Performance of doubly reinforced concrete beams with GFRP bars

1 Introduction

The corrosion of steel bars, which shortens the lifespan of reinforced concrete structures, is one of the most prevalent issues. Therefore, utilizing fiber-reinforced polymer (FRP) bars can delay the structure’s degradation and enhance its durability. FRP bars are now widely regarded as an effective and affordable solution to the corrosion issues that steel rebars in severe environments are prone to. One of the alternatives put forth to address the corrosion issue with steel bars structural concrete members is glass fiber-reinforced polymer (GFRP) bars [1].

GFRP is a composite and anisotropic material consisting of a polymer matrix reinforced with glass fibers. The most popular are GFRP bars since they are widely available and reasonably priced [2]. GFRP offers several advantages over traditional construction materials like steel and concrete, making it suitable for various applications in civil infrastructures, such as marine structures, bridge decks, and parking garages. GFRP rebars are corrosion-resistant, lightweight, and have a high strength-to-weight ratio [3,4,5,6,7,8,9,10].

Meanwhile, the disadvantages of the GFRP reinforcing bars, compared to conventional steel, include a comparatively low elasticity modulus, low ductility, and low stiffness. Also, the brittle failure behavior of GFRP-reinforced concrete members is one of the major obstacles to the use of GFRP bars as a replacement for steel bars [11]. At any load level, the decreased stiffness of GFRP bars, along with additional factors like different bond behavior, lower tension stiffening, and anisotropy of GFRP bars, causes crack width and deflection that are greater than those of conventional steel-reinforced structural concrete members [12,13]. Therefore, the structural designs of such members may be restricted by deflection limitations as a result of these significant deflections [14].

The behavior of GFRP-reinforced concrete beams under static loads has been the subject of much research [15,16,17,18,19,20,21,22,23].

Design guidelines and codes for FRP bars reinforced concrete structures have been developed as a result of many extensive research works. These include “Guide for the Design and Construction of Structural Concrete Reinforced with Fiber-Reinforced Polymer (FRP) Bars” (ACI 440.1R-15 [24]) and “Design and Construction of Building Structures with Fibre-Reinforced Polymers” (CSA S806-12 (R2021) [25]). Recently, GFRP bars have specific code outlined “Building Code Requirements for Structural Concrete Reinforced with Glass Fiber-Reinforced Polymer (GFRP) Bars-Code and Commentary” (ACI CODE-440.11-22 [26]).

The design of GFRP-reinforced concrete members for flexure is analogous to the design of steel-reinforced concrete members. Experimental data on concrete members reinforced with FRP bars show that flexural capacity can be calculated based on assumptions similar to those made for members reinforced with steel bars [24]. Concrete sections reinforced by steel bars are designed to ensure tension-controlled behavior exhibited by yielding steel before the crushing of concrete. The yielding of the steel provides a warning of failure of the member and significant ductility. However, it should be noted that the flexural behavior of GFRP-reinforced concrete beams is less ductile due to the linear elastic-brittle nature of GFRP bars. The nonductile behavior of GFRP reinforcement necessitates reconsidering the recommended tension-controlled approach for the concrete section. Accordingly, compression-controlled behavior is marginally more desirable for flexural members reinforced with GFRP bars. By experiencing concrete crushing before tensile rupture of the GFRP reinforcement, a flexural member does exhibit some inelastic behavior before failure [24,26]. So, over-reinforcing GFRP-reinforced concrete beams is recommended to ensure failure occurs through concrete crushing rather than bar rupture, which can be catastrophic. Although concrete crushing falls under the brittle category, this failure is preferable for GFRP RC flexural members. The margin of safety for the design of FRP RC flexural members is larger than the margin of safety for steel RC flexural members to account for the lack of ductility [24].

ACI CODE-440.11-22 [26] determines the controlling limit state by comparing ρ f (GFRP reinforcement ratio) to ρ fb (GFRP balanced reinforcement ratio), where ρ fb predicted assuming that the strain in the extreme concrete compression fibers attains the crushing value of 0.3% at the same time when the GFRP attains ε fu (design rupture strain). To satisfy the serviceability requirements, Vijay and GangaRao [27] recommended that ρ f for the GFRP-reinforced concrete member should be higher than 1.4 ρ fb . However, Xue et al. [23] concluded that the reinforcement ratio of ρ f = 1.5 ρ fb can be adopted as the upper bound for such flexural members in the transition zone. This was based on a statistical analysis of 173 flexural tests of GFRP-reinforced concrete beams gathered from various research.

