Application Of Fiber Reinforced Polymer Research Articles

Numerical Investigation on Strengthening of Steel Beams for Corrosion Damage or Web Openings Using Carbon Fiber Reinforced Polymer Sheets

Fiber-reinforced polymers (FRPs) have been widely used to strengthen steel structures, which could suffer from corrosion or the introduction of web openings, for utilities such as ductwork, plumbing, electrical conduits, and HVAC systems. The present numerical study involves the application of unidirectional carbon FRP (CFRP) sheets to steel I-beams, damaged due to corrosion or web openings, to regain their lost load-carrying capacity. Finite element analysis (FEA) was utilized to develop and validate three beam models against existing experimentally tested specimens. Subsequently, a parametric study was conducted investigating the effect of various corrosion levels and the number of circular web openings on the yield and ultimate load capacities of the beams. The optimum number of CFRP layers needed to strengthen corroded beams was determined and six CFRP strengthening scenarios were adopted to determine the best configurations to retrofit steel beams with openings (SBWOs). The results revealed that corrosion, introduced by thinning the bottom flange, reduced both yield and ultimate load capacities, with a nearly perfect linear reduction in ultimate load for each 2.5% thickness loss. The optimum number of CFRP layers depended on the level of corrosion damage. Furthermore, while maintaining a constant total opening area, beams with a greater number of smaller circular web openings demonstrated higher yield and ultimate load capacities than those with fewer larger openings. Out of the six adopted CFRP strengthening scenarios, three configurations that involved applying CFRP sheets to both flanges and the web effectively restored the strength of SBWOs, when adequate CFRP layers were used.

Axial stress-strain model for concrete in partially FRP wrapped reinforced concrete columns

The application of fiber-reinforced polymer (FRP) composites has become a commonly-used technique for the strengthening/retrofitting of existing reinforced concrete (RC) columns. To date, extensive experimental studies have been conducted in this field, resulting in many stress-strain models of FRP-confined concrete for analysis or design use. Few models, however, are concerned with the concrete in FRP-confined RC columns, especially for the columns under partial FRP confinement. This paper first investigates the mechanical properties of the concrete under FRP strip-transverse steel reinforcement composite confinement via the assessment of existing analysis-oriented models (AOMs). Then, the peak stress of actively confined concrete and the dilation model in AOM are calibrated based on existing research, leading to a new AOM for FRP strip-steel confined concrete. Finally, a test database is assembled to evaluate the reliability of the new model in terms of the predictions of ultimate conditions and stress-strain curves. By comparing the experimental results and theoretical predictions, the proposed model exhibits higher accuracy for the FRP strip-steel confined concrete compared with the other existing models.

Experimental Studies and Application of Fiber-Reinforced Polymers (FRPs) in Civil Infrastructure Systems: A State-of-the-Art Review.

The application of FRPs in civil infrastructure has increased, particularly in the last 20 years. FRPs have gained importance because of their resistance to harsh environments, high strength-to-weight ratio, and good corrosion resistance, and they are faster and easier to apply than other traditional methods. The rehabilitation of structures is the main area in which FRPs have been developed, because they have allowed for compliance with architectural restraints in historic structures. This review is a compilation of the research conducted on the laboratory and field applications of FRPs, highlighting the different applied methods, installation difficulties, and failure modes of FRPs. Moreover, this review compares studies on the types of fibers such as CFRPs, GFRPs, and AFRPs, and their effects would affect the mechanical properties of civil infrastructure and the durability characteristics of civil infrastructure in challenging environmental conditions. In addition, this review focuses on the modification of the mechanical properties of structural elements using different methods of installing FRPs, including externally bonded reinforcement (EBR), and their main problem: debonding failure before the ultimate load.

