Bond-type Anchorage Research Articles

Mechanical performance of a bond-type anchorage system for CFRP cable exposed to elevated temperature

Both high-temperature pullout tests without and with pre-tension load were conducted on the bond-type anchorage system specimens with bonding medium of UHPC (Ultra-high Performance Concrete) for Carbon fiber reinforced polymer (CFRP) cable in order to fully understand the bonding behavior of CFRP cable-UHPC interface under high temperature. The variation laws of ultimate pullout load, average bond strength of CFRP cable-UHPC interface and slippage corresponding to ultimate pullout load were uncovered in two types of high-temperature pullout tests. Then, the bond performances of CFRP cable-UHPC interface in high-temperature pullout tests with pre-tension load ratio from 0.2 to 0.6 and target temperature in the range of 100–210 ℃ were compared to these in high-temperature pullout tests without pre-tension load in order to identify the effect of temperature-load path. Finally, theoretical models for determining average bond strength of CFRP cable-UHPC interface and critical bond length of CFRP cable for the bond-type anchorage system under high temperature were developed by incorporating effects of high temperature and pre-tension load ratio. The obtained results demonstrate that the dominant failure mode of the bond-type anchorage system in high-temperature pullout tests is slip failure of CFRP cable-UHPC interface, and shear failure morphologies of embossed rid for CFRP tendon are closely correlated with target temperature. In high-temperature pullout tests without pre-tension load, the average bond strength of CFRP tendon-UHPC interface gradually decreased as the increasing target temperature, the corresponding attenuation ratios in temperature ranges of 25–300 ℃ and 300–400 ℃ are 84% and 47%, respectively. In high-temperature pullout tests with pre-tension load, the average bond strength of CFRP tendon-UHPC interface approximately linearly decreased as the increasing target temperature or pre-tension load ratio. The presence of pre-tension load results in acceleration of damage of CFRP cable-UHPC interface, and the damage degree is proportional to pre-tension load. The developed theoretical models of mechanical properties for the bond-type anchorage system exposed to high temperature can accurately predict average bond strength of CFRP cable-UHPC interface and critical bond length of CFRP cable.

Effect of various factors related to the bond-type anchorage system on tensile performance of carbon fiber-reinforced polymer strand cables

Steel strands, which are most frequently used as internal/external tendons of prestressed concrete (PSC), are highly susceptible to corrosion, which degrades the structural stability of the PSC structures. Studies are underway to utilize carbon fiber-reinforced polymer (CFRP) strands in PSC structures as tendons to achieve structural performance comparable to that of existing steel strands, with the additional feature of corrosion resistance. However, such applications of CFRP strands require the accurate identification of the intrinsic properties of the material. This study conducted an analysis to establish a test method using bond-type anchorage that can evaluate the intrinsic properties of CFRP strands by setting several factors related to the bond-type anchorage system as variables. Tensile tests were conducted on the CFRP strands after fabricating the specimens according to the variables of the bond-type anchorage system (shape of the CFRP strand located inside the steel pipe and type of internal filler material). In addition, the compressive strength was measured to determine the mechanical properties of the cementitious filler materials. Based on the experimental results, the load-displacement curves, stress-strain curves, fracture shapes, and tensile strengths of various cases of CFRP strands were analyzed. The results of the study revealed that the split-strand CFRP fabricated with CP0.25 mixture as the bond-type anchorage system had the ability to fully obtained intrinsic tensile properties.

Experimental tensile tests on carbon fibre cords with bond-type anchorages

Despite the potential interest for civil engineering structural applications, few studies have explored the feasibility of employing carbon fibre cords as prestressed elements in strengthening systems. This research presents a large experimental campaign to investigate the tensile behaviour of straight carbon fibre cords connected to a bond-type anchorage. Specifically, 78 tensile tests have been performed varying several parameters: anchorage geometry, resin type, cord cross sectional area, and fibre free-length and treatment (unimpregnated or impregnated with resin). The results shed light on their role on the structural response, and highlight the existence of size effects regarding fibre free-length and cross sectional area of the cord. These phenomena are magnified in unimpregnated specimens, and, de facto, may prevent their use in full-scale post-tensioned applications.

