GFRP Beams Research Articles

Non-destructive degradation assessment of GFRP beams subjected to hygrothermal ageing

This work used free vibration tests based on impulse excitation technique and experimental modal analysis using an impact hammer and an accelerometer to assess the local and global effects of the hygrothermal ageing of GFRP specimens exposed to salt-spray environment at 35°C and 60°C over a period of 136 days. Through the change in elastic properties, fifteen natural frequencies and damping ratios, the effects of degradation are associated with reductions in elastic properties and natural frequencies and an increase in damping ratios. In turn, the increase in elastic properties and natural frequencies – associated with a reduction in damping ratios – is mainly attributed to the post-curing effect.

High‐speed observation of dynamic delamination failure in tapered composite laminates under tensile loading

AbstractThis article presents high‐fidelity observations of the time evolution of unstable delamination growth in tapered composite beams under tensile loading via ultra‐high‐speed camera in conjunction with digital image correlation. Asymmetrically tapered GFRP laminates, with a thickness drop from 18 plies to 12 plies, are manufactured in three different layup configurations with grouped drop‐offs: [06/(02)3/06], [06/06/06], and [06/(±45)3/06]. Beam specimens are subjected to quasi‐static tensile loading in a servo‐hydraulic axial testing machine, and the damage evolution on one edge of the tapered beam is monitored in situ at 124,000 fps with a high‐speed camera (HSC). In selected tests, digital image correlation (DIC) analyses are conducted either on the edge or on the tapered surface to obtain the full‐field strain and elucidate failure mechanisms. Real‐time HSC observations of the damage sequence consistently affirm that the initial failure mechanism is a transverse crack at the nearest drop‐off to the thin section, which is followed by delaminations at interfaces of sublaminates. Unstable delamination growth is characterized by measurements of lower bounds of crack tip speeds. The unique crack speed data provide evidence for the existing effect of through‐the‐thickness stresses on delamination growth. The detailed sequence and patterns of dynamic failure presented in this paper can serve as a benchmark to validate damage models used in simulations of tapered laminates.Highlights The sequence of unstable delamination growth in tapered GFRP beams is investigated experimentally. Characterized unstable delamination growth based on crack tip speed measurements. Strain fields are evaluated along beam edges using DIC in real‐time. In‐situ observations of dynamic failure can serve as a benchmark to validate damage models.

A comparative life cycle assessment of fiber-reinforced polymers as a sustainable reinforcement option in concrete beams

Environmental awareness and the need for sustainable construction inspired researchers and practitioners to explore innovative alternatives that might reduce greenhouse gas emissions and energy use related to excessive structural work. One such alternative is the utilization of Fiber-Reinforced Polymer (FRP) bars as a reinforcement in reinforced concrete members. FRP bars possess favorable characteristics like high tensile strength, lightweight and corrosion resistance compared to steel. This feature makes FRP bars a potential solution for utilizing seawater instead of fresh water in concrete mixtures, especially in areas facing a harsh climate and water shortage like the Arabian Peninsula. This paper aims to assess and evaluate the environmental impacts through life cycle assessment of glass fiber-reinforced polymer bars, carbon fiber-reinforced polymer, and steel glass fiber reinforced polymer bars compared to steel bars. Moreover, another LCA was conducted comparing steel-reinforced beams made with desalinated fresh water to GFRP/CFRP reinforced beams made with seawater for the concrete mixture. The results indicate that the GFRP bar performed better than the steel bar in 10 out of 14 categories, while the carbon fiber-reinforced polymer bar performed worse than the steel bar in 10 out of 14 categories. The SGFRP bar had a result between the steel and GFRP bar, outperforming the steel bar in 10 categories. Furthermore, the GFRP beam exhibited better environmental performance than the steel beam in 9 out of 14 categories, while the CFRP beam performed better than the steel beam in 8 categories, attributed to the reduction in reinforcement ratio due to the high tensile strength of CFRP and GFRP bars compared to steel bars. Overall, this study sheds light on the possible environmental advantages of using FRP bars in construction and highlights the importance of sustainable construction practices in minimizing environmental impacts.

