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This paper presents a study on the interlaminar shear strength (ILSS) retention of three types of glass fiber–reinforced polymer (GFRP) bars with different surface textures subjected to four types of conditioning environments (alkaline, alkaline, salt, acidic, and water) at two temperature levels (ambient laboratory and high temperature) for 3, 6, and 12 months. The conditioning temperature plays a critical role in reducing the strength of the bars. Scanning electron microscopy revealed the extent of damage to the fibers, resin, interface, and fracture morphologies in the cross sections. The causes of fiber cracking and lower strength upon exposure were validated by point energy-dispersive X-ray spectroscopy analyses, which detected the leaching of silicon from the fiber structure. Prediction models using multiple linear regression (MLR) and artificial neural networks (ANNs) were developed using Matrix Laboratory (MATLAB R2023b) software and compared. The coefficients of determination of the MLR and ANN prediction models were found to be 0.29 and 0.90, respectively, indicating the superiority of machine learning–based models in identifying and accounting for nonlinearities and highlighting their potential application in GFRP bars. Finally, the correlation between the transverse shear strength (TSS) and ILSS of the tested GFRP bars was identified. The ILSS of the bars was found to be approximately 0.26 times the TSS for any given conditioning scenario. [ABSTRACT FROM AUTHOR]

The purpose of this study was to investigate the two-way shear strength of precast concrete box culverts reinforced with glass fiber–reinforced polymer (GFRP) bars. The investigations included testing four full-scale specimens reinforced with GFRP bars under truck wheel load in accordance with current Canadian design codes. The load was applied to the top slab at three different distances: d (effective depth), 1.5d, and 2.5d from the tip of the haunch to the edge of the load plate. One of the specimens was placed and tested on an aggregate bedding material instead of the rigid floor of the test laboratory. Following experimental testing, a theoretical study was conducted to evaluate experimental shear strength to predicted values using different provisions of several North American and international design standards. Two-way shear failure in the top slab occurred in all tested box culverts, indicating that GFRP-reinforced concrete box culverts are critical in shear under traffic wheel loads. The behavior of the tested box culverts was significantly affected by changing the load location or testing the specimen on an aggregate bedding material. On the other hand, the available two-way shear equations conservatively predicted the two-way shear strength of the top slab of the box culverts. Moreover, the two-way shear action equation used in the Canadian standards considers only the cracking strength of concrete. Therefore, an equation has been proposed to consider the characteristics of the GFRP bars and shear span to effective depth ratio. The proposed equation accurately predicted the two-way shear strength and may be considered in future provisions. Finally, the findings demonstrated the feasibility and efficiency of using GFRP bars as internal reinforcement in concrete box culverts. [ABSTRACT FROM AUTHOR]

Glass fiber–reinforced polymer (GFRP) composites have emerged as alternative materials for building applications, and one common loading scenario for GFRP members in building structures is eccentric compression. This compression may occur due to the locations of these members in structures or shapes of their cross sections, causing compressive loads not in alignment with the centerlines of these members. Under this loading scenario, the shear stresses induced by second-order effects may lead to shear and delamination failure prior to compressive or tensile failure due to the low shear strength of GFRP composites compared with their compressive and tensile strengths. This paper presents a study on pultruded GFRP laminated plates subjected to eccentric compression loading, including experimental investigations, numerical modelings, and analytical derivations, with a focus on the effects of the slenderness of the GFRP plate and the eccentricity of the compression load on their failure mode and compressive capacity. Two types of failure mode were observed from the experiments. One was compressive/tensile failure mode, the other was shear and delamination failure mode. In a coordinate system with slenderness as the horizontal axis and eccentricity ratio as vertical axis, zones for shear failure and compressive/tensile failure were identified and a curve that delineates the two zones was developed. Furthermore, predictions of shear and delamination failures based on the results obtained from numerical and analytical studies were presented and compared with the actual failure observed from the experiments. [ABSTRACT FROM AUTHOR]

Glass fiber–reinforced polymer (GFRP) composites have been used in civil construction because of their high strength, lightweight, and corrosion resistance. However, their thermal sensitivity due to the polymer resin requires further understanding of the fire performance of these structures, because the heat from the fire could cause glass transition and decomposition of GFRP composites and degrade their mechanical properties. Fire dynamic simulations were conducted in this study to investigate heat propagation, which considered airflow aerodynamics, in typical single-story residential houses with walls and roofs in the form of GFRP web–flange sandwich structures. The temperature progressions and gradients in the GFRP wall and roof members were quantified, which allowed for the identification and further understanding of the locations and development of glass transition and decomposition in the GFRP composites during fire exposure. The effects of the building floor layouts, fire source locations, additional fire resistance gypsum plasterboard, and a fresh air supply were further discussed and clarified. [ABSTRACT FROM AUTHOR]

