Use Of Glass Fiber Reinforced Polymer Research Articles

Flexural behavior of high strength concrete shallow wide beams reinforced by hybrid longitudinal reinforcement

ABSTRACT One of the most common statistical systems used in structures especially for wide span slabs are ribbed slabs with shallow wide beams (SWB). This experimental study aimed to investigate and enhance the flexural behavior of high-strength concrete SWB using hybrid longitudinal reinforcement from steel and advanced composite materials as a tensile main reinforcement in SWB. Longitudinal advanced composite bars locally manufactured from ribbed glass fiber reinforced polymer (GFRP) and the second type was ribbed basalt fiber reinforced polymer (BFRP). A group of six half scale SWB were examined in structures laboratory of American University in Cairo with dimensions 2.1 × 0.6 × 0.25 m for length (L), width (B) and depth (d) respectively with constant size effect (d/B). The first three specimens were completely reinforced at tension side with Steel, GFRP or BFRP ribbed bars to be considered a control specimen. Use of GFRP and BFRP bars enhanced the flexural capacity of SWB with 41% and 43% respectively compared to specimen completely reinforced with steel. But on the other hand, the crack propagation of specimens completely reinforced with GFRP and BFRP developed more quickly and had larger crack width compared to specimen completely reinforced with steel. Hybrid reinforcement from Steel with GFRP, Steel with BFRP and Steel with GFRP and BFRP specimens are used to enhance the crack pattern and mode of failure without a significant loss in flexural capacity of SWB. The flexural capacity of these three specimens was enhanced with 26%, 30% and 41% with a significant enhancement in crack pattern and ductility.

Study on the Manufacturing of Composite Materials Made from Glass Fiber Reinforced Polymer (GFRP) in Indonesia for Use as Lining in Open Channels

This study explained the potential use of glass fiber-reinforced polymer (GFRP) composite materials as an alternative lined material for irrigation channels in Indonesia. Currently, only four recommended materials are used as lining in irrigation channels in Indonesia, i.e., stone masonry, concrete, soil-cement, and ferrocement. Almost all lined material's main constituents are sourced from nature/environment. The exploitation of these mined materials will impact environmental destruction. This study focused on the manufacturing process of GFRP material, GFRP surface roughness testing, and the water flow characteristics in the hydraulic model experimental testing. The manufacturing process of GFRP material used polyester resin as the polymer matrix, E-glass type with a combination of woven roving mat covered by non-woven standard mat as the glass fiber reinforcement, and manufacturing process with a combination of hand lay-up and spray-up techniques. The GFRP material product has an average surface roughness coefficient value of Ra around 5.19 to 5.97 μm. The GFRP manufacturing has a good uniform product, as the average surface roughness coefficients of GFRP material have relatively the same values. It is shown that a factory in Indonesia has sufficient capacity to manufacture GFRP material for lining in open channels. The water flow characteristics in the flume were turbulent during testing in the hydraulic laboratory. The experimental study concluded that the GFRP composite materials could be implemented as preliminary references for alternative lined material in irrigation channels in Indonesia.

Shear performance of glass fiber reinforced concrete beams with diverse embedded GFRP trusses

