Glass Fiber Reinforced Polymer Sheets Research Articles

Investigation of Monotonic and Cyclic Response of Fiber-Reinforced Polymer Strengthened Beams

This study investigates the hysteretic characteristics, ductility and moment redistribution capacity of beams strengthened with fiber reinforced polymer (FRP) materials. Three different FRP strengthening schemes were tested for their effectiveness in improving strength and ductility of existing, nonconforming reinforced concrete beams. Eight full-size, two-span rectangular beams were considered in pairs, tested under monotonic or cyclic loading. Six were strengthened in flexure using top, bottom, or side face FRP sheets or surface mounted FRP rods, while transversely-wrapped glass FRP sheets were applied in all three pairs to prevent shear failure. One control pair was detailed with conventional steel reinforcement only for ductile flexural response. Results showed that monotonically loaded beams failed in flexure. Unlike top and bottom face strengthened beams, side strengthened beams exhibited superior performance comparable with the control, in terms of overstrength, ductility, and deformation capacity. All beams under increasing amplitude cyclic response were unable to develop the montonic capacity of a flexural mechanism. No matter which method of FRP strengthening had been used, cyclic behavior exhibited severe pinching and gradual strength and stiffness degradation.

Behavior of Split Timber Stringers Reinforced with External GFRP Sheets

A large number of timber bridges are at the end of their service life in North America and the prohibitive costs of replacement make owners face the challenge of developing efficient rehabilitation techniques. This paper presents the results from an experimental program of testing old full scale timber stringers with longitudinal splits. Stringers were reinforced for shear and bending using glass fiber-reinforced polymer (GFRP) sheets. A total of nine full-scale Douglas-fir beams were tested in three-point bending after strengthening for flexure and shear with GFRP sheets. Horizontal shear forces in shear reinforcement were calculated using a simplified model. Beams that failed by debonding of shear reinforcement, failed at horizontal shear forces within the range of 150–266 kN . Design charts were constructed on the basis of these calculated forces to simplify the design of shear reinforcement for different sizes and locations of splits.

Corrosion of steel reinforcements embedded in FRP wrapped concrete

A large number of reinforced concrete (RC) structures that have been damaged due to corrosion of steel reinforcements are rehabilitated with fiber-reinforced polymer (FRP) composites. This paper investigates the progression of corrosion of steel in concrete after it has been treated with surface bonded FRP. Concrete cylinders with embedded steel bars are immersed in salt water and anodic current is passed through the reinforcement to initiate cracking in concrete due to accelerated corrosion of steel. Glass and carbon FRP sheets have been adhesively bonded on the cylinders. Anodic current was continued for specified times. Pull out strength, mass loss, half cell potential of the steel and cell voltage have been reported as metrics of performance of the samples. FRP wrapped samples have shown substantially higher resistance to corrosion.

유리섬유시트로 휨보강된 RC보의 부착파괴 방지 상세에 관한 실험적 연구

This study investigates the failure mechanism of RC beams strengthened with GFRP (glass fiber reinforced polymer) sheets. After analyzing failure mechanisms, the various methods to prevent the debonding failures, such as increasing bonded length of GFRP sheets, U-shape wrappings and epoxy shear keys are examined. The bonded length of GFRP sheets are calculated based on the assumed bond strengths of epoxy resin. The U-shape wrappings are either adopted at the end or center of the CFRP sheets bonded to the beam soft. The epoxy shear keys are embedded to the beam soft to provide sufficient bond strength. The end U-wrappings and the center U-wrappings are conventional, while epoxy shear keys are new details developed in this study. A total six half-scale RC beams have been constructed and tested to investigate the effectiveness of each methods to prevent debonding failure of GFRP sheets. From the experimental results, it was found that increasing bonded length or end U-wrappings do not prevent debonding failure. On the other hand, the beams with center U-wrappings and shear keys reached an ultimate state with their sufficient performance. The center U-wrappings tended to control debonding of the longitudinal GFRP sheets because the growth of the longitudinal cracks along the edges of the composites was delayed. In the case of shear keys, it was sufficient to prevent debonding and the beam was failed by GFRP sheets rupture.

