Bond-slip Performance Research Articles

Advanced Prediction for Cyclic Bending Behavior of RC Columns Based on the Idealization of Reinforcement of Bond Properties

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.

Bond-Slip Performances of Ultra-High Performance Concrete Steel Tube Columns Made of a Large-Diameter Steel Tube with Internally Welded Steel Bars.

Large-diameter concrete-filled steel tube (CFST) members are being increasingly utilised owing to their ability to carry larger loads and resist bending. Upon incorporating ultra-high-performance concrete (UHPC) into steel tubes, the resulting composite structures are lighter in weight and much stronger than conventional CFSTs. The interfacial bond between the steel tube and UHPC is crucial for the two materials to effectively work together. This study aimed to investigate the bond-slip performance of large-diameter UHPC steel tube columns and the effect of internally welded steel bars in steel tubes on the interfacial bond-slip performance between the steel tubes and UHPC. Five large-diameter UHPC-filled steel tube columns (UHPC-FSTCs) were fabricated. The interiors of the steel tubes were welded to steel rings, spiral bars, and other structures and filled with UHPC. The effects of different construction measures on the interfacial bond-slip performance of UHPC-FSTCs were analysed through push-out tests, and a method for calculating the ultimate shear bearing capacities of the interfaces between steel tubes containing welded steel bars and UHPC was proposed. The force damage to UHPC-FSTCs was simulated by establishing a finite element model using ABAQUS. The results indicate that the use of welded steel bars in steel tubes can considerably improve the bond strength and energy dissipation capacity of the UHPC-FSTC interface. R2 exhibited the most effective constructional measures, resulting in a significant increase in ultimate shear bearing capacity by a factor of approximately 50 and energy dissipation capacity by a factor of approximately 30 compared to R0 without any constructional measures. The load-slip curve and ultimate bond strength obtained from finite element analysis and the interface ultimate shear bearing capacities of the UHPC-FSTCs obtained using the calculation method agreed well with the test results. Our results provide a reference for future research on the mechanical properties of UHPC-FSTCs and their engineering applications.

Bond-slip performance of seawater sea sand concrete filled filament wound FRP tubes under cyclic and static loads

Adequate bond strength of concrete filled tubes is required to ensure full composite action and prevent premature bond failure before ultimate bending capacity is reached. This study investigates the bond strength and bond slip mechanisms of FRP tubes filled with seawater sea sand concrete (SWSSC) under static and cyclic axial loads using a push-out test. Glass and carbon fibre reinforced polymer (FRP) and two different diameters (100 mm and 165 mm) were tested to investigate the effect of changing parameters on the bond strength. Each group of specimen was tested under static load (SL) and various different cyclic loading (CL) regimes. An ANSYS FE model was created to simulate a static pushout test for FRP SWSSC composites under varying parameters to quantify the induced tube and confinement stress. Confinement and accumulated damage were found to be the two main factors determining the change in bond strength between cyclic and static load conditions. The high active confinement of the smaller diameter GFRP tubes resulted in a slight increase in bond strength for most samples under CL. The larger diameter CFRP tubes generally exhibited a slight drop in bond strength under CL due to the more pronounced effects of accumulated interface damage.

Experimental Study on the Bond Performance of Steel–Basalt Fiber Composite Bars in Concrete

Steel–basalt fiber composite bars (SBFCBs) exhibit excellent strength, elastic modulus, toughness, corrosion resistance, and low cost. Understanding the bond performance between SBFCBs and concrete is important for evaluating the mechanical behavior of SBFCB-reinforced concrete structures. In this study, the bond–slip performance of SBFCB in concrete was experimentally assessed via pullout and beam bond tests. The influence of various factors on the bond performance was discussed, and the bond mechanism between SBFCB and concrete was analyzed. The results indicate that reducing the thread pitch ratio in the SBFCB can reduce slippage at the postpeak bonding stress–slip curve. The bond strength of the SBFCB was significantly improved by sandblasting. Longer bond lengths correspond to smaller average bond strengths in SBFCB. The load corresponding to the maximum bond strength of a specimen with a bond length of 10d was determined as the ultimate load value for the SBFCB. An increase in the SBFCB diameter had a negative impact on the bond strength. Moreover, an increase in the concrete cover thickness was conducive to improving the bond strength; if the thickness of the concrete cover was sufficiently increased, failure occurred owing to SBFCB tension rather than bonding. Based on the test results and the existing bond–slip model, a simple bond–slip constitutive model of the SBFCB embedded in concrete was proposed to simulate the pullout process of the SBFCB. Subsequently, the established bond–slip model can be used to analyze the mechanical performance of SBFCB-reinforced concrete structures.

