Fiber-reinforced Polymer Reinforcement Research Articles

The mechano-sorptive creep behaviour of basalt FRP reinforced timber elements in a variable climate

The use of Fibre Reinforced Polymer (FRP) reinforcement has been shown to improve the short-term flexural behaviour of timber elements. This is particularly important when reinforced elements are subjected to a variable climate condition, which is known to accelerate long-term or creep behaviour. In this paper, both unreinforced and Basalt FRP reinforced beams are subjected to creep tests at a common maximum compressive stress of 8 MPa over a 75-week period. Results demonstrated a significant reduction in total creep deflection due to the FRP reinforcement. Using matched groups, experimentally measured total strain behaviour is decomposed into the elastic, viscoelastic, mechano-sorptive and swelling/shrinkage strain components. Analysis has shown that the mechano-sorptive component is similar in unreinforced and reinforced beams. The reduction in creep behaviour of the reinforced members was primarily due to the restrained swelling/shrinkage response of the reinforced beams and was independent of the mechano-sorptive effect. This finding demonstrates the positive influence of FRP reinforcement on the long-term behaviour of timber elements and indicates a potential to describe the long-term deflection performance of FRP reinforced elements from short-term swelling/shrinkage tests.

Seismic performance improvement of GFRP-RC moment frames

Although structures made of concrete reinforced with fiber-reinforced polymers (FRP) have shown promising performance under gravity loads, their performance under cyclic loading is still one of the main concerns. Although the linear nature of FRP reinforcement could be advantageous in terms of limiting the residual damage after an earthquake event, it lowers the energy dissipation of the structure, which can compromise its seismic performance. In this research, adding steel plates at selected locations in moment-resisting frames is proposed as a solution to improve seismic performance of FRP-reinforced concrete (FRP-RC) structures. Three full-scale cantilever beams, one steel-RC, one FRP-RC, and one FRP-RC with proposed steel plates, were constructed and tested under reversed cyclic loading. The results indicated that the proposed mechanism effectively improves the seismic performance of FRP-RC beams by increasing their initial stiffness and energy dissipation. Moreover, a computer simulation, using the moment–curvature determination process, was conducted to calculate bending moment capacity of FRP-RC beams with steel plates.

Effectiveness of Glass Fiber-Reinforced Polymer Stirrups as Shear Reinforcement in Glass Fiber-Reinforced Polymer Reinforced Concrete Edge Slab-Column Connections

Effectiveness of Glass Fiber-Reinforced Polymer Stirrups as Shear Reinforcement in Glass Fiber-Reinforced Polymer Reinforced Concrete Edge Slab-Column Connections

An EMI-Based Clustering for Structural Health Monitoring of NSM FRP Strengthening Systems.

The use of fiber-reinforced polymers (FRP) in civil construction applications with the near-surface mounted (NSM) method has gained considerable popularity worldwide and can produce confident strengthening and repairing systems for existing concrete structures. By using this technique, the FRP reinforcement is installed into slits cut into the concrete cover using cement mortar or epoxy as bonding materials, yielding an attractive method to strengthen concrete structures as an advantageous alternative to the external bonding of FRP sheets. However, in addition to the two conventional failure modes of concrete beams, sudden and brittle debonding failures are still likely to happen. Due to this, a damage identification technology able to identify anomalies at early stages is needed. In this work, some relevant cluster-based methods and their adaptation to electromechanical impedance (EMI)-based damage detection in NSM-FRP strengthened structures are developed and validated with experimental tests. The performance of the proposed clustering approaches and their evaluation in comparison with the experimental observations have shown a strong potential of these techniques as damage identification methodology in an especially complex problem such as NSM-FRP strengthened concrete structures.

