Composite Anchorage Research Articles

Tensile Bearing Performance and Mechanical Transfer Mechanism of Coal-Rock Composite Anchor Bodies Under Different Height Ratios of Rock to Coal

Tensile Bearing Performance and Mechanical Transfer Mechanism of Coal-Rock Composite Anchor Bodies Under Different Height Ratios of Rock to Coal

Finite Element analysis and experimental study of static performance of multi‐CFRP tendon composite anchorage system

<scp>Finite Element</scp> analysis and experimental study of static performance of multi‐<scp>CFRP</scp> tendon composite anchorage system

Anchorage Research for CFRP Tendons: A Review.

Carbon fiber reinforced polymer (CFRP) tendons are composite materials that offer significant advantages in terms of tensile strength and lightweight properties. They are being increasingly utilized in the construction industry, particularly in bridge cables and building structures. However, due to their relatively poor transverse mechanical properties compared to steel cables, securing these tendons with anchors presents a challenge. This paper reviews the structure and force characteristics of three types of anchors for CFRP tendons-clamping anchorage, bonded anchorage, and composite anchorage-analyzes and summarizes the anchorage characteristics and damage mechanisms of each type of anchorage, and highlights that the optimization of the mechanical properties of the tendons is key to the design and research of anchoring systems. The new composite anchorage offers comprehensive advantages, such as minimal tendon damage at the anchorage section, more uniform stress distribution, and better anchorage performance, despite being more complex in design compared to single-type anchorages. However, there remain challenges and research gaps in testing and validating these anchoring systems under realistic loading and environmental conditions, including impacts, cyclic stresses, humidity, and high temperatures. Future efforts should focus on developing new testing techniques and models to simulate real-world conditions, enabling more accurate assessments of anchorage performance and longevity. By doing so, we can fully harness the mechanical properties of CFRP tendons and further enhance the safety and efficiency of our built environment.

Investigation on the flexural–tensile behaviour of CFRP tendon composite anchorage system

The cable at the anchorage end is in a bending–tension condition in service due to the variable loads. A new composite anchorage system was proposed to study the flexural–tensile behaviour of the anchorage system with CFRP tendon. Four groups of single-tendon composite anchorage and three groups of five-tendon composite anchorage with bend restrictor were tested. Besides, one group of five-tendon composite anchorage without bend restrictor was tested as a control group. The effects of the bending angle, inner cone angle of the steel barrel and pre-tension force on the flexural–tensile behaviour of the anchorage system were investigated. The internal force state of the tendon inducing different failure modes was analysed. A finite element method was used to analyse the failure mechanism of the anchorage system under the bending–tension condition. Moreover, the flexural–tensile behaviours of the anchorage systems with different elastic moduli of the bonding medium were compared. Results showed that the efficiency coefficients of the composite anchorage with multi-tendon exceeded 0.9 when the end bending angle was less than 4.2°. The setting of the bending restrictor improves the flexural–tensile bearing capacity of the anchorage system and increases the maximum allowable bending angle. A larger bending angle will lead to a faster increase in the transverse shear stress at the loading end. Furthermore, increasing the pre-tension force can prompt the cooperation ability of the tendons and reduce the ultimate slips, thus improving the ultimate load-bearing capacity of the anchorage. The increase in the elastic modulus remarkably reduces the slip of the tendon, but increases the shear stress at the loading end under the bending–tension condition.

Finite element model analysis of long-term performance of composite anchorage based on double-material parameters

Carbon fibre-reinforced polymer (CFRP) tendons demonstrate the advantages of light weight, high strength, and superior corrosion resistance and have broad application prospects for long-span cable structures. However, given the low transverse shear strength of CFRP tendons, how to achieve long-term and reliable anchorage for CFRP tendons is a critical issue. The long-term performance (LTP) of a novel composite anchorage for CFRP tendon was assessed in this study. Then, a finite element model (FEM) with double-material creep parameters was established to reliably model the LTP experiment according to the creep parameters of the bonding medium and CFRP tendon. Finally, the effects of the free section tendon length, pre-tightening force, over-tensioning force, and elastic modulus of the bonding medium were analysed using the established FEM with double-material creep parameters. Results revealed no visible damage to the CFRP tendon and anchorage after the LTP experiment. The maximum tendon slippage was 0.054 mm, and the residual load ratio was 0.826. These phenomena indicate that the novel composite anchorage has excellent LTP. The FEM modelling results based on double-material creep parameters were in good agreement with the experiment results. The residual load ratio calculated by the FEM was 1% lower than the experimental value. Through the parameter analysis, the residual load ratio of the specimen was effectively improved under longer free section tendon condition, but tendon slippage increased to a certain extent. In addition, the LTP of the composite anchorage can be effectively improved by appropriately decreasing pre-tightening force and over-tensioning force. When the over-tensioning force was 1.4 times the test load, the tendon slippage was reduced by 34.2%, and the residual load ratio increased by 4.8%. The greater elastic modulus of the bonding medium in the range of 2.1 GPa–3.1 GPa, the worse the LTP of the composite anchorage.

