Post-tensioned Carbon Fiber Reinforced Polymer Research Articles

Enhancing the Flexural Capacity of Deteriorated Low-Strength Prestressed Concrete Beam Using Near-Surface Mounted Post-Tensioned Carbon Fiber-Reinforced Polymer Bar

This study aimed to address the critical issue of age deterioration in prestressed concrete (PSC) structures by investigating the strengthening of aged PSC structures using a near-surface mounted (NSM) post-tensioned carbon fiber-reinforced polymer (CFRP). A total of nine PSC beams, each with a length of 6.5 m, were fabricated for a four-point bending test. Various experimental parameters were taken into account, including the strengthening method, compressive strength of concrete in the PSC beam, and the prestressing force of the PSC beam. The results indicated that the NSM post-tensioned CFRP strengthening system proved more efficient when compared to the NSM non-post-tensioned CFRP strengthening system. The flexural capacity of the NSM post-tensioned CFRP strengthening system, under the deteriorated low-strength PSC beam, increased by up to 30.9% compared to the PSC reference beam. Additionally, the experimental results were compared to a finite-element analysis, and a parametric study was conducted to examine the material properties of the PSC beam. Consequently, the NSM post-tensioned CFRP strengthening system is expected to be an effective solution for addressing the issue of deteriorated low-strength PSC structures.

Prestressed CFRP Plates and Tendon Strengthening of Steel–Concrete Composite Beams

This study aims to enhance the ultimate capacity and stiffness of steel–concrete composite beams through external strengthening with prestressed carbon fiber-reinforced polymer (CFRP) plates and post-tensioned CFRP tendons. A 3D finite element model was developed using ANSYS and validated using experiments. The impact of various parameters on the capacity of the beam was investigated, including the level of post-tensioning in the CFRP tendons, tendon profile, degree of shear connection, and beam load level when adding strengthening CFRP tendons. Results indicate that reinforcing composite beams with bonded CFRP plates using post-tensioning tendons with trapezoidal and parabolic profiles can increase maximum load capacity by 37% and 60%, respectively, while maintaining high stiffness. This study also indicates that the optimal strengthening conditions for the composite beam are when the beam is loaded up to 70% of its capacity and has a composite action degree of 100%.

Experimental study on the flexural performance of prestressed RC beams with post-tensioned CFRP strands

Carbon fiber reinforced polymer (CFRP) exhibits multiple advantages over conventional steel, such as high strength and corrosion resistance. By replacing prestressing steel with prestressing CFRP in new prestressed reinforced concrete (RC) structures, the corrosion issue of prestressing steel can be resolved. At present, there remains scarce research on the application of CFRP strands in the prestressed RC structures. An experimental study was conducted on prestressed RC beams with internal post-tensioned CFRP strands under flexure. The study aimed to analyze the effects of the prestress level, number of CFRP strands, layout shape of CFRP strands, bonding layer, and reinforcement ratio of steel bars on the flexural behavior. The test results indicated that all specimens experienced concrete crushing failure. After applying prestressing CFRP strands to ordinary RC beams, the cracking load increased by 50.0% to 102.2%, the yielding load increased by 20.2% to 38.6%, and the ultimate load increased by 20.3% to 41.4%. Reducing the reinforcement ratio of steel bars had a minor effect on the cracking load but resulted in a noticeable decrease in the yielding and ultimate loads of the prestressed CFRP strand-reinforced concrete beams. Moreover, the bonded specimen showed a slight increment in the cracking, yielding, and ultimate loads as well as stiffness compared to the unbonded specimen, while the deformation capacity of the unbonded specimen remained superior. The specimens with curved and straight prestressing CFRP strands exhibited very similar mechanical properties.