GFRP bars possess high tensile strength only in the direction of the reinforcing fibers, which affects shear strength, dowel action, and bond performance; thus, design equations for shear strength and development length are necessarily different from the equations used for steel reinforcement in ACI 318-19 [28], although the design procedures themselves are similar [26].

The dowel action of the GFRP bars has a considerable impact on the shear strength of GFRP-reinforced concrete beams [29]. Additionally, GFRP-RC beams have a much lower shear capacity than traditional RC beams. That could be because the interlocking mechanism between the aggregates in GFRP-reinforced concrete beams has been broken by wider cracks that have appeared. Increasing the elastic modulus of GFRP bars will significantly improve the shear resistance of these beams [30].

Johnson [31] evaluated the GFRP reinforcement for its suitability as shear reinforcement for concrete structures, and based on the research results, the GFRP stirrups reached stresses that exceeded the minimum design limits. The increased stirrup strength led to overall beam strengths that exceeded the estimated values based on code design provisions. When transverse shear strength is provided by GFRP stirrups, the shear design problem is made significantly more difficult. The strength at bend points is significantly lower for hooked bars than for comparable straight bars due to the available production process. Additionally, since very significant transverse strains are necessary for a GFRP stirrup to fail, shear design with GFRP transverse reinforcement is often focused on limiting strains in the stirrup.

The stiffness of GFRP reinforcement can be as small as one-fourth that of steel reinforcement [26]. Due to this, significant differences between ACI CODE-440.11-22 [26] and ACI 318-19 [28] occur in serviceability design for deflection and crack control.

Shin et al. [32] focused on the performance of concrete beams reinforced with five ratios of GFRP bars (0.24, 0.36, 0.48, 0.72, 0.96%) and two concrete strengths (30 and 50 MPa). Their investigation showed that the behavior of the GFRP-reinforced beam was bilinear-elastic up to failure; also, its stiffness was reduced after crack appearance compared to conventional steel-reinforced concrete beam. They reported that to achieve adequate stiffness for deflection to be safe for serviceability, the flexural design of such members should achieve over-reinforced sections.

The post-cracking performance and deformability are significantly affected by the abrupt loss of the flexural stiffness experienced by the GFRP-reinforced concrete beams after the cracking of concrete [33,34]. Bischoff and Gross [33,34], Mousavi and Esfahani [35], Murthy et al. [36], and Chellapandian et al. [37] claimed that the low elastic modulus of GFRP bars accounts for the abrupt loss of concrete stiffness.

The use of high-strength concrete allows for better exploitation of the high-strength properties of the GFRP bars and assists in increasing the flexural stiffness of the cracked section, but the brittleness of high-strength concrete, as compared to normal-strength concrete, could reduce the overall deformability of the flexural member [38].

Adam et al. [39] and Elgabbas et al. [40] reported that increasing the concrete compressive strength f c ′ and the reinforcement ratio ρ f of GFRP-reinforced concrete beams can significantly improve their flexural behaviors as they can reduce the crack width and the deformability of beams.

A limited number of studies have been reported discussing the impact of compressive GFRP bars on the flexural behavior of beams, despite extensive research on the use of GFRP bars as tensile reinforcement in RC members [3,41].

The fundamental objective of this investigation is to present the major findings of the research project that was carried out to study the overall performance at different loading stages of GFRP-reinforced concrete beams under monotonic static loading, including the effect of compression GFRP bars on deformability, ductility, cracking, and failure load.

2 Test program and methodology

The experimental program was designed in such a way as to study the effect of the longitudinal GFRP bars in the compression zone of the section on the load-carrying capacity and the performance of GFRP-reinforced concrete beams.

The experimental program involved testing six GFRP-reinforced concrete beams using GFRP bars in longitudinal and transverse directions. All beams had an overall length of 2,400 mm, with a rectangular cross-section of 300 mm (wide) × 250 mm (deep). The specimens were tested under four-point flexure loading, with an effective loading span ( l ) of 2,100 mm, achieving a constant shear span ( a ) of 700 mm ( a / l = 1 / 3 ) for all tests, providing a shear span-to-depth ratio of 3.1. A concrete cover of 25 mm at the top and bottom reinforcement of the beam’s section was maintained for all the tested specimens. In all tested beams, GFRP bars with a diameter of 15 mm were used for main reinforcement in both tension and compression zones, while closed GFRP stirrups with a diameter of 8 mm were used for transverse reinforcement with uniform, along the beam axis, a spacing of (100) mm, except the reference beam, where the GFRP bars were replaced by steel bars in the compression zone of the section.