Advanced Strengthening of Steel Structures: Investigating GFRP Reinforcement for Floor Beams with Trapezoidal Web Openings

Enhancing existing steel structures becomes imperative upon alterations in usage or geometric configurations, such as introducing web openings in floor beams to accommodate various services. The utilization of welded steel plate and conventional strengthening methods often presents challenges, which may be mitigated through the adoption of composite materials like Fiber Reinforced Polymers (FRP). However, research on the application of FRP to steel beams with web openings remains limited, predominantly focusing on beams with rectangular openings of modest dimensions. This study delves into the application of Glass Fiber Reinforced Polymers (GFRP) to strengthen reinforced steel floor beams featuring trapezoidal openings. Leveraging a rigorously validated numerical model derived from previously published findings by a contributing researcher, the investigation showcases that the proposed GFRP reinforcement scheme exhibits performance comparable to conventional steel plate welding techniques, while preserving the inherent strength of the original solid beams.

Recent advancements in the applications of fiber‐reinforced polymer structures in railway industry—A review

AbstractThe application of fiber‐reinforced polymer (FRP) composite materials and structures in various industrial sectors is expanding significantly to meet the rising demand for efficient, reliable, and functional building materials. Using FRPs can be an excellent strategy for enhancing railway structures and equipment because of their high strength‐to‐weight ratio, tailorable mechanical properties, and suitable long‐term characteristics. However, the railway industry appears to be hesitant to adopt composite materials compared to other transportation sectors like aerospace. It seems that there is still a long way to go before FRPs reach their full potential in railway applications. The goal of the current study is to explore the current uses of FRPs in the railway industry and the significant challenges, obstacles and difficulties that must be overcome to put FRP‐based concepts into practice for structural and rail vehicle applications.Highlights Applications of FRPs in railway vehicles and rail lines are reviewed. Main challenges for utilization of FRP in railway industry are studied. Future trends and applications of FRPs in the railway sector are introduced.

Damage and Defects in Fiber-Reinforced Polymer Reinforced and Strengthened Concrete Elements

Fiber-reinforced polymer (FRP) composites are becoming increasingly popular as an alternative to conventional civil engineering materials in existing structures as externally applied systems for strengthening purposes, and in new structures as internal reinforcements in the form of bars, meshes, and strands. The next phase of development in the application of FRPs in concrete structures could culminate in elements possessing both internal and external FRP systems simultaneously. With these advancements in the application of FRP in civil engineering, it is conceivable that traditional steel reinforcements could become obsolete in certain aggressive and hostile environments, such as coastal areas. Although higher durability and performance are associated with FRP materials in some respects when compared to steel, concerns remain regarding the damage and defects in this material, many of them related to their unique features. Regardless, similarly to other structural materials, it is necessary to understand the damage and defects associated with the use of FRP composites, as well as to identify their sources. This knowledge will support the positive prospects for FRP technology, promoting its application in civil infrastructure. Accordingly, this study investigated the types, characteristics, and identification of the observed or expected damage and defects associated with using FRP in reinforced and strengthened concrete elements. The damage was classified according to location and time of initiation. In addition, the sources of these defects and damage were determined, and a damage etiology was established for preventing the occurrence of such damage in future use. The results of this study are intended to provide the background for the development of a guide and training material for the inspection of structures that use FRP materials. The ability to inspect and properly maintain structures containing FRP will result in the enhanced durability and service life of concrete structures reinforced or strengthened with FRP materials.

Strengthening of RC beams in shear with novel near-surface mounted (NSM) U-shaped fiber-reinforced polymer (FRP) composites

