Prestressed Carbon Fiber Reinforced Polymer Plates Research Articles

Prestressed CFRP-strengthening and long-term wireless monitoring of an old roadway metallic bridge

This paper presents an application of prestressed carbon fiber-reinforced polymer (CFRP) plates for the strengthening of metallic girders of a roadway bridge in Melbourne, Australia. The study also describes the application of a wireless sensor network (WSN) system for long-term structural monitoring of the retrofitted bridge girders. A flat prestressed unbonded retrofit (FPUR) system was developed to apply prestressed CFRP plates to the steel girders of the Diamond Creek Bridge (122 years old), which is subjected to daily passenger and heavy vehicles. The first section explains the results of sets of static and fatigue tests performed in the laboratory to examine the efficiency of the proposed FPUR system prior to its installation on the bridge. The second section presents details of different aspects of the CFRP strengthening of the bridge girders, fatigue design criteria, and layouts for short- and long-term monitoring. For the short-term measurements, the bridge was loaded with a 42.5-ton semi-trailer before and after strengthening. The CFRP plates were prestressed up to approximately 980 MPa (≈38% of the CFRP ultimate tensile strength), which resulted in about 50% reduction in the maximum tensile stress in the bridge girders. The third section discusses the development, installation, and preliminary results of the WSN system used to monitor the pre-stress level in the CFRP plates. The results of the short- and long-term measurements in this study show that the FPUR system is very effective for flexural and fatigue strengthening of bridge girders. Finally, a set of recommendations for long-term structural monitoring is provided.

Determination of S-N fatigue curves for damaged steel plates strengthened with prestressed CFRP plates under tension loading

To promote a straightforward design guideline, a determination model of S-N fatigue curves was established to consider effects of the initial crack and stress ratio (R-ratio) on the fatigue performance of damaged steel plates strengthened with non- and prestressed CFRP (Carbon Fiber-reinforced Polymer) plates. The modified Paris’ law employing the effective stress intensity factor range was first used to model the fatigue crack growth data obtained from an extensive literature review for various R-ratios, including edge- and center-notched reinforced steel plates under fatigue loadings. Based on these analysis, the fatigue S-N curve function including the fatigue strength Δσc and fatigue threshold ΔσL, was derived to consider the effects of the initial crack and R-ratio. The model was validated using fatigue results of approximately two hundred specimens with various notch sizes and stress ratios. Specific handbooks provided distinctly different values of C and m for mild steel, and among them the recommended values are 6.86 × 10−12 (with the unit of MPa and meter) and 3.0 through the validation using existing test data reported in the literatures. The comparison of the experimental and predicted fatigue lives confirms the feasibility of the proposed S-N curve determination. Furthermore, the practical value U of the crack closure effect is recommended as 1.0 in the negative R region (R < −0.5) considering the crack closure effect would be overestimated. The sensitivity analysis of critical factors also shows that the initial damage level dramatically influences the S-N curve, and the prestress level also has a dominant impact not only on the reduction of stress range but also the upgrade of fatigue threshold.

Design and experimental analysis of a novel wedge anchor for prestressed CFRP plates using pre-tensioned bolts

Abstract A novel friction-based wedge anchor system was developed experimentally and numerically for the prestressed carbon fiber reinforced polymer (CFRP) plates with several commercial widths and thicknesses. A simple analytical model was first developed to investigate the CFRP compression distribution. Both static and fatigue tests were then conducted to determine the anchor performance. The effects of the barrel and wedge thickness, the wedge shape and contact surface (corrosion and cross knurling) were investigated experimentally on the anchor behavior. The design parameters of the new anchor were recommended through the pull-off experiments, and this anchor can be capable of not only anchoring at least 90% of the CFRP plate specified strength of 2000 MPa statically, but also maintaining the stress level of 900 MPa under a fatigue stress range of 100 MPa. Both the simulation of the CFRP stress distribution and a sensitivity analysis were also conducted on finite element numerical models. The numerical analysis shows that the barrel flexural deformation occurs across the CFRP width, and leads to the bimodal stress distribution across the CFRP plate width. The stress sensitivity results show the stress distribution is significantly sensitive to the wedge shape and contact surface, the bolt pretension and the CFRP width.

Experimental Study on Fatigue Behavior of Cracked Rectangular Hollow-Section Steel Beams Repaired with Prestressed CFRP Plates

AbstractThe bending fatigue test results on cracked rectangular hollow section (RHS) steel beams repaired with prestressed carbon fiber-reinforced polymer (CFRP) plates are presented. The steel bea...

