Glass Fiber Reinforced Polymer Bars Research Articles

Experimental and Numerical Investigation of Compressive Membrane Action in GFRP-Reinforced Concrete Slabs

Experimental and numerical analyses of eight in-plane restrained slabs (1425 mm (length) × 475 mm (width) × 150 mm (thickness)) reinforced with glass fiber-reinforced polymer (GFRP) bars are reported in this paper. The test slabs were installed into a rig, that provided 855 kN/mm in-plane stiffness and rotational stiffness. The effective depths of the reinforcement in the slabs varied from 75 mm to 150 mm, and the amount of reinforcement changed from 0 to 1.2% with 8, 12, and 16 mm bar diameters. A comparison of the service and ultimate limit state behavior of the tested one-way spanning slabs shows that a different design approach is necessary for GFRP-reinforced in-plane restrained slabs that demonstrate compressive membrane action behavior. Design codes based on yield line theory, which considers simply supported and rotationally restrained slabs, are not sufficient to predict the ultimate limit state behavior of restrained GFRP-reinforced slabs. Tests reported a higher failure load for GFRP-reinforced slabs by a factor of 2, which was further validated by numerical models. The experimental investigation was validated by a numerical analysis, and the acceptability of the model was further confirmed by consistent results obtained by analyzing in-plane restrained slab data from the literature.

Initial stage degradation of GFRP bars based on functional group ratio change using FTIR in high temperature and alkaline solution

Although extensive research has been conducted on the use of glass fibre-reinforced polymer (GFRP) bars in concrete, one factor that hinders their widespread use in civil engineering is the lack of prediction of degradation properties in concrete for long-term applications. This paper presents the tensile strength (TS) retention and microstructure evolution of GFRP bars in high-temperature and alkaline solutions by Fourier transform infrared (FTIR) spectroscopy. The test results indicated that with TS retention above 70%, the main reason for the mechanical property loss was resin degradation. Significant chemical degradation of the rod surface, namely, the breaking of ester bonds and the formation of carboxylates, was observed by FTIR and scanning electron microscopy (SEM). However, when the TS retention was less than 70%, damage to the bars was induced by debonding of the resin/fibre and localized damage to the resin and fibres. Finally, the relationship between the functional group ratio change and TS retention of GFRP was established using FTIR, revealing a linear relationship and introducing a coefficient k for modification. This can provide a scientific basis for the subsequent method to predict the degree of mechanical property degradation of GFRP bars by FTIR monitoring of the functional group ratio change.

Contribution of longitudinal GFRP bars in concrete filled FRP tubular (CFFT) cylinders under monotonic or cyclic axial compression

Most of the current design guidelines/codes ignore the compressive contribution of glass fiber reinforced polymer (GFRP) bars in compression members, due to: (1) the compressive strength of GFRP bars is significantly lower than their tensile strength due to fiber micro-buckling or shear failure of GFRP bars under compression; (2) the peak axial load of an unconfined concrete column is achieved at a relatively low axial strain at which the GFRP bars develop small axial stresses due to their low elastic modulus. However, existing studies have demonstrated that, if adequate transverse bars are provided, the contribution of longitudinal FRP bars to the total load resistance of the column is significant partially due to the enhanced axial strain at peak axial load because of the confinement provided by the transverse bars. In concrete filled FRP tubular (CFFT) columns, which is an emerging and attractive form of columns for new construction, the ultimate axial strain of concrete is significantly enhanced by FRP confinement and thus the contribution of internal longitudinal GFRP bars is also expected to be enhanced. However, the compressive behavior of GFRP bars in CFFT columns has never been investigated. This paper therefore presents the results of an experimental program on CFFT cylinders with internal longitudinal GFRP bars. The test results demonstrated that FRP bars contribute significantly to the total load resistance of CFFT cylinders. The FRP bars in CFFT cylinders experienced crushing failure with load resistance close to that derived based on the compression tests on bare FRP bars. A simple analysis method for the axial load at FRP bar crushing for CFFT cylinders was finally proposed.

