Glass Fiber Reinforced Polymer Sheets Research Articles

Internal GFRP Reinforcement of Low-Grade Maritime Pine Duo Timber Beams.

This paper presented an experimental structural-scale test campaign used to analyze the flexural behavior of low-grade maritime pine (Pinus pinaster Ait.) duo timber beams reinforced with an internal glass fiber-reinforced polymer (GFRP) sheet. For this purpose, thirty (30) unreinforced duo beams and thirty (30) duo beams internally reinforced with a unidirectional GFRP sheet with an areal mass of 1200 g/m2 were produced and tested. The addition of a low GFRP reinforcement ratio (1.07%) in the tension zone of the duo beams provided an average improvement of 8.37% in bending stiffness (EI) and an increase of up to 18.45% in ultimate moment capacity. In addition to this improved bending behavior, the internal GFRP reinforcements seemed to decrease the influence of wood singularities and wood heterogeneity on mechanical properties, which allowed for better characteristic values to be reached and for the achievement of results with less variability.

Comparison Experimental Study on Retrofitting Methods of Partially Damaged Timber Columns

This paper presented the experimental study on two different strengthening methods for partially damaged timber columns, GFRP (Glass Fiber Reinforced Polymer) sheets and sprayed FRP (Fiber Reinforced Polymer). Detail comparison was carried out between the mechanical properties of 25% or 50% damaged timber short columns under uniaxial or biaxial eccentric compression. The ultimate bearing capacity of retrofitted columns increased obviously. The biggest improvement after SFRP (Sprayed FRP) retrofitting was 62.7%. Compared with that of undamaged columns, the ultimate bearing capacity of partially damaged columns after retrofitting was recovered up to 48 to 98%. SFRP method is a reasonable and better substitute method of GFRP sheets retrofitting.

Durability Test on the Bond Strength between SFRP Layer and Masonry Surface

The mechanical properties of masonry structural members strengthened by FRP (Fiber Reinforced Polymer) are affected by the bond strength of the reinforcement interface, in addition to the strength of the material FRP itself. This project is aimed at the new technology of Sprayed Fiber Reinforced Polymer Composites (SFRP), which is currently attracting attention. The bond strength between SFRP layer and masonry surface under high-humidity condition during strengthening construction and dry-wet cycle conditions after reinforcement were studied by experimental method. Different masonry substrates and different reinforcement methods were set as the test parameters. It is concluded that, compared with the currently used GFRP (Glass Fiber Reinforced Polymer) sheets reinforcement method, the SFRP reinforcement method has an significant improvement in the bond strength and the durability.

Shear strengthening of RC beams using GFRP sheets

This paper presents an experimental investigation on the shear behaviour of RC beams strengthened with externally bonded glass fibre reinforced polymer (GFRP) sheets. The externally applied GFRP technique is significantly effective to enhance the ultimate load carrying capacity of RC beams. Two beams without GFRP and nine beams wrapped in different lay-up patterns with one/two layers of GFRP sheets have been tested for shear under two-point loading. Loads at first crack of beam/delaminating of GFRP, tearing point of GFRP and ultimate failure of the beam has been noted and types of failure have also been observed. Thereafter, a critical discussion is made with respect to increase in the strength of retrofitted beams with respect to the beam without GFRP in order to explore the optimal use of GFRP for strengthening the RC beams. The comparison is also made between the shear strength obtained from experimental results and that predicted from different design proposals available in the literature.

Strengthening of shear deficient RC deep beams using GFRP sheets and mechanical anchors

This paper presents the test results of an experimental study on shear deficient reinforced concrete (RC) deep beams strengthened with externally bonded glass fibre reinforced polymer (GFRP) sheets and mechanical anchors. A total of nine deep beams are prepared. One beam is kept as un-strengthened. Four beams are strengthened using GFRP sheets only at shear spans by varying the number of layers. The remaining four beams are strengthened using both GFRP sheets and mechanical anchors at shear spans. The shear capacity, failure mode, and deflections are studied with respect to the different strengthening techniques. The optimum enhancement in shear capacity of these beams is observed as 25.64% and 55.5% for GFRP strengthened beams and GFRP strengthened anchored beams, respectively with respect to the un-strengthened beam. Moreover, the experimental results are also compared with the results predicted from the design guidelines and models available in the literature, which shows good agreement.

