Fiber Reinforced Plastic Plates Research Articles

Indentation and penetration of carbon fibre reinforced plastic laminates

Static tests were carried out on circular carbon fibre reinforced plastic plates of various thicknesses, which where loaded at the centre by a hemispherical steel indentor. The tests were stopped at predetermined values of the displacement, and the indentation after the loading stage was evaluated. Tests were also performed up to complete penetration, using different indentor diameters. The data generated were compared with similar results previously obtained under low-velocity impact conditions, and treated according to models developed for the dynamic case. Apparently, both the penetration energy and indentation were not affected by the loading speed. The new experimental results showed that an empirical law previously proposed by the authors, aiming to predict the indentation as a function of the absorbed energy, is inaccurate when high energy levels are imparted to the material. A new empirical law, more efficient than the earlier, was assessed. The data collected indicate that the constants appearing in the new model are negligibly influenced by the laminate type and thickness, and constraint conditions adopted.

931 FRP 中の層間はく離き裂近傍における弾性応力分布の 3 次元メゾメカニックス解析

Three-dimensional meso-mechanical analysis was conducted by the finite element method (FEM) in order to determine the elastic stress distribution around a crack tip in fiber-reinforced plastics (FRP). FRP plates were modeled as a typical 'one-fiber slice' model, represented by the fiber-resin model. The fibers were arranged in a square array with a fiber volume fraction of 0.60. Matrix crack plane parallel to the fiber direction was placed in the matrix and is subjected to mode I loading. The half-crack length normalized by fiber diameter was varied from a/d_f=0.2 to 200. For long crack, the matrix-stress distribution ahead of delamination front can be divided into three regions : Region I, II and III (IIIa, IIIb) in the order of increasing distance from crack tip. The matrix-stress in Region I had a singularity of 1/√<r>, but was smaller than that of homogeneous FRP. Region IIIa has a singularity, too. But stress intensity factor of Region III was not equal to that of Region I. Region II was transitional region from Region I to IIIa.

350 繊維強化複合材料の減衰特性評価における支持条件の影響について

This paper studies the experimental damping evaluation of Fiber Reinforced Plastic (FRP) materials. For this purpose, FRP laminated composite plates are made of unidirectional FRP pre-preg sheets, and FRP beam test pieces are cut out from it. Free vibration experiments are carried out by the cantilevered beams. There is a discussion about the effects of the compression torques of squall vices when making FRP plates and the support torques at fixed edge of the test beams on the evaluation for natural frequencies and damping ratios (logarithmic decrements) obtained from the experimental data.

Investigation on lap-joint behaviour of GFRP plates bonded to silica fume and rice husk ash concrete

Fibre-reinforced plastic (FRP) materials are increasingly being used for the rehabilitation of concrete structures. Various adhesives are being employed for attaching FRP materials to concrete and for creating force-transmitting joints between structural elements. Although various existing models focus on predicting the behaviour of FRP–concrete composites, a fundamental understanding of the lap-joint behaviour of FRP plates bonded to concrete still needs to be gained. In particular, there is a lack of a simple and reliable method that allows defining the stiffness of the adhesive in the FRP–concrete lap-joint area. In this study, GFRP plates were bonded to concrete blocks incorporating various proportions of silica fume and rice husk ash. A test set-up was developed to induce shear stresses in the GFRP–concrete lap-joint area. Specimens were instrumented with strain gauges at key locations to establish local stress–strain behaviour. Three-dimensional solid finite elements were used to model the GFRP plates and concrete block. The adhesive was modelled as a spring system with stiffness k v and k p simulating the shear and peel rigidity of the adhesive, respectively. Although it still needs future developments, the finite element model thus developed coupled with the simple test procedure provide a simple means for calculating the stiffness of the adhesive between the GFRP and concrete. Knowledge of this stiffness is expected to allow a more realistic modelling of the lap-joint behaviour of GFRP–concrete composites.

Experimental Investigation of Lap Splices in Externally Bonded Carbon Fiber-Reinforced Plastic Plates

This paper identifies a primary mode of failure of lap splices in externally bonded carbon fiber-reinforced polymer (CFRP) tension reinforcement. Results of small-scale tension tests are compared to large-scale beam tests. The small-scale tension tests show promise as a means of identifying a combination of adhesive and splice plate material that will optimize splice performance.