Finite Element Analysis of Load-Bearing Characteristics and Design Method for New Composite-Anchor Uplift Piles

This paper introduces a new type of uplift pile known as the composite-anchor pile, which employs a composite anchor composed of steel strands, grouting materials, and steel pipes as the main reinforcement. This paper extensively analyzes this pile’s load-bearing capacity and deformation characteristics through full-scale field tests and three-dimensional finite element numerical simulations. The results show that the composite-anchor pile has a more even distribution of stress, and its endurance and mechanics performance are better than others. Furthermore, this study utilizes a three-dimensional finite element refined model that has been validated using on-site test results to examine the influence of key parameters, such as the pile diameter, the number of composite-anchor cables, and the diameter of steel strands, on the load-bearing capacity of uplift piles. Building upon these findings, this paper introduces a calculating method to determine the bearing capacity of composite-anchor piles, thereby addressing the existing gap in this field.

Experimental study and failure mechanism analysis at the meso-scale of the fatigue performance of a CFRP tendon novel composite anchorage

This paper investigates the fatigue performance of CFRP tendon novel composite anchorages. The fatigue mode of the novel composite anchorage was analysed. Furthermore, based on the meso-morphology of the contact surface between tendons and epoxy resin, the fatigue mechanism of composite anchorage was explored. Finally, the effects of fatigue cyclic load on the slippage of tendons at both free end and loaded ends and clamps, the barrel strain and the stiffness of CFRP tendons were investigated. Results revealed that the novel composite anchorage can subject 2 million fatigue cycles load under 0.45 fu fatigue maximum stress and 200 MPa stress range. The failure modes of FS-2, FS-3 and FTD-1 specimens with fatigue failure were the damage of the contact surface between the tendons and the epoxy resin, which leads to the tendons slip out from the epoxy resin. Furthermore, the fatigue performance of the three-tendon specimens with dispersed anchoring was worse than that of the anchorage with parallel anchoring. Steel barrels and clamps can work effectively in all specimens, but the tendons stiffness increases slightly initially and then decreases rapidly. In summary, the novel composite anchorage has good fatigue performance and the potential for practical application.

Experimental Investigation on the Anchorage Performance of a Tension–Compression-Dispersed Composite Anti-Floating Anchor

Rapid advancements in construction technologies have accelerated the development of complex and deep underground structures, raising concerns about the impact of groundwater on structures, particularly anti-floating measures. Traditional tensioned anchors, commonly used for preventing flotation, suffer from limitations like low pull-out bearing capacity, shallow critical anchoring depth, and localized stress concentration. To overcome these limitations, this paper introduces a tension–compression dispersed composite anchor, which combines casing, load-bearing plates, and tensioned anchors. Comparative tests were conducted between these composite anchors and traditional tensioned anchors to analyze their anchoring behavior. Our results show that tensioned anchors exhibit a stable axial force distribution as anchoring length increases. By identifying abrupt changes in the axial force curve, optimal anchoring lengths for load-dispersed anchors can be determined, thereby enhancing rock and soil strength utilization. The tension–compression-dispersed composite anchor outperforms tensioned anchors, with 1.44 times the ultimate bearing capacity for equivalent anchoring lengths and 1.1 times the capacity for an additional 1 m length. It also displays superior deformation adaptability and structural ductility under high-bearing loads compared to tensioned anchors with extended anchoring lengths. Effectively mobilizing the strength of the lower anchoring segment within the rock and soil results in a lower critical anchoring depth and a more uniform distribution of lateral friction resistance. In conclusion, the tension–compression-dispersed composite anchor offers significant advantages, making it a promising engineering solution for anti-floating anchor systems in complex underground environments.

