Bond-slip Behavior Research Articles

Distributed fiber optic strain sensing in axially loaded glued-in steel rods in glued-laminated timber

The rise in popularity of mass timber structures globally has increased the demand for high-performance timber connections. Glued-in rod connections which are advantageous compared to other dowel-type connections because of their high strength and stiffness, have been the subject of extensive research in the literature; However, the lack of an in-depth understanding of their behavior and a uniform set of guidelines for their design continues to limit the use of glued-in rods in practice. To develop an improved understanding of the behavior of glued-in rod connections this paper examines, for the first time, the use of distributed fiber optic sensors to measure the complete strain distribution along the length of a glued-in rod connection. Axial pullout tests were conducted on twenty-five glued-in rod connections in glued-laminated timber with varying embedment lengths and glue-line thicknesses. Results of the study demonstrate the ability of fiber optic sensors to capture the full strain distribution along the length of the steel rod and along the epoxy-adhesive interface, enabling the study of localized behavior that would be difficult to measure using conventional strain gauges. In addition, results demonstrate the ability of distributed fiber optic strain sensors to infer axial stress and force distributions along the length of a glued-in rod connection, which are compared with theoretical distributions from the Volkersen model, as well as measure bond-slip behavior.

Bonding Performance of Glass Fiber-Reinforced Polymer Bars under the Influence of Deformation Characteristics.

Glass fiber-reinforced polymer (GFRP) of high performance, as a relatively ideal partial or complete substitute for steel, could increase the possibility of adapting structures to changes in harsh weather environments. While GFRP is combined with concrete in the form of bars, the mechanical characteristics of GFRP cause the bonding behavior to differ significantly from that of steel-reinforced members. In this paper, a central pull-out test was applied, according to ACI440.3R-04, to analyze the influence of the deformation characteristics of GFRP bars on bonding failure. The bond-slip curves of the GFRP bars with different deformation coefficients exhibited distinct four-stage processes. Increasing the deformation coefficient of the GFRP bars is able to significantly improve the bond strength between the GFRP bars and the concrete. However, while both the deformation coefficient and concrete strength of the GFRP bars were increased, the bond failure mode of the composite member was more likely to be changed from ductile to brittle. The results show members with larger deformation coefficients and moderate concrete grades, which generally have excellent mechanical and engineering properties. By comparing with the existing bond and slip constitutive models, it was found that the proposed curve prediction model was able to well match the engineering performance of GFRP bars with different deformation coefficients. Meanwhile, due to its high practicality, a four-fold model characterizing representative stress for the bond-slip behavior was recommended in order to predict the performance of the GFRP bars.

Experimental and numerical simulation of bond-slip in textile-reinforced concrete for multiple bond lengths

The rise in the use of lightweight and sustainable structural systems in the construction industry opened the chance to improve conventional construction methods. To produce a slender structural member, the use of textile in concrete, herein referred to as textile-reinforced concrete (TRC), has been explored. The textile used is primarily carbon, producing a lightweight and durable construction material. The TRC possesses vast possibilities in terms of its usage, however, identification of accurate bond-slip behaviour at the materials interface is one of the limitations that need to be addressed. Based on the literature, there are difficulties in determining the bond-slip relationship both experimentally and numerically, creating inconsistency in the results. This study aims to determine the bond-slip relation of TRC through pull-out tests and finite element analysis in order to replicate the actual bond-slip behaviour at the interface. The bond characteristics of TRC were assessed using pull-out specimens with different bond lengths of textile, i.e.; 20 mm, 40 mm, and 60 mm. A double-sided unsymmetrical test setup with equal clamp lengths is used for the experimental work. Using a tri-linear bond-slip interface relation, the numerical model is developed to establish the microscopic interface behaviour. The bond failure due to pull-out and rupture are observed in the pull-out test. Finally, the experimental results are compared with numerical modelling, and the results are in good agreement.

