Bond-slip Relationship Research Articles

Comparative bond-slip responses of CFRP tubes in seawater sea sand concrete after epoxy mortar modification

The initial bond stress between carbon fiber reinforced polymer (CFRP) and concrete is low, and installing shear connectors on FRP profiles disrupts the integrity of the material. As a result, sand coating is the preferred method for interface treatment. Epoxy mortar, known for its high bond strength and strong permeability, is used to enhance the roughness of the interface. Push-out tests were carried out on interfaces between seawater sea sand concrete (SWSSC) and CFRP coated with epoxy mortar. The results demonstrated that the epoxy mortar bonded well with SWSSC, with failure primarily occurring at the epoxy mortar-CFRP interface. A few specimens exhibited concrete cohesive failure or interlayer fiber cracking. The application of epoxy mortar limited the extrusion behaviour of the core concrete, as evidenced by the reduced critical slip value at the loading end and the low tensile strain measured on the FRP tube. Bond-slip curves were more likely to show peak values for specimens with rougher interfaces or shorter lengths along the push-out direction. For specimens with CRFP tube diameters of 75mm and 110mm, epoxy mortar coating increased the critical bond stresses at the SWSSC-CFRP interface by more than 43.4% and 67.1%, respectively. The epoxy mortar provided mechanical interlocking, reducing the loss of bond stress caused by insufficient confinement or concrete self-shrinkage from 61.4% to 19.6%. This indicates that the epoxy mortar is an effective material for improving the initial FRP interface. In this study, existing bond-slip relationship models were reviewed, suitable parameters for epoxy mortar-modified interfaces were proposed, and the general applicability of the model was verified.

Out-of-plane shear behavior of BFRP-reinforced geopolymer concrete one-way slabs: Experimental and numerical investigations

Sustainability and durability in construction are vital considerations that involve using environmentally friendly materials and implementing efficient design and construction techniques to minimize the environmental impact. This research study investigated the structural behavior of one-way solid slabs incorporating basalt fiber-reinforced polymer (BFRP) reinforcement and geopolymer concrete to develop an environmentally sustainable and durable structural member. Six full-scale BFRP-reinforced geopolymer concrete one-way slab specimens were prepared and subjected to four-point loading tests to assess their out-of-plane shear performances. The considered experimental parameters were compressive strength of concrete (i.e., 30, 40 and 50 MPa) and longitudinal tensile reinforcement ratios (i.e., 1.20% and 2.18%). The structural performance of the slabs was carefully investigated in terms of crack patterns, failure modes, load-deflection relationships and load-strain relationships. The obtained shear resistances from tests were compared with predicted results from the Codes of Practice and design guidelines. A two-dimensional (2D) finite element (FE) analysis was conducted, considering the bond-slip relationship between BFRP rebar and geopolymer concrete. It was found that all tested specimens were governed by shear failure and had similar shear resistance for the chosen values of considered parameters. The JSCE shear design method provided the closest prediction of shear resistance of BFRP-reinforced geopolymer concrete one-way slab. The developed FE models predicted the out-of-plane shear performance with reasonable accuracy and revealed that the slip distribution of the BFRP rebar presents a sawtooth shape owing to concrete cracking.

A Novel Analytical Bond Model for ETS FRP Bars in Shear Rehabilitation of Concrete Members

In this article, an unprecedented fracture mechanics-based bond model for embedded through-section (ETS) fibre-reinforced polymer (FRP) bars installed in concrete blocks is proposed. Various methods have emerged for rehabilitating substandard and deteriorated concrete structures. The ETS FRP bar method provides numerous advantages over existing shear strengthening methods, but no reliable and comprehensive bond–slip model exist to predict the method’s bond behaviour. In this study, a state-of-the-art analytical bond model is derived for determining the debonding force of the ETS FRP bars from concrete blocks using a newly proposed bi-linear bond–slip relationship that is expressed as a function of the maximum shear stress and its corresponding slip. The accuracy of the results predicted by the proposed model is verified with the existing push–pull data of ETS FRP/concrete joints in the literature. The results show that the newly proposed model can be used for both carbon FRP (CFRP) and glass FRP (GFRP) ETS bars with an average Pexp/Pmax ratio of 1.04 with superior statistical accuracy measures when compared to the existing bond models’ predictions.