Study on the bond properties between steel bar and fiber reinforced concrete after high temperatures

The bond-slip performance between steel bar and normal concrete (NC) and steel fiber reinforced concrete (SFRC) after high temperature were investigated in this paper. The central pull-out test was performed on 40 specimens with specific parameters including the fraction of steel fiber by volume (Vf = 0 %, 0.5 %, 1.0 %, and 1.5 %) and temperature (T = 20 °C, 200 °C, 400 °C, 600 °C, and 800 °C). The results demonstrate that the bond strength increased with the increase of Vf. The increase in bond strength of SFRC specimens compared to NC specimens is more than 66.9 % after 600 °C. As the temperature increases, the bond strength decreases. The bond strength loss after 600 °C compared to room temperature was more than 46.6 % for SFRC and NC specimens. The synergistic effect of steel fibers and aggregates formed a rigid skeleton for bridging cracks, improving the bond strength between steel bar and SFRC. The cumulative initial damage (interface and thermal cracks) generated by temperature reduced the bond strength. An empirical formula for predicting the bond strength was proposed. The bond stiffness decreased with the increase of temperature and increased with the increase of Vf. SFRC specimens with Vf = 1.5 % exhibited insignificant changes in bond toughness after high temperature compared to those with Vf = 1.0 %. The steel fibers significantly improved the bond toughness of SFRC specimens at room temperature. Empirical formulas for predicting bond stiffness and bond toughness were proposed. A prediction model for the bond-slip relationship between steel bar and SFRC after high temperature considering Vf and temperature was proposed. It is found that the established model of the bond-slip relationship agreed well with the experimental results.

A comparative study on strength, bond-slip performance and microstructure of geopolymer/ordinary recycled brick aggregate concrete

Geopolymer recycled brick aggregate concrete (GRBC), which is a new kind of sustainable eco-friendly material, has the potential to be widely used in engineering applications. However, little research has been done on its basic mechanical properties and microstructures. Accordingly, a series of tests such as uniaxial compressive test, splitting tensile test and pull-out test were carried out in this paper. Taking recycled brick aggregate (RBA) replacement ratio (0%, 25%, 50%, 75% and 100%) as the main variable, 60 cubes and 40 pull-out specimens with steel bars were fabricated and tested. The compressive strength, tensile strength and bond-slip performance of GRBC were investigated and compared with the ordinary recycled brick aggregate concrete (ORBC). The analysis using scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) was conducted to study the microstructure characteristics of GRBC and ORBC. The results show that the compressive strength, splitting tensile strength and bond strength between concrete and steel bar decrease with the increase of RBA replacement ratio, and the decrease rate of GRBC is faster than that of ORBC. For GRBC, when RBA replacement ratio varies from 0% to 50% and 100%, the compressive strengths decrease by 32.25% and 57.49%, respectively; the splitting tensile strengths decrease by 33.11% and 53.20%, respectively; while the bond strengths decrease by 19.91%–28.11% and 46.32%–49.63%, respectively, depending on different bond length. ORBC pull-out specimen is more prone to splitting failure than GRBC specimen. The aluminosilicate gel formed by the hydration of geopolymer matrix has a denser structure than the gel of ordinary concrete matrix. Incorporating the RBA results in the failure order change in weakness of GRBC and ORBC, and the failure of interfacial transition zone (ITZ) between matrix and aggregate is transformed into the failure of RBA.