The test program consisted of six GFRP-RC beams divided into reference specimens and two groups based on the GFRP reinforcement ratio ( ρ f ) relative to the GFRP reinforcement ratio producing balanced strain condition ( ρ fb ) in tension and compression zones of the section, where ρ fb was determined according to the ACI Committee 440 [24] using the following equation:

where β 1 is a factor relating the depth of equivalent rectangular compressive stress block to the depth of the neutral axis, f c ′ is the specified cylinder compressive strength of concrete, E f is the modulus of elasticity of GFRP reinforcement, and f fu is the design tensile strength of GFRP longitudinal reinforcement.

The reference beam (R-1) was singly reinforced in the tension zone with four longitudinal bars each of Ø 15 mm diameter, achieving GFRP tension reinforcement ratio ( ρ f = 1.885 ρ fb ), while the compression zone was supplied with 2 Ø 8 mm longitudinal steel bars to ensure the installation of the transverse stirrups in the required position.

The first and second groups consist of five doubly reinforced concrete beams, where GFRP bars were used as main reinforcement in the longitudinal direction in tension and compression zones to resist bending loads with different values of ρ f and ρ f ′ , respectively.

The first group includes three beams (G1GS1, G1GS2, and G1GS3) reinforced with GFRP bars that achieve in the tension zone of the section constant reinforcement ratio ( ρ f = 1.885 ρ fb ) and in the compression zone of the section, variable reinforcement ratios have different ratios of ( ρ f ′ / ρ f ) equal to 0.5, 0.75, and 1.0.

The second group consists of two beams (G1GS4 and G1GS5) reinforced with GFRP bars in both zones of the section, where the GFRP reinforcement ratio in the tension zone was constant ( ρ f = 2.357 ρ fb ) and variable in the compression zone to have two different ratios of ( ρ f ′ / ρ f ) equal to 0.4 and 0.6. Details of tested beams are shown in Table 1, Figures 1 and 2.

Figure 1

Details of all tested beams.

Figure 2

Reinforcement overall view tested beams.

2.3 Test setup and procedure

Testing was done at the Structures Laboratory at the University of Baghdad using testing closed-loop rig with a 150 metric-ton capacity static actuator and with load control capability. All beams were tested under four-point bending. The applied rigid supports allowed horizontal and angular displacement of the tested beams and, hence, simulated roller supports. The specimens were exposed to a monotonically increasing load of 5 kN loading step to failure using a load control test. Depending on the load-carrying capacity and ductility of the tested beam, the total testing time consumed an average of 2–3 h. The load was applied vertically at the midspan of the rigid distributor steel beam, which distributed the load evenly between the two bearings positioned on its top and spaced by 700 mm.

At the midspan section, the strains in the GFRP-reinforcing bars during testing were measured using prewired electrical resistance strain gauges Type UBFLA-1-5L with 1 mm length attached to the surface of the bars in compression and tension zones. For concrete at the midspan section, strain gauges Type PL-60-11-3LJC-F with a length of 60 mm were adhered to the concrete, extreme top and bottom fibers. At the section located at a distance ( d ) from the face of support, for steel stirrups, strain gauges Type FLAB-3-11-3LJC-F with 3 mm length were employed on the two legs of the stirrup.

Displacement of the beams was measured at midspan, under one of the applied two-point loads, and near the left support using three linear voltage differential transducers (LVDTs). Crack width microscope was used to record the progress of cracking. During testing, strain gauge and LVDT readings were monitored automatically using a computerized data acquisition system. Also, cracks were fixed where their spacing, depth, and opening width were investigated systematically. Blue lines that depict the crack and the applied load in kNs that generated it were utilized to identify the cracks. All test results were recorded by data logger and stored in a personal computer in tables consisting of hundreds of thousands of instantaneous data until the final failure stage of the concrete beams. A typical view of the beams during testing is shown in Figure 3.

Figure 3

Typical view of the test setup.

