Carbon Fiber Reinforced Polymer Cables Research Articles

Numerical Investigation on the Structural Behavior of a Short-Span Cable-Stayed Bridge with Steel and CFRP Hybrid Cables.

In this paper, a thorough investigation is presented on the static and dynamic behaviors of a short-span cable-stayed bridge (CSB) incorporating steel and carbon fiber reinforced polymer (CFRP) hybrid cables. The study focuses on the world's largest span and China's first highway, CFRP CSB. The performance of the CSB was compared using numerical simulations under four different cable patterns: steel cables, CFRP cables, and steel, and two types of hybrid cables with different structural arrangements. The results indicate that the use of the use of CFRP cables in the long cable region in the short-span CSB project investigated in this study offers improved performance in terms of stability, seismic response, and reduced displacements. In comparison to CFRP cables, hybrid cables have demonstrated a reduction of 12% in the maximum vertical displacement of the main girder. On the other hand, the hybrid cables result in reduced maximum internal forces and longitudinal and lateral displacements of the main girders and towers compared to steel cables. The difference in the arrangement of CFRP cables in the long cable region or short cable region is not obvious under dead loads, but significant differences still exist between the CFRP cable bridges in the short cable region and the long cable region in terms of live load effects, temperature effects, and dynamic characteristics.

Aerodynamic performance and wind-induced response of carbon fiber-reinforced polymer (CFRP) cables

To study the aerodynamic performance and wind-induced response of carbon fiber-reinforced polymer (CFRP) cables, CFRP cable was designed by replacing a steel cable in a tied arch bridge based on stiffness, strength and area equivalent criteria, respectively. The aerodynamic performance and wind-induced response of CFRP cable and steel cable were studied and compared by computational fluid dynamics (CFD) model. Based on the computational results, optimal cable replacement criterion was proposed for CFRP cable to replace steel cable. In addition, surface modification was conducted by engrooving vertical symmetric (VS), vertical asymmetric (VA) and helical symmetric (HS) V-shaped grooves to improve the aerodynamic performance and wind-induced response of CFRP cable. Results showed that CFRP cables exhibited inferior aerodynamic performance and wind-induced response in most cases. However, CFRP cable based on stiffness equivalent criterion exhibited better aerodynamic performance and wind-induced vibration properties compared to the other two cable replacement criteria, thus is regarded as the optimal substitute for steel cable. In addition, HS grooves generated symmetric disturbances and caused approximately equivalent boundary layer separation delays uniformly and continuously along the cable length, thus exhibiting better effect in decreasing the reverse flow region, the maximum negative flow velocity, the vortex shedding frequency and the wind-induced vibration amplitude of CFRP cable. Hence, the stiffness equivalent criterion combined with surface modification with HS V-shaped grooves was proposed to replace steel cable with CFRP cable. This study can provide insights into the aerodynamic performance and wind-induced response of CFRP cable and instructions for cable replacement practice.

Rapid design for large-scale parallel CFRP cable with multi-source experimental data

With advancements in material properties and reduced costs, carbon fibre reinforced polymer (CFRP) cables are gaining popularity in engineering applications due to their superior strength-to-mass ratio and durability. However, the tensile strength of large-scale parallel CFRP cables remains a critical issue, warranting further research and engineering expertise. To address this issue, this paper proposes a method to rapidly predict and adaptively correct the tensile strength of large-scale parallel CFRP cables using multi-source experimental data and an integrated approach that incorporates Monte Carlo simulations, Neural Network algorithms, and Genetic algorithms. This comprehensive method takes into account the influence of various factors including small-scale material strength and its coefficient of variation, cable length, the number of parallel wires, installation errors, and anchorage errors. Validated by reported experimental data, the method demonstrates its effectiveness in accurately predicting the tensile strength of parallel CFRP cables. Moreover, a design method for large-scale parallel CFRP cables is proposed based on the reliability theory. Lastly, the efficiency and effectiveness of the proposed method are validated through the design and optimization of a cable-stayed bridge featuring a main span of 1984 m, utilising both parallel steel and CFRP cables.