Strengthening of Fibre Reinforced Concrete Elements: Synergy of the Fibres and External Sheet

In structural rehabilitation and strengthening, the structural members are often required to cope with larger design loading due to the upgrading of building services and design standard, while maintaining the member size to preserve the architectural dimensions and headroom. Moreover, durability enhancement by mitigating or eliminating the reinforcement corrosion problem is often desired. Concrete cracking is a major initiating and accelerating factor of the corrosion of steel reinforcement. The application of fibres is a prominent solution to the cracking problem. Furthermore, the fibres can increase the mechanical resistance of the strengthening systems. This study reveals the synergy effect of the combined application of steel fibres and external carbon fibre-reinforced polymer (CFRP) sheets. The investigation encompasses the use of fibre-reinforced polymer (FRP) reinforcing bars, discrete steel fibres, externally bonded and mechanically fastened FRP sheets in different combinations. It is discovered that the steel fibres can help to control concrete cracking and eventually alter the failure mode and enhance the flexural resistance. The FRP reinforcement system, together with the steel fibres, radically resolves the structural safety problem caused by corrosion of the steel bar reinforcement. Finally, the impact of the external sheet on the fire limit state performance needs to be resolved, such as by adopting fire protection rendering for the finishes layer.

Experimental study on seismic behaviours of hybrid FRP–steel-reinforced ECC–concrete composite columns

Owing to the high strength, noncorrosive property, and linear stress–strain relationship of fibre-reinforced polymers (FRPs), hybrid FRP–steel-reinforced concrete members exhibit higher strength, superior durability, and lesser residual deformation compared to steel-reinforced concrete members and higher ductility compared to FRP-reinforced concrete members. Hybrid-reinforced members have been widely used as flexural-dominated members rather than compression-dominated members owing to the poor compression performance of the FRP reinforcement. This paper proposes a novel approach for improving the seismic behaviour of such members through the use of high-ductility engineered cementitious composites (ECCs) in the plastic hinge zone. Numerous hybrid FRP–steel-reinforced ECC–concrete columns were tested under reversed cyclic loading. The effects of the matrix type, reinforcement type, axial force ratio, and reinforcement ratio on the seismic behaviours, including the failure mode, crack pattern, load-carrying capacity, residual deformation, ductility, and energy-dissipation capacity, of the columns were systematically investigated. The replacement of concrete with ECC in the plastic hinge zone efficiently eliminated the local buckling of the FRP bars and significantly improved the seismic performance of the column. Compared with the steel-reinforced ECC–concrete composite column, the hybrid-reinforced composite column exhibited significantly less residual deformation and higher post-yielding stiffness. With an increase in the axial force ratio, the ultimate strength increased, while the deformation capacity decreased.

Splice Strength of Staggered and Non-Staggered Bundled Glass Fiber-Reinforced Polymer Reinforcing Bars in Concrete

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Cracking and Failure Mode of the Self-Stressed Members with FRP Bars

Fiber reinforced polymer (FRP) bars represent a combination of the polymer binder and reinforcing fibers (glass, basalt, aramid, carbon). The main features of FRP bars are high tensile strength on the background of the relatively low elasticity modulus. To prevent development of the excessive both crack opening and deflections in the FRP reinforced concrete structures it can be effective to implement FRP reinforcement pretensioning with a limited level of created stresses. As a good option can be considered a physico-chemical method of FRP bars pretensioning based on the self-stressing concrete utilizing. In the self-stressed FRP reinforced members it is possible to obtain a considerable values of the early age restrained expansion strains (in comparison with steel reinforced self-stressed members because of FRP bars lower elasticity modulus), which will not disappear after air-dry shrinkage strains realization. In addition, another concern that have to be considered in the field of FRP reinforced self-stressed members is bond performance of the different FRP bars types, especially in combination with self-stressing concrete that within its expansion can provoke decompacting of the transit zone «bar-concrete». Moreover, taking into account that FRP bars is a composite material, its bond properties are strongly influenced by the types of the polymer binder, reinforcing fibers, ratio between binder and fibers, bar coating. Presented studies is consisted in the experimental investigations of the features in the crack development and depended on it occurred failure mode of the self-stressed members reinforced by the different types of FRP bars.

