Glass Fiber Reinforced Polymer Profiles Research Articles

Development of a novel beam-to-column connection system for pultruded GFRP tubular profiles

Despite the increasing use of pultruded glass fibre reinforced polymer (GFRP) profiles in civil engineering structural applications, most common beam-to-column connection systems still mimic those used in steel frame structures, not accounting for the inherent differences of mechanical properties between the GFRP and steel. Therefore, due to the low transverse modulus and strength of GFRP profiles, these connection systems have several limitations in terms of stiffness and load carrying capacity. This paper presents the development of an innovative beam-to-column bolted connection system for GFRP tubular profiles comprising tailor-made steel connection parts that are positioned inside the GFRP sections. The experimental investigations first included double-lap tests to characterize the behaviour of bolted connections between GFRP and steel plates. Next, tests were performed on full-scale beam-to-column connections using the novel connection system, in which the following configurations were assessed: (i) one bolt per web (W1), (ii) two bolts per flange and short edge distance (F2), (iii) two bolts per flange and long edge distance (F2S), and (iv) four bolts per flange (F4). Results showed that the stiffness of the connection system is mainly influenced by the number of bolt rows, while the strength depends on the bolt edge distance – the maximum stiffness and strength were provided by configurations F4 and F2S, respectively. Moreover, with these configurations it was possible to obtain a pseudo-ductile failure behaviour. The stiffness of each connection type was estimated with reasonable accuracy using the “component method”. On the other hand, estimates of the failure load using the same method and the available design guides were non-conservative and presented poor correlation with the test results, suggesting the occurrence of mechanisms more complex than those considered to estimate the loads. Therefore, numerical models were developed to estimate the stress resultants in the bolts, which allowed to predict the strength of the connection series.

Structural Analysis of GFRP Truss Bridge Model

Experimental investigation of structural behavior of glass fiber reinforced polymer (GFRP) space truss bridge model subjected to static loading is discussed in this paper. Bridge prototype was assembled using GFRP profiles produced by Fiberline Composites Ltd, steel bolts and GFRP brackets. In order to load the structure, wooden bridge deck was installed. Total load of 13.3kN was applied in four stages while measuring the bridge node displacement. Flexural behavior of the truss structure was monitored at every loading stage. In order to perform the comparison analysis of truss structural behavior, numerical model was created employing finite element software Solidworks. Comparative analysis has shown good agreement between experimental and numerical results (the margin of error varied from 0,3 up to 10,5%). The obtained results show, that designed and tested bridge model has a sufficient reserve of structural stiffness. Performed investigation reveals that GFRP profiles are suitable for real pedestrian bridge superstructures.

Two-Dimensional Modeling of Thermomechanical Responses of Rectangular GFRP Profiles Exposed to Fire

In the past three decades, one-dimensional (1D) thermal model was usually used to estimate the thermal responses of glass fiber-reinforced polymer (GFRP) materials and structures. However, the temperature gradient and mechanical degradation of whole cross sections cannot be accurately evaluated. To address this issue, a two-dimensional (2D) thermomechanical model was developed to predict the thermal and mechanical responses of rectangular GFRP tubes subjected to one-side ISO-834 fire exposure in this paper. The 2D governing heat transfer equations with thermal boundary conditions, discretized by alternating direction implicit (ADI) method, were solved by Gauss-Seidel iterative approach. Then the temperature-dependent mechanical responses were obtained by considering the elastic modulus degradation from glass transition and decomposition of resin. The temperatures and midspan deflections of available experimental results can be reasonably predicted. The overestimation of deflections could be attributed to the underestimation of bending stiffness. This model can also be extended to simulate the thermomechanical responses of beams and columns subjected to multiside fire loading, which may occur in real fire scenarios.