Investigation on bond behavior of GFRP bar embedded in ultra-high performance polyoxymethylene fiber reinforced concrete

The combination of glass fiber reinforced polymer (GFRP) bars and polyoxymethylene (POM) fiber reinforced ultra-high performance concrete (UHPC) can create a structural system with excellent service performance and exceptional durability. Bond is a critical factor affecting the service performance of structures constructed using GFRP bars and POM fiber reinforced UHPC. Therefore, this paper investigates the bond behavior between GFRP bar and POM fiber reinforced UHPC by using a direct pull-out test. The test variables were reinforcement type, volume fraction of POM fiber, embedment length, diameter of reinforcement, thickness of concrete cover, and compressive strength of concrete. The effects of these test variables on the failure mode, bond stress-slip curve and bond strength of GFRP bar with POM fiber reinforced UHPC were discussed. The test results revealed that the volume fraction of POM fibers and the reinforcement diameter have barely effect on the bond strength. The bond strength initially increases with increasing concrete cover thickness, and then plateaus after the concrete cover thickness reaches 3.35 times the reinforcement diameter. Furthermore, a predictive model for bond strength of GFRP reinforced UHPC specimens was proposed and validated using test data from other literature. A general bond-slip constitutive model was established to accurately describe the bond-slip relationship of GFRP bar and UHPC.

Bond performance and damage assessment of self-sensing steel–fiber composite bar with geopolymer concrete

This study employed a novel steel–fiber composite bar (SFCB) enhanced with Distributed Optical Fiber Sensors (DOFS) technology to reveal the local bonding and damage mechanisms between composite reinforcement and seawater sea sand geopolymer concrete. By embedding DOFS within the steel core of the SFCB reinforcement, the local bond stress between the reinforcement and geopolymer concrete was monitored. The continuous measurement provided by DOFS revealed a non-uniform strain distribution along the length of the SFCB reinforcement and an uneven distribution of bond stress within the bonded section. Based on test results, a modified bond–slip model was utilized to predict the bond–slip relationship between the SFCB reinforcement and the geopolymer concrete, taking into account the influence of surface treatment on the descending branch of the bond–slip curve. Additionally, a damage model was employed to evaluate the extent of damage at the bond interface between the SFCB reinforcement and the geopolymer concrete under different load levels. Finally, the modified bond–slip model was also used to propose the anchorage length for SFCB reinforcements, which was compared with ACI, CSA, and JSCE codes.

Pullout behavior of recycled macro fibers embedded in ultra-high performance seawater sea-sand concrete

Recently, an eco-friendly ultra-high performance seawater sea-sand concrete (UHPSSC) has been developed using the recycled macro fiber (REF) processed from waste wind turbines, which is more suitable in remote islands and can address the corrosion issue of concrete structures with steel reinforcements. The interface bond of the UHPSSC/macro fiber is lack of investigation and a significant factor influencing the tensile characteristics of macro fiber reinforced UHPSSC. In the present study, the pullout test of the single macro fiber was conducted to investigate the bond behavior of such interface. The test variables included the macro fiber width (4, 6, and 8 mm), the embedded length (5, 10, and 15 mm), and the type of matrix. Then, the local bond-slip relationship at the fiber/UHPSSC interface was obtained by finite element analysis (FEA) to provide a more precise display of interface bond mechanisms. The results revealed that the bond of UHPSSC/macro fiber was stronger with increased fiber embedded length and width due to the greater frictional interactions and better overall integrity of fibers. Additionally, the FEA method proposed here to obtain the local bond-slip relationship was reliable and effective. This study could serve as a basis for further research on the tensile properties of UHPSSC reinforced with macro fibers.

