Glass Fibre Reinforced Polymer Stirrups Research Articles

Ductility assessment of GFRP reinforced concrete beams with a wedge-based mechanical model accounting for discrete fibers and confinement

Glass fiber-reinforced polymer (GFRP) bars for internal reinforcement for concrete have gained attention due to their non-corrosive properties, high resistance, and electromagnetic transparency. On the other hand, the brittle behavior and low modulus of elasticity of FRP bars limit their application and diffusion in the civil construction market. From this perspective, this work investigates the influence of three components on the increase of ductility of GFRP beams: i) discrete alkali-resistant glass fibers added to the concrete; ii) confinement of the concrete with GFRP stirrups; and iii) use of longitudinal reinforcement on the compression zone. An experimental program including four over-reinforced beams with different reinforcement configurations was conducted. The beams were tested in four-point bending configuration and the use of fibers, stirrups and compression reinforcement contributed to substantially increasing the beam ductility index. Finally, a concrete wedge model was developed to obtain equivalent stress-strain relationships for the concrete in compression. The model was successfully validated against experiments and proved to be a useful tool for rationally evaluating GFRP RC beams’ ductility.

A Comparative Study of the Structural Behavior of Concrete Beams Reinforced with Different Configurations of GFRP and Steel Bars

This study examined experimentally and numerically the performance of five concrete beams reinforced with longitudinal and transverse bars made of Glass Fiber Reinforced Polymer (GFRP) or steel. All beams had the same dimensions of 2700 mm in length, 180 mm in width, and 260 mm in depth. The beams were classified into two groups with different variables and compared with a reference beam reinforced with longitudinal and transverse steel bars. The first group consisted of two beams with longitudinal GFRP bars and no stirrups, varying the main reinforcement ratio. The second group comprised two beams with longitudinal GFRP bars and transverse GFRP or steel stirrups, varying the stirrup type. The results indicated that the beams with GFRP bars improved their flexural strength for different ratios but had limited shear resistance when using GFRP stirrups because increased deflection causes the number and width of cracks to grow, reducing the shear strength. All the tested beams exhibited linear elastic behavior until failure, with GFRP being more brittle than steel due to no yield point or plastic behavior in GFRP. The numerical simulation of the five beams using ABAQUS software showed good agreement with the experimental data obtained in the laboratory.

Tensile strength retention of glass fibre-reinforced stirrups subjected to aggressive solutions: effect of environmental condition, stirrup shape and stirrup diameter

The aim of this study was to examine how the tensile strength of glass fibre reinforced polymer stirrups is affected by different types of solutions, including alkaline, seawater, tap water, and acidic solutions. The study involved the production and testing of 260 stirrups in two different shapes (L and U) with diameters of 6 and 8 mm. The stirrups were immersed in different solutions for a period of 9 months at different temperatures (25, 40, and 60 °C). The findings indicated that the alkaline solution was the most aggressive environment, resulting in a maximum reduction of 92% in tensile strength after 9 months at 60 °C. Seawater and acidic solutions were the second and third most aggressive environments, causing maximum tensile strength reductions of 34 and 22% respectively, after 9 months at 60 °C. On the other hand, tap water was found to be the least aggressive environment, causing a maximum tensile strength reduction of 20% after 9 months at 60 °C. Furthermore, the study observed that the L-shaped stirrups exhibited slightly superior performance compared to the U-shaped stirrups. However, the diameter of the stirrups was found to be a negligible factor.

