Glass Fiber Reinforced Polymer Rods Research Articles

Form-finding of elastic gridshell based on spatial elastica model

In engineering design, elastic gridshells, which are composed of a number of elastic rods, are advantageous because they are lightweight, easy to construct, and low-cost as well as have a long-span space. However, the form-finding of a gridshell is challenging owing to the large deformation and strong geometric-nonlinearity of the structure.In this paper, a new form-finding method based on spatial elastica model (FMSE) is proposed. The deformations of elastic rods, obtained via the elliptic integral solution of spatial elastica, is integrated into the overall deformation of the gridshell. A set of transcendental equations is solved using the quasi-Newton method to ensure that the deformation of the gridshell satisfies the given boundary conditions. To validate the proposed FMSE method, desktop experiments (designed using the theory of Chebyshev nets) are performed on gridshells made of glass fiber reinforced polymer rods. The predictions of the FMSE method agree well with the experimental results.Accordingly, the proposed FMSE method is expected to have potential applications in elastic gridshells, on the investigations of form-finding, load-bearing capability, non-local deformation behavior, and also stability of structures.

Fiber and interface failure characterization of glass fiber reinforced polymer for composite insulators after liquid permeation

Composite insulators are of great significance in power systems due to their excellent electrical and mechanical properties. The mechanical load of insulator is borne by the rod made of glass fiber reinforced polymer (GFRP). Despite the considerable load margin, abnormal fractures have been reported continuously during actual operation. Among them, the evolution of decay-like fracture has still not been illustrated, which is why no effective preventive measures can be proposed. Liquid permeation, especially nitric acid, is supposed to play a vital role in the fracture. Thus, in this paper, the characteristics of glass fiber, fiber-epoxy interface, and GFRP-sheath interface immersed in different liquids are investigated. Based on the results, the significant role of boron element in the stress corrosion of glass fiber is illustrated. Therefore, the application of glass fiber without B is rather necessary. Also, the failure of fiber-epoxy interface by acid is identified by broadband dielectric response, which forms the channels of current concentration. It is key for the development of decay-fracture. Moreover, the degradation of GFRP-sheath interface after immersion is recognized by the measurement of interfacial resistivity. Consequently, coupling agents with good resistance to acid should be adopted, in order to avoid further liquid permeation into the GFRP rod.

Performance of NSM and EB methods on the flexural capacity of the RC beams strengthened with reinforced HSC layers

The near-surface mounted (NSM), in which strips or rods are fixed by an adhesive in slits formed inside the concrete cover, and the externally bonding (EB), in which the reinforcement is glued to the concrete surface, are well-known strengthening methods. In the present work, an experimental and numerical study was carried out on reinforced concrete (RC) beams strengthened with NSM and EB-reinforced high-strength concrete (RHSC) layers. The RHSC layers were reinforced by steel or glass fiber reinforced polymer (GFRP) rods and bonded to the RC beams without and with a concrete cover. Seven specimens were cast and loaded in flexure up to failure to investigate the effect of RHSC layer position and reinforcement on the RC beams' efficiency. The three-dimensional finite element program (ABAQUS) verified the experimental results numerically. Also, a parametric study was numerically performed to examine the factors affecting the flexural performance of the strengthened RC beams using NSM and EB RHSC layers. The strengthened beams by NSM steel RHSC layers increased the load capacity by 147.9% compared to the control beam (CB). Changing the RHSC layer reinforcement from steel to GFRP bars enhanced the load's efficiencies from 147.9% to 172.0% compared to the CB. Decreasing the width and reinforcing area of the RHSC layer decreased the beam load capacity by about 17.5 %. Due to their longer bending arms, the EB RHSC layers showed lower load capacity than the NSM ones, which accelerated the EB RHSC failure. When the carbon fiber-reinforced polymer bars were utilized to reinforce the HSC layers, the strengthened beams showed higher load efficiency than those strengthened with HSC layers reinforced by GFRP rods.

