Fiber Reinforced Polymer Strengthening Research Articles

Numerical and experimental investigation into the fatigue life of FRP bonded to concrete and anchored with bidirectional fabric patches

Although extensive research has been conducted into the use of fibre reinforced polymers (FRPs) in strengthening of concrete structures under static loads, their fatigue behaviour when subjected to cyclic loading still requires investigation. The issue of fatigue performance of FRP strengthening systems is mostly relevant to the strengthening of concrete bridges which are subjected to significant traffic loading cycles throughout their lifetime. In order to offset some of the shortcomings of externally bonded FRPs, anchorage systems are commonly used in bridge strengthening applications in conjunction with FRPs externally bonded to concrete in order to mitigate premature debonding failure. This paper presents a summary of numerical and experimental investigations conducted to evaluate the fatigue performance of externally-bonded FRP laminates anchored with bidirectional fibre patch anchors. The anchored laminates were bonded to reinforced concrete (RC) blocks and subjected to various cyclic loading scenarios. Parameters such as the stress range, peak cyclic stress level, and the corresponding number of cycles prior to failure were noted. The results were used to generate an S-N curve relationships. A finite element model was developed and calibrated based on the experimental results. Good correlation was achieved between the experimental and FE results in relation to the maximum number of cycles, strain distribution, and mode of failure. The outcomes of this study showed that no fatigue degradation was observed when the peak cycling stress level was less than 60% of the ultimate static capacity. Further details of the results and recommendations for future research work are also provided.

A Review on experimental and numerical studies of Glass Fibre Reinforced Polymer (GFRP) strips strengthened Reinforced Concrete (RC) slab subjected to low velocity impact

This paper reviewed the previous research on experimental and numerical studies on the impact behaviour of fibre reinforced polymer (FRP) strips reinforced concrete (RC) slab with various (FRP) strips arrangement. This review focusses on the effect of thicknesses, arrangements of FRP strips and type of support layouts. Initially, a throughout investigation was made on the FRP and its properties. Experiments associated to impact resistance of RC slabs was also performed. Furthermore, numerous finite element model (FEM) of RC slabs externally strengthened with different arrangement FRP strips were developed with ABAQUS and ANSYS. The numerical simulations on impact resistance of RC slab models externally strengthened with different arrangement FRP strips were performed. Generally, the experimental results displayed the diagonal two-way arrangement FRP strips externally bonded on bottom surface of RC slabs and four hinge supports applied had improved the impact strength significantly. The experimental and numerical impact results obtained for RC slabs externally strengthened with FRP strips were better as compared to the control RC slabs without FRP strengthening. Afterwards, the results gained from numerical was validated with experimental results. Finally, the methods and results of experimental and numerical reviewed was reliable as a reference for the study of RC slab externally strengthened with GFRP strips subjected to low velocity impact.

Optimizing natural fiber reinforced polymer strengthening of RC beams

The performance of natural fiber reinforced polymer (NFRP) in the flexural strengthening of reinforced concrete (RC) beams is evaluated and optimized in this paper. The optimization comprehensively considers the structural performance, cost efficiency and environmental impacts. Main design parameters – such as the fabrication, the bond condition and the section shape of NFRP laminates – are investigated. The test results revealed that the partial bonded NFRP laminates tended to increase the flexural stiffness within the elastic range. Given the same reinforcement ratio, narrow and thick NFRP yielded the best structural performance. The prefabrication of NFRP laminates using vacuum infusion method greatly decreased the volume fraction of epoxy resin and the related environmental impacts without changing structural performance. The assessment of material cost and environmental impacts indicated that the prefabrication NFRP laminates had obvious advantages over the carbon FRP laminates.