Compressive Behavior of Concrete Filled Glass Fiber Reinforced Polymer (GFRP) Box Profiles

The use of concrete filled fiber reinforced polymer (FRP) profiles for beams and columns has been studied extensively in recent years. Glass Fiber Reinforced polymers (GFRP) profiles are one of these materials. GFRP box profiles serve as formwork, and provide shear and flexural reinforcement in novel hybrid GFRP–concrete structural system. GFRP box profiles also protect the concrete and increase the strength of hybrid materials. This study presents results of an experimental study using concrete filled pultruded GFRP profiles. A series of compression tests were carried out to study the compression behavior of the proposed hybrid GFRP-concrete materials. Hybrid compression samples were fabricated and tested in three different strength classes. The results showed that compressive strength of hybrid material significantly increased when compared to reference samples.

Influence of infill concrete strength on the flexural behaviour of pultruded GFRP square beams

This paper presents experimental and analytical studies on the effect of the compressive strength of the concrete infill on the flexural behaviour of composite beams. Hollow pultruded Glass Fibre Reinforced Polymer (GFRP) square beams (125mm×125mm×6.5mm) filled with concrete having 10, 37 and 43.5MPa compressive strength were tested under static four-point bending. The results indicate that filled GFRP beams failed at a load 100–141% higher than hollow beams and showed 25% increase in stiffness. However, the increase in concrete compressive strength from 10 to 43.5MPa increased the ultimate load by only 19% but exhibited almost the same flexural stiffness indicating that a low strength concrete is a practical solution to fill the GFRP profiles to be used as beam applications. Moreover, the concrete infill prevented the premature buckling and web crushing of the GFRP tube. The maximum strain measured at failure is similar to the compressive strain determined from the coupon test indicating the effective utilisation of the GFRP material. Finally, Fibre Model Analysis which considered the partial confined stress–strain curve for the concrete infill gave an accurate prediction of the flexural behaviour of the concrete filled GFRP sections.

Member Capacity of Pultruded GFRP Tubular Profile with Bolted Sleeve Joints for Assembly of Latticed Structures

AbstractThe use of bolted sleeve joints has been proposed for assembling pultruded glass fiber-reinforced polymer (GFRP) tubular profiles into space lattice shell structures. Such joint configurations may introduce a semi-rigid end condition and further affect the capacity of the connecting members in compression. Three batches of specimens assembled with pultruded GFRP profiles of different lengths and bolted sleeve joints at both ends were prepared and tested under static axial compression. A detailed three-dimensional finite element model considering bolt geometry, contact behavior, bolt pretension, initial geometric imperfection, and failure criterion for fiber-reinforced polymer (FRP) composites was developed and validated with experimental results showing good comparisons. It was found that the bolted sleeve joints exhibited semi-rigid behavior and that the failure modes and the effective length factor were dependent on member slenderness. The relationship between effective length factor and member ...

Experimental study of GFRP-concrete hybrid beams with low degree of shear connection

Recent developments in the design of advanced composite materials for construction have led researchers to create novel high-performance structural elements that combine fiber-reinforced polymer (FRP) shapes with traditional materials. The current study analyzes the experimental structural response of eight hybrid beams made of pultruded glass FRP (GFRP) profiles mechanically connected to reinforced concrete (RC) slabs, suitable for building floors as well as footbridge and marine pier superstructures. The influence of partial interaction is studied by considering a low degree of shear connection and an analytical assessment of the whole response is carried out using previous formulations, highlighting a good accuracy. The behavior of the hybrid beams is further evaluated against that of equivalent reinforced concrete beams and single GFRP profiles, thus proving the feasibility of the solution.

