Bond-slip Model Research Articles

Bond-slip model for rebar mounted to high-strength grouting material

The anchorage performance of reinforcement in high-strength grouting materials plays a decisive role in the safety of prefabricated reinforced concrete structures. At present, the design value of anchorage length of reinforcement in grouting materials or concrete in the codes of various countries is conservative, generally greater than 20 times the diameter of reinforcement. Moreover, the anchorage length is the empirical value obtained from the test of connecting the reinforcement with the grouting sleeve and is not based on the bond-slip performance of the reinforcement and the grouting material. Therefore, based on the interface bond-slip performance test of two media, this paper comprehensively considers the influence of reinforcement diameter, strength grade, anchorage length, and high-strength grouting material strength on the ultimate bond strength, gives the calculation formula of anchorage length and establishes a nonlinear three-segment bond-slip constitutive model. The research in this paper shows that the anchorage length between high-strength grouting material and reinforcement to ensure bonding safety is 7.1 d–10.8 d, which is far less than the recommended anchorage length in the specification. It can provide a reference for the design of prefabricated structures based on grout-anchored reinforcement connections.

Bonding properties between 3D printed coarse aggregate concrete and rebar based on interface structural characteristics

The bonding properties between 3D printed concrete and rebar are a critical factor in determining the performance and service life of 3D printed concrete building structures. Due to the difficult elimination of pores formed at the interface between the rebar and concrete during rebar placement, it becomes a key factor affecting the interfacial bonding performance. This work focuses on the structural defect characteristics of the bonding interface between 3D printed natural coarse aggregate concrete (3DPNAC) and ribbed rebar, the bonding properties of 3DPNAC-rebar with different rebar arrangement directions (parallel, vertical, 45°) were investigated through artificial placement of the rebar and compared with those of 3D printed mortar (3DPM) and cast concrete. The results showed that the bonding strength between 3DPNAC and rebar was higher than that of 3DPM, and the distribution characteristics of pore defects and natural coarse aggregate were the primary causes of the structural differences between the bonding interfaces of 3DPNAC and 3DPM with rebar. The partition distribution and geometric configuration of pore defects in the bonding interface area were identified as pivotal factors in the degradation of the bond strength between 3DPNAC and rebar. Based on the structural composition of the 3DPNAC-rebar bond interface, a bond interface-partitioning model was proposed to elucidate the bond-slip damage mechanism. Finally, a bond-slip model of 3DPNAC and rebar was established. This study can provide important guidance for the structural design and application of 3D printed concrete structures with rebar.

Study on the Load Transfer Behaviour and Bond-Slip Model of Fully Grouted Rockbolt

Rockbolts are often subjected to loads during service, and the load transfer behaviour of rockbolts is very important. Therefore, in this study, pullout tests were performed on two kinds of rockbolt systems, with and without defects, and the load transfer behaviour and failure modes were analysed. According to the load transfer process between the rockbolt and cement mortar interface, a bond-slip model considering the yield of the rockbolt was proposed, and the nonlinear behaviour in the softening stage was considered. The test results showed that the evolution of the interface load between the rockbolt and cement mortar in the grouted rockbolt systems without defects underwent four stages of gradual failure, namely, elasticity, yield, softening, and complete slip, and its failure mode involved the rockbolt being pulled out accompanied by splitting cracks and tensile cracks on the concrete surface. The proposed bond-slip models considering the nonyielding and yielding of the rockbolt can accurately reflect the actual load transfer behaviour of a fully grouted rockbolt.

Experimental Study on the Bond Performance between Glass-Fiber-Reinforced Polymer (GFRP) Bars and Concrete

By investigating the bond performance between glass-fiber-reinforced polymer (GFRP) bars and concrete, GFRP bars can be better applied to concrete structures as a building material. This paper considered the effects of three different GFRP bar surface treatments, three bonding lengths, corrosive solution, and immersion time on the bonding strength. The test results indicated that the bond strength decreases with the increase in the diameter and bond length. The bonding between GFRP bars and concrete can be improved by treating the surface of the bars in different ways. Compared with the control group, the bond strength of the specimens in the saline solution decreased by 1.3–21.4%, and the bond strength of the specimens in the alkaline solution decreased by 26.5–38.8%. In the corrosive environment, the bond properties are degraded. A bond strength calculation formula considering the surface treatment method of the GFRP bars was proposed. The prediction formula of the bond strength retention rate between the GFRP bar and concrete in the corrosive environment was established. The formula was validated with the available research data and the calculated values agreed well with the test values. The MBPE model and CMR model are modified to establish the bond-slip model of the GFRP bars and concrete in the corrosive environment. The model curve is close to the test curve. This paper provides a theoretical basis for future research on the bond-slip performance of GFRP bars and concrete.

