Fiber-reinforced Polymer Reinforcement Research Articles

Circular Concrete Columns and Beams Reinforced with GFRP Bars and Spirals under Axial, Eccentric, and Flexural Loading

Abstract Glass fiber-reinforced polymer (GFRP) reinforcement has been considered as a replacement for the traditional steel reinforcement, mainly due to its corrosion resistance. In this paper, a t...

Identification of bond behavior between FRP/steel bars and self-compacting concrete using piezoceramic transducers based on wavelet energy analysis

The civil infrastructures constructed using self-compacting concrete (SCC) reinforced with fiber-reinforced polymer (FRP) bars are advocated for engineering applications due to corrosion resistance and environmental-friendly performance. The bond behavior between FRP reinforcement and SCC is a significant factor affecting the serviceability and failure mechanism of this composite structure. However, it is hard to identify the damage mechanism and failure mode of the interface bond using the traditional test methods. Therefore, an effective monitoring method of interface damage using piezoceramic transducers is proposed in this paper. A series of pull-out tests were performed, and the test variables involved concrete materials and reinforcing bar types. A lead zirconate titanate (PZT) patch transducer acting as an actuator was bonded on the outer surface of reinforcing bars, and a piezoceramic smart aggregate transducer acting as a sensor was embedded in the SCC. A wavelet energy ratio index (WERI) is proposed to identify the damage mechanism of interface between reinforcing bars and SCC. The experimental test results reveal that the damage mechanism and failure mode of the bond between different reinforcing bars and concrete materials can be identified effectively and the peak of bond stress can be captured accurately by using WERI values.

A Research on Modification Method for NSM FRP-Concrete Bonded Joints Strength Models

A modification method was proposed for near-surface mounted (NSM) fiber-reinforced polymer (FRP)-concrete bonded joints strength prediction models considering model uncertainty. A database consisting of 246 test records was involved. Three bonded joints strength prediction models for NSM FRP reinforcement system were selected for modification. All the three selected models have model uncertainty factors associated with input design parameters. Spearman correlation analysis was used to prove the systematic correlation of the model uncertainty factors. For each model, a regression functionfwas established to eliminate the systematic nonrandom part of the model uncertainty factor. Then, the model uncertainty factors could be described by random variables obeying logarithmic normal distribution. A reliability analysis using the JC method was carried out to validate the practical significance and value of model modification. This study improves the predictability of FRP NSM reinforcement systems and provides valuable references for model calibration in practical engineering.

Reliability analyses of shear strengthened RC beams with externally bonded fiber reinforced polymer

Different methods for the estimation of fiber reinforced polymer (FRP) contribution to shear strength in reinforced concrete (RC) beams were evaluated and compared through reliability analysis using FRP rupture and debonding failure functions. The carbon fibers properties were obtained through laboratory tests allowing to define the probability distribution function of the fiber tensile strength and elastic modulus. Uncertainties associated with the load, material properties were taken into account in order to compare two standards (ACI 440.2R and CNR-DT200) and two more sophisticated methods proposed in the literature. The Monte Carlo method and an improved first order reliability method (FORM iHLRF) were used to determine the structural reliability of an RC beam with externally bonded FRP. The results show the effects of the different mechanical methods in the reliability indices of the strengthened RC beam. The performance function related to FRP rupture presented a much higher reliability index than the other failure function related to FRP debonding for all four methods. A reliability-based design optimization was also performed to measure the effects of the assumptions and uncertainties associated with each method regarding the design variable (width of the reinforcement) for the same target reliability. The most conservative methods were the standards (ACI 440.2R and CNR-DT200), leading to a wider FRP reinforcement than the ones estimated by the other methods for the same reliability safe level design.

Assessment of the flexural behavior of continuous RC beams strengthened with NSM-FRP bars, experimental and analytical study

