Anchorage Bond Research Articles

Short‐length mechanical bond anchorage for reinforcement bars made of FRP: Experimental and numerical investigations

Short‐length mechanical bond anchorage for reinforcement bars made of <scp>FRP</scp>: Experimental and numerical investigations

Anchorage Bond Strength of Glass Fibre Polymer Reinforced Concrete with Palm Kernel Shells as Partial Coarse Aggregate

Anchorage Bond Strength of Glass Fibre Polymer Reinforced Concrete with Palm Kernel Shells as Partial Coarse Aggregate

Anchorage Bond Strength of Glass Fibre Polymer Reinforced Concrete with Palm Kernel Shells as Partial Coarse Aggregate

Anchorage Bond Strength of Glass Fibre Polymer Reinforced Concrete with Palm Kernel Shells as Partial Coarse Aggregate

Bond-Slip Model of Corrosion-Resistant Rebar and Fiber-Reinforced Seawater Sea-Sand Concrete

Abstract To study the bond performance between fiber-reinforced seawater sea-sand concrete and corrosion-resistant rebars (glass fiber–reinforced polymer [GFRP] bars and epoxy resin–coated rebars) in extremely hot and humid marine environments, bond anchorage tests between reinforcement and seawater sea-sand concrete are conducted to study bond performance. The failure morphology of reinforced concrete was investigated, and the bond-slip curves of different types of rebar and concrete were compared. According to the research results, the addition of basalt and polypropylene fibers to seawater sea-sand concrete changed the distribution of bonding stress, which was conducive to an improvement in the anchorage efficiency of reinforcement and concrete. The chemical bonding performance between the fiber-reinforced seawater sea-sand concrete and rebar is improved, wherein the bond stress increases by 94.01 % at the beginning of the slip, and the residual bond stress increases by 91.72 %. Compared with ordinary seawater sea-sand concrete, the bonding strength between ordinary reinforced rebar and fiber-reinforced seawater sea-sand concrete increased by 20.75 %, and the bonding strength between the GFRP bar and fiber-reinforced concrete decreased by 15.37 %. Based on the friction mechanism of rebars and concrete, bonding strength models of ordinary rebar, epoxy resin–coated rebar, and GFRP bars with fiber-reinforced seawater sea-sand concrete are presented.

Experimental Study on Tensile Performance of FRP Tendons/Cables with Varied Bond Anchorage Factors.

FRP tendons and cables are increasingly being used in civil engineering structures due to their high strength-to-weight ratio and corrosion resistance. The bond anchorage factors, which characterize the bond strength between the FRP tendon/cable and the surrounding materials, play a critical role in determining the overall performance of the system. In this study, a series of tensile tests were conducted on FRP tendons/cables with different bond anchorage factors to evaluate their load-carrying capacity, load-displacement curve, and strain distribution. The study considered different types and surface shapes of FRP tendons/cables, and determined the influence of anchoring length, bonding medium type, and bonding medium thickness on the performance. The strain distribution of FRP tendons/cables at the anchorage end gradually increased along the loading section to the free end. A stress analysis model of the anchoring section was proposed and found to be consistent with the test results.

Experimental Study on Secondary Anchorage Bond Performance of Residual Stress after Corrosion Fracture at Ends of Prestressed Steel Strands

In order to explore the secondary bond anchorage performance between prestressed tendons and concrete after the fracture of steel strands in post-tensioned, prestressed concrete (PPC) beams, a total of seven post-tensioned, prestressed concrete specimens with a size of 3 × 7ϕ15.2 mm were constructed firstly, and the steel strands at the anchorage end were subjected to corrosion fracture. Then, the pull-out test of the specimens was conducted to explore the secondary anchorage bond mechanism of the residual stress of prestressed tendons experiencing local fracture. Moreover, the influences of factors such as the embedded length, release-tensioning speed, concrete strength, and stirrup configuration on anchorage bond performance were analyzed. Finally, the test results were further verified via finite element analysis. The results show that the failure of pull-out specimens under different parameters can be divided into two types: bond anchorage failure induced by the entire pull-out of steel strands and material failure triggered by the rupture of steel strands. The bond anchorage failure mechanism between steel strands and the concrete was revealed by combining the failure characteristics and pull-out load–slippage relation curves. The bond strength between prestressed steel strands and concrete can be enhanced by increasing the embedded length of steel strands, elevating the concrete strength grade, and enlarging the diameter of stirrups so that the specimens are turned from bond anchorage failure into material failure.

