress-Slip relationship of Corroded small diameter Reinforcing bars

A novel bond stress-slip model for 3-D printed concretes

<p style='text-indent:20px;'>This paper considers the 3D printing process as a discontinuous control system and gives a simple and coherent bond stress-slip model for a new and intelligent building 3-D printed concrete. The previous models focused on either the maximal stress or the maximal slip, however, the novel model uses an energy approach by the dimension analysis, so that the main factors affecting the bond stress-slip relationship can be clearly revealed, mainly including the concrete's properties (its porous structure and its strength), the steel bar's properties (its printing direction, its strength, its surface roughness and its geometrical property) and the printing process. It is confirmed that the proposed model, similar to the constitutive relationship in elasticity, plays a key role in concrete mechanics, and it can conveniently explain the observed phenomena from the experiment.</p>

Determination of bond model for 7-wire strands in pretensioned concrete beam

A correct choice of a bond model for prestressing tendons is crucial for the right modelling of a structural behaviour of a pretensioned concrete structure. The aim of this paper is the determination of an optimal bond model for 7-wire strands in a prestressed concrete beam produced in a precast concrete plant of Consolis Poland. ATENA 3D is used to develop finite element models of the beam that differ only in a bond stress-slip relationship of tendons. The bond stress-slip relationships for modelling are taken from the results of bond tests carried out by different researchers in previous years. Moreover, for comparison purposes, a simplified 2D model of the beam is created in Autodesk Robot. The strain distribution at the time of the strand release is found for each of the finite element models. The determined strain distributions are compared with the strain distribution in the beam established by an experimental test using a measuring system based on a digital image correlation. On the basis of the comparison results, the most appropriate bond models for 7-wire strands used in the beam are identified.

Fundamental Investigations of Bond Behaviour of High-Strength Micro Steel Fibres in Ultra-High Performance Concrete under Cyclic Tensile Loading.

The objective of the contribution is to understand the fatigue bond behaviour of brass-coated high-strength micro steel fibres embedded in ultra-high performance concrete (UHPC). The study contains experimental pullout tests with variating parameters like load amplitude, fibre orientation, and fibre-embedded length. The test results show that fibres are generally pulled out of the concrete under monotonic loading and rupture partly under cyclic tensile loading. The maximum tensile stress per fibre is approximately 1176 N/mm2, which is approximately one third of the fibre tensile strength (3576 N/mm2). The load-displacement curves under monotonic loading were transformed into a bond stress-slip relationship, which includes the effect of fibre orientation. The highest bond stress occurs for an orientation of 30° by approximately 10 N/mm2. Under cyclic loading, no rupture occurs for fibres with an orientation of 90° within 100,000 load changes. Established S/N-curves of 30°- and 45°-inclined fibres do not show fatigue resistance of more than 1,000,000 load cycles for each tested load amplitude. For the simulation of fibre pullout tests with three-dimensional FEM, a model was developed that describes the local debonding between micro steel fibre and the UHPC-matrix and captures the elastic and inelastic stress-deformation behaviour of the interface using plasticity theory and a damage formulation. The model for the bond zone includes transverse pressure-independent composite mechanisms, such as adhesion and micro-interlocking and transverse pressure-induced static and sliding friction. This allows one to represent the interaction of the coupled structures with the bond zone. The progressive cracking in the contact zone and associated effects on the fibre load-bearing capacity are the decisive factors concerning the failure of the bond zone. With the developed model, it is possible to make detailed statements regarding the stress-deformation state along the fibre length. The fatigue process of the fibre-matrix bond with respect to cyclic loading is presented and analysed in the paper.

