Enhancing the Flexural Behavior of Over-Reinforced Concrete Beams

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.

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

The bond performance of glass fibre reinforced polymer (GFRP) bars and that of steel bars embedded in Alkali Activated Cement (AAC) concrete are analysed and compared using pull-out specimens. The bond failure modes, the average bond strength and the free end bond stress-slip curves are used for comparison. Tepfer’s concrete ring model is used to further analyse the splitting failure in ribbed steel bar and GFRP bar specimens. The angle the bond forces make with the bar axis was calculated and used for comparing bond behaviour of ribbed steel bar and GFRP bars in AAC concrete. The results showed that bond failure mode plays a significant role in the comparison of the average bond stress of the specimens at failure. In case of pull-out failure mode, specimens with ribbed steel bars showed a higher bond strength while specimens with GFRP bars showed a higher bond stress in case of splitting failure mode. Comparison of the bond stress-slip curves of ribbed steel bars and GFRP bars depicted that the constant bond stress region at the peak is much smaller in case of GFRP bars than ribbed steel bars indicating a basic bond mechanism difference in GFRP and ribbed steel bars.

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

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.

The current study presents an experimental investigation performed on slender reinforced concrete shear walls, representing a common lateral-load resisting system of mid-rise buildings. The walls were reinforced with steel and glass fiber-reinforced polymer (GFRP) bars and tested up to failure under reversed quasi-static cyclic loading to investigate the capability of GFRP bars in reinforcing RC shear walls under seismic loads. Moreover, the effect of the GFRP reinforcement ratio on the structural response, deformation performance, and failure mode resulting in RC walls, compared with its behavior when reinforced with steel bars, is also investigated. Six full-scale shear walls with an aspect ratio of 3.25 were constructed. The reference wall was entirely reinforced with steel bars. Two specimens were reinforced by hybrid scheme of GFRP–steel bars. The remaining three shear walls were entirely reinforced with GFRP bars. The overall performance of each wall was characterized by investigating the lateral load capacity, hysteretic response, cracks propagation, ductility, and the behavior of energy dissipation. The experimental results showed that GFRP-reinforced concrete walls had an elastic behavior characterized by a stable hysteretic response with recoverable deformation of more than 80% of the ultimate load. However, sudden and brittle failure was attained for the wall with a high GFRP reinforcement ratio. GFRP decreases the displacement ductility of the shear walls by an average of 32.9%, depending on the reinforcement ratio, compared to that reinforced by steel bars. Moreover, lower energy dissipation through inelastic deformation was obtained for the walls reinforced with GFRP bars. Nonetheless, when GFRP bars are combined with steel bars, acceptable levels of dissipated energy are attained compared to the steel-reinforced wall.

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

Effect of stirrups on the bond behavior of lap spliced GFRP bars in concrete beams

Mechanical behavior of concrete prisms reinforced with steel and GFRP bar systems

This study investigates the bonding performance between Glass Fiber-Reinforced polymer (GFRP) bars and Lightweight Aggregate Concrete (LWAC). We established 81 central pull-out numerical simulation scenarios to analyze the influence of four factors—lightweight aggregate concrete strength grade, GFRP bar diameters, GFRP bar rib height, and GFRP bar bonding length—on the bonding performance between LWAC and GFRP bars. The results indicated that considering the surface characteristics of GFRP and the intrinsic model of LWAC, the bonding damage pattern between GFRP and LWAC can be accurately reflected. The damage patterns observed in the simulations were generally consistent with experimental findings. The ultimate bond strength between GFRP and concrete increased with the increase in LWAC strength. However, beyond a concrete strength of 50 MPa, the enhancement in ultimate bond strength becomes marginal. Within a certain range, the ultimate bond strength decreases with increasing GFRP diameter and bond length, while it increases with increasing GFRP rib height. The predictions from our GFRP and LWAC bonding strength model closely matched the experimental values, with prediction errors within 15%. The numerical simulation method and the ultimate bond strength prediction model established in this paper provide scientific reference and theoretical support for the evaluation of the bonding performance between lightweight aggregate concrete and GFRP bars.