Flexural response of GFRP RC beams strengthened with side and bottom NSM GFRP bars

This study exhibits the bending performance of reinforced concrete (RC) beams with glass fiber-reinforced polymer (GFRP) rods. The beams were strengthened with the bottom or side near surface mounted (BNSM or SNSM) methods. Applying BNSM strengthening to the RC beam is difficult in some cases, so the SNSM became essential. Due to the limited research dealing with this type of beam, this study focuses on the effect of internal and NSM reinforcement areas and the NSM position on the response of the beams. Two un-strengthened and six strengthened RC beams were tested in bending. The GFRP RC beams upgraded with SNSM GFRP bars showed higher deflection, energy dissipation, ductility, and ductile failure than those upgraded with BNSM ones. On the contrary, the load-carrying capability and flexural stiffness of GFRP RC beams strengthened with BNSM GFRP rods were slightly higher than those strengthened with SNSM GFRP. Consequently, a parametric investigation relying on the verified finite element (FE) model was executed. This parametric work aimed to add additional data to the literature related to the influences of the internal and NSM reinforcement type and area on the performance of beams with ‎SNSM. According to the FE results, increasing the NSM reinforcement area improved the capacity and stiffness of the upgraded beams regardless of the combination of the internal and NSM reinforcement. The relative axial stiffness between internal and NSM materials significantly impacted the beam performance. Moreover, using GFRP with CFRP or steel with CFRP indicated higher performance than using steel with GFRP, regardless of which one was located as NSM.

Experimental investigation on the structural behaviour of novel non-metallic pultruded circular tubular GFRP T-joints under axial compression

Different uniplanar T-joints made from pultruded glass-fibre reinforced polymer (GFRP) circular tubular sections (CHS) incorporating different innovative non-corrosive reinforcements with structural adhesives, carbon-fibre laminates (CFRP) and concrete-filled GFRP rods were developed, and their structural performance was tested under axial compression. The hollow T-joints without any connection reinforcements displayed brittle failure with out of plane longitudinal shear failure while the ones reinforced with CFRP and concrete-filled GFRP rods shows superior ultimate strength and ductility with diverse failure modes including interlaminar failure within the pultruded chord. With CFRP wrapping and concrete filling, increases in strength and ductility of up to eightfold and fortyfold were seen, respectively. Design oriented equations and analytical formulations were developed for the T-joints and their predictions were compared with experimental results. These novel connections presented in this study are recommended for future construction of offshore tubular structures.

Design of concrete beam reinforced with GFRP bars as per ACI codal provisions

This document provides design principles for concrete beams reinforced with glass fiber reinforced polymer (GFRP) bars per the ACI 440.1R-15 regulation. One of the main advantages of using glass fiber reinforced polymer rods instead of traditional steel reinforced rods is their lighter weight and higher corrosion resistance. However, the bending failure mode of FRP reinforced concrete (FRP-RC) beams is brittle rather than ductile because the elasticity of fiber reinforced polymer (FRP) bars is linear until failure and the elongation at break is small. For FRP-RC elements, concrete crushing compression failure, which gives various warnings before failure, is the preferred failure mode. In other words, unlike the usual design practice for reinforced concrete (steel-RC) beams, for FRP-RC beams, an over-reinforced structure is preferable to an under-reinforced structure. In addition, since the FRP RC member has low rigidity of the FRP rod, it bends more and cracks larger than the steel RC member. These factors limit the field of application of FRP. Here is a design example of a rectangular beam with tension reinforcement according to ACI regulations.