Bond-slip behavior between high-strength steel tube and Ultra-high Performance Concrete

To satisfy the requirement of super high-rise buildings and large-span structures, an Ultra-high Performance Concrete Filled High-Strength Steel Tube (UHPC-FHSST) is presented. The effects of concrete strength, length-to-diameter ratio, and diameter-to-thickness ratio on interfacial bond-slip performance are investigated through push-out tests of 12 UHPC-FHSST specimens. The bond-slip process of the UHPC-FHSST is revealed and its strain evolution is analyzed. The research results show that the bond strength between the high-strength steel tube (HSST) and the UHPC core increases with the decrease of the diameter-to-thickness ratio and the length-to-diameter ratio, and the increase of concrete strength will lead to the decrease of bond strength. The longitudinal strain increases with the growth of the axial load. Based on the experimental results, the shear transfer length is determined and computed, and the mathematical model to reflect the bond-slip behavior of UHPC-FHSST is developed, which can provide valuable instruction for the engineering application of UHPC-FHSST.

Enhancement of the bond behaviour between sand coated GFRP bar and normal concrete using innovative composite anchor heads

Anchor heads could efficiently address the bond weakness between Fibre-Reinforced Polymer bars and concrete. This experimental study enhanced the bond behaviour between GFRP bars and concrete using three innovative anchorage systems made from glass fibre cloth and epoxy resin. A direct pullout test was used to study the bond-slip performance between the bar and the concrete. Test variables were GFRP bar diameter (3 diameters), concrete compressive strength (20.4 and 40.2 MPa), and anchor system (three different types). Based on the test results, in low-strength concrete (i.e. 20.4 MPa) samples, the anchor system efficiency was not promising, and the failure occurred between the concrete and anchors. However, for higher strength concrete (i.e. 40.2 MPa) samples, the ultimate developed tensile load increased between 14 and 68% for different bar sizes and anchorage systems compared to the unanchored control specimens.

An experimental behavior of the bond-slip performance of hybrid fiber concrete-filled steel tube columns with shear studs

An experimental behavior of the bond-slip performance of hybrid fiber concrete-filled steel tube columns with shear studs

Bond behavior of coral aggregate concrete and corroded Cr alloy steel bar

In the extremely hot and humid marine environment in the South China Sea, the application of Cr alloy steel bars and coral aggregate concrete (CAC) overcomes the problems of low durability of ordinary reinforced concrete structures and lack of construction materials, accelerates the construction of reefs. The bond-slip performance between CAC and Cr alloy steel bars is the basis of their cooperative work. Considering the complex composition of the microstructure and the structure of the interface of CAC, and the excellent corrosion resistance of Cr alloy steel bars, the bond properties between Cr alloy steel bars and CAC are different from those of ordinary reinforced concrete. Therefore, in this study, the influence of the corrosion ratio of the Cr alloy steel bar was considered, the corrosion of steel bars was accelerated via electricity, and a pull test was conducted to study the bond-slip constitutive relationship between the corroded Cr alloy steel bar and CAC. Through experimental research and theoretical analysis, the distribution law of the bond stress and slip value between the Cr alloy steel bar and CAC along the anchorage length was obtained under different corrosion ratios. The transfer mechanism of the bond stress and the difference in the bond anchorage position between the Cr alloy steel bar and CAC before and after corrosion were analyzed. A bond anchorage position function model reflecting the actual bond distribution law under different corrosion ratios was proposed and the bond-slip constitutive model was established, providing a reference for island construction in the South China Sea.

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.

Experimental study on interface performance between implantable cement-based sensor and matrix concrete

Design and manufacturing the implantable cement-based sensor have attracted more and more attentions in the field of the concrete infrastructure health monitoring due to the mechanical and deformational integrity feature between the cement-based sensor and the infrastructure. The good coupling through the interface between the implantable cement-based sensor and the matrix concrete is the key to maintain such integrity to achieve the long-term and accurate health monitoring. A new interface double shear test device is designed and manufactured in this study to investigate the interface behavior between the implantable cement-based sensor and the matrix concrete. The measurement on the interface bond-slip performance is conducted considering the factors such as the water-to-cement ratio of the matrix concrete, whether the sensor surface is coated/grooved or not, the coating thickness, the grooving depth. The experimental results of the load-slip curve, the shear strength, and the failure mode are analyzed to reveal the shear bonding mechanism and to establish the interface bond-slip model for the implantable cement-based sensor and the matrix concrete. The findings of this study can benefit the interface design and manufacturing of the implantable cement-based sensors to achieve good cooperative working relationship with the surrounding structures for long-term and accurate monitoring the infrastructures.

