Fiber Reinforced Plastic Bars Research Articles

Investigation on the Alkali-Resistance Properties of Basalt Fiber Reinforced Plastics Bars in Concrete

As a new type of building material, Basalt Fiber Reinforced Plastics is employed in concrete in place of steel reinforcement under such strongly-corrosive environment as marine engineering projects to avoid durability problem caused by corrosion. But BFRP bars’ alkali-resistance must be considered and studied. In this study, BFRP was soaked in saturated Ca(OH)2 solution and its tensile strength was measured through long-period immersion and high-temperature immersion experiments respectively. Besides, accelerated high-temperature method was adopted to detect its main ingredients: continuous Basalt fiber and resin. The results indicate that BFRP has poor alkali-resistance and its alkali-resistance must be improved if it is applied in concrete for long-term purpose.

Bending Strength of Timber Beams Rehabilitated with Reinforced Epoxy Mortar Plates

The need for restoration of the built heritage increases the demand for new strengthening and rehabilitation techniques of structures. This paper discusses a rehabilitation system for timber beams, consisting of the replacement of the decayed parts by new ones of nearly the same material, connected to the sound parts by reinforced epoxy mortar plates. The use of this technique allows for lighter and less intrusive works, compatible with the normal building occupation during the rehabilitation process. The experimental analysis undertaken focused on the flexural bonding behavior with stainless steel, reinforcement steel, and glass fiber reinforced plastic bars being used as alternatives. A simple analytical model, based on the usual assumptions of the bending theory, is proposed, leading to a reasonable agreement with the experimental results. In spite of a reduction of strength when compared to the original elements, the safety level of the rehabilitated elements is high enough to comply with the Eurocode 5 requirements and is, therefore, suitable for actual works.

Experimental study on ductility improvement of reinforced concrete rectangular columns retrofitted with a new fiber reinforced plastics method

Reinforced concrete (RC) columns lacking adequately detailed transverse reinforcement do not possess the necessary ductility to dissipate seismic energy during a major earthquake without severe strength degradation. In this paper, a new retrofit method, which utilized fiber-reinforced plastics (FRP) confinement mechanism and anchorage of embedded bars, was developed aiming to retrofit non-ductile large RC rectangular columns to prevent the damage of the plastic hinges. Carbon FRP (CFRP) sheets and glass FRP (GFRP) bars were used in this test, and five scaled RC columns were tested to examine the function of this new method for improving the ductility of columns. Responses of columns were examined before and after being retrofitted. Test results indicate that this new composite method can be very effective to improve the anti-seismic behavior of non-ductile RC columns compared with normal CFRP sheets retrofitted column.

Pilot Study of Behavior of Concrete Beams Reinforced with Shape Memory Alloys

This paper discusses the superelastic behavior of shape memory alloy, Nitinol (NiTi) , when used as reinforcement in concrete beams. The ability of NiTi to recover and reduce permanent deformations of concrete beams was investigated. Small-scale concrete beams, with NiTi reinforcement were tested under half-cycle loads. The reinforcement ratio varied from 0.1 to about 0.9%. The experimental results showed that the average residual displacement in the NiTi reinforced beams was less than one-fifth of that of the steel reinforced test beams. The stiffness of NiTi reinforced test beams however was lower than those of the steel reinforced test beams. An analytical study of load–deflection relationship for a series of hybrid beams was undertaken. It was found that a hybrid system that incorporated NiTi combined with high strength steel or carbon fiber reinforced plastic bars was a better choice for design because of their relatively high stiffness.

FE modelling of bond interaction of FRP bars to concrete

In this paper a computational modelling approach is used to investigate the bond behaviour of fibre-reinforced plastic (FRP) bars in concrete. Two finite element packages (ANSYS and ABAQUS) are used to model the bond interaction of FRP reinforcing bars in cubes and beams. The main purpose of this work is to develop additional understanding of how FRP bars ‘cooperate’ with concrete to sustain the pullout load. Two modelling approaches are presented. In the first approach, a spring describing the behaviour of short embedment lengths in pullout tests was used for predicting the behaviour of longer embedment lengths. In the second approach, spring characteristics obtained from an experimentally determined bond stress against anchorage length envelope are used in FE modelling of beams. Both approaches showed good agreement between analytical and experimental results. However, further development on the analytical modelling of the bond interaction is required, in order to consider the effect of all parameters that influence bond.

