Carbon Fiber Reinforced Polymer Tendons Research Articles

Shear behavior of ultra-high-performance concrete beams prestressed with external carbon fiber-reinforced polymer tendons

Shear behavior of ultra-high-performance concrete beams prestressed with external carbon fiber-reinforced polymer tendons

Flexural Behavior of UHPC Beams Prestressed with External CFRP Tendons

This paper presents an experimental investigation on the flexural behavior of ultra-high-performance concrete (UHPC) beams prestressed with external carbon fiber-reinforced polymer (CFRP) tendons. A total of eight T-shaped beam specimens were fabricated and tested, and the effects of the effective prestressing stress, partial prestressing ratio, deviated angle, and loading condition on the flexural behavior were analyzed. The experimental results indicate that the fully prestressed beams experienced a brittle failure, and the shear capacity of these beams was mainly controlled by the effective prestressing stress in CFRP tendons and the ultimate tensile strength of UHPC, whereas the partially prestressed beams failed in a ductile manner. The presence of internal steel reinforcement could significantly improve the flexural capacity and deformation ability. Thus, internal reinforcements should not be omitted from UHPC beams with CFRP tendons. A higher effective prestressing stress resulted in enhanced cracking load and flexural capacity. The deviated angle enhanced the utilization efficiency of high strength CFRP tendons. The loading condition exerted a slight influence on the flexural behavior of the specimens. Moreover, a method considering the effect of steel fibers was proposed and verified to predict the flexural capacity of UHPC beams prestressed with external CFRP tendons.

Centrifugirani betonski stupovi armirani nemetalnom armaturom

The article describes the testing of poles for electric power transmission lines, which are made of centrifugally-cast concrete and ultra-high strength concrete, and which are prestressed with Carbon Fibre Reinforced Polymer tendons (CFRP). The presented results of pole ultimate load testing suggest the potential for usage of this construction product, particularly in aggressive environments with high probability of steel corrosion. Part of the tested poles had shear reinforcement in the form of confined Glass Fibre Reinforced Polymer (GFRP) grid, while one share of samples had no shear reinforcement, but the concrete matrix was strengthened with synthetic macro fibres. A review is given on similar product testing, calculation methods, and guidance is provided for further research.

Shear Behavior of Post-Tensioned Concrete Beams with Draped FRP Tendons and without Transverse Reinforcement

To investigate the shear behavior of post-tensioned concrete beams with fiber-reinforced polymer (FRP) reinforcements, six large-scale post-tensioned beams without transverse reinforcement and with a shear span-to-effective depth ratio of approximately 3.0 were tested to failure. All beams were longitudinally reinforced with draped prestressed carbon FRP tendons and non-prestressed glass FRP bars. The test variables included the amount of flexural reinforcement and the prestressing level. With the aid of full-field measurement on the beam surface using digital image correlation, the kinematics of the critical shear crack of each beam were tracked. Two shear failure modes, including shear compression and shear tension, were observed in the tested beams. Generally, when the amount of flexural reinforcement increased, there was a corresponding increase in the maximum shear force. When the total prestressing force was increased from 360 to 440 kN, the shear cracking strength and the maximum shear strength increased by 6.9% and 10.0%, respectively. It was demonstrated that an arch mechanism formed in the tested FRP post-tensioned beams, although the contribution of aggregate interlock to the shear capacity was negligible. The predictions of the shear capacity calculated from various shear design models showed that the American and Japanese recommendations were highly conservative, whereas the Canadian recommendations were more consistent with the experimental results.

Time-Dependent Behavior of Concrete Beams Externally Prestressed with Carbon Fiber-Reinforced Polymer Tendons for 1000 Days

Time-Dependent Behavior of Concrete Beams Externally Prestressed with Carbon Fiber-Reinforced Polymer Tendons for 1000 Days

Experimental Investigation on the Mechanical Properties of a Noval Bond-Type Anchorage for Carbon Fiber Reinforced Polymer Tendons