Static Experimental Study on New Arc Multi-Tendon CFRP Cable Anchorage System

CFRP has the potential to replace steel cables in large-span cable-stayed bridges due to its high strength and lightweight material properties. However, the weak lateral force performance of CFRP material creates the challenge of anchoring. This study introduces a new inner cone + arc + straight cylinder bond-type anchorage system to optimize CFRP tendons’ force state. Experimental and finite element analyses verified the new anchoring system’s performance. In static load tensile tests, six groups of seven CFRP tendon anchorage systems with different sleeve grooves were used to study the failure mode and load–strain variation law. The difference in mechanical properties between the new and traditional anchorage is evaluated in the finite element analysis. The results indicate that the new anchorage system can lower the stress concentration in the anchorage zone and enhance anchorage performance. The groove design of the sleeve can effectively increase the anchoring efficiency, where the groove depth is proportional to the anchoring efficiency and the groove spacing is inversely proportional to the anchoring efficiency. The magnitude of the stress inhomogeneity in the multi-tendon anchoring system during tensioning is proportional to the beginning conditions and the load size. When the inner wall of the sleeve becomes more abrasive, the force heterogeneity of the anchorage system reduces. The tests and finite element analysis show that the new anchoring may improve stress distribution and anchorage efficiency. In engineering practice, it can be utilized as a dependable anchorage system.

Bond behavior of an ultra-high performance concrete-filled anchorage for carbon fiber-reinforced polymer tendons under static and impact loads

To investigate the bond behavior of an ultra-high performance concrete (UHPC)-filled bond-type anchorage for carbon fiber-reinforced polymer (CFRP) tendons, both static tensile tests and impact tests were performed on 20 groups of specimens. The anchorages with embedded lengths of 50, 100, 150 and 200 mm were subjected to the static tension and longitudinal impact loads with drop heights of 150, 300, 600 and 900 mm. During the tests, the longitudinal tension and slip of the anchorage were obtained, and the effect of anchorage length and loading rate on the bond behavior was discussed. The results show that in the static tests, slip failure occurred for the anchorages with lengths from 50 to 150 mm, and CFRP bar ruptured as the length raised to 200 mm. When subjected to impact loads, slip failure was observed for all specimens. The damages on the CFRP bar to UHPC interface under impact loads were slighter than those under static tension, and correspondingly the dynamic bond strength was approximately half of the static one owing to the weakened mechanical interlocking. With increasing the embedded length, the bond strength and slip increased due to the radial constraining effect of outside steel tube. Based on the experimental results, a strain rate-dependent function was proposed to quantify the retention of bond strength under impact loads, and prediction formulas were established for determining the dynamic bond strength and critical embedded length of the bond-type anchorage.

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.

Evaluation of a new bond-type anchorage system with expansive grout for a single FRP rod

Prestressed concrete applications require a high strength prestressing material that could apply and maintain effective compressive force to concrete members. Although fiber reinforced polymer (FRP) materials, especially carbon FRP (CFRP), have the desired strength, no efficient system for its anchorage to concrete has been devised yet. This paper presents an experimental evaluation on a new bond-type anchorage system using an expansive grout as a filling material to anchor CFRP rods. A total of twelve specimens were fabricated and tested. Short-term and long-term pullout tests were performed. The CFRP rods were 0.375 in. (10 mm) and 0.50 in. (13 mm) in diameter. The parameters investigated were the bond length, rod diameter, and curing time of the expansive grout. The experimental results showed that 12 in. (305 mm) and 15 in. (381 mm) were adequate bond lengths to effectively anchor the 0.375 in. (10 mm) and 0.50 in. (13 mm) CFRP rods, respectively. The results also indicated that the anchor strength and stiffness were directly proportional to the bond length, and cross-sectional area ratio of CFRP rods to anchor borehole affected the stiffness and bonding capacity of the proposed anchor. Finally, a numerical analysis was carried out to predict the tensile behavior of FRP anchors. The numerical results had good agreement with the experimental results.

