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This paper presents a study to investigate serviceability, strength, and deformability of normal- and high-strength concrete beams reinforced with deformed glass-fiber-reinforced-polymer (GFRP) bars under flexural loading. Understanding the flexural behavior of concrete beams reinforced with deformed GFRP bars with normal- and high-strength concrete would contribute to the existing literature and would provide information critical to the further use of deformed GFRP bars as internal reinforcement for concrete structures. Eight beams with a cross-sectional width and height of 200 mm and 300 mm, respectively, and a clear span of 2700 mm were tested under two-point flexural loading until failure. Four beams were made with 35 MPa normal-strength concrete (NSC); the other four with 65 MPa high-strength concrete (HSC). The bottom/tensile reinforcement of each beam consisted of two GFRP bars. Four different GFRP bar sizes (12 mm, 16 mm, 20 mm, and 25 mm in diameter) were used with reinforcement ratios ranging from 0.38% to 1.63%. Seven beams failed in concrete compression and the eighth beam failed in tension when the FRP ruptured. The test results showed that increasing the FRP reinforcement ratio had a greater effect on the service moment than the resistance moment. The effects of bar spacing on the behavior of wide beams were also investigated, revealing that the service moment increased when the bar spacing decreased, while the resistance moment increased when the concrete strength increased. In addition, the deformability concept produced significantly higher ductility indices than the energy-based concept. Neither method evidenced a clear trend in the ductility indices of the tested beams. A new approach was proposed to determine the ductility index of concrete beams with FRP bars based on beam curvature. This approach demonstrated a clear trend with the tested beams: the high-strength concrete beams had higher ductility indices than the normal-strength concrete beams.

In recent decades, high-strength concrete (HSC) has been widely used in bridge elements, tunnels, and precast-concrete members. Only a limited number of studies, however, have investigated the structural behavior of HSC columns reinforced with glass-fiber-reinforced-polymer (GFRP) bars. Moreover, most concrete codes do not explicitly cover concrete with strengths above 55 MPa. This paper investigates the structural behavior of HSC columns reinforced with GFRP bars and ties when subjected to eccentrically axial loads. Eight full-scale concrete columns with a 400 × 400 mm cross section and 2000 mm in height were tested under axial monotonic loading. The test variables were the eccentricity-to-width ratio, concrete strength, and reinforcement type using steel and GFRP bars and ties. The test results indicate that the failure of the test specimens under different levels of eccentricity was not triggered by rupture of the GFRP bars on the tension side, up to attaining the maximum section capacity governed by concrete-strain limitation. The load–axial displacement, load–lateral displacement, failure mode, and reinforcement strain responses of all the GFRP-reinforced HSC columns are presented and compared to that of the steel-reinforced HSC columns. The structural behavior of HSC columns reinforced with GFRP bars and ties subjected to eccentric axial loads were evaluated by drawing axial force–flexural moment interaction diagrams and comparing them to that for the steel-reinforced columns. An analytical method (layer-by-layer approach) was applied to predict the axial- and flexural-load capacity of the GFRP-reinforced HSC columns. A parametric study was used to examine the effect of increasing the reinforcement ratio and concrete strength and to investigate the strength contribution of GFRP compression bars.

This research work presents new design equations to adequately determine the effective flexural stiffness (EIe) of concrete-filled fiber-reinforced polymer (FRP)-tubes (CFFTs) columns. Based on an experimental parametric study and theoretical simulation, factors influencing the effective stiffness of reinforced CFFT columns are discussed. The main variables considered are: the axial load ratio (Pu/Po), the eccentricity to diameter ratio (e/D) and the slenderness ratio (L/D). Approximately 3,400 reinforced CFFT columns with different combination of specified variables, in symmetric single curvature bending were simulated to generate the stiffness data. Extensive comparison for the proposed stiffness expressions is made with the results of 74 experimental tests conducted by the authors and others. It is shown that the proposed stiffness equations have a good correlation with the test results. The proposed equations are applicable for any load levels including both service and ultimate loads. Since the proposed expressions give a realistic representation of the actual column behavior, they are recommended for general use in the design of FRP-confined concrete columns under different load levels.