Experimental Study on the Mechanical Properties of Vertical Corrugated Pipe Grout Anchor Connection Joints

Prefabricated buildings’ quality, safety, and construction efficiency are closely related to the connections between various prefabricated components. This study optimizes the design of corrugated pipe-restrained grout anchor lap connections, further simplifying the construction methodology while ensuring reliable connection performance. The objective is to achieve cost savings and accelerate construction progress. A pull-out test of this new type of joint is conducted, generating two sets of 17 specimens each. The research examines the effects of grouting material strength, grout anchor steel bar anchorage length, and U-shaped stirrup spacing on the connection performance of corrugated pipe grout anchor connections. The results indicated that the specimens primarily experience two types of failure: anchorage failure with steel bar pull-out and steel bar tensile failure without anchorage failure. The strength of the grouting material and the anchorage length of the grout anchor steel bar positively correlate with bond anchorage performance. U-shaped stirrups contribute to restraint and enhance the bonding force between the corrugated pipe, grouting materials, and the grout anchor steel bar to a certain extent.

Study on bond properties of corroded NPR (negative Poisson’s ratio) steel bar embedded in marine concrete

In this work, 48 pull-out test specimens of 150 mm × 150 mm × 150 mm have been examined to assess the bond behavior between corroded NPR (negative Poisson’ s ratio steel bar) and marine concrete with different anchorage bond length. Three variables are considered: two types of steel bar (NPR bar and HRB400 steel bar), theoretical corrosion ratio of steel bar (ρ=0,1\\%,2\\%,3\\%), anchorage length (5 or 7 times of steel bar diameter). Experiment results showed that under the same extent of bars theoretical corrosion ratio and anchorage length, the bond between NPR and marine concrete exhibits lower value than that of HRB400. Moreover, as measured mass corrosion ratio increases, the bond strength of NPR and HRB400 embedded in marine concrete shows a trend of first rising and then falling. For NPR bas, the measured mass corrosion ratio corresponding to the peak value of bond strength is about 1.8 %. Furthermore, considering the condition of ρ=0,1\\%,2\\%, NPR bar specimens with anchorage length of 7d show slightly lower bond capacity than that of specimens with anchorage length of 5d due to the inhomogeneity of bond stress distribution of steel bar and surrounding concrete. Finally, the bond stress-slip constitutive model between two types of steel bars and marine concrete considering different working conditions has been proposed.

Research on the Bonding Performance of BFRP Bars with Reactive Powder Concrete

In recent years, replacing steel bars with basalt fiber-reinforced polymer (BFRP) bars and replacing ordinary concrete with reactive powder concrete (RPC) are considered effective solutions to the corrosion problem of steel bars in ordinary reinforced concrete structures. In order to study the bonding performance between BFRP bars and RPC, a total of 27 bonding specimens were tested by pull-out test. The effects of steel fiber volume content (0%, 1.5%, 2%), protective layer thickness (25 mm, 40 mm, 55 mm, 69 mm), and bond anchorage length of bars (3 d, 4 d, 5 d; d is the diameter of the bars) on the bond performance were studied. The experimental results indicated that the BFRP bar and reactive powder (RPC) concrete interface exhibited better bonding performance, and the steel fibers mixed in RPC can play the role of crack-blocking enhancement in the specimen, which improves the shear and tensile properties of the concrete, thus improving the bond strength between BFRP bar and RPC. Three failure modes were observed in the pull-out tests: BFRP bar shear failure, splitting failure, and concrete shear failure. The bond strengths of BFRP bars and RPC with 0%, 1.5%, and 2% steel fiber content were 24.2 MPa, 32.1 MPa, and 34.5 MPa, respectively. With the increase in bond anchorage length, the ultimate bond strength tended to increase first and then decrease. There may be an optimal bonding length between BFRP bar and reactive powder concrete, and when the optimal bonding length is exceeded, the bond strength decreases with the increase in bonding length. With the increase in the protective layer thickness, the improvement in the bond strength of the BFRP bar and RPC was not very significant.