In order to effectively alleviate the stress concentration phenomenon of the inner-cone bond type anchorages and improve the ultimate anchoring capacity of the anchorages, a new kind of arcuate-cone bond type anchorage for carbon fiber reinforced polymer (CFRP) tendons was designed. The stress distribution curves, load-slip curves and failure modes of anchorages are obtained by tension test of a group of innner cone and arcuate cone anchors with different parameters. According to the test results, the influence of anchorage types, inclination angles and radius of arc on anchorage performance is analyzed. The results show that ultimate anchoring capacity is directly proportional to the slip between anchor cup and grout during loading. The slip of arcuate cone anchorage is larger than that of inner-cone anchorage, and the anchor with smaller inclination angles of anchor cup slips larger. The ultimate anchoring capacity of the novel arcuate cone bond-type anchorages is larger than that of the traditional inner cone anchorages, and the phenomenon of stress concentration on the surface of CFRP tendons is effectively alleviated by using arcuate cone anchorages.

Study on the stiffness degradation in concrete continuous beam with externally prestressed CFRP tendons under fatigue loading

This paper presents fatigue behaviors and the stiffness degradation law of concrete continuous beams with external prestressed carbon fiber-reinforced polymer (CFRP) tendons. Three specimens were tested under fatigue loading, and the influence of different load levels on the stiffness degradation and fatigue life were studied, and it was found that the stiffness degradation of three test specimens exhibited a three-stage change rule, namely rapid decrease, stable degradation, and sharp decline, but there are obvious differences in the rate and amplitude of stiffness degradation. The load level has a significant influence on the fatigue life of the test specimens. An analytical model with load level considered was proposed to calculate the residual stiffness and predict the stiffness degradation, which is in good agreement with the test results. The model of stiffness degradation presents a possible solution for practical engineering applications of concrete continuous beams with externally prestressed CFRP tendons subjected to different fatigue loadings.

Prestressing low clinker structural concrete elements by ultra-high modulus carbon fibre reinforced polymer tendons

The combination of low clinker high-performance concrete (LCHPC) and ultra-high modulus (UHM) carbon fibre reinforced polymer (CFRP) tendons was recently proposed for prestressed structural elements. The 70% reduction in cement content resulting in limited creep and shrinkage of the LCHPC in comparison to a conventional high-performance concrete (HPC) and the very high UHM-CFRP tendon stiffness (> 509 GPa) were expected to impact the mechanical behaviour of such structures. This study focuses on the behaviour of 3 m-long beam specimens during prestressing, concrete hardening and in 4 point-bending experiments. Fibre optic sensors were implemented inside the CFRP tendons to measure strain during those stages and a digital image correlation system was employed to monitor the 4-point-bending tests. After 28 days, the LCHPC recipe, despite a 70% cement reduction and much smaller environmental footprint, did not show measurable differences in the prestress loss behaviour in comparison to a conventional HPC. The UHM-CFRP prestressing tendons, because of their stiffness, showed both higher prestress losses of around 40% and on average a nearly doubled prestress transfer length. However, they increased the beam`s maximum load-bearing capacity by 21% and showed 47% less deflection at failure in comparison to beams prestressed with the standard modulus (UTS)-CFRP tendons.

Comparative study of the flexural behavior of steel fiber-reinforced lightweight aggregate concrete beams reinforced and prestressed with CFRP tendons

A comparative experimental investigation of flexural behavior of lightweight aggregate concrete (LWC) beams reinforced and prestressed with carbon fiber reinforced polymer (CFRP) bars was presented and an unbonded prestressing anchorage system for CFRP tendons was introduced. A total of four beams prestressed with unbonded CFRP bars and four reinforced with CFRP bars were tested under four-point bending, taking into account the effect of steel fiber content and clear span length. Based on the experimental results, the application of prestressing force and the addition of steel fibers reduced the deflection and crack width of the beams. The larger clear span length resulted in wider crack width and lower tendon stress increment in the prestressed specimens. A geometry-based model was proposed to calculate the tendon stress increment in terms of deflection. Accordingly, decomposing analytical procedure into a bonded beam analysis and an unbonded member analysis, an iterative algorithm for the deflection of beams prestressed with unbonded FRP tendons was developed. The proposed models yielded reasonable stress increment and deflection predictions at service load level.

Experimental and Analytical Study on Residual Stiffness/Strength of CFRP Tendons under Cyclic Loading.