Effect of External Expanded Polystyrene (EPS) Panels on Slabs Subjected to Impact Load

The current research addresses the effect of impact load on Reinforced Concrete (RC) slabs strengthened by Expanded Polystyrene (EPS) and/ or Glass Fiber Reinforced Polymer (GFRP) sheets. A total of five slabs were tested; one control specimen without EPS or GFRP, two slabs with two EPS panels with different densities on their impact side, one slab with GFRP sheet on impact side and finally one slab with EPS panel on impact side and GFRP on the tension side. To test the effect of the presence of EPS panels and GFRP sheets, the RC slabs were supported on a table centered below a drop tower. A weight of 3.245 kg was dropped freely from the drop tower to hit the slab. The energy that the slab could withstand was calculated based on the weight, height and number of drops. Results varied according to the variation of parameters; the combination of EPS on the impact side and GFRP on the tension side yielded double the energy the specimen could withstand compared to the control specimen. Results also showed that EPS acted like a cushion that is capable of absorbing a portion of the impact energy. Another finding is that the higher the density of the EPS the more energy it can absorb. This paper proves that EPS is a promising material that could be utilized in reducing the effects of impact loads on concrete structures.

Enhancing the interface friction between glass fiber-reinforced polymer sheets and sandy soils through sand coating

ABSTRACT Soil-pile interface friction is an important geotechnical engineering factor to be considered in achieving a safe and cost-effective design. Conventional materials such as concrete, steel, and wood exhibit serious long-term soil substructure problems, particularly with regard to durability, deterioration, and corrosion. Fiber-reinforced polymer (FRP) composites are potential alternatives for addressing these long-term problems. This paper describes the results of an experimental study of the interface friction between sandy soil and glass FRP (GFRP) sheets coated with different ratios of sand per unit of surface area. A direct shear test was used to study 18 different groups of GFRP specimens. The test parameters were the amount of silica sand coating and normal stresses in the direct shear tests. The GFRP specimens were sheared against three types of soil: sand, silty sand, and sandy lean-clay, of which the first two were used in both dense and loose states. The experimental results showed that coating the GFRP sheets with silica sand was effective in enhancing the interface friction with sandy soils under different normal stresses. A pile implication analysis was also performed to compare the effect of sand coated GFRPs on the load capacity of friction piles with different length to diameter ratios.

Improving the resistance of concrete panels to hard projectile impact

In this article, the response of nine plain concrete panels to an impact of hard projectiles was examined in an experimental study. The tests were planned with an aim to observe the influence of compressive strength on the performance of concrete under impact loading. Concrete panels with compressive strengths within the range of 26 to 92 MPa subjected to impact by 23 mm hard projectile at velocities within the range of 270 to 348 m/s were studied. Also, using a glass fiber reinforced polymer sheet, as a liner on the rear face of the plain concrete panel, to strengthen the panel was examined. The experimental results indicate that strengthening concrete panel with a rear glass fiber reinforced polymer sheet showed more satisfactory performance under the impact load than increasing compressive strength of concrete. Also, the use of glass fiber reinforced polymer sheets as rear liners in addition to increasing the concrete strength showed superior performance of concrete panels against impact; it is recommended to be used in protective structures.

GFRP-sheet strengthened RC beams after seawater immersion under monotonic and fatigue loads

This study aims to analyse glass fibre reinforced polymer (GFRP) reinforcement on reinforced concrete beams under fatigue and monotonic loads influenced by sea water. The research was conducted in the laboratory on flexural concrete beams with the quality of f´c= 25 MPa. One normal concrete flexural beam (BN) with repetitive load was without seawater and no reinforcement. One flexural beam was without sea water immersion but with GFRP-reinforcement. Another flexural beam reinforced by GFRP sheets is immersed in a pond containing seawater with time variations up to 12 months. The test was performed with a fatigue load of 1.25 Hz frequency to failure. The results showed an increase in capacity due to 58.3% for GFRP-reinforcement. There is a decrease in the capacity of GFRP sheet influenced by seawater immersion. The same trend with the decrease in ductility occurred in the flexural beam to 14% due to seawater immersion. Maximum beam failure repetition occurred at 1,230,000 cycles on beam with reinforcement (BF). The failure occurring in the flexural beam was preceded by the failure of the attachment between the concrete and the GFRP sheet at the load centre (mid of span) slowly to the support until failure (debonding) initialized. The GFRP-S bonding capacity to the concrete skin has decreased in 12 months by 15%. Therefore, there is a significant effect of decreasing strength due to fatigue loads and seawater immersion.