Structural performance evaluation of thin‐walled concrete filled steel tube column to reinforced concrete wide beam connection

Abstract[Abstract: This study summarized the full scale test results of the thin walled concrete filled steel tube column to reinforced concrete wide beam connection. The thin walled concrete filled steel tube column to reinforced concrete wide beam connection does not have any structural element that can reliably transfer shear forces and moments between steel column face and concrete, while in the conventional reinforced concrete system, continuity is ensured by the monolithic casting of concrete. The composite anchor is needed to effectively transfer the moment and shear force of the wide beam to the column. In order to verify the efficiency of the proposed composite anchor, nine full size specimens were fabricated and tested by applying a load downward to the upper column of the specimen upside down in order to simulate the gravity load imposed on the beam. Experimental results show that the strength of thin walled concrete filled steel tube column and reinforced concrete wide beam connections with the proposed composite anchor can exhibit superior performance than that of the conventional reinforced concrete beam to column system.

Short-Term Performance of New Composite Anchorage with Multiple CFRP Tendons

The relatively low shear strength of carbon fiber-reinforced polymers (CFRPs) makes it difficult to anchor CFRP tendons. Although many anchorages with CFRP tendons have been developed, few studies have been conducted on composite anchorages with multi-CFRP tendons. In this study, four groups of new mechanical clamping–bonding composite anchorages with multi-CFRP tendons were designed, and the stress of each component of the anchorage was analyzed to reveal the force transmission mechanism of the anchorage. Moreover, the short-term performance of the anchorages was experimentally investigated. The key parameters, including the elastic modulus of the bonding medium, preloading force, cone angle, and bond length, were further analyzed using the finite-element method. The results showed that the composite anchorage reliably anchored multiple CFRP tendons, and the efficiency coefficients of the four anchorages were greater than 0.95. The suggested minimum bond length was approximately 35 times the diameter of the CFRP tendon when anchoring fewer than five tendons. Finally, a sufficient preloading force could effectively reduce the initial slip, whereas increasing the cone angle and elastic modulus could reduce the final slip.

Experimental study on the mechanical properties and failure modes of BFRP bar anchor systems under static tension loading

Basalt fiber-reinforced polymer bars are lightweight composite materials with high strength, low density, and excellent corrosion resistance. The anchor system made from basalt fiber-reinforced polymer bars is worthy of being developed and expected to be used in rock anchoring projects. In this work, four different basalt fiber-reinforced polymer anchor systems were designed, the influences of different design parameters on the ultimate bearing capacity of the anchor system were investigated through tension tests, and the failure modes of different anchor systems were elucidated. The test results indicated that failure modes, such as the transverse fracture of these bars and debonding of the bonding medium, were widely present in the wedge-modified anchor system and the steel-pipe-protected anchor system. These two anchor systems performed poorly with the wedge anchorage, whereas the basalt fiber-reinforced polymer bars protected by seamless steel pipes burst under the tension imposed by a universal testing machine. The threaded steel-pipe-bonded anchor system and the steel strand–basalt fiber-reinforced polymer bar composite anchor system had maximum anchorage efficiency coefficients of 97.7% and 98.5%, respectively. The bars in the corresponding test groups all exhibited burst failure, indicating that these two anchoring structures achieved effective anchorage of the basalt fiber-reinforced polymer bars.

Experimental and theoretical analysis on the long-term performance of novel carbon fibre-reinforced polymer tendon composite anchorage

Carbon fibre-reinforced polymer (CFRP) has the advantages of light weight, high strength and superior corrosion resistance. In this study, the long-term performance of novel CFRP tendon composite anchorages was assessed, and the influences of the number of tendons, load level and over-tensioning was analysed. Then, the residual anchoring capacity of the anchorage after long-term performance test was determined. Finally, the slippage of CFRP tendons and the load loss were analysed based on the time strengthening theory. Results revealed that the composite anchorage had excellent long-term performance, and the six groups of specimens were intact after a long-term experiment. Over-tensioning significantly improved the long-term performance of specimens by reducing the load loss caused by the tendon slippage and the slippage of each measuring point. Furthermore, results of the long-term experiment showed that the residual anchoring efficiency of the remaining specimens was greater than 0.95, except for one group of specimens, because of incomplete axial tension. Eventually, the theoretical analysis results showed that over-tensioning can effectively reduce the load loss caused by the creep effect of the free section tendon. In summary, the novel composite anchorage displayed excellent reliability. This study provides a research case for the long-term performance of CFRP tendon anchorage and a basis for the application of the novel composite anchorage in practical engineering.