Study on bonding behavior of FRP grid-ECC composite layer and concrete with quantitative interface treatment

The interface bonding effect can determine the overall mechanical properties of the reinforced components to a large extent. This paper proposed an improved interface treatment method between FRP grid-ECC composite layer and concrete that could quantify the interface roughness, and the effect of this method on the interface bonding behavior was investigated through the double-shear test. Four groups of twelve specimens, including one group without interface treatment and three groups with different interface treatment rates, were tested to reveal their bond-slip relationship. The test results demonstrated that the improved method was effective, with the ability to inhibit interface peeling; moreover, as the interface treatment rate increased, the bonding effect enhanced, and the failure mode gradually transitioned from critical fracture to composite layer fracture. Furthermore, the bond-slip model and the bearing capacity formula for the improved method were established, and the predicted values were well matched to their corresponding test results.

Theoretical analysis and numerical simulation of axial tensile behavior of pipe joints based on bi-linear cohesive bond-slip model

PurposeDue to its inexpensive production costs, low stress concentration and maintenance-friendliness, the adhesive bonded pipe joint is frequently utilized for pipe connection. However, further theoretical analysis is needed to understand the debonding failure mechanism of such bonded pipe joints under axial tension.Design/methodology/approachIn this study, based on the bi-linear cohesive zone model, the integrated closed-form solutions were derived by considering the axial stiffness ratio and failure stage to determine the relative interfacial slip, interfacial shear stress and relationship of tension–displacement in the bonded pipe joint.FindingsAdditionally, solutions for the critical bonded length and the ultimate load capacity were put forth. Besides, the numerical study was conducted to verify the theoretical solutions regarding the load–displacement relationship. The interfacial shear stress distribution at different failure stages was presented to understand the interfacial shear stress transmission and debonding process. The effect of bonded length on the ultimate load and ductility of pipe joints was also discussed.Originality/valueThe findings in this study can give a reference for the design of bonded pipe joints in their actual engineering applications.

Bond–slip behavior of steel and fiber fabric based on experiment and numerical method

The study of bond–slip behavior is important in understanding the implications of fiber fabric-to-steel joints. Most studies have focused on fiber-reinforced polymer panels and fiber fabric, including carbon fiber and basalt fiber, which are also analyzed in the present work. The bond–slip behavior is initially investigated via an experiment. Test specimens are designed to avoid the influence of steel plate. The study reveals how bond length, fiber type, and fiber layer affect bond–slip curves. Following the experiment, a bond–slip model is constructed and validated accordingly. To take the analysis a step further, notable parameters on bond–slip curves are analyzed through parametrical analysis. Then, a stochastic numerical model that considers the randomness of fiber strength, area of fiber sheet, and strength of adhesives, is proposed and used to obtain the probabilistic distribution characteristic of the bond–slip curves.

Early-Age Bond Behavior of Deformed Bars in Concrete Subjected to Bilateral Pressures

In RC structures during construction, the bond behavior of deformed bars in concrete is governed by the age-related concrete strength, the local confining pressure, the bar diameter, and the concrete cover thickness. In this paper, an experimental investigation was performed to quantify the influences of the curing age and the bilateral pressure on the bond behavior of deformed bars in early-age concrete with 204 pull-out specimens for different concrete strengths, bar diameters, and relative concrete cover thicknesses. It was shown that the failure mode was associated greatly with the age-related concrete strength, the concrete cover thickness, and the pressure level, and that the bond strength increased with the pressure level and curing age, whereas the corresponding slip decreased with the curing age. Based on the regression analysis, calculation models were developed to predict the ultimate bond stress and the corresponding slip. A bond–slip model is proposed to describe the bond stress–slip relationship of deformed bars in early-age concrete under bilateral pressures, and the model was verified with the test results.