Based on tension–tension fatigue tests, this paper investigated the mechanical property degradation of carbon fiber reinforced polymer (CFRP) tendons from a macroscopic perspective. According to the degradation regularity, this paper proposed a normalized phenomenological fatigue model based on the residual stiffness/strength of CFRP tendons during the fatigue loading process. In this paper, the residual stiffness of CFRP tendons were tested at five stress ranges, while the residual strength was tested at four stress ranges. In order to validate the reliability and applicability of proposed fatigue damage model, the predictions of proposed model and cited models from the literature are discussed and compared. Furthermore, experimental results from literatures were adopted to verify the accuracy of the proposed model. The results showed that the proposed model is applicable to predict both residual stiffness and residual strength throughout fatigue life cycle and has a better accuracy than models from the literature. Moreover, the three-stage degradation can be observed from the degradation processes of stiffness and strength at each stress level.

Analytical predictive model for the long-term bond performance of CFRP tendons in concrete

The bond between Carbon Fiber Reinforced Polymer (CFRP) tendons and concrete depends on the resin mechanical properties that can degrade under environmental conditions. An analytical model to predict the combined effects of temperature and humidity fluctuations on the bond behaviour of CFRP tendons embedded in concrete is presented. The interaction between a CFRP tendon and concrete is studied by considering different competing mechanisms such as tendon swelling and plasticisation effects due to the concrete internal humidity, differential thermal expansion, concrete autogeneous shrinkage, Poisson’s ratio effects and radial bond stresses generated during the pulling out of a tendon from concrete. The analytical bond failure predictions correlate reasonably well with experimentally observed radial-cracking failure modes of CFRP tendons in high strength concrete. Matrix plasticisation appears to influence the long-term bond strength of FRP rods in normal or high strength concrete. Swelling and shrinkage effects become significant in uncoated tendons due to their impact on the frictional bond component. Deviations between measured and predicted bond strength values are attributed to a possible overestimate of the moisture-induced swelling expansion of CFRP tendons. The research findings suggest the introduction of environmental bond factors to consider durability effects in the design of FRP prestressed concrete structures.

Mechanical properties of pultruded high-temperature-resistant carbon-fiber-reinforced polymer tendons at elevated temperatures

Cable roof structures built with carbon-fiber-reinforced polymer (CFRP) cables instead of steel cables, which are called CFRP cable roofs, represent a new structure with great development potential. However, as one of the main stressed components of structures, CFRP cables are required to have better fire resistance. In this paper, the fire resistance of a type of high-temperature-resistant (HTR) CFRP tendon is studied. A total of 39 specimens with a diameter of 5 mm are performed in this study, among which 33 specimens are for steady-state tensile tests and 6 for transient state tests. Steady-state tensile tests are conducted over in the 20–600 °C range, and transient state tests are conducted for stress levels ranging from 0.19 to 0.57. The steady-state test results show that HTR CFRP tendons have excellent room-temperature and high-temperature mechanical properties. The strength remained 78% at 200 °C and the elastic modulus remained 82% at 300 °C, indicating the effectiveness of high-temperature resistant resin matrix. When the temperature reaches 600 °C, the strength remains 19%. The transient state test results show that the high initial stress (stress level of 0.57) can aggravate damage to CFRP tendons at high temperatures. Finally, a high-temperature equation is obtained for the temperature dependence of the strength and modulus of HTR CFRP tendons by developing a mathematical model that is fitted to the test data.

Fatigue Behavior of Stirrup Free Reactive Powder Concrete Beams Prestressed with CFRP Tendons

Abstract A comprehensive study on the fatigue behavior of stirrup free reactive powder concrete (RPC) beams prestressed with carbon fiber-reinforced polymer (CFRP) tendons is presented in this pape...