Load-bearing performance of caisson-bored pile composite anchorage foundation for long-span suspension bridge: 1-g model tests

Load-bearing performance of caisson-bored pile composite anchorage foundation for long-span suspension bridge: 1-g model tests

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

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

Development of a New Uplift Pile with Prestressed Semi-Bonded Composite Anchor

This paper introduces a new type of prestressed uplift pile that adopts the semi-bonded composite anchor as the main reinforcement. An in-situ experimental study was carried out to investigate the new pile’s deformation, stress, bearing capacity, and cracking characteristics, which were then compared with the conventional piles. Results show that although the reinforcement ratio of the new pile is only 0.75%, much less than that of the conventional pile (i.e., 3.84%), it achieves similar or even better mechanical properties under uplift loads. The cost of the pile’s anchorage system is reduced by 43.8%, and the total cost of a single pile is reduced by 33.6%. Compared with the conventional pile, the new pile makes better use of the lateral friction resistance of the lower pile body, and the uplift bearing capacity and the uplift resistance of the pile are improved correspondingly. In addition, the cracking resistance of the new pile is significantly improved, with the cracking load increased by 88.2% and the cracking area reduced by 48.3%. In addition, the multi-layer structure of the composite main bar provides better protection for the load-bearing steel strands against corrosion. As such, the new type of pile is expected to gain much better durability than the conventional ones.

Optimal Design of a Novel Composite Anchorage for Carbon-Fiber-Reinforced Polymer (CFRP) Tendons.

In this study, we proposed a novel composite anchorage that considers the anchoring performance and dimension simultaneously. The design concept of this composite anchorage was first introduced, followed by comparison with the traditional inner-cone bond-type anchorage and traditional composite anchorage through theoretical and experimental methods. Then, a parametric study was conducted to determine the influence of different parameters on the anchoring performance, and the optimal design parameters were recommended according to the finite element (FE) and test results. Finally, the practicability of the optimal design parameters were validated through experiments on the anchorage with multiple CFRP tendons. Results showed that the novel composite anchorage could improve the anchoring performance compared with the traditional inner-cone bond-type anchorage by promoting increased anchorage efficiency by 60.4% and, with an ideal failure mode of tendon rupture. Moreover, the novel composite anchorage had smaller dimensions and avoided the presence of a vulnerable position at the junction of the mechanical and bond parts compared with the traditional composite anchorage. In addition, a group of optimal design parameters of this composite anchorage with a pre-tightening force of 130 kN, an inclinational differential angle of 0.1°, an inclination angle of 2.9°, and an embedded length of 30 d~40 d were proposed. The composite anchorage with five CFRP tendons designed with the proposed parameters failed with the rupture of the tendons and exhibited an anchoring efficiency of 1.05. This result showed that the optimal parameters were suitable for this novel composite anchorage to grip multiple tendons. This study can provide an experimental and theoretical basis for designing large-tonnage anchorage for multiple FRP tendons used as hangers or cables in real bridges.

Analysis of Multi-Tendon Friction-Based Composite Anchorage Device for CFRP Cables and Its Anchorage Mechanism