Shear strengthening of existing concrete bridges

The shear capacity of existing concrete bridge beams is often inadequate and unable to meet current code requirements. This is often due to increased traffic loads, inadequate shear-resistance provision in the original design or deterioration of materials due to aggressive environments. This paper deals with a new type of shear strengthening for existing concrete bridges. It is proposed that vertical steel or fibre-reinforced plastic bars be inserted into pre-drilled holes and fastened in place using epoxy resin. This method has the advantage that only the soffit of the concrete bridge beam (or slab) is required for access, allowing the top surface to remain undamaged during strengthening. This could allow the bridge to be used during strengthening works, with traffic relatively unhindered by work being carried out below. Further, no threaded bars and plates are required in this scheme, solving the notorious installation and maintenance problems associated with present shear-strengthening schemes. Ten laboratory tests are presented here to demonstrate the system, and comparisons are made against current code predictions for the strength of such concrete beams with and without transverse reinforcement. An upper-bound plasticity-based solution is also provided as a means to explain enhancement in shear capacity in specimens with very few embedded vertical bars. The results of this work show that the proposed strengthening scheme is effective and provides significant improvement in the shear-carrying load capacity. Additionally, code predictions for capacity of the strengthened beams are rather accurate, so that this strengthening method may be adopted with confidence.

Shear strengthening of existing concrete bridges

The shear capacity of existing concrete bridge beams is often inadequate and unable to meet current code requirements. This is often due to increased traffic loads, inadequate shear-resistance provision in the original design or deterioration of materials due to aggressive environments. This paper deals with a new type of shear strengthening for existing concrete bridges. It is proposed that vertical steel or fibre-reinforced plastic bars be inserted into pre-drilled holes and fastened in place using epoxy resin. This method has the advantage that only the soffit of the concrete bridge beam (or slab) is required for access, allowing the top surface to remain undamaged during strengthening. This could allow the bridge to be used during strengthening works, with traffic relatively unhindered by work being carried out below. Further, no threaded bars and plates are required in this scheme, solving the notorious installation and maintenance problems associated with present shear-strengthening schemes. Ten laboratory tests are presented here to demonstrate the system, and comparisons are made against current code predictions for the strength of such concrete beams with and without transverse reinforcement. An upper-bound plasticity-based solution is also provided as a means to explain enhancement in shear capacity in specimens with very few embedded vertical bars. The results of this work show that the proposed strengthening scheme is effective and provides significant improvement in the shear-carrying load capacity. Additionally, code predictions for capacity of the strengthened beams are rather accurate, so that this strengthening method may be adopted with confidence.

Performance of glass fiber reinforced plastic bars as a reinforcing material for concrete structures

Abstract The increasing use of fiber reinforced plastic (FRP) bars to reinforce concrete structures necessitates the need for either developing a new design code or adopt the current one to account for the engineering characteristics of FRP materials. This paper suggests some modifications to the currently used ACI model for computing flexural strength, service load deflection, and the minimum reinforcement needed to avoid rupturing of the tensile reinforcement. Two series of tests were conducted to check the validity of the suggested modifications. The first series was used to check the validity of the modifications made into the flexural and service load deflection models. The test results of the first series were also analyzed to develop two simple models for computing the service load deflection for beams reinforced with glass FRP (GFRP) bars. The second series was used to check the accuracy of the modification suggested into minimum reinforcement model. Test results of the first series indicate that the flexural capacity of the beams reinforced by GFRP bars can be accurately predicted using the ultimate design theory. They also show that the current ACI model for computing the service load deflection underestimates the actual deflection of these beams. The two suggested models for predicting service load deflection accurately estimated the measured deflection under service load, and the simpler of the two pertains better predictions than those of the models available in the literature. Test results of the second series reveal that there is an excellent agreement between the predicted and recorded behavior of the test specimens, which suggests the validity of the proposed model for calculating the required minimum reinforcement for beams reinforced by GFRP bars.

