Fiber Reinforced Polymer Tendons Research Articles

Stress of Carbon Fiber Reinforced Polymer Tendons in Prestressed Simply Supported Beams

The law of stress increment of unbonded carbon fiber reinforced polymer (CFRP) tendons at service stage and flexural load bearing capacity limit state is unclear, so it is difficult to accurately calculate crack width, deflection and load bearing capacity. In order to calculate the stress of CFRP tendons, deformation compatibility condition and moment-curvature analysis method are used to compile nonlinear full-range analysis programs of simply supported concrete beam partially prestressed with unbonded CFRP tendons. The computing results of stress in CFRP tendons are in good agreement with the tested results as a whole, so it indicates that the simulation analysis programs are reliable.

Computational Modeling of Aramid Fiber-Reinforced Polymer Prestressed Girder in Composite Action with Bridge Deck

Aramid fiber-reinforced polymer (AFRP) tendons, which are inherently corrosion-resistant, can be used to replace steel prestressing strands in bridge girders to enhance bridge sustainability. Despite ongoing experimental research, there is a lack of uniformity and consistency in testing procedures, definitions of material characteristics, and results. Therefore, a robust computational model is needed to perform a refined nonlinear analysis of full-scale AFRP prestressed girders. This paper presents the development of a computational model to numerically evaluate the flexural behavior of an AASHTO (American Association of State Highway and Transportation Officials) I-girder (Type I) prestressed with AFRP tendons in comparison to its conventional prestressing steel counterpart. Numerical results match experimental test data with a high degree of accuracy and reveal that an AASHTO I-girder prestressed with AFRP meets service and strength limit states. Numerical results also show that the deflection equation in ACI 440.4R overestimates the maximum deflection of the AFRP prestressed girder.

Experimental Evaluation of Connections in Hybrid Precast Concrete Bridge Truss Girders

An innovative, corrosion-free, precast, prestressed concrete truss girder has been developed for short- and medium-span, slab-on-girder bridges. The girder consists of top and bottom concrete flanges connected by precast vertical and diagonal members and made of fiber-reinforced polymer (FRP) tubes filled with concrete. The verticals and diagonals are connected, respectively, to the concrete flanges by means of glass FRP dowels and stud reinforcement made of corrosion-resistant steel or FRP material. The flanges are pretensioned with carbon FRP tendons. The deck slab is reinforced with corrosion-resistant steel bars in the bottom transverse layer and with glass FRP bars in the bottom longitudinal and the top layers. The girders may be posttensioned with external carbon FRP tendons to balance the slab weight and to provide continuity in multispan bridges. The new system has the advantages of light weight and enhanced durability. The light weight reduces the initial cost and allows for longer spans. The improved durability reduces the maintenance cost and extends the structure's life span. This paper describes the general details of the system and presents an experimental evaluation of its critical components, namely, the FRP tubes and the truss connections. Two types of FRP tubes and four types of connections were investigated. The results are presented of tests of eight connection specimens under static loading and four specimens under fatigue. The tests showed excellent performance of the connections when filament-wound tubes and continuous double-headed studs were used.

Effect of Prestressing on the Performance of GFRP-Reinforced Concrete Slab Bridge Strips

Deterioration of reinforced concrete structures caused by corrosion of steel reinforcement is currently a major concern affecting the safety and functionality of our infrastructure. Fiber-reinforced polymer (FRP) materials have shown tremendous potential as an alternative reinforcement for reinforced and prestressed concrete structures. FRPs have been used in a wide variety of structural applications, from reinforced concrete deck slabs to posttensioned parking garages. However, one promising application for FRP reinforcing bars which has yet to be investigated thoroughly is their use in reinforced concrete slab bridges. This paper presents the results of an experimental study on 10 full-scale glass FRP (GFRP)-reinforced slab bridge strips posttensioned with 0, 2, or 4 carbon FRP (CFRP) tendons with and without shear reinforcement. The tendons were either fully bonded or fully nonbonded to evaluate the effect of bond on the serviceability and ultimate performance of the slabs, particularly in terms of their deformability. Based on the test results, the addition of prestressed CFRP tendons resulted in significantly improved serviceability and ultimate load-carrying capacity with good deformability.

Numerical analysis of behaviour of concrete beams with external FRP tendons

The use of FRP (fibre reinforced polymer) composites as external prestressing tendons is expected to be popular. A numerical investigation is conducted to evaluate the short-term behaviour of external FRP tendon beams, and the results are compared with those of external steel tendon beams. The analysis shows that beams prestressed with external CFRP and steel tendons exhibit similar behaviour, and that external GFRP tendon beams have lower flexural strengths but better ductility behaviour than do external steel tendon beams. The type of external tendons has no important effect on the redistribution of moments in continuous beams. The amount of prestressing reinforcement significantly affects the member behaviour, including cracking and ultimate loads, ductility, neutral axis depth and reinforcement stress. The crack pattern is greatly improved by providing a minimum amount of bonded reinforcement. The analysis also indicates that the ultimate load decreases linearly with increasing deviator spacing, provided that failure happens at midspan. A method for determining the optimum deviator spacing is proposed.