A RETROFIT SOLUTION FOR UNCODED STEEL RAFTER TO CONCRETE RING BEAM CONNECTIONS

Some building contractors in the Caribbean have been constructing non-coded steel rafter to concrete ring beam connections on low budget residential buildings. These connections may resist failure under normal loading conditions, but critical connections fail under moderate to high loads resulting in partial or full dislodgement of the roof. In this study, the performance of non-coded steel rafter to concrete ring beam designs were analyzed in a finite element program and a retrofit solution for the failed uncoded connections were designed and modeled. Nine versions of the connection were identified and consisted of several variations including mechanically anchoring the rebar to the rafter without welds, using one and two rebars, varying the rebar embedment depth and using 90 degree hooks and straight rebars. A standard, code-compliant, bolted-endplate connection was used as the control for the investigation. The connections were analyzed in “ABAQUS” with a bond slip and damage plasticity model. The maximum load resistances were compared with category 1 hurricane loads for the region. The load capacities of all the connections were found to be lower than the control connection but were still adequate for hurricane category 1 loads, with the exception of the connection in which the rebars were mechanically anchored to the rafter without welds. Connections with welds to the top flange of the rafter were less stiff, experienced larger rafter displacements, inflicted less damage on the concrete ring beam, and required less rebar embedment to prevent pull out failure than the connections to the bottom flange.

A Simplified Method for Predicting Bond-Slip Behaviour of Ribbed Bars and Threaded Rods Glued in Glulam along the Grain.

The bond between a steel reinforcement/rod and glulam plays a crucial role in the resistance and deformation capacity of timbers joints. Existing studies provide different bond-slip models for reinforcements and rods with different anchorage lengths, in which the relationship between local bond stress and global bond behaviour cannot not be established. This study presents a unified analytical method for predicting the bond-slip behaviour of ribbed bars and threaded rods along the grain using a local bond-slip model of reinforcement at the elastic and post-yield stages. In the analytical method, equilibrium, compatibility, and constitutive models for reinforcement and rods are considered. The method is verified using test data of rebars and rods with different anchorage lengths. Comparisons between the experimental and calculated results suggest that the analytical method yields reasonably good predictions of the load-slip relationship and failure mode. Furthermore, the embedment lengths required for yield and the ultimate strengths of the reinforcement and rods along the grain are determined by assuming uniform bond stress distributions over the elastic and post-yield steel segment. The average bond stress over the entire anchorage length is calculated and compared with existing equations. Design recommendations for anchorage lengths are proposed for ribbed bars and threaded rods glued in glulam.

Experimental study of interfacial adhesion performance of prefabricated UHPC-NC diagonal shear groove

The reinforced lining of the tunnel was carried out using a prefabricated composite structure consisting of Ultra-High Performance Concrete (UHPC) and Normal Concrete (NC), utilizing a semi-post-pouring method. The bond performance between UHPC and NC is crucial for enhancing the overall stability and safety of the tunnel. To investigate the influence of interface construction on the bond performance at the UHPC-NC interface, inclined shear tests were conducted with variations in groove density, groove morphology, groove aspect ratio, and interface angle. The results revealed four different failure modes of the grooved specimens, with over 80% exhibiting failure at the interface between UHPC and NC. The average interface bond strength of the grooved specimens was found to be 5.8 times higher than that of the untreated interface group, indicating a significant improvement in the bond performance of the UHPC-NC interface due to the presence of grooves. When the volume loss ratio was below 0.09, the interface bond strength of the UHPC-NC interface increased with an increase in groove density. The interface bond strength of the 60° trapezoidal grooves was 80% higher than that of the right-angle grooves, while the interface bond strength of the 40° trapezoidal grooves was 28% higher than that of the right-angle grooves. Furthermore, the interface bond strength decreased as the angle between the interface and the horizontal plane increased. The precast inclined shear grooves exhibited a bond-slip curve that consisted of an initial slow-rise stage, an elastic rise stage, a yield stage, and a failure descent stage, with some specimens not exhibiting a distinct yield stage. In this study, a bond-slip model for the precast UHPC-NC inclined shear grooves was proposed, and recommendations for bond stiffness were provided.

