Fiber Reinforced Plastic Sheets Research Articles

Impact resistant behaviour of RC slab strengthened with FRP sheet

To investigate the impact resistance of RC slabs strengthened with Fibre Reinforced Plastic (FRP) sheet to the back of the slab, falling-weight impact tests were conducted. Two loading types were applied: iterative loading and single loading. The impact load was applied to the centre of the RC slab with a free falling 300 kg steel striker with a diameter of 60 mm. A total of 12 RC slabs that were 1,650 (L) × 1,650 (W) × 150 (h) mm were used for these experiments. In this study, the strengthening method and material properties of the FRP sheet and the number of FRP sheet layers were varied. The results obtained from this study are as follows: (1) the impact resistance of the RC slabs can be improved by attaching a strengthened FRP sheet to the back surfaces; (2) the load bearing mechanism of RC slabs depends on the loading type and strengthening volume of the FRP sheet; and (3) the dynamic amplification factor is about two, which is independent of the load bearing mechanism of the RC slab and the strengthening volume and tensile rigidity of the FRP sheet.

아라미드 섬유 쉬트를 이용한 철골 보 부재의 휨 보강 성능에 관한 실험적 연구

강 구조물의 보강공법으로는 강판 보강공법이 대표적인 방법으로 통용되고 있으나, 일부 구조물에서는 고정 설비 및 기타 간섭물로 인하여 보강 시공이 번거롭고, 보강부재 접합시 원부재의 단면 손실이 수반되는 단점이 있다. 최근, 강재의 원가 상승으로 강판 보강공사의 시공비가 증가되고 있는 실정이다. 반면, 복합소재를 이용한 보강공사의 경우는 재료의 자중이 가벼워서 보강재 취급이 수월하고 내화학성능이 우수하기 때문에 유지비용이 절감되기 때문에 콘크리트 구조물에서는 널리 사용되고 있다. 본 논문에서는 복합소재를 이용한 강 구조물의 보강의 기술적 가능성을 검증하기 위해 강재와 복합소재와의 부착성능 및 보 부재를 통해 휨 보강 성능을 평가하였다. 그 결과, 항복 이전까지는 강재와 아라미드섬유 쉬트가 일체 거동에 따른 보강효과를 예상할 수가 있었다. 또한, 보강 겹수가 증가함에 따라 무보강 실험체 대비 내력이 증가했지만, 예상 보강효과(1 겹에서 12.5 %, 2겹에서 25 %)에 비해 절반 정도의 수준의 개선효과를 보였다. 그 이유는 모든 보강 실험체가 계면파괴로 파단되었고, 이후 아라미드섬유 쉬트가 실험체 내력 개선에 영향을 미치지 못했기 때문이다. 따라서, 최근 복합소재의 재료적 개선 및 접착제의 부착성능 향상으로 인하여 강 구조물의 보강공사에 적용할 수 있는 가능성을 찾을 수 있었으나, 보강성능을 향상시키기 위한 부착성능 향상을 위한 방법에 대한 연구가 필요하다고 판단된다. Fiber Reinforced Plastic (FRP) sheets have been widely used to retrofit and rehabilitate RC structures, while in case of retrofitting steel structures, there are no codes and researches. It stems from configuration of member and characteristics of bonding behavior. This study focused on the static behavior of steel beams reinforcement by AFRP sheets. The main objective of the experimental programme was the evaluation of the force transfer mechanism, the increment of the beam load carrying capacity and the bending stiffness. A bending test was conducted on a H-shaped steel beam, with aramid FRP sheets bonded to its flanges. The mid-span deflection and the strain from three points along AFRP sheets were recorded Test results exhibit that the increment of the load-carrying capacity with reference to a mid-span deflection level of 15 mm(1/125mm of the clear span) was equal to 9.4% and for the two layers case, an elastic stiffness increment is slightly higher than one layer case.