Effects of simulated seawater on static and fatigue performance of GFRP bar–concrete bond

Due to their excellent resistance to chloride ions, glass-fiber-reinforced polymer (GFRP) bars are employed to replace steel bars in seawater–sea-sand concrete (SWSSC). The performance of the concrete beams reinforced with GFRP bars depends on the bond between GFRP bars and SWSSC, which is significantly influenced by the marine environment and fatigue loading. Thus, the present study uses pullout tests to investigate the effects of simulated seawater on the static and fatigue properties of the GFRP bar–concrete bond. The impacts of the immersion time, environmental temperature, concrete type, and fatigue loading level are examined. The static interfacial bond strength and the corresponding slip of GFRP bar–SWSSC and GFRP bar–river-sand concrete (RSC) composites increase with the immersion time and the environmental temperature. Coupling the immersion environment and fatigue loading does not affect the failure mode of the GFRP bar–SWSSC and GFRP bar–RSC composites. Fatigue loading eliminates the defects in the interface between the GFRP bar and concrete, and the effects of eliminating the interfacial defects lessen with the immersion time and the environmental temperature. The fatigue load controls the performance degradation of the interfacial bond between the GFRP bar and concrete under coupling fatigue loading and immersion in simulated seawater. Meanwhile, there is no difference in the bond strength of the GFRP bar–RSC and GFRP bar–SWSSC composites under coupling fatigue loading and immersion in seawater. Nevertheless, the GFRP bar–SWSSC composite offers better static bond stiffness than the GFRP bar–RSC composite.

Bond-slip Behaviour of NSM GFRP Bars in Reinforced Recycled-Aggregate Concrete: Experiments and a Modified Model

Bond-slip behaviour of glass fiber-reinforced polymer (GFRP) bars embedded in conventional concrete has been widely investigated. In contrast, the bond-slip behaviour of near-surface mounted (NSM) GFRP bars bonded in reinforced recycled aggregate concrete (RAC) seems to be less explored, while recycled materials have been increasingly used due to reasons of environmental pollution and resource exhaustion. This study aimed to experimentally and theoretically examine the bond-slip behaviour of NSM GFRP bars in reinforced RAC under monotonic and cyclic loadings. To achieve this aim, twenty-four tests were performed, which were divided into two groups by monotonic and cyclic loadings. In each group, twelve tests were performed on ten reinforced RAC specimens and two reinforced normal aggregate concrete (NAC) specimens. The test results confirmed the brittle shear failure of concrete in the proximity of a resin-concrete surface. Bond-slip behaviour can be characterized by nonlinear and linear branches, in which the linear branch dominates the behaviour. Under monotonic and cyclic loadings, the average slips of GFRP bars in reinforced RAC were 0.238 and 0.284 mm, and their coefficients of variation (COV) were relatively large at 0.142 and 0.130, respectively. In contrast, ultimate loads had a relatively low COV of around 0.038. The effect of cyclic loading significantly increased the ultimate slip by 19.3%, whereas it negligibly reduced the ultimate load; consequently, the stiffness was reduced by 19.4%. A modified smooth model was proposed to predict the bond-slip behaviour of NSM GFRP bars in reinforced RAC under monotonic and cyclic loadings. The simplicity and accuracy of the model can be useful for engineers in structural retrofitting using NSM FRP technique. Doi: 10.28991/CEJ-2023-09-02-01 Full Text: PDF

Bond between Sand-Coated GFRP Bars and Normal-Strength, Self-Compacting, and Fiber-Reinforced Concrete under Seawater and Alkaline Solution

Bond durability between fiber-reinforced polymer (FRP) bars and concrete is a significant point of concern with respect to structural integrity, performance, and retrofit purposes. This experimental study addresses the bond durability of glass-FRP (GFRP) bars embedded in different concretes after exposure to harsh environmental conditions (i.e., seawater and an alkaline solution at 60° C). A total of 54 beam specimens of self-compacting, fiber-reinforced, and normal concretes were constructed, conditioned, and tested under flexural pullout according to RILEM provisions, which simulate the reinforcement behavior as a structural element in buildings. Sand-coated GFRP bars and steel bars were used to reinforce concrete beams. The obtained results demonstrated that the bond strength of beams with sand-coated GFRP bars decreased less after exposure to seawater in comparison with alkaline solution. However, the converse outcome was found for beams with steel bars. In addition to the reinforcing bars, the type of concrete was found to be effective in the bond durability of beams with both GFRP and steel bars under aggressive environments. Generally, the higher the density and strength, and the lower the permeability, the greater the bond strength and less its reduction.