Effects of solution exposure on the combined axial-shear behaviour of unidirectional CFRP rods

In fibre reinforced polymer (FRP) prestressed concrete applications, an FRP tendon must sustain high axial tensile stresses and, if cracks occur, additional dowel forces. The tendon may also be exposed to solutions and so the combined axial-shear stress performance after long-term environmental exposure is important. Experiments were conducted to investigate the combined axial-shear stress failure envelope for unidirectional carbon FRP tendons which had been exposed to either water, salt water or concrete pore solution at 60°C for approximately 18months. The underlying load resisting mechanisms were found to depend on the loading configuration, restraint effects and the initial stress state. When saturated, CFRP tendons are likely to exhibit a reduced shear stiffness. However, the ultimate limit state appeared to be fibre-dominated and was therefore less susceptible to reductions due to solution uptake effects.

Reinforced Concrete T-Beams Externally Prestressed with Unbonded Carbon Fiber-Reinforced Polymer Tendons

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Fatigue of reinforced concrete beams strengthened with externally post-tensioned CFRP tendons

The fatigue performance of reinforced concrete beams strengthened with externally post-tensioned carbon fiber-reinforced polymer (CFRP) tendons was examined in an experimental and analytical study. Five unstrengthened and 13 strengthened reinforced concrete beams were tested under various fatigue load ranges until failure. The strengthened beams were post-tensioned with two external CFRP tendons on a double-harped profile. The results demonstrated that external post-tensioning significantly decreased the stresses in the internal reinforcement at all stages of loading, and hence extended the fatigue life of the strengthened beams. All beams failed due to the fatigue fracture of the internal steel reinforcing bars. The CFRP tendons demonstrated excellent fatigue performance, with no indication of distress at the deviated points or at the anchors. A fatigue model based on a strain-life approach was proposed to predict the fatigue life of the strengthened beams. The model allows the effect of strengthening on the fatigue life of the beams to be explicitly evaluated during the strengthening design process.

A Bridge in China Externally Prestressed by Carbon Fiber Reinforced Polymer Tendons

The Hewei Bridge in Huai’an, Jiangsu Province, is the first example of a traffic bridge in China using the carbon fiber r einforced polymer (CFRP) tendons instead of steel tendons. The bridge is an overpass crossing the Nanjing–Xuzhou Expressway, Jiangsu, China. The four middle spans of this bridge are made of a continuous concrete box girder and prestressed by internal steel strands, while both side spans are designed to be simply supported monolithic concrete girders of 20 m length and prestressed by the external tendons. One side span is prestressed by external CFRP cables, and the other by external ordinary steel tendons for the purpose of comparison. The Hewei Bridge was completed in April 2007, and on monitoring the bridge for almost four years it has been observed that its performance is stable.

Axial Compression Properties of Recycled-Concrete-Segment/Lump Filled Steel Tubular Columns with Inner CFRP Tendons

Recycling of waste concrete is beneficial and necessary from the viewpoint of environmental preservation and effective utilization of resources. The carbon fiber reinforced polymer tendon (CFRP tendon) has been widely used in concrete structures due to its high-strength, lightweight, good erosion-resistance, diamagnetism and anti-fatigue. The compressive behavior of recycled-concrete-segment/lump filled steel tubular columns with inner CFRP tendons are investigated in this paper. The formula of ultimate capacities of the columns under axial compression has been derived based on unified strength theory. Good agreement can be found from the comparison of the analytical results obtained in this paper and experimental data. Parametric studies are carried out to evaluate the effects of intermediate principal stress, mixture ratio of the recycled concrete and reinforcement ratio on the bearing capacities of the columns.

Shear Behavior of CFRP Prestressed Concrete Beams without Stirrups

Five beams were tested up to failure to study the shear behavior of concrete beams prestressed with fiber reinforced polymer (FRP). Different factors were taken into consideration: the type of prestressing tendons and the shear span ratio. The shear failure modes and the influence of different factors on shear behavior were investigated in details. The test results showed that FRP prestressed beams without stirrups had two shear failure modes: diagonal compression failure and shear compression failure; the shear span ratio was the most important factor to determine the failure mode and shear capacity of the prestressed beams. The shear capacity of concrete members prestressed with FRP tendons was lower than that of concrete beams prestressed with steel cables.