Experimental and numerical study on FRP-upgraded RC beams with large rectangular web openings in shear zones

This paper studies experimentally and numerically the effect of large rectangular web openings in the shear zone on the response of unstrengthened and upgraded reinforced concrete (RC) beams. Studied parameters were opening size and strengthening scheme. Seven simply supported RC beams were prepared and tested under the action of two point loads. Beams comprised of one reference specimen without opening (i.e. solid beam) and six beams constructed with two large rectangular web openings, symmetrically located near supports. Out of the six beams with openings, two specimens were unstrengthened and four beams were strengthened with two fiber reinforced polymer (FRP) strengthening schemes. In one of the schemes, beams were strengthened using two layers (0°/90°) of carbon FRP (CFRP) sheets. However, the second scheme was a hybrid system comprising of glass FRP (GFRP) sheets anchored with bolted steel plates. The numerical models were prepared and the results of finite element (FE) analysis were validated with experiments. The validated numerical analysis was then used for some useful parametric studies in which the effect of different parameters was investigated.

The long-term evaluation of FRPs bonded to timber

This research investigated the long-term environmental effects on bond strength at the interface between fiber- reinforced polymers (FRPs) and timber. A total of 581 timber specimens were bonded with seven types of FRP sheets (unidirectional and bidirectional glass, carbon, aramid, and hybrids) using a wet lay-up technique. The specimens were exposed to acidic, alkaline, fresh water, and sea water solutions with pH of 2.5, 7, 7.25, 10, and 12.5 for 1, 3, 6, 9, and 12 months. A chamber was also used to simulate ultraviolet radiation after 6 months. A series of single-lap shear tests were then conducted to determine the interfacial bond strength reduction. The results showed that bidirectional carbon and glass FRP sheets demonstrated better bond strength as compared to unidirectional carbon and glass FRP sheets in most cases after exposure to the chemical solutions and ultraviolet radiation. Moreover, acidic and sea water solutions, respectively, had the most and the least effects on the reduction of bonds at the interface between hybrid FRPs and timber. Meanwhile, bidirectional aramid FRPs showed high deterioration in the interfacial bond strength under the effect of water and alkaline (pH 12.5) solutions. Finally, the failure modes on timber substrates were explored and classified.

Hybrid confinement of concrete through use of low and high rupture strain FRP

This study investigates the behavior mechanisms and efficiency of concrete confinement formed with the hybridization of two different types of fiber reinforced polymer (FRP) sheets with the aim of utilizing superior features of these two FRP types. The originality of the study is to combine carbon or glass FRP sheets (CFRP or GFRP) with polyethylene terephthalate FRP sheets (PET-FRP), which have different mechanical features, particularly in terms of deformability. While CFRP and GFRP sheets have relatively high tensile strength and low rupture strain capacity, PET-FRP sheets have low tensile strength but remarkably high rupture strain capacity. Hybridization is performed through external wrapping of two different FRP sheets in a successive way. 24 standard cylinder concrete specimens are tested under compression loading. The test variables of the study are the types and number of layers of the inner and outer FRP constituents of hybrid jacket. Test results show that hybrid confinement of FRP sheets with low and high rupture strain capacities offers an enhanced ductility. Furthermore, it is seen that through the hybridization of FRP sheets with different mechanical properties, stress-strain relationship of FRP confined concrete can be tailored. Several available analytical models developed for stress-strain relationship of the concrete confined with a single type of FRP sheet and one model developed for the hybrid FRP confined concrete are used to predict key stress and strain values of the hybrid confined concrete. Considering the behavior mechanisms of the hybrid confined concrete specimens, several assumptions are made during the application of these models. It is shown that key stress and strain values of hybrid confined concrete can be reasonably predicted.

Strengthening Steel Members with Holes Under Tension Using Unidirectional GFRP Sheets

Steel structure sections are often connected using bolts and rivets, which necessitates the need for holes. These holes provide a zone of failure during loading. In the present work an attempt is made to strengthen the steel members under tensile loading with hole provision for bolts, using Glass Fiber Reinforced Polymer (GFRP) sheets. The performance of FRP wrapping is assessed by changing the angle of orientation of fiber. The experimental investigation is conducted for one hole, two hole and staggered hole arrangement and the results are compared with finite element analysis. The difference between experiment and finite element modeling are within allowable limits. From the study it is found that GFRP wrapping with 0° orientation of fiber is the most suitable in terms of ultimate strength for all the three hole configurations.

