A comparative study between the flexural behaviour of high-strength steel fibre concrete beams reinforced with glass fibre reinforced polymer (GFRP) and steel bars

To address the problem of corrosion, glass fiber-reinforced polymer (GFRP) bars have been introduced as a viable alternative to conventional steel reinforcement in concrete structures. While extensive research has been conducted on the flexural behavior of RC beams reinforced with steel and GFRP bars over both normal-term and long-term periods, studies focusing on fresh concrete beams are almost non-existent. Consequently, this research investigates the impact of steel and GFRP longitudinal reinforcement, as well as the influence of varying concrete compressive strengths, on the flexural behavior of RC beams. The study employs 3-point bending experiments and machine learning (ML) predictive analyses. Specifically, the short-term (fresh) concrete reinforcement compatibility and the effects of steel and GFRP bar reinforcements on beam flexural behavior were examined across three concrete compressive strength categories: low (C25), moderate (C35), and high (C50). A notable contribution of this research is the application of different ML regression models, utilizing Python’s library, for deflection prediction of RC beams. The failure mechanisms of the beams under static loading conditions were analyzed, revealing that composite bar RC beams failed through flexural cracking and demonstrated ductile behavior, whereas steel bar RC beams exhibited brittle failure characterized by shear cracks and sudden failure modes. The ML regression models successfully predicted the deflection values of RC beams under ultimate loads, achieving an average accuracy of 91.3%, which was deemed highly satisfactory. Among the 18 beams tested, the highest ultimate load was obtained for the SC50-1 beam at 87.46 kN. In contrast, while the steel-reinforced beams exhibited higher load-bearing capacities, it was observed that the GFRP-reinforced beams showed greater deflection and ductility, particularly in beams with low and medium concrete strengths. Based on these findings, it is recommended that the Gradient Boosting Regressor, an AI regression model, be utilized to guide researchers in evaluating the load-carrying and bending capacity of structural beam elements.

It became common practice to utilize near-surface mounted (NSM) bars to improve the shear capacity of steel-reinforced concrete (RC) beams. Consequently, carbon fiber-reinforced polymer (FRP) is usually used to improve RC beams' shear performance. Conversely, the use of Glass FRP (GFRP) for enhancing the shear behavior of the steel-RC and GFRP-RC beams is still limited. This study used NSM GFRP or steel bars to strengthen RC beams reinforced in tension with steel or GFRP bars. In addition, a new NSM technique was conducted using high-strength concrete (HSC) layers reinforced with GFRP or steel bars bonded within grooves to enhance beams' shear capacity. The results of seventeen beams used in the tests showed that NSM HSC layers improved the shear performance of RC beams more than NSM bars. Also, the beams reinforced in tension with steel bars had higher shear efficiency and were stiffer than those reinforced with GFRP bars. Conversely, the shear efficiency of steel RC beams strengthened in shear with internal stirrups or NSM reinforcement (or both) increased by 142.8–211.7% compared to GFRP RC beams without internal and NSM shear reinforcement. Conversely, the shear capacity of the steel-RC beams strengthened in shear with internal stirrups or NSM reinforcement (or both) increased by 153.5–279.9% compared to the corresponding beam without GFRP RC beam without internal and NSM shear reinforcement. The numerical analysis using the ABAQUS program showed great effects of the tension reinforcement and the NSM materials on the strain of longitudinal bars, stirrups and NSM reinforcement.

Effect of the NSM material and area on the flexural response of normal strength concrete beams internally reinforced with GFRP and steel bars

Strengthening is a process of upgrading to increase the strength of structural components to carry additional loads. Strengthening methods include externally bonded (EB) Fiber Reinforced Polymer (FRP) plates, (or wet laid-up fabrics) and Near Surface Mounted (NSM) FRP rods. The present investigation study the enhancement in flexural performance of un-cracked RC beams strengthened with either a single ply or a 2-ply wet laid-up carbon fiber reinforced polymer (CFRP) fabric(s) or NSM glass fiber reinforced polymer (GFRP) rods. An identical RC beam in its un-strengthened form is used as the control. A series of RC beams of dimensions 170 mm width × 270 mm depth × 2325 mm length were tested to destruction under four point bending. The variables are the number of carbon plies in a wet laid-up scheme and the number of GFRP rods in a NSM scheme. The RC beams were designed to have excess reinforcement in shear to allow the beams to fail in bending. The flexural performance was assessed in terms of the enhancement in the ultimate load carrying capacity, load-deflection characteristic up to and beyond peak, initial stiffness, and strain development in the RC beams, due to the attached carbon fiber reinforced polymer (CFRP) sheets and GFRP rods. Test results show that the RC beams strengthened with two (2) NSM GFRP rods recorded the highest of about 88% increase in strength capacity over the control beam and 34% increase corresponding to those of strengthened with a GFRP rod. The strength capacity of the beam specimens strengthened with a rod and two (2) rods of NSM GFRP recorded an ultimate load of about 62% higher and 29% respectively than those beams strengthened with a layer and two (2) layers of EB CFRP sheets. The higher performance enhancing ability of the NSM strengthening scheme is therefore evident compared to that of the conventional and industry preferred wet laid up.

