GFRP-reinforced Concrete Beams Research Articles

Shear Strength of GFRP-Reinforced Concrete Continuous Beams with Minimum Transverse Reinforcement

This paper investigates the shear behavior of continuous concrete beams reinforced with glass fiber–reinforced polymer (GFRP) bars and stirrups. A total of six beams, with 200×300 mm rectangular cross section and continuous over two spans of 2,800 mm each, were constructed and tested. Three main variables, namely, concrete strength, longitudinal reinforcement ratio, and transverse shear-reinforcement ratio, were investigated. Two beams were without transverse reinforcement to evaluate the concrete contribution to the shear strength and four beams had GFRP stirrups to examine the minimum shear-reinforcement contribution to the shear strength. All test specimens were designed to satisfy an assumed 20% moment redistribution. It was observed that all test specimens failed in shear near the interior support after significant moment redistribution from hogging moment to sagging moment regions. In addition, the test results were compared with the predictions of the CSA-S806-12, CSA-S6-06, and ACI 440.1R-06.

Shear characteristics of GFRP-reinforced concrete deep beams without web reinforcement

This article investigates the shear behavior of deep concrete beams reinforced with glass fiber reinforced polymer for flexure and without shear reinforcement. A total of 13 beams were tested under four-point loading until failure. Nine of which reinforced with glass fiber reinforced polymer bars and four with steel bars. The ultimate shear capacity along with the load–deformation relationship of all beams was studied. The effects of the shear span to depth ratio a/d, reinforcement ratio ρ, beam effective depth d, and concrete compressive strength on the ultimate shear capacity and mode of failure of all beams were also investigated. Results show that the stiffness of steel-reinforced concrete beams (slope of the ascending portion of load–deflection curve) is higher than that of beams reinforced with fiber-reinforced polymer bars as expected, due to the low axial stiffness of the fiber-reinforced polymer material. A slight variation in the ultimate shear capacity was noticed but no clear trend was observed. In addition, beams reinforced with fiber-reinforced polymer exhibited larger deformation at their ultimate failure load, after which a sudden failure occurred especially for beams having high shear capacity.

Flexural Behavior of Innovative Hybrid GFRP-Reinforced Concrete Beams

Fiber-reinforced polymer (FRP) bars are emerging as a competitive option for replacing steel bars as reinforcement in various concrete structures exposed to aggressive environments. However, the low elastic modulus and brittleness of FRP bars significantly reduce the stiffness and the ductility of FRP-reinforced concrete (FRP-RC) members. In order to improve the flexural behavior of FRP-RC members and meanwhile ensure their satisfactory corrosion-resistant performance, an innovative FRP-reinforced concrete encased steel composite (FRP-RCS) member, which consists of ductile structural steel shapes in combination with corrosion-resistant FRP-reinforced concrete, was conceived and studied. An experimental investigation on the flexural behavior of the proposed FRP-RCS beams was conducted by testing a total of five large-scale simply supported beam specimens subjected to four-point bending loads. The test specimens included one FRP-RC beam reinforced with GFRP bars only and four FRP-RCS beams reinforced with both GFRP bars and encased structural steel shapes. The main parameters considered in this study were concrete compressive strength and amounts of GFRP reinforcement. The test results indicated that using encased steel shapes provided a significant enhancement in load carrying capacity, stiffness, ductility and energy absorption capacity of test beams. The tested FRP-RC beam suffered a brittle failure caused by sudden fracture of tensile GFRP bars whereas the proposed FRP-RCS beams behaved in a ductile manner due to the beneficial residual strength of encased steel shapes following concrete crushing. In addition, the experimental results also demonstrated that the concrete compressive strength had little effect on load carrying capacity of FRP-RCS beams whereas the load carrying capacity can be enhanced by increasing the reinforcement ratio. Analytical methods were also constructed using OpenSEES2.2.2 to simulate the load-deflection response of tested beams..

Serviceability Limit State of FRP RC Beams

Owing to the particular mechanical properties of FRPs, the design of Fiber Reinforced Polymer (FRP) Reinforced Concrete (RC) structures is often governed by serviceability requirements, rather than ultimate capacity. The low stiffness of FRPs generally results in large strains being mobilized already at low levels of externally applied load, and in turn can lead to significant crack widths and deflections. This paper reviews and discusses the serviceability limitations inherent in current design codes and guidelines in terms of stress limitation, cracking and deflection control. The predictions obtained in accordance to these code equations, as well as other existing proposals for the design of FRP RC structures, are then compared to the results of an experimental program on 24 GFRP RC beams tested under four-point load.