Experimental and analytical investigations on bond–slip behavior of steel reinforcement inUHPFRCconsidering yielding

AbstractThe bond behavior between ultra‐high‐performance fibre‐reinforced concrete (UHPFRC) and steel rebars plays an important role in the load‐bearing capacity and serviceability of structural members. A suitable bond–slip model is essential for predicting the load resistance and deformation capacity of members, after cracking of the UHPFRC. This paper studies the bond strength between ribbed steel bars and the surrounding UHPFRC before and after yielding of the steel reinforcement. To determine the corresponding bond–slip relationship, pull‐out tests, with varying embedment lengths of the reinforcement, namely 2 times and 10 times the rebar diameter, and diameter of reinforcing bars ranging from 10 mm to 16 mm were conducted. The bond stress, strain and slip along the embedment length of the steel rebars were measured by strain gauges and displacement transducers. Based on the test data, a bond stress–slip model was derived before (elastic stage) and after (inelastic stage) yielding of the reinforcement. The slip at the yield point is suggested through theoretical equations. The post‐yield bond–slip model is based on yield bond stress and frictional bond stress. The two‐part model was validated through iterative procedures and is able to predict the applied force, bond stress and strain distribution along the reinforcing bar. A comparison between the test data and analytical results demonstrates a good predictive capacity on the bond behavior of reinforcement in UHPFRC both before and after yielding of the reinforcement.

Experimental investigation of GFRP bar bonding in geopolymer concrete using hinged beam tests

Geopolymer concrete reinforced with Glass fiber-reinforced polymer (GFRP) bar presents a novel, durable, eco-friendly strengthening system with significant promise for practical engineering. To employ this strengthening system, a clear understanding of the bond performance between GFRP bars and geopolymer concrete under bending conditions is essential. Interface behaviors of GFRP bars-geopolymer concrete was investigated using hinged beam tests, considering the following parameters: concrete type(geopolymer and ordinary), concrete strength(C30, C50, C70), surface treatment of bars(shallow thread, spiral wrap ribs, and sandblasted), bar diameters(6 mm, 10 mm, and 16 mm), and bond lengths(2, 4, and 8 times the bar diameter). Results indicate a consistent bond mechanism between geopolymer and ordinary concrete. The bond strength increases with higher concrete strength, and the initial bond stiffness is improved by spiral wrap ribs. Moreover, the mBPE model was used to describe the local bond-slip relationship, and the effects of different parameters on interface shear stress distribution were discussed. The development length of GFRP bars in concrete was evaluated and compared with existing codes. These findings provide valuable references for the performance assessment and optimization of GFRP bar-reinforced geopolymer concrete structures in engineering applications.

Effect of corrosion on bond between reinforcement and concrete-an experimental study

The presence of cracks in concrete structures can lead to corrosion as it exposes the steel reinforcement to environmental factors. When moisture and oxygen reach the steel, corrosion weakens the bond between the steel and the surrounding concrete. This weakening can reduce the load-carrying capacity and, in severe cases, lead to failure. Understanding the relationship between corrosion and bond strength is vital for reinforced concrete structures. This paper investigates the impact of corrosion on bond strength in reinforced concrete structures by examining the bond performance of concrete with both corroded and uncorroded reinforcement bars. The study considers concrete grades M20, M25, and M30, as well as corrosion levels varying from 0 to 20% in intervals of 5%. To conduct the study, cylindrical samples with different levels of corrosion were created using the corrosion acceleration process with the impressed current technique. Pull-out tests were then carried out to determine the bond-slip relationship and the degradation of bond strength due to corrosion. The test results show that lower-grade concrete (M20) experiences a significant decrease in bond strength compared to higher grades (M25 and M30), with M20 showing a 30.7% reduction and M25 showing a 25.8% reduction in bond strength relative to M30 in controlled specimens. The bond stress-slip relationship reveals a non-linear response, with reduced bond stress and slips for all grades of concrete as corrosion levels increase. Additionally, the reduction in bar diameter due to corrosion ranged from 11.3 to 11.6 mm at 5% corrosion and from 9.4 to 9.7 mm at 20% corrosion, significantly impacting the load-carrying capacity of the reinforced concrete structures. These findings underscore the importance of considering concrete grade and corrosion levels when assessing and maintaining bond performance in reinforced concrete structures.