Study on a Parameter Determination and Calculation Method for the Stress Loss of Prestressed CFRP Plates in Bridge Reinforcemen

On the basis of Chinese and foreign specifications and the latest research findings, an appropriate parameter determination method for bridge reinforcement with prestressed carbon-fiber-reinforced polymer (CFRP) plates was proposed to determine the key design indices and calculation coefficients. Each item of prestress loss was studied and a novel calculation method was proposed to determine the usage amount and effective stress of prestressed CFRP plates for reinforcement design, in consideration of the relevant construction technology and anchorage system. The feasibility and reliability of the suggested method in this paper were verified by using an RC simply supported beam bridge reinforcement project as an example.

Mode I fatigue crack arrest in tensile steel members using prestressed CFRP plates

Numerous studies in the literature have shown that the strengthening of steel members using carbon fiber reinforced polymer (CFRP) composites can significantly extend the fatigue life of these structures. However, not enough attention has been focused on the potential of prestressed CFRP reinforcements for fatigue crack arrest in such members. In the current study, a simple analytical model is proposed to calculate the required prestressing level in the CFRP reinforcements in order to arrest the propagation of an existing fatigue crack in tensile steel members. Furthermore, a novel mechanical unbonded system is developed to anchor the high prestressing forces in CFRP reinforcements to the steel substrate using friction. A set of fatigue tests are performed on unstrengthened and strengthened precracked steel plates to verify the proposed model. The experimental results of the current study showed that the application of nonprestressed ultra-high modulus CFRP plates as externally bonded reinforcements can increase the fatigue life of precracked steel plates by a factor of 4.3. However, fatigue crack arrest is only possible when prestressed CFRPs of a certain prestressing level are used. Based on the analytical, numerical, and experimental results of the current study, it can be concluded that existing fatigue cracks in tensile steel members can be arrested using the proposed prestressed unbonded reinforcement system with the initial prestressing level calculated using the proposed model. In addition, some design recommendations are provided for fatigue crack arrest in practical cases.

Analytical and numerical solution of the interfacial stress in reinforced-concrete beams reinforced with bonded prestressed composite plate

The objective of this present research is to propose a simplified analytical and numerical approach to predict the interfacial stress of simply supported reinforced-concrete beams reinforced with prestressed carbon fiber-reinforced polymer composite plate. Analytical design methodology is based on equilibrium and deformations compatibility requirements in and all parts of the strengthened beam, i.e. the concrete beam, the prestressed carbon fiber-reinforced polymer plate, and the adhesive layer. The results show that there exists a high concentration of both shear and normal stress at the ends of the laminate, which might result in premature failure of the strengthening scheme at these locations. In numerical analysis, the mesh sensitivity test shows that the finite element results for interfacial stresses are not sensitive to the finite element mesh. The finite element analysis then is used to calculate the interfacial stress distribution and evaluate the effect of the structural parameters on the interfacial behavior. Numerical results from the present analysis are presented both to demonstrate the advantages of the present solution. This research is helpful for the understanding on mechanical behavior of the interface and design of the interfacial stress in reinforced-concrete beams reinforced with bonded prestressed carbon fiber-reinforced polymer plate.

A Probabilistic Model for the Flexural Capacity of Reinforced Concrete Structures Strengthened with Prestressed CFRP Plates

Strengthening concrete structures with prestressed carbon fiber reinforced polymer (CFRP) materials has gained popularity in recent years due to its ability to efficiently utilize the material's strength. However, the reliability of structures strengthened with prestressed CFRP laminates is a key issue. In this paper the statistical characteristics of design variables of reinforced concrete beams strengthened with prestressed CFRP plates are assessed. Accounting for the gradient effects, the Weibull distribution is used to describe the probability distribution function of the size and stress. The loss of prestressing force is analyzed considering the prestressing method. The probabilistic models of the flexural capacity are established for the three failure models, and the influence of variables on the flexural capacity is also studied. The probabilistic model derived in this paper can be used as the theoretical basis of reliability analysis and safety assessment of structures strengthened with CFRP materials.