Effects of GFRP Stirrup Spacing on the Behavior of Doubly GFRP-Reinforced Concrete Beams

This study investigates the impact of varying glass fiber-reinforced polymer (GFRP) stirrup spacing on the performance of doubly GFRP-reinforced concrete beams. The research focuses on assessing the behavior of GFRP-reinforced concrete beams, including load-carrying capacity, cracking, and deformability. It explores the feasibility and effectiveness of GFRP bars as an alternative to traditional steel reinforcement in concrete structures. Six concrete beams with a cross-section of 300 mm (wide) × 250 mm (deep), simply supported on a 2100 mm span, were tested. The beams underwent four-point bending with two concentrated loads applied symmetrically at one-third of the span length, resulting in a shear span (a)-to-depth (h) ratio of 2.8. The experimental findings reveal that altering the GFRP stirrup spacing along the longitudinal axis of the beams, from 200 mm (equivalent to the effective depth (d)) to 50 mm (equal to (d⁄4)), altered the mode of failure from flexure-shear to flexure-compression. However, when the spacing was equal to or less than (d⁄3), there was no significant improvement in load-carrying capacity, as the contribution of GFRP bars in resisting shear loads was limited. Under service loads, the GFRP-reinforced beams exhibited wider cracks, but reducing the stirrup spacing helped restrain crack widening. Incorporating GFRP bars in the compression zone had a positive effect on reducing crack width in the tension zone. Additionally, using GFRP stirrups with spacing varying between (d) and (d⁄2) in the pure bending region increased the deflection ductility indexes. To enhance the ductility of GFRP-reinforced concrete beams, it is recommended to use GFRP stirrups in the pure bending region with spacing greater than the spacing between GFRP stirrups in the shear spans. The study highlights that the current ACI code overestimates the shear capacity provided by GFRP stirrups, particularly when the spacing is less than or equal to (d⁄3). Doi: 10.28991/CEJ-2024-010-02-011 Full Text: PDF

Performance of doubly reinforced concrete beams with GFRP bars

Abstract The study focused on examining the behavior of six concrete beams that were reinforced with glass fiber-reinforced polymer (GFRP) bars to evaluate their performance in terms of their load-carrying capacity, deflection, and other mechanical properties. The experimental investigation would provide insights into the feasibility and effectiveness of GFRP bars as an alternative to traditional reinforcement materials like steel bars in concrete structures. The GFRP bars were used in both the longitudinal and transverse directions. Each beam in the study shared the following specifications: an overall length of 2,400 mm, a clear span of 2,100 mm, and a rectangular cross-section measuring 300 mm in width and 250 mm in depth. To apply loads for testing, two-point static loads were placed at the middle third of the beam’s span, creating a shear span of 700 mm in length. The beams were categorized into three groups depending on the GFRP longitudinal reinforcement ratio in the tension and compression zones of the section. GFRP bars with a diameter of 15 mm were employed as longitudinal reinforcement, while closed GFRP stirrups with a diameter of 8 mm at 100 mm were utilized as transverse reinforcement throughout the structural element. Test results have indicated that the ultimate load capacity of doubly GFRP-reinforced concrete beams varies compared to singly GFRP-reinforced beams. The range of variation observed is between an increase of 8% and a decrease of 4%. Accordingly, the contribution of the GFRP bars in the compression zone is insignificant and could be ignored in design calculations. It was observed that 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.

Shear behaviour of SWSS-SCC beams reinforced with GFRP bars and Stirrups: Experimental and analytical investigations

This paper presents a study of shear behaviour of sea-water and sea sand self-compacting concrete (SWSS-SCC) beams reinforced with glass fibre reinforced polymer (GFRP) bars and stirrups. Nine full-scale beams were conducted and tested under four-point loading up to failure. The investigated experimental variables were the shear-span ratio, configuration of GFRP stirrups, type of the concrete, longitudinal reinforcement ratio and beam depth. The crack pattern, failure mode, load–deflection response, load–strain response and shear capacity of concrete beams were discussed. It is evident in the test results that the ultimate shear capacity of test specimens is enhanced by reducing the shear-span ratio, using the GFRP stirrups, improving the longitudinal FRP reinforcement ratio and increasing the beam depth. The shear behaviours of SWSS-SCC beam reinforced by GFRP bars and stirrups were found to be similar to that of fresh-water and river sand self-compacting concrete (FWRS-SCC) beam. The ultimate shear capacity of the test beams was predicted by the theoretical models reported in the literature. In addition, the effect of the experimental parameters on shear capacity was discussed and the theoretical models of shear strength were evaluated based on the summarized database. It is found that the nominal shear strength is barely affected by the axial compressive strength and is optimal when the longitudinal reinforcement ratio is about 2%. The CSA-S806 2012 specification has more accurate prediction results for the shear capacity of concrete beams reinforced with FRP bars and stirrups.

