Fibre Reinforced Polymer Pultruded Profiles Research Articles

Tensile strength and modulus of FRP pultruded composites at varying load angles relative to the pultrusion direction

Tensile strength and modulus are key material properties for the design of pultruded fiber reinforced polymer (FRP) composite members and connections. Pultruded FRP composites are orthotropic materials and thus both the tensile strength and modulus vary with the angle between the pultrusion direction and the applied force. In current design standards, the variation of material properties with load direction is addressed by prescribing the use of longitudinal properties for angles between zero and five degrees, and the use of transversal properties for angles greater than five degrees. To derive a more precise and representative equational relationship between load angle and tensile material properties, 228 coupons extracted from pultruded FRP profiles were tested in tension in accordance with ASTM D638-22 to determine the resulting average tensile strength and tensile modulus values. Coupons were taken from different profiles from different manufacturers, different section locations (e.g., web versus flange), as well as varying angles between the pultrusion direction and the applied force. The characteristic design value of the tensile strength and tensile modulus at each tested angle was determined in accordance with ASTM D7290-22. Using this dataset, a predictive relationship based on a generalized form of Hankinson’s equation was developed for both average and characteristic tensile strength and both average and characteristic tensile modulus as a function of three factors: 1) the differential angle between the pultrusion direction and the applied force, 2) the longitudinal tensile property (i.e., strength or modulus), and 3) the transverse tensile property (i.e., strength or modulus). The average relative difference between tested and predicted values using the developed equations varied between 4.4% and 8.3%, depending on the considered mechanical property.

An experimental study of FRP truss side plate joint

Ultra-high performance concrete (UHPC) slab - fiber reinforced polymer (FRP) truss hybrid beam has been proved as an effective and advanced bridge system. However, the limited shear strength and the significantly lower transverse properties compared with its longitudinal counterparts result in low rigidity and load carrying capacity of bolted FRP truss joints, which governs the overall performance of the UHPC slab- FRP truss hybrid beam. A FRP truss side plate joint was proposed which integrates a steel U-shaped gusset plate (SUGP) to reinforce the traditional bolted joint. The proposed joint outperformed the conventional bolted joints in terms of the failure mode, load carrying capacity, and stiffness. The load carrying capacity of the proposed joint can be improved by up to 63% and the ultimate deflection was reduced by up to 33%. The effects of a variety of key design parameters, including adhesive, bolt diameter, pre-torque, and length and thickness of the gusset plate, on the performance of the SUGP joint were evaluated. Test results showed that: (i) the adhesive between the pultruded FRP profiles and the steel gusset plate could increase both the initial stiffness and ultimate load carrying capacity of the steel SUGP joint; (ii) length and thickness of the steel gusset plate did not result in notable difference in the behavior of the steel SUGP joint for the range of parameters investigated herein; and (iii) application of pre-tightening torque within the thread of the bolts slightly improved the load carrying capacity but significantly improved the ductility of the steel SUGP joint.

A Review of Fibre Reinforced Polymer Structures

This paper reviews Fibre Reinforced Polymer (FRP) composites in Civil Engineering applications. Three FRP types are used in Structural Engineering: FRP profiles for new construction, FRP rebars and FRP strengthening systems. Basic materials (fibres and resins), manufacturing processes and material properties are discussed. The focus of the paper is on all-FRP new-build structures and their joints. All-FRP structures use pultruded FRP profiles. Their connections and joints use bolting, bonding or a combination of both. For plate-to-pate connections, effects of geometry, fibre direction, type and rate of loading, bolt torque and bolt hole clearance, and washers on failure modes and strength are reviewed. FRP beam-columns joints are also reviewed. The joints are divided into five categories: web cleated, web and flange cleated, high strength, plate bolted and box profile joints. The effect of both static and cyclic loading on joints is studied. The joints’ failure modes are also discussed.

Structural safety of pultruded FRP profiles for global buckling. Part 2: Reliability-based evaluation of safety formats and partial factor calibration

This two-part paper presents a study about the structural safety of pultruded fibre-reinforced polymer (FRP) profiles with respect to global buckling phenomena, which often govern their ultimate limit states design: flexural buckling, flexural-torsional buckling and lateral-torsional buckling. The first part [1] presented the resistance models for those buckling mechanisms, the probability models for model uncertainties of resistance, and a preliminary set of partial factors related to the model uncertainty, all consistent with the Eurocodes. Aiming at validating the resistance format proposed and that set of partial factors, this second part presents explicit reliability analyses of pultruded FRP profiles designed for the different global buckling failure mechanisms, so that the design equations proposed comply with the target reliability index recommended in EN 1990 for common structural elements. The reliability-based calibration followed similar methodology of documents that assessed the reliability of design with the Eurocodes, including the stochastic modelling of loads and geometry. Partial factor calibration was made through iterative reliability analyses on representative structural elements defined from the proposed design equations. This calibration process allowed defining (i) recommendations for partial factor γRd and (ii) the representative material property used to define γm for each buckling mechanism. The final part of the paper includes recommendations for future research, towards the validation of assumptions made in this study and the standardization of FRP materials.

