FRP Plates Research Articles

Dependence on winding tensions for stability of a superconducting coil

The purpose of this study is to manufacture a high performance superconducting pulse coil by using high strength polyethylene fiber (DF; Dyneema ® fiber) reinforced plastic (DFRP) or Dyneema–glass hybrid composite fiber reinforced plastic (DGFRP) as material of a coil bobbin, which has negative thermal expansion, low frictional coefficient and high thermal conductivity. Description in this paper is as follows. First, thermal strains of several kinds of FRP pipes made by filament-winding (FW) method are measured, and the measured results well agreed with calculated ones by our proposed calculation method about thermal strains of a FW-pipe form. This shows that thermal expansion can be controlled by the proposed design technique of a DGFRP FW-pipe. Moreover, frictional coefficients of FRP plates using as coil structural material are measured and frictional heats are calculated for respective material when contact forces are changed. From these results, we find that the lower winding tension of a coil generates the smaller frictional heat when the frictional coefficient of the coil structural material is low. Furthermore, we systematically measure quench characteristics of many specimens of small superconducting coils using DFRP or DGFRP bobbins with different thermal expansions. From the results of quench tests, we find that the higher winding tension’s coils tend to decrease quench current when the coil’s bobbin expanded to a direction of circumference during the cooling down to cryogenic temperature, and suitable values of winding tension in a coil are located in region of 2–4 kg/mm 2. Finally, we design and manufacture 100 kJ class superconducting pulse coil by using a DGFRP bobbin, which wound in winding tension of 4 kg/mm 2. In addition, we prepare another 100 kJ class coil with the higher winding tensions of 8 kg/mm 2, and the quench characteristics of the coils are compared. The quench currents in the coils exceed the 95% rating on the load line for critical current value of a conductor, and a coil with winding tension of 4 kg/mm 2 is more stable.

A structural engineering approach to adhesive bonding longitudinal plates to RC beams and slabs

Retrofitting by plating structures has been found to be very efficient. However, tests have shown that externally bonded longitudinal plates are prone to premature debonding. Furthermore, a comprehensive study of published research has also shown that there can be large discrepancies between debonding mathematical models and tests. To overcome this problem and to allow structural engineers to adhesively bond plates with safety and efficiently, a structural engineering approach is suggested whereby many of the debonding mechanisms can be prevented by judicious detailing; this approach can be applied to tension face plates, compression face plates, side plates, U-sectioned plates, and angle-sectioned plates. Four continuous reinforced concrete beams have been retrofitted with adhesively bonded longitudinal plates and tested in order to illustrate this design approach, to directly compare the performance of longitudinal side plates with longitudinal tension face plates, to compare FRP plating with steel plating, and in particular to illustrate the effect of debonding on the sectional ductility of longitudinally plated continuous RC beams.

Closed form equations for FRP flexural strengthening design of RC beams

FRP external strengthening has proven its success in structural rehabilitation and upgrade. Researchers and practicing engineers are working towards introducing its design procedures to standard codes of practice. The current state of the art flexural design process suggests an iterative approach, which may lead to tedious calculations. This paper provides a direct approach furnishing calculation simplicity and design efficiency. It also proposes equations to design doubly strengthened sections for the first time. The expressions derived for doubly reinforced rectangular and Tee sections are written in a compact form based on those formulated for singly reinforced rectangular sections. Verifications against experimental results are performed. The solution, using the closed form equations, is compared to that of other procedures available in the literature through design examples. Tee section design is also presented and illustrated through a comparison with an analysis example. A doubly strengthened beam design example is also solved. The prevention of premature FRP plate separation using U-wraps to develop the full flexural capacity is also discussed.

Mechanical analysis of a cracked beam reinforced with an external FRP plate

A theoretical method to predict the loading capacity of a cracked FRP reinforced concrete flexural beam is developed. The beam subjected to three-point bending is externally reinforced with unidirectional FRP plate near the bottom surface of the tensile zone. No slip between the FRP plate and plain concrete is assumed. A fictitious crack approach which has been used previously in conjunction with finite element method in the fracture analysis of concrete is adopted here to estimate the equivalent bridge effect of the fracture process zone of concrete. The predicted results of loading capacities are then shown graphically.

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

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

Non-linear model for R/C tensile members strengthened by FRP-plates

Transverse cracking in reinforced concrete (R/C) members strengthened by FRP plates and subjected to axial loads is analyzed. A non-linear model is developed, where cohesive stresses in concrete across cracks and non-linear bond–slip law between steel bars and concrete are used. The non-linear governing equations are solved via finite difference method. Comparisons with experimental results confirm the validity of the model. Numerical examples are also presented, simulating tests on plated and unplated R/C members with displacement, force, or crack opening control. The examples show that external FRP-plating is effective in reducing crack width and, consequently, in increasing axial stiffness of tensile members.

