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Fibre Reinforced Polymer (FRP) Composites in Structural Applications

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A special issue of Polymers (ISSN 2073-4360). This special issue belongs to the section "Polymer Composites and Nanocomposites".

Deadline for manuscript submissions: closed (25 January 2023) | Viewed by 14778

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Special Issue Editor

Dr. Saeed Mahini

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Guest Editor

Center for Timber Durability and Design Life, University of the Sunshine Coast, Sippy Downs, QLD 4556, Australia
Interests: fibre reinforced polymer (FRP)- strengthening; CFRP/Sprayed FRP, concrete, metallic and timber structures, weathering, epoxy composites; coating systems; sustainable materials in construction; non-linear analysis and finite element modelling; earthquake engineering and structural dynamics; performance and resilience based design; structural health monitoring

Special Issue Information

Dear Colleagues,

This Special Issue aims to present current research on Fibre Reinforced Polymer (FRP) Composites in Structural Applications with emphasize on improving performance and durability of civil structures.

Issues that will be addressed include ‘prevention of environmental degradation of epoxy resins modified with the addition of different fillers’ as coating systems applied to timber structures (reinforced with microcrystalline cellulose/multi-walled carbon nanotube/calcium sulphate, as chemical stabilisers), durability, treatment and coating timber species and also anchor devices for improving the bond between CFRP/ Sprayed FRP for the repair and rehabilitation of concrete, metallic and timber structures.

An in-depth understanding of the performance and fragility function of FRP-retrofitted multi-storey buildings, seismic response and plastic hinging mechanism of FRP-retrofitted RC frames, engineered timber and sandwich beams, anchorage devices for concrete/timber structures (bound–slip response of polymers and concrete/timber substances) and the effect of accelerated weathering exposure on the properties of advanced epoxy coating systems applied to wood species are highly focused in this Special Issue.

Dr. Saeed Mahini
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

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Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2700 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

epoxy resins
polymers
coating systems
chemical stabilisers
durability
fibre reinforced polymer (FRP)
sprayed FRP
repair & rehabilitation
anchor devices
concrete, metallic and timber structures
fragility
seismic response
plastic hinging
composite failure criteria

Published Papers (9 papers)

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Research

31 pages, 17893 KiB

Open AccessArticle

Hybrid Steel/NSM/GFRP System versus GFRP Wrapping for Upgrading RC Wall-like Columns

by Hussein Elsanadedy, Husain Abbas, Nadeem Siddiqui, Tarek Almusallam and Yousef Al-Salloum

Polymers 2023, 15(8), 1886; https://doi.org/10.3390/polym15081886 - 14 Apr 2023

Cited by 1 | Viewed by 986

Abstract

Reinforced concrete (RC) wall-like columns are commonly employed in structures in Saudi Arabia. These columns are preferred by architects owing to their minimum projection in the usable space. However, they often need strengthening due to several reasons, such as the addition of more stories and increasing the live load as a result of changing the usage of the building. This research aimed to obtain the best scheme for the axial strengthening of RC wall-like columns. The challenge in this research is to develop strengthening schemes for RC wall-like columns, which are favored by architects. Accordingly, these schemes were designed so that the dimensions of the column cross-section are not increased. In this regard, six wall-like columns were experimentally examined in the event of axial compression with zero eccentricity. Two specimens were not retrofitted to be used as control columns, whereas four specimens were retrofitted with four schemes. The first scheme incorporated traditional glass fiber-reinforced polymer (GFRP) wrapping, while the second one utilized GFRP wrapping combined with steel plates. The last two schemes involved the addition of near-surface mounted (NSM) steel bars combined with GFRP wrapping and steel plates. The strengthened specimens were compared with regard to axial stiffness, maximum load, and dissipated energy. Besides column testing, two analytical approaches were suggested for computing the axial capacity of tested columns. Moreover, finite element (FE) analysis was performed for evaluating the axial load versus displacement response of tested columns. As an outcome of the study, the best strengthening scheme was proposed to be used by practicing engineers for axial upgrading of wall-like columns. Full article

(This article belongs to the Special Issue Fibre Reinforced Polymer (FRP) Composites in Structural Applications)