This paper deals with strengthening statically indeterminate reinforced concrete (RC) beams with carbon and glass Fiber Reinforced Polymers (FRP) rods by using the Near Surface Mounted (NSM) technique. The test program consisted of six two-span beams; one control beam, which had exploited for comparison purposes, and five others initially strengthened in flexure with NSM-FRP rods in both hogging and sagging regions. The main test parameters were type, ratio and length of the FRP bars as well as characteristics of the filling material. The study presents and discusses their impacts on the global flexural behavior of continuous RC beam that mainly includes investigating the overall capacity, failure mode, moment redistribution and ductility state.All NSM-FRP strengthened beams displayed higher overall capacity than the control beam; the test results showed that implementing the NSM technique in an appropriate way could significantly improve the yielding capacity and load-carrying capacity of RC beams without large decrease in the ductility index or the moment redistribution degree despite the non-conventional failure mode. The beam failure was primary affected by the strengthening length; terminating the FRP bars before the zero moment point caused to change the failure mode from pull out of the FRP bars to premature peeling off of the concrete cover. On the other hand, moment redistribution and ductility of the NSM-FRP beams were negatively affected by: (I) Increasing the FRP reinforcement, (II) Decreasing the FRP length or (III) Using mortar as a filling material instead of epoxy-resin. Adopting a nonlinear analysis of the cross-sections could accurately quantify the moment–curvature and the ultimate load of the NSM-FRP continuous beams.

Study on the flexural strengthening effect of RC beams reinforced by FRP grid with PCM shotcrete

Recently a new repair and retrofit method of reinforced concrete (RC) members that uses fibre-reinforced-polymer (FRP) grid with polymer-cement-mortar (PCM) shotcrete has been proposed. Four RC beams externally strengthened with CFRP grid-PCM at the bottom and one non-reinforced RC beam were tested to reveal their flexural behaviour and strengthening effect. The number of FRP layers and reinforcement amount per unit length of the CFRP grid were selected as the two main parameters in the test programme. The test results indicated that the flexural strengthening effect of the CFRP grid-PCM was sufficient; moreover, two-layer reinforcements were effective as one-layer ones under similar unit-reinforcement values. Furthermore, a new analytical model was proposed to evaluate the flexural capacities of RC beams strengthened with CFRP grid, and the predicted values were well matched to the test results and collected data.

Experimental investigation on hollow-steel-tube columns with external confinements

Tubular steel members with slender cross-sections in compression are prone to local buckling. Different approaches, such as infilling concrete, installation of internal stiffeners and externally bonding fiber-reinforced polymer reinforcement, have been developed to retard the local buckling of steel tubular sections, and hence to improve the performance of tubular structures. In this study, a total of 35 circular hollow-steel-tube (HST) stub columns with both non-slender and slender cross-sections confined by different types of external confinements, namely steel ring, spiral and jacket confinements were tested in the experimental program. The uni-axial behavior of externally confined HST columns, including the failure mode, ultimate load-carrying capacity, stiffness and ductility, were studied and discussed. The enhancements in strength, stiffness and ductility of HST columns with different external confinements were assessed. The results indicated that the improvements on strength and stiffness of the confined HST columns were insignificant for columns with non-slender cross-sections and were considerable for columns with slender cross-sections, whilst the ductility of the HST columns was substantially enhanced by external confinements. Based on the results, equations for column ductility evaluation considering the effects of cross-section slenderness ratio, steel strength and external confinement, are proposed in this study, which are able to predict the column ductility for unconfined and externally confined HST columns.

Experimental and theoretical investigation on shear behaviour of small-scale timber beams strengthened with Fiber-Reinforced Polymer composites

This paper presents an experimental program conducted on small-scale timber beams strengthened with Fiber-Reinforced Polymer (FRP) shear reinforcement at shear spans to evaluate the strengthening efficiency of FRP shear reinforcement. The experimental variables involve FPR type, different layers, and attaching configurations. Tests results indicate that the Carbon-FRP (CFRP) shear reinforcement generally shows higher strengthening efficiency than Glass-FRP (GFRP) shear reinforcement. In particular, the shear capacity of the timber beams strengthened with longitudinally attached unidirectional CFRP can be improved by 32.9% for one-layer and 68.6% for two layers, respectively. Transversally attached unidirectional FRP reinforcement at the shear spans of timber beams contributes insignificant increase of shear capacity. The bidirectionally weaving GFRP provides the strengthened timber beams with a limited increase of shear capacity compared to the bidirectionally attaching unidirectional GFRP. Finally, an analytical solution is driven for predicting the shear capacity of the FRP strengthened timber beams. It is shown that the calculated values are in good agreement with the experimental results indicating the theoretical derivations can be used to predict the shear capacity of the timber beams strengthened with FRP shear reinforcement effectively.

Bridge Case Study: What a Contractor Needs to Know on an FRP Reinforcement Project

AbstractCivil works construction is now facing a transformational change with the growing implementation of fiber-reinforced polymer (FRP) materials as rebars and tendons for concrete structures. T...