Experimental study of bond-slip relationships in high-performance self-consolidating concrete with plain steel bars

Self-consolidating concrete is being used more frequently in structures with high density of reinforcement bars or prestressing strands therefore, it is important to carefully consider whether bond stress-slip relations defined for normal strength concrete can be safely applied to high-strength and self-consolidating concrete. This paper aims to investigate the bond behaviour between plain steel bars and high-performance self-consolidating concrete, with a focus on studying the effect of embedment length and concrete compressive strength on bonding performance. The main parameters that were tested are the active bonded length and the compressive strength of the concrete. The value of adhesive bond stress is discussed, as a factor in determining whether the bar slips against the adhering concrete. Based on the results, it can be observed that the maximum bond stress tends to increase with higher concrete compressive strength, while it decreases with longer embedment length of plain steel bar. Conversely, the adhesive bond tends to increase with longer embedment length and higher concrete compressive strength. The experimental investigations indicate that the bond strength increases proportionally to the square root of the compressive strength of concrete, regardless of the concrete compressive strength. Furthermore, a new bond stress-slip model has been analyzed, which takes into account the initial bond strength (adhesive bond) and the lower convex property to predict the post-peak branch. The model has been compared to the test results, and good agreement has been achieved.

Dynamic behaviors of bridge with corroded RC piers under barge collisions

Reinforced concrete (RC) bridge piers located in navigable waterways are susceptible to chloride-induced corrosion, which may cause severe damage or even entire collapse of bridge under potential barge collisions. The present study aims to examine the failure patterns and dynamic responses of typical simply supported girder bridge with corroded RC piers under barge collisions. Firstly, nine RC column specimens with three designed corrosion degrees and two corrosion strategies were prepared using the impressed anodic current technique. Secondly, the drop hammer impact and axial compression tests were successively performed to examine the residual axial load bearing capacities of both unimpacted and impacted specimens. Furthermore, by comprehensively considering the effects of corrosion-induced deteriorations on the effective cross-sectional area and yield strength of reinforcements, concrete strength, as well as the rebar-concrete bond-slip relationship, the refined finite element (FE) models of specimens were established and validated. Finally, the dynamic behaviors of a prototype simply supported girder bridge with corroded RC piers under barge collisions at different service lives, i.e., 0–60 years, were numerically assessed. It indicates that: (i) under drop hammer impact, six specimens all exhibit global flexure failure, and relatively severe concrete cracking and spalling occur in the specimens with 15 % designed corrosion degree; (ii) the axial load bearing capacities of specimens with 5 % and 15 % designed corrosion degrees are reduced by 15.46 % and 34.86 % compared to the unimpacted non-corroded specimen, and 11.29 % and 43.30 % compared to the impacted non-corroded specimen; (iii) the transverse impact resulted in 25.93 %, 22.27 % and 35.53 % reductions in axial load bearing capacities for 0 %, 5 % and 15 % designed corrosion degree, respectively; (iv) for the prototype barge-bridge collision scenario, the failure patterns vary from minor bending cracks to remarkable flexural failure as the service live increases from 0 to 60 years. The corrosion-induced degradations of bridge performance should be concerned for the vessel collision-resistant design of bridge.