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14 pages, 3641 KiB

Open AccessArticle

Energy Consumption Modeling of 3D-Printed Carbon-Fiber-Reinforced Polymer Parts

by Akash Shashikant Tiwari and Sheng Yang

Polymers 2023, 15(5), 1290; https://doi.org/10.3390/polym15051290 - 03 Mar 2023

Cited by 1 | Viewed by 1394

Abstract

Three-dimensionally printed carbon-fiber-reinforced polymer (3DP-CFRP) has become an important contributor to commercialized additive manufacturing. Due to carbon fiber infills, the 3DP-CFRP parts can enjoy highly intricate geometry, enhanced part robustness, heat resistance, and mechanical properties. With the rapid growth of 3DP-CFRP parts in the aerospace, automobile, and consumer product sectors, evaluating and reducing their environmental impacts has become an urgent yet unexplored issue. To develop a quantitative measure of the environmental performance of 3DP-CFRP parts, this paper investigates the energy consumption behavior of a dual-nozzle fused deposition modeling (FDM) additive manufacturing process which includes melting and deposition of the CFRP filament. An energy consumption model for the melting stage is first defined using the heating model for non-crystalline polymers. Then, the energy consumption model for the deposition stage is established through the design of experiments approach and regression by investigating six influential parameters comprising the layer height, infill density, number of shells, travel speed of gantry, and speed of extruders 1 and 2. Finally, the energy consumption models are combined and experimentally tested with two different CFRP parts. The results show that the developed energy consumption model demonstrated over 94% accuracy in predicting the energy consumption behavior of 3DP-CFRP parts. The developed model could potentially be used to find a more sustainable CFRP design and process planning solution. Full article

(This article belongs to the Special Issue Fibre Reinforced Polymer (FRP) Composites in Structural Applications)

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15 pages, 3012 KiB

Open AccessArticle

Prediction of Ultimate Capacity of Concrete Columns Reinforced with FRP Bars

by Jacek Korentz and Witold Czarnecki

Polymers 2023, 15(5), 1161; https://doi.org/10.3390/polym15051161 - 25 Feb 2023

Viewed by 1360

Abstract

FRP bars are used in concrete structures as an alternative to steel bars as they have many advantages such as high tensile strength, high strength-to-weight ratio, electromagnetic neutrality, lightweight and no corrosion. There is a perceived lack of standard regulations for the design of concrete columns with FRP reinforcement, e.g., in Eurocode 2. This paper describes a procedure for predicting the bearing capacity of concrete columns with FRP reinforcement based on the interaction of axial force and bending moment, which was developed on the basis of existing design recommendations and standards. It was shown that the bearing capacity of eccentrically loaded RC sections depends on two parameters, which are the mechanical reinforcement ratio ω and the location of the reinforcement in the cross-section expressed by the β factor. The analyses carried out showed the existence of a singularity in the n–m interaction curve indicating the fact that in a certain loaded range, the curve is concave, and more it was shown that the balance failure point for sections with FRP reinforcement takes place for eccentric tension. A simple procedure for calculating the required reinforcement from any FRP bars in concrete columns was also proposed. Nomograms developed from n–m interaction curves provide for the accurate and rational design of FRP reinforcement in columns. Full article

(This article belongs to the Special Issue Fibre Reinforced Polymer (FRP) Composites in Structural Applications)

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24 pages, 7923 KiB

Open AccessArticle

Enhancement of the Fragility Capacity of RC Frames Using FRPs with Different Configurations at Joints

by Saeed Jafari and Seyed Saeed Mahini

Polymers 2023, 15(3), 618; https://doi.org/10.3390/polym15030618 - 25 Jan 2023

Cited by 2 | Viewed by 1121

Abstract

This paper reports the results of an investigation into the effectiveness of different lengths of Fiber-Reinforced Polymer (FRP) sheets in retrofitting the joints of Reinforced Concrete (RC) frames to improve the fragility function of ordinary RC frames. Several 8-storey RC buildings were investigated through FE modelling. The accuracy of the FE models was verified using peer research results. Fragility curves of FRP-retrofitting joints of two referenced RC frames were carried out by OpenSees, through Incremental Dynamic Analysis (IDA) analysis under 22 far-field earthquake records from 0.1 g to 4.0 g (with 0.1 g interments), based on FEMA P-695. Two types of retrofitting methods, web and flange bonding, were modeled and studied. The results showed that the fragility capacity of the retrofitted RC frames was significantly improved. Moreover, frames with longer sheets of FRP showed increased performance. In the complete state, the range of probability of exceedance grew from 2–2.5 g to 3–3.5 g (nearly 1 g), whereas, in the minor state, this growth was nearly 0.05 g. However, the fragility function of the flange-bonding was enhanced at a higher rate compared with that of the web-bonding RC frames. Carbon Fiber-Reinforced Polymer (CFRP) and Glass Fiber-Reinforced Polymer (GFRP) materials improved the probability of exceedance of the complete state from 3 g to 4.5 g and 4.8 g in flange bonding frames. This enhancement for both types of frames was more significant when joints were retrofitted with 400 and 500 mm compared with 600, 700, and 800 mm. The midpoint of the PGA at the complete damage state in the web-bonding frame increased from 1.076 g to 1.664 g and in the flange-bonding frame retrofitted with GFRP and CFRP raised from 1.551 g to 2.769 and 3.076, respectively. The collapse margin ratio (CMR) indicates an acceptable improvement in the retrofitted frames. Overall, the rate of enhancement in fragility function from the original frame to the frame with 500 mm FRP was significant; however, the slope of this rate declined for longer FRP sheets. The fragility performance improvement resulted in controlling plastic hinging by FRPs. Full article