Design of Automotive Metal and Composite Chassis Structures

This paper reviews recent patents covering automotive metal and composite chassis structures. Automotive chassis are very complex structures and the variety of different types is vast. This paper attempts to reveal modern chassis design looking at composite structures, bonding methods, front sub-frames, complete space-frames, uni-body, integral frame and monocoque structures. Automotive chassis designs have had considerable developments in recent years. This is attributed to recent legislation taking particular interest in after service disposal and more prominently crash, impact and occupant safety. Automotive manufacturers continue to develop new, innovative and novel approaches to achieving rigidity and stiffness in torsion and bending to achieve optimal suspension geometry, safety and occupant comfort. Recent patents in automotive chassis design refer mainly to stiffening support structures, composite structures, retractable roofs and by far the most common, front crash sub frames. Keywords: Chassis, metal chassis, composite chassis, bonded chassis, crash box, sub frames, spaceframe, monocoque, heat affected zone, epoxy resins, Cycom 977, honeycomb sandwich material, resin transfer moulding, RTM, Cabriolet space-frame, CNC bending, computer controlled welding, fibre-reinforced plastic sheets, multi utility vehicle, Audi spaceframe (ASF) chassis, resilient aluminium alloy, frontal collision, FRP COMPOSITES, torsion beam, Rear sub-frame, Shock absorbing crash element, Honeycomb core profile, noise and vehicle harshness

Square concrete columns strengthened with carbon fiber reinforced plastics sheets at low temperatures

Twenty-one square concrete columns were constructed and tested. The testing results indicate that bonded carbon fiber reinforced plastics (CFRP) sheets can be used to increase the strength and improve the serviceability of damaged concrete columns at low temperatures. The failure of the specimens, in most cases, takes place within the middle half of the columns. And the failure of strengthened columns is sudden and explosive. The CFRP sheets increase both the axial load capacity and the ultimate concrete compressive strain of the columns. The ultimate loads of strengthened columns at −10, 0 and 10 °C increase averagely by 9.09%, 6.63% and 17.83%, respectively, as compared with those of the control specimens. The axial compressive strength of strengthened columns is related to the curing temperatures. The improvement of axial compressive strength decreases with reducing temperature, and when the temperature drops to a certain value, the improvement increases with falling temperature.

Design provisions for crack spacing and width in RC elements externally bonded with FRP

Verification of serviceability is a key issue in reinforced concrete (RC) elements; for RC elements externally bonded with fibre reinforced plastic (FRP) laminates and sheets cracking phenomena are usually verified by adopting the same approach used for steel RC elements. The available code provisions for crack width and spacing in steel RC elements are reviewed in this paper in order to ascertain the reliability of their application to RC elements strengthened with FRP sheets. Experimental results belonging to test programmes performed by the authors and other researchers on RC elements externally bonded with FRP were compared with existing code provisions in terms of crack width and spacing. A new formula for crack spacing, calibrated on the experimental results, is proposed for use in the expression given by the published version of EC2 for calculating crack width in RC elements externally bonded with FRP.

Buckling response of glue-laminated columns reinforced with fiber-reinforced plastic sheets

In the past two decades, the use of fiber-reinforced polymer (FRP) for strengthening structural members has shown to be an effective method, with respect to both structural performance and economic features. This paper presents the results of a study conducted to investigate the feasibility of glue-laminated (glulam) timber columns strengthened with fiber-reinforced polymer (FRP) sheets. Experimental and computational investigations were conducted on axially loaded glulam timber columns strengthened with FRP. Several parameters such as slenderness ratio, boundary conditions, FRP reinforcement length, and relative cost were considered in this study. The principal aim of this study was to produce data and information for practicing engineers and architects. The main objective was to justify promotion of the use of cost-effective glulam timber components as a viable alternative in structural applications.

Experimental study on ductility improvement of reinforced concrete rectangular columns retrofitted with a new fiber reinforced plastics method

Reinforced concrete (RC) columns lacking adequately detailed transverse reinforcement do not possess the necessary ductility to dissipate seismic energy during a major earthquake without severe strength degradation. In this paper, a new retrofit method, which utilized fiber-reinforced plastics (FRP) confinement mechanism and anchorage of embedded bars, was developed aiming to retrofit non-ductile large RC rectangular columns to prevent the damage of the plastic hinges. Carbon FRP (CFRP) sheets and glass FRP (GFRP) bars were used in this test, and five scaled RC columns were tested to examine the function of this new method for improving the ductility of columns. Responses of columns were examined before and after being retrofitted. Test results indicate that this new composite method can be very effective to improve the anti-seismic behavior of non-ductile RC columns compared with normal CFRP sheets retrofitted column.