An experimental investigation of the bond performance of BFRP bars with recycled-aggregate concrete of different particle sizes

The pull-out test was performed in this study to investigate the bond performance between basalt fiber reinforced polymer (BFRP) bars and recycled concrete. Three factors were considered: aggregate size (5–10 mm, 11–15 mm, and 16–20 mm), bond anchorage length of bars (3D, 5D, and 7D), and the recycled aggregate replacement rate (0%, 30%, 60%, and 100%). The bond–slip mechanism, failure mode, bond stress distribution, and bond–slip curves were all analysed. Based on the results, it was found that situations with a high recycled aggregate replacement rate, large aggregate particle sizes, or long bond lengths have an increased likelihood of experiencing splitting failure. As the aggregate size increases, the bond strength between the BFRP bars and the concrete would also increase, in ordinary concrete, a 22.54% increase was observed, whereas in recycled concrete, the maximum increase reached 48.20%. The effect would be more pronounced on recycled concrete compared to ordinary concrete, and it would also be more significant in specimens with BFRP bars compared to steel bars. Additionally, the optimal bond anchorage length was determined to be 5D. The bond strength exhibited a trend of decrease followed by an increase as the recycled aggregate replacement rate increased. The maximum reduction of 59.7% in bond strength was observed when the replacement rate of recycled aggregate reached 60%. Moreover, when the replacement rate of recycled aggregate increased to 100%, there was a decrease of 19.05% in bond strength compared to the specimen without recycled aggregates. Based on the experimental test data and existing models, an improved two-stage bond–slip constitutive model was proposed.

Experimental study and analysis of the bond-anchorage properties of laminated flattened-bamboo lumber connections with glued-in steel rod

To improve the utilization rate of raw bamboo and reduce the amount of adhesive, this paper studied a new type of laminated bamboo lumber, that is, laminated flattened bamboo lumber. The monotonic pull-out tests were carried out on 56 specimens with glued-in steel rods of three different diameters (12 mm, 16 mm, and 20 mm, respectively; the thickness of the adhesive layer was 3 mm) of laminated flattened bamboo lumber, and the effect of anchorage length and diameter of the steel bar on the mechanical properties of bond anchorage were studied. In addition, the specimens with a diameter of 12 mm and an anchorage length of 100 mm were selected to study the effect of different thicknesses of the adhesive layer (between 2 mm and 4 mm) on the mechanical properties of bonded anchorage. The results showed that the failure modes could be divided into three types. For the specimens with the same anchorage length, the larger the diameter of the glued-in steel bar was, the larger the ultimate pullout load would be; when the diameter of the steel bar was the same, the ultimate pullout load of the specimens increased with the increase of the anchorage length. When the diameter of the glued-in steel bar was 12 mm, the average bond strength decreased with the increase in slenderness ratio. When the diameter of the glued-in steel bar was 16 mm and 20 mm, the average bond strength first increased and then decreased with the increase of the slenderness ratio, and the turning slenderness ratio points were 8.75 and 5, respectively. The ANOVA analysis with parameters revealed that the rebar’s diameter and length significantly impacted the bond-anchorage characteristics of the glued-in rod connection in laminated flattened bamboo lumber.

Experimental Research on Bonded Anchorage of Carbon Fiber Reinforced Polymer Prestressed Strands.

Aiming at the problems of a large number of corrosion and fatigue damage of the current prestressed steel strands, this paper adopts carbon fiber-reinforced composite (CFRP) strand with better corrosion resistance and fatigue resistance and uses it in concrete structures. The bond anchorage is usually used to anchor CFRP tension members, which bonds the CFRP through the binding medium. Through experimental research on the CFRP strand bond anchorage, the inner taper of the CFRP prestressed strand cone was anchored and the influence of different anchor lengths and bonding media on the anchorage performance was determined. The test results demonstrate that the taper of the conical anchorage described in this paper is a key factor affecting its anchorage performance and increasing the inner taper within a certain range is beneficial to improving the anchorage performance of the conical anchorage. The bonded anchorage of the CFRP prestressed strand with a 200 mm anchor is the most reliable and efficient, as the taper of the 200 mm anchor is the largest. The average anchoring efficiency coefficient of the 200 mm anchor was 96.4%, which is 3.7% and 2.6% higher than the average anchoring efficiency coefficient of 220 mm and 250 mm anchors, respectively. The anchoring efficiency of the anchor is also high (94.1%) when the epoxy resin mortar is used as the bonding medium. Moreover, after an appropriate amount of quartz sand is added to the epoxy resin, the overall comprehensive performance of the anchor can be improved to a certain extent and the stress of the CFRP strand can be improved. The coupling between ultra-high-performance concrete dry mix (UHPC-GJL) and CFRP strand materials is not suitable for UHPC-GJL being used, as its binding medium as the average anchoring efficiency coefficient is only 44.5% when UHPC-GJL is used as the anchor bonding medium.