This paper investigated the shear performance of internal embedded glass fiber reinforced polymer (GFRP) trusses as a novel shear reinforcement instead of conventional steel stirrups for concrete beams reinforced with top and bottom GFRP bars, and for this goal, different proposed patterns of embedded GFRP trusses were offered. In addition, the effect of GFRP stirrup spacing and the comparison with steel stirrups are also studied. For this purpose, an experimental program consisting of nine specimens was utilized that tested under one concentrated load with an unequal span-to-depth ratio up to failure. The program included one specimen with no stirrups in the studied shear zone as a control beam. The GFRP stirrups or proposed trusses were cut as single straight legs without bends or hooks, and they were then linked together with plastic ties to create the necessary shape. Besides, numerical analysis using the finite element program ANSYS V-19.2 was utilized for computational modelling as a 3-D model to examine the capability of the model to capture the observed shear behaviour and to obtain extra results in order to better comprehend the shear behaviour. Cracking patterns, ultimate loads, failure mechanisms, load-deflection relationships, load versus strain in GFRP bars, and strain distribution along the height of the GFRP truss member were evaluated. The shear capacity was enhanced via the use of internal GFRP embedded trusses by about 56–80 % compared to the control beam (BC) without stirrups, while these forms improved the capacity by about 29–50 % compared to the specimen that had only vertical stirrups. In addition, the normal strain distribution along the GFRP truss member height was non-uniform and significantly affected by the member location. The shear capacity was also increased by decreasing the GFRP stirrups' spacing, while the use of GFRP stirrups instead of steel stirrups decreased the ultimate load by about 3–10 %, according to stirrup spacing. Finally, the comparison between the results obtained from the numerical model and the experimental work showed a good agreement.

Experimental and analytical investigation of precast fiber-reinforced concrete (FRC) tunnel lining segments reinforced with glass-FRP bars

A hybrid use of glass fiber-reinforced polymer (GFRP) reinforcement and fiber-reinforced concrete (FRC) could be a viable option for producing durable precast concrete tunnel lining (PCTL) segments. There is, however, a gap in the literature regarding the behavior of GFRP-reinforced FRC PCTL segments with typical amounts of reinforcement. This paper presents results obtained from both experimental and analytical studies on the behavior of GFRP-reinforced FRC PCTL segments under bending load (flexure). Four full-scale tunnel segment specimens were constructed and tested monotonically under three-point bending load. The influence of concrete type, reinforcement ratio, and tie configurations on the cracking behavior, deflection behavior, failure mechanism, load-carrying capacity, strain behavior, and deformability was evaluated. There is a limited analytical procedure available to predict the shear and flexural capacities of GFRP-reinforced FRC PCTL segments. Therefore, an analytical investigation was carried out in order to propose and evaluate different methods for predicting the flexural and shear capacities of such elements. The results indicate that the use of FRC significantly improved the cracking behavior and failure mechanism while also increasing the load-carrying capacity and deformability by 12% and 71%, respectively. Increasing the reinforcement ratio by 86% enhanced the post-cracking stiffness and peak load by 92% and 31%, respectively, while reducing the service-load crack width by 57%. According to the analytical investigation, the introduced direct method based on the stress–strain behavior of the FRC and the proposed simplified method based on ACI 440.1R-15 could predict the flexural capacity of GFRP-reinforced FRC PCTL segments with high accuracy. Furthermore, the method proposed to modify CAN/CSA S806-12, R2017 to consider the contribution of fibers in shear transferring mechanism yielded rational conservative values for the shear capacity of GFRP-reinforced FRC PCTL segments.

Effect of main and NSM reinforcing materials on the behavior of the shear strengthened RC beams with NSM reinforced HSC layers and bars

It became common practice to utilize near-surface mounted (NSM) bars to improve the shear capacity of steel-reinforced concrete (RC) beams. Consequently, carbon fiber-reinforced polymer (FRP) is usually used to improve RC beams' shear performance. Conversely, the use of Glass FRP (GFRP) for enhancing the shear behavior of the steel-RC and GFRP-RC beams is still limited. This study used NSM GFRP or steel bars to strengthen RC beams reinforced in tension with steel or GFRP bars. In addition, a new NSM technique was conducted using high-strength concrete (HSC) layers reinforced with GFRP or steel bars bonded within grooves to enhance beams' shear capacity. The results of seventeen beams used in the tests showed that NSM HSC layers improved the shear performance of RC beams more than NSM bars. Also, the beams reinforced in tension with steel bars had higher shear efficiency and were stiffer than those reinforced with GFRP bars. Conversely, the shear efficiency of steel RC beams strengthened in shear with internal stirrups or NSM reinforcement (or both) increased by 142.8–211.7% compared to GFRP RC beams without internal and NSM shear reinforcement. Conversely, the shear capacity of the steel-RC beams strengthened in shear with internal stirrups or NSM reinforcement (or both) increased by 153.5–279.9% compared to the corresponding beam without GFRP RC beam without internal and NSM shear reinforcement. The numerical analysis using the ABAQUS program showed great effects of the tension reinforcement and the NSM materials on the strain of longitudinal bars, stirrups and NSM reinforcement.