Cyclic Bond-Slip Behavior of Partially Debonded Tendons for Sustainable Design of Non-Emulative Precast Segmental Bridge Columns

The precast segmental bridge columns incorporating resettable sliding joints have been proposed to extend the accelerated bridge construction techniques to regions of moderate to high seismicity while fulfilling the sustainability-based resilient seismic design concept. Following a rethink of the design strategy in the light of inspirations from hybrid sliding-rocking joints, the design of resettable sliding joints can accommodate a certain amount of horizontal sliding displacement and adopt partially debonded tendons in a vertical manner, probably resulting in complicated tensile-flexural loading scenarios in these tendons during earthquakes, which is rarely considered in practice. In this paper, the sustainable design of resettable sliding joints is introduced. A tailor-made setup was established and simplified cyclic bond-slip tests were conducted to validate the practicality of the proposed partially debonded tendon system. Twelve specimens were fabricated using different strands and grouting techniques, and a two-stage numerical model was proposed to interpret the experimental results of seven typical specimens. The results suggest that the deterioration of reloading stiffnesses can be captured by an additional effective length caused by bond failure, and the strands perform mostly elastically under relatively large transverse displacements. The loading stiffness of the anchorage is 26.3 kN/mm, and it has significant effects and the proposed two-stage model can satisfactorily capture the envelope of the response of the partially debonded tendons, providing practical design for the proposed partially debonded tendons used in sustainable non-emulative precast segmental bridge columns.

Review of Bond-Slip Behavior between Rebar and UHPC: Analysis of the Proposed Models

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.

Numerical Prediction of Bond-Slip Behavior in Simple Pull-Out Concrete Specimens

In this study the simple pullout concrete cylinder specimen reinforced by a single steel bar was analyzed for bond-slip behavior. Three-dimension nonlinear finite element model using ANSYS program was employed to study the behavior of bond between concrete and plain steel reinforcement. The ANSYS model includes eight-noded isoperimetric brick element (SOLID65) to model the concrete cylinder while the steel reinforcing bar was modeled as a truss member (LINK8). Interface element (CONTAC52) was used in this analysis to model the bond between concrete and steel bar. Material nonlinearity due to cracking and/or crushing of concrete, and yielding of the steel reinforcing bar were taken into consideration during the analysis. The accuracy of this model is investigated by comparing the finite element numerical behavior with that predicted from experimental results of three pulloutspecimens. Good agreement between the finite element solution and experimental results was obtained.

Bond performance of carbon fiber reinforced polymer rebars in ultra-high-performance concrete

This paper investigated the bond performance between carbon fiber reinforced polymer (CFRP) bars and ultra-high-performance concrete (UHPC) by a hinged beam test investigation. A total of 11 sets of beam tests were carried out to investigate the effect of different parameters on the bond performance, including steel fiber volume fraction, bonded length, reinforcement diameter, and concrete cover. The tests showed that the bond damage modes between CFRP bars and UHPC were dominated by pull-out damage, with the surface of the bonded section of CFRP bars being peeled off from the internal core and no damage observed in the UHPCs. An increase in the cover and steel fiber volume fraction improves the bonding performance, while an increase in diameter reduces the bond performance. Based on this study, the formulae for calculating the ultimate bond strength and development length that integrated the effects of CFRP bar diameter, bonded length, and cover thickness were proposed. The bond-slip curve shows three stages, i.e., ascending section, descending section, and a residual section showing periodic fluctuations. The fluctuation period showed a certain degree of linear correlation with the rib spacing of CFRP bars. Based on the characteristics of tested curves, a bond-slip constitutive model was proposed to simulate the bond-slip behavior of CFRP bars in UHPCs with good agreement to test results.