High-temperature axial tensile property and fire resisting performance of CFRP strand cable

High-temperature tensile tests and fire resisting performance tests were conducted on carbon fiber reinforced polymer (CFRP) strand cable, respectively, to identify axial tensile property deterioration of CFRP strand tendon (i.e., cable without initial tensile load) under 100–600℃ temperature range and determine fire resisting duration and ultimate temperature of CFRP strand cable with initial tensile load ratio from 0.2 to 0.8. High-temperature axial tensile property and fire resisting performance of different cables including CFRP and steel cables were compared to identify influence of non-uniform load distribution. The obtained results demonstrated that the dominate failure modes of specimen in both high-temperature tensile test and fire resisting performance test are tensile failure. Due to the degradation of mechanical property of resin matrix and bonding performance for resin matrix-fiber bundle interface exposed to elevated temperature, axial tensile strength of CFRP strand tendon degraded by 33.4% and 80.8% under 210℃ (glass transition temperature) and 600℃, respectively, compared to that under ambient temperature. Fire resisting duration of CFRP strand cables varied from 1.3 to 16.4 mins, indicating poor fire resisting performance. Reduction coefficient of bearing capacity for CFRP strand tendon decreased from 0.96 to 0.74 as temperature varied from 25 to 400℃, and then increased to 1.54 at 600℃. Compared to ribbed CFRP cable, CFRP strand cables with initial tensile load ratios ranging of 0.4 ∼ 0.8 (low ultimate temperatures) display worse fire resisting performance due to the prominent non-uniform load distribution among seven wires. Axial tensile strength and reduction coefficient of bearing capacity for CFRP strand tendon exposed to elevated temperature and fire resisting duration of CFRP strand cable and ribbed CFRP cable can be accurately predicted by the developed practical models.

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.

A novel integrated sleeve-wedge anchorage system for multi-tendon CFRP cable utilized in cable roof structures: Concept and numerical investigation

Carbon fiber-reinforced polymer (CFRP) cables demonstrate exceptional mechanical properties and offer significant potential for utilization in large-span cable roof structures. However, the implementation of efficient CFRP cable anchorage systems specifically designed for cable roofs remains an urgent necessity. In this paper, a novel integrated sleeve-wedge anchorage system (NISWAS) consisting of two components, a multi-channel integrated sleeve-wedge (MCISW) and a barrel, has been proposed to achieve the anchorage of CFRP cable with multiple tendons. Compared to the traditional wedge-type anchorage system (WTAS), which can only clamp a single CFRP tendon, the use of the novel integrated steel wire anchorage system (NISWAS) reduces both the volume and self-weight of the cable anchorage end, significantly improving construction efficiency. The design concept of NISWAS was validated through finite element method (FEM) as an example of a 6-Φ5 CFRP cable, and its anchor performance was systematically evaluated. Three key factors affecting the anchor performance were analyzed: the slope angle of MCISW, the anchor length and the differential angle between barrel and MCISW. The results show that the NISWAS is an effective way of anchoring multiple CFRP tendons, and the design of the MCISW can prevent excessive transverse stress on the CFRP cable at the loaded end of the anchorage. The slope angle of the MCISW exerts the most significant impact on the anchor performance. The optimal choice of angle is 3°, beyond which the effect of the anchorage system on the sliding of CFRP cable becomes less significant, while excessive transverse stress may cause premature failure of the cable. The differential angle between barrel and MCISW has a secondary influence on the anchor performance. A moderate angle difference value (0.1° to 0.2°) can alleviate the transverse stress on the CFRP cable, but a too large value (more than 0.3°) will reduce the force transmission between the MCISW and barrel, resulting in premature cable pullout. Increasing the anchor length can reduce transverse stress and cable slip, but the reduction effect is not significant. After analysis, the anchor length of 90 mm can satisfy the anchoring requirement. According to the influence law of the above three factors, the parameter design scheme of the NISWAS was finally proposed.

A Novel Smart CFRP Cable Based on Optical Electrical Co-Sensing for Full-Process Prestress Monitoring of Structures.

Carbon-fiber-reinforced polymer (CFRP) is a type of composite material with many superior performances, such as high tensile strength, light weight, corrosion resistance, good fatigue, and creep performance. As a result, CFRP cables have great potential to replace steel cables in prestressed concrete structures. However, the technology to monitor the stress state in real-time throughout the entire life cycle is very important in the application of CFRP cables. Therefore, an optical-electrical co-sensing CFRP cable (OECSCFRP cable) was designed and manufactured in this paper. Firstly, a brief description is outlined for the production technology of the CFRP-DOFS bar, CFRP-CCFPI bar, and CFRP cable anchorage technology. Subsequently, the sensing and mechanical properties of the OECS-CFRP cable were characterized by serious experiments. Finally, the OECS-CFRP cable was used for the prestress monitoring of an unbonded prestressed RC beam to verify the feasibility of the actual structure. The results show that the main static performance indexes of DOFS and CCFPI meet the requirements of civil engineering. In the loading test of the prestressed beam, the OECS-CFRP cable can effectively monitor the cable force and the midspan defection of the beam so as to obtain the stiffness degradation of the prestressed beam under different loads.