Nowadays, design guidelines and codes contain valuable shear provisions for the design of concrete bridge members reinforced with fiber-reinforced-polymer (FRP) bars. Limited researches seem to have assessed the shear strength of circular concrete members reinforced with FRP reinforcement. Therefore, these standards do not provide specific formulae for circular RC members designed with FRP bars, hoops and spirals under shear loads. This paper reports experimental data about the shear strength of circular concrete specimens reinforced with FRP bars, discrete hoops and continuous spirals. Full-scale circular concrete specimens with a total length of 3,000 mm and 508 mm in diameter were constructed and tested up to failure. The test parameters included the type of reinforcement (glass FRP and carbon FRP versus steel) and configuration of the shear reinforcement (discrete hoops versus continuous spirals). The investigation revealed that the specimen reinforced with FRP hoops exhibited high load-carrying capacity comparable to the counterpart reinforced with FRP spirals. The experimental shear strengths of the FRP-reinforced concrete specimens were compared to theoretical predictions provided by current codes, design guidelines. The results of this study can be used as a fundamental step toward code provisions for using GFRP or CFRP spirals and hoops as internal shear reinforcement.

This paper presents the test results of an experimental study aimed at investigating the behavior of concrete-filled fiber-reinforced-polymer (FRP) tube (CFFT) long columns internally reinforced with longitudinal steel or carbon and glass FRP bars tested under axial compression loading. A total of ten reinforced concrete (RC) and CFFT columns measuring 1900-mm in height and 213-mm in diameter were constructed and tested until failure. The test parameters were: (1) internal reinforcement type and amount; (2) GFRP tube thicknesses; and (3) nature of axial loading (i.e. monotonic and cyclic). The experimental results showed that the GFRP-reinforced CFFT columns had comparable ultimate axial strength and strain capacities compare to their counterparts reinforced with steel bars. As expected, an increase in the FRP tube thickness (or stiffness) resulted in an increase in the strength and strain enhancement ratios. The results also indicated that the residual plastic strain of FRP-reinforced CFFT columns is linearly related to the envelope unloading strain, and this relationship is not influenced significantly by the FRP confinement level but strongly influenced by the internal reinforcement amount and type, particularly when the envelope unloading strain (>0.0035). The presented study showed the applicability of exclusively reinforcing the CFFT columns with FRP bars and subjected to axial compression load. However, further experimental investigations on the axial cyclic behavior of CFFT columns internally reinforced with FRP bars are required to establish such key relationships.

This study concerns the feasibility of using innovative glass fiber-reinforced polymer (GFRP) bars, spirals, and hoops in constructing sustainable marine reinforced concrete structures. The experimental investigation aimed at assessing the durability and structural performance of GFRP-reinforced concrete (RC) circular piles exposed to two simulated marine environments in the laboratory. A total of 15 GFRP-RC circular piles measuring 304 mm in diameter and 1000 mm in height were longitudinally reinforced with GFRP bars and transversely with GFRP spirals or hoops. Five specimens were fabricated as references (unconditioned). The remaining 10 specimens were continuously immersed in simulated marine environments (conditioned) for 12 months: five were kept in seawater at room temperature (22 °C), while the other five were stored in a large chamber that produced hot waves at high temperature (60 °C). After conditioning, all the specimens were tested under axial compression loads. Two structural variables were considered: the transverse reinforcement configuration (spirals versus hoops) and the confinement level (spiral spacing). The durability assessment included microstructure examinations (i.e., differential scanning calorimetry (DSC) and scanning electron microscopy (SEM)) were performed on GFRP bars and spirals taken from the conditioned piles. Furthermore, the bond between concrete and bars or spirals was checked by optical microscopy (OM). The microanalysis observations indicate no visible damage in the contact surface between concrete and GFRP bars or individual fibers and the resin matrix. The compressive test results pointed out that the GFRP-RC piles subjected to severe marine environments experienced 19% enhancement in their axial capacities compared to their reference counterparts. The GFRP spirals and hoops performed well in severe marine environments. The nominal axial capacities of the columns were predicted with the available design equations and are presented and discussed herein.