Short-term durability of GFRP stirrups under wet-dry and freeze–thaw cycles

GFRP stirrups are a promising alternative to conventional steel stirrups due to their non-corrosive nature. However, their performance under cyclic exposure to wet-dry and freeze–thaw conditions in seawater needs to be evaluated to ensure their long-term durability and sustainability. This study investigates the tensile strength of glass fibre reinforced polymer (GFRP) stirrups under seawater wet-dry cycles and seawater and tap water freeze–thaw cycles. In total, 220stirrups in two different shapes, i.e. U and L shapes, and two different diameters, i.e. 6 mm and 8 mm were manufactured, conditioned, and tested under stirrup tensile test. Conditioned stirrups were subjected to 9 months and 18 months wet-dry cycles in seawater at 25 ℃, 40 ℃, and 60 ℃, and 9 months and 18 months freeze–thaw cycles in seawater and tap water. At first, the samples underwent a fast deterioration rate, which then decreased as the conditioning period progressed from 9 months to 18 months. The strength retention values of L-shaped stirrups were found to be higher than those of U-shaped stirrups, regardless of the environmental conditions or diameter. The maximum tensile strength reductions of 31%, 28% and 16% were observed, respectively after exposure to 18 months conditioning in seawater wet-dry cycles at 60 ℃, freeze–thaw in seawater, and freeze–thaw in tap water.

Shear performance of glass fiber reinforced concrete beams with diverse embedded GFRP trusses

This paper investigated the shear performance of internal embedded glass fiber reinforced polymer (GFRP) trusses as a novel shear reinforcement instead of conventional steel stirrups for concrete beams reinforced with top and bottom GFRP bars, and for this goal, different proposed patterns of embedded GFRP trusses were offered. In addition, the effect of GFRP stirrup spacing and the comparison with steel stirrups are also studied. For this purpose, an experimental program consisting of nine specimens was utilized that tested under one concentrated load with an unequal span-to-depth ratio up to failure. The program included one specimen with no stirrups in the studied shear zone as a control beam. The GFRP stirrups or proposed trusses were cut as single straight legs without bends or hooks, and they were then linked together with plastic ties to create the necessary shape. Besides, numerical analysis using the finite element program ANSYS V-19.2 was utilized for computational modelling as a 3-D model to examine the capability of the model to capture the observed shear behaviour and to obtain extra results in order to better comprehend the shear behaviour. Cracking patterns, ultimate loads, failure mechanisms, load-deflection relationships, load versus strain in GFRP bars, and strain distribution along the height of the GFRP truss member were evaluated. The shear capacity was enhanced via the use of internal GFRP embedded trusses by about 56–80 % compared to the control beam (BC) without stirrups, while these forms improved the capacity by about 29–50 % compared to the specimen that had only vertical stirrups. In addition, the normal strain distribution along the GFRP truss member height was non-uniform and significantly affected by the member location. The shear capacity was also increased by decreasing the GFRP stirrups' spacing, while the use of GFRP stirrups instead of steel stirrups decreased the ultimate load by about 3–10 %, according to stirrup spacing. Finally, the comparison between the results obtained from the numerical model and the experimental work showed a good agreement.