Stress Transfer between FRP Laminates and Concrete through Deteriorated Concrete Surfaces

This study investigated the mechanism of stress transfer between glass and carbon fiber-reinforced polymer (FRP) laminates and concrete beams with deteriorated surfaces. Thirty-six beams were prepared with either a solid concrete cross section, or with a weak concrete layer at the surface, simulating the state of a deteriorated surface. The beams were reinforced with glass or carbon FRP sheets and tested in flexure. Strain development in the laminate and in the concrete layers was recorded and analyzed. The mode of failure changed from shear within the deteriorated layer of concrete to delamination at the interface between the resin and the concrete in the solid high-strength concrete. A significant amount of stress was transferred between the FRP laminates and the concrete surface probably by residual frictional stresses after shear cracks developed in the deteriorated layer, leading to a remarkable load bearing capacity of these beams.

Behavior of FRP Strengthened Infill Walls under In-Plane Seismic Loading

The present paper investigates the suitability and effectiveness of fiber-reinforced polymers (FRP) in strengthening and/or repairing unreinforced masonry infill walls in reinforced concrete frames which are subjected to in-plane seismic/cyclic loading. For this purpose, a detailed experimental program was conducted. Specimen geometry, test setup, instrumentation, and a loading procedure that simulates earthquake loading are presented in a detailed fashion. Results of experimental observations are discussed in the form of load-displacement hysteretic loops and envelopes; column profiles; strain diagrams, and wall shear distortion. The test results, in general, indicate that the use of glass FRP (GFRP) sheets as strengthening materials provides a degree of enhancement to the infill wall, upgrades its deformation capacity, and makes the wall work as one unit. These results thus show great potential for externally bonded GFRP sheets in upgrading and strengthening the infill walls under in-plane seismic loads.

FRP로 횡구속된 콘크리트의 응력-변형률 거동 특성

Recently, fiber-reinforced plastic(FRP) wraps are blown as an effective material for the enhancement and rehabilitation of aged concrete structures. The purpose of this investigation is to experimentally investigate behavior of concrete cylinder wrapped with FRP materials. Experimental parameters include compressive strength of concrete cylinder, FRP material, and confinement ratio. This paper presents the results of experimental studies on the performance of concrete cylinder specimens externally wrapped with aramid, carbon and glass fiber reinforced Polymer sheets. Test specimens were loaded in uniaxial compression. Axial load, axial and lateral strains were investigated to evaluate the stress-strain behavior, ultimate strength ultimate strain etc. Test results showed that the concrete strength and confinement ratio, defined as the ratio of transverse confinement stress and transverse strain were the most influential factors affecting the stress-strain behavior of confined concrete. More FRP layers showed the better confinement by increasing the compressive strength of test cylinders. In case of test cylinders with higher compressive strength, FRP wraps increased the compressive strength but decreased the compressive sham of concrete test cylinders, that resulted in prominent brittle failure mode. The failure of confined concrete was induced by the rupture of FRP material at the stain, being much smaller than the ultimate strain of FRP material.

Effectiveness of GFRP Sheets for Shear Strengthening of Timber

The objective of this study was to develop a cost-effective shear-strengthening technique for timber stringers that is environmentally friendly and leads to a durable structure. Testing was performed on creosote-treated Douglas fir beams, with dimensions of 100×400×3,650 mm , removed from a 40 year old bridge. Two strengthening schemes were investigated; incorporating vertical and diagonal glass fiber-reinforced polymer (GFRP) sheets applied to both shear spans. The diagonal scheme proved effective in increasing the average ultimate load, flexural stiffness, and deformability of the beams. Performance of the members reinforced using the vertical scheme, however, was poor compared to diagonally reinforced beams. The contribution of the diagonal sheets to the shear capacity of the stringers was around 12% at service loads and 40% at ultimate load. In conclusion, this study has shown that diagonal GFRP sheets are more effective than vertical sheets in shear-strengthening timber stringers with horizontal spli...