Pullout behavior of steel fiber embedded into cement matrix under low humidity curing

An experimental was presented in this article to investigate the impact of the low relative humidity (low RH) on the pullout properties of the straight and hooked-end fibers embedded into cement matrices. It was shown that decrease in curing RH results in a reduction in the interfacial carrying capacity and the pullout energy absorption ability, owing to the microstructure of the fiber-matrix ITZ deteriorating as the humidity decreased for all types of fibers. Besides, a novel model was developed to simulate the bond-slip behaviors of the steel fiber-matrix interface under low RHs, and a theoretical method was carried out to estimate the parameters in the model. Furthermore, various analytical models were proposed based on the bond-slip model to simulate the pullout behaviors of the steel fibers embedded in matrix under low RHs, and the validation results revealed that the suggested model is consistent with the experimental data.

Progressive collapse behaviour of advanced precast reinforced concrete joints with headed bars and plastic hinge relocation

This study proposed three types of precast concrete (PC) wet joints, viz., using Headed bars (Type H) to replace hooked bars, placing an Additional bottom bar layer (Type A), or implementing plastic hinge relocation method with X-bent bars (Type X) in the beam-joint region. These detailing features could compensate for negative effects caused by geometric discontinuity at the joint interface and prevent pull-out failure, as observed in conventional PC joints with hooked bars. An experimental investigation based on four interior joints showed that based on the steel content in Type H joint, by increasing respective steel contents of 7% and 8% in Type A and Type X joints, structural resistance to collapse could be enhanced by 34% and 47%, respectively. A fourth specimen of Type A joint incorporated the slab. It was found that although the slab could slightly enhance flexural resistance, it also reduced the joint rotational capacity. Subsequently, component-based joint models (CBM) with a bond-slip model of headed bars were proposed for the three types of PC joints and validated against the test results with satisfactory accuracy. Based on the validated CBMs, parametric studies were conducted for different cases, such as exterior and penultimate joints, under a penultimate column removal scenario. It was found that if the exterior column was too weak, compressive arch action and catenary action could not be effectively triggered, and column failure governed joint behaviour. Hence, to mitigate progressive collapse, the exterior columns and joints must be required to possess a sufficient level of horizontal resistance and stiffness.

Bond assessment between rebars embedded into a parent material using a single-function bond-slip model

The pull-out test is usually used to evaluate the local bond behaviour between a rebar such as a ribbed steel rebar or a Fiber Reinforced Polymer (FRP) and a parent material, like concrete or timber. Although some codes recommend using a piecewise bond-slip model for ribbed or round steel rebars embedded in concrete, there is no globally accepted bond-slip model for FRP composites. Consequently, this piecewise bond-slip model is usually adapted for FRP composites embedded in a parent material (substrate). The present work therefore aims to propose a novel single-function bond-slip model that may be calibrated and used to model the pull-out test and the detachment process of an embedded rebar from a parent material. The model requires the calibration of three parameters that may vary according to the type of rebar and its parent material. Since the governing equation of the detachment between the rebar and the parent material during a pull-out test has no known analytical solution, the Finite Difference Method (FDM) was applied to find the interfacial slips throughout the embedded length. The results were compared and validated with the experimental pull-out tests of ribbed steel rebars embedded into a concrete block as well as with the numerical results obtained from the use of the Finite Element Method (FEM). To cover a broader range of materials and show the versatility of the novel bond-slip model, the results were also compared with other experimental data available in the literature. The results showed a very high precision of the new bond-slip model when applied to several pull-out tests especially when ribbed steel rebars-to-concrete and FRP-to-concrete interfaces or FRP-to-timber interfaces were used.