Strengthening of corroded reinforced concrete slabs under multi-impact loading: Experimental results and numerical analysis

Corrosion is one of the major causes of significant deterioration in Reinforced Concrete (RC) structures. Dynamic loads and local impacts can exacerbate the conditions of structures caused by corrosion. This paper investigated the dynamic behavior of RC slabs with corroded reinforcement and evaluated the effects of strengthening using externally bonded Fiber Reinforced Polymer (FRP). Five RC slabs of 1100 × 450 × 60 mm were subject to accelerated corrosion using a constant current technique. One control slab, two corroded, and two strengthened corroded slabs were tested under low-velocity impact loads. A simple yet practical macro-scale Finite Element (FE) model was developed and validated using the experimental results with an average error of 10 and 13% for positive and negative peak acceleration, respectively. The FE model employed concrete damage plasticity and accounted for the steel mass losses and the volumetric changes of the corrosion products. Finally, a parametric study quantified the relations of carbon FRP strengthening ratio and the corrosion levels. Results indicated that FRP strengthening improved the dynamic behavior of corroded slabs. The number of impacts that the slabs with 15 and 30% corrosion could take increased to 13 and 10, respectively, for the FRP strengthened slabs from 2 and 1 for the unstrengthened slabs. It was found that FRP strengthening was more effective in improving the peak acceleration behavior of the less corroded slabs.

Behavior and design of FRP bonded autoclaved aerated concrete beams

Fiber Reinforced Polymers (FRPs) have advantages such as lightness, high strength, and suppressing corrosion risk. There is a vast amount of research on the FRP strengthening of reinforced concrete elements. However, the behavior of FRP bonded Autoclaved Aerated Concrete (AAC) beams has not been extensively investigated in the past. In this study, several experiments were conducted to explore the performance of FRP bonded AAC beams. In this scope, unidirectional single layer carbon and glass fiber laminates with half or full of the beam width were bonded to the AAC. Test results were mainly evaluated by comparing the stiffness, strength, ductility, energy absorption capacity, and the cost of materials. Additionally, a numerical study (based on section analysis and finite element simulation) was conducted to estimate the load-deformation response of the specimens. Based on the analysis results, effective FRP strains were evaluated and compared with the recommendations given in the ACI 440.2R design guidelines for FRPs bonded to reinforced concrete. According to the limited test data, a 60% reduction appears to be appropriate while computing the effective FRP strains for FRP bonded AAC beams.

Modeling Strategies of Finite Element Simulation of Reinforced Concrete Beams Strengthened with FRP: A Review

Fiber-reinforced polymer (FRP) composites do not only possess superior mechanical properties, but can also be easy to tailor, install, and maintain. As such, FRPs offer novel and attractive solutions to facilitate strengthening and/or retrofitting of aging, weakened, and upgraded structures. Despite the availability of general code provisions, the design and analysis of FRP-strengthened concrete structures is both tedious and complex—especially in scenarios associated with unique loading conditions. As such, designers often leverage advanced finite element (FE) simulation as a mean to understand and predict the performance of FRP-strengthened structures. In order to narrow this knowledge gap, this paper details suitable strategy for developing and carrying out advanced FE simulations on FRP-strengthened concrete structures. The paper also covers techniques related to simulating adhesives (bonding agents), material constitutive properties and plasticity (cracking/crushing of concrete, yielding of steel reinforcement, and delamination of FRP laminates), as well as different material types of FRP (CFRP, GFRP, and their hybrid combinations), and FRP strengthening systems (sheets, plates, NSM, and rods) under various loading conditions including ambient, earthquake, and fire. The principles, thumb rules, and findings of this work can be of interest to researchers, practitioners, and students.

U-type mechanical clamping to anchor the CFRP composites in strengthening of RC beams subjected to bending

The present study investigates the performance of U-type clamp anchorage on external strengthening of reinforced concrete beams using carbon fibre-reinforced polymer composites. Unidirectional carbon fibre was used to strengthen the beam having a cross-section of 150 × 200 mm2 and the fabricated U-type clamp was used as a clamping device to enhance the fibre-reinforced polymer (FRP) bonding. To test the beam, four-point bending system was adopted and the experimental parameters were the number of FRP layers. The failure mode of strengthened beams with U-type clamp was very similar (rupture of FRP composites) to the beams without U-type clamp. However, the delamination of FRP was evaded by counteracting the peeling stress development at the edge of fibre. Since the beams strengthened with U-type clamp exhibited more linear behaviour than that of the beams strengthened without U-type clamp, there may be a higher possibility for abrupt/rapid/brittle mode of failure and the ductility index of the beam with U-type clamp confirmed the above behaviour. However, the introduction of U-type clamp enhanced the flexural stiffness and ultimate strength by counteracting the debonding, and the beam with U-type clamp exhibited a maximum of 58.33% and 20.37% enhancement in flexural stiffness and ultimate strength than that of the beam without U-type clamp, respectively. The theoretical strength value of all strengthened beams was evaluated using models proposed in the previous research and compared with experimental results. It is inferred that the use of U-type clamp in FRP strengthening provides economic and structural benefits compared to a beam without U-type clamp.