Investigating the effect of steel fiber content on bond behavior between externally bonded CFRP-to-concrete joints

A number of studies have identified interfacial debonding as a major challenge in externally bonded FRP strengthened systems. The addition of steel fiber into concrete enhances the debonding resistance, ductility and subsequently increase the strength of FRP laminate-concrete interface. The main purpose of this experiment is to explore the incorporation of different steel fiber contents in the interfacial bond between CFRP laminates and concrete substrate. Five groups of the double shear specimens were fabricated with hooked-end short steel fibers having five different volume contents namely; 0, 0.25%, 0.5%, 1.0%, and 1.5%. The impact of different fiber volume content on the maximum shear stress, slip at maximum shear stress and interfacial bond stress-slip relationship were analyzed. Results showed specimens with 0.25%–1.5% short steel fibers improved their maximum shear stress considerably over the control specimens. The failure modes of specimens were debonding in concrete substrate and concrete shear failure. Finally, an analytical interfacial bond-slip model considering the influence of volume fraction of short steel fibers is proposed.

Experimental study on the cyclic bond behavior of corroded rebar based on modified beam test

The corrosion of rebar results in the degradation of bond between rebar and concrete, thus is unfavorable to the safety of reinforced concrete structures. So far, many studies were undertaken to investigate the bond behavior of corroded rebars under monotonic loading, however, only a few considered the effect of cyclic loading. Moreover, in these researches, the bond behavior of corroded rebars under cyclic loading were generally studied with pull-out specimens, which cannot ensure an actual stress state of the rebar and concrete during loading. Therefore, in this paper, an experimental study is made to further investigate the cyclic bond behavior of corroded rebars based on a modified beam test, in which the stress state of the rebar and concrete is consistent with reality. Based on the test results, the effects of corrosion level and loading history on the bond stress at a given slip are evaluated. A cyclic bond-slip model is proposed, in which the degradation rule of bond stiffness is calibrated by the test results. The model is implemented in a user-defined bond element and validated with the test results. The predictions of the model show great agreement with the test results, meaning that the proposed model is feasible to simulate the bond stress-slip relationship of corroded rebars under cyclic loading.

Load-deformation behaviour of weft-knitted textile reinforced concrete in uniaxial tension

Weft-knitted textiles offer many advantages over conventional woven fabrics since they allow the fabrication of doubly curved geometries without the need of stitching multiple patches together. This study investigated the use of high-strength continuous fibres as knitted textile reinforcement, focusing on various knitting patterns, fibre materials, coating types and spatial features to enhance the bond conditions between concrete and reinforcement. The bond is of particular interest since the contact surface of knitted textiles is fundamentally different due to their closed surface, compared to commercially available textile reinforcement, which is normally formed as orthogonally woven grids of rovings. An experimental campaign consisting of 28 textile-concrete composites was conducted, where digital image correlation-based measurements were used to assess the load-deformation behaviour and to analyse the crack kinematics. The results showed a beneficial post-cracking behaviour for epoxy coated configurations with straight inlays. The comparison of these configurations with conventional textile reinforcement generally showed a similar behaviour, but with higher utilisation compared to the filament strength. The Tension Chord Model, which assumes a constant bond stress-slip relationship, was adapted for the specific geometry of the knitted reinforcement, and it was used for the estimation of bond stresses and a post-diction of the experimental results, generally showing a good agreement.

Experimental study on the steel–concrete bond behaviour of circular concrete-filled stainless steel tubes

The paper reports an experimental investigation on the bond stress–slip relationship in concrete-filled stainless steel tube (CFSST) structures. Push-out tests were conducted on twelve specimens covering two stainless steel grades, two concrete grades, two cross-sectional dimensions and two internal ring conditions (with and without the internal ring). The effects of these factors on the bond stress–slip relationship in CFSST members were analysed and discussed. A theoretical model, based on the assumption that no restraining force from the steel tube was applied to the concrete core, was developed to predict the bond stress–slip response of CFSSTs and was evaluated against the test results. An empirical model was also proposed based on regression analysis to replicate the experimental bond stress–slip relationships, which can be used as input data for analytical and numerical simulations in future studies of CFSST structures.