Concrete containing wastes from the demolition of old deteriorated buildings are produced enormously. Concrete is a brittle matrix that is usually reinforced by ductile reinforcement such as steel bars. However, due to the susceptibility of steel to corrosion, fiber-reinforced polymers (FRP) bars are used as an alternative reinforcement. The main drawback of FRP bars is their brittleness. These two types of reinforcements, i.e. steel and glass FRP (GFRP) bars, have been used in the present work. The flexural behavior of twelve RC beams reinforced with different ratios of GFRP or steel areas containing recycled aggregate has been experimentally studied and compared with beams without recycled aggregate. The present results show that beams reinforced with GFRP and containing recycled aggregate exhibit a lower load-carrying capacity, lower first crack, and higher deflection than all beams. All GFRP RC beams exhibited brittle failure, i.e., concrete crushing in the compression zone, except one beam, with 2f16 bars and concrete without recycled aggregate, which showed catastrophic failure, i.e., the rupture in GFRP bars. However, the ductile failure mode is observed for all beams reinforced with steel bars, i.e., yielding in steel bars followed by concrete crushing

This paper presents an experimental and numerical study of the flexural behavior of high concrete deep beams reinforced with locally produced glass fiber reinforced polymers (GFRP) bars using high strength concrete (HSC). Both studies were carried out to study the effect of using (GFRP) bars with different ratios of reinforcement and concrete compressive strengths on the behavior of these beams.A total of eight beams, measuring 150 mm wide 500 mm depth and 1800 mm length, were cast, and tested up to failure under two-point loading. The main parameters were the types of reinforcement used, whether steel or GFRP bars. Also, concrete compressive strengths of 50 MPa and 60 MPa were used. In addition, different reinforcement ratios of 0.0033 for steel reinforcement and ratios (0.8, 1.0 and 1.2) of the balanced condition were used. The mid-span deflections, failure loads and GFRP reinforcement strains of the examined deep beams were recorded and compared with each other.The test results revealed that the crack widths and mid-span deflections significantly decreased when using 1.2μb of GFRP reinforcement ratio compared with beams reinforced with steel bars where μb is balanced reinforcement ratio of beam. The decrease in deflection varied between 20%–39.0% for specimens having 50 and 60 MPa respectively, with a significant decrease in the concrete cracks’ widths. Also, the ultimate load slightly increased by 2.5 % and 4.0 % as the concrete strengths increased.A Non-Linear finite element analysis (NLFEA) using ANSYS 2019-R1 was constructed to simulate the flexural behavior of the tested deep beams, in terms of failure load, crack pattern and load deflection behavior. Comparison between the experimental and numerical methods showed good agreement between both results.

Experimental and analytical investigation on structural behavior of two-layer fiber-reinforced concrete beams reinforced with steel and GFRP rebars

Experimental and numerical investigation of flexural behaviour of concrete beams reinforced with GFRP bars

Concrete beams are commonly used in construction projects to provide structural support. Reinforcing these beams with steel and Glass Fiber Reinforced Polymer (GFRP) can increase their strength and durability. Steel reinforcement is a traditional method used for decades, while GFRP is a newer material that offers several advantages, including corrosion strength and lighter weight. Combining both materials to reinforce concrete beams can result in a stronger and more resilient structure, making it an ideal choice for many construction projects. In this study, the behavior of reinforced concrete beams with steel and GFRP reinforcement is numerically investigated, and the effect of steel percentage and GFRP percentage on the mechanical strength and energy response of the beam is determined using the Response Surface Methodology (RSM). Using the ABAQUS software, a widely used Finite-Element Analysis (FEA), the numerical modeling is first verified, and then targeted analyses are performed on the beam using the tests specified by the RSM. Then, based on the strength and energy of the beam, a two-variable Analysis of Variance (ANOVA) and two-objective optimization are performed to investigate the effect of changing each parameter of steel percentage and GFRP percentage on beam strength and energy. Several laboratory studies have been conducted on the behavior of concrete beams with steel and GFRP bars, but no research has statistically and numerically examined their behavior. We also simultaneously optimized both strength and energy parameters based on the ratio of steel and GFRP and compared them with numerical values. We show an interaction relationship between steel and GFRP ratio in the strength and energy of concrete beams. In the beam with hybrid reinforcement, with the increase of steel and GFRP ratios, the amount of strength and energy does not increase linearly, and there is a quadratic relationship between them.