The influence of load transfer medium creep on the load-carrying capacity of the bond-type anchors of CFRP tendons

The epoxy resin used as a load-transfer medium (LTM) to fill the bond-type anchors of carbon fiber reinforced polymer (C225FRP) will creep under three-dimensional compressional conditions, thereby decreasing the carrying capacity of the anchorage. In this paper, a shear stress distribution model is proposed for the tendon–LTM bonding interface in the anchorage zone of CFRP tendon bond-type anchors. Based on this distribution model, a model for evaluating the load-carrying capacity of such anchorages is established after considering LTM creep. Creep deformation data were obtained via model tests of an anchorage epoxy resin LTM subjected to three compressive magnitudes of stress under lateral restraint conditions for 3 years. The influence of LTM creep on the load-carrying capacity of the anchors is evaluated, and theoretical methods for eliminating the negative effect of the LTM creep of the anchor were proposed. The two load-carrying capacity prediction models established before and after considering LTM creep were verified by experiments. The experimental results pertaining to load-carrying capacity are in good agreement with the theoretical prediction; the creep strain of the LTM will reach 0.004 and 0.038 under axial compressive stresses of 50 MPa and 250 MPa, respectively, and lateral restraint conditions. LTM creep will lead to an obvious reduction in the radial compressive stress of the bonding interface, and the loss of the load-carrying capacity of the anchorage can reach 12%. Increasing the axial preset load acting on the LTM or extending the length of the anchor can counteract the adverse effects of creep.

Mechanical Behavior and Optimal Design Method for Innovative CFRP Cable Anchor

AbstractTo overcome the drawbacks of bond-type anchors for carbon fiber–reinforced polymer (CFRP) cables, an innovative bonded anchor with steel wedges at the free end is developed in this study. T...

A theoretical solution for the pullout properties of a single FRP rod embedded in a bond type anchorage

ABSTRACTThis paper proposes a theoretical solution for predicting the pullout properties of a single fiber-reinforced polymer (FRP) rod embedded in a bond type anchorage based on a trilinear bond–slip model. The radial variation of the shear stress and reaction of the steel sleeve are considered in the solution. Pullout procedure with elastic, elastic-softening, elastic-softening-debonding, pure softening, softening-debonding, and debonding stages, as well as the corresponding critical stages, are analyzed. In this theoretical solution, the maximum pullout load, shear stress along the rod–grout interface, axial tensile stress of the FRP rod, and load–slip relationship are derived with explicit formulations. Effective bond length of bond type anchorage is also discussed. The solution is validated against experimental results available in literature. The theoretical solution reveals that the anchorage may attain its maximum pullout load in the elastic-softening, pure softening, or elastic-softening-debonding stage. Moreover, the effects of embedded length, ultimate shear stress, and residual shear stress on maximum pullout load closely related with the stage in which the anchorage attains its maximum pullout load. However, the effect of radius of FRP rod on the maximum pullout load increases with the embedded length, no matter in which stage the anchorage attains its maximum pullout load.

Experimental investigation on the mechanical properties of a bond-type anchor for carbon fiber reinforced polymer tendons

Carbon fiber reinforced polymer (CFRP) has gained popularity in civil engineering applications due to its high tensile strength, light weight, corrosion resistance, and fatigue resistance. However, the anchorage of CFRP tendons has been a challenge due to the relative low transverse shear strength of CFRP. To study the mechanical properties of bond-type anchor for CFRP tendons, straight-type, inner-cone-type, and composite-type anchors were developed in this study. The bond-slip behavior of CFRP tendons inside anchors and multiaxial stresses of the steel sleeve were experimentally tested. The effects of anchor type and length on the anchorage performance of CFRP tendons were studied with the focus on the anchoring mechanism. Test results demonstrate that the composite-type anchor exhibits the most reliable load-transfer mode and can eliminate the notch effect occurred in the inner-cone-type anchor. The peak bond stress initially occurs at the loading end of the anchor and gradually moves to the free end of the anchor as the load increases. This is related to the gradual failure of chemical adhesive between the CFRP tendon and the colloid. Besides, bond-slip relationship of CFRP tendon inside anchor is nonlinear. The slippages of CFRP tendons are initially small but increase quickly with increasing load. When approaching failure, the slippages increased significantly. In addition, the slippage of the anchor with scattered-end tendon is smaller than that with non-scattered-end tendon, indicating that the anchor with scattered-end tendon has superior bonding property.

Bond characteristics of near-surface-mounted anchorage for prestressing

The external bonds of carbon fiber reinforced polymers (CFRP) used to strengthen structures are known to be vulnerable to delamination. To prevent FRP delamination and efficiently strengthen structures, post-tension CFRP rods are installed for near-surface-mounted (NSM) strengthening. For post-tensioning, grouted anchorage systems have been applied to the NSM strengthening technique. The bond behavior between the CFRP rods and the filler in the anchorage for the post-tension rods should be investigated. This study evaluates the behavior and failure characteristics of bond-type anchorage systems based on the results of 40 pullout tests with different mortar fillers and diameters of the anchorage sleeve. The optimum mortar filler strength and sleeve diameters have been proposed to ensure proper bond behavior in NSM anchorage systems.