Semi-analytical solution for interfacial debonding of high-speed railway ballastless track under thermal loading using a quasi-dynamic method

Interfacial debonding of multi-layered ballastless track systems has proved to be one of the most common diseases in the high-speed railway during long-term operations. This paper focuses on the theoretical modeling of track temperature field and consequent bond-slip behavior between track layers under thermal loading. By establishing heat conduction differential equations, whose boundary conditions are combined with complicated geographical and meteorological factors, the temperature field of a multi-layered track structure is obtained via the integral transform technique. The reliability of the heat conduction model is well-validated by an on-site experiment in a high-speed railway line. Then, we originally extend an explicit integration algorithm for dynamics analysis to solve nonlinear statics problems with small deformation by proposing a quasi-dynamic method (QDM). Equilibrium equations of a track slab subjected to quasi-dynamic equivalent thermal loads and mixed-mode interfacial cohesive forces are constructed based on the Mindlin plate in-plane and flexural vibration equations. The application of the QDM to solve interface responses is verified by comparing results obtained from finite element (FE) software. Finally, numerical discussions are conducted to reveal the nonlinear distribution characteristics of temperature field, evolution process of the interface damage and failure modes under time-varying thermal loads, which provide a better understanding of the interfacial debonding phenomenon encountered in ballastless track systems.

Hybrid machine learning-based prediction model for the bond strength of corroded Cr alloy-reinforced coral aggregate concrete

This study investigated the bond–slip behavior between newly developed Cr alloy steel bars and coral aggregate concrete (CAC) on the basis of experimental and hybrid machine learning. Several variable parameters were examined: (a) corrosion ratio, (b) diameter, (c) CAC strength, (d) anchorage length, and (e) relative protective layer thickness. Results showed that bond strength is positively correlated with relative protective layer thickness and CAC strength, whereas it is negatively correlated with diameter and anchorage length. The bond strength initially rose and subsequently fell as the corrosion ratio increased, with a critical threshold of 1%. The bond–slip curve of Cr–CAC had four stages: microslip, slip, declining, and residual stages. Additionally, the empirical, particle swarm optimization backpropagation (PSO-BP), BP, and support vector machine regression (SVR) models were evaluated using various performance evaluation metrics. The PSO-BP model outperformed the empirical, BP, and SVR models in all evaluation metrics. Compared with the PSO-BP model, the BP and SVR models had a 6.12% and 2.0% reduction in R2, 87.67% and 58.90% increase in root mean square error, 52.27% and 4.54% increase in mean absolute error, 254.72% and 152.83% increase in mean square error, and 76.52% and 52.22% increase in mean absolute percentage error, respectively. The PSO-BP model established in this research can quickly and accurately predict the bond strength of corroded Cr–CAC, providing a rapid assessment method for its application.

Experimental investigation on the bond-slip behavior between TRC-confined concrete and rebars after exposure to elevated temperatures

In this study, the bond-slip behavior between textile reinforced concrete (TRC)-confined concrete and rebars both at ambient temperature and after ISO 834 standard fire was investigated experimentally through pull-out tests. The failure modes, ultimate load, average ultimate bonding stress and energy consumption were obtained and discussed. Effects of rebar diameters (12 mm, 14 mm and 16 mm), bonding lengths (2.5d, 5d and 7.5d) and high-temperature exposure durations (30 min and 60 min) on the bonding behavior between TRC-confined concrete and rebars were examined emphatically. It was observed that the damage modes of specimens changed from pull-out failure at ambient temperature into splitting failure for both TRC-confined specimens and companion unconfined specimens exposed to high temperatures. The results obtained demonstrated that both the ultimate load and the average ultimate bonding stress can be significantly improved by the utilization of TRC jackets after 30 min exposure, and the increment of the average ultimate bonding stress can reach up to 90% as compared to those unconfined specimens. However, the enhancement of TRC jackets became unobvious after 60 min. Finally, based on test results and Prigogine’s dissipative structure theory, the energy analysis of bond-slip curves was evaluated to verify the enhancement of TRC jackets quantitatively.