This study developed prestressed high-strength concrete (PHC) piles reinforced with high-strength materials (glass fiber-reinforced polymer (GFRP) bars) for flexural performance enhancement. Flexural strengths and behaviors of PHC piles reinforced with hybrid GFRP and steel bars were experimentally investigated, respectively. Large-scale specimens with total lengths of 12,000 mm and diameters of 600 mm were constructed and tested under bending, accompanied by evaluation of effects of non-prestressed reinforcement type and longitudinal reinforcement ratio. J-factors were calculated to evaluate deformability of all the specimens. PHC piles reinforced with GFRP bars were demonstrated to have much higher flexural capacity than those reinforced with steel bars. Moreover, strains at the midspans of cross sections of all the specimens basically conformed to the assumption of plane section. Failure of PHC piles reinforced with GFRP bars was attributable to gradual concrete crushing, while that of PHC piles reinforced with steel bars resulted from steel yielding. Results of this study were expected to provide theoretical basis for wide engineering applications of PHC piles reinforced with hybrid GFRP bars and steel bars in marine structures.

Performance evaluation of normal- and high-strength concrete column specimens reinforced longitudinally with different ratios of GFRP bars

Traditionally, reinforced concrete structures are constructed using steel rebars as reinforcement which is more susceptible to reinforcement corrosion in severe exposure conditions. This leads to many disadvantages, like deterioration of concrete, reduction in strength, and increase in maintenance costs, which leads to a decrease in the serviceability of critical infrastructure. Fiber Reinforced Polymer bars are often used as alternative materials for steel bars because they are anti-corrosive, exhibit an excellent strength-to-weight ratio and are easy to handle but the main disadvantage is its brittle nature. Hence, the combination of steel and FRP bars was effectively used to augment both flexural capacity and ductility. As the ductility performance of hybrid Reinforcement is lower than conventional reinforced beams, Polyvinyl Alcohol Fibers in volume fraction were added in this investigation. The present investigation aims to determine the flexural capacity of reinforced concrete beams using Glass Fiber Reinforced Polymer (GFRP) bars and Steel bars. The optimum dosage of PVA fibers while evaluating compressive and split tensile strength is observed at 0.25% in volume fraction. Total six types of concrete beam specimens with and without PVA fibers were experimentally under four-point bending test tested such as beams reinforced with only steel bars, only GFRP bars, GFRP and steel bars. From the experimental results, it is observed that inclusion of PVA fibers in proposed beams with hybrid reinforcement enhanced the crack resistance by 80% and ultimate load capacity by 39% when compared with conventional beam.

Traditionally, reinforced concrete structures are constructed using steel rebars as reinforcement which is more susceptible to reinforcement corrosion in severe exposure conditions. This leads to many disadvantages, like deterioration of concrete, reduction in strength, and increase in maintenance costs, which leads to a decrease in the serviceability of critical infrastructure. Fiber Reinforced Polymer bars are often used as alternative materials for steel bars because they are anti-corrosive, exhibit an excellent strength-to-weight ratio and are easy to handle but the main disadvantage is its brittle nature. Hence, the combination of steel and FRP bars was effectively used to augment both flexural capacity and ductility. As the ductility performance of hybrid Reinforcement is lower than conventional reinforced beams, Polyvinyl Alcohol Fibers in volume fraction were added in this investigation.The present investigation aims to determine the flexural capacity of reinforced concrete beams using Glass Fiber Reinforced Polymer (GFRP) bars and Steel bars. The optimum dosage of PVA fibers while evaluating compressive and split tensile strength is observed at 0.25% in volume fraction. Total six types of concrete beam specimens with and without PVA fibers were experimentally under four-point bending test tested such as beams reinforced with only steel bars, only GFRP bars, GFRP and steel bars. From the experimental results, it is observed that inclusion of PVA fibers in proposed beams with hybrid reinforcement enhanced the crack resistance by 80% and ultimate load capacity by 39% when compared with conventional beam.

Bond between glass fibre reinforced polymer bars and high - strength concrete