FRP Plates Research Articles

Effect of the tapered end of a FRP plate on the interfacial stresses in a strengthened beam used in civil engineering applications

The interfacial stresses of a beam strengthened with a FRP plate, which is widely employed in the civil engineering for rehabilitation and retrofitting of conventional structures, is investigated. An important feature of the reinforced beam is significant stress concentrations in the adhesive at the ends of the FRP plate. To reduce these interfacial stresses, a FRP plate with a tapered end is often used. The finite-difference method is utilized in this work to predict the distribution of interfacial stresses in beams strengthened with a FRP plate having a tapered end. Numerical results from the analysis are presented to demonstrate the advantages of using tapers in the design of strengthened beams.

Finite Element Analysis of Shearing Bond Behavior of CFRP-Concrete Interface

The debonding behavior at the interface between carbon fiber-reinforced plastic (CFRP) sheet and concrete is a key problem for the application of FRP plate, which has been widely applied in the civil engineering for rehabilitation and retrofitting of conventional structures. This paper presents the nonlinear finite element analysis results of the CFRP-strengthened high-strength concrete member. On the basis of the test, considering of the bond-slip relationship, explicit finite element is used for simulating the shear failure of CFRP-strengthened concrete, obtain three-dimensional deformation development diagram, describe the failure mode and the relationship between the shearing bond behavior and concrete strength. The FE results coincide with the experimental results.

Time-variant flexural reliability of RC beams with externally bonded CFRP under combined fatigue-corrosion actions

Time-variant reliability analysis of RC highway bridges strengthened with carbon fibre reinforced polymer CFRP laminates under four possible competing damage modes (concrete crushing, steel rupture after yielding, CFRP rupture and FRP plate debonding) and three degradation factors is analyzed in terms of reliability index β using FORM. The first degradation factor is chloride-attack corrosion which induces reduction in steel area and concrete cover cracking at characteristic key times (corrosion initiation, severe surface cover cracking). The second degradation factor considered is fatigue which leads to damage in concrete and steel rebar. Interaction between corrosion and fatigue crack growth in steel reinforcing bars is implemented. The third degradation phenomenon is the CFRP properties deterioration due to aging. Considering these three degradation factors, the time-dependent flexural reliability profile of a typical simple 15m-span intermediate girder of a RC highway bridge is constructed under various traffic volumes and under different corrosion environments. The bridge design options follow AASHTO-LRFD specifications. Results of the study have shown that the reliability is very sensitive to factors governing the corrosion. Concrete damage due to fatigue slightly affects reliability profile of non-strengthened section, while service life after strengthening is strongly related to fatigue damage in concrete.

Analytical modeling of bond behavior between FRP plate and concrete

The bonding of FRP plate on the tensile side of concrete members has been accepted as an effective and efficient technology for improving the strength and stiffness of concrete structures. Intermediate crack induced debonding is a common failure mode for FRP strengthened concrete beams. This kind of failure mode can be studied with direct shear test, which involves a FRP plate bonded on a concrete prism with a stretching force acting on one end of the plate. To investigate the failure mechanism of the plate-to-concrete joint, a simplified bond slip model with a linear ascending segment and an exponential softening segment is proposed for the plate-to-concrete interface. With the bond–slip model, the closed-form solutions for the tensile stress in FRP plate, interfacial shear stress and displacement of the FRP plate are derived and verified with experimental results. With the analytical model, a theoretical model is proposed for calculating the effective bond length of a plate-to-concrete joint. Effect of different parameters including stiffness of FRP plate, interfacial fracture energy and interfacial shear strength on the effective bond length are comprehensively studied. Finally, a simple analytical solution of the bond strength for the cases with bond length smaller than the effective bond length is derived and compared with the complicated closed-form solution reported in the literature.

Interfacial Shear Stress Calculation of Concrete Beams Strengthened with FRP Plate Based on Energy Theory

The collaborative work between FRP plate and concrete is achieved through the binder, so the interface of them is the weak links. Under external loading, the relative slip occurred on the interface between FRP plate and concrete causes the redistribution of stress and then the bearing capacity of the member will be reduced. Especially the FRP plate is a kind of resin material and its physical and mechanical properties will change with temperature and time. Based on energy variation principle, the differential equations of interfacial shear stress meanwhile to considering temperature and creep effect of concrete beams strengthened with FRP plate are established, in which the strain-energy of concrete beam, FRP plate and glue layer are calculated. And the calculated formulas of interfacial shear stress for a single point load are given.