Over the last three decades, various researchers have proven the high efficiency of the near-surface-mounted (NSM) fiber-reinforced polymer (FRP) method for strengthening reinforced concrete (RC) beams. The shear strengthening of RC beams by embedding FRP bars or strips onto the side concrete cover is a primary application of NSM FRP investigated in numerous studies. These studies revealed that despite the high bond efficiency between the NSM FRP and concrete, NSM FRP shear-strengthened beams frequently failed in debonding modes, such as FRP–concrete interfacial debonding or side concrete cover separation. Such debonding failures limit the strength utilization and strengthening efficiency of the FRP material. Anchoring measures have been proposed for NSM FRPs to mitigate such debonding failures. However, the manufacturing and installation processes of these anchoring devices are complicated. Moreover, interfacial debonding between the NSM FRPs and anchoring devices can still occur. Therefore, this study proposes a novel NSM U-shaped FRP (NUF) device for the shear strengthening of RC beams. The proposed NUF device was fabricated using a fiber sheet through a wet lay-up process. The device can effectively increase the bond efficiency between the FRP and strengthened beam. The concept, manufacturing, and installation processes of this device are discussed. Subsequently, an experiment was performed on seven full-scale RC beams. The test results showed that the proposed NUF device is able to postpone/prevent the debonding failure between NSM FRP and concrete thus largely increase the strengthening efficiency of NSM FRP method.

Retrofitting and rehabilitation of masonry structures using FRP composites

Fibre Reinforced Polymer (FRP) is used to reinforce a range of structural elements, including masonry walls, slabs, beams, and columns. By attaching FRP strips along the axis of bending at the soffit portion of beams and slabs, flexure can be reinforced. Wrapping around the cross-section of beams in a U-shape can strengthen beams under flexure and shear. The ultimate stress and strains of FRP composites are far higher than most of the alternatives available for structural strengthening. The density of FRP composites is low, thus adding less additional dead weight to the structure. Compression members like columns may be strengthened by externally wrapping them with FRP, or by casting them in FRP stay-in-place formwork. The externally bonded FRP imparts passive confinement to the column, improves the axial stiffness, reduces lateral expansion for given load levels, allows the column to reach higher stress and strain levels than the unwrapped columns. Recent years have seen a substantial increase in the adoption of seismic retrofit using FRP materials among the civil engineering community. The current state of using FRP materials as a retrofitting strategy for structures not built to withstand seismic activity is presented in this study in a representative overview. It provides an overview of the applications and range of FRP materials in seismic retrofitting plans for RC structures. The study also discusses the benefits, design principles, and restrictions of FRP applications for seismic retrofit. A case study revealed that using the FRP strengthening method improved the performance of the existing structure. Aesthetic appearance of the building maintained and also improved the strength aspects. After rehabilitation the structure requires less maintenance due to adherence of FRP laminates.

Evaluation of flexural strengthening methods for beams with simulated deterioration using spike-anchored FRP externally bonded sheets and near-surface-mounted strips

• 20 beams were tested to evaluate FRP flexural strengthening techniques. • Specimens were detailed to mimic the common deterioration of bridge beams. • The effect of FRP spike anchor arrangements were evaluated. • Results show that more FRP spike anchors may not translate to superior performance. • Unsymmetrical steel and NSM reinforcement layouts were considered. In consideration of past research on both externally bonded and near-surface-mounted (NSM) fiber-reinforced polymer (FRP) reinforcement for the strengthening of deteriorated reinforced concrete elements, additional work is needed to investigate the application of FRP for flexural strengthening in specific scenarios and for specific member types. Furthermore, the need exists for guidance regarding reliable anchorage of externally bonded sheets for flexural strengthening. An experimental investigation was conducted on 20 reinforced concrete beam specimens with details and simulated deterioration patterns representative of the beams of in-service adjacent box beam bridges. Special focus was placed on the effective arrangement of FRP spike anchors for externally bonded FRP, unsymmetrical deterioration of steel reinforcement, and the eccentric placement of NSM strips. The results show that spike anchors located only at the ends of the externally bonded FRP sheets provided superior performance compared to anchors placed at multiple locations along the sheets. Moreover, the eccentricity of reinforcement did not play a significant role in the effectiveness of the strengthening systems. The test results also highlight the importance of bond on the performance of members strengthened with NSM reinforcement. Overall, the findings extend beyond adjacent box beam bridges and have a wide applicability to other flexural members.