Static Analysis of Reinforced Concrete Pipe Strengthened with GFRP Laminates

This paper presents a study of reinforced concrete pipe with the application of continuous glass fiber reinforced polymer sheet (GFRP). The pipe material is considered to be composed of reinforced concrete and the pipe is strengthen by using glass fiber reinforced polymer sheet. The reinforced concrete pipe is analyzed with different layers of externally applied GFRP sheet. Analysis is carried out in commercially available ANSYS software. A finite element model is developed for the pipe wherein the material properties as mentioned are used. The solid 186 layered structural solid element has been used for discretization of the model. Two sets of GFRP sheets (4 layer and 8 Layer) were considered for the analysis. Results obtained were compared with the controlled pipe made up of reinforced concrete. Results are presented for simply supported boundary conditions for the pipe. The deformation and stress distribution across the pipe has also been analyzed

Aligning carbon nanofibres in glass-fibre/epoxy composites to improve interlaminar toughness and crack-detection capability

An electric field is used to align carbon nanofibres (CNFs) in the matrix of a glass-fibre reinforced-polymer (GFRP) composite to simultaneously improve the (a) delamination toughness, (b) electrical conductivity, and (c) damage-sensing capability. The CNFs are added to the epoxy resin prior to the manufacture of the GFRP composites. To align the CNFs, an alternating current (AC) electric field of 30 V/mm at 10 kHz is applied across the GFRP sheet throughout the matrix-curing process. The electromechanical force induced by the electric field, applied in the through-thickness direction of the composite sheet, rotates and aligns the CNFs in the direction of the applied electric field prior to the gelation of the epoxy matrix. After curing, the resultant aligned, ‘chain-like’, microstructure of the CNFs in the epoxy matrix significantly enhances both the interlaminar fracture toughness and the through-thickness electrical conductivity of the GFRP composite. Specifically, the addition of 0.7 vol% of randomly-orientated CNFs in the GFRP composite yielded an ∼50% and 25% increase in the values of the mode I fracture toughness pertinent to the initiation, GIci, and steady-state growth, GIcss, of delamination crack, respectively, compared to the control GFRP composite. The alignment of the CNFs, in the transverse direction to the direction of the crack growth, increases the mode I toughness values of GIci and GIcss by ∼100% and ∼80%, respectively, compared to the control GFRP composite. These significant increases are attributable to multiple toughening mechanisms, including debonding of the CNFs from the matrix, void growth of the epoxy matrix, pull-out and rupture of the CNFs. Further, the electric-field induced alignment of the CNFs, in the through-thickness direction, increases the out-of-plane electrical conductivity of the GFRP by about twenty-six times, compared to the GFRP composite containing randomly-orientated CNFs. Of particular interest, the damage-sensing capacity is enhanced for the GFRP composite with aligned CNFs in the epoxy matrix, which stems from the greatly increased out-of-plane electrical conductivity, as confirmed by a modelling study. Therefore, this present work has identified a new strategy to develop GFRP composites with greatly improved delamination toughness, electrical conductivity, and higher crack-detection sensitivity.

Internal reinforcement of laminated duo beams of low-grade timber with GFRP sheets

The purpose of this work is to study the flexural behaviour of Populus×euroamericana I-214 low-grade glulam timber beams, internally reinforced with Glass Fibre Reinforced Polymer (GFRP). To this end, 30 unreinforced beams and 60 reinforced beams, with two ratios of GRFP reinforcement, were produced and tested. Results show an improvement in the flexural behaviour of reinforced beams, with noticeable increases in stiffness (MOE) and ultimate moment capacity (MOR). By using relatively low reinforcement ratios (1.07%, 1.6%) in the tension zone, we have measured an average improvement of 12.1% and 14.7% in stiffness, and an increase up to 23% in moment capacity. GFRP reinforced seems to reduce the influence of timber heterogeneity and singularities (knots, cracks …), which translates into less scattered results and better characteristic values.