FRP-confined concrete members: Axial compression experiments and plasticity modelling

The behaviour and modelling of circular sections confined by Fibre Reinforced Polymer (FRP) reinforcement have been examined extensively recently. This study concentrates on FRP confined specimens with square sections under axial loading. An experimental programme was designed in which 101 prismatic concrete specimens of different strengths were tested. The specimens had dimensions of 200×200×320 mm. They were externally confined by carbon or glass FRP sheets in different confinement volumetric ratios. Monotonic as well as cyclic axial compressive loads were applied. The testing results indicate that square concrete sections, properly confined by FRP reinforcement, can achieve high levels of strength and ductility. It was found that glass FRP is less effective in terms of strength and ductility enhancement when compared with carbon FRP confinement of same axial rigidity for low volumetric ratios. A plasticity model capable of reproducing hardening–softening behaviour is also presented here to predict the response of the FRP confined specimens. The model generates the stress–strain curves for axially loaded square columns confined by FRP sheets or tubes. The predicted curves are compared successfully to the present as well as other published experimental data.

Load–deflection behavior of RC beams strengthened with GFRP sheets subjected to different environmental conditions

An investigation to examine the durability of reinforced concrete beams strengthened with glass fiber reinforced polymer (GFRP) laminates is performed. A total of 84 beam specimens were prepared for this study. The performance of these specimens was assessed through evaluating the flexural capacity and load–deflection relationships of the beams after placing them in different environments directly or indirectly with simulated field condition for a specified period of time. The specimens were divided into six categories which include controlled laboratory environment (unexposed category), outside environment (direct exposure to hot–dry field conditions), wet–dry normal water environment, wet–dry saline (NaCl) water environment, and wet–dry alkaline (NaOH) environment. Each category consisted of unstrengthened and strengthened beams. Furthermore, some of the specimens of the hot–dry field exposure were coated with protection paint against ultra violet (UV) rays. The specimens of different wet–dry environments were exposed to a time cycle of two weeks inside the solution and two weeks outside the solution. The test results carried out after 6, 12 and 24 months of exposure to different environmental conditions, show that none of the aforesaid environmental conditions have a noticeable influence on the flexural strength of the beams.

THE PERFORMANCE OF LIGHTWEIGHT CONCRETE CONFINED BY FIBER COMPOSITES

Degradation of infrastructure due to overloading and corrosion is a major concern. FRP materials are now increasingly being used in the construction industry. Confinement of circular concrete members using FRP is a popular application. As such, studying the performance of concrete members confined by FRP jackets is quite important for both rehabilitated and new structures. This thesis presents results of an experimental study on the performance of concrete cylinders confined with glass-FRP (GFRP) sheets, carbon-FRP (CFRP) sheets. While the subject of FRP-confinement of circular concrete columns has been extensively studied experimentally and analytically, more emphasis has typically been put on the characteristics of the FRP jackets in comparison to the concrete core properties. In this paper, the performance of the lightweight concrete core on FRP jackets is explored in order to simulate the worst case scenario in old structures that were built several decades ago, and maximize the damaging effect of concrete durability. This study simulates wrapping of circular columns with FRP sheets for retrofitting applications; concrete core with different strengths has been used to evaluate the different levels of confinement induced by GFRP and CFRP jackets of different thicknesses, specimens were tested to failure under axial compression, the study showed that wraps provide substantial increase in strength and ductility of different lightweight concretes. However, increasing the strength of concrete core shows a decreasing in the confined strength gain of tested specimens with any improvement in ductility.

Load Capacity of Concrete Masonry Block Walls Strengthened with Epoxy-bonded GFRP Sheets

Epoxy bonding a thin layer of composite materials to the exterior surfaces of unreinforced masonry (URM) walls forces the individual brick or block elements to act as an integrated system. The high tensile strength of composite materials can be utilized to increase the shear and flexural capacity of URM walls significantly. This article presents the results of the experimental work carried out to investigate the capability of glass fiber reinforced polymer (GFRP) laminates in strengthening the concrete block walls subjected to out-of-plane and in-plane vertical and lateral stresses. A significant strength increase was observed for all strengthened specimens. Based on deformation compatibility and force equilibrium, simple design equations are presented to estimate the strength of masonry walls and their possible mode of failure. An excellent agreement between measured and predicted values of ultimate strength of wall specimens has been observed.