Shear behavior of two-span continuous concrete deep beams reinforced with GFRP bars

To investigate the shear behavior of reinforced concrete (RC) continuous deep beams with glass fiber reinforced polymer (GFRP) bars, four large-scale beams with a constant shear span-to-overall depth ratio of 1.2 and different GFRP shear reinforcement ratios were tested. Digital image correlation technology was used to track the kinematics of diagonal shear cracks in the shear span. It was found that the moment redistribution in the deep beams was very limited. A tie-arch action was confirmed in the tested deep beams with the crack propagation and the strains developed in longitudinal reinforcements. For the beams without GFRP stirrups, the aggregate interlock contribution constituted 46.3% of the total shear resistance. For the beams with GFRP stirrups, however, the shear contribution of aggregate interlock was less significant. As the GFRP shear reinforcement ratio increased from 0% to 0.47%, the failure mode changed from shear compression failure to compression strut failure. As the shear GFRP reinforcement ratio increased from 0.24% to 0.32% and 0.47%, the load-carrying capacity increased by 35.5% and 73.5%, respectively. The minimum required GFRP shear reinforcement in ACI 440.1R-15 was ineffective for the tested GFRP-RC continuous deep beams in terms of shear capacity enhancement and shear crack control. Finally, a database of shear tests on continuous GFRP-RC beams was collected to assess the ability of strut-and-tie methods in three code guidelines.

Shear-transfer mechanisms in reinforced concrete beams with GFRP bars and basalt fibers

An increase in the use of glass fiber reinforced polymer (GFRP) bars and discrete fibers in reinforced concrete structures, associated with the limited understanding of the shear behavior of concrete beams, highlights the need for a comprehensive study of various force transfer mechanisms. This article investigates the experimental behavior of four slender reinforced concrete beams with GFRP bars. The testing program includes beams with and without GFRP stirrups and dispersed basalt fibers in the concrete matrix. The displacement fields throughout the shear span were monitored according to the digital image correlation (DIC) technique and shear-transfer constitutive models from the literature assessed the contribution of each mechanism. The sum of such contributions consistently agreed with the experimental shear strength and the use of fibers in beams with GFRP stirrups modified the relative influence of both shear reinforcements, i.e., one of them can preponderate over the other in function of load stage and failure mode.

Study on the bond performance of glass fiber-reinforced polymer bars considering the relative position between longitudinal bars and stirrups

Fiber-reinforced polymer (FRP) reinforcements are increasingly recognized as an effective solution to the corrosion problems faced by reinforced concrete structures, and the bond between FRP bars and concrete is an essential basis for the application. Previous research has shown that stirrup restraints on the concrete can significantly enhance the bond performance of middle-arranged longitudinal FRP bars. However, in practical applications, longitudinal bars are typically placed at the corners or sides of stirrups to form reinforcement cages, and there has been limited research on the effects of stirrups on the bond performance of FRP bars under these conditions. To address this gap, this study attempts to further reveal the stirrup effects by varying the relative positions between the longitudinal bars and stirrups. Based on forty-four axial pull-out tests on glass fiber-reinforced polymer (GFRP) bars equipped with Distributed Optical Fiber Sensors (DOFS), the overall and local bond performances of three GFRP bars (sand-coated, helical wound, single helical wrapped) considering four relative positions between the GFRP bars and stirrups (no stirrups, side, middle, corner) were investigated. The test results indicated that the bond strength of FRP bars increased significantly, up to 71.5%, for the relative position of the middle case, but could be reduced by up to 17.5% for the side and corner positions compared with the no-stirrup situation. DOFS proved to be an effective method to obtain the continuous strain distribution and reveal the interfacial bond mechanism. Based on DOFS results, a bond stress-slip model considering the effect of relative positions was developed. Using this model, the development lengths of GFRP bars were proposed and compared with the ACI, CSA, and JSCE codes.