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.

Application of an iron-based shape memory alloy for post-tensioning glass elements

Previous research has evidenced that by adding a ductile reinforcement on the tension side of a glass beam, for instance by adhesive bonding, its post-cracking behaviour and redundancy were improved, while an additional pre-stressing of this reinforcement further helped to increase the initial cracking resistance. Past investigations used steel tendons or stainless steel strips, which required rather complex setups and procedures for mechanical pre-stressing. This study aims to introduce an easier-to-apply procedure with strips made of an iron-based shape memory alloy (Fe-SMA), which has the property of remembering its initial shape after a phase transformation from austenite to martensite. The Fe-SMA strips can be anchored to a parent structure as pre-strained strips, in case of a glass substrate by adhesive bonding. After activation of the Fe-SMA through a heating and cooling process, a tensile stress is generated in the strip, which applies a compressive stress field into the parent structure. This work discusses the results from first feasibility investigations dealing with the choice of adhesive and identifying a suitable activation procedure for Fe-SMA strips adhesively bonded to glass elements. The effective bond length, which needs to be considered when defining the anchorage length, was determined for two structural adhesives. While for the high-strength, brittle 2c-epoxy adhesive SikaPower®-1277, shorter bond lengths of a little more than 120 mm were sufficient, for the more ductile 2c-methacrylate adhesive Araldite® 2047-1, longer bond lengths were necessary for the same load level (more than 240 mm). Furthermore, an activation procedure by electrical resistive heating was applied, which (i) allowed sufficient heating of the Fe-SMA for activation, (ii) avoided too high instant temperature changes in the glass and (iii) did not affect the required anchorage bond length.

Mechanical performance evolution and life prediction of prestressed CFRP plate exposed to hygrothermal and freeze-thaw environments

The long-term prestressed loss of anchorage system and mechanical property evolution play the significant role for the steel/concrete structures strengthened with prestressed CFRP plates. In the present study, a wedge-extrusion bond anchorage system was applied to provide the reliable anchorage load-bearing capacity for CFRP plate. A new prestressed tension device was put forward to realize the coupling exposure of elevated temperature (20 °C, 60 °C and −20 to 30 °C), distilled water and sustained loading (20%, 40% and 60%). The mechanical and thermal properties of CFRP plate were conducted to obtain the long-term evolution exposed to the above environments. The mechanical analysis and tensile tests of anchorage system showed the tensile failure modes under the static and cyclic loads were the CFRP burst, and there was no debonding occurring in the anchor. The higher anchorage capacity was attributed to the uniform stress distribution of CFRP plate parallel to the greatest dimension of cross section in the anchor. The new prestressed tension device can realize the maximum prestressed level (∼70%) with an allowable prestressed loss (∼300 με). Meanwhile, the prestressed loss of CFRP plate exposed at the maximum temperature (60 °C) and longest time (90 days) was found to be ∼300 με. Immersed at higher temperature and prestressed level brought about an additional degradation rate of tensile strength (5%∼10%). The minimum strength retention of CFRP plate was found at the freeze-thaw exposure for 90 days. The long-term life prediction showed the residual tensile strength retentions of CFRP plates were more than 50% for the maximum prestressed level (60%) for the service life of 30 years in civil engineering structures.

Effects of natural minor corrosion levels on mechanical property and bond anchorage behavior of CRB600H steel bars

Mechanical property tests and bond anchorage tests of the natural minor corrosion CRB600H steel bars were carried out, and corrosion levels of the steel bars were 0.0%, 1.8%, and 2.1%, respectively. The mechanical property test results showed that the yield strength of the CRB600H steel bars with corrosion levels of 1.8% and 2.1% was approximately 10% and 15% lower than that of intact steel bars, respectively. Still, the strains at the maximum force of the two corrosion levels showed no noticeable change with intact steel bars. The yield strength formula of the natural minor corrosion CRB600H steel bars was regressed. The load-slip curves, failure modes, bond toughness, and bond strength influential factors of natural minor corrosion bond specimens were analysed in the bond anchorage tests. Compared with the control bond anchorage specimens, the bond strength of the specimens with steel bar corrosion levels of 1.8% and 2.1% decreased by 5.4% and 6.3%, respectively. The ultimate bond strength of the natural minor corrosion CRB600H steel bars embedded in concrete was regressed. The development length of the natural minor corrosion CRB600H steel bars satisfying the reliability requirements was calculated using the first-order second-moment method. Based on the calculation results, the calculation formula of the development length for the natural minor corrosion CRB600H steel bars in concrete was regressed.