Determination of minimum CFRP pre-stress levels for fatigue crack prevention in retrofitted metallic beams

The majority of fatigue strengthening studies focus on reducing propagation rates of existing cracks, ignoring the crack initiation stage. Many existing metallic bridge members however do not contain existing cracks, but rather are nearing their design fatigue life. Limited research exists on the prevention of crack initiation using carbon fiber reinforced polymer (CFRP) materials. In this paper, constant life diagrams (CLDs) are used to determine the minimum level of CFRP pre-stress required to indefinitely extend the fatigue life of existing metallic beams. It is shown that by applying a compressive force to an existing fatigue-susceptible detail using pre-stressed CFRP plates, the mean stress level can be reduced such that the detail is shifted from the ‘finite life’ regime to the ‘infinite life’ regime. The proposed fatigue strengthening approach is advantageous particularly when the stress history from the prior traffic loadings is not known. To validate the proposed method, a pre-stressed un-bonded CFRP reinforcement system is introduced and tested on four metallic beams. The proposed un-bonded CFRP system is advantageous over traditional bonded CFRP systems as it can be applied to rough or obstructed surfaces (surfaces containing rivet heads or corrosion pitting for example). Additionally, the new un-bonded CFRP system offers a fast on-site installation (no glue and surface preparation are required) and an adaptive pre-stress level. Experimental results show that strengthening using pre-stressed CFRP plates are capable of shifting the working stresses from a finite fatigue-life zone to an infinite fatigue-life zone preventing crack initiation. Although according to many structural standards, the stress range is the main parameter that affects the fatigue life of a metallic detail, the results of this study clearly show that the mean stress level also plays a significant rule in the detail fatigue life. Based on the proposed CLD approach in this paper, the combined effects of the stress range and mean stress level can be taken into account for prediction of fatigue life of metallic members.

Design criterion for fatigue strengthening of riveted beams in a 120-year-old railway metallic bridge using pre-stressed CFRP plates

This study presents a design criterion developed for fatigue strengthening of a 120-year-old metallic railway bridge in Switzerland and presents a pre-stressed un-bonded reinforcement (PUR) system developed to apply the strengthening. The PUR system uses carbon fiber reinforced polymer (CFRP) plates; however, unlike conventional pre-stressed CFRP reinforcement methods, preparation of the existing metallic bridge surface is not required. This decreases the time required for on-site strengthening procedures. The principle of the constant life diagram (CLD) and two fatigue failure criteria (Johnson and Goodman) are described. Analytical formulations are developed based on the CLD method to determine the minimum CFRP pre-stress level required to prevent fatigue crack initiation. The PUR system uses an applied pre-stress force to reduce the mean stress level (and stress ratio) to shift an existing fatigue-susceptible metallic detail from the ‘at risk’ finite life regime to the ‘safe’ infinite life regime. The applied CLD method is particularly valuable when the stress history of the detail is not known and it is difficult to assess the remaining fatigue life. Moreover, it is shown that the currently adopted approach in many structural codes which emphasizes stress range as the dominant parameter influencing fatigue life are non-conservative for tension–tension stress patterns (i.e., stress ratios of 0<R<1). Analyses show that the modified Johnson formula accurately reflects the combined effect of stress range, mean stress level, and material properties, and offers a relatively easy design procedure. Details of a retrofit field application on members of a riveted wrought iron railway bridge are given. A wireless sensor network (WSN) system is used for long-term monitoring of the on-site CFRP stress levels and temperature of the retrofitted details. WSN measurements indicate that increases in ambient temperature result in increased CFRP pre-stress levels.

Calculation Methods for Flexural Capacity of Normal Section of Concrete Beams Strengthened with Prestressed CFRP Plates

Existing experimental studies showed that the reinforced concrete (RC) beams strengthened with prestressed carbon fiber-reinforced polymer (CFRP) plates had two possible flexural failure modes (including the compression failure and tension failure) according to the CFRP reinforcement ratio. Theoretical formulas based on the compatibility of strains and equilibrium of forces were presented to predict the nominal flexural strength of strengthened beams under the two failure modes, respectively. It can provide a reference for engineering application of strengthening design.