Influence of interfacial bond between rebar and concrete on the lateral resistance of RC columns under different loading rates

The interfacial bond between rebar and concrete is a critical factor that influences the performance of reinforced concrete (RC) structures because it affects the effective force transfer between concrete and rebar and hence the composite actions. In finite element modelling of RC structures, the bond-slip relation between rebar and concrete is generally neglected due to the increased model complexity by considering debonding behaviours. Limited studies show the debonding performance is loading rate dependent, neglecting it in numerical modelling may lead to inaccurate structural response predictions, but there is no systematic investigation of bonding performance on responses of structures under load of different loading rates. The influences of neglecting debonding in structural response analysis are therefore not properly defined yet. In this study, the finite element model was established and validated by the available impact test data. The lateral resistance and damage modes of the column considering and neglecting bond-slip behaviour between rebar and concrete were examined under various loading rates ranging from 50 kN/s to 1.0 × 106 kN/s. It is found that neglecting bond-slip relation in finite element modelling of RC columns leads to underprediction of the peak force and damage. The assumption of perfect bond has a significant influence on predicting the peak force and damage of column under low loading rates, but its influence reduces with the increase in loading rate, especially when the loading rate exceeds 1.0 × 105 kN/s. The maximum relative difference in peak force between considering and neglecting bond-slip at 50 kN/s is 18.63 %. Parametric studies were conducted to investigate the effects of bonding performance on columns of different width, depth, height, and concrete strength. Based on the numerical results, an analytical formula is developed to quantitatively predict the errors in peak force predictions by neglecting debonding between concrete and rebars of RC columns. The results highlight the importance of considering bond-slip in finite element modelling of RC structures subjected to quasi-static and low-rate dynamic loadings, and demonstrate it is reasonable to neglect debonding in structural response analysis under high-rate dynamic loadings.

An alternative modeling approach to incorporate bond-slip effects in fiber-based elements

Fiber-based elements can provide accurate estimates of the global and local inelastic response of RC members subjected to reversed cyclic loads. However, fiber-based elements per se do not account for the localized deformations that arise from strain penetration or bond-slip effects at the member ends. To account for bond-slip effects, some researchers have suggested the use of modified properties for the steel reinforcement fibers, or that a zero-length element be attached at the element ends. In this study, a modified modeling procedure is proposed to include anchorage-slip effects in reinforced concrete frame members modeled with fiber-based beam-column elements. The proposed modeling approach is based on local bond-slip laws that can be implemented in general-purpose fiber-element software, and it differs from existing approaches in that it does not require the use of a zero-length element (though it could be used), and that it can be used with any local bond-slip relationship representative of a variety of bar embedment conditions. As such, the model can be used to simulate the effects of bond-slip of short or long embedment lengths in confined or unconfined concrete. The proposed modeling procedure is validated by comparing the calculated response with experimental data from four independent investigations. The test data included three columns and two beam specimens with various confinement and reinforcement configurations and included members reinforced with conventional and high-strength steel reinforcement. The results from the analyses show that the proposed modeling procedure provides a very good estimate of both the global and the local responses (anchorage-slip rotation) of the specimens.

Theoretical study on the bond performance of CFRP-to-steel single-lap shear tests with multiple debonding defects

The amount of research on the external bonding of Carbon Fiber Reinforced Polymers (CFRP) to degraded structures has increased recently. The adhesive is the weakest element of the joint and the bonding of the adherends is critical for the efficiency of the joint. Therefore, the influence of multiple debonding defects on CFRP-to-steel joints has still not been correctly quantified nor fully understood. For this reason, the current work proposes a new numerical strategy that allows for studying the influence of multiple debonding defects when a brittle and ductile adhesive is used. A new nonlinear bond-slip relationship is used and four different ratios between the debonded and the bonded area (η) are assumed: 0%, 25%, 50%, and 75%. The proposed model is based on the Finite Difference Method (FDM) and validation is carried out with a commercial Finite Element Method (FEM) package. The load-slip curves allowed for observing that the proposed FDM and the FEM are consistent and both revealed degradation of the load capacity of the joints with the increase of η. Moreover, by adopting a displacement control at the CFRP-free end, a snap-through and snap-back phenomenon are observed in the specimens with a localized debonding defect.