3 Experimental results and discussion

3.1 General behavior and modes of failure

All tested GFRP-reinforced concrete beams develop first flexural cracks at the mid-span section. In general, during the crack development phase, it was noted that cracks occur at random locations, almost vertically, and beginning in the pure bending region and spread towards supports covering the entire length of the tested beam. Cracks were noted to be very few in number, distanced farther apart, and wider. These cracks grew and propagated upwards until failure happened.

However, all beams were designed to fail by the crushing of concrete, and it was observed that the mode of failure was clearly by flexure-shear crack. Despite the fact that the section was intended to be over-reinforced, this pattern of failure in all beams leads to the conclusion that the design of GFRP-reinforced concrete beams should place a greater emphasis on shear strength rather than on flexure. The GFRP stirrup rupture may be distinguished by the audible crackling sound of fibers just before the collapse. At this load stage, the beam failed, and the load suddenly dropped. The crack pattern of the tested beams is illustrated in Figure 4. Table 5 displays a summary of the first cracking load ( P cr ), midspan deflections corresponding to the first cracking load ( ∆ cr ), failure load ( P u ), midspan deflections corresponding to the failure load ( ∆ u ), and the mode of failure for all tested beams.

Figure 4

Crack pattern for the tested beams.

Table 5

Experimental outcomes of tested beams

Specimen encoding	ρ f ′ ρ f	P cr (kN)	∆ cr (mm)	P ser (kN)	P u (kN)	∆ u (mm)	P cr / P u (%)	P ser / P u (%)	P cr / P cr , R − 1 (%)	P u / P u , R − 1 (%)	Failure mode
R-1		32.0	0.85	87.5	218.46	30.09	14.65	40.0			Flexure-shear
G1GS1	0.5	27.5	1.02	74.1	216.38	57.89	12.71	34.2	85.94	99.05	Flexure-shear
G1GS2	0.75	31.0	1.03	77.8	236.49	42.77	13.11	32.9	96.88	108.25	Flexure-shear
G1GS3	1.00	30.0	1.58	81.0	229.98	34.42	13.04	35.2	93.75	105.27	Flexure-shear
G1GS4	0.4	27.5	0.84	90.8	223.45	32.6	12.31	40.6	85.94	102.28	Flexure-shear
G1GS5	0.6	30.0	1.17	85.7	211.70	29.19	14.17	40.5	93.75	96.91	Flexure-shear
Average		29.7			222.74
Standard deviation		1.8			9.19

Because the mode of failure is flexure-shear and not tensile rupture of the bar, it should be emphasized that the high standard deviation in the failure load does not necessarily indicate a great variability in the bar’s mechanical properties. The failure load was greatly influenced by the characteristics of the concrete.

Referring to Table 5, it can be noted that the failure load of doubly GFRP-reinforced concrete beams of Groups I and II is variable compared to singly GFRP-reinforced beam (R-1). The difference between the load capacity of the reference (R-1) and the other beams (G1GS1, G1GS2, G1GS3, G1GS4, and GIGS) carries an unstable character. It fluctuates between −3.09 and +8.25%. Some doubly GFRP-reinforced beams show lower strength than the corresponding singly CFRP-reinforced beam. This is attributed to the variation in material properties, especially for concrete.

An insignificant effect on the load capacity was recorded in Group I due to using different cross-sectional areas of compression GFRP-bars in specimens (G1GS2) and (G1GS3) with 3 Ø 15 mm and 4 Ø 15 mm , respectively, compared to beam (G1GS1) with 2 Ø 15 mm , where the increase in load capacity attained 9.29 and 6.29%, respectively. While, in Group II, a negative effect was observed on the load capacity called by the increase of the area of compression GFRP-bars of specimen G1GS5 with 4 Ø 15 mm compared to G1GS4 with 3 Ø 15 mm , where the decrease in the failure load reached to 5.26%. This evidence declares that the GFRP bars in the compression zone in Groups I and II did not improve the ultimate load capacity of doubly GFRP-reinforced concrete beams. This fact is caused by the limited contribution of the compression bars in resisting the applied load. Referring to the strain compatibility analysis of the section, low strain values were generated in these bars at the failure stage. Considering the low modulus of elasticity of CFRP bars, insignificant forces were generated in the top bars, which led to a small positive or negative effect on the load capacity.