New Analytical Analysis-Oriented Stress-Strain Model for FRP-and-Steel Confined Concrete

Application of fiber-reinforced polymer (FRP) composites in the strengthening of reinforced concrete (RC) structures has become an increasingly accepted engineering practice. In particular, the use of externally bonded FRP wraps as a confining material for concrete can enhance both the compressive strength and the ultimate strain of concrete, making it suitable for strengthening and/or seismic retrofit of existing RC columns. This paper focuses on a recently developed analysis-oriented iterative FRP-and-steel confinement model for concrete and proposes a new optimization procedure to obtain an analytical expression for the corresponding monotonic envelope, reduce the associated computational cost, and increase the corresponding numerical robustness. Several analytical functions were evaluated in terms of their capability to fit the iteratively-generated stress-strain monotonic envelope for confined concrete. The newly proposed analytical formulation of the confined concrete stress-strain model was compared with the original iterative formulation in terms of computational cost for two examples of nonlinear seismic response analyses for: (1) an experimentally-tested concrete-filled FRP tube bridge column of a two-column bridge pier; and (2) a five-span bridge structure with FRP-retrofitted RC piers. It is found that the use of the newly proposed optimization-based analytical monotonic envelope can reduce by more than 30% the computational time associated with the original iteration-based monotonic envelope with negligible changes in the structural response prediction at both global and local levels.

The use of a general method for calculating the resistance of strengthened concrete columns

Columns are one of the basic types of vertical load-bearing elements. In buildings, they are used where there is a requirement to create free spaces. This results in an effort to minimize the cross-section dimensions of the column and to maximize the use of its resistance. The need of the increase in resistance is the reason for columns strengthening. The choice of a suitable strengthening method must take into account the way the column is loaded. Some methods are universal, the others are more effective in the case of predominant compressive, or predominant bending loading. In presented research, the attention is focused on strengthening slender reinforced concrete columns by progressive methods - FRP (fibre reinforced polymer) and FRC (fibre reinforced concrete) applications. For slender columns, second-order effects must be taken into account. The current Eurocode lists three methods of analysing these effects. The simplified methods proposed for the analysis of a reinforced concrete column cannot be applied directly to the calculation of the resistance of a column strengthened by any of the progressive methods. The article is devoted to the calculation of column resistance using a general method that allows the contribution to column resistance from strengthening to be considered.

An Economic Approach to the Confinement of Different Concrete Classes with Carbon and Glass Fibers Reinforced Polymers

One of the current approaches for concrete retrofitting is called fiber reinforced polymer (FRP) wrapping. In this study, concrete retrofitting means compressive strength and seismic parameters improvement (such as failure strain, energy absorption, and ductility). Cost analysis may raise issues of concern regarding the economic value of this kind of retrofitting and for this reason, economic analysis was conducted based on experimental works. In this regard, 21 samples were prepared for three compressive strengths of concrete (20, 35, and 50MPa) and warped with different layers of carbon and glass fiber reinforced polymers (0, 1, 3, and 5 layers). Samples were subjected to stress-strain tests and concrete properties were estimated. The results showed that carbon and glass fibers, respectively, are more effective in improving the compressive strength and seismic parameters of concrete. But, the economic analysis indicated that glass fiber is more cost-benefit than carbon fiber in improving the concrete properties, especially for one layer of FRP. The economic analysis was not able to specify the application of FRP for which concrete samples are more economical, and for this reason, statistical analysis was used to respond to this vague and achieve a comprehensive assessment. The analysis indicated that the use of FRP is more cost-benefit for lower concrete strength.