Proposed Development Length Equations for GFRP Bars in Flexural Reinforced Concrete Members

The bond at the interface between concrete and the surface of a glass fiber–reinforced polymer (GFRP) bar is the most critical parameter to ensure that the strains between the GFRP bar and the surrounding concrete are compatible. To prevent bond failure, an adequate development length should be provided. This study evaluated the current recommended equations for the development length using an approach based on the regression analysis of an experimental database of results from 431 recent tests of beam bonding reported in the literature. The main objective of this work is to optimize the development length equation through a comprehensive assessment of the influencing parameters. The parameters studied in this investigation are the concrete compressive strength, concrete cover, confinement effect, bar diameter, bar location, bar surface profile, and bar tensile stress. The proposed equations were compared with the equations in current design codes.

Study on Shear Behaviors and Damage Assessment of Circular Concrete Short Columns Reinforced with GFRP Bars and Spiral Stirrups.

This study investigated the shear resistance and damage evolution of glass fiber-reinforced polymer (GFRP)-reinforced concrete short columns. Five circular concrete short columns reinforced with GFRP bars and spiral stirrups were fabricated and tested under lateral thrust in the laboratory. The test variables involved the stirrup reinforcement ratio, the longitudinal reinforcement ratio and the type of stirrups. The failure modes, load-displacement curves, strain responses and crack characteristics of these columns were documented and discussed. The accuracy of shear design equations in predicting shear capacity of such columns was evaluated. In addition, the digital image correlation (DIC) instrument was used to identify the full-field strain and damage zones of circular concrete short columns. Several smart aggregate (SA) transducers coupled to the surface of these columns were used to monitor its damage status. The energy ratio index (ERI) and the damage index based on smart aggregate were established to characterize damage level of such columns. The test results indicate that the shear capacity is improved 5.6% and 31.1% and the lateral ultimate displacement is increased 67.7% and 400% as the stirrup reinforcement ratio of the concrete short column is increased from 0 to 0.19% and 0.47%, respectively. The shear capacity equation proposed by Ali and his co-workers, considering a strain limit of 0.004Efv, gives accurate predictions of the shear capacity of circular concrete short columns reinforced with GFRP bars and spiral stirrups. The variation in ERI values is explained by the development of damage zones of the column obtained with DIC technology and with the proposed damage index based on the smart aggregate it is feasible to evaluate the damage level of circular short concrete columns.

Experimental and theoretical studies on bond behavior between concrete and FRP bars with different surface conditions

Design of bond length of over-crowded rebar becomes a remarkable challenge in the critical loaded structure members. Enhancing bond strength between concrete and rebar is a feasible way to improve this situation, which can be realized by improving the bar surface condition (i.e., rib height and rib space). However, effect of these two parameters on the bond performance are not comprehensively studied. In this paper, 16 groups including 48 samples were tested, in which three types of bars (i.e., steel bar, glass fiber-reinforced polymer (GFRP) bars and basalt fiber-reinforced polymer (BFRP) bars) with different surface conditions were considered. To study the adhesion and friction effect, Scanning-Electron-Microscope (SEM) observations were performed. When the rib effect on the bond performance was investigated, the bond strength caused by adhesion and friction effect was excluded from the bond strength of ribbed bars. Experimental results indicate that bond strength can be enhanced if bars with larger rib height is used. To predict the bond strength that can consider the effect of rib height, a theoretical model is developed.

Shear strength of functionally graded self-compacting concrete deep beams reinforced with steel and GFRP bars

Glass fiber-reinforced polymer (GFRP) bars are emerging as a potential replacement for steel rebars due to their vulnerability to corrosion. However, the shear behavior of GFRP bars is not well established, especially in functionally graded self-compacting concrete (SCC) deep beams reinforced with hybrid rebars (GFRP and steel). This article experimentally explores the behavior of functionally graded high-strength SCC deep beams having a hybrid of steel and GFRP bars as tension reinforcement. A total of fourteen deep beams were prepared with varying reinforcement ratios and steel fiber volume fractions. There were three groups of deep beams: (i) plain SCC (i.e., no fibers) beams, (ii) fiber-reinforced SCC (FRSCC) beams having 0.6 % and 1.2 % steel fibers, and (iii) functionally graded deep beams. The functional grading was achieved by casting beams in two layers, with the first layer of lower two-thirds depth having steel fibers and the second layer without fibers. The beams were shear deficient and tested in flexure. The shear resistance of functionally graded deep beams was compared with beams having fibers in full depth and without fibers. The test results reveal the significance of the hybrid system of rebars, which is found to effectively improve the structural capacity of concrete beams and increase the load required to initiate cracking. In addition, the mixing of fibers in concrete enhanced the deep beam shear capacity by 15–23 % for 0.6 % fibers and 37–39 % for 1.2 % fibers. The increase in the shear resistance of concrete deep beams was not influenced by the use of hybrid rebars compared to using GFRP bars only. A model is developed for assessing the shear resistance of functionally graded fiber-reinforced concrete deep beams by incorporating the dowel action of hybrid longitudinal reinforcing bars. The study indicates that the dowel action provided by GFRP bars is comparable to the steel bars of the same area.