Effects of corrosive environments on properties of pultruded GFRP plates

Glass Fiber Reinforced Polymer (GFRP) composites have low permeability and high corrosion resistance. In recent years, as the use of GFRP in applications requiring high corrosion resistance has gradually expanded, its long-term performance in highly corrosive environments has caught public attention worldwide. Nevertheless, there is only limited theoretical research and accumulated test data on the corrosion resistance of GFRP. This paper analyses the long-term performance of GFRP in highly corrosive environments. Samples cut from pultruded GFRP profiles were exposed to alkaline, saline, and acidic solutions of different concentrations at 60°C. Additionally, the effects of acidic solutions at high temperature (90°C) were investigated. Flexural properties, changes in the flexural fracture mechanism, hardness, the rate of weight gain, changes in appearance, and scanning electron microscopy (SEM) images of fracture sections were analyzed over periods of 7, 15, 30 and 90days. Results indicate that flexural strength decreases with increased exposure time to both acidic and alkaline solutions. Under conditions of high concentration acidity and high temperature acidity, respectively, flexural strength decreases even more drastically. Additionally, it was found that saturated NaCl solution has little effect on GFRP.

Effects of thermal cycles on the mechanical response of pultruded GFRP profiles used in civil engineering applications

This paper presents a literature review and results of an experimental study about the effects of thermal cycles on the physical and mechanical properties of pultruded glass fibre reinforced polymer (GFRP) profiles used in civil engineering structural applications. The GFRP profiles used in this study present similar fibre architecture, differing only in their matrix nature: unsaturated polyester and vinylester. Small-scale coupons obtained from both types of GFRP profiles were exposed to a Mediterranean range of thermal variations (−5°C to 40°C) for up to 190 cycles in a dry condition. The effects of such exposure on the physical and mechanical response of the GFRP materials were assessed and compared using the following experimental techniques: (a) dynamic mechanical analyses (DMA) to assess the viscoelastic behaviour; (b) tensile, flexural and interlaminar shear tests, to evaluate the mechanical properties; and (c) scanning electron microscopy (SEM), to monitor the potential changes in the microstructure due to the degradation (if any) caused by the thermal cycles, as well as the possible changes into the main mechanisms of fracture. After exposure to thermal cycles, the viscoelastic behaviour of the GFRP profiles presented only slight changes, indicating no significant degradation, neither in the matrix structure nor at the fibre–matrix interphase. In terms of mechanical properties, both types of GFRP materials suffered slight changes regarding tensile and interlaminar shear properties. Flexural properties were more affected, particularly the flexural modulus, especially in the first cycles, as degradation tended to stabilize for increasing cycles. The GFRP profile made of vinylester resin presented better overall performance than the one made of polyester, especially regarding the tensile properties. SEM observations of the surfaces of fracture of mechanically tested pultruded specimens showed two main mechanisms of crack propagation: cohesive rupture (matrix cracking), where the crack propagates inside the matrix, and adhesive rupture (fibre–matrix debonding), where the crack propagates at the interface fibre–matrix. Degradation of the polyester matrix caused by the thermal cycles is evidenced by extensive matrix microcracking and increased fibre–matrix debonding. The vinylester matrix resists better to such degradation as fibre–matrix debonding occurs in less extent, and matrix microcracking is scarcely present.

Experimental Investigation of the Behavior of a Lattice Steel Column Repaired with Pultruded GFRP Profiles

AbstractIn this paper, a series of joint tests and full-scale structural tests were performed to assess the effectiveness of pultruded glass fiber-reinforced polymer (GFRP) profiles for rehabilitating lattice steel columns. The data for the displacements and strains of typical members were recorded. The experimental results showed that the failure modes are generally identical for the original column, the column restored using angles, and the column that adopted the stiffer GFRP-to-steel bolted joints (using steel cover plates, bolts, and nuts) repaired with pultruded GFRP sections. In contrast, the failure pattern of the column that used the ordinary GFRP-to-steel bolted joints (only using bolts and nuts) was not the same. Additionally, the ultimate strength of the specimen that employed the stiffer GFRP-to-steel connections was slightly higher than that of the specimen retrofitted by angles, and the ultimate capacity of the sample that adopted the ordinary GFRP-to-steel connections was significantly low...