Initial stage degradation of GFRP bars based on functional group ratio change using FTIR in high temperature and alkaline solution

Although extensive research has been conducted on the use of glass fibre-reinforced polymer (GFRP) bars in concrete, one factor that hinders their widespread use in civil engineering is the lack of prediction of degradation properties in concrete for long-term applications. This paper presents the tensile strength (TS) retention and microstructure evolution of GFRP bars in high-temperature and alkaline solutions by Fourier transform infrared (FTIR) spectroscopy. The test results indicated that with TS retention above 70%, the main reason for the mechanical property loss was resin degradation. Significant chemical degradation of the rod surface, namely, the breaking of ester bonds and the formation of carboxylates, was observed by FTIR and scanning electron microscopy (SEM). However, when the TS retention was less than 70%, damage to the bars was induced by debonding of the resin/fibre and localized damage to the resin and fibres. Finally, the relationship between the functional group ratio change and TS retention of GFRP was established using FTIR, revealing a linear relationship and introducing a coefficient k for modification. This can provide a scientific basis for the subsequent method to predict the degree of mechanical property degradation of GFRP bars by FTIR monitoring of the functional group ratio change.

Hydrothermal Ageing of Glass Fibre Reinforced Vinyl Ester Composites: A Review.

The use of glass fibre-reinforced polymer (GFRP) composites in load-carrying constructions has significantly increased over the last few decades. Such GFRP composite structures may undergo significant changes in performance as a consequence of long-term environmental exposure. Vinyl ester (VE) resins are a class of thermosetting polymers increasingly being used in such structural composites. This increasing use of VE-based GFRPs in such applications has led to an increasing need to better understand the consequences of long-term environmental exposure on their performance. The reliable validation of the environmental durability of new VE-based GFRPs can be a time- and resource-consuming process involving costly testing programs. Accelerated hydrothermal ageing is often used in these investigations. This paper reviews the relevant literature on the hydrothermal ageing of vinyl ester-based GFRP with special attention to the fundamental background of moisture-induced ageing of GFRP, the important role of voids, and the fibre-matrix interface, on composite mechanical performance.

Experimental Comparison of the Bearing Capacity of GFRP Beams and 50% Recycled GFRP Beams

This manuscript investigates the possibility of using recycled glass fiber-reinforced polymer for the production of load-bearing elements in construction. Due to the increasing use of GFRP in the world, an increasing amount of waste is generated. The main objective of this research is to expand the use of composite materials in construction and, in particular, to examine the possibilities of original and recycled GFRP. Firstly, the basic characteristics of two different but very similar materials were determined using standard testing samples. Subsequently, experimental beam models were tested as a four-point bending beam model. The beam models used in this experiment were made of two types of materials, glass fiber reinforced polymer (GFRP) and recycled glass fiber-reinforced polymer (RGFRP). The experiments were conducted until the failure of the beam models. The test results are presented in the form of a force/displacement diagram, and the confirmation of the experimental results is shown by means of a numerical model of the beam. Both materials exhibited a very good strength-to-weight ratio, rendering them a suitable choice of material for load-bearing beam elements. Finally, the justification for recycling and the comparison of original and recycled material are presented in a dimensionless diagram. The comparison of these two materials provides some good insights for future research into GFRP beams. Doi: 10.28991/CEJ-2022-08-12-017 Full Text: PDF

Development and mechanical performance evaluation of a GFRP-reinforced concrete boat-approach slab