A simplified approach for design of steel-GFRP hybrid reinforced concrete sections

The corrosion of steel reinforcement is one of the main reasons for the deterioration of reinforced concrete (RC) structures subjected to harsh environments. Glass fibre-reinforced polymer (GFRP) reinforcing bars have emerged as an ideal solution at an affordable cost for eliminating this issue. The design of steel RC elements can be controlled by ultimate limit state (ULS) requirements, resulting in over-designed sections for the serviceability limit state (SLS). On the other hand, the design of GFRP RC elements is typically controlled by SLS checks, resulting in over-designed sections for the ULS. Replacing some steel rebars with GFRP bars could be an economical solution in the case of a shortage in the supply of steel rebars, especially in large quantities of steel reinforcement. This replacement with GFRP bars would be even more economically attractive if the replaced steel bars were stainless, epoxy-coated, zinc-coated or galvanized. This research aims to set a platform for designing steel-GFRP hybrid RC sections. Based on fundamental theories of reinforced concrete beams and the available literature, design considerations are suggested for the design of steel-GFRP hybrid RC flexural elements. Using the proposed design recommendations, an analytical study was undertaken to develop simplified design charts for transforming steel RC sections to alternative steel-GFRP hybrid RC sections with the same total number of bars. This research proposes a step-by-step design procedure using design charts to find a replacement ratio of an alternative steel-GFRP hybrid RC section using properties of a steel GFRP RC section that would suit its design purpose.

Flexural response of GFRP RC beams strengthened with side and bottom NSM GFRP bars

This study exhibits the bending performance of reinforced concrete (RC) beams with glass fiber-reinforced polymer (GFRP) rods. The beams were strengthened with the bottom or side near surface mounted (BNSM or SNSM) methods. Applying BNSM strengthening to the RC beam is difficult in some cases, so the SNSM became essential. Due to the limited research dealing with this type of beam, this study focuses on the effect of internal and NSM reinforcement areas and the NSM position on the response of the beams. Two un-strengthened and six strengthened RC beams were tested in bending. The GFRP RC beams upgraded with SNSM GFRP bars showed higher deflection, energy dissipation, ductility, and ductile failure than those upgraded with BNSM ones. On the contrary, the load-carrying capability and flexural stiffness of GFRP RC beams strengthened with BNSM GFRP rods were slightly higher than those strengthened with SNSM GFRP. Consequently, a parametric investigation relying on the verified finite element (FE) model was executed. This parametric work aimed to add additional data to the literature related to the influences of the internal and NSM reinforcement type and area on the performance of beams with ‎SNSM. According to the FE results, increasing the NSM reinforcement area improved the capacity and stiffness of the upgraded beams regardless of the combination of the internal and NSM reinforcement. The relative axial stiffness between internal and NSM materials significantly impacted the beam performance. Moreover, using GFRP with CFRP or steel with CFRP indicated higher performance than using steel with GFRP, regardless of which one was located as NSM.

Evaluation of deflection and flexural performance of reinforced concrete beams with glass fiber reinforced polymer bars

This paper aims to experimentally evaluate the load-deflection curve and flexural performance of reinforced concrete (RC) beams with glass fiber reinforced polymer (GFRP) bars. Twelve RC beams were well instrumented and tested under four-point loading for failure. The RC beams had a constant large scale size of 2400 mm long, 250 mm deep, and 180 mm wide. The main test variables are the reinforcement materials (GFRP and steel bar), the concrete strength (36, 73, and 84 MPa), the GFRP reinforcement ratio (0.39–1.19%), and the GFRP bar diameter (8, 12, and 14 mm). The test results of the RC beams including failure mode, load-deflection response, and nominal moment-materials strain curves were compared and discussed. ACI 440, ISIS, and fib for GFRP RC beams, and ACI 318, CAS A23.3, and EC2 for steel RC beams were evaluated to predict failure modes and flexural capacities. Furthermore, nine theoretical models were applied to find the effective moment of inertia and then to predict load-deflection curves. The ratios of experimental to theoretical results were reported and discussed at service and failure loads. It was found that several models can reasonably predict deflection up to 40% of failure load whereas the majority underestimate the deflections at failure with various accuracies. The experimental results revealed that using high strength concrete significantly improved the failure load up to 28% and reduced deflections and crack widths of GFRP RC beams.