It is unclear how the increased area of GFRP bars in the tension zone impacts the load capacity of the tested specimens. Comparison of the load capacity of specimens of Group II and Group I (i.e., specimen G1GS4 with 5 Ø 15 mm and specimen G1GS1 with 4 Ø 15 mm and specimen G1GS5 with 5 Ø 15 mm and specimen G1GS2 with 4 Ø 15 mm ) led to a conclusion that there is no regularity of the action of increasing the area of GFRP bars in the tension zone on the load capacity. It is varied between −11.48 and +3.27%.

According to what has been discussed above, it is clear that the strength of compression GFRP bars may be ignored in the design calculation of GFRP-reinforced flexural members.

3.2 Load–deflection response of tested beams

The midspan deflection was recorded using data from each LVDT, and the results were plotted against the load readings collected from the load cell in the jack system of the testing closed-loop rig.

The load–displacement curves of the six GFRP-reinforced concrete beams demonstrate some of the key behavior characteristics of a GFRP-reinforced concrete sections including (i) bilinear behavior and (ii) linear-elastic behavior to failure after concrete crack appearance (Figure 5).

Figure 5

Load–midspan displacement plots for tested beams.

The degree of stiffness at large displacements is one characteristic that makes GFRP RC unique. Figure 5 depicts how each tested beam maintained its post-cracking stiffness up until failure despite midspan deflection of up to 30 mm.

As shown in Figure 5, the load–deflection behaviors of the tested beams followed two distinct routes. The behavior of the GFRP-reinforced concrete beams is linear up to cracking and decreasing stiffness up to failure. Responses exhibit a bilinear relationship after cracking. The post-peak behaviors of all tested beams (Figure 5) are due to the contribution of the un-ruptured GFRP bars in the reinforcing cage. The un-ruptured GFRP bars maintained the structural integrity of the tested beams.

It becomes evident that increasing the number of GFRP bars in the compression zone of the section (i.e., in beams G1GS2 and G1GS3 of Group I and beam G1GS5 of Group II) led to a reduction in displacement compared to beams G1GS1 and G1GS4, respectively. This fact confirms that the increase of the compression GFRP bar area effectively enhances the rigidity of the beam, improving its resistance to displacement under maximum load conditions. Comparing the experimental curves of Figure 5 leads to conclude that larger deformations accompany the lower reinforcement ratios, and vice versa, as shown in Table 5.

ACI 440.1R-15 [24] and ACI CODE-440.11-22 [26] consider the assumed service deflection limit ( ∆ ser ) of l / 240 under total service load ( P ser ), i.e., 8.75 mm for the tested in this study beams. According to the mentioned limitation, the total service load ( P ser ) was calculated using the experimental load–deflection curves.

It is evident that the total service load corresponding to a midspan deflection of 8.75 mm ranged between 32.9 and 40.6% of the failure load. So, the range of the assumed total service load for GFRP-reinforced concrete flexural members is much lower than the assumed range for steel-reinforced concrete members considered by ACI 318-19 [28], which consists 60–70% of the ultimate load. This fact ensures the importance of the service load state on the reliability of the design of GFRP-reinforced concrete flexural members.

3.4 Crack width

Since it has a significant impact on the steel reinforcement’s resistance to corrosion, the crack width is a crucial metric that should be investigated when evaluating the performance of reinforced concrete structures. Contrary to structural concrete members reinforced by steel bars, the durability of GFRP-reinforced concrete members is not largely reliant on the size of the cracks in the structural concrete members. The experimental crack width at the flexural zone was measured at every load step. A mechanical extensometer with demec points having an accuracy of 0.002 mm and a gauge length of 200 mm was used to measure the crack width at the middle of the pure bending moment span, as shown in Figure 6. The demec points were fixed on the side face of the beam section at midspan and distributed across the depth of the section at the spacing between 50 and 100 mm on centers. Only the width of three primary cracks (first cracks), which occur in the pure bending moment span, were measured during the stages of loading across the depth and soffit of the beams. Primary cracks are defined as cracks which occur at low steel stress and approximately penetrated to the neutral axis.

Figure 6

Progress of crack width for tested beams.

