Journal of Composites for Construction

Extensive experimental investigations were carried out to investigate the serviceability (deformations and crack opening width) of fiber–reinforced polymers (FRP) reinforced concrete members. However, most of the tests were limited to conventional arrangement of bars in a section. Considering glass fiber–reinforced polymer (GFRP) bars (one of the most frequently used types of composite reinforcement), this study experimentally and analytically investigated the serviceability behavior of beams with different arrangements of reinforcement bars in the tensile zone. With particular emphasis on tension-stiffening and bond behavior, the experimental program consisted of full-scale beams and bending bond specimens. The tests revealed specific features in the behavior of the beams due to distribution of tensile bars in three layers or enlarging the cover. A numerical procedure, based on local interaction of reinforcement and surrounding concrete, was applied for serviceability analysis. Several bond stress-slip models were employed in the numerical analysis. Despite the satisfactory prediction of crack opening and deformations in general, neither of the bond models was able to give accurate results for all the beams.

Although the use of glass fiber–reinforced polymer (GFRP) reinforcing bars is gaining acceptance as an alternative to conventional steel reinforcement in concrete structures, little empirical data exist on the long-term fatigue performance of GFRP bars in concrete. Abrasion at the bar–concrete interface is known to have an adverse effect on bonds and on the overall member response under cyclic loading, although this effect was not adequately quantified until now. This paper presents the results of an experimental study comparing the fatigue performance of GFRP bars in air with the behavior of similar bars embedded in concrete. The experimental findings showed that the GFRP bars tested in air survived fatigue lives that were approximately a full order of magnitude longer than similar bars in concrete beams. The results were used to calibrate a statistical fatigue life model and a residual stiffness model for GFRP bars in reinforced concrete flexural members.

Due to the complex mechanism of shear behavior, most current empirical methods do not physically simulate the shear behavior as seen in practice. These approaches, therefore, cannot be directly applied to accommodate advanced technologies such as in the use of fiber-reinforced polymer (FRP) or fiber-reinforced concrete. With FRP reinforcement widely used nowadays, there is a need for a mechanics-based approach to explain and simulate the shear failure mechanism. In this paper and from a mechanics-based segmental approach, a generic closed-form solution is derived for quantifying the shear capacity of RC beams and one-way slabs without stirrups and in theory with any type of reinforcement and concrete. The model is validated with 209 published shear tests of FRP-reinforced specimens with normal concrete and, to show the generic nature of the model, with a further 626 published shear tests on beams with steel reinforcement. The generic closed-form solution is further simplified to facilitate shear design. A comparison to the predictions made by design recommendations shows a reduction to different degrees in both mean and scatter of the measured-to-predicted shear strength ratio for the proposed approaches.

Interface crack propagation of FRP (fiber-reinforced polymer) strengthened reinforced concrete (RC) flexural member is often initiated from the toes of the intermediate cracks and propagates towards the supports. This type of FRP delamination is commonly termed intermediate crack (IC) debonding and is common for flexural members with high shear span-to-depth ratios. If the ultimate FRP strain at IC debonding failure is known, the moment capacity of the member can be obtained through a simple section analysis. This research deals with the prediction of ultimate FRP strain at IC debonding, using neural networks and regression models. Basic information on neural networks and the types of neural networks most suitable for the analysis of experimental results are given. A set of experimental data for FRP-strengthened RC beams and one-way slabs, covering a large range of parameters, for the training and testing of neural networks is used. The available test results were not only compared with current code provisions but with equations proposed by other researchers as well. The prediction models based on neural network are presented. A new design equation is also suggested.

Concrete structures deteriorate for various reasons and upgrading is needed to ensure their continued safe working conditions. Retrofitting reinforced concrete (RC) beams have been accomplished using various techniques, namely, steel plates, external posttensioning, externally bonded fiber-reinforced polymer (FRP), and near-surface-mounted FRP systems to increase flexural and shear capacity. The objective of this paper is to investigate the feasibility of fabric-reinforced cementitious-matrix (FRCM) materials as an alternative external strengthening technique for RC members. The FRCM is a composite material consisting of one or more layers of cement-based matrix reinforced with dry-fiber fabric. The experimental program consists of testing 18 RC beams strengthened in flexure with two different FRCM schemes (one and four reinforcement fabrics). An analysis and design are conducted following the well-established formulation to calculate the flexural capacity of the beams and compare their results with the experimental database.

Biocomposites are emerging as a possible sustainable alternative in structural applications, and as a result, a major focus should be on their durability. This study focuses on the environmental aging of bioresin glass fiber–reinforced polymer (GFRP) through immersion in saltwater at elevated temperatures. The resin is furfuryl alcohol based, derived from renewable resources, such as corncobs and sugarcanes. Deterioration was quantified by tensile testing of unidirectional bioresin GFRP coupons at various stages of exposure, and compared to conventional epoxy GFRP coupons under the same conditions. A total of 150 specimens were exposed to three different environments, namely 23°, 40°, and 55°C water with 3% salt concentration, for up to 300 days. It was found that the bioresin GFRP retained 80, 44, and 39% of its original strength at the three temperatures, respectively. On the other hand, the epoxy GFRP exhibited 86, 72, and 61% strength retentions, respectively. No reductions occurred to the Young’s moduli. The Arrhenius model was applied, assuming environments with mean annual temperatures of 3°, 10°, and 20°C, representing different regions in North America. It was estimated that bioresin GFRP strength retentions after 100 years, at the three mean temperatures, are 65, 61, and 50%, respectively.

An analysis model for the nonlinear response behavior of RC shear walls repaired and strengthened in flexure with externally bonded fiber-reinforced polymer (FRP) sheets using the FEM is presented. A novel component of the research reported in this paper is the implementation of a computationally simple procedure to account for the debonding between the FRP and concrete substrate due to the opening of flexural cracks in the shear walls, also termed the intermediate crack (IC) debonding mechanism or IC debonding. In previous analytical research of shear walls reinforced with FRP tow sheets, IC debonding has not been taken into account. The analysis model developed in the research reported in this paper has been validated using experimental results of shear walls repaired/strengthened with FRP sheets available in the literature. Neglecting the influence of IC debonding produces significant overestimations of the load-carrying capacity of the walls and an overall poor correlation between the analytical and experimental hysteretic nonlinear response behavior. Including IC debonding effects, a close agreement between calculated and measured results for key structural response parameters is obtained.

This paper presents the results of an experimental study conducted to investigate the effectiveness of different types of fabric-reinforced cementitious matrix (FRCM) composite systems to strengthen shear critical reinforced concrete (RC) beams. Seven shear-critical RC beams were tested. The test variables included the strengthening material (glass FRCM or carbon FRCM) and the strengthening scheme (side bonded or u-wrapped). The test results revealed that FRCM strengthening is effective in enhancing the load-carrying capacity of shear-critical RC beams. The increase in load-carrying capacity of the FRCM-strengthened beams ranged between 19 and 105%. Both strengthening schemes (side bonded and u-wrapped) exhibited similar behavior, suggesting that the excellent bond of the FRCM to concrete may not require u-wrapped applications for anchorage. The experimental results were also compared with theoretical predictions according to fiber-reinforced polymer (FRP) design guidelines in North America with some modifications. The American Concrete Institute (ACI) predictions were in good correlation with experimental results, whereas the Canadian Standards Association (CSA) predictions were slightly unconservative.