Pullwinding technique for realizing hybrid roving architecture in pultruded GFRP composites

In this work, pullwinding technique is adopted to realize the hybrid roving architecture in pultruded GFRP composites so as to improve their transverse properties as well as the flexural performance of GFRP beams. First, small-scale material characterization tests and large-scale four-point bending tests were conducted to evaluate the mechanical performance of pullwound composites and the flexural behavior of pullwound box-beams. Second, analytical study was performed to calculate the strength and modulus of laminated plates with hybrid roving architectures. Then, finite element modeling was conducted to assess the strength and stability limit states of pullwound beams. The hybrid roving architecture could effectively reduce the material orthotropy, thus improving the transverse properties of GFRP composites as well as the flexural performance of GFRP beams. In the end, a design procedure is proposed to facilitate the design of roving architecture of pullwound composites to achieve the desired mechanical properties.

Piezoelectric energy harvesting from vortex-induced vibrations on a GFRP beam with embedded piezoelectric patch

In the present era, the demand for energy continues to increase and nevertheless, energy resources are gradually decreasing. Therefore, extracting energy from the operating ambient is of great importance especially for industrial applications. Among the numerous available ambient energy sources, wind energy is one of the most promising and prevalent energy sources existing in the environment. In this study, a piezoelectric energy harvester (PEH) consisting of an electromechanical coupling of GFRP cantilever beam with an embedded piezoelectric patch is developed for wind energy harvesting. The cantilever beam under the wind flow vibrates due to the pressure field that occurs on the leeward side of the beam. The generation of the pressure field is based on the vortex shedding phenomenon. Theoretical model of the regarding electromechanical coupling subjected to vortex induced vibration is presented and the effect of the pressure field having various vortex shedding frequencies on harvested power is investigated by means of numerical simulations validated with an experimental study. In order to determine the effect of the direction in which the wind excites the PEH, two wind flow conditions are considered; cross wind and head wind. According to the results, it was found that the PEH generates considerably more voltage outputs under cross wind loading than that obtained from the head wind excitation. In cross wind case, maximum open circuit voltage of 82.4 V is obtained at the wind speed of 6 m/s with the vortex shedding frequency of 18 Hz, which is very close to the second resonance frequency of the PEH. With a calculated load resistance of 100 kΩ, the resulting maximum direct voltage and electric power is 58.7 V and 11.5 mW, respectively. As far as the energy efficiency of PEH is concerned, it is determined that the efficiency is about 0.75 for the frequency of 18 Hz, which is quite acceptable for energy harvesting. It is concluded that a composite PEH with an embedded piezoelectric patch can be used as an effective energy harvester for the vortex induced vibration when the vortex shedding frequency is close to its resonance frequency.

Experimental and Theoretical Study on Flexural Behavior of GFRP- and CFRP-Reinforced Concrete Beams after High-Temperature Exposure.

In this study, in order to study the flexural behavior of fiber-reinforced polymer (FRP) bars with reinforced concrete beams under static loads after high-temperature exposure, seven pieces of FRP-reinforced concrete beams were subjected to static bending tests and calculation model derivations. Four-point bending tests were carried out on FRP-reinforced concrete beams after high temperature treatment. The effects of high temperature and types of FRP bars on the cracking load, crack development, deflection and ultimate capacity, and failure mode of concrete beams were investigated. The test results show that the maximum crack width, deflection, and ultimate bearing capacity of GFRP- and CFRP-reinforced concrete beams decrease obviously with a rise in high temperature. After the exposure of 400 °C for 2 h, compared with the behavior of concrete beams at room temperature, the maximum crack width of GFRP and CFRP-reinforced concrete beams increased by 42.9% and 41.7%, respectively, the deflection increases by 103.6% and 22.0%, and the ultimate bearing capacity decrease by 11.9% and 3.9%. Meanwhile, through the analysis of the existing research results and test results, the calculation models for the maximum crack width, deflection, and residual ultimate capacity of FRP-reinforced concrete beams after exposure of high temperature were proposed. For FRP-reinforced concrete beams after high-temperature exposure, the errors between the measured maximum crack width, stiffness, residual bearing capacity, and their corresponding calculated values using the model were mostly less than 10%. The calculated value using the proposed model in this research is in good agreement with the measured value. The mechanical properties of FRP-reinforced high-strength concrete structures after high-temperature exposure can be preliminarily predicted, which provides a new theoretical basis for the application of FRP-reinforced concrete structures.