Flexural behaviour of pultruded circular tubular GFRP composite truss bridges with novel non-corrosive connections

Five multiplanar truss bridges (MTBs) made of glass-fibre reinforced polymer (GFRP) circular tubular profiles incorporating different innovative non-metallic connections with adhesives, grouted GFRP rods and GFRP laminate wrapping are proposed. These MTBs were tested under flexure with static loading, and their performance surpassed the design load demands required by pedestrian bridges. One of the MTBs showed sufficient load capacity for heavy load platforms in Australian road bridge applications. Failure of the MTBs was triggered by member connections, and no damage such as local or member buckling of the individual members was observed. It was found that the combined effect of GFRP rods and GFRP wrapping on the connections increased the ultimate strength and the ductility of the MTBs. The capacity of the members and connections for the MTBs were calculated using available design guidelines and analytical equations which were compared and discussed with the experimental results.

Investigation on the structural failure behaviour of pultruded circular tubular GFRP multiplanar truss bridges with non-metallic connections through finite element modelling

The finite element (FE) method was used to investigate the failure of member connections of five glass fibre-reinforced polymer (GFRP) multiplanar truss bridges (MTB) with non-metallic connections. Three-dimensional FE models for the MTBs were developed and validated against previous experimental results and were accompanied by multiple parametric studies. Adhesive failure of the brace occurs progressively around the perimeter of the brace and GFRP laminate wrapping failure was not observed before adhesive bond failure of the brace. Furthermore, the failure sequence of the GFRP laminate layer and the adhesive bonding between the brace and chord was found to be dependent on the brace wall thickness. Extent of the predicted fibre tensile rupture of the GFRP laminate was greater for cement mortar grouted GFRP rods than its non-GFRP grouted counterpart.

Comparison of the Flexural Behavior of High-Volume Fly AshBased Concrete Slab Reinforced with GFRP Bars and Steel Bars

Fiber-reinforced polymer (FRP) rods are advanced composite materials with high strength, light weight, non-corrosive properties, and superior durability properties. Under severe environmental conditions, for concrete structures, the use of glass-fiber-reinforced polymer (GFRP) rods is a cost-effective alternative to traditional steel reinforcement. This study compared the flexural behavior of an OPC concrete slab with a high-volume fly ash (HVFA) concrete slab reinforced with GFRP rods/steel rods. In the fly ash concrete slabs, 60% of the cement used for casting the slab elements was replaced with class F fly ash, which is emerging as an eco-friendly and inexpensive replacement for ordinary Portland cement (OPC). The data presented include the crack pattern, load–deflection behavior, load–strain behavior, moment–curvature behavior, and ductility of the slab specimens. Additionally, good agreement was obtained between the experimental and nonlinear finite element analysis results using ANSYS 2022-R1. The study also compared the experimental moment capacity with the most commonly used design standard ACI 440.1R-15. This investigation reveals that there is a huge potential for the utilization of GFRP rods as reinforcement in fly ash concrete slabs.

Cyclic Loading of Glued-In FRP Rods in Timber: Experimental and Analytical Study

The axial load capacity and stiffness of carbon fiber–reinforced polymer (CFRP) and glass fiber–reinforced polymer (GFRP) rods glued in timber is investigated under cyclic loading as the main design consideration for structures that experience load reversal (e.g., due to wind loading). Load cycles at 20%, 40%, 60%, and 80% of the ultimate load and three repetitions per load cycle were considered. The main parameters examined are the effect of FRP rod, anchorage length, and construction scenario. The construction scenarios represent full contact between timber faces, gaps in joints due to long-term effects (e.g., viscoelastic creep) and manufacturing tolerances, and contact with other materials. The GFRP rods exhibit 23% higher axial load capacity and 20% lower axial tensile stiffness than CFRP rods for an embedment length of 5D, where D = diameter of the rod. The axial load capacity of the GFRP rods tends to plateau with increasing bonded length at anchorage lengths greater than 10D. Small gaps significantly decrease the axial compressive stiffness of the glued-in FRP rods at the first load cycles and the axial stiffness varies along the bonded length. An analytical methodology is presented to describe the bond stress transfer mechanism and the progressive bond degradation. The analytical tensile slip values agree fairly well with the experimental results when debonding takes place at 80% of the ultimate load.