Test analysis for FRC beams strengthened with externally bonded FRP sheets

Performances of two different types of fiber reinforced concrete (FRC) beams, which are strengthened with three different types of fiber reinforced plastic (FRP) sheets, respectively, are analyzed in this paper. A series of four-point bending tests for beams are carried out to investigate the effect of fiber reinforcement on FRP sheet strengthening. Three types of concrete beams have been tested, which are plain concrete beams for reference, polypropylene fiber (PF) reinforced concrete beams, and polypropylene fiber (PF) together with steel fiber (SF) hybrid reinforced concrete beams. Three strengthening schemes have been used, which are mono-layered carbon fiber reinforced plastic (CFRP) sheet strengthening, mono-layered glass fiber reinforced plastic (GFRP) sheet strengthening and CFRP mixed GFRP bi-layer sheets strengthening, respectively. Crack developing mechanism and variations of displacements with curvatures for different beams are analyzed. Test and numerical simulation results show that PFs and SFs are able to control the propagation of micro cracks, the development of macro cracks in concrete, and to improve the concrete strength. The ultimate failure modes of test beams also chang from peeling-induced debonding into FRP rupture, which shows that the FRP sheets can exert its strengthening effect sufficiently. Test and numerical results indicate it is an effective method for CFRP mixed GFRP to strengthen FRC beams, which can improve the toughness of concrete, reduce strengthening cost and meanwhile enhance bearing capacity of concrete beams.

Analytical prediction of the linear and nonlinear behaviour of steel beams rehabilitated using FRP sheets

The importance to rehabilitate ageing and deteriorated existing steel structures has motivated researchers to develop simple and efficient rehabilitation techniques. One of the currently developed techniques involves bonding Fibre Reinforced Plastic (FRP) sheets to the flanges of steel beams. This paper presents an analytical model to predict the linear and nonlinear behaviour of steel beams rehabilitated using this technique. The model is based on the solution of the differential equations governing the composite behaviour of a rehabilitated steel beam and includes representation of the peel and shear behaviour of the adhesive material. A bending test was conducted on a W-shaped steel beam, with glass FRP sheets bonded to its flanges, and the experimental results were used to validate the model. The model predictions for the failure load, failure mechanism, midspan deflection, steel strains, and FRP strains were found to be in excellent agreement with the experimental results. The model was also used to predict some parameters that were difficult to evaluate experimentally. This provided a better understanding of the behaviour of the rehabilitated beam.

Effect of tapered FRP sheets on interlaminar fracture behaviour of FRP–concrete interface

Abstract External bonding of fibre reinforced plastic (FRP) sheets to reinforced concrete beams has been accepted as an effective strengthening method. The use of taper ended FRP sheets can further enhance the strengthening performance, improving both the load carrying capacity and the corresponding deflection beyond those of the beams bonded with FRP sheets of a constant thickness. This paper presents experimental and analytical investigations regarding the influence of tapered FRP sheets on interlaminar fracture resistance between the FRP and concrete. The asymmetric double cantilever beam test was used to measure the interlaminar fracture resistance. The results showed that the taper configuration could significantly affect the interlaminar fracture behaviour in terms of both the load–displacement behaviour and the variation of critical strain energy release rate with crack propagation.

Bond analysis of masonry structures strengthened with CFRP sheets

The use of fiber reinforced plastic (FRP) plates and sheets for strengthening masonry structures is a promising technique but further investigations are needed in this area in order to carry out design guidelines. A considerable world wide effort has been expended into investigating the bond characteristics between RC elements and composite materials but little work has been undertaken in the sphere of masonry structures. The present paper reports part of a research project, still in progress, devoted to the analysis of the bond performance between FRP sheets and typical natural stones utilized for masonry structures in Southern Italy. The test procedure will be given and the results obtained discussed. Two commercially available CFRP sheets and two different types of masonry blocks have been used in the first stage of the analysis. Bond stresses at the interface between the two adherents have been evaluated and slip values determined. The influence of the specimens’ geometry has also been considered as well as the bond length parameter.