Structural behaviour of a GFRP-concrete hybrid footbridge prototype: Experimental tests and numerical and analytical simulations

Glass fibre reinforced polymer (GFRP) pultruded profiles are being increasingly used in the construction industry since the last few decades. The high potential of GFRP profiles for structural applications stems from their high strength, low self-weight and corrosion resistance. In opposition, the high deformability, the susceptibility to instability phenomena and the lack of specific design codes have been hindering a wider use of these advanced composite materials. Several hybrid systems in which GFRP materials are combined with traditional materials, namely concrete, have been proposed in order to overcome the aforementioned limitations of the GFRP material. This paper presents experimental, analytical and numerical investigations about the flexural behaviour of a GFRP-concrete hybrid footbridge prototype comprising two I-shaped GFRP main girders and a thin steel fibre reinforced self-compacting concrete (SFRSCC) deck. With the aim of limiting the structure’s deformability, the footbridge features an external prestress system consisting of two ordinary steel rebars screwed tighten to the structure at the support sections. A small-scale footbridge prototype, 6.0m long and 2.0m wide, was built and tested in a 5.5m simply supported span. The experimental programme included (i) serviceability tests, with and without the application of the external prestress system, and (ii) failure tests. Results of flexural tests proved the feasibility and advantages of the structural concept proposed: the judicious combination of GFRP and SFRSCC enabled the development of a lightweight, high performance and relatively inexpensive structural system for footbridges; furthermore, the external prestress system was very effective in limiting deflections. The analytical and numerical models developed in this study were able to predict with good accuracy (i) the linear elastic behaviour of the structure up to failure, (ii) the effects of the external prestress, and (iii) the failure mode and strength, proving to be accurate tools for the design of GFRP-concrete structural solutions.

Experimental and numerical study on the structural behavior of eccentrically loaded GFRP columns

Glass fiber reinforced polymer (GFRP) pultruded profiles are being increasingly used in civil engineering applications. Although they offer several advantages over traditional materials, such as high strength, lightness and non-corrodibility, GFRP profiles present low elasticity and shear moduli, which together with their slender walls makes them very prone to buckling phenomena. Several previous studies addressed the global and local buckling behavior of GFRP pultruded members under concentric loading. However, little attention has been given to the effect of small eccentricities, which may arise from material geometrical imperfections or construction errors. This paper presents results of experimental and numerical investigations about the structural behavior of GFRP pultruded columns subjected to small eccentric loading about the major (strong) axis. To accomplish such goal, three series of 1.50m long GFRP I-section (120×60×6mm) columns were tested in compression applied with the three following eccentricity/height of the cross-section ratios: e/h=0.00, 0.15 and 0.30. It was found that such small eccentricities are of major importance for the behavior of GFRP pultruded columns. Although the initial axial stiffness of eccentrically loaded columns was similar to that of concentrically loaded ones, for increasing loads the stiffness considerably decreased due to bowing and second-order P–δ effects. Furthermore, results show that the load capacity of columns subjected to loads applied within the kern boundaries is reduced up to 40% at an approximately linear trend. Results obtained from the experimental campaign were compared with analytical predictions and numerical simulations using (i) the finite element method (FEM) and (ii) the generalized beam theory (GBT). In general, a very good agreement was obtained between experimental data and analytical and numerical results.

Buckling Behavior and Failure of Hybrid Fiber-Reinforced Polymer Pultruded Short Columns

AbstractThis paper addresses the buckling behavior and strength of hybrid pultruded short profiles subjected to uniform compression. Since the design of glass fiber-reinforced polymer (GFRP) pultruded profiles is often governed by deformations and buckling phenomena, the introduction of carbon fibers in GFRP (hybrid) profiles has been proved to increase both strength and stiffness of flexural members. In the context of short compression members (columns), experimental, numerical, and analytical studies were carried out, with particular attention being given to the local buckling. Two series of 660-mm-long I-section profiles (200×100×10 mm) were tested under uniform compression. In order to evaluate the advantages of introducing carbon fiber reinforcement in the flanges, two profile types were tested: bare GFRP profile (reference column) and carbon fiber reinforced polymer (CFRP) strengthened GFRP profile (hybrid column). Shell finite-element (SFE) models were developed and validated, based on experimenta...