Study on dimensions of void in GRP rod of composite insulator

As an important part of composite insulator, glass fiber reinforced polymer (GRP) rod needs to bear the main mechanical and keep certain insulation performance. The void in the material is key factor to the performance of GRP rod. The void with larger size could affect the electric field distribution significantly and lead to the “Lantern-like” heating. In this paper, the structure of void in GRP rod is studied by 3D X-ray microscope. It is found that the void dimensions in the GRP rod is generally less than 300μm, but the interconnection of linear hole makes the length of the void increase significantly. For the GRP rod with high porosity, the length of connection hole is hard to be detected directly by the existing technology, but it could be calculated based on the diameter of the hole. Based on the calculation method, the dimensions of void in GRP rod could be inspected by the observation of section using optical microscope.

Remediation of Punching Shear Failure Using Glass Fiber Reinforced Polymer (GFRP) Rods.

The results of an experimental program on shear-strengthening of flat slabs using Glass Fiber Reinforced Polymer (GFRP) rods are presented. A total of seven specimens were tested under an upward concentric monotonic loading until failure. One specimen served as a control and was tested without any modification. The remaining six specimens were strengthened with post-installed GFRP rods in single (SG), double (DB), and radial (RD) patterns within shear critical parameters around the centric column. The results of this experimental study suggest that GFRP rods are capable of enhancing both the peak load and deformation capacity. Furthermore, brittle failure associated with punching shear failure was successfully avoided by all strengthening patterns. Of all of the patterns, the RD pattern resulted in maximum peak load increase and corresponding deformation capacity while the lowest bound was created by the SG pattern. The results suggested that SG, DB and RD patterns enhanced ultimate loads up to 9.1, 11.3 and 15.7% while corresponding deflections increased up to 109, 136 and 154%. Strain measurement on flexural reinforcement suggested that all strengthened specimens were able to withstand higher longitudinal strains than yield. It was further shown that reducing the spacing between the GFRP rods efficiently enhanced peak loads, nevertheless, neither this change was proportional, nor did it result in an enhanced energy dissipation capacity. In the end, recommendations of American Concrete Institute (ACI) for the shear strength of two-way systems were modified to incorporate the contributions from GFRP rods. The results indicate that the proposed analytical approach provides an excellent match with the experimental results.

The effect of nano- and micron-scale filler modified epoxy matrix on glass-fiber reinforced polymer insulator component behavior

Glass-fiber reinforced polymer (GFRP) composite rods with epoxy matrix filled with electrically nonconducting particles find widespread use in high-voltage electrical insulator applications. The service loads require a range of different, minimum material property values, e.g. toughness, tensile, or compressive strength, but also component-specific performance, e.g. pull-out friction of surface crimped metal fittings or electric breakdown strength. The contribution discusses selected examples of the effects of different particle filler types on the properties of filled epoxy resin as well as on the behavior of GFRP rods with such a matrix. In all investigated systems CaCO3 was used as micron-sized filler, complemented by different amounts of either nanosilica or core-shell rubber (binary filler), or by both, nanosilica and core-shell rubber (ternary filler). With ternary filler combinations at a content of 36 wt%, fracture toughness GIC was improved in nanocomposite epoxy plates and in GFRP rods by 60% and 100%, respectively compared to a matrix with 20 wt% CaCO3 (used as reference system). The glass transition temperature Tg for some ternary systems dropped from 160 °C (for neat epoxy), to approximately 140 °C, the maximum allowed drop in Tg in view of requirements from further processing steps of the electrically insulating components. The ternary fillers yield transfer of the improvements of fracture properties from epoxy nanocomposite plates into the GFRP rods beyond that of the system with CaCO3 filler only. Compressive strength of the GFRP rods was improved by about 20% only for the binary nanosilica and CaCO3 filler, and was not significantly enhanced with the ternary systems. That combination, however, did not yield improvements in toughness beyond the CaCO3-filled nanocomposite plates and rods. With the range of filler types and contents investigated here, it was hence not possible to simultaneously optimize both, fracture toughness and compressive strength of the GFRP insulator rods.