Single and multiple impact behavior of CFRP cables under pretension

The vulnerable transverse behavior of the carbon-fiber-reinforced polymer/plastic (CFRP) restricts the application of CFRP cables in bridges, when considering the possible collisions from vehicles. This paper presents an experimental investigation on the transverse impact behavior of the CFRP cable system. Drop-weight impact tests were conducted on six specimens. Each specimen composed of a seven-wire CFRP strand and two reactive powder concrete (RPC)-grouted bond-type anchors at both ends. Test results showed that the RPC grouted bond-type anchor provided a reliable anchorage to the CFRP strand during both single and multiple impacts. For single impact of a specimen under a pretension of 40kN, the average transverse impact resistance and energy dissipation capacity were approximately 16kN and 727J, respectively. The successive two impacts induced damage led to reductions of 37% in transverse resistance, 30% in maximum cable tension, 39% in transverse stiffness, 20% in energy dissipation capacity. A modified SDOF model based on nonlinear geometric stiffness and available impact energy was established for the prediction of the impact force and deflection of a CFRP cable under single and multiple impacts.

An experimental study on bond-type anchorages for carbon fiber-reinforced polymer cables

It is well-known that the axial performance of carbon fiber-reinforced polymer (CFRP) cables is excellent, while the lateral compression and shear strengths are low. Thus, traditional steel cable anchorages cannot be used for CFRP cables due to the local crushing failure mode that would develop. Hence, a new bond-type anchorage filled with resin was proposed and five CFRP cables were fabricated with the new anchorage, which were tested statically to failure in tension. The tensile capacity, bond strength and pullout behavior of the new anchorage for CFRP cables were observed experimentally and are presented in this paper. The load–slip behavior of the new anchorage, sustained loading effect, load–deformation curves and the stress variation between tendons in the cables are also presented and discussed. Tensile fracture of the tendons was observed for all the five cables tested with efficiency coefficients all greater than 1.00. The tensile strength and overall performance achieved by the anchorage and CFRP cable system satisfied the design requirements for use in an experimental cable-stayed bridge constructed in China.

Application study on the first cable-stayed bridge with CFRP cables in China

In order to push forward the development of CFRP cable-stayed bridge and accumulate experiences, the study on the application of the first cable-stayed bridge with CFRP cables in China was carried out. The design essentials of main components of the bridge were introduced and its integral performances, including static properties, dynamic properties and seismic response were analyzed using finite element method. A new bond-type anchorage was developed and the processes of fabricating and installing CFRP cables were elaborated. Based on the results of construction simulation, a tension scheme for bridge was propound. During constructing, the stresses and displacement of girder and pylon, as well as the forces and stresses of cables, were tested. The results indicate that all sections of the bridge could meet the requirements of the ultimate bearing capacity and normal service; the performance of the anchorage is good and the stresses in each cable system are similar; the tested values accord well with the calculated values. Further, creep deformation of the resin in anchorages under service load is not obvious. All these results demonstrate that the first application of CFRP cables in the cable-stayed bridge in China is successful.

A Fundamental Study on Anchor Performance of CFRP Tendons with Compressed Anchor Sleeve

The anchoring of CFRP tendon can be performed by wedging, bonding or compressing. The wedge type anchor, used for PS steel tendon, is inappropriate for direct application to the CFRP tendon due to its low lateral stiffness. Since the bond performance of the CFRP tendon depends on the anchor performance, the bond type anchor presents the problem of requiring long steel sleeve in case of low bond performance or high tensile performance. Compared to the bond type anchor, the compressing type anchor offers better applicability but necessitates the development of a sleeve fitted to the dimensions of each CFRP tendon. This study intends to examine the anchoring characteristics of the compressed sleeve for the temporary anchorage of a CFRP tendon with diameter of 10 mm. To that goal, the properties of the 10 mm-diameter CFRP tendon were assessed using the bond type anchor and the corresponding anchor performance is compared to that of the compressed anchor. The test results revealed that the use of spacers in the compressed anchor provided lower anchor performance due to the characteristics of the spacers. For the specimen without spacer, the micro-deformations formed inside the sleeve were seen to compress the CFRP tendon by gearing directly the tendon and to provide anchor performance reaching about 72% of the tensile strength of the CFRP tendon. Further study shall develop a sleeve with increased compress force on the CFRP tendon so as to improve the anchor performance of the compressed sleeve. Moreover, solution shall also be provided to introduce a uniform compress force.