Finite element modeling of precast reinforced concrete wall with dual boundary elements under lateral load

This study aimed to stimulate the structural behaviour of the precast wall PC with dual boundary elements under constant axial load and incremental lateral load in terms of displacement control and assess its response based on the load–displacement response, stiffness degradation and modes of failure using Abaqus Software and validate the result of the tested specimen. Two approaches were used for defining the interaction between the steel reinforcement and the surrounding concrete where the high-stress regions are. Friction and cohesive behaviour using traction separation law were employed to define the interaction between the interfaces of the PC wall and post-cast concrete boundary elements. Furthermore, this study primarily focused on the nonlinear behaviour of concrete and steel materials, the bond-slip behaviour between concrete-to-steel interface, the interaction between precast and post-cast concrete interfaces, and load and boundary conditions. The concrete damage plasticity model was adopted to simulate the concrete behaviour and the cohesive and frictional behaviour to model the interaction between precast and post-cast concrete interfaces. The findings show that the initial response of both FE models agreed well with test rested specimen. However, Model I exhibited a stiffer response up to the yielding point. Furthermore, both FE models continued to exhibit ductile response, showing that the right-hand side post-cast cornet boundary element didn’t experience total crushing at the bottom right concrete.

Finite element simulation of precast moment resisting reinforced concrete beam-column joint subjected to monotonic load

This paper investigated the structural behaviour of a monotonically loaded reinforced concrete (RC) beam-column joint with the precast moment-resistant connection situated distant from the face of the column. This study used ABAQUS software to perform the three-dimensional (3D) non-linear finite element (FE) analysis. The non-linear behaviour of the concrete and steel materials, the concrete-to-concrete interface behaviour and the bond-slip behaviour, were mainly focused on in this paper as they are key factors for modelling precast beam-column joints. Three approaches were used to simulate the concrete-to-concrete contact: cohesive and friction model, friction model only, and a thin layer of concrete with reduced strength. The FE results are verified by comparing them to the previously published experimental results of the precast beam-column joint under monotonic load in terms of the load–displacement curve and crack pattern. The FE results based on the three different modelling methods of the concrete-to-concrete interface were able to replicate the load–displacement response and crack patterns observed in the experimental test with an adequate level of accuracy. However, a slight difference in the predicted crack distribution among the three FE models was noticed. Overall, the FE model developed in this study, along with its modelling strategy, can be utilized as a useful tool for predicting the behaviour of precast structures with various design parameters.

Effect of nano cementitious composites on corrosion resistance and residual bond strength of concrete

The interconnection between the steel and concrete is frequently weakened by corrosion. Interestingly, it has been observed that nano pozalonic materials offer an economical approach for lowering the permeability of concrete by enhancing its morphological characteristics. This research discusses the impact of nano pozalonic materials on strengthening the corrosion resistance and pull-out behaviour of steel reinforcement in concrete. In order to treat concrete specimens with accelerated or immersion-based corrosion procedures, the cement is replaced with nanocement (NC) or nano fly ash (NFA).The performance of concrete is tested by evaluating its compressive strength, chloride ion penetration, corrosion potential, and water permeability. The steel reinforcement is examined to assess the residual yield strength and mass loss. In order to assess the bond-slip behaviour between concrete and the reinforcing steel, pull-out tests are performed. Our findings indicate that concrete with nano cement and nano fly ash exhibited excellent corrosion resistance by retaining the yield strength of reinforcement steel and corresponding bond strength.

Bond-slip behavior between multi-partition steel tubes and concrete

Bond-slip behavior between multi-partition steel tubes and concrete

Local bond-slip behaviour of reinforcing bars in fibre reinforced lightweight aggregate concrete at ambient and elevated temperatures