Shear resistance of GFRP-reinforced concrete beams

This paper deals with the behaviour and shear capacity of concrete beams reinforced with glass-fibre-reinforced polymer (GFRP) reinforcing bars. Twelve large-scale beams with a shear span to effective depth of beam ratio of less than 2·5 were tested. The beams were divided into two groups each comprising three GFRP-reinforced beams and three control conventional steel-reinforced beams. Concrete grade and longitudinal reinforcement ratio were varied. A new semi-analytical formula for estimation of the shear capacity of GFRP concrete beams was proposed based on the fracture mechanics approach. The accuracy of the proposed formula was verified using test results of the authors and other researchers. As a characteristic resistance model according to Eurocode 0, it was also compared with existing formulae published in various codes, manuals, guidelines and other studies. The formula was proved to be valid and thus could be applied to predict the shear capacity of beams more accurately.

Probabilistic assessment on flexural capacity of GFRP-reinforced concrete beams designed by guideline ACI 440.1R-06

The provisions in the guideline ACI 440.1R-06 (call ACI guideline thereafter) on the flexural design of concrete beams reinforced with glass fiber reinforced polymer (GFRP) rods are assessed from the probabilistic point of view by using the Rackwitz–Fiessler method. The assessment reveals that the design provisions in ACI guideline are really conservative. Among all resistance-related random variables, sectional width and height-to-width ratio have put significant influence on average reliability level in either failure mode. GFRP strength does not have any effect on reliability level in concrete crushing mode. Concrete strength shows a negligible effect in the failure mode of GFRP rupture. In the case of GFRP rupture, as the mean-to-nominal ratio of GFRP strength increases, the average reliability index at first increases and then decreases. Design of GFRP-reinforced concrete components subject to aggressive exposure conditions would achieve higher reliability level. As a result of the investigation on the relation between average reliability index and resistance reduction factor, a modified value of 0.81 for the factor is suggested.

Behavior of reinforced concrete beams reinforced with GFRP bars

The use of fiber reinforced polymer (FRP) bars is one of the alternatives presented in recent studies to prevent the drawbacks related to the steel reinforcement in specific reinforced concrete members. In this work, six reinforced concrete beams were submitted to four point bending tests. One beam was reinforced with CA-50 steel bars and five with glass fiber reinforced polymer (GFRP) bars. The tests were carried out in the Department of Structural Engineering in São Carlos Engineering School, São Paulo University. The objective of the test program was to compare strength, reinforcement deformation, displacement, and some anchorage aspects between the GFRP-reinforced concrete beams and the steel-reinforced concrete beam. The results show that, even though four GFRP-reinforced concrete beams were designed with the same internal tension force as that with steel reinforcement, their capacity was lower than that of the steel-reinforced beam. The results also show that similar flexural capacity can be achieved for the steel- and for the GFRP-reinforced concrete beams by controlling the stiffness (reinforcement modulus of elasticity multiplied by the bar cross-sectional area - EA) and the tension force of the GFRP bars.

Flexural and shear capacities of concrete beams reinforced with GFRP bars

This paper reports test results of 12 concrete beams reinforced with glass fibre-reinforced polymer (GFRP) bars subjected to a four point loading system. All test specimens had no transverse shear nor compression reinforcement and were classified into two groups according to the concrete compressive strength. The main parameters investigated in each group were the beam depth and amount of GFRP reinforcement. Two modes of failure were observed, namely flexural and shear. The flexural failure is mainly occurred due to tensile rupture of GFRP bars either within the mid-span region or under the applied point load. The shear failure is initiated by a major diagonal crack within the beam shear span. This diagonal crack extended horizontally at the level of the GFRP bars indicating bond failure. Simplified methods for estimating the flexural and shear capacities of beams tested are presented. The flexural capacity is estimated based on the compatibility of strains and equilibrium of forces. Comparisons between the flexural capacity obtained from the theoretical analysis and that experimentally measured in the current investigation and elsewhere show good agreement. To predict the shear capacity of the beams tested, four methods recently proposed in the literature for GFRP-reinforced concrete beams are used. These methods have been developed by modifying the ACI 318-99 shear capacity formula for steel-reinforced concrete beams to account for the difference in the axial stiffness of GFRP and steel bars. It has been shown that the theoretical predictions of the shear capacity obtained from these methods are inconsistent and further research needs to be carried out in order to establish a rational method for the shear capacity calculation of GFRP-reinforced concrete beams.

Effective Moment of Inertia for Glass Fiber-Reinforced Polymer-Reinforced Concrete Beams

This paper investigates deflection behavior of concrete flexural members reinforced with glass fiber-reinforced polymer (GFRP) reinforcing bars. It is recognized that serviceability plays a major role in the design of GFRP-reinforced concrete beams. Therefore, accurate modeling of flexural stiffness is critical and the effect of influencing parameters must be considered. This study accounts for variations in concrete strength, reinforcement density, and shear span-depth ratio. Experimental results from 48 simply supported concrete beams reinforced with GFRP are compared with ACI Committee 440's published deflection model. The ACI 440.1R model is found to overestimate the effective moment of inertia, and an appropriate modification is presented.