Hygrothermal effect on interfacial properties of CFRP-steel joint modified by nanosilica

The interface between the carbon fiber reinforced polymer (CFRP) reinforcement system and steel substrates may deteriorate in service environments. This study is concerned with the effect of moisture and temperature conditions on the interfacial performance of CFRP-steel joints using neat/modified adhesive. Tensile and shear tests were conducted on both unmodified adhesive specimens and those modified with nanosilica to assess the impact of nanoparticles. Water immersion tests were carried out on adhesive specimens with different nanosilica contents to determine the water absorption law of the adhesives at different immersion temperatures. The interfacial properties of CFRP-steel bonded joints were tested before and after hygrothermal aging. The results show that nanosilica significantly influences the mechanical properties of the adhesive, as well as CFRP-steel joints. In dry conditions, tensile and shear strengths, Young’s modulus and the elongation of adhesive are improved by increasing the nanosilica content up to about 1.4 wt%. A higher content of nanosilica reduces adhesive strength and modulus, while the elongation increases continuously with nanoparticles increasing to 7 wt%. The water absorption of the adhesive is significantly influenced by the content of nanosilica. More nanosilica particles lead to slower diffusion in adhesion and smaller saturated water absorption. A high immersion temperature speeds up the moisture diffusion, resulting in a larger moisture content and a more severe degradation in adhesive performance with the same immersion duration. Hygrothermal aging can be delayed by the addition of nanosilica with low content. The interfacial properties of CFRP-steel joints, including interfacial shear strength, load capacity and plasticity, are weakened by hygrothermal aging. Changing the main failure mode from cohesive failure to interfacial debonding may occur in CFRP-steel joints due to aging. The more severe deterioration is caused by longer immersion or a higher immersion temperature. However, the addition of nanosilica can enhance the durability of the aged joints in the long run by improving the water resistance, although peak shear stress decreases when the nanosilica content exceeds 1.4 wt%. The trilinear bond-slip model of reinforced adhesive joints may be reduced to a bilinear model by hygrothermal aging. The incorporation of nanosilica helps to mitigate the reduction in fracture energy due to water immersion at normal and high temperatures.

The shear strength of existing non-seismic RC beam-column joints strengthened with CFRP Sheets: Numerical and analytical study

A key part of RC structure seismic performance is the effective distribution of earthquake forces across all resistance elements through reinforced concrete (RC) beam-column (B-C) joints. By virtue of their ease of implementation and convenient material properties, Carbon-Fiber-Reinforced Polymers (CFRP) are highly utilized for strengthening existing structures with inadequate reinforcement or insufficient confinement. Previous experimental research revealed that debonding failure widely occurs on CFRP shear-strengthened B-C joints. The experimental research as well showed the value of column axial load makes a great contribution to such joint’s failure mode. Using CFRP U-jacketing to strengthen non-seismically B-C joints, this article presents a non-linear, two-dimensional FE model for investigating shear behavior. The developed FE model considered the adhesive layer between CFRP sheets and concrete to capture the debonding and a bond-slip model was implemented between concrete-to-CFRP sheets using connector elements. The FE results were verified versus experimental works from literature to prove the proposed FE model's accuracy with appreciate to load-deformation relation and failure modes. Depending on the verified FE model, a parametric study on shear-strengthened RC B-C joints with CFRP U-jacketing with free and fixed ends was performed below monotonic loading. In the existing study, several parameters, including column-to-beam flexural strength ratio (over strength ratio), concrete strength, and value of column axial load, were investigated on the structure's strength and ductility. Using the developed strut-and-tie model (STM), new design equations were proposed to calculate strengthened RC B-C joint's shear strength using CFRP. The proposed equations incorporate the interfacial bond among concrete and CFRP effect, as well CFRP sheet end boundary (free or fixed). The developed design equation’s ability to estimate shear strengths of strengthened B-C joints with CFRP was verified through experimental works and FE results. It was evident from verification results that the produced design equations were compatible with experimental and FE model results.

Experimental Study of a Bond-Slip Model of CFRP Bonding Adhesive after Exposure to High Temperature

Experimental Study of a Bond-Slip Model of CFRP Bonding Adhesive after Exposure to High Temperature

Bonding Properties between Fly Ash/Slag-Based Engineering Geopolymer Composites and Concrete.