Improving the impact resistance of concrete panels by glass fiber reinforced polymer sheets

In this article, the response of 12 plain concrete specimens to an impact of hard projectiles was examined in an experimental study. The tests were planned with an aim to observe the influence of using glass fiber reinforced polymer sheets to strengthen plain concrete panels on the performance of concrete under this type of loading. The main findings show that strengthening plain concrete panels with glass fiber reinforced polymer sheets showed satisfactory performance under the impact load; the glass fiber reinforced polymer sheets can be used for strengthening or upgrading concrete structures to improve their resistance against impact. Also, the location of the glass fiber reinforced polymer sheet affects the front and rear face craters.

Experimental study on durability of strengthened corroded RC columns with FRP sheets in tidal zone of marine environment

The main objective of this paper was to illuminate the effect of marine environmental condition on durability of reinforced concrete (RC)-corroded columns strengthened with carbon fiber reinforced polymer (CFRP) and glass fiber reinforced polymer (GFRP) layers. Small-scale columns were prepared and corroded by an accelerated corrosion process. After strengthening, compressive strength tests were carried out on control and weathered specimens. In this research, a marine simulator was designed and constructed similar to the tidal zone of marine environment in south of Iran which was selected as a case study in this research. Mechanical properties of wrapped specimens were studied after placing them inside the simulator for 3000 hours. Marine environment decreased ultimate strength by 4.5% and 26.3% in CFRP and GFRP-wrapped columns, respectively. In some corroded-columns, strengthening was carried out after replacing damaged cover by self-compacted mortar. In this method, by confining with one layer of CFRP and GFRP, 4.2% and 22.4% reduction in ultimate strength was observed, respectively, after exposure. Furthermore, the elastic-brittle behavior has been verified in this retrofit method. Also results of tension tests revealed, the ultimate tensile strength was degraded by 2% and 28.8% in CFRP and GFRP sheets, respectively, after applying marine exposure.

Effect of cement based coatings on durability enhancement of GFRP-wrapped columns in marine environments

The main objective of this paper is to study the effects of marine environments on cement based coatings for enhancing the durability of Glass Fibre Reinforced Polymer (GFRP) sheets. Despite of durability degradation in harsh environments, GFRP sheets are widely used to repair the existing structures in the marine environment. Mean while there is no comprehensive analysis has described how the environmental conditions affect these sheets, and there is no any appropriate solution has been provided to date. In this research, a marine environment simulator was designed and constructed similar to the real conditions. Mechanical properties of wrapped specimens were studied after placing them inside the simulator. Two types of cement based mortar, namely polymeric and self-compacted, were applied on the sheets. The polymeric mortar increased the ultimate strength of the specimens wrapped with one and two layers of GFRP by 5.4% and 4.7% respectively, compared with similar specimens in the marine environment without the protective mortar. The ultimate strength was increased by 2.4% and 1.8% in specimens with self-compacted mortar coatings. Marine environments caused better curing of the self-compacted mortar and conversely a slight reduction of polymeric mortar’s durability. Also, the bond strength of the polymeric mortar to GFRP sheets was more than those with self-compacted mortar.

FRP Confinement of Heat-Damaged Circular RC Columns

To investigate the effectiveness of using fiber reinforced polymer (FRP) sheets in confining heat-damaged columns, 15 circular RC column specimens were tested under axial compression. The effects of heating duration, stiffness and thickness of the FRP wrapping sheets were examined. Two specimen groups, six each, were subjected to elevated temperatures of 500 °C for 2 and 3 h, respectively. Eight of the heat-damaged specimens were wrapped with unidirectional carbon and glass FRP sheets. Test results confirmed that elevated temperatures adversely affect the axial load resistance and stiffness of the columns while increasing their ductility and toughness. Full wrapping with FRP sheets increased the axial load capacity and toughness of the damaged columns. A single layer of the carbon sheets managed to restore the original axial resistance of the columns heated for 2 h yet, two layers were needed to restore the axial resistance of columns heated for 3 h. Glass FRP sheets were found to be less effective; using two layers of glass sheets managed to restore the axial load carrying capacity of columns heated for 2 h only. Confining the heat-damaged columns with FRP circumferential wraps failed in recovering the original axial stiffness of the columns. Test results confirmed that FRP-confining models adopted by international design guidelines should address the increased confinement efficiency in heat-damaged circular RC columns.