Novel Joint for Assembly of All-Composite Space Truss Structures: Conceptual Design and Preliminary Study

A space truss is formed of interconnected structural components that transfer loads axially. Pultruded glass-fiber reinforced polymer (GFRP) composites exhibit their best material strength in the axial (pultrusion) direction, and their inherent lack of material stiffness can be compensated by the structural stiffness achieved by space configuration. A novel connector made of pultruded GFRP profiles is proposed in this paper to join diagonal and chord members and to form all-composite free-form space trusses. The proposed truss unit was assembled and tested statically, and the load-displacement responses were recorded. The final collapse of the structural unit evidenced a pull-out shear failure mode in the bolt connections, and the ultimate load can therefore bewell predicted by this mechanism. A detailed finite element (FE) analysis considering the interaction between the bolts and FRP profiles was conducted for the structural unit to investigate the effects of pretension force of bolted connections and the stress concentration at the joint region. A simplified FE approach was used to demonstrate one- and two-dimensional space trusses with satisfactory structural stiffnesses. DOI: 10.1061/(ASCE)CC.1943-5614 .0000304. © 2013 American Society of Civil Engineers. CE Database subject headings: Space truss; Fiber reinforced polymer; Pultrusion; Joints; Stiffness; Serviceability. Author keywords: Space truss; Glass-fiber reinforced polymer; Pultrusion; Joints; Stiffness; Serviceability.

A numerical and experimental study of the material properties determining the crushing behaviour of pultruded GFRP profiles under lateral compression

The present work aims at determining the critical material properties that can be used to tailor the crush behaviour of pultruded GFRP (Glass Fibre Reinforced Polymer) box-beams, as can be found in, for example, roadside furniture such as guard-rails. For this purpose, the mechanical behaviour and energy absorption mechanisms of the constituent pultruded box-beam sections subjected to lateral compressive loading, the dominating load case in composite structures when used as roadside furniture, have been studied. The analysed pultruded profiles consist of E-glass fibre reinforcements with two different lay-up configurations in a polyester matrix. The lateral crushing of profile sections is experimentally evaluated and further numerically studied using commercially available tools, applying readily available models incorporated in the software, in analogy to common practice in designing structures, to identify design and material parameters for improving the fracture behaviour of pultruded GFRP profiles. From the analyses, it is shown that the junctions between flanges and webs are the weakest points of box-beam sections: here, high shear stress concentrations in combination with occurring matrix failure lead to further damage such as delamination and tearing. This behaviour is well-described using the Hashin damage model within ABAQUS. Predicted failure behaviour corresponds with observed experimental results, whereas the material stiffness is underestimated. It is shown that the out-of-plane properties (transverse tensile and shear strength) are the dominant parameters affecting the overall performance.

Artificial Accelerated Ageing of GFRP Pultruded Profiles Made of Polyester and Vinylester Resins: Characterisation of Physical–Chemical and Mechanical Damage

Abstract: This article presents results of experimental investigations of the durability of glass‐fibre‐reinforced polymer (GFRP) pultruded profiles exposed to typical environments of civil engineering applications. Specimens obtained from commercial GFRP profiles made of unsaturated polyester and vinylester resins were subjected to immersion in (i) demineralised water and (ii) salt water at 20 °C, 40 °C and 60 °C for up to 18 months, (iii) continuous condensation at 40 °C for up to 9 months and (iv) accelerated ageing in a QUV chamber for up to 3000 h. The effects of such exposure conditions on both types of profiles were analysed in what concerns their (i) mass changes, (ii) viscoelastic response, evaluated by means of dynamic mechanical analysis (DMA), (iii) mechanical response in tension, bending and interlaminar shear, and (iv) chemical changes, assessed through Fourier transformed infrared spectroscopy (FTIR). Hygrothermal ageing had significant influence on the material performance, namely on the mechanical response – demineralised water immersion caused a higher level of degradation, compared with salt water immersion, and results show a clear competition between moisture‐induced plasticisation and residual post‐curing of the composite matrix. Following QUV exposure, although considerable aesthetical changes were observed, the viscoelastic response and mechanical performance of both profiles were not remarkably affected, confirming that UV radiation affects essentially the outermost layers of GFRP profiles. In general, the GFRP profile made of vinylester resin exhibited better durability performance, when compared with its polyester counterpart.