Numerical Performance Analysis of Concrete-Filled Hollow GFRP Beams including Inner Surface Bearing Stresses at the Interface

GFRP sections with filler concrete material form promising structural components for structures; therefore, the structural performance of them has been investigated with increasing popularity. However, the performance of these composites degrades when fully composite action cannot be developed at the interface in where the literature hosts limited knowledge. Different techniques, such as abraded and sand-bonded surface treatments, were investigated experimentally to improve the bond-slip behavior between GFRP and concrete; however, there is a need to define shear mechanism at the interface of the numerical models. In this study, first, the average frictional bearing strengths were extracted for the treated and untreated inner surfaces using experimental results; then, the coulomb friction model was utilized to transfer the shear stresses between two dissimilar materials. Numerical models were verified by the experimental results, and different parametric studies were investigated by varying the amount and shape of GFRP in the cross section, compressive strength of concrete including the non-linear material behavior and interface frictional contact models. The findings showed that the interface strength can improve the flexural capacity of the concrete-filled GFRP beams by about 15.4%. Square GFRP box sections can be suggested for the construction of hybrid beams instead of rectangular sections, whereas the 10% areal ratio in a square cross section reached 103% load capacity improvement. The increased nominal compressive strength of concrete in hybrid beams can increase the hollow GFRP beams’ nominal load capacities and elastic stiffness of the hybrid beams in between; however, the relative gain is reduced due to increased compressive strength of concrete.

Experimental Investigation Of Steel Fibre Reinforced Concrete Beam Using Gfrp Rebar

The experimental investigation of flexural behaviour of SFRC beam reinforced with GFRP rebar and compared with steel reinforcement beams is presented in this project. Three beams were casted using SFRC and longitudinally reinforced with GFRP rebar. Three beams were casted with conventional concrete and steel bar. Six beams were casted and tested under two-point load. Along with beam, cube, cylinder and prism were casted and tested for compressive strength, split tensile and flexural strength. To improve the concrete’s property steel fibres were utilized. From testing of beam load vs deflection, load carrying capacity and stiffness were also calculated. The average load carrying capacity of GFRP rebar is 125.3kN and the average load carrying capacity of normal steel is 99.3kN.The highest deflection found in the GFRP rebar and standard steel reinforcement beam at their ultimate load is 21.5mm& 16.87mm respectively. It was also discovered GFRP beam returned to its original position

Comparison of shear behaviour of concrete beams reinforced with GFRP bars and steel bars

This paper presents the results of an experimental program focused on a comparison of the shear behaviour of concrete beams reinforced by longitudinal GFRP bars and beams reinforced by ordinary steel reinforcement. Altogether, 24 tests were conducted on 12 beams reinforced with GFRP bars and 28 tests on 14 beams reinforced with steel reinforcement. The beams were subjected to three-point loading with shear slenderness of 3.0. An effect of axial stiffness of longitudinal reinforcement was examined. Six different reinforcement ratios, ranging from 1.34% to 7.44%, in the case of beams with GFRP bars and six reinforcement ratios ranging from 0.89 % to 2.38% in the case of beams with steel reinforcement were tested until its failure occurred. An effective depth of the beams of 100 mm was kept constant and beams were without any transverse reinforcement. The results show a favourable effect of the axial stiffness of the longitudinal reinforcement on the shear capacity in both cases. However, in the case of beams with GFRP bars, a better shear performance per unit increase of the axial stiffness was observed than in beams with steel bars. The experimental program revealed that the relation between the reinforcement ratio and the shear strength can be approximated by the cubic root of the ratio. A comparison of measured shear strengths with state-of-art design provisions for predicting shear capacity indicates good quality of all the considered models when the CoV of shear strength ratio Vtest/Vmodel ranged from 0.079 to 0.109 in the case of beams with GFRP bars and from 0.062 to 0.110 in the beams with steel bars.