Experimental Investigation of Fatigue Capacity of Bending-Anchored CFRP Cables.

In this study, the variation of fatigue stiffness, fatigue life, and residual strength, as well as the macroscopic damage initiation, expansion, and fracture of CFRP (carbon fiber reinforced polymer) rods in bending-anchored CFRP cable, were investigated experimentally to verify the anchoring performance of the bending anchoring system and evaluate the additional shear effect caused by bending anchoring. Additionally, the acoustic emission technique was used to monitor the progression of critical microscopic damage to CFRP rods in a bending anchoring system, which is closely related to the compression-shear fracture of CFRP rods within the anchor. The experimental results indicate that after the fatigue cycles of two million, the residual strength retention rate of CFRP rod was as high as 95.1% and 76.7% under the stress amplitudes of 500 MPa and 600 MPa, indicating good fatigue resistance. Moreover, the bending-anchored CFRP cable could withstand 2 million cycles of fatigue loading with a maximum stress of 0.4 σult and an amplitude of 500 MPa without obvious fatigue damage. Moreover, under more severe fatigue-loading conditions, it can be found that fiber splitting in CFRP rods in the free section of cable and compression-shear fracture of CFRP rods are the predominant macroscopic damage modes, and the spatial distribution of macroscopic fatigue damage of CFRP rods reveals that the additional shear effect has become the determining factor in the fatigue resistance of the cable. This study demonstrates the good fatigue-bearing capacity of CFRP cable with a bending anchoring system, and the findings can be used for the optimization of the bending anchoring system to further enhance its fatigue resistance, which further promotes the application and development of CFRP cable and bending anchoring system in bridge structures.

Development and sensing performance study of a smart CFRP cable assembled by multi-group anchorage units

ABSTRACT Carbon fiber reinforced polymer (CFRP) can be applied for bridge cables due to its excellent properties. As the important load-bearing structural component, real-time force monitoring of the CFRP cable is required. This paper presents a new smart CFRP cable that combines the self-sensing rods with embedded sensors and the anchorage system using extrusion technology. By embedding optical fiber (OF) and coaxial cable Fabry-Perot interferometer (CCFPI) into CFRP rods respectively, two types of self-sensing rods (CFRP-OF rod and CFRP-CCFPI rod) were fabricated. A new anchorage unit using an extrusion process was proposed as a basic component of smart CFRP cables. Anchorage units holding a CFRP-OF rod and a CFRP-CCFPI rod were tested to obtain their sensing and mechanical properties. Three anchorage units were assembled to form a smart CFRP cable with self-sensing functionality. A verification test was carried out to confirm the capability of monitoring the cable force. The test results demonstrate that the smart CFRP cable composed of multiple anchorage units has good potential in bridge engineering.

Smart Stressing of Concrete Beams with Nitinol Shape Memory Alloy Cables

In this study, a novel method is presented to smartly prestress concrete beams using Nitinol Shape Memory Alloy (SMA) cables. Concrete beams having different compressive strengths and steel fiber contents prestressed with SMA cables are studied in comparison with concrete beams prestressed with steel and carbon fiber reinforced polymer (CFRP) cables. SMA cables with Nickel: Titanium ratio of 0.558:0.442 are embedded in concrete beams and prestrained at temperatures below their martensite start temperature, <img src=image/14829457_01.gif>=20℃±1℃. Smart prestressing is accomplished by heating the Nitinol SMA cables to temperatures above their austenite finish temperatures, <img src=image/14829457_02.gif>=28℃±1℃, and thus subjecting the concrete to compressive forces as the SMA cables attempt to regain their parent form. The study shows that SMA prestressed concrete beams have improved cracking behavior with fewer cracks, larger crack spacing, partial crack closure upon load removal, and an increase in cracking loads. The 35MPa beams prestressed with SMA had 24.2% and 6% higher cracking loads than beams prestressed with steel and CFRP cables, respectively. Meanwhile, SMA prestressed concrete beams had reduced failure loads varying from 4% to 34% in comparison with beams prestressed with steel and CFRP cables. The addition of steel fiber increased the magnitudes of the failure loads in SMA loaded beams. Further, SMA loaded beams possessed large load deflections accompanied with a unique shape retaining capability. This study adverts that SMA cables are attractive alternatives to steel and CFRP cables in post-tensioned beams and slabs, where the use of a complicated jacking system could be substituted by a self-prestressing cable.