Modified Epoxy for Fibre Reinforced Polymer Strengthening of Concrete Structures

Fibre-Reinforced Polymer (FRP) is a preferable material for repairing concrete structure due to excellent material properties and effective installation cost over the long-term maintenance of structures. The successful application of FRP strengthening system very much depends on the bond between the concrete substrate and the FRP material using epoxy adhesive. Epoxy acts as a bridge to transfer stress from the concrete to the FRP material. The use of wet lay-up technique to apply FRP onto concrete structure requires epoxy to undergo a curing process normally referred to as cold curing. This paper intends to give a review of the problems with cold-cured epoxy and its effect on structural performance. Cured epoxy is characterised as brittle; therefore, modifications of epoxy are required to toughen the epoxy to suit the purpose of repairing a concrete structure. The methodological approaches from previous studies on modified epoxy were collected and reviewed in this paper. This review also offers some important insights regarding the use of sustainable materials, as well as recommendations for new epoxy in the future.

Effect of FRP Spike Anchor Installation Quality and Concrete Repair on the Seismic Behavior of FRP-Strengthened RC Columns

The use of fiber-reinforced polymer (FRP) to repair and seismically strengthen existing deficient or damaged structural elements is now widespread. FRP anchors have become an important component of such FRP strengthening. However, while reasonable quality control and field quality assurance measures exist for FRP fabrics and plates, such attention has not yet been given to FRP anchors. It seems logical to expect that poor FRP anchor installation will adversely impact the performance of the repaired element. This experimental program was envisaged to assess the level of such an adverse impact. It consists of six RC columns subjected to axial load and quasi-static cyclic load. Of the six columns cast for the experimental work, three columns had good concrete placement, while the remaining three showed poor consolidation, with substantial honeycombing and segregation at the base. It was decided that the latter columns could be used as examples of damaged concrete and so they were repaired by a local contractor by removing the poor concrete and replacing it with a commercially available bagged concrete repair material. One column of each set of three was designated as a control column without any FRP strengthening, while the four remaining columns were strengthened using longitudinal FRP sheets for flexural strengthening, anchors to develop the FRP into the foundation, and transverse FRP sheets for confinement. It was observed that the concrete repair did not adversely affect the behavior of the columns or the interaction between the concrete and the FRP. The FRP anchors were installed to replicate poor installation in the field. Those with improperly placed fans, or splays, did not perform at all as intended and it is recommended that such anchors be removed and replaced without exception. Inadequately saturated anchors were able to achieve their design rupture capacity but failed in a more brittle manner than adequately saturated anchors. Based on the observations from the experimental program, several ideas and options are proposed to enhance the quality of FRP anchors. Accompanied with onsite testing and mockups, these suggestions will substantially contribute to the mitigation of the associated variability in the performance of the rehabilitation.

Numerical analysis of the shear behavior of FRP-strengthened continuous RC beams having web openings

Web openings are usually constructed in continuous reinforced concrete (RC) beams to accommodate the utility pipes and cables. This paper investigates numerically shear strengthening of continuous RC beams having web openings with FRP layers. The finite element analysis software ABAQUS/standard was used to construct non-linear finite element model (FEM) to analyze continuous RC beams having web openings strengthened with different schemes of fiber reinforced polymers (FRP) layers. The FEM was verified using the available experimental studies of both FRP-strengthened simply supported and continuous RC beams with/without openings found in literature before conducting the numerical investigation. The numerical investigation was carried out using the validated numerical FEM to investigate the impacts of crucial parameters such as opening location, opening area and strengthening configuration on the shear behavior of continuous RC beams strengthened with FRP layers. Three different locations were suggested along the length of the RC beam to construct the web openings. On the other hand, the effects of five different opening area on the load capacity and failure patterns were investigated. Moreover, two different FRP strengthening configurations were considered either strengthening above and below the opening or strengthening the whole RC beam height. Results showed that continuous RC beams containing openings at zone II group was the most affected among analyzed locations. The reduction in load capacities of this group ranged from 7.3 to 66.1% compared to the solid beam. The ultimate loads of specimens strengthened over the whole RC beam height exhibited the highest values among analyzed specimens.