Concrete infrastructure repair remains a formidable challenge. The application of engineering geopolymer composites (EGCs) as a repair material in the field of rapid structural repair can ensure the safety of structural facilities and prolong their service life. However, the interfacial bonding performance of existing concrete with EGCs is still unclear. The purpose of this paper is to explore a kind of EGC with good mechanical properties, and to evaluate the bonding performance of EGCs with existing concrete using a tensile bonding test and single shear bonding test. At the same time, X-ray diffraction (XRD) and Scanning electron microscopy (SEM) were adopted to study the microstructure. The results showed that the bond strength increased with the increase in interface roughness. For polyvinyl alcohol (PVA)-fiber-reinforced EGCs, the bond strength increased with the increase in FA content (0-40%). However, with the change of FA content (20-60%), the bond strength of polyethylene (PE) fiber-reinforced EGCs have little change. The bond strength of PVA-fiber-reinforced EGCs increased with the increase in water-binder ratio (0.30-0.34), while that of PE-fiber-reinforced EGCs decreased. The bond-slip model of EGCs with existing concrete was established based on the test results. XRD studies showed that when the FA content was 20-40%, the content of C-S-H gels was high and the reaction was sufficient. SEM studies showed that when the FA content was 20%, the PE fiber-matrix bonding was weakened to a certain extent, so the ductility of EGC was improved. Besides, with the increase in the water-binder ratio (0.30-0.34), the reaction products of the PE-fiber-reinforced EGC matrix gradually decreased.

Experimental and numerical evaluations of the bond behaviour between ribbed steel rebars and concrete

The study of interfacial behaviour between ribbed steel rebars and concrete is a subject that has been widely studied. However, the definition of the bond stress distribution throughout the embedded length of the steel rebar is still controversial due to the difficulty of experimentally obtaining such distribution for a fixed load magnitude. It is also undeniable its relevancy for the better understanding and model reinforced concrete (RC) structures. So, the definition of the local behaviour between the ribbed steel rebar and concrete is critical to correctly simulate the adherence between both materials. In this matter, the local bond-slip models recommended in codes seem to satisfy some researchers while others suggest prudence in using them. Therefore, only choosing the correct bond-slip relationship may lead to exact interpretations and conclusions of the structural behaviour of a concrete structure but with the existing different bond-slip types, researchers can be misled inadvertently. This work aims to clarify some of these aspects by numerically simulating several pull-out tests under different conditions and checking their influence (or not) on real-scale specimens. After the validation of the numerical model through a proposed new bond-slip relationship, other parameters were studied also. Although the type of the bond-slip relationship influences the detachment of the steel rebar from the concrete, the yielding of the former material was found to be the main parameter that masks the differences in the behaviour of real-scale RC structures when different types of bond-slip relationships were considered in the numerical simulations.

Bond-slip model of anchor-soil interface and analysis of bearing capacity of anchor in frozen soil

It has been recognized that temperature and moisture have obvious influence on the bonding characteristics of anchor-frozen soil interface. Following the principle and method used to explore the interface performance of microelement anchor-soil, this research starts by performing the pullout tests of anchor-soil under different temperature and moisture content conditions. Then, we analyze the characteristics of interface bond stress-displacement and compare the effects of temperature and moisture content on interface mechanical properties. The test results show that the failure mode of anchor changes slightly when soil temperature and moisture content vary, wherein the shear failure which shows brittle characteristics at the anchor-frozen soil interface is dominant. Additionally, we have found that the effect of temperature on the peak bond stress is more significant than moisture. Under different soil temperatures and moisture content, the shape of bond stress-displacement curve of anchor-frozen soil interface is similar. Furthermore, the bond stress-displacement relationship of anchor-frozen soil interface can be fitted by a composite function which is composed of exponential and ideal elastic-plastic model function. Thus, this research recommends to propose a bond-slip model of anchor-frozen soil interface considering temperature effect. Combined with the load transfer method, the force and deformation equation of anchor in frozen soil is derived. Through example analysis, it is discovered that the pullout bearing capacity of anchor increases with the decrease of soil temperature. Moreover, the initial shear stiffness of anchor-soil interface is positively related to the bearing capacity of anchor. At the end, the influence of interfacial residual strength on the bearing capacity of anchor in the later stage of pullout is superior to that in the earlier stage.