Analytical and experimental study on seismic performance of RC T-beams with design deficiency in steel bar curtailment

In this study, a seismic assessment model using traditional RC section analysis and variable-angle truss model for prediction of angle of concrete diagonal cracks, can provide a simple evaluation of the seismic performance of beams with longitudinal rebar curtailment. A preliminary test programme was performed to verify the prediction of the assessment model and to investigate the seismic response of existing building frames and their rehabilitation. Analytical and experimental results show that reinforced concrete beams with beam bar cut-off designed according to earlier codes, such as ACI 318-71, may have deficiencies and require retrofitting. The presence of FRP plates can successfully correct the bar curtailment deficiencies and achieve rotation levels greater than those expected to be imposed during an earthquake.

Analytical study on reinforced concrete beams strengthened for flexure and shear with composite plates

The results of an analytical study on the behaviour of reinforced concrete T-beams retrofitted with carbon fibre reinforced polymer (CFRP) plates for flexure and glass fibre reinforced polymer (GFRP) plates for shear are discussed in this paper. A test series comprising four 5 m long simply supported beams were tested under monotonic load to verify the analytical model. Particular emphasis was given to the performance of predicted model building upon discrete element analytical methodology incorporating the dual effects of flexure and shear in beams. The effects of curtailed longitudinal CFRP plates bonded to the soffit of test beams were also analysed to examine the prediction accuracy of the model. An important conclusion in this paper is that the predicted model can be used to accurately predict the behaviour of load versus displacement and FRP plate bond stresses.

Interaction between Flexure and Shear on the Debonding of RC Beams Retrofitted with Compression Face Plates

Steel and FRP plating reinforced concrete structures is increasingly being used for retrofitting. Plates can be bonded to any surface of a beam or slab, although it is common practice to adhesively bond plates to the tension faces. The addition of these tension face plates reduces the sectional ductility of the beam. Furthermore, these tension face plates are prone to premature debonding because the stress concentrations induced by these plates overlap with those induced by the tension reinforcing bars adjacent to the plate. Solutions to these two problems, which are the subject of this paper, consist of: adhesively bonding plates to the compression faces to counterbalance the tension face plates and, hence, improve the beam sectional ductility; and to extend the tension face plates, in continuous beams, past the points of contraflexure so that they terminate in a compression face. In this paper, eleven new tests on 340 mm deep beams are presented that show that compression face plates are less prone to debonding than tension face plates.

Sensitivities of Strength and Ductility of Plated Reinforced Concrete Sections to Preexisting Strains

Existing reinforced concrete ~RC! beams are commonly enhanced in flexure by bonding steel or fiber-reinforced polymer ~FRP! plates to their tension faces. At the time of plating, preexisting loads, such as dead loads, are present on the beams. Although these loads clearly do not induce strains in the plates, flexural capacity design calculations for plated beams using RC theory tacitly incorporate the corresponding fictitious preexisting strains in the plates. If the plates are elastic at section flexural failure, as might be the case for steel plates and is always the case for FRP plates, this design approach underestimates the area of plate required for a given increase in flexural capacity, thus giving a weaker plated RC section than required. For steel-plated sections in which both the internal steel and plate steel yield before concrete crushing occurs, preexisting strains do not influence the area of plate required, but they do delay yield and so reduce ductility. In such cases, neglect of preexisting strains does not affect strength, but it does lead to overestimate of available ductility. This has implications for design of statically indeterminate plated RC beams. Owing to uncertainties in parameters such as creep and differential settlement, preexisting strains do not lend themselves to accurate evaluation. Hence it seems prudent, as a first step, to establish the sensitivity of the flexural failure behavior of plated RC sections to varying preexisting strains. In this paper, mechanical models for plated RC section flexural behavior, which allow for steel and concrete material nonlinearities and for preexisting strains, are presented. The models are first verified by comparison with experimental data, and are then used to determine areas of FRP or steel plating required for stated flexural capacity increases of a given RC section, based on either ignoring or fully recognizing varying levels of preexisting strain. The moment-curvature characteristics, based on the models, of the latter plated RC sections are then presented, using the preexisting strains considered at the design stage. The results confirm that both the ductility and strength of plated sections are appreciably sensitive to preexisting strains. It is concluded that existing approaches for design of plating for RC members should take cognizance of these potentially debilitating effects of preexisting strains.

Comparison of strength and damage for notched FRP plates made by injection molding with that from machining

The strength and damage for two kinds of notched specimen have been investigated. We used an injection molded specimen (IM specimen) made by injection molding using a metal mold of a notched specimen, and a machined specimen (M specimen) made from plate by machining. The orientation of the fiber near the notch roots in the IM specimen and the M specimen is slightly different. The investigation was accomplished by obtaining experimental data of the static tension and fatigue tests on the notched plate of a short glass fiber-reinforced polycarbonate. To evaluate the damage near the notch root, we measured the luminance distributions by means of a luminance-measuring system with a CCD camera. The stress concentration and the similarity of stress distribution near the notch root of the IM specimen were compared with those of the M specimen. For the two kinds of specimen, for both of which the maximum elastic stress, σ max, and notch-root radius ρ were equal to each other, the strength and the process of damage initiation were similar under static tension. On the other hand, the number of loading cycles to fatigue damage initiation of the M specimen was fewer than that of the IM specimen.