S1720105 劣化を検知するセンシングシステムを埋設したFRP製貯槽のメンテナンス手法に対する一考察([S172]プロセスセイフティマネージメント,産業・化学機械と安全部門)

To evaluate the degradation of FRP storage tank in chemical plant, embedded optical fiber type sensing systems were studied about maintenance method matching with situation of setting the equipment. When it can be installed in opportunity of new construction of a FRP, it can be easily embedded in the FRP plate. When new FRP tank is supplied without embedding the sensor, blind flange type sensor with same resin system is convenient to install the monitoring system. For the old one already started to work, blind flange embedded tow or more sensors in it can monitor the penetration rate may be effective to evaluate the remaining life and decision of how to maintenance the FRP chemical storage equipment.

Effects of plate volume on load-carrying capacity of flexural reinforced RC beam with submerged FRP plate

Effects of plate volume on load-carrying capacity of flexural reinforced RC beam with submerged FRP plate

10202 有限要素法を使用した緩衝材による生体模擬材への衝撃低減効果の検討

The purpose of the absorber is to reduce the energy propagated to the object when an impact occurs. However, the optimal size and material of the absorber depends on impact condition. In addition, research is not enough for the case that the deformation of the absorber is in huge strain rate. Impacting the fragment to the biological simulant attached FRP plate and absorber, by varying the material and thickness of the absorber has been studied using the finite element method. By examining the energy propagated to the biological simulant, the impact reduction effect of the absorber has been investigated. The densification strain and the apparent density is the important factor to design the effective impact reduction form.

Two-Dimensional Shear Stress on Bonding Interface of FRP Plate Reinforced Hydraulic Concrete

The bonded interface between FRP plate and the hydraulic concrete is a key part while reinforcing the hydraulic concrete structure with FRP plate. The bond property of the interface directly decides the results of structural reinforcement. In most of the external loading conditions, this interface is under the shear stress state. Therefore, accurate measurement and analysis of interfacial shear stress distribution is the guarantee of FRP reinforced hydraulic concrete structure the premise of success. Focusing on the shear-resisting bonding strength of FRP-concrete interface, this paper improved the ASTM D905 standard shear sample and carried out numerical simulation of shear test to the bonded interface of FRP-reinforced hydraulic concrete structure by adopting the bi-dimensional finite element method, and conducted parameter analysis of the influence factors (elasticity modulus of FRP and concrete, shear modulus and thickness, etc) of shear stress on the FRP-concrete bonded interface and finally the distribution characteristics of shear stress on the bonded interface were obtained. This paper mainly discussed the influence rules of stress concentration to the distribution of shear stress on the bonded interface, which provides theoretical guidance and direction to the shear-resisting bonding strength test in the next step as well as technical support to the processing of FRP-strengthened hydraulic concrete bonded interface.

Tests investigating the punching shear of a column-slab connection strengthened with non-prestressed or prestressed FRP plates

This paper investigates the effectiveness of bonding non-prestressed and prestressed carbon fibre reinforced polymer (CFRP) plates to the tension surface of concrete column-slab connections in both the serviceability and ultimate limit state. For the prestressed plates different prestressing forces were applied to the CFRP as part of the strengthening technique. The structural response of the strengthened specimens was compared with a non-strengthened reference specimen in terms of punching shear strength, deflection profile, strain, crack opening displacement and failure modes. It was found that using prestressed CFRP plates improved the serviceability; in terms of deflection and cracking, but did not enhance the ultimate behaviour as much as the non-prestressed CFRP plates. The development of the critical diagonal crack (CDC) was the main reason for the reduction in the ultimate capacity of the strengthened slabs.

Critical thrust force predicting modeling for delamination-free drilling of metal-FRP stacks

The aim of this paper is to study about delamination during drilling metal-FRP (Fiber Reinforced Polymer Composite) stacks, with the effect of the metal part taken into account. Two cases were studied, case (a): drilling form metal to FRP and case (b): drilling form FRP to metal. In case (a), a mechanical model for predicting the critical thrust force (CTF) was established based on linear elastic fracture mechanics, classical bending plate theory and the mechanics of composites. In case (b), plate shape and edge conditions were taken into consideration to analyze the deformation of the metal plate. The superposition principle was applied to calculate the effect of the deformation of the metal plate and FRP plate on the CTF, and a mechanical model was established based on the analysis in case (a). A series of experiments have been performed and the rationality of the models was testified.