Fracture Resistance of a Cracked Concrete Beam Post-strengthened with FRP Sheets

Fibre-reinforced plastic (FRP) composites have been increasingly used in rehabilitation and strengthening of concrete structures. Significant increases in stiffness and strength have been achieved by applying this technique. However, there is concern about the ductility or toughness performance of FRP/concrete hybrid structures, which is critical in the application of this technology. This paper presents a new theoretical method to predict the fracture resistance behaviour of FRP post-strengthened concrete flexural beams. No slip between the FRP and plain concrete matrix is assumed and Mode I fracture propagation is considered. The model is valid for a wide range of span-to-depth ratios and any crack length. The influence of the bridging stresses provided by the fracture process zone (FPZ) at the tip of a fictitious fracture is examined. The effect of various material and geometric parameters on the resistance curve and toughness of the hybrid structure is discussed, based on the numerical results from the developed theoretical formulae. The results provide a useful insight into the strengthening/toughening and the design of FRP sheet/concrete beam structures.

Creep Deformation of Fiber Reinforced Plastics-Plated Reinforced Concrete Tensile Members

The problem of long-term creep deformation of reinforced concrete tensile elements strengthened by external fiber reinforced plastic (FRP) plates is studied. Formation of discrete cracks in concrete under tension is taken into account. A kinematic model is used, where relative slips between concrete, steel bars, and FRP plates are considered, governed by viscous interface shear stress–slip laws. Bazant’ solidification theory and exponential algorithm are used to obtain incremental constitutive equations for concrete as well as for steel-concrete and FRP-concrete interface laws. Moreover, cohesive normal stresses across transverse cracks in concrete are considered. The incremental differential system of equations is transformed into a nonlinear algebraic system by a finite difference discretization with respect to axial coordinate. Several numerical examples are presented, concerning both short-term and long-term loadings. It is shown that reinforcing by means of FRP plates or sheets has significant benefi...

Development of the Nonlinear Bond Stress–Slip Model of Fiber Reinforced Plastics Sheet–Concrete Interfaces with a Simple Method

In this paper, a new analytical method for defining the nonlinear bond stress-slip models of Fiber Reinforced Plastics (FRP) sheet-concrete interfaces through pullout bond test is proposed. With this method, it is not necessary to attach many strain gages on the FRP sheets for obtaining the strain distributions in FRP as well as the local bond stresses and slips. Instead, the local interfacial bond stress-slip models can be simply derived from the relationships between the pullout forces and loaded end slips. Based on a series of pullout tests, the bond stress-slip models of FRP sheet-concrete interfaces, in which different FRP stiffness, FRP materials (Carbon FRP, Aramid FRP, Glass FRP), and adhesives are used, have been derived. Only two parameters, the interfacial fracture energy and interfacial ductility index, which can take into account the effects of all interfacial components, are necessary in these models. Comparisons between analytical results and experimental ones show good accordance, indicating the reliability of the proposed method and the proposed bond stress-slip models.

Strength and strain enhancements of concrete columns confined with FRP sheets

The compressive behavior up to failure of short concrete members reinforced with fiber reinforced plastic (FRP) is investigated. Rectangular cross-sections are analysed by means of a simplified elastic model, able also to explain stress-concentration. The model allows one to evaluate the equivalent uniform confining pressure in ultimate conditions referred to the effective confined cross-section and to the effective stresses in FRP along the sides of section; consequently, it makes it possible to determine ultimate strain and the related bearing capacity of the confined member corresponding to FRP failure. The effect of local reinforcements constitute by single strips applied at corners before the continuous wrapping and the effect of round corners are also considered. Analytical results are compared to experimental values available in the literature.

Role of Fiber Reinforced Plastic Sheets in Shear Response of Reinforced Concrete Beams: Experimental and Analytical Results

The paper is principally aimed at analyzing the role of externally applied fiber reinforced plastic (FRP) sheets in the shear ultimate behavior of reinforced concrete elements. A theoretical model for predicting the shear resisting contribution of FRP sheets is illustrated. The proposal is based on a complete equilibrium/compatibility approach for reinforced concrete beams failing in shear and considers the possible interactions between the composite contribution and the resisting mechanisms of an ordinary reinforced concrete beam. The proposal is discussed and tested by means of an experimental investigation carried out on beams reinforced by glass FRP composite sheets with a shear span to depth ratio equal to 3. Further comparisons are then performed that consider the predictions of other existing approaches reported in the literature.