Postrepair Fatigue Performance of FRP-Repaired Corroded RC Beams: Experimental and Analytical Investigation

This paper presents the results of an experimental and analytical study of the fatigue performance of corroded reinforced concrete (RC) beams repaired with fiber-reinforced polymer (FRP) sheets. Ten RC beam specimens (152×254×3,200 mm) were constructed. One specimen was neither strengthened nor corroded to serve as a reference; three specimens were corroded and not repaired; another three specimens were corroded and repaired with U-shaped glass FRP sheets that wrapped the cross section of the specimen; and the remaining three specimens were corroded and repaired with U-shaped glass FRP sheets for wrapping and carbon-fiber-reinforced polymer (CFRP) sheets for flexural strengthening. The FRP sheets were applied after the main reinforcing bars were corroded to an average mass loss of 5.5%. Following FRP repair, some specimens were tested immediately to failure, while the other repaired specimens were subjected to further corrosion before being tested to failure to investigate their postrepair (long-term) per...

Strengthening reinforced concrete beams using prestressed glass fiber-reinforced polymer-Part I: Experimental study

This work is aimed at studying the strengthening of reinforced concrete (R. C.) beams using prestressed glass fiber-reinforced polymer (PGFRP). Carbon fiber-reinforced polymer (CFRP) has recently become popular for use as repair or rehabilitation material for deteriorated R. C. structures, but because CFRP material is very stiff, the difference in CFRP sheet and concrete material properties is not favorable for transferring the prestress from CFRP sheets to R. C. members. Glass fiber-reinforced polymer (GFRP) sheets with Modulus of Elasticity quite close to that of concrete was chosen in this study. The load-carrying capacities (ultimate loads) and the deflections of strengthened R. C. beams using GFRP and PGFRP sheets were tested and compared. T- and Z-shaped beams were used as the under-strengthened and over-strengthened beams. The GFRP sheets were prestressed to one-half their tensile capacities before being bonded to the T- and ~-shaped R. C. beams. The prestressed tension in the PGFRP sheets caused cambers in the R. C. beams without cracks on the tensile faces. The PGFRP sheets also enhanced the load-carrying capacity. The test results indicated that T-shaped beams with GFRP sheets increased in load-carrying capacity by 55% while the same beams with PGFRP sheets could increase load-carrying capacity by 100%. The Z-shaped beams with GFRP sheets could increase load-carrying capacity by 97% while the same beams with PGFRP sheets could increase the loading-carrying capacity by 117%. Under the same external loads, beams with GFRP sheets underwent larger deflections than beams with PGFRP sheets. While GFRP sheets strengthen R. C. beams, PGFRP sheets decrease the beams' ductility, especially for the over-strengthened beams (⊥shaped beams).

Punching Shear Behavior of Flat Slabs Strengthened with Fiber Reinforced Polymer Laminates

This article reports the test results of seven full-scale reinforced concrete slab-column edge connections strengthened against punching shear using different methods. In this study, three slabs contained openings in the vicinity of the column, and the other four were without openings. The dimensions of the slabs were 1,540X1,020X120 mm with square columns (250X250mm). The openings in the specimens were square (150X150 mm) with the sides parallel to the sides of the column. The slabs were reinforced with an average reinforcement ratio of 0.75 percent. Except for the two reference slabs, two different strengthening techniques were considered. Technique I applies externally bonded fiber reinforced polymer (FRP) flexible sheets on the slab around the column in two schemes with one or two layers of FRP sheets glued to the tension face or both tension and compression faces of the slab. Both glass and carbon FRP sheets were considered. Technique II applies externally bonded FRP sheets using either the first or second scheme combined with installing steel bolts through holes across the slab thickness around the column. Based on the test results, the authors conclude that the presence of FRP sheets and steel bolts substantially increased the punching capacity of the connections. Code design expressions were conservative in predicting the experimental results.

Shear Strengthening Masonry Panels with Sheet Glass-Fiber Reinforced Polymer

This paper investigates strengthening masonry walls using glass-fiber reinforced polymer (GFRP) sheets. An experimental research program was undertaken. Both clay and concrete brick specimens were tested, with and without GFRP strengthening. Single-sided strengthening was considered, as it is often not practicable to apply the reinforcement to both sides of a wall. Static tests were carried out on six masonry panels, under a combination of vertical preload, and in-plane horizontal shear loading. The mechanisms by which load was carried were observed, varying from the initial, uncracked state, to the final, fully cracked state. The results demonstrate that a significant increase of the in-plane shear capacity of masonry can be achieved by bonding GFRP sheets to the surface of masonry walls. The experimental data were used to assess the effectiveness of the GFRP strengthening, and suggestions are made to allow the test results to be used in the design of sheet GFRP strengthening for masonry structures.