Mechanical properties under high-temperature and fire resistant limit of carbon fiber reinforced polymer cable

To fully understand the fire resistant performance of Carbon fiber reinforced polymer (CFRP) cable with high-temperature-resistant resin matrix, both steady state and fire resistant tests were conducted on specimens. The degradation law for axial tensile properties of CFRP cable without pre-tension load under high temperature from 100 to 600 °C was uncovered in steady state tests in order to develop the corresponding constitutive models. Failure temperatures and fire-resistant limits of CFRP cables with pre-tension load heated following the equivalent standard temperature rise process were obtained in fire resistant tests, and were compared to the predicted results using the developed constitutive models and finite element thermal analysis. Then, a practical calculation model for determining fire-resistant limit of CFRP cable was developed and the effect of temperature-load path on mechanical properties of CFRP cable under high temperature was identified. The obtained results demonstrate that the rupture morphologies of tensile failure of CFRP cable in both steady state and fire resistant tests varied with the failure temperature. In steady state tests, mechanical properties of CFRP cable at high temperature are closely correlated with glass transition temperature Tg = 211.6 °C and decomposition temperature Td = 409.6 °C, and effect of high temperature on elastic modulus is more significant than that of tensile strength. In fire resistant tests, failure temperature and fire resistance limit of CFRP cable gradually decreased as pre-tension ratio increased. The fire resistance limits of CFRP cables with pre-tension ratios of 0.2 ∼ 0.6 vary from 3.26 to 15.40mins and its fire performance are very poor. The presence of pre-tension load with ratio R from 0.6 to 0.7 resulted in acceleration of damage for CFRP cable at high temperature. The developed constitutive models of mechanical properties under high temperature and the practical calculation model of fire-resistant limit with high accuracy can be adopted in fire resistant design and analysis of the structures with CFRP cable.

Testing and Evaluation of Flexural Tensile Strength of Prestressed CFRP Cables.

To expand the application scope of prestressed carbon fiber-reinforced polymer (CFRP) cables in civil engineering, the ultimate tensile strength of these cables was tested and evaluated under bending conditions. First, the study analyzed the tensile failure mechanism of CFRP cables under bending conditions based on elastic bending analysis theory. Thereafter, the ultimate stress state of individual tendons and cables was derived and a calculation model for the tensile strength of bent CFRP cables was established. Second, 14 sets of test conditions were created for CFRP cables under bending angles of 20–40° and bending radii of 1.5–3 m. Then, bending tensile tests were conducted to evaluate the effects of the above factors on the ultimate tensile strength, and the correctness of the computational model was verified using experiments. Finally, the ultimate performance of CFRP cables was theoretically predicted using the established model. The results showed that the cable bending tensile strength was associated with the radius r, tensile strength f, and elastic modulus E of the reinforced material and the bending radius R, but was not correlated with the interface buffer material or the bending angle of the steering system. Moreover, the flexural tensile residual strength was only affected by R/r and E/f. When E/f involved conventional material parameters, the residual strength increased nonlinearly with increased R/r. When R/r ≥ 600, the residual strength reached more than 80%. Therefore, R/r at 600 could be used as the design basis for a safe critical radius.

Effects of High Temperatures on the Performance of Carbon Fiber Reinforced Polymer (CFRP) Composite Cables Protected with Fire-Retardant Materials.