Role of Bond in RC Beams Strengthened with Steel and FRP Plates

This paper looks at the problem of predicting the stiffness, load capacity, and failure modes of RC members strengthened in bending with bonded steel or carbon-fiber--reinforced plastic thin plates. A critical issue of this strengthening technique is that, when the plate debonds, the load capacity suddenly drops and the failure mode is typically brittle. Because of the concrete cracking diffusion and the yielding of the steel rebars, a significant amplification of the bond stresses takes place at the beam-plate interface. Delamination occurs when the bond strength is reached locally. To properly describe and adequately predict the behavior of the strengthened beams, a displacement-based fiber beam model is used. Bond slip between the beam and the plate is included by assuming separate displacement fields in the beam and in the strengthening plate. The proposed model is used to confirm and investigate distinct failure modes observed in experimental investigations. The discussion is limited to shallow beams, where shear deformations are neglected.

Analysis and design of FRP externally-reinforced concrete beams against debonding-type failures

Epoxy-bonding of FRP plates to the tensile face of RC beams has been shown to be an effective repair and strengthening technique. However, local failure by debonding or ripping of concrete cover has been reported in experiments to be a likely mode of failure due to high interfacial shear and normal stress concentrations. Predictive models for finding the interfacial shear stress have been reviewed and evaluated using experimental data reported in the literature. The most critical parameters governing the interfacial shear strength and stress as determined by the models were also examined. Through understanding of the conditions that result in debonding failure, a better approach towards designing FRP-plated RC beams against this mode of failure might be achieved.

Shear Strength of RC Beams Strengthened with Bonded Steel or FRP Plates

Bonding by epoxy resins of metallic or nonmetallic plates to the tension face of a reinforced concrete (RC) member (i.e., plate bonding technology) is now a widely used technique to retrofit/upgrade existing RC structures that have been damaged or are structurally inadequate. To ensure successful and cost-effective applications, engineers must improve their knowledge of the actual behavior of these structures, especially with regard to the interaction mechanisms between concrete and the bonded plate. This paper presents a truss model capable of describing the ultimate behavior of externally bonded RC beams. The effectiveness of the proposed approach is validated by comparing the obtained numerical results with some experimental data that is available in the literature.

K-0931 引張りを受ける短繊維強化PC切欠平板における微小破壊(J05-5 強度・破壊機構解析(2))(J05 複合材料の加工と評価)

An experimental program is presented which examines the microfracture in the damaged zone near the notch root of FRP plates. This is accomplished by observation of the damaged zone in notched plates of a glass fiber-reinforced polycarbonate under tension. The process of initiation and growth of damage was measured by means of the luminance measurement technique with a CCD camera during loading and unloading in tension tests. Closer observation on the cracks on the notch root surface revealed that numerous microcracks initiated on the notch root at the early stage. Several microcracks joined together and grew into a crack. The process of initiation and growth of the microcracks produced the decline of luminance near the notch root.

Free Vibrational Responses of FRP Composite Plates: Experimental and Numerical Studies

A combined experimental and numerical study of the free vibration of composite FRP plates has been carried out. Modal testing has been conducted using impact excitation to determine the respective frequency response functions from which the modal parameters are extracted. A finite element method based computer code using an isoparametric element has also been developed to determine the modal characteristics. A commercial finite element package (NISA) has been used to validate the present code. Both theoretical and experimental results are compared and causes of discrepancies are investigated. The experimental data were found to correlate well with the numerical predictions.

ENERGY RELEASE RATES FOR INTERFACIAL CRACK IN LAMINATED STRUCTURES

According to elastic beam theory, in this paper the energy release rate is derived and calculated without the need of a detailed analysis of the crack-tip stress and displacement fields and it is then successfully partitioned into two parts which can reflect the mode I and mode II components. The partitioning of this total value is especially significant because there is considerable ambiguity regarding the values of the energy release rate components at the tip of a crack lying along the interface between two dissimilar isotropic media. An application of the basic solution for concrete stnictures strengthened with steel or FRP plates is made to illustrate its utility.

117 FRP 切欠平板の疲労損傷の金型材と切削材との比較

117 FRP 切欠平板の疲労損傷の金型材と切削材との比較

617 射出成形によるFRP切欠平板の疲労損傷(材料力学III)

617 射出成形によるFRP切欠平板の疲労損傷(材料力学III)

繊維強化プラスチック成形板の屋外ばくろ試験 : 耐候性に及ぼす洗浄と風を伴う降雨の影響

繊維強化プラスチック成形板の屋外ばくろ試験 : 耐候性に及ぼす洗浄と風を伴う降雨の影響