Standardised double-shear test for determining bond of FRP to concrete and corresponding model development

Bond stress – slip characteristics play a major role in the behaviour of EBR FRP strengthened RC beams. These characteristics are normally determined by using experimental data from small-scale bond tests. However, the research community is yet to agree on a unified experimental set-up and testing procedure for these tests. The lack of standard tests leads to high variability in published results and hinders the development of reliable design models. The testing programme presented herein was part of an international Round Robin Test (iRRT) exercise, aimed at assessing the suitability of double shear tests to characterise the bond behaviour of FRP strengthening systems. A total of 20 tests were performed on different FRP plates. Recommendations on how to improve the iRRT methodology are given. Based on the results, an improved capacity model that accounts for concrete surface preparation is proposed and validated against an extensive database of published results. The outcome of the current research is expected to provide engineers with more confidence in designing safely strengthening applications whilst making the best use of the FRP materials.

A finite-difference model with mixed interface laws for shear tests of FRP plates bonded to concrete

In the last years the strengthening of existing structures by means of externally glued fiber-reinforced polymer has become increasingly popular. This stimulated the study of new numerical and analytical models to understand the ultimate behavior of this reinforcement technique. Simultaneously, many experimental tests permitted to identify the main parameters involved in the failure process, which often occurs by debonding (i.e. with a crack propagating into the support underneath the reinforcement). Recent studies clarified the role of the coupling between normal and tangential stresses, pointing out that tensile stresses orthogonal to the bonding plane (peeling stresses) could be detrimental to the bond behavior. The effects of the peeling stresses are substantially related to a local reduction of the shear strength along the bonded length and to a variation of the failure mechanism. To investigate these issues, here a numerical model for debonding of FRP reinforcements is proposed by adding the effects of normal stresses to the classic pure shear cohesive zone model. The interaction between the reinforcement and the support is accounted for using an interface cohesive law, coupling tangential and normal behaviors. Finally, comparisons with experimental evidences and already validated models are presented to assess the capabilities of the proposed approach.

Fibers orientation optimization for concrete beam strengthened with a CFRP bonded plate: A coupled analytical–numerical investigation

Important failure mode of such plated beams is the debonding of the FRP plates from the concrete due to high level of stress concentration in the adhesive at the ends of the FRP plate. This paper presents a new method for reducing interfacial stresses in a concrete beam bonded with the FRP plate by including the effect of the fiber orientation in the FRP plate. This work is divided into two parts; the first one is based on the laminates theory for the analytical solution where a minimization method is used to directly determine the fiber orientation reducing the interfacial stresses. The second part consists into a Finite Element modeling where the analytical solution and different fibers orientation combinations are tested for improving strengthening quality. Numerical results from the present analysis are presented in order to show the advantages of the present solution over existing ones and to reconcile debonding stresses with strengthening quality.

Iterative determination of threshold FRP area needed to avoid non-ductile longitudinal shear failures in yield-zones of FRPRC members

This paper presents a novel nonlinear iterative scheme to determine threshold areas of FRP plating which avoid longitudinal shear failure of the FRP-to-concrete connection in yield zones of FRPRC beams. Implicit differentiation of an experimentally-verified predictive model for longitudinal shear failure and of associated FRPRC section equations is used to generate incremental expressions which underpin the iterative scheme. Iterations are driven by the disparity between the longitudinal shear stress for the updated area of plate and the connection’s longitudinal shear strength. For different load types on a FRPRC beam, the scheme is shown to exhibit robust convergence characteristics in regimes of pronounced nonlinearity, with reliable gravitation toward the correct plate area from a wide range of starting values of this plate area. The study produces the counter-intuitive result that stiffer plates reduce longitudinal shear requirements, probably owing to the associated shorter yield zones of reduced yield activity at the specified peak load of the FRPRC member.