The use of glass fiber-reinforced polymer (GFRP) composite bars as internal reinforcement in concrete structures exposed to marine and aggressive environments has gained popularity in recent years. The fact that designers and workers are unfamiliar with the design and handling of GFRP bars contributes to GFRP bars being used less often than traditional steel reinforcement bars. This case study presents the construction and loading test for GFRP-reinforced concrete boat-approach slab. Two types of reinforcement mesh stemmed from a similar design requirement were implemented: 16 mm diameter bars spaced 150 mm apart in both directions and 24 mm diameter bars spaced 300 mm apart in both directions to evaluate the fabrication and installation efficiency with GFRP bars. Loading tests and monitoring were employed to evaluate the field performance of the GFRP-reinforced slab. The results show that a slab reinforced with 16 mm diameter GFRP bars can be durable and reliable, and can increase worker productivity during handing and installation. Moreover, considering the appropriate subgrade modulus for the supporting ground in the design and analysis can lead to a more cost-effective design of GFRP-reinforced concrete approach slabs. Lastly, this case study demonstrates the durability and resilience of GFRP-reinforced concrete as boating infrastructure.

Valorization of macro fibers recycled from decommissioned turbine blades as discrete reinforcement in concrete

The extensive use of glass fiber-reinforced polymer (GFRP) composites has inevitably resulted in a large amount of FRP waste, posing a significant environmental threat. A recent study performed by the authors’ group of the present study pioneered a new mechanical method of recycling GFRP wind turbine blades into macro fibers, in which the macro fibers characterized by a fixed-length have been produced using a manual process of low efficiency and high cost, making it impossible for use in a practical application. In the present study, a shredding machine has been therefore used to efficiently process waste GFRP wind turbine blades into macro fibers of hybrid lengths lesser than 100 mm for being incorporated into concrete. A series of tests were carried out to investigate the properties of the resulting concrete, and the test results of beam specimens were then analyzed using a twice inverse analysis approach. The results of compression tests and four-point bending tests showed that the incorporation of recycled macro fibers led to a slump loss of 54%, a compressive strength reduction of 14.07%, a flexural strength improvement of 37.85% and a significant flexural toughness enhancement of 36.8 times at a fiber volume ratio of 2.5%, as compared to those of plain concrete. The direct-tensile strength and the corresponding tensile strain obtained by a twice inverse analysis approach were about 2.26 MPa and 134 με, respectively, as predicted by the inverse analysis based on flexural load-deflection curves. The macro fibers processed using a shredding machine are feasible for enhancing the performance of the resulting concrete, and can be economic-efficiently used for industrial scale applications.

Bending Behaviour of Prestressed T-Shaped Concrete Beams Reinforced with FRP-Experimental and Analytical Investigations.

Materials such as high performance (HPC) or ultra-high performance concrete (UHPC), and fibre-reinforced polymer (FRP) reinforcement can be used to improve the resource efficiency in concrete construction by, for example, enabling the production of thin-walled structures. When building filigree concrete beams two essential factors must be considered: the low stiffness of the structure and the bond between the materials. By prestressing the structural stiffness is improved while an adequate concrete cover ensures sufficient bond strength. Based on this the bending behaviour of prestressed T-shaped beams reinforced with FRP, focussing on determining the influence of four parameters on the bearing capacity, bond behaviour and failure mode, is investigated in this paper. Comprehensive experimental investigations prove the potential of the approach and show that a reduction of the web thickness down to 40 mm, a lower concrete quality, and the use of glass FRP instead of carbon FRP allow a more resource-efficient structure while the applied prestressing leads to a higher utilisation of the high performance materials.