Local Buckling of Elastically Restrained Fiber-Reinforced Plastic Plates and its Application to Box Sections

An analytical study of local buckling of rectangular composite plates rotationally restrained elastically along unloaded edges and subjected to nonuniform in-plane axial action at simply supported loaded edges is presented. A variational formulation of the Ritz method is used to establish an eigenvalue problem, and by using combined harmonic and polynomial buckling deformation functions, which satisfy all the restrained boundary conditions, the explicit solution of plate local buckling coefficients is obtained. The explicit formulas for local buckling strength of orthotropic plates are simplified to the cases of isotropic plates, which are consistent with classical solutions. The elastically rotationally restrained plates are further treated as discrete plates or panels of fiber-reinforced plastic (FRP) box shapes, and by considering the effect of elastic restraints at the joint connections of flanges and webs, the local buckling strength of FRP box shapes is predicted. The theoretical predictions are in good agreement with transcendental solutions and finite-element eigenvalue analyses for local buckling of FRP box columns. The present explicit formulation can be applied to determine local buckling capacities of composite plates with elastic restraints along the unloaded edges and can be further used to predict the local buckling strength of FRP shapes.

Finite element modelling of flexural behaviour of externally bonded CFRP reinforced concrete structures

This paper focuses on the flexural behaviour of RC beams externally reinforced using Carbon Fibre Reinforced Plastics (CFRP) plates. A non-linear finite element (FE) analysis is proposed in order to complete the experimental analysis of the flexural behaviour of the beams. An elasto-plastic behaviour is assumed for reinforced concrete and interface elements are used to model the steel-concrete bond and the adhesive. The numerical analysis also includes simulations on pre-cracked beams.

On the parameters influencing the performance of reinforced concrete beams strengthened with FRP plates

This paper presents a summary of our investigations that were aimed to assess the influence of various physical and mechanical parameters on the performance of reinforced concrete (RC) beams strengthened with fiber reinforced plastic (FRP) plates. The work was divided into two phases. The first phase investigated the influence of FRP plate length, fiber orientation, and surface preparation on the performance of FRP-reinforced RC beams. The FRP in this phase of the work was E-glass/epoxy. The second phase of the study was designed to confirm the validity of our hypothesis, which postulated that the delamination of the FRP plate would be a function of the Poisson ratio mismatch between concrete and FRP plate. Results from the second phase also suggested that less expensive glass FRP plates could adequately replace the more expensive carbon FRP plates by offering the beam more ductility, without sacrificing its expected performance. Moreover, results from both phases showed that the lateral stiffness of the FRP plate contributed to the overall flexural stiffness of the strengthened beam.

Analytical and numerical investigation of interfacial stresses of FRP–concrete hybrid structure

This paper presents a study on interfacial stresses of a concrete column confined by fiber-reinforced plastic (FRP) plate, which has been widely applied in the civil engineering for rehabilitation and retrofitting of conventional structures. It is assumed that both the FRP plate and concrete structures are elastic and the interface between them is perfectly bonded. An analytical model for analysis of the interfacial stresses is developed and the finite element modeling is carried out for an axisymmetric FRP–concrete hybrid column. Components of the FRP plate with different geometric and material properties are considered to study their effects on the interfacial stresses. The study shows that the interfacial stresses are influenced by several factors, such as modulus ratio of FRP and concrete and thickness of FRP. This work provides a comprehensive investigation on the mechanical behavior of the interface in hybrid structures.

Shear Peeling of Steel Plates Bonded to Tension Faces of RC Beams

The technique of adhesively bonding steel or fiber-reinforced plastic plates to the surfaces of reinforced concrete (RC) structural elements is being adopted worldwide to strengthen or repair reinforced concrete buildings and bridges. However, the prevention of premature debonding or peeling of externally bonded plates is a most critical aspect of design. One of the major modes of debonding in plated RC beams is shear peeling induced by the formation of critical diagonal cracks caused by the applied vertical shear forces. In this paper, mathematical models are developed for quantifying the shear peeling resistance of RC beams bonded with plates of different configurations. These models are based on the simplified theory of plasticity concepts for shear in reinforced concrete beams and also on procedures to compute the bond strength between an adhesively bonded plate and a concrete element. The models are validated against 32 test results from reinforced concrete beams adhesively bonded with either steel p...