Multilateral Assessment of Anchorage Bond Characteristics in Steel Fibre Reinforced Concrete.

Anchorage to concrete is a recurring application in construction. For such applications, bonded anchors, formed by means of a polymer adhesive injection into a borehole, are a widely used product due to their flexibility in regards to the construction logistics and positioning of the attached element as well as high load capacities. At the same time, fibre-reinforced concrete is the material of choice for many engineering applications where anchors have to be installed. Moreover, the use of steel fibre-reinforced concrete is likely to increase, since it now falls in the scope of the second-generation Eurocode 2 (exp. 2023). Therefore, the condition of the anchor installation borehole—mainly the roughness and grip of its internal surface—is known to play a critical role in the stress transfer from the attached component, through the fastening and into the concrete, and, hence, to the load-bearing performance. At the same time, drilling through the steel fibre reinforcement, along with the accelerated wear of the drilling tools, can in turn influence the borehole’s roughness and the overall installation quality. Furthermore, steel fibre may lead to an additional local stiffening of the concrete where the anchor is installed. These complex elements are discussed herein on the basis of multiple tests on anchors in plain and steel fibre concrete, as well as numerical analyses. The results indicate particular aspects of bonded anchor design and product certification for different polymer-based construction adhesives.

Experimental study on the bond-slip behavior and stress transfer mechanism between shaped steel and high-performance fiber-reinforced concrete

In light of the weak bond strength between the two materials in steel reinforced concrete (SRC) and the brittleness of high-strength concrete, the use of high-performance fiber-reinforced concrete (HPFRC) was proposed with the addition of cellulose fiber and rice husk ash (RHA) in high-strength concrete. The purpose of this study is to investigate the bond behavior of shaped steel embedded in HPFRCs. Thirteen push-out test specimens of steel high-performance fiber-reinforced concrete (SHPFRC) were cast. The test parameters considered in this study were the HPFRC strength, cover thickness, embedment length, and stirrup ratio. The experimental process and failure modes were analyzed, and the influence of various test parameters on the average bond strength was studied. The average effective bond stress was introduced to study the whole process of bond failure and the stress transfer mechanism. Then, a method for calculating the bond stress was established. The results showed that the failure modes of the specimens were classified into bond splitting failure, bond anchorage failure, and mixing failure. The parameters have various effects on the average bond strength. The introduction of the average effective bond stress reflected the transfer mechanism of bond stress at the interface. The largest component of bond stress was chemical adhesion, and mechanical interaction was the smallest.

STUDY ON BONDING PROPERTY OF POLYURETHANE CEMENT (PUC) TO STEEL BAR

The pull-out test of the bar and PUC is carried out in this paper, the effects of protective layer thickness, reinforcement anchorage length, diameter and shape of reinforcement on bonding properties were studied. The results show that the bond strength between reinforcement and PUC material increases with the increase of the thickness of the protective layer, but decreases with the increase of the anchorage length and diameter of reinforcement. The bond strength of bare round steel is significantly lower than that of ribbed steel, and the maximum bond strength is about 47.4% of ribbed steel. By analyzing the bond slip curve obtained from the pull-out test, the stress process of bond anchorage between reinforcement bar and PUC material is mainly summarized into three stages: the rising stage, the falling stage and the residual stage. The characteristics of the curve, the stress process and the failure mode of specimen at each stage are analyzed.

Bond-slip behavior between basalt fiber reinforced plastic bars and recycled aggregate concrete

Corrosion of steel bars is one of the key factors undermining the stability of reinforced concrete structures. Internal defects of the recycled aggregates used in recycled aggregate concrete (RAC) decrease the durability of concrete structures, and may accelerate steel corrosion. The use of corrosion-resistant materials as substitutes for steel bars in RAC may solve this problem. Basalt fiber reinforced Polymer (BFRP) is a corrosion-resistant material. This study assessed the bonding properties between BFRP bars and RAC using pull-out tests. The following five factors were considered: RAC strength grade, the RAC cover thickness, bond anchorage length of BFRP bars, diameter of BFRP bars, and replacement rate of the recycled concrete aggregate (RCA). The effects of these factors on failure mode, bond strength, and the bond-slip curve were assessed. Finally, the bond-slip relationship between BFRP bars and RAC was established by improving the mBPE model, which can describe the bond behavior between BFRP bars and RAC with satisfactory accuracy.