Structural Performance of GFRP Bars Based High-Strength RC Columns: An Application of Advanced Decision-Making Mechanism for Experimental Profile Data

Several past studies have shown the use of glass fibre-reinforced polymer (GFRP) bars to alleviate the reinforced steel rusting issue in different concrete structures. However, the practise of GFRP bars in concrete columns has not yet achieved a sufficient confidence level due to the lack of a theoretical model found in the literature. The objective of the current study is to introduce a novel prediction model for the axial capability of concrete columns made with bars of GFRP. For this purpose, two different approaches, such as data envelopment analysis (DEA) and artificial neural networks (ANNs) modelling, are used on a collected dataset of 266 concrete column specimens made with GFRP bars from previous literature works. Eight parameters were used to predict the axial performance of GFRP-based RC columns. The proposed DEA and ANNs predictions demonstrated a good correlation with the testing dataset, having R2 values of 0.811 and 0.836, respectively. A comparative analysis of the DEA and ANNs models is undertaken, and it was found that the suggested models are capable of accurately forecasting the structural response of GFRP-made RC column structures. Then, a comprehensive parametric analysis of 266 GFRP-based columns was performed to study the effect of different materials and their geometrical shape.

Experimental behaviour of FRP reinforced concrete structural elements

Reinforced concrete structures form a major part of the Engineering infrastructures of all developed countries and their integrity over long periods of service is of vital economic importance. However, there are a number of factors that can endanger the serviceability of reinforced concrete structures. These factors result in high maintenance costs (or) the early replacement of structures. The most widespread problem of premature deterioration is caused by deterioration of steel reinforcement. Corrosion induced deterioration of steel reinforcement in concrete has increasingly become a major problem use of non-metallic reinforcement such as GFRP (Glass Fibre Reinforced Polymer) rebars helps to rise the mechanical characteristics of concrete structure as it does not corrode. The GFRP rebars look like steel with similar, properties such as high tensile strength and bond characteristics. The key aim of this project is to replace the steel reinforcement by using GFRP rebars in concrete structural elements and to find the load carrying capacity etc., and comparing with the test results of the experiment carried out on the same size of beams with use of GFRP and tor steel as reinforcement. Reinforcement rod 8 mm size 3 at bottom and 2 at top is placed with stirrup spacing of 100 mm c/c. Load applied in 3 Kn variation and 7 cycles of load was applied. Load carrying capacity was good at 0.1 % GFRP addition.

Seismic performance of ductile corrosion-free reinforced concrete frames

<abstract> <p>Corrosion of steel bars is the main cause of the deterioration of reinforced concrete (RC) structures. To avoid this problem, steel rebars can be replaced with glass-fiber-reinforced-polymer (GFRP). However, the brittle behaviour of GFRP RC elements has limited their use in many applications. The use of shape memory alloy (SMA) and/or stainless steel (SS) rebars can solve this problem, because of their ductile behaviour and corrosion resistance. However, their high price is a major obstacle. To address issues of ductility, corrosion, and cost, this paper examines the hybrid use of GFRP, SS, and SMA in RC frames. The use of SMA provides an additional advantage as it reduces seismic residual deformations. Three frames were designed. A steel RC frame, SS-GFRP RC frame, and SMA-SS-GFRP RC frame. The design criteria for the two GFRP RC frames followed previous research by the authors, which aimed at having approximately equal lateral resistance, stiffness, and ductility for GFRP and steel RC frames. The three frames were then analyzed using twenty seismic records. Their seismic performance confirmed the success of the adopted design methodology in achieving corrosion-free frames that provide adequate seismic performance.</p> </abstract>

Artificial Neural Network (ANN) and Finite Element (FEM) Models for GFRP-Reinforced Concrete Columns under Axial Compression