Flexural behaviour of GFRP reinforced high strength and ultra high strength concrete beams

The use of glass-fiber-reinforced polymer (GFRP) bar to replace steel reinforcement in concrete structures is a relatively a new technique. The GFRP bars possess mechanical properties different from steel bars, including high tensile strength combined with low elastic modulus and linear stress–strain relationship up to failure. Therefore, design procedures and process should account for these properties. This paper presents the experimental work on the flexural behavior of concrete beam reinforced with GFRP bars and strengthen with CFRP plate. A total of ten reinforced concrete beams reinforced with either steel and GFRP bars were cast and tested under four point loads. Eight concrete beams (200x250x2800mm) were reinforced with 13mm diameter GFRP bars together with strengthening using CFRP plate and two control beams reinforced with 12mm diameter steel bars were tested. The experimental results show that although the stiffness of the beams reduced but the ultimate load of the GFRP reinforced concrete beam is bigger than steel reinforced beam. It was also found that strengthening using CFRP plate will further enhanced the flexural performance of the beams with GFRP bars.

Evaluation of post-heating flexural behavior of steel fiber-reinforced high-strength concrete beams reinforced with FRP bars: Experimental and analytical results

Soft rock slopes were anchored with traditional steel bars and new Glass Fibre Reinforced Polymer (GFRP) bars. The difference in the anchorage performance of the two kinds of anchorage elements in soft rock and expansive soil was studied by an in-situ test. The results show that cyclic load can aggravate the bond damage of the interface between grouting body and both kinds of bars used in soft rock. Compared with the number of cyclic loads applied, the previous maximum load is the main factor that influences the bond damage of the anchorage bar. Under constant loading, the interface bond behaviour of GFRP bar is better than the steel bar. Because of the small difference in elastic modulus between the GFRP bar and the grouting body, the interface bond around the GFRP bar can invoke more resistance of the grouting body efficiently which demonstrates its more effective anchorage performance than the steel bar under the same conditions. The anchorage structure of steel bar in soft rock can generate larger interfacial relative displacement with increasing load than the GFRP bar in the anchorage section, even though the elastic modulus of steel is much larger than GFRP. In the expansive soil, the anchorage structure deformations of steel and GFRP bars are almost the same because of the weaker bond at the interface of the grouting body and the surrounding soil than that of the bar interface. Under the ultimate loading of the anchorage structure in soft rock, the steel bar with 450 MPa which is less than its ultimate strength shows the failure of the bar body pulling-out, and the GFRP bar with 508 MPa which is larger than its ultimate strength shows the failure of the bar body by fracture. The steel bar anchorage structure in soft rock is destroyed at the interface around the grouting body. The results show that the GFRP bar performs more efficiently than the steel bar.

Materials technology is an excellent opportunity to be developed industrially and on a needs scale according to the demands of society, namely supporting the environment, low maintenance, and long-term use. Using composite materials with reinforced polymers is a hot topic of discussion in civil engineering as new materials, strength/stiffness enhancers, or applications in building rehabilitation or renovation. Fiber Reinforced Polymer (FRP) is excellent as a new material because, in addition to being lightweight, corrosion resistant, and easy to work with, it also has high flexural strength, so it is a consideration to replace and or strengthen steel materials that are high in cost value. However, until now there has not been found the correct pattern or variant and volume of fibre so that it can be an alternative to the use of steel. The purpose of the study was to experimentally determine the flexural strength of Glass Fiber Reinforced Polymer (GFRP) hybrid beams either with steel reinforcement, with GFRP reinforcement, or with steel and GFRP combination reinforcement and different GFRP ratios (variants) through two-point load bending tests.The designed model is a development of a previous study that used one layer of 4 mm and produced a flexural strength smaller than the targeted flexural strength, so in this study, two layers of 8 mm were used. In addition, other experimental data that has been carried out from the literature is also used where the results of parametric studies provide evidence of the positive effect of hybrid steel and GFRP reinforcement ratios when obtaining GFRP models and volumes.The materials used to manufacture concrete beam test specimens 53x15x15 cm3 with quality of fc'35MPa have been tested according to SNI standards and meet both the minimum and maximum requirements specified. Based on the results of the material test, it is planned that the characteristic concrete quality fcr'=40.31 MPa, and based on the compressive strength test, the quality fcr'=41.68MPa is produced.The hybrid designed material with concrete or concrete and steel has been tensile tested with a maximum arcing load for the two layers = 8 mm variant; the tensile strength of the GFRP woven roving type with two layers 2 x 4 mm is 92.66 MPa. While plain steel reinforcement Diameter 8mm quality 280 MPa has a minimum tensile strength of 350 MPa (3.8 times the tensile strength of GFRP 8 mm).The results of testing and calculating the effect of GFRP as a substitute for steel reinforcement contributed to the flexural strength of concrete beams on average by 47.52%. In comparison, the contribution of flexural strength produced by concrete with steel reinforcement was 107.09%. The concrete variant of hybrid steel reinforcement and GFRP contributes to an increase in the average flexural strength of 117.02% > 4.8% compared to steel-reinforced concrete beams alone.

Effect of macro-synthetic structural fibers on the flexural behavior of concrete beams reinforced with different ratios of GFRP bars