An Interface Model for the Mechanical Interaction between FRP Bars and Concrete

An interface model for characterizing the interaction between fiber-reinforced plastic (FRP) bars and concrete is examined. When the bars have a significant surface structure, the interaction (commonly called bond) can be dominated by a mechanical interlocking. The model provides a macroscopic characterization of the bond behavior within the mathematical framework of elastoplasticity theory. While the bond model has been applied to both steel and FRP bars, the failure mechanisms can be quite different, thus application of the model to the bond of FRP bars merits critical evaluation. Among the important differences is the potential failure of the surface structure of the bar. Calibration and validation results are presented to highlight the potential strengths and weaknesses of the model. The model gives surprisingly accurate predictions of bond strength for four independent experimental studies. Additional experimental data for evaluation of the model are needed, but the initial results indicate the model could potentially be used to evaluate the behavior of structural components reinforced with FRP bars.

Ductility of Concrete Beams Reinforced with FRP Bars and Steel Fibers

A total of 18 concrete beams were tested to study the influence of adding steel fibers (SF) to concrete mix on the ductility of concrete beams reinforced with fiber reinforced plastics bars (FRP beams). The main variables in the study were the type and volume fraction of the steel fiber. The study also investigated the accuracy of an available model, developed originally to predict the flexural strength of concrete beams reinforced with SF and steel bars (SF-steel beams), after modification in estimating the flexural capacity of the fibrous FRP beams (SF-FRP beams). The results indicate that the ductility of FRP beams is less than 50% of that of the respective steel beams. The results also reveal that the ductility of SF-FRP beams is directly related to the fiber content. In addition, the test results show that inclusion of 1% of hooked SF can improve the ductility of FRP beams to be the same as that of the steel beams. Furthermore, comparison between the predicted and measured flexural capacity of SF-FRP beams shows that the modified model can predict the measured results within a reasonable accuracy.

Durability of AR Glass Fiber Reinforced Plastic Bars

Since the development of reinforced concrete over a century ago, engineers have constantly struggled with the corrosion problem of steel reinforcement. The new advances in the field of materials science have resulted in the development of fiber reinforced plastic (FRP) materials that could potentially be used as bars in reinforced concrete structures. The attractive features of this type of bars include high strength, light weight, and resistance to electrochemical corrosion. E-glass is the most widely used fiber material in FRPs; however, studies have shown that this type of fiber is susceptible to degradation in alkaline environments (i.e., concrete). This paper presents the results of a durability study on FRP bars made from an alternative glass fiber, alkali resistant (AR) glass, that could potentially improve the durability of FRP bars. A total of 160 bar samples were tested after exposure to corrosive solutions at temperatures of 25°C and 60°C. These solutions were designed to simulate accelerated exposure to adverse conditions in the field. Test variables included two matrix materials (polyester and vinyl ester), seven chemical solutions, and ultraviolet radiation. Moisture absorption by bars and associated changes in the mechanical properties were the focus of this study. In addition, 10 reinforced concrete beams were tested in flexure until failure, to examine the effects of exposure to concrete and deicing salts. Test results indicated that significant loss of strength could result from exposure of AR glass FRP bars to simulated aggressive field conditions. An analytical study based on diffusion models and Fick’s law was also conducted to predict the loss of strength. In the Fickian range of diffusion, the models predicted the loss of strength with a reasonable accuracy.

Flexural Behaviour of Concrete Beams Reinforced with FRP Bars

An experimental study of the behaviour of concrete beams reinforced with fibre reinforced plastic (FRP) bars in three-point bending was undertaken. The load-deflection response was monitored throughout the test. The results from the flexural tests on FRP reinforced concrete beams were compared with those obtained with steel reinforcement. The failure mechanisms and the ultimate loads and displacements for the FRP and steel reinforcement of concrete were analysed and compared.