Development of a pedestrian bridge with GFRP profiles and fiber reinforced self-compacting concrete deck

In recent years, the number of pedestrian bridges built from composites materials has notably increased. The combination of fiber reinforced polymers (FRP) profiles with fiber reinforced concrete (FRC) elements is being adopted in this type of structures, since the ductility, high post-cracking tensile strength, compressive stiffness and strength of FRC can be combined with the benefits derived from the use of FRP’s profiles to obtain high performance structural systems. In the context of the present work a 12 m long single span pedestrian bridge with two composite I-profiles was designed. In terms of deflection requirements imposed by serviceability limit states, the influence of the height and thickness of glass fiber reinforced polymer (GFRP) profiles, as well as the addition of a thin layer of prestressed carbon fiber sheet in the bottom flange of the GFRP profile was evaluated. Using software based on the finite element method, the structural behavior of the developed structural systems was analyzed. Furthermore, two prototypes of this structural system were built and monitored in order to assess their long-term deformational behavior when subjected to a loading configuration correspondent to the load combination for the deflection serviceability limit states. The main results obtained are presented and discussed.

Vacuum Formed GFRP Profiles Used as External Reinforcement in Damaged Concrete Structures- Comparison from Test Results and Simulation

The knowledge of the behavior of damaged beams is important to predict the behavior of structural members and to know how the structure can be affected by damages. In this work, it is simulated and analyzed experimentally the behavior of reinforced concrete beams after tested up to ultimate limit state (ULS) reinforced by vacuum form glass fiber reinforced polymer (GFRP). Firstly, it is used the finite element analysis (FEA) to compare the experimental results with the simulated ones. Secondly, the same technique is used to generate a (GFRP) profile to reinforce the damaged beam. Finally, the results were compared and discussed.

Fire protection systems for building floors made of pultruded GFRP profiles – Part 2: Modeling of thermomechanical responses

A recently developed thermomechanical model to predict the time-dependent thermal and mechanical responses of pultruded glass fiber-reinforced polymer (GFRP) profiles subjected to fire was extended to include the beneficial effects of passive fire protection systems. The model extension was validated by comparing predicted and measured thermomechanical responses of pultruded GFRP tubes subjected to four-point bending and exposed to an ISO834 fire from their underside. The profiles were protected using passive and active methods, including a calcium silicate board, a vermiculite/perlite-based mortar, and a water-cooling system. Variations resulted mainly from the unavailability of accurate time-dependent thermophysical properties for the protection materials. The benefits provided by the fire protection systems could be quantified and the model therefore can be used for the selection and design of passive fire protection measures.

Flexural behaviour of GFRP–concrete hybrid beams with interconnection slip

The design of glass fibre reinforced polymer (GFRP) pultruded beams is usually governed by deformability or instability phenomena. To obtain a better use of the material properties, the GFRP profiles can be connected to concrete elements with several advantages, associated with the global stiffness and strength of the structural elements. This leads to solutions particularly useful for rehabilitation of old floors or even new construction slabs. This paper presents the results of an experimental research developed to characterize the flexural behaviour of a GFRP–concrete hybrid solution. Shear connection tests were first performed on GFRP I-profiles, connected to concrete with stainless steel bolts, to evaluate the behaviour of the shear connection. The results of those tests were then used to design simply supported GFRP–concrete hybrid beams that were tested under bending conditions. The flexural behaviour of the GFRP–concrete hybrid beams is discussed, with particular relevance to the effect of the interconnection slip. The overall behaviour of the hybrid beams is compared with that corresponding to a simple GFRP I-profile beam, demonstrating the structural advantages of this new hybrid constructive solution.