(This article belongs to the Special Issue Fibre Reinforced Polymer (FRP) Composites in Structural Applications)

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13 pages, 3373 KiB

Open AccessArticle

Efficient Depolymerization of Glass Fiber Reinforced PET Composites

by Jose Jonathan Rubio Arias and Wim Thielemans

Polymers 2022, 14(23), 5171; https://doi.org/10.3390/polym14235171 - 28 Nov 2022

Cited by 3 | Viewed by 1891

Abstract

The transition to an eco-friendly circular materials system for garbage collected after use from end-users is a serious matter of concern for current society. One important tool in this challenge to achieve a truly circular economy is the chemical recycling of polymers. It has previously been demonstrated that chemical recycling is a feasible alternative to reach carbon circularity, which promotes the maximization of carbon recovery through all possible means. Among the advantages of chemical recycling, one must highlight its ability to selectively attack one or several target functionalities inside a complex mixed stream of polymers to obtain pure monomers, which can then be used to prepare virgin-like polymers as a final product. In previous works from our group, we used a microwave-heated potassium hydroxide in methanol (KMH) system to instantaneously depolymerize PET bottles. The KMH system was also effective for polycarbonate (PC), and intimately mixed PET/PC blends. In the present study, glass fiber reinforced (GFR) PET composites were submitted to depolymerization using the KMH system, and it was verified that more strict conditions were required for full depolymerization of GFR pellets than for pure PET pellets. Evidence of the reorganization of PET chains leading to increased crystallinity were obtained through DSC and WAXD. Surface adhesion of PET and crystallization onto glass fibers led to a different crystalline phase that seems to be more protected against the depolymerization solution, thus increasing the time required for full depolymerization when compared to unreinforced PET. An activation energy of 123 kJ/mol was estimated, in the same range of pristine PET pellets and PET bottles. The optimization of depolymerization conditions permitted 100% depolymerization within 5 min of reaction at 120 °C using 30 mL of KMH solution per g of composite. The green chemistry metrics reflect that our system is more efficient than most of the depolymerization systems found in the literature. The optimal depolymerization conditions here reported for GFR PET composites represent another step towards a total recycling system that includes not only pure polymers but also composites, commonly present in daily life. Full article

(This article belongs to the Special Issue Fibre Reinforced Polymer (FRP) Composites in Structural Applications)

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16 pages, 3989 KiB

Open AccessArticle

The Effects of Eccentric Web Openings on the Compressive Performance of Pultruded GFRP Boxes Wrapped with GFRP and CFRP Sheets

by Emrah Madenci, Yasin Onuralp Özkılıç, Ceyhun Aksoylu and Alexander Safonov

Polymers 2022, 14(21), 4567; https://doi.org/10.3390/polym14214567 - 27 Oct 2022

Cited by 32 | Viewed by 1440

Abstract

Pultruded fiber-reinforced polymer (PFRP) profiles have started to find widespread use in the structure industry. The position of the web openings on these elements, which are especially exposed to axial pressure force, causes a change in the behavior. In this study, a total of 21 pultruded box profiles were tested under vertical loads and some of them were strengthened with carbon-FRP (CFRP) and glass-FRP (GFRP). The location, number and reinforcement type of the web openings on the profiles were taken into account as parameters. As a result of the axial test, it was understood that when a hole with a certain diameter is to be drilled on the profile, its position and number are very important. The height-centered openings in the middle of the web had the least effect on the reduction in the load-carrying capacity and the stability of the profile. In addition, it has been determined that the web openings away from the center and especially the eccentric opening significantly reduces the load carrying capacity. Furthermore, when double holes were drilled close to each other, a significant decrease in the capacity was observed and strengthening had the least effect on these specimens. It was also determined that the specimens reinforced with carbon FRP contribute more to the load-carrying capacity than GFRP. Full article

(This article belongs to the Special Issue Fibre Reinforced Polymer (FRP) Composites in Structural Applications)

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28 pages, 3343 KiB

Open AccessArticle

Two-Way Shear Resistance of FRP Reinforced-Concrete Slabs: Data and a Comparative Study

by Fahid Aslam, Mohamed AbdelMongy, Majed Alzara, Taha Ibrahim, Ahmed Farouk Deifalla and Ahmed M. Yosri