Machine Learning Assessment of Fiber-Reinforced Polymer-Strengthened and Reinforced Concrete Members

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Fiber-Reinforced Polymer Strengthening of Steel Beams under Static and Fatigue Loadings

AbstractIn this paper, nonlinear finite element analysis (FEA) was used to investigate the behavior of fiber-reinforced polymer (FRP) retrofitted steel beams subjected to static and fatigue loading...

Efficiency of flexural strengthening RC beams using fiber reinforced polymer materials

The purpose of this study is to evaluate the efficiency of the flexural strengthening of reinforced concrete (RC) beams using the fiber reinforced polymer (FRP). The calculation procedures according to design standards including ACI 440.2R-17 and FIB-2019 are employed to assess the flexural capacity of strengthened RC beams. Three types of FRP materials, which are glass FRP (GFRP), aramid FRP (AFRP), and carbon FRP (CFRP), are used. For CFRP, three kinds of tensile strengths consisting of low (CFRP-L), medium (CFRP-M), and high (CFRP-H) levels are also utilized in calculations and assessments. A numerical model of FRP strengthening beam is developed in ANSYS and then verified with the results of design standards. Comparative studies on the efficiency of flexural capacity and cost benefit between the use of FRP sheets and a conventional retrofitting method are conducted considering a specific area of FRP sheets and 50% flexural strengthening target. The results reveal that flexural strength after strengthening based on ACI and FIB is very similar. The optimal options considering the strength and cost effects are CFRP-L and CFRP-M when using a constant area of FRP. Additionally, we suggest using CFRP-H or CFRP-M for strengthening the RC beams with satisfying a target strength improvement of 50%. Comparing with the conventional method such as section increment, using FRP is more beneficial for both required strength and costs as well.

Behaviour of RC beams with a fibre-reinforced polymer (FRP)-strengthened web opening

The beam opening (BO) technique, which involves (1) the creation of a web opening in the beam to weaken its flexural capacity and (2) the fibre-reinforced polymer (FRP) shear strengthening around the opening to avoid shear failure of the beam, was proposed to realize the strong column-weak beam hierarchy in existing reinforced concrete (RC) frames, which were designed using previous codes and thus violated such hierarchy. In the present study, six large-scale T-section beams with a web opening of different sizes and made by different methods (pre-formed and post-cut) were tested to assess the effectiveness of BO technique and the test results are presented. The experimental study shows that the post-cutting method is feasible for making web openings in existing RC beams, the BO technique can effectively reduce the flexural capacity of the beam to the desired value if the size of web opening is appropriate, and the FRP strengthening can well compensate the loss of shear capacity and ductility of the beam caused by the creation of web opening. The present study provides a basis for the safe use of BO technique to achieve the strong column-weak beam hierarchy in existing RC frames.

Performance of Different Glass Fibre-reinforced Polymer Strengthening Schemes on Masonry Infilled RC Frames under Seismic Loading

ABSTRACT In this study is investigated the performance of different glass fibre-reinforced polymer strengthening schemes on infilled reinforced concrete (RC) frames. The main objective was to limit the damage to beam–column joints and inter-storey drift ratios and to protect RC frames against the negative effects caused by infill-RC frame interaction. Five specimens were tested: one without infill and four infilled with full-scale hollow clay block masonry unit, three of which were strengthened with different schemes. Results showed that the beam–column joints could remain undamaged, lateral strength and stiffness were enhanced, inter-storey drift was limited, and new load carrying systems are generated.