Fatigue behavior of notched steel beams reinforced with bonded CFRP plates: Determination of prestressing level for crack arrest

This paper presents the findings of an experimental and theoretical study on the behavior of notched steel beams reinforced by non-prestressed and prestressed bonded CFRP (carbon fiber reinforced polymer) plates under cyclic loading, with specific attention to the effect of crack propagation and FRP-to-steel debonding on the fatigue crack growth (FCG) rate. A fracture mechanics based model is proposed in order to estimate the required prestressing level needed to arrest the crack propagation in the notched beams. Several strengthened beams are tested under different fatigue loading ranges and the experimental results show good agreement with the proposed fracture model. An optical image correlation system (ICS) is used to track the crack tip and observe the crack development pattern as well as to provide information about stress distribution at the vicinity of the crack tip. Experimental results show that the fatigue life of a beam reinforced by the prestressed CFRP plate increases more than five times of that of an identical beam reinforced by non-prestressed CFRP plate. Prestressing also significantly reduces the residual deflection during the FCG process. Furthermore, it is shown that as the stiffness of the FRP-to-steel bond joint reduces the FCG rate increases, while as the crack grows (in steel web) the FCG rate decreases.

Performance of Concrete Beams Strengthened with Prestressed CFRP Plates

Six reinforced concrete beams were constructed and tested to investigate the effectiveness of strengthening with prestressed carbon fiber reinforced polymer (CFRP) plates. One of the beams served as a control specimen, another was strengthened with nonprestressed CFRP plates, and the remaining four were strengthened with prestressed CFRP plates. A set of self-developed anchorage devices for CFRP plates were introduced in this program. Monotone static loading experiments was carried out, and comparisons are made between the control beam, the nonprestressed beam and the prestressed beams. The serviceability and the ultimate performance of the concrete beams were improved by strengthened with prestressed CFRP plates.

Study on Flexural Performance of RC Beams Strengthened with Prestressed CFRP Plates

For RC beams strengthened with prestressed carbon fiber reinforced polymer (CFRP) plates, calculate methods for the cracking load, the yield load and the ultimate load are derived base on the analysis of normal section stress. The test of reinforced concrete beams strengthened with prestressed CFRP plates were carried out, and analytical results are compared with experimental results. Comparisons show that the calculated values agree well with the experimental results.

Flexural Strengthening of Reinforced Concrete Beams with Prestressed CFRP Plates

Four medium -scale reinforced concrete beams were constructed and tested to investigate the effectiveness of external poststrengthening with prestressed carbon fiber reinforced polymer (CFRP) plates. The various variables included the strengthening method and the amount of prestressing. The experiments consisted of one control beam, one nonprestressed CFRP-bonded beam, and two prestressed CFRP-bonded beams, all the beams were subjected to four-point bending tests. In comparison to the control beam and the nonprestressed CFRP-bonded beam, the cracking load, yield load, ultimate load and stiffness of the beams with bonded prestressed CFRP plates were increased. The failure mode of the prestressed CFRP-plated beams was not debonding, but concrete crushing. After the debonding of the CFRP plates, the behaviour of the bonded CFRP-plated beams changed to that of unbonded CFRP-plated beams due to the effect of the anchorage system. The ductility of the beams strengthened with CFRP plates having the anchorage system was considered high if the ductility index was above 3.

Design Method of Reinforced Concrete Beams Strengthened with Prestressed CFRP Plates Base on Ductility

For reinforced concrete beams strengthened with prestressed carbon fiber reinforced polymer (CFRP) plates, design methods are derived for determining the allowable plate area or initial tension control stress of CFRP plate to achieve a targeted value of ductility. The derivation of equilibrium and compatibility equations for a rectangular cross section is presented. Base on the test of 2 reinforced concrete beams strengthened with prestressed CFRP plates, analytical results are compared with experimental results. Comparisons show that the design methods have good applicability. It can provide a reference for engineering application of strengthening design.

Flexural response predictions of reinforced concrete beams strengthened with prestressed CFRP plates

Existing experimental studies showed that the reinforced concrete (RC) beams strengthened with prestressed carbon fiber-reinforced polymer (CFRP) plates had three possible flexural failure modes (including the compression failure, tension failure and debonding failure) according to the CFRP reinforcement ratio. Theoretical formulas based on the compatibility of strains and equilibrium of forces were presented to predict the nominal flexural strength of strengthened beams under the three failure modes, respectively, and a limitation on the tensile strain level developed in the prestressed CFRP plate was proposed as the debonding failure occurred. In addition, the calculation methods for cracking moment, crack width and deflection of strengthened beams were provided with taking into account the contribution of prestressed CFRP plates. Experimental studies on five RC beams strengthened with prestressed CFRP plates and a nonlinear finite element parametric analysis were carried out to verify the proposed theoretical formulas. The available test results conducted by other researchers were also compared with the predicted values.