Seismic performance evaluation of steel and GFRP reinforced concrete shear walls at high temperature

Fire-induced structural damage to the seismic performance of reinforced concrete shear walls is critical in the event of a fire-earthquake scenario. However, only few researchers have studied the seismic performance of reinforced concrete shear walls at high temperatures. This study focuses on the seismic performance of fiber reinforced concrete shear walls at high temperatures by using finite element (FE) software, ABAQUS. The experimental test available in a literature on seismic behavior of shear walls exposed to fire and thermal properties of glass fiber reinforced polymer (GFRP) bars were used to validate the FE model and showed good agreement and thus used in the simulation.The FE results showed that exposure of RC shear wall to fire reduced the strength of the wall. The strength of walls at the maximum applied drift of 3.2% with concrete cover thicknesses of 20 mm, 25 mm, and 30 mm was dropped by about 70%, 76%, and 85% of the reference shear wall, respectively. Similarly, the strength of RC walls was reduced by about 80%, 75%, and 68% of the reference shear wall for the duration of fire exposure of 30 min, 60 min, and 120 min, respectively. Additionally, the strength of walls due to one side, two sides, or all sides’ exposure to fire was decreased by about 68%, 56%, and 50% of the reference shear wall, respectively. It can generally be concluded that the fire exposure sides has largely affected the strength of the shear wall compared to the other parameters and GFRP bars were more sensitive to temperature than steel bars.

In-plane shear strengthening of traditional unreinforced masonry walls with near surface mounted GFRP bars

In this study, the effectiveness of Near Surface Mounted (NSM) method, for in-plane shear strengthening of traditional and historical Unreinforced Masonry (URM) walls, is investigated through a comprehensive experimental study. For this purpose, square solid clay brick masonry wallettes (42 samples) with three different types of traditional mortars including gypsum mortar, lime-cement-sand mortar and lime-sand mortar are prepared and retrofitted with NSM Glass Fiber Reinforced Polymer (GFRP) bars. Then, diagonal shear tests are conducted to evaluate the in-plane shear behavior of the masonry wallettes. The effects of some key variables such as wall thickness, the retrofitted face of the wall, reinforcement ratio, and the type of paste for mounting the reinforcing bars, on the effectiveness of the retrofitting method are investigated. The results of the tests are presented in terms of the failure modes and the lateral shear stress-drift curves of the test specimens. Accordingly, the retrofitting method can enhance the in-plane shear strength, and the ultimate lateral drift capacity of the URM wallettes. According to the test results, the type of filler paste and reinforcement ratio influence the strength enhancement of the test specimens. Furthermore, in specimens retrofitted with the one-side retrofitting scheme, due to the asymmetry of walls under in-plane loads, an unexpected out-of-plane deformation is induced in the walls under in-plane load which adversely affects its global behavior.

Experimental investigations on bond performance of GFRP bars

Corrosion of steel is one of the major problems concerning construction field which becomes more severe when the structures are subjected to harsh environment which is harmful to structure as well as costs high for repair. Hence, deviating to alternate building materials is essential in upcoming years. One of the latest findings among them is replacement of steel with Glass Fiber Reinforced Polymer (GFRP) bars. Experimental and numerical studies on various strength parameters of these bars are being undertaken to examine their replacement to steel. This work contains experimental investigations on bond performance of Glass Fiber Reinforced Polymer (GFRP) bars. In the present study the bond behavior GFRP bars with and without wrapping of binding wire embedded in polypropylene fibers reinforced concrete and conventional steel rebar embedded in plain concrete was tested. The grade of concrete used for investigation was M40 and for bond testing 10, 12 mm diameter steel and GFRP bars were used in this experimental work. Pull-out test was conducted in Universal Testing Machine (UTM). It was observed that bond behavior of GFRP bar and concrete were lesser than steel bar by 41.06 % for 10 mm diameter bars and by 31.63 % for 12 mm diameter bars. Although it was observed that GFRP bar wrapped with binding wire possessed lesser bond stress than steel bars, it has improved bond stress compared to GFRP without wrapping by 16.06 % for 10 mm diameter bar and by 14.22 % for 12 mm diameter bars. Also maximum slippage was observed for GFRP than steel bar and GFRP with binding wire wrapping. GFRP bar slippage of 10 mm and 12 mm diameter is 130.88 % and 63.64 % and respectively higher than steel bars. The bond strength and maximum slippage of GFRP bar is found to be decreased with increase in diameter.