Torsion in concrete beams reinforced with GFRP spirals

Abstract Current FRP guidelines do not have enough evidence on the torsional performance of beams reinforced with glass fiber-reinforced polymer (GFRP) reinforcement due to the lack of research and complexity of the problem. A review of the past work was presented in the state-of-the-art section to stand on mile-stone prospective considering the variety and development of GFRP manufacturing. This study examined the rectangular spirals and rectilinear stirrups to reinforce concrete beams in the transverse direction under pure torsion loading. The test parameters included four levels of transverse reinforcement ratio and the type of transverse reinforcement in terms of rectilinear stirrups vs. spirals. The test results demonstrated that rectangular GFRP spirals provided superior tensile resistance required to develop high ultimate torsional moments after cracking and hence can be effectively used. The failure of the tested beams was attributed to the rupture of GFRP rectangular spirals at bent portions. The test results of the spiraled specimens were discussed and compared with predictions from a developed analytical model and based on CSA equations. Two values of failure plane angle and stress levels were considered. The 45-degree inclination angle provided safe predictions with an average experimental-to-practiced result of 1.16 compared to 0.99 using the 37.5-degree. Design equations were proposed and validated for the ACI code for a probable future incorporation.

Assessment Study of Glass Fiber-Reinforced Polymer Reinforcement Used in Two Concrete Bridges after more than 15 Years of Service

Assessment Study of Glass Fiber-Reinforced Polymer Reinforcement Used in Two Concrete Bridges after more than 15 Years of Service

Deformability and Stiffness Characteristics of Concrete Shear Walls Reinforced with Glass Fiber-Reinforced Polymer Reinforcing Bars

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A flexure-capacity design method and seismic fragility assessment of FRP/steel double-reinforced bridge piers

Lack of post-yield stiffness and corrosion resistance could inevitably result in a considerable loss of seismic performance for steel reinforced concrete (RC) piers. Fibre reinforced polymer (FRP) reinforcement can provide high tensile strength and protection from corrosion. To achieve a better post-yield stiffness and durability for piers, FRP/steel double-reinforced configurations were designed by the proposed flexural-capacity design method. A seismic fragility assessment was also conducted to investigate the effectiveness of design parameters, namely the ultimate tensile strength of FRP reinforcement, elastic modulus of FRP reinforcement, and ratio of steel reinforcement for a double-reinforced configuration to that for a steel RC configuration (). The results demonstrated that the FRP/steel double-reinforced piers satisfied the mentioned objectives, while the fragility of these piers was a 30.2% less than that of conventional steel RC piers. A 79.9% higher median PGA at the collapse damage state was achieved, when the elastic modulus of FRP reinforcement changed from 164 to 80.7 GPa. An increase in the median PGA of 34.8% can be achieved along with the increase of the ultimate tensile strength of FRP reinforcement. When was approximately 66%, FRP reinforcement exhibited the highest effectiveness on the seismic performance of piers.

Numerical Analysis on Flexural Behavior of Steel Fiber-Reinforced LWAC Beams Reinforced with GFRP Bars

Three-dimensional nonlinear finite-element (FE) models using an explicit algorithm were established to simulate the behavior of beams reinforced with glass fiber-reinforced polymer (GFRP) bars cast using lightweight aggregate concrete (LWAC) with and without steel fibers, and the progressive damage model was employed to simulate the rupture of GFRP. The developed FE model was evaluated by test results, and it exhibited good agreement with the test results in terms of moment–deflection response, serviceability performance, ultimate capacity, and failure mode. Influencing factors, including the section height, reinforcement ratio, and span length were discussed according to the established FE model. It was revealed that the reinforcement ratio corresponding to balanced failure was higher than that given by code ACI 440.1R, which confirmed the necessity of the amplification factor of a balanced reinforcement ratio to ensure concrete crushing of the beam. For specimens that failed due to concrete crushing, the increase in fiber-reinforced polymer (FRP) reinforcement ratio did not significantly improve the ultimate capacity, but it did have an obvious effect on the reduction of deflection at service load. Moreover, a greater reinforcement ratio was needed for beams when the span length increased.