Flexural performance of pretensioned ultra-high performance fibre reinforced concrete beams with CFRP tendons

In this paper, the mechanical performance of pretensioned concrete girders manufactured with ultra-high performance fibre reinforced concrete (UHPFRC) and carbon fibre reinforced polymer (CFRP) tendons is explored both experimentally and analytically. For the experimental investigation, four UHPFRC beams with either steel or CFRP tendons are tested under four point bending to failure. Digital image correlation is used to monitor the development of cracks. These results are then used to validate a rational analysis technique based on the modelling of concrete cracking and crushing through the application of partial interaction mechanics which is then compared to that suggested by codes of practice

Chemical prestressing of high-performance concrete reinforced with CFRP tendons

Chemical prestress (self-prestress) is a process, in which expansion of concrete with special additives can be used to generate tension in the reinforcement and prestress in the concrete. Until now, the prestress levels that could be reached with this technique were usually lower than with traditional (external) prestressing. With the new family of expansive high-performance concretes (HPC) developed by us, very high levels of residual expansion can be achieved without compromising the durability and still reaching very good mechanical properties of the concrete. In this paper, we combine the expansive HPC with tendons made of ultra-high modulus (>400 GPa) carbon fiber reinforced polymers (CFRP). Through the expansion of the concrete and its bond with the sand-coated tendons, we could introduce tensile stresses of more than 600 MPa in the tendons (for 1% reinforcement ratio), corresponding to more than 4 MPa compressive stress (prestress) in the concrete. 4-Point bending tests show that the chemical prestress increased the cracking moment of slender concrete beams more than three times compared to the reference concrete. Our long-term tests of the strains of the tendons show that the losses of prestress due to shrinkage and compressive creep are very low.

Experimental study on wedge-bonded anchors for CFRP tendons under cyclic loading

This paper is concerned with an experimental study on a wedge-bonded anchor for carbon fibre reinforced polymer (CFRP) tendons under cyclic loading. The adhesive reinforced by quartz sand was tested to be superior as a bonding material for the anchor when compared to the adhesive reinforced by ferrous powder or aluminate powder. Structural responses of the wedge-bonded anchor under cyclic loading were analyzed with regard to system slip, sleeve strain, temperature rise in the anchor zone and residual tensile load capacity. The results indicate that the maximum stress level and stress ratio influence significantly the fatigue performance of wedge-bonded anchors. A cyclic loading with a high stress ratio and low stress level is beneficial due to the synergetic effect of the components in the wedge-bonded anchors. However, enhancing the stress level or lowering the stress ratio leads to a larger slip, greater damage and more loading cycles are needed for the stabilization of wedge-bonded anchors. When the stress ratio exceeds 0.4 and the maximum stress is less than 0.5, damage in anchor zone is initiated and developed in the early stage of cyclic loading, but the anchor becomes stable finally. A large decrease in stress ratio may result in a continuous development of microstructural damage and the eventual failure of the anchor, accompanied by continuously increasing energy dissipation under cyclic loading. The axial strain of sleeve in a wedge-bonded anchor is influenced by the extent of damage evolution and the synergetic effect of anchor assemblies; thereby resulting in different trends in sleeve strain-cycle curves under different stress ratios and stress levels. The temperature rise may be pronounced at a loading frequency of 10 Hz or less, which is related to the stress ratio. The damage development in the wedge-bonded anchor with an infinite fatigue life was analyzed. The mechanism of fatigue damage in wedge-bonded anchors is different from that of adhesively bonded anchors. Moreover, wedge-bonded anchors have a stronger resistance against fatigue due to the interaction between the wedges and the other assemblies.

Experimental investigation on the mechanical properties of a novel anchorage for carbon fiber reinforced polymer (CFRP) tendon

Carbon fiber reinforced polymer (CFRP) has the advantages of light weight, high tensile strength, superior corrosion resistance, and anti-fatigue properties. However, its low transverse compressive strength and inner-laminar shear strength render it difficult to be anchored through traditional anchorages for steel cables. This study proposes a novel composite anchorage for CFRP tendon and validates its novelty by finite element (FE) method. Then the mechanical performance of this novel anchorage was experimentally compared with that of traditional inner cone anchorage. The effects of parameters such as pre-tightening force, embedded length, inclination angle of the barrel, and grouted material on the anchorage performance of the novel composite anchorage were further studied. Results reveal that this novel composite can increase the load-carrying capacity by 60.4% and exhibits an ideal anchorage efficiency above 0.9, largely reduce the slip of the CFRP tendon under both ultimate and short-time sustained loads, and prevent stress concentration at the loaded end. For further design of this novel anchorage, an empirical embedded length of 30d–40d is proposed. Besides, the anchorage performance of this anchorage does not always increase with the dosage of the sand. The optimum dosage of sand should not exceed 10%. This study provides insights into the mechanical properties of the novel composite anchorage and design guidance for the novel composite anchorage.