Study of bond-slip performance and ultimate bearing capacity calculation under static and reciprocating action of folded perfobond shear keys

The PBL (Perfobond Leiste) shear key has advantages such as high load capacity and high restraint capacity. However, at the same time, there are also problems such as insufficient deformation capacity and low stiffness along the weak axis direction. In addition, shear key performance degradation, ductility, and other problems are not yet clear under the reciprocal seismic action. To this end, a folded perfobond shear key is proposed in this paper to solve the problems of insufficient deformation capacity and uneven stiffness distribution of the traditional PBL shear key. At the same time, numerical analysis is carried out to investigate the seismic performance of the shear key under earthquakes, such as stiffness degradation, ductility, and energy dissipation. Through the push-out test, it is found that the steel plate outside the shear key deforms, showing a certain semi-rigid characteristic; concrete forms a trapezoidal constraint area centered on shear keys, and the constraint effect is significantly improved compared with the point constraint of studs. On the whole, under the condition of a similar shear section, the bearing capacity of the shear key is 1.5 times that of the stud. The ductility coefficient is above 3.0, showing good deformation ability. Through parameter analysis, it is found that the bearing capacity of shear keys increases with the increase of web width-thickness ratio, but the deformation capacity degenerates. The opening rate mainly affects the embedded effect of shear keys and concrete. Based on the fitting analysis, the variation laws of web width influence coefficient γB, web height influence coefficient γH, and embedded effect influence coefficient γD are obtained, and the calculation formula of shear key bearing capacity is proposed. Finally, based on the push-out test, the hysteretic behavior of the shear key is studied. It is found that the load-displacement hysteretic curve of the shear key is full, the ductility coefficient is 4.2, and the equivalent viscous damping coefficient is 0.27, which shows good seismic capacity. In summary, the new shear key realizes the good unity of bearing capacity and deformation and has high engineering application value.

Performance Evaluation of Reinforced Concrete Columns under Simultaneously Combined Fire and Cyclic Loads

Reinforced concrete (RC) structures could suffer from the combined action of fires, earthquakes, and other loads during their life cycle; more importantly, coupled disasters lead to further deterioration and damage to structural performance. This paper investigated the multiple performances and distinguished the safe working conditions of the RC column subjected to simultaneously combined fire and cyclic loads. The numerical model considered the degradation of the mechanical properties of steel and concrete and the bond-slip performance between steel and concrete at high temperatures. The results show that the performance of RC columns with different section sizes, longitudinal reinforcement ratios, cover thicknesses, axial load ratios, and cyclic loads differs greatly under simultaneously combined fire-cyclic loads. In specific, when the cyclic load application time is less than 2 h, the cyclic load has little effect on the response of the RC column. According to the different characteristics of RC columns when subjected to combined fire-cyclic loads, the firing process of RC columns is divided into four stages. To avoid the excessive performance degradation of RC columns, the minimum designed fire resistance time of RC columns is recommended to be 2.5 times the fire resistance time of the RC column under static loads.

Analytical model for the bonding performance between HSSWM-ECC and concrete

Due to the excellent capacities on crack-width controlling and deformation, the high strength steel wire mesh reinforced engineering cementitious composites (HSSWM-ECC) have been used as an ideal material in structure strengthening engineering. However, limited literatures are available on the interfacial bond-slip model and the interfacial load carrying capacity between HSSWM-ECC and concrete. In this study, the modified hinged beam tests were carried out on nine groups of typical specimens to investigate the bonding performance at interface between HSSWM-ECC and concrete. A bond-slip model for the interface was proposed to predict the bond-slip performance between HSSWM-ECC and concrete, which was well agreed with the experimental result. Moreover, the micro-segment analysis method was developed considering the stress transfer at interface, accurately describing the mechanical characteristic of the interface. Finally, the analytical models for estimating the effective anchorage length and the interfacial load carrying capacity of the interface were established.