Flexural Performance of Encased Pultruded GFRP I-Beam with High Strength Concrete under Static Loading.

There is an interesting potential for the use of GFRP-pultruded profiles in hybrid GFRP-concrete structural elements, either for new constructions or for the rehabilitation of existing structures. This paper provides experimental and numerical investigations on the flexural performance of reinforced concrete (RC) specimens composite with encased pultruded GFRP I-sections. Five simply supported composite beams were tested in this experimental program to investigate the static flexural behavior of encased GFRP beams with high-strength concrete. Besides, the effect of using shear studs to improve the composite interaction between the GFRP beam and concrete as well as the effect of web stiffeners of GFRP were explored. Encasing the GFRP beam with concrete enhanced the peak load by 58.3%. Using shear connectors, web stiffeners, and both improved the peak loads by 100.6%, 97.3%, and 130.8%, respectively. The GFRP beams improved ductility by 21.6% relative to the reference one without the GFRP beam. Moreover, the shear connectors, web stiffeners, and both improved ductility by 185.5%, 119.8%, and 128.4%, respectively, relative to the encased reference beam. Furthermore, a non-linear Finite Element (FE) model was developed and validated by the experimental results to conduct a parametric study to investigate the effect of the concrete compressive strength and tensile strength of the GFRP beam. The developed FE model provided good agreement with the experimental results regarding deformations and damaged patterns.

Natural Frequency based delamination estimation in GFRP beams using RSM and ANN

The importance of delamination detection can be understood from aircraft components like Vertical Stabilizer, which is subjected to heavy vibration during the flight movement and it may lead to delamination and finally even flight crash can happen because of that. Any solid structure's vibration behaviour discloses specific dynamic characteristics and property parameters of that structure. This research investigates the detection of delamination in composites using a method based on vibration signals. The composite material's flexural stiffness and strength are reduced as a result of delaminations, and vibration properties such as natural frequency responses are altered. In inverse problems involving vibration response, the response signals such as natural frequencies are utilized to find the location and magnitude of delaminations. For different delaminated beams with varying position and size, inverse approaches such as Response Surface Methodology (RSM) and Artificial Neural Network (ANN) are utilized to address the inverse problem, which aids in the prediction of delamination size and location.

Numerical Analysis of Structural Performance of Concrete-GFRP Composite I-Beam

The concrete-GFRP composite beams have received extensive attention in civil engineering. However, the ambiguity of the fracture, debonding of the interface, and the GFRP profile limit the precise design of the composite beam. This article presents a comprehensive numerical study for the structural performance of composite pultruded GFRP beams to provide a better understanding of the mechanism of interfacial debonding and GFRP matrix fracture. The failure and delamination process of pultruded GFRP for anisotropy of materials is modeled using the Hashin criteria. The bond–slip behavior between the concrete slab and the top flange of the GFRP I-beam is simulated by the bilinear cohesive interface element. The availability and accuracy of the finite element model are verified by comparison with the four-point bending test results of the pure GFRP I-beam and composite beams as well. Based on the proposed comprehensive finite element model, the effects of the strength, thickness, and width of the concrete slab and the shear-span ratio of the beam on the structural behavior of the composite beam are studied. According to the parametric analysis, the excessive high strength of concrete, the width, and/or thickness of the concrete slab would lead to shear failure of the slab rather than significantly increasing the ultimate load of the composite beam. When having a small shear-span ratio, the matrix fracture and delamination will occur in the web of the GFRP profile. In addition, the height of the I-profile web has a significant effect on the stress and strain distribution of the composite beam. These parametric analyses could provide the numerical basis for the design of the GFRP composite beams.