FRP 긴장재를 이용한 프리스트레스트 콘크리트 보의 피로 거동

최근 PS 강연선의 대체재로서 높은 인장강도와 훌륭한 내부식을 가진 FRP(fiber rienforced polymer)를 이용한 조사가 활발히 진행되어지고 있다. 따라서, 이 연구는 FRP 긴장재를 이용한 프리스트레스트 콘크리트 보를 제작하여 반복 하중에 따른 피로거동의 특성을 분석함으로써 프리스트레스트 콘크리트 보의 안전성을 평가하고자 하였다. 또한 기존 PS 강연선을 이용한 프리스트레스트 콘크리트 보를 제작하여 피로 성능을 비교하였다. 반복 하중은 정적 실험을 통해서 얻은 극한 하중의 40%를 최소 하중으로 일정하게 고정하고 최대 하중은 극한 하중의 60%, 70%, 80%로 결정하였다. 반복 하중은 4점 재하방식으로 sine파를 이용한 1~3 Hz의 속도 재하하였다. 피로한계는 100만회로 하였다. 40~60% 범위의 시험체는 100만회까지 피로 파괴가 나타나지 않았지만, 반복 횟수가 증가함에 따라 콘크리트와 긴장재 사이의 부착력이 저하되었고, 수평방향의 균열이 나타났다. FRP 긴장재를 이용한 프리스트레스트 콘크리트 보의 피로 실험 결과 사용 하중 상태에서의 반복 하중에 대해서 안전한 것으로 나타났다. 피로한계 100만회에 대한 피로 강도는 FRP 긴장재를 이용한 프리스트레스트 콘크리트 보의 경우 69.2%, PS 강연선을 이용한 프리스트레스트 콘크리트 보는 59.8%에 해당함을 알 수 있었다.

CALCULATING THE CARRYING CAPACITY OF FLEXURAL PRESTRESSED CONCRETE BEAMS WITH NON-METALLIC REINFORCEMENT

The article reviews moment resistance design methods of prestressed concrete beams with fibre-reinforced polymer (FRP) reinforcement. FRP tendons exhibit linear elastic response to rupture without yielding and thus failure is expected to be brittle. The structural behaviour of beams prestressed with FRP tendons is different from beams with traditional steel reinforcement. Depending on the reinforcement ratio, the flexural behaviour of the beam can be divided into several groups. The numerical results show that depending on the nature of the element failure, moment resistance calculation results are different by using reviewed methods. It was found, that the use of non-metallic reinforcement in prestressed concrete structures is effective: moment capacity is about 5% higher than that of the beams with conventional steel reinforcement.

Flexural Capacity of Concrete Beams Prestressed with Carbon Fiber Reinforced Polymer (CFRP) Tendons

Fiber reinforced polymer (FRP), particularly those incorporating carbon fiber (CFRP), has high strength, high stiffness-to-weight ratio and high resistance to corrosion, which shows potential for use as prestressing tendons in corrosive environment. However, concrete beams prestressed with FRP tendons have showed brittle flexural failure due to the elastic rupture of FRP tendons. In order to improve the ductility, a combination of bonded and/or unbonded prestressing tendons was used. Nine prestressed concrete beams were tested up to failure to study the effect of bonded and unbonded FRP tendons on their flexural capacity. Three factors were taken into consideration; the bonding condition of CFRP tendons, the location of CFRP tendons and the prestressing ratio. Also an analytical investigation was carried out to extend some flexural capacity calculation equations to this beam type. The results of the experimental showed that under the same condition, the carrying capacity of concrete beam prestressed with bonded FRP tendons was 20% higher than that of internal unbonded prestressed beam, and was 40% higher than that of external unbonded prestressed beam without deviators. By combination of bonded and unbonded FRP tendons, the ductility of prestressed concrete beams can be improved.

Friction Loss of Externally Prestressed Concrete Beams with Carbon Fiber-Reinforced Polymer Tendons

Friction loss is an important component of the calculation of prestressing loss for external prestress strengthening technology. Unfortunately, the test data of relevant curvature friction and wobble coefficients is scarce, especially for beams strengthened by external prestressing Carbon Fiber-Reinforced Polymer (CFRP) tendons. Through the experiment of 12 concrete beams strengthened by external prestressing CFRP tendons, this study attempts to discuss the friction loss algorithm and the reasonable value of friction coefficient. The test results demonstrated that traditional friction loss algorithm for prestressed steel tendons is also suit to external prestressing CFRP tendons, but the value of curvature and wobble coefficients should be determined by different types of CFRP tendons and saddle design. What is more, aiming at the domestic production of CFRP tendons and the adopted special saddle design in this paper, the curvature friction coefficient is 0.263 and the wobble coefficient is 0.0067 at the deviator. Results of the research provide a reference for external prestress strengthening design with CFRP tendons.