Using geopolymeric recycled aggregate concrete (GRAC) rather than conventional concrete to fill glass fiber–reinforced polymer (GFRP) tubes to produce high-performance structural members is a promising green construction technique. In this article, an experimental study investigating the impact behavior of GFRP tube-confined GRAC under axial impact loadings is presented. Moreover, split Hopkinson pressure bar (SHPB) impact tests were conducted, with several variable parameters: (1) confinement ratio (0, 6-ply, and 8-ply GFRP tubes); (2) recycled aggregate (RA) replacement ratio (0%, 50%, and 100%); and (3) strain rate (ranging from 29.4 to 263.3 s−1). In addition, the experimental results of the impact behavior of GFRP-confined GRAC were compared with those of confined ordinary portland cement (OPC) concrete. The test results showed that the confinement of the GFRP tube can remarkably improve the impact resistance of GRAC. The dynamic increase factor (DIF) of confined GRAC was higher than that of confined OPC-based concrete. Similar to OPC-based concrete, the incorporation of RA negatively influenced the impact properties of GRAC, but these influences could be alleviated by GFRP tube confinement. The compressive properties of GFRP-confined GRAC exhibited a strong strain-rate dependency, while the DIF slightly decreased with an increasing confinement ratio. Finally, a model was developed to predict the dynamic strength of GFRP-confined GRAC by reasonably considering the coupling effects of the RA replacement ratio and confinement ratio. [ABSTRACT FROM AUTHOR]

The new American Concrete Institute (ACI) design code for glass fiber–reinforced polymer (GFRP)–reinforced concrete (RC) members specifies a single value of 1.20 for the bond-dependent coefficient (kb) of all types of GFRP bars. This value was chosen based on test data from this project, as well as a compilation of data available in the literature. This paper reports on an experimental study that assessed the kb for the new generation of GFRP bars from five different manufacturers with different surface types: deformed/ribbed, helically deformed, helically grooved, double-helical wrap/sand-coated, and sand-coated. Two bar sizes (No. 5 and No. 8)—with 15.9 and 25.4 mm nominal diameters representing the typical range of GFRP-reinforcing bars used in practice as longitudinal reinforcement in concrete members subjected to bending—were selected from each of the manufacturers. Five RC beam replicates were used to increase experimental accuracy. Therefore, a total of 60 beams, including 50 beams reinforced with GFRP bars and 10 control beams reinforced with conventional steel bars for comparison purposes, were constructed and tested to failure according to a predetermined test method. Based on the analysis, the study confirms using the bond-dependent coefficient value of 1.20 as adopted in the new ACI design code for GFRP–RC members. This value is recommended for GFRP bars complying with (or exceeding) the material specification listed in the ASTM International standard specification for solid round GFRP bars for concrete reinforcement. [ABSTRACT FROM AUTHOR]

This study proposes using glass fiber–reinforced polymer (GFRP) as a stay-in-place structural formwork for casting bridge decks with ultrahigh-performance concrete (UHPC). The GFRP stay-in-place formworks completely replace the bottom layer of rebars, and the top steel reinforcement is also replaced by a GFRP mesh to mitigate the corrosion damage. The formworks were either a flat GFRP plate with square hollow section (SHS) stiffeners or a flat GFRP plate with new Y-shape stiffeners. Concentric static tests on five 1:2.75 scale decks were performed to investigate the effect of stiffener's configuration and the influence of the concrete strength on the performance of bridge decks. Rotational fixity support was used to simulate a real bridge deck connection of supporting girders. All specimens with the stay-in-place formwork exhibited punching shear failure. It was found that the use of Y-shape stiffeners significantly improved the load-carrying capacity of the proposed deck. Replacing normal concrete with UHPC further improved the loading capacity of the deck. The decks demonstrated excellent performance, with the load-carrying capacity 3.8–9.5 times higher than the established equivalent service load depending on the concrete strength and configuration of the GFRP stay-in-place formwork. Deflection at service load was less than span/1,600 for all the decks. Compared with normal-strength concrete (34 MPa), UHPC improved the maximum load-carrying capacity of the deck from 91.4 to 149 kN. [ABSTRACT FROM AUTHOR]