Reliability analysis of footbridges pre-tensioned with carbon fiber reinforced polymer tendons under flexural loading

A common problem of concrete bridges is corrosion damages of the steel reinforcement. The related loss of capacity as well as visual effects often require expensive and elaborate refurbishment or even reconstruction. To overcome these drawbacks, the application of non-corrosive fiber reinforced polymer (FRP) reinforcement in concrete structures has been established and investigated throughout the last three decades. The successful application of prestressed carbon fiber reinforced polymer (CFRP) reinforcement in bridge constructions was demonstrated by several projects realized in the United States and Canada. Nevertheless, despite the successful realization of these projects, a widespread application has not yet been possible due to the lack of consistent and approved design regulations. In Germany and Europe, the use of FRP reinforcement in bridge construction is even limited to individual cases and non-prestressed reinforcement. Thus, further investigations are necessary to develop a comprehensive guideline for the design of members with pre-tensioned CFRP tendons in compliance with current codes of practice.In order to achieve this objective, a flexural design model for the design of bridge girders prestressed with CFRP reinforcement was developed. In this paper, the reliability analysis of the flexural design model applied to a modular footbridge system pre-tensioned with CFRP tendons is presented. Stochastic simulations are conducted to evaluate the safety of the developed footbridge concepts and to determine an appropriate partial safety factor for the CFRP tendons. For this purpose, the reliability requirements according to the specifications of Eurocode 0 (EC0) are analyzed and evaluation benchmarks are defined to allow for a sufficient reliability of the bridges. The statistical characteristics of the variable parameters needed for the analysis were defined based on a literature review and own investigations.

Numerical Study on the Flexural Behaviour of Concrete Beams Reinforced by GFRP Bars

Enhancement of the response of reinforced concrete (RC) beams applying fiber-reinforced polymer (FRP) reinforcement bars has become a popular structural technique over the past two decades as a result to the well-known advantages of FRP composites including their high strength-to-weight ratio and excellent corrosion resistance. This study presents numerical investigation of 20 concrete beams internally reinforced with GFRP bars without web reinforcement. The accuracy of the non-linear finite element model in ABAQUS software is first validated against experimental data from the literature. The study presents an investigation into the behaviour of FRP reinforced concrete beams including the evaluation of geometrical properties effects. In particular, the study is focused on the effects of span/depth ratio, the reinforcement ratio and the effective depth of the beam, aiming to correct deficiencies in this area in existing knowledge. It’s been revealed that the finite element model is capable of accurately simulating the flexural behaviour of FRP reinforced beams. It was able to predict, with high accuracy, the force-displacement response the beam. Results manifested that FRP reinforcement is a proper solution in order to boost the ductility of RC beam members. Moreover, although that increasing in the span/depth ratio of the beam decreases beam’s rigidity, however; it also postpones the yielding point in the beam’s flexural response and leads to a higher level of displacement ductility for the beam.

State-of-the-Art on Fire Resistance Aspects of FRP Reinforcing Bars

The behaviour of Fibre-Reinforced Polymer (FRP) bars and Fibre-Reinforced Polymer reinforced concrete (FRP-RC) members under fire exposure is quite different from conventional means. This may be attributed to the complex behaviour of the bars when they are subjected to fire, as well as to the complexity of fire test procedures. The thermomechanical properties of FRP bars depend on the chemical composition of their constituents, their interface performance and the production process. The choice of the type of fibres and matrix with characteristics suitable for the desired purpose, as well as their balanced proportions in FRP bar can be the key factors affecting the overall resistance of an FRP element in the event of fire. The work presents a theoretical background and is intended to identify existing gaps in knowledge to justify the need for the present study.

NURBS-based kinematic limit analysis of FRP-reinforced masonry walls with out-of-plane loading

A three-dimensional (3D) general upper-bound limit analysis procedure for the determination of the collapse load of out-of-plane loaded masonry walls with Fiber Reinforced Polymer (FRP) reinforcement strips is presented. The geometry of a given FRP reinforced masonry wall of arbitrary shape is represented by its Non-Uniform Rational B-Spline (NURBS) description in the three-dimensional Euclidean space. The NURBS parameter space is partitioned by means of a number of possible fracture lines and the original reinforced wall geometry is subdivided into an initial set of rigid elements, accordingly. An upper-bound limit analysis formulation, accounting for the main characteristics of both masonry material and FRP reinforcement by means of homogenization techniques, is deduced. Internal dissipation is allowed along element edges only and the effect of vertical loads and membrane stresses is considered as well. Numerical experiments show that a good estimate of the load bearing capacity is obtained provided that the initial arrangement of yield lines is adjusted by means of a suitable Genetic Algorithm (GA).

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.