Experimental and numerical investigations on shear behavior of RC beams strengthened with U-wrapped PET FRP

This paper reports the investigations of experimental and numerical programs on the shear performance of U-shaped Polyethylene Terephthalate (PET) FRP-retrofitted RC beams. Twelve RC beams were fabricated and tested under monotonic three-point loading with the test parameters being FRP strip width and shear span-to-effective depth ratio. A comprehensive analysis and investigation were conducted in terms of the failure modes, shear load–deflection responses, shear capacities, the strain evolution of FRP and stirrups, and the interaction of shear contributions among FRP, stirrups and concrete. Larger debonding strains were observed for PET FRP. Five design guidelines and two models available in the literature were assessed against the measured PET FRP shear contribution. A modified model of the shear contribution for PET FRP was developed and verified by the test results. Finally, a finite element model was established to further understand the shear performance of retrofitted beams, in which the bond-slip relationship between concrete and FRP was considered. The FE model was validated by comparing the test and FE results. The proposed FE model could accurately capture the propagation of shear critical cracks and FRP debonding failure for the specimens with medium and large shear spans.

Experimental investigation on anchoring and bonding properties between Fe-SMA strip and concrete

In the technical system of the previous investigations, the prevalent method for external prestressed strengthening of concrete structures with iron-based shape memory alloy (Fe-SMA) strips is mechanical anchoring (without bonding). However, there is currently a lack of research on the adhesively bonded situation. In order to enhance the comprehension of the mechanical behavior of Fe-SMA/concrete joints, a total of 18 lap-shear test specimens were meticulously prepared, encompassing three distinct anchorage methods (single anchor-bolt anchorage, single-adhesive anchorage, and hybrid anchorage). The test series encompasses three varying bond lengths (300 mm, 350 mm, and 400 mm), three different activation temperatures (non-activated state, 200 ℃, and 300 ℃), as well as three diverse numbers of anchor bolts (1 bolt, 2 bolts, and 3 bolts). The bond-slip relationship before and after thermal activation was analyzed based on the data obtained from digital image correlation (DIC) tests. The results indicated that two or more anchors ensured strip rupture, exerting 40 % of its tensile strength. Single-adhesive bonding results highlighted the necessity for preventing debonding. The hybrid-anchorage method with anchor bolts and adhesive exerted 47 % strip strength and higher bond-slip stiffness. At 200 ℃ activation temperature, the interface rupture energy of the single-adhesive bonded specimen increased by approximately 30 %, but decreased by 22 % at 300 ℃. This paper provided an important reference for external prestressed strengthening of concrete structures with Fe-SMA strips under different situations.

Experimental study on bond behavior between wet lay-up CFRP and corroded steel plates

Corrosion of steel in marine environments is a major safety concern for marine steel structures throughout their service lives. Strengthening these corrosion-damaged structures with carbon fiber-reinforced polymer (CFRP) shows great potential for extending their service lives. However, the bond behavior between CFRP and corroded steel, especially the influence from adhesive properties and corrosion degree, has not been fully understood. This paper therefore presents the results of a comprehensive experimental study on the bond behavior between wet lay-up CFRP and corroded Q355B steel plates. Tensile tests on double-lap CFRP-to-steel joint specimens with different bonded lengths, adhesives and corrosion durations were then conducted. The failure modes, load-displacement curves, strain and local shear stress distributions, effective bond lengths, and bond-slip relationships of the test joint specimens were investigated in detail. The result showed that the influence of corrosion on the CFRP-to-steel bond performance varied depending on the failure modes resulting from the material properties of adhesives. However, corrosion has insignificant influence on the general patterns of load-displacement curves, strain distribution, local shear stress distribution, local bond-slip curves with same adhesives. When failure occurred in the adhesive or the steel-adhesive interface, the corrosion tended to have a more accentuated effect on the bond performance.