Design of concrete beam reinforced with GFRP bars as per ACI codal provisions

This document provides design principles for concrete beams reinforced with glass fiber reinforced polymer (GFRP) bars per the ACI 440.1R-15 regulation. One of the main advantages of using glass fiber reinforced polymer rods instead of traditional steel reinforced rods is their lighter weight and higher corrosion resistance. However, the bending failure mode of FRP reinforced concrete (FRP-RC) beams is brittle rather than ductile because the elasticity of fiber reinforced polymer (FRP) bars is linear until failure and the elongation at break is small. For FRP-RC elements, concrete crushing compression failure, which gives various warnings before failure, is the preferred failure mode. In other words, unlike the usual design practice for reinforced concrete (steel-RC) beams, for FRP-RC beams, an over-reinforced structure is preferable to an under-reinforced structure. In addition, since the FRP RC member has low rigidity of the FRP rod, it bends more and cracks larger than the steel RC member. These factors limit the field of application of FRP. Here is a design example of a rectangular beam with tension reinforcement according to ACI regulations.

Shear strengthening of RC beams with NSM FRP. I: Review of strength models

Near-surface mounted (NSM) fiber-reinforced polymer (FRP) technique is known as a promising alternative to the externally bonded (EB) FRP technique for strengthening reinforced concrete (RC) members, on account of its many advantages such as high bond efficiency with concrete and good durability. Shear strengthening of RC beams by near-surface mounting the FRP bars/strips into the concrete cover on beam sides is one of the most prevalent applications of NSM FRP. Abundant experimental studies have been conducted to investigate the behaviour of NSM FRP shear strengthened beams, and many strength models for predicting the contribution of NSM FRPs to the shear capacity of the beam have been proposed. The present paper presents a comprehensive review of these strength models, in which all the models collected from the existing literature are first classified into three categories based on their used approach and then summarized and discussed. This paper not only aims to bring a deep understanding of the existing strength models for NSM FRP shear strengthened RC beams, but also provides a background and basis for the assessment of these models by using the newly-generated experimental database in the companion paper.

Mechanical properties of SAC-ECC reinforced with fiber-reinforced polymer mesh

Fiber-reinforced polymer (FRP) is widely used in the repair and strengthening of concrete structures, owing to its high strength-to-weight ratio, excellent mechanical properties, and good durability. However, during the application of FRP, an organic resin is typically used as the binder between the FRP and concrete, which leads to poor bonding, peeling, and poor high-temperature resistance. The emergence of engineered cementitious composites (ECCs) solves these problems and improves the ductility of the structure. However, most materials must be maintained for an extended period before use, which is not conducive to projects that require rapid repair. Therefore, this study proposes a high-early-strength and high-efficiency composite repair and reinforcement layer, and an ECC based on sulfoaluminate cement and FRP mesh (FRP-ECC(S)) has been developed. Uniaxial tensile tests and four-point bending tests were performed to study the mechanical properties and strengthening effects of the composite plate. The effects of carbon-fiber mesh, mesh size, mesh reinforcement rate, different matrices, and age on the failure mode, crack, stress–strain, and load deflection of composite plates and strengthened beams are discussed. The results showed that the composite plate has excellent mechanical properties, and the FRP-ECC reinforced layer has a significant effect on controlling the crack development of the reinforced concrete beam. In addition, the cast-in-place composite layer did not peel from the bottom of the beam, which improves the durability of the structure.

Strengthening Timber Structural Members with CFRP and GFRP: A State-of-the-Art Review.

The application of fibre-reinforced polymers (FRP) for strengthening timber structures has proven its efficiency in enhancing load-bearing capacity and, in some cases, the stiffness of structural elements, thus providing cost-effective and competitive alternatives both in new design and retrofitting existing historical buildings. Over the last few decades, several reinforcing materials and techniques evolved, and considerable progress was made in numerical modelling, especially using the finite element method. As this field of research has become extensive and diversified, as well as numerous contradicting results have emerged, a thorough review is necessary. This manuscript covers the topics of historical preliminaries, reinforcing with carbon and glass fibre composites, bond characteristics, main reinforcing techniques, modelling of knots, and the effects of the fibre waviness on the composite behaviour. A detailed overview is given on the experimental and numerical investigation of mechanics of strengthened beams. A one-of-a-kind table is presented that compares the stiffness improvement observed in several studies with analytical estimates. Attention is drawn to a number of challenges that have arisen, e.g., the moderate stiffness enhancement, composite-to-wood interface, modelling of knots, and strengthening of defected timber members. This paper can be used as a starting point for future research and engineering projects.