Efficiency of (GFRP- Steel) Stirrups in Reinforcing the Punching of Slab-Column Connections subjected to Eccentric Load

The effectiveness of inner stirrups as the punching shear reinforcement forslab-column connections under eccentric loading was studied in this research withthe purpose of improving the punching behaviour. This research experimental dataand results study the effect of using steel, and glass fiber reinforced polymerstirrups (GFRPS) as punching shear reinforcement for interior slab-columnconnections (S-C-C) under eccentric loading. The experimental program consistsof six flat slabs with dimensions of 1600*1600 *150 mm, stub column having a200*200 mm cross-section with 700 mm total height extended outside both sidesof the slab. The variables were the materials used for manufacturing stirrups (Steel- GFRP), the distance between stirrups (50 or 70) mm, and the case of loading(eccentric or centric load). The experimental results showed a noticeable increasein punching shear resistance for the slabs reinforced with stirrups ranged from 28to 63% compared to the control specimen. Finite element analysis was performedusing the Abaqus/CAE6.14 software, and the results were compared to the

Feasibility of using Static-Cast Concrete Transmission Poles fully reinforced with glass-fibre reinforced polymer bars and stirrups: A case study

The findings of cantilever beam bending tests conducted on a series of full-scale glass fibre-reinforced polymer (GFRP) and steel-reinforced concrete utility poles are presented. The poles were reinforced by (i) longitudinal steel bars and steel stirrups (ii) longitudinal GFRP bars and steel stirrups, and (iii) longitudinal GFRP bars and GFRP stirrups. Crack initiation and propagation as well as load carrying capacity and free end deflections of GFRP reinforced poles were obtained and compared with their counterpart steel reinforced poles. Based on the results all longitudinal GFRP reinforced poles have shown higher load-carrying capacity than that of steel reinforced poles, while due to the lower stiffness of GFRP bars in comparison to steel bars, at a certain load, higher free-end deflections were observed in GFRP reinforced poles. However, the permanent deformation of GFRP-reinforced poles was small. Furthermore, comparable results obtained for poles reinforced with GFRP stirrups than those of poles reinforced with steel stirrups, showed that GFRP stirrups could also be used safely instead of steel stirrups. However, due to the low elastic modulus, GFRP-reinforced poles likely fail to satisfy the deflection criterion specified in some standards. But, if adequate stiffness is provided for GFRP-reinforced concrete poles to satisfy the deflection criterion, due to the vulnerability of steel-reinforced utility poles when subjected to corrosive environments, using fully GFRP-reinforced concrete poles could be a feasible option.

Experimental and theoretical analysis on shear behavior of RC beams reinforced with GFRP stirrups

The objective of this paper is to experimentally study the shear behavior of reinforced concrete (RC) beams reinforced with glass fiber reinforced polymer (GFRP) stirrups. Six specimens including five RC beams reinforced with GFRP stirrups (GFRP-S-RC beams) and one beam strengthened with steel stirrups (RC beam) are fabricated. The effects of several parameters (i.e., stirrup type, the shear span ratio, and stirrup spacing) on the failure modes, shear crack width, shear capacity, strain variation of stirrup and longitudinal rebar, and the mid-span deflection are investigated. Similar to the conventional RC beam, three different types of shear failure modes including the shear compression failure, the diagonal compression failure, and the diagonal tension failure are observed on the GFRP-S-RC beams. The shear capacity of GFRP-S-RC beams decreases as the shear span ratio or stirrup spacing increases. GFRP stirrups exhibit a slight opposite effect on the shear capacity. The average and maximum strain of the stirrup both increase as the shear span ratio increases. The increase in the shear span ratio and the stirrup spacing adversely affects the ultimate deflection and longitudinal steel strain. A modified formula for the allowable strain of FRP stirrup is proposed. Considering the effect of uneven stress of stirrups, a model for predicting the shear capacity of GFRP-S-RC beams is proposed, and it shows good agreement with various test data.