Estimation of the bar stress based on crack width measurements in reinforced concrete structures

AbstractEstimating the stress of reinforcing bars and its variations in service conditions can be useful to determine the reserve capacity of structures or to assess the risk of fatigue in the reinforcement. This paper investigates the use crack width measurements to estimate the stress in the bars. In existing structures, crack width formulations can be used to estimate the stress in the reinforcement from crack width measurements, profiting from additional information that can be measured in‐situ, such as the crack spacing. Recent experimental results show that the values of the mean bond stress typically considered in code formulations overestimate the actual bond stresses activated in cracked concrete specimens. This paper presents the results of an experimental program consisting of reinforced concrete ties and beams instrumented with Digital Image Correlation and fiber optical measurements. The results confirm the differences with typically assumed bond stresses. A formulation to estimate the bond stresses in service conditions is derived from the results of the numerical integration of a previously developed local bond–slip relationship. Their pertinence for the estimation of the stress in the reinforcement from the measured crack width is evaluated with satisfactory results for monotonic loading and for the maximum force in cyclic tests.

Features of bond-slip relations: 3D finite element analysis based on tests of short RC ties

The interaction between concrete and reinforcement is highly complex and is of fundamental importance for predicting the behaviour of reinforced concrete (RC) structures. While the interaction of the two materials is often characterised by a bond – slip law, there are currently no such laws capable of accurately predicting serviceability characteristics, such as deflection, crack spacing, and width. This paper examines the effect of various parameters on the shape of bond – slip relation at loads before yielding of reinforcement. The study is based on a mesoscopic numerical analysis, utilizing the finite element method along with a friction cohesive zone model to explore the bond-slip phenomena in short RC ties. The numerical model is combined with an experimental campaign involving six short concrete ties reinforced with 20 mm bars. Steel strain profiles were monitored within the reinforcement using electrical strain gauges. These experimental steel strain profiles served as a robust tool for controlling and calibrating numerical models. The numerical models employed solid finite elements to simulate both reinforcement and concrete, with special zero-thickness plain elements applied to simulate the friction cohesive contact at the steel-concrete interface. Bond-slip relations were obtained from the numerically modelled reinforcement strain profiles. It was shown that concrete strains can be ignored when assessing slip. The effect of the embedded length of reinforcement under the fully confined conditions was demonstrated to have little effect on bond-slip relations. It was also shown that the maximum bond stress is strongly related to the thickness of the concrete cover. The effect of load intensity on the bond – slip behaviour was investigated. It was shown that under full confinement, the initial bond stiffness was not affected by load intensity. However, degradation of bond stiffness with increasing load due to internal cracking took place in the RC ties with a small cover/diameter ratio.

Three-dimensional elastoplastic analysis of strain-softening surrounding rock based on the non-linear bond-slip relationship considering hydraulic-mechanical coupling

After the anchor is installed, relative slip between the anchor and the surrounding rock will occur in the actual engineering. Based on the proposed nonlinear bond-slip model, a three-dimensional elastoplastic analysis of the strain-softened surrounding rock is performed in this study while considering hydraulic-mechanical coupling. A numerical iterative method of surrounding rock analysis is proposed, which considers the relative slip between the anchor and the surrounding rock. These stresses and displacements of the surrounding rock, as well as the anchor shear stress distribution, can be obtained using the proposed method. Furthermore, the calculation results of the program are compared with the existing field test results and with the calculation results of other methods to verify the accuracy of the proposed method. The results indicate that the calculation results of the proposed method are generally in line with the test results, and the largest slips occurring at the two ends of the anchors. Meanwhile, the proposed method is applied to an actual engineering, and the results agree well with the field data. Finally, the effects of seepage and strain softening of the surrounding rock on the interaction between the surrounding rock and the anchors are investigated by parametric analysis.