This paper presents an experimental investigation of the bond-slip behaviour of reinforcing bars in fibre-reinforced lightweight aggregate concrete (FRLWAC) at ambient and elevated temperatures. Sixty-four bond-slip specimens with four target temperature exposures, two concrete covers and four steel fibre contents were tested to failure. The experimental results showed that exposure to elevated temperature shifted failure pattern from more ductile pull-out to brittle splitting modes, and reduced the peak bond strength and toughness of bond-slip behaviour. Scanning electron microscope (SEM) images of the concrete-steel interface showed that thermal mismatch induced microcracks contributed to degradation of bond strength, in addition to temperature induced degradation of concrete materials. The temperature exposure also negated beneficial effect of concrete cover in enhancing bond behaviour. Addition of steel fibre helped in preventing brittle failure mode, enhancing bond strength in specimens with small concrete cover and improving the post-peak bond-slip behaviour at all target temperatures. A simple semi-analytical bond-slip model that considers different failure modes and incorporates fibre-reinforced concrete tensile behaviour from Swedish Code SS 812310 was proposed and validated based on the test results in this study.

Bond behavior of recycled tyre steel fiber reinforced concrete and basalt fiber-reinforced polymer bars under static and fatigue loading conditions

Nowadays, there is a growing demand for the development of structures and construction materials from recycled or reused and renewable resources, in line with circular economy principles and the goal of sustainable development. The present study explores promising solutions for increasing the sustainability of concrete structures, through the application of basalt fibers reinforced polymer (BFRP) rebars, whose raw materials show an unlimited availability on earth, as well as recycled steel fibers from waste tyres (RTSF), for RTSF reinforced concrete structures with BFRP reinforcements. Three different types of self-compacting concretes with 1.1% fiber volume fractions of industrial and/or recycled steel fibers were developed, where 50% and 100% of the industrial steel fibers (ISF) weight was replaced by RTSF. Five different groups of pull-out specimens, with total number of 26 specimens, were fabricated to evaluate bond performance of BFRP rebar embedded in RTSF reinforced concrete. The understanding of the bond behaviour is critical to the effective design of reinforced concrete structures under both static and dynamic loadings. The influence of the type of reinforcement, dosage of the adopted RTSF, type of loading, and concrete flow direction on bond stress versus slip behavior, maximum bond stress, and failure mode are analysed and discussed. One of the main contributions of this research regards the understanding of the effect of RTSF orientation on bond performance obtained when BFRP rebars are pulled out from RTSF reinforced concrete. Compared to ISF, using RTSF for reinforcing concrete can increase the bond strength between BFRP rebars and fiber reinforced concrete up to 6.3% under static and 9.7% under fatigue loading regime. As the future research in this area, it is recommended to evaluate the long-term bond durability of BFRP reinforced FRC embedded in seawater, the environmental and economic feasibility of using BFRP and TRSF for reinforcing concrete structures, and fiber orientation and dispersion using image analysis and 3D visualization.

Effect of Marble Waste Powder and Silica Fume on the Bond Behavior of Corroded Reinforcing Bar Embedded in Concrete

Bond behavior is the mutual effect and the force transmission between concrete and reinforcing bar that directly influence the behavior of reinforced concrete structures. Considering the silica fume (SF) and marble waste powder (MWP) could enhance the concrete matrix and improve its adherence, the bond-slip behavior of corroded reinforcing bar in concrete containing SF and MWP as ordinary portland cement (OPC) is examined in this work. Three of 16 concrete mixes were selected for this investigation: one control mix, a second mix containing 10% SF and 5% MWP as OPC replacements, and the third containing 10% SF and 20% MWP as OPC replacements. The pullout test was applied to the specimens with 0%, 2%, 5%, and 10% corroded reinforcement. According to the results of specimens with uncorroded reinforcement, replacing 10% of cement by SF and 5% or 20% by MWP, the bond strength between concrete and reinforcing bar increased by 27% and 13%, respectively, compared to that of the control specimens. Also, the samples containing SF and MWP showed higher corrosion resistance and their bond strength’s loss due to the corrosion of reinforcing bars was less than the control samples. The results also indicate that bond stress at low corrosion (2%) levels is partially increased because of the friction resulting from the accumulation of corrosion products on reinforcement’s surface. However, for higher corrosion levels (5% and 10%), the bond strength decreases. By comparing the two diameters of reinforcing bars (12 and 16 mm), it was recognized that the reduction of bond strength due to the corrosion is more severe in the reinforcements with greater diameters.