Experimental and analytical study on the behavior of hybrid GFRP/steel bars in reinforced concrete deep beams

Abstract The deep beam is one of the essential members of high-rise buildings structures, so the deep beams are used as a transfer girder; in walls water structures, the deep beam behavior is different from the slender beam behavior; the deep beam plane section before does not remain plane after bending. In recent years, the use of FRP as a composite material in reinforced concrete structures has been growing up to cover problems by weight of structure buildings, corrosion, repairing, and construction cost. This paper presents an experimental, analytical study to assign the variation of mechanical properties of reinforced concrete deep beams using vertical and horizontal GFRP stirrups. This paper investigates the mechanical properties of test specimens for deep beams reinforced in shear with GFRP or steel bars as web reinforcement. The deep beams are reinforced with glass fiber reinforced polymer (GFRP) in various ratios as a web reinforcement configuration (0, 0.25%, and 0.40%) rather than traditional steel web reinforcement. All tested specimens have the same span to depth ratio of 0.40 (a/d); the primary and secondary reinforcement is steel bars. The web reinforcement ratio significantly affected deep beams’ load capacity and mechanical behavior. The GFRP enhancement the mechanical behavior of the reinforced concrete deep. Increasing the GFRP web reinforcement ratio enhances the deep beam load capacity. The test results compared with the traditional ACI design method strut-tie model to demonstrate the effect of web reinforcement ratio on deep beam load capacity and strut width. The test results have been verified by ABAQUS 6.13.

Experimental investigations of GFRP-reinforced columns with composite spiral stirrups under concentric compression

In this study, a new way to transversely reinforce square concrete columns using glass fiber reinforced polymer (GFRP) composite spiral stirrups composed of several outer rectangular GFRP stirrups and an inner spiral GFRP stirrup was proposed. The double restraints of the composite spiral stirrups overcame the shortcoming of the relatively lower elastic modulus of GFRP compared with steel and provided effective lateral restraint for the core concrete. The axial compressive performance of GFRP-reinforced square concrete columns with composite spiral stirrups was experimentally investigated. The test variables, including the stirrup spacing, stirrup diameter, longitudinal bar type and stirrup configuration, were discussed. The results indicate the following: (1) By the application of GFRP composite spiral stirrups, both a higher core concrete strength and ultimate load could be achieved compared to GFRP rectangular stirrups and GFRP composite rectangular stirrups. (2) Except for specimens 12S-150G-G and 8S-100G-G, the load versus axial concrete strain curves of GFRP-reinforced columns with composite spiral stirrups did not drop after reaching the peak but went through a stable stage, showing excellent ductility. (3) With a decrease in stirrup spacing from 100 mm to 50 mm, secondary peaks appeared on the load versus axial concrete strain curves. The decrease in the stirrup spacing effectively enhanced the core concrete strength and ductility of the columns. (4) Considering the contribution of the GFRP bars and the restraint effect of stirrups, a new method to calculate the ultimate bearing capacity of GFRP-reinforced columns with composite spiral stirrups was proposed and verified with experimental results.

Experimental study on shear response of GFRP reinforced concrete beams strengthened with externally bonded CFRP sheets

An experimental investigation into the shear behavior of Glass Fiber Reinforced Polymer (GFRP) reinforced concrete beams is presented. The study also looks at the effectiveness of shear strengthening of such beams using externally-bonded Carbon Fiber Reinforced Polymer (EB-CFRP) sheets and investigates the possibility of interaction between internal and externally bonded shear reinforcement. A total of 18 beams, 2.4 m long with a rectangular cross-section of 300x200, reinforced with GFRP bars and stirrups were tested. Three types of concrete were used in this study; ordinary Portland cement (OPC) concrete, Fiber Reinforced concrete (FRC), and Geopolymer concrete (GPC). Six beams, two for each concrete type, severed as control while the other twelve were strengthened using “U” shape EB-CFRP sheets. The CFRP sheets were placed in two different arrangements, above and in-between internal stirrups locations. The results indicate that GFRP is a viable reinforcement for GPC, OPCC, and FRC, whereas EB-CFRP proves to be a feasible strengthening technique for such composite systems. The gain in shear strength for EB-CFRP strips beams on the location of internal stirrups is 5–10% lower as compared to the other arrangement. The difference in the strength gain may indicate a possible interaction between the internal and external shear reinforcement.