Development of design rules for retrofitting by adhesive bonding or bolting either FRP or steel plates to RC beams or slabs in bridges and buildings

Bonding plates to reinforced concrete (RC) structures is a mechanically efficient form of retrofitting that is also inexpensive and unobtrusive. However, bonding plates to RC structures is an extremely complex engineering problem as research has shown that bonded plates are prone to about 30 mechanisms of failure. This paper describes the various techniques of plating that are now available for retrofitting, illustrates some of the various failure mechanisms that can occur and the development of their design rules, and discusses the choices between adhesive bonding and bolting, and the choice between steel and fibre reinforced plastic (FRP) plating.

Retrofitting Of Reinforced Concrete Beams Using Externally Bonded FRP Plates

The need of increasing the serviceability loads, upgrading of provisions or deterioration of the structures due to corrosion or other types of degradation generally lead to the necessity of repair andlor strengthening. Although a variety of strengthening techniques are available such as jacketing or strengthening with externally bonded steel plates, it is getting more popular to use FRP materials because of their excellent properties. This study is about the experiments in which RC beams were retrofitted with FRP (Fiber Reinforced Plastics) materials. All beams have the same material properties and dimensions. The effect of FRP ratio and reinforcement ratio on the behaviour of test specimens has been investigated as well as the effect of anchorage and, finally, conclusions were drawn.

Mechanics of bonds in an FRP bonded concrete beam

Abstract Fibre-reinforced plastic (FRP) materials have been recognised as new innovative materials for concrete rehabilitation and retrofit. Since concrete is poor in tension, a beam without any form of reinforcement will fail when subjected to a relatively small tensile load. Therefore, the use of the FRP to strengthen the concrete is an effective solution to increase the overall strength of the structure. The attractive benefits of using FRP in real-life civil concrete applications include its high strength to weight ratio, its resistance to corrosion, and its ease of moulding into complex shapes without increasing manufacturing costs. The speed of application minimises the time of closure of a structure compared to other strengthening methods. In this paper, a simple theoretical model to estimate shear and peel-off stresses is proposed. Axial stresses in an FRP-strengthened concrete beam are considered, including the variation in FRP plate fibre orientation. The theoretical predictions are compared with solutions from an experimentally validated finite element model. The results from the theory show that maximum shear and peel-off stresses are located in the end region of the FRP plate. The magnitude of the maximum shear stress increases with increases in the amount of fibres aligned in the beam's longitudinal axis, the modulus of an adhesive material and the number of laminate layers. However, the maximum peel-off stress decreases with increasing thickness of the adhesive layer.

Design against premature peeling failure of RC beams with externally bonded steel or FRP plates

The salient features are presented of a recently reported semi-empirical model for predicting the lower/upper bounds to plate peeling loads of simply supported RC beams strengthened in flexure by gluing external steel or fibre reinforced plastic (FRP) plates to their soffits. The original model was, however, computer based, and involved certain iterative procedures. This potential drawback is overcome in the present paper, which reports details of some simplified (but still reasonably accurate) procedures for predicting the lower bound (i.e. safe) steel or FRP plate peeling loads, with the proposed formulations being amenable to hand calculations, using a pocket calculator, hence, of value to busy practising engineers.

Design against premature peeling failure of RC beams with externally bonded steel or FRP plates

The salient features are presented of a recently reported semi-empirical model for predicting the lower/upper bounds to plate peeling loads of simply supported RC beams strengthened in flexure by gluing external steel or fibre reinforced plastic (FRP) plates to their soffits. The original model was, however, computer based, and involved certain iterative procedures. This potential drawback is overcome in the present paper, which reports details of some simplified (but still reasonably accurate) procedures for predicting the lower bound (i.e. safe) steel or FRP plate peeling loads, with the proposed formulations being amenable to hand calculations, using a pocket calculator, hence, of value to busy practising engineers.

FRP or steel plate-to-concrete bonded joints: Effect of test methods on experimental bond strength

The strengthening of reinforced concrete structures using externally bonded steel or advanced fibre reinforced plastic (FRP) composites is becoming increasingly common. A key factor affecting the behaviour and reliability of such strengthened structures is the bond strength between the steel or FRP plate and the concrete substrate. Several different experimental set-ups have previously been used to determine bond strength. This paper presents a careful finite element analysis of the stress distributions in these test set-ups. Results show that stress distributions can be significantly different for different set-ups, for similar materials and geometry.