The flexural cracks appearing under the load points were observed to either widen more than the rest of the cracks in the central zone or appear at a lower spacing. This effect was attributed to a probable increase of curvature and strains at these zones. Figure 6 illustrates the evolutions of the crack width of the first appeared crack. Due to the low elastic modulus of GFRP bars, these tests reveal that GFRP-reinforced beams often have a wider crack width than steel-reinforced beams under the same applied stresses [41]. From Figure 6, it can be concluded that, under service load, the crack width decreases as the compression GFRP-reinforcement ratio increases. This fact demonstrates that the GFRP-reinforcement ratio significantly influences the crack width.

It is typically permissible to limit crack widths in the range of 0.4 to 0.7 mm in cases where crack widths are regulated for aesthetic reasons [24,25,26] for the GFRP-reinforced concrete flexural members. Following ACI 318M-19 [28], the crack width for the steel-reinforced concrete beam is generally limited to 0.4 mm. Table 7 summarizes the resulting service load at which the maximum crack width attained 0.4 mm ( P 0.4 ) and 0.7 mm ( P 0.7 ) for each tested beam.

Table 7

Experimental load at maximum crack width equal to 0.4 and 0.7 mm

Specimen encoding	P u (kN)	P 0.4 (kN)	P 0.7 (kN)	P 0.4 / P u (%)	P 0.7 / P u (%)
R-1	218.46	46.0	60.0	21.0	27.46
G1GS1	216.38	46.0	60.0	21.2	27.72
G1GS2	236.49	60.0	90.0	25.37	38.05
G1GS3	229.98	57.5	90.0	25.0	39.13
G1GS4	223.45	60.0	95.0	22.37	33.56
G1GS5	211.70	70.0	110.0	33.0	51.96

For the tested beams, the maximum crack width reached the maximum crack width of 0.7 mm at a service load of (27.46%) of the experimental failure load for the singly GFRP-reinforced concrete beam and (27.72–51.96%) for doubly GFRP-reinforced concrete beams. This means that the presence of GFRP bars in the compression zone leads to improving the performance of the concrete beam by reducing the width of the cracks in the tensile zone, and thus increasing the design values of service load, in the case beam design according to serviceability requirement.

In conclusion, the crack width limitation results are more restrictive than the allowable deflection and stresses in GFRP-reinforced concrete beam. Moreover, the service load that fulfills the serviceability requirements at a cross-section level ranges between 27 and 50% times the ultimate load for sections dimensioned to fail in concrete crushing. The determinant criterion is the crack width and deflection limitation.

4 Conclusions

The most relevant conclusions of the present work can be summarized as follows:

1. The failure load of doubly GFRP-reinforced concrete beams is variable compared to singly GFRP-reinforced beams. The difference between the load capacity of the reference beam and the other beams carries an unstable character. It fluctuates between −3.09 and +8.25%. Some of the doubly GFRP-reinforced beams show lower strength than the corresponding singly GFRP-reinforced beam. This is attributed to the variation in material properties, especially for concrete. It is clear that the strength of compression GFRP bars may be ignored in the design calculation of GFRP-reinforced flexural members.

2. The predominant mode of failure is flexure-shear crack. This pattern of failure in all beams leads to conclusion that the design of GFRP-reinforced concrete beams is more dependent on shear strength rather than bending.

3. It is evident that the total service load corresponding to the midspan deflection of l / 240 ranged between 32.9 and 40.6% of the failure load. So, the range of the assumed total service load for GFRP-reinforced concrete flexural members is much lower than the assumed range for steel-reinforced concrete members considered by the ACI 318-19, which consists 60–70% of the ultimate load. This fact ensures the importance of the service load state on the reliability of the design of GFRP-reinforced concrete flexural members.

4. The average crack spacing for tested beams ranged between 100.7 and 150.7 mm. The loading level at which crack spacing stabilized ranged between 31.3 and 87% of the experimental failure load. It seems that the crack spacing decreased with the increase in the reinforcement ratio.

5. The presence of GFRP bars in the compression zone leads to improving the performance of the concrete beam by reducing the width of the cracks in the tensile zone, and thus increasing the design values of service load, in the case beam design, according to serviceability requirement.

6. The crack width limitation results are more restrictive than the allowable deflection and stresses in the GFRP-reinforced concrete beam. Moreover, the service load that fulfills the serviceability requirements at a cross-section level ranges between 27 and 50% times the ultimate load for sections dimensioned to fail in concrete crushing. The determinant criterion is the crack width and deflection limitation.

7. It is recommended to study the performance of reinforced concrete beams with longitudinal and transverse GFRP bars under impact loading.