Flexural and Shear Behavior of Beams Reinforced with GFRP Rebars

A new inexperienced constructing material is glass fibre reinforced polymer (GFRP) rebar. GFRP rebars are non-corrosive, non-conductive, light-weight substances and have an excessive longitudinal tensile capacity that is beneficial for use in civil infrastructure applications. In this analysis, the overall performance of GFRP rebar-reinforced concrete beams was assessed. Full scale exams had been conducted underneath four-point bending on eight one hundred fifty x 250 x 1500 mm beams to inspect the influence of GFRP specimens reinforced through both GFRP or metal rebars with flexural reinforcement ratios (ρf) ranging from 0.53 to 1.45 times the balanced ratio (ρfb). In phrases of crack pattern, load deflection behaviour, load strain conduct and peak capacity, the check facts used to be analysed to decide the flexure and shear conduct of GFRP RC beams. The find out about confirmed that the ultimate load capacity of beams is immediately proportional to the flexural reinforcement ratio, and for steel bolstered specimens, cracking moments had been greater, relative to GFRP. For GFRP RC beams, the peak carrying ability is extra than steel beams. GFRP beams confirmed greater deflections than bolstered beams of steel. The findings additionally confirmed that the building of GFRP bolstered beams in concrete with GFRP stirrups can be influenced by means of shear failures. The reinforcement ratio and shear design of GFRP bolstered concrete beams is affected by way of their behaviour.

Shear Behavior of Concrete Beams Reinforced With A New Type of Glass Fiber Reinforced Polymer Reinforcement: Experimental Study.

The article presents experimental tests of a new type of composite bar that has been used as shear reinforcement for concrete beams. In the case of shearing concrete beams reinforced with steel stirrups, according to the theory of plasticity, the plastic deformation of stirrups and stress redistribution in stirrups cut by a diagonal crack are permitted. Tensile composite reinforcement is characterized by linear-elastic behavior throughout the entire strength range. The most popular type of shear reinforcement is closed frame stirrups, and this type of Fiber Reinforced Polymer (FRP) shear reinforcement was the subject of research by other authors. In the case of FRP stirrups, rupture occurs rapidly without the shear reinforcement being able to redistribute stress. An attempt was made to introduce a quasi-plastic character into the mechanisms transferring shear by appropriately shaping the shear reinforcement. Experimental material tests covered the determination of the strength and deformability of straight Glass Fiber Reinforced Polymer (GFRP) bars and GFRP headed bars. Experimental studies of shear reinforced beams with GFRP stirrups and GFRP headed bars were carried out. This allowed a direct comparison of the shear behavior of beams reinforced with standard GFRP stirrups and a new type of shear reinforcement: GFRP headed bars. Experimental studies demonstrated that GFRP headed bars could be used as shear reinforcement in concrete beams. Unlike GFRP stirrups, these bars allow stress redistribution in bars cut by a diagonal crack.

Concrete beams with different arrangements of GFRP flexural and shear reinforcement

This paper presents experimental research on the flexural and shear behaviour of concrete beams reinforced with glass fibre reinforced polymer (GFRP) composite reinforcement. Three-point bending tests on shear critical concrete beams reinforced with GFRP longitudinal bars and GFRP stirrups are presented. The test variables were the size and spacing of closed loop stirrups as well as the size, amount, and arrangement of longitudinal reinforcement. Twelve beams were tested with four different stirrup arrangements and three different longitudinal reinforcement arrangements. Longitudinal bars were instrumented at mid-span and stirrups were instrumented at the straight and bent portions. The beams had a shear-span-to-effective-depth ratio of 2.5 and behaved like deep beams. The beams without stirrups failed in shear-tension while the beams with stirrups failed in shear-compression with no ruptured stirrups. Longitudinal reinforcement strains showed evidence of a tied arch mechanism. The analysis found diminishing increases in shear strength with increasing shear reinforcement ratio when failure occurred as a result of crushing of confined concrete.