Performance of damaged concrete stub columns strengthened with post-tensioned CFRP under freezing-thawing environment

Reinforced concrete structure with directly bonded fiber reinforced polymer (FRP) on the surface showed obvious stress hysteresis under load, which caused that the strengthening materials cannot be fully utilized. The strengthening system formed by carbon fiber reinforced polymer (CFRP) and shrinkage compensating self-consolidating concrete (ESCC) applied posttensioning stress to the external CFRP shell as a stay-in-place strengthening method, which eliminated stress hysteresis and exerted the restraint effect immediately after being loaded. This paper explored whether this method can be applied to concrete compression members damaged by freeze–thaw environment and its effect. Experimental variables include the number of freezing-thawing cycles, FRP shell plies and types of strengthening concrete. The experimental results showed that the damage of concrete under freezing-thawing environment was an incremental process: the dynamic elastic modulus loss rate and the mass loss rate of specimens damaged by 50 freeze–thaw cycles were 5.9% and 0.4%, respectively. When the freezing-thawing cycles reached 125, the dynamic elastic modulus loss of concrete compression members reached 24.8% and the mass loss rate was 5.3%. Compared with concrete compression specimens after 125 freeze–thaw cycles, the load capacity of specimens strengthened with single-ply and double-ply CFRP were increased by 63.1% and 114.1% respectively, which fully compensated the damage caused by freeze–thaw cycles. It was indicated that when single-ply CFRP was used for strengthening, ordinary self-consolidating concrete specimens exhibited higher hoop strain and less loss of ultimate load capacity than ESCC. When two-ply CFRP was used for strengthening, concrete compression members strengthened with ESCC showed higher strength and less loss of ultimate load-bearing capacity than specimens strengthened with ordinary self-consolidating concrete (SCC). With the increase of freezing-thawing cycles, the normalized inflection stress, intercept stress as well as ductility coefficient of strengthened specimens showed decreasing trend. The theoretical value of normalized peak stress and corrected strain were in good agreement with experimental value and it shows that the maximum error were 10.74% and 24.88%, respectively

Vehicle-bridge coupling dynamic response of a box bridge after reinforcement with prestressed CFRP

The dynamic response of vehicle bridge coupling before and after strengthening with post-tensioned carbon fiber reinforced polymer (CFRP) is analyzed. To obtain a better dynamic response of vehicle bridge coupling, the theory of vehicle moving load is deduced and transformed. To obtain the dynamic response of the vehicle bridge coupling before and after the post-tensioned CFRP reinforcement, a numerical model of the vehicle bridge coupling before and after the post-tensioned CFRP reinforcement is established, and the vertical acceleration time history curve and vertical displacement time history curve of the 1/4, 1/2, and 3/4 sections of the side span and the middle span of the bridge before and after post-tensioned CFRP reinforcement are obtained under different speeds of heavy vehicles. The results show that with the increase in vehicle speed, the vertical displacement of the bridge has almost no change, but the increase in the vertical acceleration peak value is obvious, which results in a faster arrival of the vertical displacement and the vertical acceleration peak value and also causes the amplitude of the vertical acceleration of the bridge to increase greatly, and the vertical acceleration increase in the side span is significantly larger than that in the middle span. Post-tensioned CFRP can effectively reduce the vertical displacement and acceleration of the bridge, but there are some deficiencies in reducing the vertical displacement of the bridge. With the increase in speed, the effect of the post-tensioned method is better.

Flexural Strengthening of Deficient Reinforced Concrete Beams with Post-Tensioned Carbon Composites Using Finite Element Modelling

The application of external post-tensioned steel bars as an effective way to strengthen an existing bridge has been so far used in many different countries. In recent decades, however, they have been replaced by bars made from Carbon Fiber Reinforced Polymer (CFRP), as a material with high tensile strength and corrosion resistance, to address several concerns with steel bars such as their application costs and difficulties, and also their durability. Post-tensioning these sheets can be a new efficient method in strengthening the beams and utilizing the high strength of these material.This study has focused on the flexural behavior of beams reinforced by Post-tensioned non-bonded CFRP sheets. 15 beams were categorized in 3 groups of 5m-, 10m-, and 15m-span in order to evaluate the effect of some parameters such as level of post-tensioning, sheet length, and beam span on its load capacity, failure mode, ductility, and cracks behavior. The results indicate that even though the increase in post-tensioning levels improves the effectiveness of the method, but this capacity improvement is much more for small span beams especially when CFRP sheets are 90% of the beam span, compared to long span beams. There has been a noticeable capacity increase around 50% in the beams when decreasing the sheet length from 90% to 45% of the beam span and also causing 11-14% increase in ductility in various conditions.