Bond-slip performance of GFRP and steel reinforced beams under wet-dry and freeze-thaw cycles: The effect of concrete type

In this experimental study, the bond-slip performance between glass fibre reinforced polymer (GFRP) bars and three different concrete types, namely normal, self-compacting, and fibre-reinforced concrete under freeze-thaw and wet-dry cycles have been studied. Steel reinforced concrete beams were also tested for comparison purposes. In total, 54GFRP and steel reinforced concrete beams were prepared, conditioned, and tested using RILEM recommendations. 18 specimens were subjected to 200 wet-dry cycles between ambient and 60 ˚C and another 18 specimens were subjected to 200 freeze-thaw cycles between -18 ˚C and 4 ˚C for 150 days. The results showed the bond strength reductions of 12, 3 and 9 % between steel bars and beam specimens cast with normal, self-compacting, and fibre-reinforced concrete, respectively after exposure to 200 wet-dry cycles. However, the corresponding values for GFRP reinforced concrete beams under the same conditioning environment were 1, 1, and 16 % respectively. With respect to freeze-thaw cycles, bond strength of steel reinforced normal, self-compacting, and fibre-reinforced concretes experienced only about 5, 2, and 4 % reductions, respectively, after 200 cycles. The corresponding reduction values for GFRP reinforced beams were insignificant and about 2, 1, and 4%. Steel reinforced beams fail due to the concrete crushing, while GFRP reinforced beams fail due to GFRP surface peeling-off. Generally, GFRP reinforced beams experienced fewer bond strength reductions compared to steel reinforced beams. Also, regardless of concrete type, due to their corrosion vulnerability, steel reinforced beams experienced greater stiffness reductions than that of GFRP reinforced beams when subjected to seawater wet-dry cycles. However, such a difference was not drastic.

Bond-slip behaviors of composite steel-reinforced high strength lightweight aggregate concrete columns with innovative X-shaped steel sections

This paper provides an insight into the bond-slip performance of the new type of steel-reinforced high strength lightweight aggregate concrete (SRLWAC) column with innovative X-shaped steel sections through experimental and theoretical studies. Three SRLWAC specimens were tested under push-out force; the variables are the confinement by stirrups (ρsv) and shear connectors (SCs). Force-slip curves, force axial and horizontal deformations, failure modes, and crack patterns of the specimens were investigated; the force transfer, bond-stress, bond shear transmission length, and strains were studied. Comparisons between the bond strength of the studied specimens and ordinary types column specimens from 13 previous studies showed a superior bond capacity for the new type specimens. Five related models of bond capacity were discussed, and the utility of the models was put forward. A simplified load-slip model was proposed and verified. The most feasible model and the simplified model were used in the parametric study. The results showed that the material strengths and geometric configurations parameters affect the bond strength capacity. The confinement and SCs have effects on the bond and failure mode. The natural bond-stress combined with SCs produced smaller bond strength than that from both natural bonds and using higher ρsv. Recommendations for future works are developed.

Bond-Slip Performance between High-Strength Steel Wire Rope Meshes and Engineered Cementitious Composites

Engineered cementitious composites (ECC) are distinguished by ultrahigh ductility and multiple cracking. High-strength stainless steel wire rope (HSSSWR) meshes have been successfully applied to strengthening existing structures. Taking advantage of both ECC and HSSSWR meshes, HSSSWR mesh–reinforced ECC promises to be an innovative strengthening material for significantly improving overall performance of existing structures. In order to capture the bond performance between HSSSWR meshes and ECC, direct pull-out tests on HSSSWR meshes embedded in ECC were performed considering the effects of spacing of transverse wire ropes, bond length, and nominal diameter of HSSSWR. The influence laws of the considered factors on the bond behavior between HSSSWR meshes and ECC were investigated. The failure characteristics and bond-slip relationship between HSSSWR meshes and ECC were revealed through analyses of experimental results. A bond-slip model was proposed to predict the bond-slip behavior of HSSSWR meshes in ECC, which was verified to be acceptable by comparing it with test results.

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.

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.