Structural behavior of axially loaded high strength concrete columns reinforced longitudinally with glass fiber reinforced polymer bars

This study investigated the behaviour of axially loaded high strength concrete columns reinforced longitudinally with glass fibre reinforced polymer bars. Total six Reinforced Concrete (RC) columns and six Glass Fibre Reinforced Polymer (GFRP) reinforced concrete columns made with High Strength Concrete (HSC) with the addition of 1.20% of Alkali Resistant Glass Fibre (ARGF). The columns were cast with 1000 mm height and cross-sectional area is 150 mm x 150 mm and were tested under axial loading. The main objective of this study including to increase axial load carrying capacity and stiffness and reduce the ductility, mode of failure, and axial load-displacement response of columns. The RC columns are compared to the GFRP RC columns, and the GFRP RC columns are only carried 90% of the axial load compared to the RC columns. The Finite Element Model (FEM) was used to analyses all columns, and FEM helps predict the axial load.

Effects of concrete cover thickness and concrete strength on temperature transfer in high temperature exposed FRP reinforced concrete

While Fibre-Reinforced Plastics are lightweight, show a high tensile strength, and have no issue with corrosion, they are unfortunately brittle and perform poorly against temperature. Therefore, it is important to know the time and magnitude of the temperature reaching the bars in the high-temperature effect of FRPs produced in the form of bar in reinforced concrete structural elements in concrete. This study set out to examine the time and temperature values of glass fiber reinforced polymer (GFRP) reinforced concrete under high-temperatures. The effects of concrete cover thickness and concrete strength on temperature transfer were researched experimentally. GFRP bars were placed in specimens prepared in three concrete strengths and three different concrete cover thicknesses (20-40-60 mm) exposed to temperature, and temperature-time graphs were created by measuring bar temperature, concrete surface temperature and ambient temperature. The critical time to a glass transition temperature, and optimum cover thickness of GFRPs according to concrete strength and concrete cover thickness were discussed. The study results appeared to indicate that the thickness of the concrete cover is very effective in protecting the bar against temperature in reinforced concrete structural elements, as concrete strength, itself, has only a limited effect.

Numerical study on the behavior of RC beams by using GFRP bars as an alternate to steel bars

The numerical study of the behavior of reinforced concrete beams by using Glass fiber reinforced polymer (GFRP) bars as an alternate to steel bars has been explored in this research. The numerical modelling of the beams is done using Finite element analysis (FEA) software ABAQUS. In the present study the beam with Glass fiber reinforced polymer (GFRP) bars as both longitudinal & transverse reinforcement is compared with conventional reinforced concrete beam. The numerical simulation is performed for three-point bending for displacement control. The results of load, strain and deflection data has been obtained from the numerical modelling. Stress versus strain curves, load versus strain curves and load versus deflection curves are plotted using the output data. The displacement, strain developed in longitudinal bars and stirrups, load carrying capacity, energy absorbed are then calculated using the data and are compared. From the results, it is observed that the Glass fiber reinforced polymer (GFRP) reinforced concrete beams have load carrying capacity par with conventional reinforced concrete beam. Further, Glass fiber reinforced polymer (GFRP) reinforced concrete beams have higher yield strains and experienced more energy absorption over conventional reinforced concrete beam.

Design of concrete beam reinforced with GFRP bars as per ACI codal provisions

This document provides design principles for concrete beams reinforced with glass fiber reinforced polymer (GFRP) bars per the ACI 440.1R-15 regulation. One of the main advantages of using glass fiber reinforced polymer rods instead of traditional steel reinforced rods is their lighter weight and higher corrosion resistance. However, the bending failure mode of FRP reinforced concrete (FRP-RC) beams is brittle rather than ductile because the elasticity of fiber reinforced polymer (FRP) bars is linear until failure and the elongation at break is small. For FRP-RC elements, concrete crushing compression failure, which gives various warnings before failure, is the preferred failure mode. In other words, unlike the usual design practice for reinforced concrete (steel-RC) beams, for FRP-RC beams, an over-reinforced structure is preferable to an under-reinforced structure. In addition, since the FRP RC member has low rigidity of the FRP rod, it bends more and cracks larger than the steel RC member. These factors limit the field of application of FRP. Here is a design example of a rectangular beam with tension reinforcement according to ACI regulations.