Concrete-filled glass fiber-reinforced polymer (GFRP) tube (CFFT) columns benefit from significant concrete confinement effects that enhance its structural performance compared to conventional internally reinforced concrete members. CFFTs are currently utilized mostly for exterior applications, as the uncertainty of their performance in fire situations has slowed their adaptation in buildings. To address this uncertainty, a series of ambient temperature and fire tests were conducted on CFFT columns with slenderness ratios (KL/r) ranging from 6.9 to 62.4, using GFRP tubes of 113 mm outer diameter and 3.8 mm wall thickness. The strength increase provided by the GFRP tubes as compared to plain concrete columns was reduced from the initial 214% increase at a KL/r of 6.9 to 104% at a KL/r of 62.4. The fire tests revealed that unprotected CFFT columns with KL/r = 57.4 were able to sustain the applied design service loads (44% of ultimate capacity) for up to 108 min in a standard fire. However, it was determined that the unprotected GFRP tubes lost their structural integrity after approximately 10 min of fire exposure, when the temperature on the inside of the tube reached 350°C, thereby only providing thermal protection to the concrete core after the 10-min mark. The unique outcomes of this new study indicate that CFFT columns can be a viable design option in fire situations. [ABSTRACT FROM AUTHOR]

A multilaboratory investigation into the durability of glass fiber-reinforced polymer (GFRP) bars extracted from eleven 15- to 20-year-old bridges in the US will be performed. Part 1 (Benzecry et al., forthcoming) of this two-paper series describes the bridges and presents data on the condition of their concrete, and Part 2 focuses on the condition of the bars. Constituent content, maximum water absorption, as-received moisture content, glass transition temperature (Tg), short bar shear (SBS) strength, and tensile strength will be evaluated. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) will be performed. The fiber mass content of all bars was close to or greater than that specified in the current ASTM E1309 (ASTM 2011a) GFRP bar standard. SEM and EDS showed only slight signs of degradation, which was predominantly near the outer radius of the bars. The loss of SBS strength was slight to moderate in bars with control data for comparison. Tensile strength, which could only be evaluated in 1 bridge, showed a reduction of only 4.2% after 17 years of service. It was concluded that GFRP bars could be considered a promising replacement for steel reinforcement in bridge decks subjected to real-time field exposure. [ABSTRACT FROM AUTHOR]

Glass fiber-reinforced polymer (GFRP) bars have been used in concrete structures as an alternative to steel bars due to their noncorrosive behavior. However, due to the lack of full understanding of long-term performance, their use as internal reinforcement is still limited. To evaluate the durability of in-service GFRP bars under natural exposure, a collaborative project including four organizations investigated the conditions of GFRP bars and their surrounding concrete from bridges with 15-20 years of service. The aim of Part I of a twopaper series is to describe the bridge structures, methods of extraction, and the results of concrete testing, wheras Part II focuses on GFRP bar performance. The extracted bars were tested for physical, mechanical, and chemical properties, and the surrounding concrete was evaluated for chloride penetration, pH, and carbonation depth at the level of reinforcement. Results showed that carbonation and chloride may have reached the depth of the GFRP bars. This paper discusses the process of extraction of the bars, including the location and type of the selected bridge, and the concrete tests performed in terms of procedure, results, and observations. [ABSTRACT FROM AUTHOR]

Hollow-core concrete columns are widely used as structural members to reduce the cost and self-weight of concrete structures. This study investigates the axial load–axial deformation behavior of glass fiber-reinforced polymer (GFRP) bar- and helix-reinforced hollow-core circular concrete columns. Four specimens of 214-mm outer diameter and 56-mm circular inner hole diameter with a height of 850 mm were tested under axial compression. One specimen was reinforced with steel bars and steel helices, and the remaining three specimens were reinforced with GFRP bars and GFRP helices. It was found that, for a similar amount of longitudinal and transverse reinforcements, the GFRP bar-reinforced specimen achieved 15% and 4% higher effectiveness of confinement reinforcement and ductility, respectively, than the steel bar-reinforced specimen. The effectiveness of confinement reinforcement and ductility of the GFRP bar-reinforced specimen was higher for the smaller pitch of GFRP helices. The GFRP bar-reinforced specimen with helices of 30 mm pitch achieved 46% and 66% higher effectiveness of confinement reinforcement and ductility, respectively, than the GFRP bar-reinforced specimen with helices of 90 mm pitch. [ABSTRACT FROM AUTHOR]