In reinforced concrete structures, the fiber-reinforced polymer (FRP) as reinforcing rebars have been widely used. The use of GFRP (glass fiber-reinforced polymer) bars to solve the steel reinforcement corrosion problem in various concrete structures is now well documented in many research studies. Hollow concrete-core columns (HCCs) are used to make a lightweight structure and reduce its cost. However, the use of FRP bars in HCCs has not yet gained an adequate level of confidence due to the lack of laboratory tests and standard design guidelines. Therefore, the present paper numerically and empirically explores the axial compressive behavior of GFRP-reinforced hollow concrete-core columns (HCCs). A total of 60 HCCs were simulated in the current version of Finite Element Analysis (FEA) ABAQUS. The reference finite element model (FEM) was built for a wide range of test variables of HCCs based on 17 specimens experimentally tested by the same group of researchers. All columns of 250 mm outer diameter, 0, 40, 45, 65, 90, 120 mm circular inner-hole diameter, and a height of 1000 mm were built and simulated. The effects of other parameters cover unconfined concrete strength from 21.2 to 44 MPa, the internal confinement (center to center spiral spacing = 50, 100, and 150 mm), and the amount of longitudinal GFRP bars (ρv = 1.78–4.02%). The complex column response was defined by the concrete damaged plastic model (CDPM) and the behavior of the GFRP reinforcement was modeled as a linear-elastic behavior up to failure. The proposed FEM showed an excellent agreement with the tested load-strain responses. Based on the database obtained from the ABAQUS and the laboratory test, different empirical formulas and artificial neural network (ANN) models were further proposed for predicting the softening and hardening behavior of GFRP-RC HCCs.

Compression behavior of GFRP bars under elevated In-Service temperatures

The use of glass fiber-reinforced polymer (GFRP) bars is becoming accepted as internal longitudinal reinforcement in concrete members subject to compressive load. In building and construction, GFRP reinforcement is subject to elevated in-service temperatures that might soften the polymer matrix and affect the mechanical properties of the reinforcement. That notwithstanding, information on the compressive behavior of GFRP bars under elevated in-service temperatures is limited. This study investigated the effects of elevated in-service temperatures ranging from 23℃ to 140℃ and different slenderness ratios (Lu/db) of 4, 8, and 16 on the compressive behavior of GFRP bars. The test results show that the failure mode of GFRP bars changed from fiber-dominant to matrix-dominant with increased temperature. Similarly, the increase in Lu/db ratio changed the failure from shear-crushing to buckling-splitting failure. Furthermore, the GFRP bars retained most of their compressive strength when exposed to temperatures of up to 60℃, but significantly decreased thereafter. The compressive strength retention of the GFRP bars at 140℃ was around 20% regardless of the Lu/db ratio. Based on these results, prediction equations were derived to reliably describe the compressive behavior of GFRP bars and to appropriately determine the minimum concrete cover needed to effectively design GFRP-reinforced concrete members under compression exposed to elevated in-service temperatures.

Pultruded GFRP Reinforcing Bars Using Nanomodified Vinyl Ester

Glass fiber-reinforced polymer (GFRP) reinforcing bars have relatively low shear strength, which limits their possible use in civil infrastructure applications with high shear demand, such as concrete reinforcing dowels. We suggest that the horizontal shear strength of GFRP bars can be significantly improved by nanomodification of the vinyl ester resin prior to pultrusion. The optimal content of functionalized multiwalled carbon nanotubes (MWCNTs) well dispersed into the vinyl ester resin was determined using viscosity measurements and scanning electron micrographs. Longitudinal tension and short beam shear tests were conducted to determine the horizontal shear strength of the nanomodified GFRP reinforcing bars. While the tensile strength of the GFRP reinforcing bars was improved by 20%, the horizontal shear strength of the bars was improved by 111% compared with the shear strength of neat GFRP bars pultruded using the same settings. Of special interest is the absence of the typical broom failure observed in GFRP when MWCNTs were used. Differential scanning calorimetry measurements and fiber volume fraction confirmed the quality of the new pultruded GFRP bars. Fourier-transform infrared (FTIR) measurements demonstrated the formation of carboxyl stretching in nanomodified GFRP bars, indicating the formation of a new chemical bond. The new pultrusion process using nanomodified vinyl ester enables expanding the use of GFRP reinforcing bars in civil infrastructure applications.