Crashworthiness of polystyrene foam and cardboard panels reinforced with carbon fiber reinforced polymer and glass fiber reinforced polymer composite rods

This article presents an experimental study on the quasi-static crushing performance of carbon fiber reinforced polymer (CFRP) rods consisting of unidirectional carbon fibers wrapped by braided glass fibers. Rods with and without a taper are tested and then inserted in extruded and expanded polystyrene foam and cardboard panels. Hybrid columnar aluminum tube–CFRP rod structures are also tested in all panel materials. These results are compared to those based on glass fiber reinforced polymer (GFRP) rods, GFRP rods in polystyrene foams, and to GFRP rods in cardboard from a previous study. Tapered CFRP rods exhibit progressive crushing behavior with specific energy absorption superior to GFRP rods, with values of 82 kJ/kg and 65 kJ/kg, respectively. Moreover, the highest specific energy absorption (111 kJ/kg) is obtained in hybrid columnar aluminum tube–CFRP tapered rods, exceeding values of aluminum tubes (89 kJ/kg) and equivalent structures containing GFRP rods (102 kJ/kg). Within panels, cardboard produces the largest increase in mean load of CFRP and GFRP rods due to most constraining fiber splaying during crushing, followed by extruded foam, and lastly expanded foam. However, crushing displacement is most restricted in cardboard due to earlier final compaction. The smallest variations in crushing load occur in extruded polystyrene due to greater homogeneity throughout the foam structure.

Experimental static and dynamic response of RC beams damaged and strengthened with NSM GFRP rod

Inserting FRP rods into grooves using the NSM technique has been demonstrated to be a suitable method for repairing reinforced concrete (RC) beams. There is limited experience with the use of GFRP in the strengthening of RC elements due to low Young’s modulus of glass fibers. The aim of the paper is to analyse the static and dynamic behaviour of RC beams damaged and strengthened by glass fiber reinforced polymer (GFRP) rods utilizing the near surface method (NSM). Undamaged and damaged three RC beams have been experimentally tested under bending loading with and without strengthening by GFRP rods. For a beam, damage has been represented firstly by notches on concrete cover. The beam has been successively strengthened by epoxy resin and NSM GFRP rod and then subjected to bending tests. Vibration tests have been adopted as nondestructive method of control during the experiments to assess the response of RC beams at different damage steps of concrete or due to decrease of bond of GFRP rod. Vibration tests foresaw two boundary conditions, respectively, free-free and hinged ends. Experimental static and vibration results are below shown; discussion and comments on the strengthening bond of NSM GFRP rod have been developed.

Alkaline Attack on Cement or Lime Mortar and Glass Fiber-Reinforced Polymer Rods

Alkaline Attack on Cement or Lime Mortar and Glass Fiber-Reinforced Polymer Rods

Degradation behavior and aging mechanism of decay-like fractured GRP rod in composite insulator

Decay-like fracture is a new type of fracture of composite insulator that is different from normal fracture and brittle fracture. The fracture surface of the glass fiber reinforced polymer (GRP) rod in the decay-like fracture is like rotten wood. There are punctures on the silicone rubber housing and abnormal temperature rise is detected on the composite insulator before fracture. However, the cause and aging mechanism of the decay-like fractured composite insulator is still unknown. In this paper, the degradation behavior of the corroded GRP rod in a composite insulator with abnormal temperature rise was studied. The basic features of the GRP rod were obtained by optical microscope, SEM and TGA. Eroded gap and dendritic shadow in parallel light were found on the GRP rod. Degradation of the epoxy resin, fracture of the glass fiber and failure of the resin-fiber interface leads to the formation of an eroded gap and decreases the GRP-rod transmittance. Chemical reactions in the corroded GRP rod were studied by XPS and FTIR The reactions of ionic exchange and hydrolysis in the area of the dendritic shadow was weaker, but the oxidation under partial discharge was much stronger. The source of water is discussed and the aging mechanism of the GRP rod is revealed and divided into four stages; namely, deterioration of end fitting, hydrolysis and ionic exchange, oxidation of the epoxy resin, and rapid development. The speed of degradation of GRP rod increases stage by stage and the mechanical properties decreases sharply, which eventually leads to decay-like fracture of composite insulator.