Reliability analysis of footbridges pre-tensioned with carbon fiber reinforced polymer tendons under flexural loading

A common problem of concrete bridges is corrosion damages of the steel reinforcement. The related loss of capacity as well as visual effects often require expensive and elaborate refurbishment or even reconstruction. To overcome these drawbacks, the application of non-corrosive fiber reinforced polymer (FRP) reinforcement in concrete structures has been established and investigated throughout the last three decades. The successful application of prestressed carbon fiber reinforced polymer (CFRP) reinforcement in bridge constructions was demonstrated by several projects realized in the United States and Canada. Nevertheless, despite the successful realization of these projects, a widespread application has not yet been possible due to the lack of consistent and approved design regulations. In Germany and Europe, the use of FRP reinforcement in bridge construction is even limited to individual cases and non-prestressed reinforcement. Thus, further investigations are necessary to develop a comprehensive guideline for the design of members with pre-tensioned CFRP tendons in compliance with current codes of practice.In order to achieve this objective, a flexural design model for the design of bridge girders prestressed with CFRP reinforcement was developed. In this paper, the reliability analysis of the flexural design model applied to a modular footbridge system pre-tensioned with CFRP tendons is presented. Stochastic simulations are conducted to evaluate the safety of the developed footbridge concepts and to determine an appropriate partial safety factor for the CFRP tendons. For this purpose, the reliability requirements according to the specifications of Eurocode 0 (EC0) are analyzed and evaluation benchmarks are defined to allow for a sufficient reliability of the bridges. The statistical characteristics of the variable parameters needed for the analysis were defined based on a literature review and own investigations.

Numerical assessment of continuous prestressed NSC and HSC members with external CFRP tendons

Carbon fiber reinforced polymer (CFRP) is a promising material for prestressing tendons. This study assesses the structural performance of continuous prestressed members with external CFRP tendons, focusing on the effect of using high-strength concrete (HSC) instead of normal-strength concrete (NSC). A nonlinear model is introduced and numerical tests are then carried out. Three concrete cylinder compressive strengths of 40, 60 and 90 MPa are used. The area of external CFRP tendons varies from 200 to 1700 mm2. The results show that the effect of using HSC instead of NSC heavily depends on the area of external CFRP tendons. In general, HSC members with external CFRP tendons exhibits considerably different response characteristics from those of NSC ones, including cracking, deformations, tendon and rebar stresses, neutral axis depths and so on. The concrete grade influence on moment redistribution is found to be negligible, provided that the members demonstrate favorable ductility. The rules in ACI 318-14 concerning the unbonded tendon stress and the redistribution of moments are evaluated.

Experimental investigation on the seismic behavior of concrete beams with prestressing carbon fiber reinforced polymer tendons.

Seven prestressed concrete beams and one normal concrete beam were tested to study the seismic performance of concrete beams with prestressing carbon fiber reinforced polymer tendons. The failure modes, hysteretic curves, ductility, stiffness degeneration, and energy dissipation capacity were studied systematically. This study shows that the partial prestressing ratio is the main factor that affects the seismic performance of carbon fiber reinforced polymer prestressed concrete beams. The beam is more resilient to seismic loads as the partial prestressing ratio decreases. Under the same partial prestressing ratio value, the energy dissipation capacity of prestressed concrete beams with unbonded carbon fiber reinforced polymer tendons was better than that of prestressed beams with bonded carbon fiber reinforced polymer tendons. When combining both bonded and unbonded prestressing carbon fiber reinforced polymer tendons, the ductility index of concrete beams was improved. Compared with that of fully unbonded and fully bonded carbon fiber reinforced polymer prestressed concrete beams, the ductility index of concrete beams with combined bonded and unbonded prestressing tendons increased by 26% and 12%, respectively.