Effect of nylon fabric reinforcement on the mechanical performance of adhesive joints made between glass and GFRP

The use of reinforcements in adhesive joints makes the stress distribution more uniform, improving their mechanical performance and adhesion. The present paper aims to verify the effectiveness and efficiency of the insertion of nylon 6 fabric in the adhesive layer, to study their applicability and functionality in building components. The increase in stiffness achieved by applying nylon 6 fabric in the adhesive layer between glass and GFRP pultruded profiles and steel laminates applied to GFRP beams is investigated. Three different epoxy adhesives and one epoxy resin are used and compared. Three different types of tests are carried out in order to study the different properties of the reinforcement system: tensile tests on GFRP/GFRP single-lap adhesive joints, with and without nylon fabric reinforcement; tensile tests on double-lap adhesive joints between float glass and pultruded GFRP profiles reinforced with nylon fabric according to four configurations (in the middle plane of the adhesive layer, on the glass surfaces, on the GFRP surfaces, on both GFRP and glass configurations) to verify the influence of its position; three-point bending tests on long GFRP tubular profiles reinforced with steel plates and nylon fabric in different configurations, to study resistance to bending loads. The results from the experimental campaign show the effectiveness of the reinforcement system using nylon fabric 6. In general, both a reduction in ultimate strength and an increase in joint stiffness compared to unreinforced configurations are observed.

Durability assessment of FRP-concrete bond after sustained load for up to thirteen years

Small-scale plain concrete notched beams strengthened with carbon and glass fiber reinforced polymer (CFRP and GFRP) sheets were tested in flexure to assess the change in debond onset strain following sustained flexural loading in indoor and outdoor environments for as long as 13 years. The bond tests were all conducted quasi-statically in a normal laboratory atmosphere. For indoor conditioning, debond onset strain was practically unchanged in the CFRP beams over 13 years, while a decrease was seen in the GFRP beams. For outdoor conditioning, which included freeze-thaw cycles, rain, hot weather, and ultraviolet exposure, clear reductions in debond onset strain were observed in both GFRP and CFRP strengthened beams.

Enhancement of Stiffness in GFRP Beams by Glass Reinforcement

Glass is a stiff material with brittle structural behaviour. Hence, it is usually a material mostly decorative or simply structurally supported, and it is hardly ever a load-bearing element within a structure. Although in recent years there have been several experiments in its use in civil engineering, to date little data has been collected or design methodologies disseminated. The present study proposes the innovative concept of considering glass as a structural material, cooperating within a structural system thanks to the adhesive joining technique. In detail, the case of a GFRP structural beam element subjected to bending is herein considered. The evaluation of the stiffness of the mentioned element is compared with that of the same element reinforced with glass plates of different thicknesses. The results show the possibility to increase the global stiffness of the structural element. These outcomes are validated by FEM analysis, which showed excellent agreement with the analytical ones. The effectiveness of the reinforced system, thanks to the considerable stiffness characteristics, allows both the use of glass and the respect of the requirements related to the displacements of the structural elements in their service life.

Flexural behavior of novel hybrid multicell GFRP-concrete beam

A novel hybrid beam consisting of pultruded GFRP three-cell box-section and concrete slab was proposed for pedestrian bridges. The flexural behavior of the proposed beam was investigated through experimental and analytical studies. First, material characterization tests were conducted to evaluate the mechanical properties of the GFRP material. Second, four- and three-point bending tests were carried out on four beams with varying span lengths. The flexural and shear stiffness of the beams were calculated and evaluated based on the experimental results. Design equations were proposed to predict the ultimate flexural strength of the hybrid beam. Finite element (FE) models were constructed to validate the effectiveness of the proposed hybrid beam. A good correlation was found between the experimental results, the analytical predictions from the proposed design equation, and the numerical results from FE modeling. The combined bolted and bonded connection provided effective shear transfer between GFRP and concrete, ensuring a good composite action of the hybrid beam. Additionally, the proposed three-cell box-beam increased the web local buckling strength of GFRP beams subjected to a concentrated load, avoiding the premature buckling failure of the entire beam. The proposed hybrid GFRP-concrete beam provides an effective approach to increase the span length of GFRP structures.