Recent progress in buckling restrained braces: A review on material development and selection

Passive energy dissipation devices are a widely accepted solution used to improve the response of the structures under seismic conditions. While several types of passive energy dissipation elements have been proposed for replaceable elements, buckling restrained braces (BRB) was one of the most effective replaceable elements which has been used to retrofit frame structures in the past few years. A traditional BRB consists of a steel brace core with a cruciform cross section that is surrounded by a stiff steel tube (restraining unit) and unbonded materials to ensure the brace to move freely. The region between the tube and brace is filled with concrete-like materials. In recent years, a significant amount of research has been carried out on new types of BRBs which are more efficient and inexpensive. This paper presents an overview of recent advances in the development of BRB materials and buckling mechanism, with an emphasis on the material development for the restraining unit. The application of fibre-reinforced polymer (FRP) as restraining unit in BRB is highlighted.

A design methodology for fiber layup optimization of filament wound structural components

The applications of fiber-reinforced polymer (FRP) composites extend rapidly along with the development of new manufacturing techniques. However, due to the complexities introduced by the material and fabrication processes, the application of conventional structural design methods for construction members has been significantly challenging. This paper presents an alternative methodology to find optimum fiber layups for a given tube-shape geometry via a graphical optimization strategy based on structural performance requirements. The proposed technique employs simplified shell element models based on classical lamination theory (CLT) to avoid explicit fiber modeling in the FEA simulations. Lamination parameters are utilized to generate the reduced stiffness matrices for continuous multi-layer FRP lamination. The fiber layup of the component is retrieved from the optimal lamination parameters that maximize the structural performance. The case study results demonstrate that the developed method provides compact solutions, linking the structural design requirements with optimal fiber orientations and volumetric proportions. In addition, the determined solutions can be interpreted directly by the winding fabrication settings.

Bond between Fibre-Reinforced Polymer Tubes and Sea Water Sea Sand Concrete: Mechanisms and Effective Parameters: Critical Overview and Discussion

Using fibre-reinforced polymers (FRP) in construction avoids corrosion issues associated with the use of traditional steel reinforcement, while seawater and sea sand concrete (SWSSC) reduces environmental issues and resource shortages caused by the production of traditional concrete. The paper gives an overview of the current research on the bond performance between FRP tube and concrete with particular focus on SWSSC. The review follows a thematic broad-to-narrow approach. It reflects on the current research around the significance and application of FRP and SWSSC and discusses important issues around the bond strength and cyclic behaviour of tubular composites. A review of recent studies of bond strength between FRP and concrete and steel and concrete under static or cyclic loading using pushout tests is presented. In addition, the influence of different parameters on the pushout test results are summarised. Finally, recommendations for future studies are proposed.

Enhanced interlaminar fracture toughness of woven carbon fabric/epoxy composites by interleaving fluffy CNT veils

While fiber reinforced polymer (FRP) composites are widely utilized in structural components due to their favorable mechanical properties, delamination between reinforcing plies remains a major problem, weakening the composite structure and limiting more widespread applications of FRPs. Carbon nanotubes (CNTs) carry the promise of enhancing this poor out-of-plane mechanical performance, although their integration has been challenging. In this work, macroscopic CNT veils with controlled nano-meso structure were drawn from the gas-phase using a semi-industrial process and then integrated into woven carbon fiber/epoxy matrix composites utilizing a facile and scalable approach. Interlaminar fracture toughness (ILFT) of the resulting composites was determined in Mode-I (opening mode) test. Additionally, crack propagation and interlaminar toughening mechanisms were systematically analyzed by means of optical microscope, SEM, and Raman analysis. The results showed that mode I ILFT was improved as much as 60% when interleaving as-received fluffy CNT veils and also revealed that interlaminar crossing between CNT veil/CF interfaces is of paramount importance in toughening mechanism.