Post-tensioned NSM CFRP strips for strengthening PC beams: A numerical investigation

This paper presents a numerical investigation into the flexure of prestressed concrete girders strengthened with post-tensioned near-surface mounted (NSM) carbon fiber reinforced polymer (CFRP) strips subjected to service load. Three-dimensional finite element analysis, validated with theory and test data, is conducted with 51 girder models to evaluate the efficacy of the post-tensioned NSM CFRP with an emphasis on strengthening schemes, deflection and strain responses, a stress-sharing mechanism, and deformability. A strengthening coefficient is proposed to identify adequate CFRP bond length that can exploit such a strengthening method (i.e., the location of anchorage for post-tensioning the CFRP). The effective length of the post-tensioned NSM CFRP is determined, beyond which the post-tensioning action does not influence the behavior of the concrete adjacent to the anchorage. The concept of potential energy is utilized to quantify the performance of the strengthened girders, including the contribution of the CFRP to the functionality of the strengthened girders.

Effect of Corrosion Damage on Service Response of Bridge Girders Strengthened with Posttensioned NSM CFRP Strips

AbstractThis paper presents the effect of corrosion damage on the service response of prestressed concrete bridge girders strengthened with posttensioned near-surface-mounted (NSM) carbon fiber–reinforced polymer (CFRP) strips. Three-dimensional finite-element modeling, validated against experimental data, is conducted to deterministically study the static and dynamic behavior of the girders subjected to chloride-induced corrosion for a period of 100 years. With an increase in corrosion damage, the efficacy of the posttensioned NSM CFRP augments from a serviceability perspective. Modal analysis identifies critical regions along the girder where strain localization occurs at certain dynamic excitation frequencies. The unstrengthened girders are more reactive to dynamic responses than their strengthened counterparts; however, both exhibit similar ride quality. Corrosion damage significantly decreases the equivalent flexural rigidity of the decrepit girders up to 30% relative to that of the control girders. ...

Repair of reinforced concrete deep beams using post-tensioned CFRP rods

Abstract A repair method for reinforced concrete deep beams with external unbonded post-tensioned carbon fiber reinforced polymer (CFRP) rods is presented. Reinforced concrete deep beams in this research were pre-damaged to simulate reinforced concrete girder webs with diagonal cracks. Experimental data and analytical methods for predicting the ultimate capacity of reinforced concrete deep beams which include the effect of externally post-tensioned CFRP rods are examined. The ultimate load capacity of the repaired beams was increased compared to the nominal capacity of the control beam while the deflection capacity remained the same. Strut-and-tie models of the control and repaired reinforced concrete deep beams predicted the ultimate load capacity with reasonable accuracy. The strut-and-tie models were optimized to reduce the ratio of experimental to analytical ultimate load capacity.

Anchorage configuration for post-tensioned NSM CFRP upgrading constructed bridge girders

This paper presents the configuration of anchorage and corresponding behavior for strengthening constructed prestressed concrete bridge girders using post-tensioned near-surface mounted (NSM) carbon fiber reinforced polymer (CFRP) strips. Optimization techniques are employed to best determine anchorage details required, based on the Localized Random Search and the Generalized Reduced Gradient associated with established design approaches. Three-dimensional finite element modeling is followed to examine the response of the strengthened girders in the vicinity of the anchorage where the NSM CFRP is terminated. The failure of the anchorage is controlled by concrete breakout rather than bolt failure in shear when post-tensioning is implemented. The NSM CFRP causes a complex strain distribution near the bottom flange, including some regional rotation of the concrete layer. An influential zone across the girder web is noticed within which the applied energy is dissipated substantially, in conjunction with the existence of a local tension field. The degree of local strain discontinuity along the strengthened girder is dependent upon the level of post-tensioning and an effective strain zone is found beyond which such a post-tensioning effect does not influence the girder concrete.