Seismic Retrofitting of Traditional Masonry with Pultruded FRP Profiles

This paper presents a study on the potentiality of seismic retrofitting solutions with pultruded Fiber Reinforced Polymer (FRP) profiles. This material can be used in connected frames providing lightweight, corrosion-free and reversible retrofitting of masonry buildings with the moderate requirements of surface preservation. In a hypothetical case study, an experimental program was designed; monotonic shear tests on a half-size physical model of the sample wall were performed to assess the structural performance before and after retrofitting with a basic frame of pultruded Glass Fiber Reinforced Polymer (GFRP) C-shaped profiles, connected to the masonry by steel threaded bar connections. During the tests, the drift, the diagonal displacements in the masonry and the micro-strain in the profiles were measured. The retrofitted system has proven very effective in delaying crack appearance, increasing the maximum load (+85% to +93%) and ultimate displacement (up to +303%). The failure mode switches from rocking to a combination of diagonal cracking and bed joint sliding. The gauge recordings show a very limited mechanical exploitation of the GFRP material, despite the noticeable effectiveness of the retrofit. The application seems thus promising and worth a deeper research focus. Finally, a finite element modelling approach has been developed and validated, and it will be useful to envisage the effects of the proposed solution in future research.

Friction coefficient between FRP pultruded profiles and concrete

This paper presents the experimental results of a direct shear test to determine the friction coefficient between fibre reinforced polymer (FRP) pultruded profiles and concrete. The FRP pultruded profile used in this study was glass fibre reinforced polymer (GFRP) I-section. The specimens were composed of a concrete block and a coupon of the GFRP pultruded profile. The experiment was conducted by using the direct shear test method. The parameters investigated included the type of concrete (self-compacting concrete and normal concrete) and the compressive strength of the concrete, as well as the different components (web and flange) of the I-section. The test results verify that the bond behaviour between the concrete and the GFRP pultruded profiles mainly depends on two factors, the friction stress and the adhesion stress. The friction coefficient between the FRP pultruded profiles and the concrete was between 0.5 and 0.6 when the normal stress fluctuated between 0.5 and 2 MPa, and the adhesion stress was about 0.2 MPa. The compressive strength of the concrete and the different components of the I-section have little effect on the friction coefficient, however, the type of the concrete significantly affects this coefficient.

Synergistic effect on the degradation rate of pultruded glass fiber-reinforced polymer bridge panel after 20 years of exploitation

Glass fiber-reinforced polymer pultruded profiles have great potential in the construction industry, presenting certain advantages when compared with traditional materials, including the potentially improved durability under fluctuating levels of environmental factors. The paper presents analysis of glass fiber-reinforced polymer composite, acquired from cable-stayed Fiberline Bridge exploited for 20 years in the fjord area of Kolding, Denmark. Fragment of composite material used for Fourier transform infrared spectroscopy, thermogravimetric analysis, differential scanning calorimetry, and dynamic mechanical analysis tests was therefore subjected to natural aging as a result of temperature amplitudes, permanent solar radiation as well as aggressive impact of sea salt contained in the moisture in the air around the coastal area. Complex comparative analysis presented in this paper, and based on Fourier transform infrared, thermogravimetric analysis, differential scanning calorimetry, and dynamic mechanical analysis tests, pertained to both unspool composite glass fiber-reinforced polymer material (composite 1) and the one after 20 years of natural aging (composite 2). Dynamic mechanical analysis was allowed to detect thermal effects based on the changes in the modulus or damping behavior. The differential scanning calorimetry experiments were performed on the glass fiber-reinforced polymer material in order to determine the mass variation and the energy changes suffered by the materials, as a function of temperature and time.

Torsional behavior of a hybrid FRP-aluminum space truss bridge: Experimental and numerical study

A novel lightweight hybrid fiber-reinforced polymer (FRP) – aluminum space truss structure that consists of two triangular deck-truss beams has been designed for rapid emergency bridging system. This paper reports a large-scale pure torsion test on a cantilever full-scale specimen to evaluate the detailed linear-elastic torsional behavior and the load-carrying mechanism of the hybrid twin-trackway spatial structure. Additionally, a structural computational finite element model (FEM) was constructed and validated against the experiments. To fully understand the load-carrying mechanism obtained from the experiments, numerical analyses were performed by equivalently converting the torsion reaction of the hybrid twin-trackway structure to the bending and torsion of its twin triangular deck-truss beams. The results indicate that the experimental structure exhibits a good and specific torsional response, which can be well described by FEM. The unidirectional pultruded FRP profiles are mainly subjected to axial forces and are thus appropriate for application to this unique twin-trackway space truss, unlike in the case of the alone single-trackway triangular beam under torsion. The vertical bending of the twin triangular deck-truss beams play a key role in the behavior of load-carrying of the entire bridge, unlike in the case of the conventional torsional calculation method for the separated box beam. In the initial design, the torsional calculation of such a novel bridge can be carried out using the flexural analytical and numerical models of the triangular deck-truss beam.