Response of Concrete Beams Partially Prestressed with External Unbonded Carbon Fiber-Reinforced Polymer Tendons

To assess the behavior of concrete beams partially prestressed with external unbonded carbon fiber-reinforced polymer (CFRP) tendons, three specimens prestressed with CFRP tendons and one reference specimen prestressed with external steel tendons were tested to failure under third point loading. It was found that the load-deflection curve of all specimens exhibited three stages, namely, elastic, cracked-elastic and plastic. The transition from the elastic to the cracked-elastic stage was caused by the development of cracks at the bottom of the beam, while the transition from the cracked-elastic to the plastic stage was caused by yielding of the non-prestressed steel. For beams prestressed with external CFRP tendons and that with external steel tendons, the relationships between the stress increment in external tendons and the mid-span deflection of specimens were linear or approximately linear. Although CFRP materials are brittle in nature and behave linearly elastically until failure, proper combination of external CFRP prestress tendons with internal steel reinforcing bars can impart ductility to the beams.

CFRP Tendons for the Repair of Posttensioned, Unbonded Concrete Buildings

The deterioration attributable to corrosion of concrete structures reinforced with unbonded, posttensioned tendons is a costly problem. Recent research has shown composite materials such as fiber-reinforced polymers (FRP) to be suitable alternatives to steel because they provide similar strength without susceptibility to electrochemical corrosion. Carbon-FRP (CFRP) in particular has great promise for prestressed applications because it shows resistance to corrosion in environments that might be encountered in concrete and experiences less relaxation than steel. This paper outlines the testing and implementation of a posttensioned system that uses CFRP tendons to replace corroded, unbonded posttensioned steel tendons. This system was then implemented in a parking garage in downtown Toronto. To the writers’ knowledge, this is the first example of an unbonded, posttensioned tendon replacement using FRP tendons. The system used split-wedge anchors designed specifically for CFRP tendons. The dead end was anchored by directly bonding the tendon to the concrete slab. The CFRP tendon was successfully inserted in the opening created by the removal of the corroded tendon and stressed. Although the system was shown to be feasible, the current anchorage configuration results in load losses of up to 60% during the transfer. Changing the orientation of the anchor was found to reduce the load loss to an acceptable range of 1–9%.

Flexural Response of Concrete Beams Prestressed with AFRP Tendons: Numerical Investigation

This paper presents the flexure of concrete beams prestressed with aramid fiber-reinforced polymer (AFRP) tendons. Three-dimensional nonlinear finite-element analysis and iterative sectional analysis are conducted to predict the behavior of AFRP-prestressed members, including experimental validation. The beams are simply supported and monotonically loaded until failure occurs. The sectional properties of the beams include a reinforcement ratio of 0.15% to 0.36% and an Ig / Icr ratio of 25 to 77, where Ig and Icr are the gross and cracked moment of inertia, respectively. Various prestressing levels are applied to the beams to evaluate the load versus displacement response, variation of neutral axis depth, effective moment of inertia, and deformability of the beams. The applicability of code provisions and existing predictive equations are examined. The prestress level in the AFRP tendons significantly influences the flexural behavior of the beams, namely, cracking load, strain development of AFRP, and neut...

Prediction of tensile capacity based on cohesive zone model of bond anchorage for fiber-reinforce dpolymer tendon

In this paper, analytical solutions based on a cohesive zone model (CZM) are developed for the bond fiber-reinforce dpolymer (FRP) tendon anchorage under axial load. With bilinear cohesive laws, the analytical solutions of tensile capacity of anchorages are derived. The concept of the minimum relative interface displacement s m is introduced and used as the fundamental variable to express all other parameters, such as external tensile load. Experimental and analytical results show that the thickness of the anchoring material is main factor affecting tensile capacity. The characteristic bond strength depends mainly on the properties of the bonding agent-anchoring material, the geometry and surface conditions of the tendon, and the radial stiffness of the confining medium. A comparison of the calculated and experimental results showed good agreement. Formulas based on fracture energy of the tension load capacity derived in the present work can be directly used in the design of FRP tendon anchorage.

Development of Mechanical Anchor for CFRP Tendons Using Integrated Sleeve

A durable and very efficient external strengthening system is achieved if steel tendons for posttensioning applications can be replaced with carbon fiber-reinforced polymer (CFRP) tendons, and if reliable anchorage systems are developed. This paper presents a newly developed and simple-to-use, two-piece wedge anchorage for CFRP tendons with an integrated sleeve and a differential angle between barrel and wedge sections. Three longitudinal slits are cut into the one-piece wedge, with one slit open and the other two stopping 1 mm from the inner wedge hole. The integrated sleeve holds the wedge’s sections together during presetting and loading, resulting in a circumferential confined gripping of the CFRP tendon and optimized surface friction area. Therefore, the one-piece wedge differs from conventional wedge systems, where the wedges act separately with adjacent spaces, wedging the separate tendon sleeve in the longitudinal direction. Evaluation of the failure modes during testing was one of the main keys i...