Experimental studies and theoretical models for concrete columns confined with FRP composites: a review

PurposeAdvanced fibre-reinforced polymer (FRP) composites have been increasingly used over the past two decades for strengthening, upgrading and restoring degraded civil engineering infrastructure. Substantial experimental investigations have been conducted in recent years to understand the compressive behaviour of FRP-confined concrete columns. A considerable number of confinement models to predict the compressive behaviour of FRP-strengthened concrete columns have been developed from the results of these experimental investigations. The purpose of this paper is to present a comprehensive review of experimental investigations and theoretical models of circular and non-circular concrete columns confined with FRP reinforcement.Design/methodology/approachThe paper reviews previous experimental test results on circular and non-circular concrete columns confined with FRP reinforcement under concentric and eccentric loading conditions and highlights the behaviour and mechanics of FRP confinement in these columns. The paper also reviews existing confinement models for concrete columns confined with FRP composites in both circular and non-circular sections.FindingsThis paper demonstrates that the performance and effectiveness of FRP confinement in concrete columns have been extensively investigated and proven effective in enhancing the structural performance and ductility of strengthened columns. The strength and ductility enhancement depend on the number of FRP layers, concrete compressive strength, corner radius for non-circular columns and intensity of load eccentricity for eccentrically loaded columns. The impact of existing theoretical models and directions for future research are also presented.Originality/valuePotential researchers will gain insight into existing experimental and theoretical studies and future research directions.

Single Crack–Based Model for FRP Shear-Strengthened RC Beams

AbstractIn this study, a single crack–based model is proposed for predicting the contribution of fiber-reinforced polymer (FRP) reinforcement to the shear resistance of FRP shear-strengthened reinf...

Experimental Study on Splice Strength of Glass Fiber-Reinforced Polymer Reinforcing Bars in Normal and Self-Consolidating Concrete

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Influence of restraint thermal effects on the bond strength of externally bonded CFRP-concrete joints

Elevated temperatures lead to a reduction of the bond strength of FRP (fibre reinforced polymer) reinforcement glued on concrete by ambient cured epoxy adhesive. This degrading behaviour is mainly observed for exposure temperatures beyond the glass transition temperature of the epoxy (Tg ≃ 60–80 °C) which is usually 2–3 times lower than the Tg of the matrix of pultruded FRP reinforcement. Contrary, lap shear tests on FRP-concrete systems made with carbon fibre reinforced polymer (CFRP) revealed an increase of the bond strength at temperatures close to the Tg of the epoxy adhesive. Several explanations have been expressed for this unexpected trend. The most accredited hypothesis describes the increase of bond strength as a consequence of the induced restraint thermal effect between the CFRP and the concrete substrate, because of the different thermal elongation of the materials. In this work, the influence of the restraint thermal effect is investigated further in terms of influence on the ultimate load recorded by lap shear tests at elevated temperature and to understand better the underlying mechanism. The obtained outcomes have revealed that the evaluation of the restrained thermal action has to consider the influence of the bond length of the joint and the thermal degradation of the adhesive.

Cyclic Load Tests on Precast Segmental Bridge Columns with Both Steel and Basalt FRP Reinforcement

AbstractThis paper presents an experimental investigation of a novel precast segmental bridge column (PSBC) that is longitudinally reinforced with both fiber-reinforced polymer (FRP) bars and conve...

Bond performance of NSM FRP bars in concrete with an innovative additional ribs anchorage system: An experimental study

Abstract Bond failure due to a lack of anchorage capacity is often observed when using FRP reinforcement as a strengthening method in RC structures, thus restricting the efficiency in upgrading their structural performance. To address this issue, our research group has recently developed a simple and innovative additional ribs anchorage system for FRP bars, which has been verified to have the high efficiency of improving the anchorage performance of FRP bars reinforced in concrete. As a promising strengthening method in RC structures, the near-surface mounted (NSM) fiber-reinforced polymer (FRP) technique has become popular. However, bond failure also exists in the NSM FRP strengthening system. It is also important to initiate a study on the bond performance of NSM FRP bars which are mounted in concrete using the proposed additional ribs. In this study, a total of 36 direct pull-out specimens and 12 beam pull-out specimens were employed. In particular, the influences of additional ribs on the bond behavior of FRP bars mounted in concrete in terms of the failure modes, local bond stress distribution, and load-slip curves were discussed. Several important parameters expected to affect the bond performance were investigated, namely, the type and the bonded length of the FRP bars, groove size and section configuration, and adhesive species. The test results and corresponding analysis in this paper demonstrated the feasibility and significant efficiency of using the proposed additional ribs anchorage system to enhance the bond performance of NSM FRP bars in concrete.