A Moving Interface Finite Element Formulation to Predict Dynamic Edge Debonding in FRP-Strengthened Concrete Beams in Service Conditions

A new methodology to predict interfacial debonding phenomena in fibre-reinforced polymer (FRP) concrete beams in the serviceability load condition is proposed. The numerical model, formulated in a bi-dimensional context, incorporates moving mesh modelling of cohesive interfaces in order to simulate crack initiation and propagation between concrete and FRP strengthening. Interface elements are used to predict debonding mechanisms. The concrete beams, as well as the FRP strengthening, follow a one-dimensional model based on Timoshenko beam kinematics theory, whereas the adhesive layer is simulated by using a 2D plane stress formulation. The implementation, which is developed in the framework of a finite element (FE) formulation, as well as the solution scheme and a numerical case study are presented.

Hybrid FRP Strengthening of Slender Steel Members for Buckling Control

Abstract In this paper, the structural properties and behavior of slender steel members strengthened against buckling by a hybrid system of fiber-reinforced polymer (FRP) shells filled with self-co...

Modeling the buckling characteristics of the metal-FRP hybrid cylinder

Buckling strength and ductility of a metallic cylindrical shell can be enhanced significantly by externally wrapping fiber-reinforced polymer (FRP) composite sheet(s). This paper presents an in-depth numerical study on inelastic buckling of glass FRP (GFRP) strengthened steel tube. The influence of boundary conditions, geometric imperfections, transverse moduli of GFRP, metal-FRP interfacial bond, FRP damage, and other challenges in numerical modeling and computation on buckling behavior are investigated. The predictions demonstrate good agreement with published experiments Teng and Hu [1]. It is shown that accurate prediction of i) post-yield behavior is possible only by the inclusion of metal-FRP interfacial damage, and ii) point of buckling and buckling failure modes require the inclusion of FRP damage as well. Further, this study reveals that i) the metal-FRP interfacial damage happens just before or immediately after the initiation of tube yielding, ii) the axisymmetric buckle initiates at same loading irrespective of amount of FRP strengthening, iii) FRP matrix compression damage and buckle growth aid each other, and iv) an increase in FRP strengthening retards the buckling growth to the point of strain localization.

A Markovian-based methodology for the life-cycle cost analysis of bridge maintenance interventions under changing deterioration rates

Markovian transition probability matrices employing condition states are often used in bridge management systems to determine optimal intervention strategies. This approach assumes a constant deterioration matrix throughout the entire analysis period. In addition, decisions to carry out interventions are normally based on deterioration to predefined condition states, which are generally not linked to structural safety. However, in order to adequately model and evaluate certain intervention options, such as fiber-reinforced polymer (FRP) strengthening, it is necessary to model the impact of the intervention on the deterioration rate, as well as the safety of the structure. This paper presents a Markovian approach to model interventions that impact deteriorating rates. A model employing this approach is proposed, which also accounts for the safety of the structure. A simplified methodology to determine the optimal intervention strategy based on steady state probabilities is also presented. The proposed model and methodology are illustrated in a hypothetical bridge example, where one of the interventions is FRP strengthening of a concrete girder bridge. Keywords: Changing Deterioration Rates; Markov Chains; Bridge Maintenance Interventions; Optimal Intervention Strategies; Life-cycle Cost Analysis;

DEVELOPMENT OF BONDING AGENT USED IN FRP STRENGTHENING SYSTEM

Fiber Reinforced Polymer (FRP) composite is an attractive material for strengthening various civil infrastructures. The strengthening system that based on FRP composites consists of many elements. These are: strengthening material (FRP), strengthened element (concrete, steel, wood, etc) and bonding agent. The latter is the most important elements which affect the performance of the whole strengthening system. Different types of bonding agent are used based on service conditions. Epoxy-based adhesive (EBA) is the most commonly used to strengthen concrete or steel structures. Due to the limitations of the application of EBA, cement-based adhesive (CBA) is utilized as an alternative bonding agent. The CBA have been developed by modifying its properties. The modification was conducted using different powder-state materials or by magnetic water treatment. The development of bonding agent that used in FRP strengthening system is addressed in this paper in order to highlight the most modern bonding agent which consider as a promising material to employ in the actual outdoor structures.