In the last decade, extensive research has been done in the field of the seismic upgrading of reinforced concrete (RC) columns using fiber-reinforced polymer (FRP). The enhancement in the column's ultimate strength and significant improvement in the column's displacement ductility combined with the ease of FRP installation resulted in an increasing use of FRP as an effective retrofit solution. Recently, similar enhancements to the RC columns have been reported for reinforced masonry columns (RMCs) upgraded using FRP. However, due to the limited available studies, a gap still exists in understanding the lateral response of the upgraded RMCs using different types of FRP. This study presents an experimental investigation of the effect of changing the FRP type (carbon and glass) on the lateral response of RMCs tested under quasistatic cyclic loading. Based on the experimental data, both FRP materials showed higher strength and ductility compared with control specimens not FRP-wrapped. However, the carbon FRP (CFRP) upgraded RMCs showed slightly higher strength and higher ductility levels than that of glass FRP (GFRP). Also, the difference between carbon and glass FRP RMCs performance was more noticeable as the confinement ratio increased. Moreover, with the current migration of the design codes from forced-based to displacement-based design, there is a need to have simple analytical tools capable of predicting the full load-displacement relationship. Therefore, 12 masonry prisms having various numbers of FRP layers and configurations were tested under concentric compression loading to calibrate the stress-strain material model. Consequently, this stress-strain model was implemented in a simple backbone model capable of predicting the lateral load-displacement backbone relationship of the upgraded RMCs. The model was capable of calculating the ultimate strength, displacement at ultimate strength, and initial stiffness of the tested RMCs with average errors of 6, 22, and 30%, respectively. [ABSTRACT FROM AUTHOR]

This paper presents the results of a collaborative research project between Quebec's Ministry of Transportation and Ontario's Ministry of Transportation, which aimed at characterizing a new type of headed glass fiber-reinforced polymer (GFRP) reinforcing bar and evaluating its suitability as internal reinforcement for concrete structures. To achieve these objectives, the project was implemented in three stages: (1) evaluation of the physical and mechanical properties; (2) determination of the pullout behavior in concrete; and (3) characterization of the long-term durability of the headed GFRP bars. A total of 57 specimens embedded in a 200-mm concrete cube were tested with the direct pullout test to investigate the effect of confinement, bar size, concrete compressive strength, and exposure conditions on the pullout behavior of the headed GFRP bars. Simultaneously, microstructural analyses and measurements of the physicochemical and mechanical properties were carried out on conditioned and unconditioned headed GFRP bars. The results show that the materials, geometry, and interface configuration of the head provided very good mechanical interlocking to the GFRP bars. Up to 63 and 53% of the guaranteed tensile strength of the straight GFRP bars were achieved for 15.9- and 19-mm diameter bars with headed ends, respectively. Scanning electron microscopy and differential scanning calorimetry showed no material changes in the head and bars after exposure to alkaline solution and freeze-thaw cycling. Exposure to the alkaline solution under sustained loading had the most detrimental effect, with the bar retaining 79.4% of its pullout strength. The results indicate that the tested headed GFRP bar has suitable mechanical and durability properties for use as reinforcement in concrete bridge components. [ABSTRACT FROM AUTHOR]

Composite sandwich panels with reinforcement ribs or webs are being increasingly considered for structural applications in civil engineering. Such panels are prone to creep when subjected to significant permanent loads and therefore the effects of this phenomenon must be duly accounted for in their design. Data regarding the viscoelasticity of sandwich panels and their constituent materials is still scarce and often cannot be directly used for creep predictions in design practice. To address this issue, this paper presents the experimental assessment and the analytical modeling of the viscoelastic response of two types of sandwich panels, with and without reinforcement ribs. Panels comprising glass fiber-reinforced polymer (GFRP) faces, cores of polyurethane (PU) foam, and longitudinal GFRP ribs are considered. The ribs increased the flexural strength and stiffness of the panels by a factor of two, while providing a threefold reduction in their creep compliance. A composite creep modeling (CCM) approach is assessed, inputting independently determined viscoelastic properties of the individual materials into Timoshenko beam theory to estimate the creep response of the full-scale panels. The predicted and experimental creep curves presented good agreement for different load levels, attesting the CCM's adequacy for the analysis of creep in sandwich panel design. [ABSTRACT FROM AUTHOR]