In this study, the safe critical temperature that can be tolerated by CFRP tendons under normal working conditions was derived through tensile tests at room and high temperatures. Next, the times required to reach a safe critical temperature for CFRP cables protected with different types of fire-retardant materials of various thicknesses were determined through fire resistance tests, Finally, fitting the surface of the finite element simulation results allowed the establishment of the temperature rise calculation model of CFRP tendons under the protection of fire-retardant materials. The results showed that 300 °C can be regarded as the safe critical temperature. Both high-silica needled felt and ceramic fiber felt exhibited high fireproof performance. With an increase in the thickness of the fire-retardant material, the time for the CFRP tendon to reach the inflection point of the heating rate increased, and the safe fire resistance time increased exponentially. According to the HC temperature rise curve, the fire resistance time of CFRP tendons protected by 24 mm thick high-silica needled felt was 45 min, and that for CFRP tendons protected by 24 mm thick ceramic fiber felt was 39.5 min. Under the action of fire corresponding to the hydrocarbon temperature rise model, the safe fire resistance time of CFRP tendons protected by 45 mm high-silica needled felt or 50 mm ceramic fiber felt was more than 2 h, sufficient to meet the specification. The proposed model of fire resistance performance enables the determination of the thickness of the fire resistance material required to obtain different degrees of fire resistance for CFRP cables for structural use.

Prediction of Elastic-Softening-Debonding behavior for CFRP Tendon-Adhesively bonded anchors

The anchor for carbon fiber reinforced polymer (CFRP) tendon is a key component applied in prestressed structures using CFRP cables. The damage due to cracking and debonding in the anchor zone influences the anchor system performance significantly. On the basis of interface mechanics theory, a trilinear bond-slip law was applied to derive the theoretical models of the stress distribution, tendon slip, and ultimate bearing capacity of the adhesively bonded anchor in various loading stages. The initiation of the local debonding as well as the softening and debonding propagation were modeled. The theoretical models were assessed with respect to experimental results. The influence of variable design parameters on the anchor performance was investigated. The results show that the proposed theoretical models are valid. The interface of the adhesively bonded anchor may undergo a series of stages; from the elastic stage to the softening stage and finally to the debonding stage when subjected to an axial tensile loading. Various closed-form solutions can be derived for different stages that leads to a discovery of an effective bond length. When the bond length is within this effective length, the tensile load capacity increases with respect to the anchor length. Otherwise, the ultimate capacity can hardly be improved by increasing the bond length. The increase in axial rigidity of the bonding medium improves the effective bond length and the ultimate load capacity of the anchor. Moreover, this growth rate is influenced by the diameter of the tendon.

Life-Cycle Cost Analysis of Long-Span CFRP Cable-Stayed Bridges

With the advantages of high strength, light weight, high corrosion and fatigue resistance, and low relaxation, carbon-fiber-reinforced polymer (CFRP) is an excellent cable material for cable-stayed bridges. However, the relatively high unit price of CFRP compared to that of steel may hinder the large-scale application of CFRP stay cables. This paper presents the economic comparison between long-span cable-stayed bridges using CFRP cables and the corresponding steel cable-stayed bridges through life-cycle cost analysis (LCCA). Three CFRP cable-stayed bridges with a main span of 600 m, 1200 m, and 1800 m, respectively, along with their steel counterparts, were designed, and their life-cycle costs (LCCs) were calculated. The comparison of LCCs was not only between the CFRP and steel cable-stayed bridges with the same span, but also between the cable-stayed bridges with different spans. Furthermore, the different unit prices of CFRP cables and different replacement frequencies of steel cables were also investigated. The results show that the initial design and construction cost of the long-span CFRP cable-stayed bridge is higher than that of the corresponding steel cable-stayed bridge, although using CFRP cables can reduce the materials used, primarily due to the higher unit price of the CFRP cable. Despite the higher initial cost, the long-span CFRP cable-stayed bridge can still achieve lower LCC than the steel cable-stayed bridge, because it has significantly lower rehabilitation cost and user cost, as well as slightly lower vulnerability cost. Furthermore, with the increase in the main span and the decrease in the unit price of CFRP cables, the LCC advantage of the long-span CFRP cable-stayed bridge becomes more obvious.

Experimental investigation on high-temperature creep behavior of carbon fiber reinforced polymer cable