An Experimental Study on Anchor Performance of Bare CFRP Tendons with Bond Type Anchor

Despite of their outstanding axial strength, CFRP tendons necessitate special anchorage due to their low lateral shear strength. In order to cope with such CFRP tendon, the conventional bond type anchor needs to be improved. The results of bond tests executed on 10-mm diameter CFRP tendons coated with sand and oxide revealed that, even if the average bond strength increases by 3 times compared to the non-coated bare tendon, the coated CFRP tendon still requires excessively long anchored length for bonding. Therefore, this study applies a method enabling to shorten the bonded length and improving further the bond performance compared to sand or oxide coating. The improvement of the bond characteristics is achieved by splitting the ends of the CFRP tendon so as to widen the bonded area by 3.5 times. The test results showed that the anchor performance of the CFRP tendon reaches 95% of its tensile strength making it applicable for the bond type anchor.

Study and Prototype Design of a Suspension Bridge with Ultra-Long Span and CFRP Main Cables

Using nonlinear numerical methods, the structural systems of cables system, stiffening beams, pylons, and bearing systems are comparatively analyzed. This study demonstrates the technical feasibility of suspension bridges with a 3,500 m main span and Carbon Fiber Reinforced Plastic (CFRP) main cables. Using fine finite element structural simulation, the parameter sensibility of a suspension bridge structural system with a 3,500 m main span and CFRP main cables is analyzed, and the influence of structural parameters on the static and dynamic performance of super-long span suspension bridges is discussed. In combination with numerical analysis of a structural system model, the optimum structural system of a suspension bridge with a 3,500 m main span and CFRP main cables is determined. The physical model is set up to allow theoretical measurements of the anchorage, sliding, and bending moment of the CFRP main cable strands as well as static load and fatigue testing. A bond-type anchorage that can be applied to real bridges is developed, which has an anchorage efficiency coefficient of 100%. The sliding resistance and bending performances are verified: the frictional coefficient between CFRP main cable strand and saddle is about 0.5, the frictional coefficient between the CFRP main cable strand and clamp is up to 0.331, the bending strength of the CFRP wire at the saddle point is over 90% of its tensile strength, and there is almost no bending problem at the clamp. A bridge prototype design is produced based on the test results.

Experimental investigation of a bond-type anchorage system for multiple FRP tendons

This paper presents a bond-type anchorage system for multi-rod CFRP (Carbon Fiber-Reinforced Polymer) tendons with a bonding medium of ultra-high performance RPC (Reactive Powder Concrete). A full-scale specimen of the CFRP tendon-anchorage assembly GA12-9 for nine 12.6-mm-diameter CFRP rods was made, and its behavior was studied extensively through tensile tests. During the tests, the load distribution among the rods in tendon was monitored until the bonds of the multi-rod system failed. The test results showed that the capacity reduction resulting from inherent non-uniformities in multi-rod anchoring systems should be considered, and the corresponding capacity reduction factor has been provided. Furthermore, the equations for evaluating the bond strength and critical bond length of either single or multiple CFRP rods embedded in RPC grout were established and shown to be in good accordance with the test results. For a CFRP rod with a wrapped surface and tensile strength of 2300MPa, a bond length of 25 times the rod diameter ensures that a tendon of 9 rods with clear spaces among rods of not less than a rod diameter can be anchored in a RPC medium of 130MPa.

The Static Test Study on Anchors of CFRP Cables

The axial performance of CFRP is excellent, while the lateral compression strength and shear strength are low, thus they can’t be anchored by traditional anchors. A new type of adhesive anchor was designed and five experimental cables were fabricated and the static tests were carried out. In the tests, the tensile capacity, bond strength and pullout behavior of CFRP cables anchors filled with resin were discussed. The efficiency coefficients and the load-slip behaviors of the bond-type anchors and the uniformities of the stresses in the tendons were studied. Several conclusions are drawn which have become powerful evidences for using the bond-type anchors in the first cable stayed bridge with CFRP cables in China.