Flexural Capacity and Deflection of Fiber-Reinforced Lightweight Aggregate Concrete Beams Reinforced with GFRP Bars

Adding fibers is highly effective to enhance the deflection and ductility of fiber-reinforced polymer (FRP)-reinforced beams. In this study, the stress and strain conditions of FRP-reinforced lightweight aggregate concrete (LWC) beams with and without fibers at ultimate load level were specified. Based on the sectional analyses, alternative equations to predict the balanced reinforcement ratio and flexural capacity for beams failed by balanced failure and concrete crushing were established. A rational equation for estimating the short-term stiffness of FRP–LWC beams at service-load levels was suggested based on Zhu’s model. In addition, the contribution of the steel fibers on the short-term stiffness was quantified incorporating the effects of FRP reinforcement ratio. The proposed short-term stiffness model was validated with measured deflections from an experimental database for fiber-reinforced normal weight concrete (FNWC) beams reinforced with FRP bars. Furthermore, six glass fiber-reinforced polymer (GFRP)-reinforced LWC beams with and without steel fibers were tested under four-point bending. Based on the test results, the proposed models and procedures according to current design codes ACI 440.1R, ISIS-M03, GB 50608, and CSA S806 were linked together by comparing their predictions. The results showed that increasing the reinforcement ratio and adding steel fibers decreased the strain of the FRP bars. The flexural capacity of the LWC beams with and without steel fibers was generally underestimated by the design codes, while the proposed model provided accurate ultimate moment predictions. Moreover, the proposed short-term stiffness model yielded reasonable estimations of deflection for both steel fiber-reinforced lightweight aggregate concrete (SFLWC) and FNWC beams.

Life-Cycle Cost and Life-Cycle Assessment Analysis at the Design Stage of a Fiber-Reinforced Polymer-Reinforced Concrete Bridge in Florida

Abstract To support and promote the deployment of innovative technologies in infrastructure, it is fundamental to quantify their implications in terms of both economic and environmental impacts. Glass Fiber-Reinforced Polymer (GFRP) bars and Carbon Fiber-Reinforced Polymer (CFRP) strands are validated corrosion-resistant solutions for Reinforced Concrete (RC) and Prestressed Concrete (PC) structures. Studies on the performance of Fiber-Reinforced Polymer (FRP) reinforcement in seawater and salt-contaminated concrete have been conducted and show that the technology is a viable solution. Nevertheless, the economic and environmental implications of FRP-RC/PC deployment have not been fully investigated. This article deals with the Life-Cycle Cost (LCC) and Life-Cycle Assessment (LCA) analyses of an FRP-RC/PC bridge in Florida. The bridge is designed to be entirely reinforced with FRP bars and strands and does not include any Carbon Steel (CS) reinforcement. Furthermore, the deployment of seawater concrete in some of the elements of the bridge is considered. LCC and LCA analyses are performed at the design stage. Data regarding equipment, labor rates, consumables, fuel consumption, and disposal were collected during the construction phase, and the analysis was refined accordingly. The FRP-RC/PC bridge design is compared with a traditional CS-RC/PC alternative. Salient differences are discussed to determine the least-impactful solution from both an economic and environmental perspective.