Effectiveness of Composites in Earthquake Damage Repair of Reinforced Concrete Flared Columns

A method to utilize fiber composites for rapid repair of earthquake damaged flared columns was developed. Two 0.4-scale reinforced concrete columns that had been tested to failure in previous research were used. Both columns had been subjected to slow cyclic loads and had failed due to low-cycle fatigue of the longitudinal bars. To repair the columns, the damaged concrete in and around the plastic hinge was removed and the steel bars were straightened. Low-shrinkage, high-strength concrete grout was placed in the column afterward. The broken longitudinal bars were not replaced. Rather, glass and carbon fiber reinforced polymer (FRP) sheets with fibers running in the axial direction of the column were added to provide flexural strength to the columns. Additionally, glass FRP sheets with horizontal fibers were attached on the column to provide confinement and shear strength. Cyclic tests of the repaired columns indicated that the method to restore the strength was effective. Analysis using conventional constitutive relationships led to a close estimate of the lateral load response of the models.

Numerical Modeling of Concrete Confined by Fiber-Reinforced Composites

Lateral confinement of reinforced concrete columns can significantly increase their lateral deflection capability and load-carrying capacity. While such retrofits were initially completed using steel jackets, fiber-reinforced polymer (FRP) composites have been used successfully and extensively for seismic and blast upgrades. Numerical modeling of such structures requires the use of a concrete material model that can accurately represent the volumetric behavior of concrete under triaxial stress states, to capture the interaction between concrete expansion and the resulting stress increase in the confining jacket. Test data by Suter and Pinzelli, Karbhari and Gao, and Mirmiran and Shahawy on concrete cylinders and prisms confined by aramid, carbon, and glass FRP sheets are analyzed numerically. The concrete material model used was developed for the study of the effect of blast loading on reinforced concrete structures and was verified and validated for a variety of triaxial stress paths. The numerical analyses closely reproduce the strength enhancements observed in the test specimens for various levels of confinement. The model also confirms the observed inefficiency of low levels of lateral confinement and the superior enhancement provided by circular cross sections as compared to rectangular ones.

Cyclic Flexure Tests of Masonry Walls Reinforced with Glass Fiber Reinforced Polymer Sheets

The research work reported here investigates the out-of-plane flexural behavior of masonry walls reinforced externally with glass fiber reinforced polymer (GFRP) sheets and subjected to cyclic loading. A full-scale test program consisting of eight wall specimens was conducted. Nine tests were performed, in which three parameters were studied. These included the level of compressive axial load, amount of internal steel reinforcement, and amount of externally bonded GFRP sheet reinforcement. Of the three parameters studied, varying the amount of GFRP sheets was the only parameter that significantly affected the behavior of the walls. The GFRP sheet reinforcement governed the linear response of the bending moment versus centerline deflection hysteresis. Increasing or decreasing the amount of GFRP sheet reinforcement either increased or decreased both the wall stiffness and the ultimate strength, respectively. Except for visible cracks, the walls maintained their structural integrity throughout the out-of-plane cyclic loading. The unloading/reloading paths for successive loading cycles were similar, indicating little degradation. Thus, the general behavior of the walls was very predictable. The system, therefore, could be used to advantageously rehabilitate older masonry structures that are inadequately reinforced to withstand seismic events. A simple model of the behavior is also presented to allow for the evaluation of the strength and deformation characteristics of these elements.

Seismic rehabilitation of beam–column joint using GFRP sheets

Techniques for upgrading reinforced concrete beam–column joints are proposed. The test specimens represent a typical joint that was built in accordance to pre-1970s’ codes. The objective of the rehabilitation is to upgrade the shear strength of these joints and reduce the potential for bond-slip of the bottom bars of the beam. Glass fibre-reinforced polymer (GFRP) sheets are wrapped around the joint to prevent the joint shear failure. GFRP sheets are attached to the bottom beam face to replace the inadequately anchored steel bars. Three beam–column joints are tested; namely, a control specimen and two rehabilitated specimens. The specimens are tested under quasi-static load to failure. The control specimen showed combined brittle joint shear and bond failure modes while the rehabilitated specimens showed a more ductile failure mode. A simple design methodology for the rehabilitation scheme is proposed.