Degradation characteristics of epoxy resin of GFRP rod in the decay-like fracture of composite insulator

The decay-like fracture is an emerging mode of abnormal mechanical failure of composite insulators the study of which is still in its infancy. The degradation of epoxy resin of glass fiber reinforced polymer (GFRP) rod caused by discharge and current distinguish the decay-like fracture from both normal mechanical fracture and brittle fracture. In the present work, the detailed degradation of epoxy resin of GFRP rod in the decay-like fracture of composite insulator were examined using scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and X-ray photoelectron spectroscopy (XPS). The results show that the generation, expansion and release of pyrolysis gas is responsible for the formation of the bubbles and holes in the epoxy resin and the initial formation of holes in the silicone rubber housing during the degradation process. The erosion and pyrolyzation of epoxy resin results in mass loss of epoxy resin leading to degradation of the GFRP rod. High resolution XPS spectra of C1s and N 1s in GFRP rod reflects that oxidization process, exposure of glass fiber, and the introduction of nitrogen-containing compounds occurs during the degradation process. Microscopic photographs to explain the degradation of the epoxy resin and the initial formation of puncture holes in the silicone rubber housing are proposed based on the experimental results.

Damaged RC beams strengthened with GFRP

In recent years one of the most important duty of civil engineers is to define methods of rehabilitation both for historic and modern structures. Reinforced concrete is a relatively modern material of construction and it is often damaged both with cracking due to loading or corrosion of reinforcement. In this paper undamaged and damaged reinforced concrete (RC) beams have been experimentally analyzed under bending loading with and without strengthening by near surface mounted (NSM) glass fiber reinforced polymer (GFRP) rod. A nondestructive method of control based on vibration tests has been utilized during the experiments on RC beams: experimental vibration tests have been carried out on RC beams without and with strengthening by GFRP rod assuming free-free ends and hinged ends. In the paper the envelope of Frequency Response functions (FRFs) obtained by the dynamic experimental tests are shown and the changes of natural frequency values are correlated to the damage degree of beam elements. A comparison of experimental and theoretical results is shown and discussed.

Numerical investigation on structural glass beams with GFRP-embedded rods, including effects of pre-stress

The bending performance of laminated glass (LG) beams with Glass-Fibre-Reinforced-Polymer (GFRP)-embedded rods is numerically assessed in this paper, based on earlier experimental investigations.Compared to existing literature efforts related to reinforced glass beams – typically including external steel or FRP tendons and/or reinforcement sections adhesively bonded to glass edges in tension – careful consideration is given to the still rather innovative concept of traditional LG beams that contain pultruded GFRP rods embedded within the interlayer foils. Taking advantage of past experimental results and preliminary Finite Element (FE) outcomes for hybrid glass beams, the quasi-static bending performance at room temperature of several geometrical configurations of LG beams with GFRP-embedded rods is compared. These geometrical configurations include variations in number, size and position of rods. The effects and possible benefits due to initial pre-stressing forces for the GFRP rods are also investigated. As shown for some selected configurations only, GFRP-embedded rods can provide active contribution to traditional LG beams, both in terms of post-cracked resistance and ductility. At the same time, given a reference geometry, a certain level of initial pre-stress can further exploit the potential of the same GFRP rods, acting as pre-tensioned tendons thereby enhancing the initial fracture strength. Several aspects should be properly taken into account to assess and optimize the overall performance of these systems, however, since both their elastic and post-cracked performance are highly sensitive to various mechanical and geometrical input parameters.