3D cohesive fracture of heterogeneous CA-UHPC: A mesoscale investigation

Ultra high performance concrete with coarse aggregates (CA-UHPC) exhibits complicated damage and failure mechanisms due to intricate interactions of irregular mesoscale phases, including random aggregates, fibres, mortar, and interfaces. This work proposes a 3D numerical framework to investigate the complex cohesive fracture of CA-UHPC at mesoscale for the first time. Automatic algorithms are proposed to model realistic aggregates, mortar, aggregate-mortar interfaces and steel fibres in large quantities. Zero-thickness cohesive interface elements are automatically inserted in the mortar and on the aggregate surfaces to capture potential cracks, and an efficient non-conforming methodology is developed to model the fibre-mortar bond-slip behaviour using orientation-dependant pullout force-slip relations. The proposed models are validated using typical uniaxial tension tests, and elucidate that the progressive interactions of aggregate barrier, interfacial cracking and fibre bridging govern the early cracking, strain-hardening behaviour, fibre activation and final crack networks. Quantitative analyses are performed to optimize the mechanical properties of CA-UHPC: as the aggregate content increases, there are more torturous crack surfaces and fewer activated fibres with lower load-carrying capacities, but the downside of coarse aggregates can be alleviated by increasing fibre content, especially when needing aggregates to reduce carbon footprints and improve anti-shrinkage performance.

Experimental Study on the Bonding Performance of FFRP Reinforced Timber Interface

ABSTRACT Although there are lots of researches about the application of FRP composites on the external bonding and reinforcement of timber structures, they are mostly aimed at Carbon FRP, which has a large difference in mechanical properties and inconsistent deformation with timber. Meanwhile, research about the interface between timber and Flax Fiber Reinforced Polymer (FFRP) with similar properties with timber is limited; hence, relevant models have not been established yet. Similar to linear elastic FRP confined timber structure, the failure of FFRP-timber structure interface is a process in which the interfacial stress is gradually transferred from the loaded end to the free end, and the interfacial stress transfer area, that is an effective bond length of the FFRP-timber interface. In order to study the interfacial stress transfer characteristics between FFRP and timber structure, based on the existing CFRP-timber structure interface bonding theory and mechanism, a single lap shear test is used to conduct a systematic study on bonding length and width are studied to optimized the application of FFRP. The bond-slip behavior is studied and fitted to provide theory support for the application of FFRP in the restoration of ancient timber structures.

Local bond stress–slip relationship of ribbed reinforcing bars embedded in UHPC: Experiment, modeling, and verification

This paper provides an experimental and analytical investigation on the bond behavior of reinforcing bars embedded in ultra-high performance concrete (UHPC) via a series of pullout tests. The local bond stress–slip relationship and global bond slip behavior were tested using specimens with embedment lengths of 2d, 5d, and 7d, where d is the diameter of the reinforcing bar. Four curing procedures and two loading ages for the UHPC were adopted to achieve different compressive strengths with the same mixture. During the test, the tension force and slip at the free end of the reinforcing bar were measured. The strain distribution along the anchorage length was measured using a distributed optical fiber sensor glued to an internal groove on the bar. The experimental results show that the ascending part of the local bond stress–slip relationship is nearly linear. A simplified local bond stress–slip model is proposed and verified using the tested strain distribution and the slip of the reinforcing bar in long specimens. This model is used to discuss the distribution form of the slip and bond stress along the anchorage length and the theoretical development length for pullout failure. The concrete surrounded reinforcing bar was subjected to the tension–compression–compression triaxial stress state, determining the higher bond strength of the UHPC compared with conventional concrete. When the anchorage length is no longer than two times the diameter of the bar, the slip and bond stress can be assumed to have a uniform distribution, whereas when the anchorage length is less than 7.5 times the diameter of the bar, the slip and bond stress can be assumed to have a linear distribution.