Carbon fiber-reinforced polymer (CFRP) cables are anticipated to be employed in larger, longer, and more durable structures in the engineering field. However, its anchorage devices and mechanism should be appropriately developed and improved. At present, mainly relying on the adhesive force, most anchorage devices may lose their efficiency because of adhesive aging and failure or the slip of an individual tendon. A friction-based composite anchorage device with an integrated bearing of inner cone filler (i.e., load transfer media (LTM)) bonding and a single extruding anchor is proposed, and the anchorage mechanism is examined for Φ7 CFRP cables of strength 2400 MPa. Firstly, sufficient conditions for anti-slip failure of CFRP tendons in the anchorage zone are derived by assuming uniform LTM bonding. The obtained results reveal that the smaller inner pore size of the barrel leads to higher efficiency. Additionally, the maximum efficiency depends on the friction coefficient of the contact surface, the inner cone angle of the barrel, and the diameter and quantity of the CFRP tendons. The necessary conditions for the safety of the CFRP tendon anchorage zone are carefully obtained based on the Tsai–Wu failure criterion. It is concluded that the compressive stress of CFRP tendons in the anchorage zone should gradually increase from the load-bearing end to the no-loading end. Additionally, the relations among the anchorage efficiency coefficient and the CFRP tendon diameter d, the anchorage length l, the dip angle of LTM external conical surface α, and the friction angle β are derived based on the equivalent failure principle. The CFRP cables of four specifications (i.e., with Φ12, Φ19, Φ37, and Φ121 tendons) are designed under theoretical guidance, and eight static tests are carried out for more verification studies. The test results indicate that the anchorage efficiency coefficient of designed anchorage devices can be over 90%, and even up to 96.8%. Further, the failure modes are divergent destruction, which verifies the reliability of friction-based anchorage devices and provides a solid theoretical foundation for the design and engineering applications of CFRP cables.

Experimental Study on the Local Behavior of CFRP Anchor Spikes Fixed to Masonry Substrates

An experimental investigation aimed to analyze the mechanical behaviour of Carbon Fiber Reinforced Composite (CFRP) anchor spikes inserted in a brick substrate is reported in this paper. As is well known, such devices can improve the structural performance of CFRP sheets externally bonded to masonry elements (as well as others substrate materials). In structural applications, spike anchors can be subjected to both shear and/or normal actions; the first commonly occurs in structural applications, while the latter may occur in specific applications, such as CFRP sheets bonded to curved surfaces. For this reason, the experimental program described in this paper analyzes the mechanical behavior of a typology of anchor spikes loaded (separately) by pure shear or normal actions. Although, obviously, in anchored CFRP sheet reinforcements the contribution to the bearing capacity of the sheet and of the anchors cannot be additively superimposed (the total capacity is of course not equal to the sum of the capacity of the sheet and of the anchor), the results described in this paper can still give useful indications in practical applications.

Load Transfer Law of Anti-Floating Anchor With GFRP Bars Based on Fiber Bragg Grating Sensing Technology

The glass fiber-reinforced polymer (GFRP) anchor, a new type of composite material anchor, has been widely used in foundation engineering of coastal areas. This study investigated the feasibility of applying the fiber Bragg grating (FBG) sensing technology to monitor the strain of the GFRP anchor during the pull test. Based on an advanced method, the FBG strain sensors were installed in GFRP anchors during the anchor manufacturing process. Then, GFRP anchors were installed into the pre-created borehole with an M30 cement mortar. Meanwhile, the FBG temperature sensors were installed next to the GFRP anchors to monitor the temperature change during the test. The axial force and average shear stress of GFRP anchors along depth during the pull test were analyzed, and the influence of temperature change on strain measurement was studied. The test results showed that the FBG sensing technology and the installation method of FBG strain sensors used in the test were feasible to monitor the mechanical properties of the GFRP anchor during the pull test. Moreover, the effect of temperature change on strain monitoring of FBG strain sensors was negligible.

Comparative Study on the Anchor Performance of Wooden Tension Anchor Bolts and Tension–Compression Composite Anchor Bolts in Earthen Sites

ABSTRACT The full-length bond wood tensile anchor system (WTS) conventionally used in earthen sites is primarily broken by the debonding of the bolt–slurry interface. To solve this limitation, material performance and pull-out tests were performed for a new type of wood tension–compression composite anchor system (WTCS) and WTS, and the strain of the bolt–slurry and the slurry–soil interface were monitored. A comparison of test results indicated the following: The average pull-out force of the WTCS is approximately 23–51% higher than that of the WTS. The WTCS has the strong ductility characteristics of small elastic and large plastic deformation. As the load increases, the strain at the bolt–slurry interface changes from a negative index of low strain to a high-strain “S” curve at the end along the bond length. The peak value of slurry–soil interface strain exhibits a transition from the front part of bond length to the middle and back parts of bond length. The mechanical operating mechanism between bolt and slurry is divided into three simplified progressive structural force models, namely “1,” “T,” and “Y.” Finally, the calculation formulas of the average pull-out force of the WTCS are provided.