Rehabilitation of Cracked and Corroded Reinforced Concrete Beams with Fiber-Reinforced Plastic Patches

The behavior under static loading of fiber-reinforced plastic (FRP) retrofitted reinforced concrete beams, possessing a high chloride content and rebar corrosion, was studied both experimentally and analytically. The test beams were characterized as falling into three different groups according to the state of their corrosion damage: (1) natural corrosion, (2) cathodic protection, and (3) accelerated corrosion. The load carrying capacities of the beams, with or without FRP patching, were tested in the laboratory. The experimental results show that the state of corrosion of the steel, the water/cement ratio of the concrete material, and the arrangement and the number of FRP patches all affect the strength as well as the failure mechanisms of retrofitted RC beams. Some simple analytical models and a design concept for retrofitting cracked and corroded RC beams with FRP sheets are also presented and discussed.

Robust Design of a Flexible Structure Reinforced by FRP Sheets

This paper presents a robust method for designing a flexible structure reinforced by fiber-reinforced plastic (FRP) sheets. An FRP sheet has a high ratio of strength to weight and is widely used to reinforce various structures. Vibration characteristics of a structure reinforced by FRP sheets can be easily modified by changing design variables such as the relative volumes of fibers and matrix, the fiber angle and the number of layers. Therefore small variation of the design variables gives rise to drastic change in the vibration characteristics. The focus of this paper is on variation of the modulus of longitudinal elasticity of a structure reinforced by FRP sheets. We propose a constraint that takes into account the variation band of the elasticity of the structure and specifies the total variation of natural frequencies of low-order modes. To maximize the natural frequencies, the design variables are determined by using an optimization technique with this constraint. The validity of the present method is verified by numerical examples and by comparison with results of experiments.

Testing and modeling of shear and peel behavior for bonded steel/FRP connections

This paper presents a technique used to evaluate the shear and peel stiffness of an adhesive system that bonds fiber reinforced plastic (FRP) and steel sections. The technique combines experimental results and analytical solutions and involves the simulation of the shear and peel behavior of the adhesive through two continuous spring systems. The experiments involve shear lap testing of FRP sheets bonded to hollow steel sections. A closed form analytical solution was derived for both the in-plane and out-of-plane behavior of the tested FRP sheets. The measured in-plane load-displacement relations were incorporated into the closed form solution to evaluate the spring constant simulating the shear behavior of the adhesive. The out-of-plane behavior of the FRP sheets was identified experimentally through outer face strain and out-of-plane displacement measurements. A curve fitting approach in which the closed form analytical solution was fitted to the measured out-of-plane displacement profile was then used to evaluate the spring constant simulating the peel behavior of the adhesive. The study focused on a methacrylate adhesive system since preliminary investigation has shown it is suitable for applications involving bonding plastic and metal surfaces. The spring constants evaluated in this study can be used to perform detailed modeling of a bonded FRP/steel connection under a general state of loading.

Fibre-optic sensors and smart composites for concrete applications

Many extensive researches in the area of utilising fibre-reinforced plastic (FRP) materials for retrofitting and repairing existing damaged concrete structures have increasingly been made in recent years. The FRP can improve the overall flexural and compressive properties of the structures by using externally bonded FRP sheets. The conventional non-destructive inspection technologies such as strain gauge, and acoustic emission become inappropriate for structures after being repaired by externally bonded FRP materials. Optical fibre sensors have attracted considerable interest recently as non-destructive structural health monitoring devices for infrastructure elements. This paper gives a brief discussion of the principles of the fibre-optic technology for concrete structure assessment and its potential use in future engineering applications. Due to the increasing use of the FRP in most civil infrastructure elements, the conceptual idea of ‘smart composites’, which can be used as reinforcements as well as real-time structural health monitoring devices for concrete structures, is also discussed.