Development of ANN-based models to predict the bond strength of GFRP bars and concrete beams

The use of glass fiber-reinforced polymer (GFRP) has gained increasing attention over the past decades, aiming at replacing traditional steel rebar in concrete structures, especially in corrosion or magnetic conditions. Understanding the working mechanism between the reinforcements and concrete is crucial in many practical applications, in which the corresponding bond strength is considered as a critical element. In this study, a database including 159 experimental beam results gathered from the available literature was used for the development of an artificial neural network (ANN) model in an effort to predict the bond strength between GFRP bars and concrete. Two ANN models using BFGS quasi-Newton backpropagation and conjugate gradient backpropagation with Polak-Ribiére algorithms were constructed and evaluated in terms of bond strength prediction accuracy. The considered database consisted of five input parameters, including the bar diameter, concrete compressive strength, minimum cover to bar diameter ratio, bar development length to bar diameter ratio, the ratio of the area of transverse reinforcement to the product of transverse reinforcement spacing, the number of developed bars and bar diameter. The evaluation of the models was conducted and compared using well-known statistical measurements, namely the correlation coefficient (R), root mean square error (RMSE), and absolute mean error (MAE). The results demonstrated that both ANN models could accurately predict the bond strength between GFRP bars and concrete, paving the way for engineers to possess a useful alternative design solution for reinforced concrete structures

Development of ANN-based models to predict the bond strength of GFRP bars and concrete beams

The use of glass fiber-reinforced polymer (GFRP) has gained increasing attention over the past decades, aiming at replacing traditional steel rebar in concrete structures, especially in corrosion or magnetic conditions. Understanding the working mechanism between the reinforcements and concrete is crucial in many practical applications, in which the corresponding bond strength is considered as a critical element. In this study, a database including 159 experimental beam results gathered from the available literature was used for the development of an artificial neural network (ANN) model in an effort to predict the bond strength between GFRP bars and concrete. Two ANN models using BFGS quasi-Newton backpropagation and conjugate gradient backpropagation with Polak-Ribiére algorithms were constructed and evaluated in terms of bond strength prediction accuracy. The considered database consisted of five input parameters, including the bar diameter, concrete compressive strength, minimum cover to bar diameter ratio, bar development length to bar diameter ratio, the ratio of the area of transverse reinforcement to the product of transverse reinforcement spacing, the number of developed bars and bar diameter. The evaluation of the models was conducted and compared using well-known statistical measurements, namely the correlation coefficient (R), root mean square error (RMSE), and absolute mean error (MAE). The results demonstrated that both ANN models could accurately predict the bond strength between GFRP bars and concrete, paving the way for engineers to possess a useful alternative design solution for reinforced concrete structures

Behavior of circular concrete columns reinforced with hollow composite sections and GFRP bars

Hollow concrete columns (HCCs) constitute a structurally efficient construction system for marine and offshore structures, including bridge piers and piles. Conventionally, HCCs reinforced with steel bars are vulnerable to corrosion and can lose functionality as a result, especially in harsh environments. Moreover, HCCs are subjected to brittle failure behavior by concrete crushing due to the absence of the concrete core. Therefore, this study investigated the use of glass fiber-reinforced polymer (GFRP) bars as a solution for corrosion and the use of hollow composite-reinforced sections (HCRSs) to confine the inner concrete wall in HCCs. Furthermore, this study conducted an in-depth assessment of the effect of the reinforcement configuration and reinforcement ratio on the axial performance of HCCs. Eight HCCs with the same lateral-reinforcement configuration were prepared and tested under monotonic loading until failure. The column design included a column without any longitudinal reinforcement, one reinforced longitudinally with an HCRS, one reinforced longitudinally with GFRP bars, three reinforced with HCRSs and different amounts of GFRP bars (4, 6, and 8 bars), and three reinforced with HCRSs and different diameters of GFRP bars (13, 16, 19 mm). The test results show that longitudinal reinforcement—whether GFRP bars or HCRSs—significantly enhanced the strength and displacement capacities of the HCCs. Increasing the amount of GFRP bars was more effective than increasing the bar diameter in increasing the confined strength and the displacement capacity. The axial-load capacity of the GFRP/HCRS-reinforced HCCs could be accurately estimated by calculating the load contribution of the longitudinal reinforcement, considering the axial strain at the concrete peak strength. A new confinement model considering the combined effect of the longitudinal and transverse reinforcement in the lateral confinement process was also developed.