This study presents a new approach for predicting the load-carrying capacity of reinforced concrete (RC) columns reinforced with fiber-reinforced polymer (FRP) bars with an eXtreme Gradient Boosting (XGBoost) algorithm. The proposed XGBoost model was developed based on a comprehensive database containing experimental data for 283 FRP-RC columns collected from the literature. The SHapley Additive exPlanations (SHAP) framework was used to interpret the output of the model. Furthermore, the efficiency and accuracy of the XGBoost model were evaluated and compared with design codes and equations in the literature. The results show that the proposed prediction model performed extremely well and was suitable for predicting the load-carrying capacity of FRP-RC columns. Moreover, the XGBoost model outperformed other numerical equations. For short columns, the mean R2 and MAPE values for the XGBoost model were 0.98% and 5.3%, respectively. In addition, the most significant input variables for predicting the maximum axial load-carrying capacity of FRP-RC columns were the eccentricity ratio, gross sectional area, compressive strength of concrete, slenderness ratio, and spacing or pitch of transversal reinforcement. Lastly, this study demonstrates the capability of machine learning models to predict the axial load-carrying capacity of FRP-RC columns. The proposed XGBoost model can provide an alternative method to existing mechanics-based models for design practice.

No research has yet been reported on the behavior of lightweight-aggregate self-consolidating concrete (LWSCC) columns reinforced with fiber-reinforced polymer (FRP) bars. LWSCC can be of great interest for reducing dead loads, section dimensions, and project costs, especially for precast elements. This paper presents, for the first time, the test results of a study conducted on 12 circular LWSCC columns reinforced with two types of FRP bars: basalt FRP (BFRP) and glass FRP (GFRP). In addition, columns with steel reinforcement were introduced into the test matrix as references. A mix design for the LWSCC with an equilibrium density of 1,807 kg/m3 and compressive strength of 52 MPa was developed and used to cast the columns. The columns were tested under concentric and eccentric loading. The test variables were the eccentricity-to-diameter ratio, and the type of reinforcement (steel versus GFRP and BFRP). The study was conducted to investigate whether the type of concrete and reinforcement affect the column performance and to develop the experimental load–moment interaction diagram. The load–strain behavior for the concrete, bars, and spirals; the load-deformation curves (axial and lateral); and the experimental P–M interaction diagrams are presented. An analytical study was conducted to predict the axial–flexural capacity. The effect of concrete density was considered in the analysis based on parameters in the codes for conventional and modified rectangular stress blocks. The test results indicate that the LWSCC columns with BFRP and GFRP reinforcement had behavior and strength comparable to their steel-reinforced counterparts when tested under different levels of eccentricity. The analytical results show that the column capacity was sensitive to variations in the rectangular stress-block parameters. Lastly, this study demonstrated the effectiveness of integrating GFRP and BFRP reinforcement into lightweight-aggregate concrete would play a role in producing lighter and more durable concrete members for precast applications.

Back in the 90′s, the shear design of FRP-reinforced concrete beams was developed based on the shear design of conventional steel reinforced concrete beams. Since then, significant changes were implemented in the shear design provisions of internationally recognized design codes for conventional beams as well as being inconsistent and lack the agreement. In addition, a much large number of FRP reinforced concrete beams without stirrups were tested, which included beams with different cross section shape as well as deep and shallow beams. Therefore, it is our mandate to update, refine, unify the current shear design of FRP reinforced concrete beams without stirrups. The purpose of this study is to examine the design of the shear strength of FRP-reinforced concrete beams without stirrups in an attempt to refine and unify that design. An extensive experimental database was gathered and compiled with a total of 510 FRP-reinforced beams without stirrups from over 67 investigations. In addition, selected design codes and available models were used to calculate the shear strength of the tested beams. These design codes and available models were assessed, and recommendations were outlined. Moreover, a unified model was proposed. The strength predicted using the proposed model, which was compared with that measured during testing and that calculated using selected models from the literature. The proposed model was found to be more refined and unified, compared to the available models from the literature.