Fatigue Behavior of Full-Scale Slab Bridge Strips with FRP Reinforcement

AbstractWidespread deterioration of reinforced concrete (RC) bridge structures due to corrosion of steel reinforcement has resulted in an increased use of glass fiber-reinforced polymer (GFRP) reinforcing bars as an alternative reinforcement type for new bridge construction. Disadvantages of glass fiber-reinforced polymer reinforced concrete (GFRP-RC) flexural elements may include increased deflections and crack widths, significant reductions in the concrete contribution to shear resistance and susceptibility to fatigue failure. Posttensioned carbon fiber-reinforced polymer (CFRP) tendons can be used to effectively improve serviceability and shear resistance while increasing the fatigue life of the structure. An experimental study on the fatigue behavior of full-scale slab bridge strips with a reinforcement system combining passive GFRP reinforcing bars and active CFRP tendons is presented, along with analytical models to predict their fatigue lives and changes in stiffness resulting from repeated loading...

Functionality of Damaged Steel Truss Systems Strengthened with Posttensioned CFRP Tendon

AbstractThis paper presents the functionality of truss systems damaged and strengthened with carbon fiber reinforced polymer (CFRP) tendon. Sixteen damage scenarios are designed by disconnecting various web members of a laboratory-scale truss. A posttensioning technique is proposed using steel tubes and non-shrink mortar embedded with the CFRP. Tension tests are conducted to evaluate the feasibility of the anchorage. Experimental trusses are monotonically loaded in service and a three-dimensional finite-element model is constructed to simulate the test data. Deflection characteristics of the truss system are influenced by the presence of local damage. The proposed posttensioning method enhances the serviceability of the strengthened truss system by reducing decompression–deflection. However, the level of posttension force is not related to the flexural stiffness of the truss from a practical perspective. Stress redistribution is observed in the truss system due to the CFRP strengthening, including a load-...

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.

Prestress Losses and Flexural Behavior of Reinforced Concrete Beams Strengthened with Posttensioned CFRP Sheets

An experimental study was conducted to investigate the flexural behavior and long-term prestress losses of reinforced concrete (RC) beams strengthened with posttensioned carbon fiber-reinforced polymer (CFRP) sheets. The experimental program consisted of tensile tests of flat CFRP coupons under sustained loads and flexural tests of a total of eight RC beams: six strengthened with posttensioned CFRP sheets, one strengthened with nonprestressed CFRP sheets, and one control beam. The main objective of the tests was to gain a better understanding of the long-term prestress losses of CFRP sheets in the posttensioned system under different prestress levels and strengthening ratios. It is shown that the prestress losses of CFRP sheets in the posttension system are mainly attributable to anchorage set (approximately 12.6 to 18.2% of the initial prestress), whereas the time-dependent losses caused by creep and shrinkage of concrete and relaxation of CFRP sheets are relatively small (approximately 2.3 to 3.9% of the initial prestress).

지속하중을 받는 탄소섬유판의 장기 거동

본 연구에서는 외부프리스트레스 탄소섬유판에 의한 보강기술에서 긴장력을 포함하는 지속하중이 작용하였을 때의 장기거동을 평가하기 위한 실험연구를 수행하였다. 지속하중 도입을 위한 실험계획은 탄소섬유판에 직접 인장력을 도입하는 직접 지속하중 방식과 휨 실험체를 통한 휨 지속하중으로 구분하여 실시하였다. 직접 지속하중에 의한 실험은 탄소섬유판의 종류별로 약 700일에 걸쳐 실시하여 탄소섬유판의 장기 크리프/릴렉세이션 등의 변형을 주로 평가하였으며, 휨 지속하중 실험에서는 탄소섬유판의 정착시 정착장치에서의 슬립량을 주로 평가하기 위해 약 90일 간으로 수행되었다. 일방향 탄소섬유판에 대한 2년간의 지속하중 실험 결과에 의하면, 탄소섬유판의 크리프나 릴렉세이션과 같은 재료자체의 변형 및 정착장치에서의 슬립에 기인한 응력손실은 적은 것으로 나타났다. 그러나, 강판매입형 탄소섬유판은 강판의 항복변형률을 초과하여 도입된 긴장력으로 인하여 재료 자체의 변형에 의한 자체 응력손실이 발생되었으므로 이에 대한 보완이 필요한 것으로 판단된다. 아울러, 탄소섬유판의 정착과정에 발생되는 긴장력의 즉시 손실량은 응력도입 초기의 약 10% 정도이므로 프리스트레스의 도입시에는 이를 고려하여 긴장력을 결정할 필요성이 있을 것으로 판단된다.