Interfacial Stresses in Beams and Slabs Bondedwith Thin Plate

A new popular method for retrofitting reinforced concrete beams and slabs is to bond fiber-reinforced plastic (FRP) plates to the soffit. An important failure mode for such strengthened members is the debonding of the FRP plate from the member due to high interfacial stresses near the plate ends. Accurate predictions of the interfacial stresses are a prerequisite for designing against debonding failures. In this paper, a theoretical interfacial stress analysis is presented for simply supported beams and slabs bonded with a thin FRP composite or steel plate and subjected to a uniformly distributed load in combination with a uniform bending moment. The analysis leads to an exact closed-form solution, in which a plane stress model is used for beams and a plane strain model is used for slabs. The salient features of the new analysis include the consideration of nonuniform stress distributions in and the satisfaction of the stress boundary conditions at the ends of the adhesive layer. Numerical results from the present analysis are presented both to demonstrate the advantages of the present solution over existing ones and to illustrate the main characteristics of interfacial stress distributions in beams and slabs.

Concrete Beams Strengthened with Externally Bonded FRP Plates

The structural behavior of reinforced concrete beams strengthened with adhesively bonded fiber-reinforced plastics (FRP) is presented. The experimental work included flexural testing of 2.3-m-long concrete beams with bonded external reinforcements. The test variables included the amount of conventional (internal) reinforcement and also the type and amount of external reinforcement. For comparison, some of the beams were strengthened with bonded steel plates. Theoretical analyses included 2D nonlinear finite-element modeling incorporating a “damage” material model for concrete. In general there were reasonably good correlations between the experimental results and nonlinear finite-element models. It is suggested that the detachment of bonded external plates from the concrete, at ultimate loads, is governed by a limiting principal stress value at the concrete/external plate interface.

Estimation of stress intensity factor (KI) for an FRP bonded concrete beam using the superposition method

The deterioration of civil concrete infrastructures has increased dramatically in recent years. The majority of recent studies have focused on the use of fibre-reinforced plastic (FRP) materials to strengthen or reinforce decayed concrete structures by bonding the FRP plate externally onto the damage surface. These studies have concentrated on the shear and peel-off effects of the adhesive material rather than the failure mechanisms of the concrete itself. However, the stress intensity factor, KI, at the crack-tip of the strengthened cracked concrete structures, cannot be overlooked. Numerical and experimental investigations have prove that KI of the strengthened structure is highly influenced by the modulus and geometry of the reinforced plate. Therefore, the failure of the strengthened specimen may be due to a high KI value in the concrete material. In this paper, a theoretical model is proposed to estimate the value of KI with different reinforced plate properties for a strengthened concrete beam using a simple superposition method. The results from the proposed method compare well with the numerical solutions obtained from the finite-element method. Both results show that the steosintensity value, of the beam decreases as the modulus and thickness of the reinforced plate increase, while the closing force of the beam, induced by the reinforced plate, increases.

Estimation of stress intensity factor (KI) for an FRP bonded concrete beam using the superposition method

The deterioration of civil concrete infrastructures has increased dramatically in recent years. The majority of recent studies have focused on the use of fibre-reinforced plastic (FRP) materials to strengthen or reinforce decayed concrete structures by bonding the FRP plate externally onto the damage surface. These studies have concentrated on the shear and peel-off effects of the adhesive material rather than the failure mechanisms of the concrete itself. However, the stress intensity factor, KI, at the crack-tip of the strengthened cracked concrete structures, cannot be overlooked. Numerical and experimental investigations have prove that KI of the strengthened structure is highly influenced by the modulus and geometry of the reinforced plate. Therefore, the failure of the strengthened specimen may be due to a high KI value in the concrete material. In this paper, a theoretical model is proposed to estimate the value of KI with different reinforced plate properties for a strengthened concrete beam using a simple superposition method. The results from the proposed method compare well with the numerical solutions obtained from the finite-element method. Both results show that the steosintensity value, of the beam decreases as the modulus and thickness of the reinforced plate increase, while the closing force of the beam, induced by the reinforced plate, increases.