Both steady state-constant load and temperature (ST-CLT), and transient state-constant load and temperature (TR-CLT) tests were conducted on carbon fiber reinforced polymer (CFRP) cable in order to investigate the corresponding high-temperature creep behavior. The failure modes, creep strains and rupture times of CFRP cables exposed to high temperature were obtained in ST-CLT and TR-CLT tests, while the residual tensile strength and elastic modulus of specimens without rupture after high-temperature creep tests were determined by conducting high-temperature tensile tests. The variation law of high-temperature creep strains and rupture times of CFRP cable obtained from ST-CLT tests were compared to these of TR-CLT tests to identify the effect of temperature-load path. A practical model for characterizing the high-temperature creep behavior of CFRP cable was developed. Finally, the sustained stress levels and rupture times of specimens exposed to high temperature were analyzed to predict the high-temperature creep rupture stress level of CFRP cable. The obtained results indicated that the rupture morphology of high-temperature creep rupture specimens was the completely soft fiber bundles with “fluffy” pattern. The high-temperature creep strains of CFRP cables in ST-CLT and TR-CLT tests were highly depended on temperature, sustained stress level and time. The presence of pre-tension load before heating accelerated the damage of strength and stiffness for CFRP cable at high temperature, and the damage degree increased with the increasing sustained stress level and high-temperature. The developed practical models for CFRP cables under ST-CLT and TR-CLT conditions can accurately predict the high-temperature creep strains. In the fire resistant design of pre-stressed structures with CFRP cables, the effect of high-temperature creep rupture stress of CFRP cable was not negligible.

Enhancement of Bond Performance of Advanced Composite Materials Used in Cable Bridge Structures Based on Tensile Tests.

Structural steel and concrete are essential materials for the construction of social infrastructures. However, these materials undergo degradation over time, thereby causing steel corrosion. To address this problem, a fiber-reinforced polymer (FRP) is used for reinforcement. In this study, tensile tests were performed to evaluate the material properties for the application of the FRP to cable bridge structures. These tests aimed to investigate various parameters to improve bond performance. Based on experiments with different parameters, sufficient bond performance could be achieved if the following conditions are met: mortar water ≤16%, regardless of the manufacturer; a depth of splitting and steel pipe length ratio ≥75%; upward/downward directions for the mortar injection; and the use of fiber-sheet reinforcement. In addition, the steel pipe used in the test (length of 410 mm and outer diameter of 42.7 mm) performed the best in terms of workability and cost effectiveness. By conducting more accurate tests to study the basic properties of materials, more accurate conditions to accomplish sufficient bond performance can likely be achieved. This will contribute to improved cost effectiveness and safety in the use of carbon FRP cables in cable bridge constructions.

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.

Evaluation of prestress relaxation loss and harping characteristics of prestressing CFRP systems

This paper presents partial results of an investigation about the use of prestressing carbon fiber reinforced polymer (CFRP) systems in prestressed bridge girders. First, stress relaxation tests were conducted on prestressing CFRP cables and bars and continued over a period of one year from the initial prestressing process. Stress relaxation loss found to be linearly related to logarithm of the time and invariant of the length of the specimen. The effect of CFRP anchor loss was also evaluated and used to develop equations for predicting prestress relaxation in both pre- and post-tensioning applications. Then, harping applications of CFRP systems under various harping angles and deviator sizes were experimentally investigated. Higher harping capacity for CFRP cable compared to bar was observed. Premature failure of the CFRP due to localized shear/contact stresses at deviaor location redulted in a significat harping capacity reduction. To maximize the contact surface and reduce the localized shear stress, new deviators were developed, which improved the results. Finally, a finite element (FE) model was developed and calibrated to better understand the harping behavior of CFRP. By performing parametric study on different harping profiles, jacking stress limitations were obtained for the use of CFRP in practical range of harping angles.

Experimental study on high-temperature relaxation behavior of carbon fiber reinforced polymer cable

In order to fully investigate the relaxation behavior of carbon fiber reinforced polymer (CFRP) cable exposed to high temperature, both steady state-constant displacement and temperature (ST-CDT), and transient state-constant displacement and temperature (TR-CDT) tests were conducted on specimens. The failure modes, stress loss laws and rupture times of high-temperature relaxation specimens were determined under ST-CDT and TR-CDT conditions. After high-temperature relaxation tests, high-temperature tensile tests were conducted on samples without rupture to obtain its residual mechanical properties. Final stress losses and stress loss rates of CFRP cable specimens determined by ST-CDT tests were compared with these of TR-CDT tests to clarify the effect of temperature-load path. A high-temperature relaxation model was developed to characterize the variation law of stress losses for CFRP cables under ST-CDT and TR-CDT conditions. A correlational model between stress loss and creep strain rates in steady stages of CFRP cables under high temperature was calibrated. The obtained results demonstrated that high-temperature stress losses of CFRP cables were closely correlated with target temperature, initial stress level and relaxation duration. The application of initial pre-tension load before heating accelerated the stress loss rate in transition relaxation stage and final stress loss of CFRP cable under high temperature.