New robust formulations for bond strength of FRP reinforcements externally glued on masonry units

The bond interface between fiber-reinforced polymer (FRP) and masonry units is one of the weakest links in tensile strengthened masonry structures. Several empirical formulae have been proposed for estimation of bond strength between FRP reinforcements and masonry units. However, the accuracy of existing formulae for predicting bond strength seems to be significantly limited. In the present study, the M5´ and Multivariate adaptive regression splines approaches are employed to predict the bond strength between FRP reinforcement and masonry units. To develop new models, a comprehensive database including 575 test series (230 distinctive specimens) is collected from different sources in the literature. The newly proposed formulations consider several preeminent parameters involved in the debonding process including the reinforcement width, the ratio between widths of FRP reinforcement and masonry unit, the tensile strength of substrate, the axial strength of reinforcement, and bond length. A comparative study is conducted to evaluate the performances of the developed models against the well-known equations. Results indicated that the proposed models remarkably outperform the existing equations in terms of accuracy. Furthermore, a sensitivity analysis is done to determine the most important parameters in predicting the bond strength. Finally, the safety of different methods is evaluated based on the demerit point classification scale.

Finite element simulation of RC beams under flexure strengthened with different layouts of externally bonded fiber reinforced polymer (FRP) sheets

DOI: 10.7764/RDLC.17.3.383 Current research work is aimed to numerically simulate the failure behavior of Fiber Reinforced Polymer (FRP) strengthened reinforced concrete beams having different FRP reinforcement ratios. Required objectives are achieved by performing a series of bending tests on RC beams carrying different FRP layout and FRP reinforcement ratio. Tested beams were numerically simulated by using a Finite Element Method based computer package. The layouts of the FRP strengthening were decided based upon the FRP reinforcement ratios ranging from fully wrapped beams to the beams having significantly lower FRP reinforcement ratios. Tests results are presented in the form of load-deflection curves for all of the beams and a comparison of different beam strengthening schemes is also presented. Failure patterns of RC beams strengthened with different layouts of externally bonded FRP sheets were also compared. Results of flexural tests on twelve beams specimens and numerical simulation have indicated that CFRP and GFRP can significantly increase the bending and shear strength of retrofitted beams. However, the use of higher FRP reinforcement ratios to get higher strength increment is not advisable as epoxy properties and concrete surface quality plays a vital role to increase flexural and shear strength.

An experimental study on the effect of CFRP on behavior of reinforce concrete beam column connections

The aim of this research is reinforcing of concrete with variety of fiber reinforced polymer (FRP) configurations and investigates the load capacity and ductility of these connections using an experimental investigation. Six scaled-down RC exterior joints were tested under moderately monotonic loads. The results show that, the shape of the FRP had a different effect on the joint capacity and the connection ductility coefficient. The greatest effect on increasing the ductility factor was seen in the sample where two reinforcement plates were used on both sides of the beam web (RCS5 sample). For the sample with the presence of FRP plates at the top and bottom of the beam (RCS3 sample), the ductility factor was reduced even the load capacity of this sample increased. Except for the RCS3 sample, the rest of the samples exhibited an increase in the ductility factor due to the FRP reinforcement.

Experimental and analytical investigation on CFRP strengthened glulam laminated timber beams: Full-scale experiments

Timber is one of the most appealing and aesthetic construction materials with excellent characteristics compared with other construction materials such as steel, concrete and clay bricks. It is one of the oldest sustainable construction materials and still continues to be a popular choice in modern infrastructure. In recent years, fibre reinforced polymers (FRP) has emerged to improve mechanical properties even further. In this study, results of experimental tests on strengthened glulam beams have been used to investigate potential parameters affecting flexural strength and ultimate load carrying capacity of glulam beams strengthened with externally bonded FRP sheets. Eight full-scale timber beams with and without FRP reinforcement were tested where the bonded length, width, and thickness of the FRP was varied for FRP strengthened beams. The test results pointed out that reduction of stress concentrations can enhance the mechanical performance of the strengthened beams. The ultimate load carrying capacity and flexural strength of reinforced beams improved significantly when bond length and bond width increased. Results of experiments showed that further increase in bond thickness predominantly improves stiffness and ductility of the strengthened timber beams which has a significant enhancement in ultimate deflection and serviceability limit state. An analytical model has been established to determine the ultimate flexural capacity of strengthened timber beam. Satisfactory correlation is achieved between measured and predicted flexural capacity, signifying the capability of the new models.