Polymers 2022, 14(18), 3799; https://doi.org/10.3390/polym14183799 - 11 Sep 2022

Cited by 6 | Viewed by 1798

Abstract

This study aims to investigate the two-way shear strength of concrete slabs with FRP reinforcements. Twenty-one strength models were briefly outlined and compared. In addition, information on a total of 248 concrete slabs with FRP reinforcements were collected from 50 different research studies. Moreover, behavior trends and correlations between their strength and various parameters were identified and discussed. Strength models were compared to each other with respect to the experimentally measured strength, which were conducted by comparing overall performance versus selected basic variables. Areas of future research were identified. Concluding remarks were outlined and discussed, which could help further the development of future design codes. The ACI is the least consistent model because it does not include the effects of size, dowel action, and depth-to-control perimeter ratio. While the EE-b is the most consistent model with respect to the size effect, concrete compressive strength, depth to control perimeter ratio, and the shear span-to-depth ratio. This is because of it using experimentally observed behavior as well as being based on mechanical bases. Full article

(This article belongs to the Special Issue Fibre Reinforced Polymer (FRP) Composites in Structural Applications)

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26 pages, 9154 KiB

Open AccessArticle

Mechanical and Fire Performance of Innovative Hollow Glue-Laminated Timber Beams

by Nikola Perković and Vlatka Rajčić

Polymers 2022, 14(16), 3381; https://doi.org/10.3390/polym14163381 - 18 Aug 2022

Cited by 3 | Viewed by 1900

Abstract

Fire safety greatly contributes to feeling safe, and it is a key parameter for the selection of building materials. The combustibility of timber is one of the main reasons to have the strict restriction on timber for use as a building material, especially for multistory buildings. Therefore, the main prerequisite for the use of timber in buildings is to ensure adequate fire resistance, using passive and active fire protection measures. This article contains the results of mechanical and fire experimental tests of both normal and innovative hollow glued laminated timber beams. A total of 10 timber beams were tested at ambient temperature, and 3 timber beams in fire conditions, which differed in cross-section type but also in the applied fire protection. The first beam was a normal GL beam without fire protection, the second a hollow beam covered by intumescent paint, while the third was also hollow, additionally protected by mineral wool infill inside the holes. The load-carrying capacity of the hollow beam in ambient conditions was estimated at 65% of the load-carrying capacity of a normal GL beam. Fire tests indicated that hollow timber beams with both intumescent paint and mineral wool infill failed at a similar time as a normal GL beam without fire protection. One-dimensional β₀ and notional charring rates β_n were obtained. Time to the protective material failure was 17 min. The main cause of failure of hollow beams was the appearance of delamination due to the reduction of the lamella bonding surface. Full article

(This article belongs to the Special Issue Fibre Reinforced Polymer (FRP) Composites in Structural Applications)

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22 pages, 9602 KiB

Open AccessArticle

Effect of Thermal Exposure on Residual Properties of Wet Layup Carbon Fiber Reinforced Epoxy Composites

by SoonKook Hong and Vistasp M. Karbhari

Polymers 2022, 14(14), 2957; https://doi.org/10.3390/polym14142957 - 21 Jul 2022

Cited by 3 | Viewed by 1775

Abstract

Ambient cured wet layup carbon fiber reinforced epoxy composites used extensively in the rehabilitation of infrastructure and in structural components can be exposed to elevated temperature regimes for extended periods of time of hours to a few days due to thermal excursions. These may be severe enough to cause a significant temperature rise without deep charring as through fires at a small distance and even high-temperature industrial processes. In such cases, it is critical to have information related to the post-event residual mechanical properties and damage states. In this paper, composites are subjected to a range of elevated temperatures up to 260 °C over periods of time up to 72 h. Exposure to elevated temperature regimes is noted to result in a competition between the mechanisms of post-cure that can increase the levels of mechanical characteristics, and the deterioration of the resin and the bond between the fibers and resin that can reduce them. Mechanical tests indicate that tensile and short beam shear properties are not affected negatively until the highest temperatures of exposure considered in this investigation. In contrast, all elevated temperature conditions cause deterioration in resin-dominated characteristics such as shear and flexure, emphasizing the weakness of this mode in layered composites formed from unidirectional fabric architectures due to resin deterioration. Transitions in failure modes are correlated through microscopy to damage progression both at the level of fiber-matrix interface integrity and through the bulk resin, especially at the inter-layer level. The changes in glass transition temperature determined through differential scanning calorimetry can be related to thresholds that indicate changes in the mechanisms of damage. Full article

(This article belongs to the Special Issue Fibre Reinforced Polymer (FRP) Composites in Structural Applications)

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