Determining rotational stiffness of flange-web junction of pultruded GFRP I-sections

In this work, the rotational stiffness of flange-web junctions of pultruded GFRP I-sections is investigated through an experimental program. Flange-web junctions of GFRP profiles are found to be non-rigid, contradicting typical design assumptions. Accounting for flange-web rotational stiffness reduces the rotational restraint of the flange/web junction; often by 15% or more, although more modest reductions were observed in this study. A discussion of different test methods for assessing flange/web junction stiffness is provided. A simple method that mitigates unfavorable effects is recommended. The effectiveness of the selected test method is demonstrated through 25 experimental tests which also serve to augment the limited data available in this area. Finite element modeling is conducted to simulate the experimental test and investigate parameters impacting the experimentally-determined rotational stiffness. Recommendations are made to standardize test parameters. Findings from this study directly support the developments of evaluation criterion for flange-web junctions and design equations; particularly those intended to capture the local buckling behavior of pultruded GFRP beams.

Comparative Approach to Flexural Behavior of Reinforced Beams with GFRP, CFRP, and Steel Bars

The replacement of conventional steel bars with GFRP or CFRP is one of the main topics discussed in this paper, including the main parameters and properties of the materials. The design procedures should account for the properties and will focus on the tensile strength and modulus of elasticity. It will also consider corrosion under environmentally aggressive conditions. This paper presents an experiment on the flexural behavior of concrete beams reinforced with GFRP and CFRP bars and compares these results with theoretical analysis based on different standards such as ACI, Eurocode, and CSA. Twelve reinforced concrete beams will be tested using four-point loading. The geometrical parameters of the tested beams are 130×220×2200 mm, reinforced with different diameters for GFRP and CFRP. The reinforcement ratio and strength of concrete influence the behavior of GFRP, CFRP, and RC beams and contribute to reduce the deflection and crack width. Based on this research, the closest approximation of the experimental results is observed with ACI standards. At this stage, these bars can be used in structures without strict requirements for exceeding the Serviceability Limit State. The non-integration of tension stiffening and regression performance of cracking moment in prediction expressions imposed the differences from experimental results.

Fe Modelling and Analysis of Two-Way Gfrp Sandwich Slim Floors

Innovative flooring systems utilizing lightweight Glass fiber reinforced polymer composite materials may have the significant potential to offer both economic and performance benefits compared to conventional concrete and steel systems. However, before widely adopted by industries, a fundamental understanding of their mechanical behavior is necessary. The key focus of this project is an investigation into the mechanical behavior of a new two-way GFRP sandwich slim floor system. The proposed new two-way GFRP sandwich slim floor system is in essence, a GFRP sandwich slab with GFRP beam. The sandwich slab assemblies were built-up sections made from pultruded web-core profiles incorporated between two flat panels, connected via adhesive bonding. A GFRP rectangular or I beam provided as the beam, and it is either partially encased or not. 3D finite element analyses are performed to provide detailed insight into the structural behavior and to predict the deformation and failure loads. Different analyses such as static, impact, modal, and buckling analyses are carried out, and the performances are evaluated. GFRP sandwich slim floor with partially encased I beam with GFRP bars has a high load-carrying capacity and bending stiffness. Also, it has better impact resistance. The fundamental natural frequency obtained from the FE analysis indicates better stiffness characteristics of the slim floor. All the buckling loads were higher than the maximum loadcarrying capacity of the GFRP sandwich slim floor. Hence, local buckling does not seem to be a crucial issue under the present loading conditions.

Load-carrying capacity of the GFRP and CFRP composite beams subjected to three-point bending test – numerical investigations

Abstract The subject of this article is the finite element method (FEM) simulation of the multi-layered rectangular composite beam subjected to three-point bending test. The study is focused on the composite beams made of glass or carbon fibre-reinforced laminates (glass fibre-reinforced polymer [GFRP] and carbon fibre-reinforced polymer [CFRP]) for which different laminate stacking were addressed. Three beam geometries with various length-to-thickness ratios included short beam shear (SBS) test, provided the beam is short relative to its thickness, which maximised the induced shear stresses. Simulation included the application of Tsai–Hill, Hoffman, Tsai–Wu, Hashin and Puck failure criteria to perform the composite beam failure analysis wherein the matrix and fibre failure were considered separately. Numerical failure studies also aimed to verify the beam failure modes and the participation of stress tensor elements in material failure.