Ductile Hybrid Fiber Reinforced Plastic Reinforcing Bar for Concrete Structures: Design Methodology

This paper addresses the need for a ductile or pseudo-ductile fiber reinforced plastic (FRP) reinforcement for concrete structures. The criteria to be met by the FRP, which are based on the properties of the steel reinforcing bar it is to replace, are threefold: high initial modulus, a definite yield point, and a high level of ultimate strain. It is shown that the use of a fiber architecture-based design methodology facilitates the optimization of the performance of FRP through material and geometric hybrid. Consequently, the advantages of FRP, such as high strength, low weight, and chemical inertness or noncorrosiveness, can be fully exploited. Using the material hybrid and geometric hybrid, it is demonstrated that the pseudoductility characteristic can be generated in FRP reinforcing bar. Critical material and geometric parameters such as elastic modulus, fiber volume fraction, twisting, crimp, and helical effect in the specimen components were investigated and parametric studies are reported. Ductile hybrid FRP bars were successfully fabricated at 3-mm and 5-mm nominal diameters using an in-line braiding and pultrusion process. Tensile specimens from these bars were tested and found to have consistent pseudoductile behavior and good agreement with the analytical predictions.

Analytical Prediction of Flexural Behavior of Concrete Beams Reinforced by FRP Bars

An analytical model to predict the flexural strength and deformations in concrete beams reinforced with fiber reinforced plastic (FRP) bars is presented. It is based on the equilibrium of forces and compatibility of deformation. The model uses a more rational representation of the behavior of all composite constituents. It also accounts for the concrete tensile stresses, the variation of stresses, strains and curvature over the depth of the cross section and the length of the beam. The model predicts the moment-curvature, load-deflection, and load-strain of any of the composite constituents. The model predictions were checked against the experimental results of nine test beams reinforced with steel or FRP bars. The behavior of the concrete tested beams were characterized by their moment-curvature, load-strain in the reinforcement, and load-deflection response up to failure. The results indicate that the analytical model predicts the behavior of GFRP reinforced concrete beams with good accuracy. Furthermore, the accuracy of the model was checked by comparing its capacity prediction with that of a parallel model available in the literature based on measured data and reported by other researchers. Results of the comparison showed that the suggested model provided better prediction.

Bond strength of cement grouted glass fibre reinforced plastic (GFRP) anchor bolts

Fibre reinforced plastic (FRP) has recently been introduced in the market in the form of bars for grouted anchor bolts. The resistance to corrosion and chemical attacks, high strength-to-weight ratio, low electromagnetic properties and ease in handling of these bars make them a better alternative to steel in some applications of grouted anchor bolts. However, to fully utilise FRP bars as tendons for cement grouted anchors, some aspects of their behaviour have to be determined, including load carrying capacity, bond strength in cement grout, long-term strength and durability in alkaline environments. In this paper, the load carrying capacity and bond strength of cement grouted glass fibre reinforced plastic (GFRP) anchor bolts are discussed in comparison with steel anchor bolts. The results of laboratory and field pull-out tests of GFRP and steel bars anchored with cement grout are presented. The pull-out tests were conducted on four types of GFRP bars and two types of steel bars installed in concrete blocks and rock mass. The experimental results have shown that the bond strength of GFRP bar anchor bolts is close to that of steel bar anchor bolts. The slip at failure of GFRP bars relative to the cement grout is greater than that of steel bars, mainly due to their low modulus of elasticity.

Local bond stress-slip relationships of glass fibre reinforced plastic bars embedded in concrete

The bond relationships between glass fibre reinforced plastic bars with polyester matrix and concrete is investigated in order to obtain information concerning the possible use of these bars for the reinforcement of concrete constructions, where the use of ordinary steel bars could have certain disadvantages due to the possibility of corrosion. The results obtained are used to develop a model of the stress-slip relationship and to estimate the anchorage lengths needed to embed these bars in concrete casts.