철근콘크리트용 FRP Box 휨 보강재의 형상 설계 및 거동 평가

This paper presents the design, fabrication and performance of a reinforced concrete beam strengthened by GFRP box plate and its possibility for structural rehabilitations. The load capacity, ductility and failure mode of reinforced concrete structures strengthened by FRP box plate were investigated and compared with traditional FRP plate strengthening method. This is intended to assess the feasibility of using FRP box plate for repair and strengthening of damaged RC beams. A series of four-point bending tests were conducted on RC beams with or without strengthening FRP systems the influence of concrete cover thickness on the performance of overall stiffness of the structure. The parameters obtained by the experimental studies were the stiffness, strength, crack width and pattern, failure mode, respectively. The test yielded complete load-deflection curves from which the increase in load capacity and the failure mode was evaluated.

Pull-out strength of glued-in FRP plates bonded in glulam

The use of FRP laminates as connectors in glulam timber members is considered to be particularly promising since the durability of the system is improved and the application is easier and faster due to the lightweight properties of FRPs. In this paper an investigation aimed at characterizing the bond performance of FRP strips glued into glulam elements is presented. Several pull-out tests were carried out to assess the influence of various parameters: the bond length, the type of fibers for the reinforcement, the direction of the fibers in the FRP with respect to the timber grain. The elastic behaviour of the joint was also studied analytically and numerically. The ultimate strength of the experiments was compared with predictive expressions available from the literature.

Structural Performance and Ductility of Fiber Reinforced Polymer Concrete Bonding System Under Tropical Climates

Tropical climate combines with saltwater exposure may influence the structural performance and durability of FRP–epoxy–concrete system over long period of time. FRP being non–corrodible material has been proven to be efficient materials in rehabilitation jobs compared to steel. Reinforced concrete structures may be required to be strengthened at a later age of their service life to overcome additional loading capacity and deterioration due to environmental effect. The main objective of the current paper is to study flexural behavior of an externally bonded reinforced concrete beams using carbon FRP plate and fabrics due to exposure to natural tropical climate. The research studies the ability of reinforced concrete beams externally bonded with CFRP plate and fabrics to resist numerous environmental conditions such as tropical weather, normal laboratory environment and saltwater solution. The bonded beams are subjected experimental evaluation by performing four points load test until failure to observe the failure loads, deflection, strain, cracking behavior and the patterns of failure. Strengthening of reinforced concrete beams using CFRP plate and fabrics demonstrated significant improvement in the flexural capacity of the beams by 30% and 16%, respectively compare to control specimen without strengthening.

콘크리트에 표면매입 보강된 FRP판의 매입간격과 길이에 따른 부착강도

Recently, experimental and analytical researches have been performed in order to find interface failure between FRP plate and concrete in near surface-mounted (NSM) retrofit using FRP plate. As a result, it was found that the bond strength between concrete and NSM FRP plate had a close relationship with shape of FRP, concrete compressive strength and bond length. However, research need is increasing about another factors such as suitable space of FRP plate and group effect. In this study, therefore, a bond test was performed with aforementioned factors and compared with a previous equation to verify its suitability for predicting bond strength of NSM FRP plate. From the test, it was found that the bond strength increased according to the increase of space of NSM FRP plates even if its bond length was same. The splitting failure of concrete governed when space of FRPs was too narrow and it changed to FRP's tensile failure with increase of the space. From the evaluation of test specimens using previous equation, it was found that the bond strength could be predicted properly with consideration of group effect.

Vibrational Energy Harvesting Using a Unimorph with PZT- or BT-Based Ceramics

Vibration-electrical energy converters based on the piezoelectric effect were investigated for energy harvesting and possible use in ultralow-power sensor modules. A patterned FRP plate was used as the base beam. PZT-based and BT-based ceramics were adhered to the FRP beam, and the unimorph structure was fabricated. The unimorphs were oscillated by vibration generator, and the generated voltage across load resistance was measured. The output voltages were proportional to g 31. The power and energy were closely related to g 31 2 or d 31 g 31/tanδ. The unimorph consisting of PZT with a higher Curie temperature produced larger power and energy. Mn-doping was also found to be effective for producing energy and power in BaTiO3-based ceramics. Two 18 × 10 × 0.5 mm unimorphs, consisting of PZT-based ceramics with a g 31 of 11.8 mV/N and Q m of 461, and lead-free Mn-0.2 mol% doped BaTiO3 ceramic with g 31 of 2.2 mV/N and Q m of 95.3, produced 1763 μJ and 432 μJ, respectively, by 45 second oscillation with a 0.8 mm displacement and a frequency of 80 Hz.