To date, the shear contribution of lightweight self-consolidating concrete (LWSCC) members reinforced with basalt fiber-reinforced polymer (BFRP) bars (LWSCC-BFRP) has not yet been investigated. Therefore, the anticorrosion properties of BFRP bars combined with the advantages of LWSCC motivated this research to assess the behavior of such members under shear. Eight beams cast using LWSCC and normal-weight concrete (NWC) reinforced with BFRP or steel bars were prepared and tested up to failure. The specimens had a total length of 3100 mm and concrete cross section of 200 mm in width and 400 mm in depth. The influence of two different types of BFRP bars of comparable quality and commercially available (sand-coated basalt and helically grooved basalt) on shear capacity was assessed. The tested beams included five beams reinforced with BFRP bars, one beam reinforced with steel bars, and two beams constructed using NWC for comparison purposes. The experimental results indicate that the adoption of LWSCC allowed for decreasing the self-weight of the reinforced concrete (RC) beams (density of 1800 kg/m3) compared to NWC. Test results show that the concrete shear capacity of the LWSCC beams increased as did the axial stiffness of the longitudinal BFRP reinforcing bars. The test results were compared with the shear capacities predicted using the provisions in several standards. Using a 0.75 concrete density reduction factor in the CSA 2012 shear equation to consider the influence of concrete density yielded a more accurate value for the concrete shear capacity. In addition, using a 0.8 concrete density reduction factor in the ACI 2015 design equation yielded an appropriate degree of conservatism compared to the NWC beams.

Hybrid externally bonded (EB) mechanically-fastened (MF) technique for carbon-fiber-reinforced-polymers (CFRP) strips offers a high potential in shear strengthening to preclude debonding phenomenon and effectively utilize the maximum use of CFRP. This study investigated the failure envelope of reinforced concrete (RC) beams, designed deficient in shear, strengthened with hybrid EB/MF technique and reduced-size CFRP strips. The investigated parameters included strip length, number, spacing, and diameter of fasteners. The beams were subjected to three-point loaded testing with a shear span-to-depth ratio of 2.5. The strengthening had an axial rigidity of 1.8 GPa. The hybrid EB/MF technique for the reduced-size CFRP strips (up to 44% length reduction) inhibited crack propagation and could preclude the debonding phenomenon provided that adequate spacings of fasteners used. The results showed that the hybrid EB/MF specimens with reduced-size CFRP strips could achieve up to 65% shear load gain over the unstrengthened specimen. Also, a theoretical evaluation was conducted using other specimens from past studies to estimate the contribution of CFRP strips with and without steel stirrups. In addition, the ultimate shear loads were predicted, as per North-America’s guidelines, and compared with the experimental results. Finally, a set of recommendations was drawn based on the results of this study and the available literature.

Fiber-reinforced polymer (FRP) bars have emerged as an effective alternative for providing shear and flexural reinforcement for reinforced concrete (RC) members in different applications. Nonetheless, the axial compression behavior of circular FRP RC columns has not yet been defined. Due to the differences in the mechanical properties of FRP and steel reinforcement, the compression behavior of concrete columns reinforced with FRP reinforcement may differ from those reinforced with steel. This study proposed a confinement model to predict the axial stress–strain behavior of RC columns reinforced with glass-FRP (GFRP) bars in longitudinal direction and confined by GFRP spirals or hoops. The model takes into account the effect of many parameters related to transverse reinforcement configuration, longitudinal reinforcement ratio, and volumetric ratio. The proposed model can be used to calculate the confining pressure, confined concrete core stress, corresponding concrete strain, and stress–strain relationship. The analytical stress–strain relationships were compared with experimental database of circular concrete columns reinforced with GFRP bars, spirals, and hoops. The proposed equations demonstrated good ability in predicting the stress–strain behavior of the tested GFRP RC column specimens.

The flexural strength and behavior of reinforced concrete-filled fiber-reinforced polymer (FRP) tube (RCFFT) beams were investigated experimentally and theoretically. A total of ten beams were tested under four-point bending load. Six beams were reinforced with glass FRP bars while the rest were reinforced with conventional steel bars. Filament winded glass FRP tubes were used to act as stay-in-place formwork for the beam specimens. The test variables were the FRP tube thickness, concrete compressive strength, type of internal reinforcement (steel or FRP bars), and type of transverse reinforcement (spiral steel or FRP tube). Yield and ultimate strengths, failure modes, and ductility are discussed based on measured load, deflection and strain data. The test results indicated that the confinement using FRP tubes provided a potential enhancement in the ductility and strength of tested beams. A simplified analytical method was developed to predict the yield and resisting moments corresponding to the failure modes of the tested RCFFT beams. The analysis was conducted according to the equations derived from linear elastic analysis. This analysis was found to be acceptable for predicting the ultimate and yield moment capacities of the beams. In addition, improvement to the crack moment equation was suggested to account for the effect of confinement using FRP tubes.