Predicted mechanical performance of pultruded FRP material under severe temperature duress

Pultruded FRP (fibre reinforced polymer) materials have attracted the attention of civil engineers with their high strength weight ratio and environmentally friendly production and use. Mechanical analysis of pultruded FRP profiles is complex since the material is anisotropic and becomes more complex when thin FRP dedicated hollow cross sections are involved. This is particularly relevant with square or rectangular construction forms where the corners of the material are suspected to produce weak points under compressive loading. FRPs are also believed to behave contrarily when subjected to heat and thermal duress. This research investigates problems in predicting their behaviour under compression (hollow square pultruded FRP sample) using different analytical and modelling approaches. The mechanical behaviour of the material is investigated under different thermal conditions through finite element simulation and the results are then compared with previously conducted laboratory research analysis. The large deformation in anisotropic materials is simulated to provide better prediction regarding the failure mechanism of this material. Finite element simulation is then used to estimate the performance of similar and often competitive construction materials to GFRP (i.e.: wood, concrete and steel) under similar thermal and compressive duress.

Experimental and numerical study of the torsional response of a modular hybrid FRP-aluminum triangular deck-truss beam

A hybrid fiber-reinforced polymer (FRP) – aluminum modular space truss emergency bridge has been designed that consists of two triangular deck-truss beams incorporating a new structural form and advanced pultruded FRP profiles. As a fundamental investigation, this paper explores the detailed torsional behaviors of the new triangular deck-truss beam. A full-scale specimen was prepared and tested under pure torsion to evaluate the representative structural performances. A three-dimensional finite element model (FEM) was constructed and validated with experimental results showing good comparisons. Furthermore, the torsional behavior of the triangular deck-truss beam was numerically investigated by removing individual primary truss members to clearly understand the load transfer mechanism. It was found that the beam exhibited a specific and unfavorable mechanical behavior prohibiting full utilization of the FRP material' potential. The external torsional moment is confirmed to be primarily resisted by the torsion of the longitudinal profiles and the in-plane bending of the bilateral Vierendeel trusses rather than the out-of-plane bending of the web diagonals. Possible improvement and optimization procedures are further suggested for this beam when solely used as a structure subjected to off-axis load or pure torsion.

Durability of Glass Fibre Reinforced Polymer Pultruded Profiles: Comparison Between QUV Accelerated Exposure and Natural Weathering in a Mediterranean Climate

Durability of Glass Fibre Reinforced Polymer Pultruded Profiles: Comparison Between QUV Accelerated Exposure and Natural Weathering in a Mediterranean Climate

Durability of Glass Fibre Reinforced Polymer Pultruded Profiles: Comparison Between QUV Accelerated Exposure and Natural Weathering in a Mediterranean Climate

This paper presents the results of an experimental study about the durability of E-glass fibre reinforced polymer (GFRP) pultruded profiles when exposed to environmental degradation agents. Small-scale coupons obtained from commercial GFRP profiles, made of either unsaturated polyester or vinylester resins, were exposed to natural ageing in the city centre of Lisbon, an urban Mediterranean environment, during 42 months (3.5 years) and to artificial accelerated ageing in a Q-Lab Ultraviolet accelerated weathering chamber (QUV) chamber up to 3000 h. The effects of such exposure conditions on both types of profiles were assessed and compared regarding the changes on the following physical, chemical, aesthetical, and mechanical properties: (1) colour and gloss variations, (2) viscoelastic response, evaluated by means of dynamic mechanical analysis (DMA), (3)mechanical response in tension, bending and interlaminar shear, and (4) chemical changes, assessed through Fourier transform infrared spectroscopy (FTIR). Both types of environmental exposure caused significant aesthetical changes. Mechanical and viscoelastic properties presented slight changes, suggesting evidence of post-curing phenomena and confirming that ultraviolet (UV) radiation affects essentially the outermost layers of GFRP profiles. In general, the GFRP profile made of polyester presented worse durability performance than the vinylester one, in terms of mechanical performance and especially of aesthetical (surface) performance. QUV and natural ageing could be correlated, particularly in what concerns colour and gloss changes; regarding physical and mechanical changes, in general, properties after ageing in those environments are of the same order of magnitude and exhibit comparable variation trends.

LRFD Factors for Pultruded Wide-Flange Columns

Fiber-reinforced polymer (FRP) pultruded profiles are produced by a number of manufacturers worldwide in similar, but nonstandard, wide-flange, I, angle, and tubular profiles. At present there is no American National Standards Institute approved design code in the United States for structural design with pultruded FRP profiles. Manufacturers of pultruded profiles each provide their own design equations, design methods, material properties, and safety factors for their pultruded products. There is a need for standardization of production and design of pultruded profiles to enable mainstream use of these profiles in structural engineering practice. The purpose of this paper is twofold: (1) to provide appropriate resistance factors ( ϕ factors) for wide-flange pultruded columns that are compatible with ASCE 7 load factors and (2) to provide a unified analytical equation for local and global buckling of concentrically loaded axial members, which may be appropriate for a future design code. The resistance fact...

Static behavior of pultruded fiber-reinforced polymer thin-walled beams

Pultruded profiles made of fiber-reinforced polymer (FRP) materials are increasingly used in the construction industry as primary and secondary load-bearing members, because of their low weight, high mechanical properties and good corrosion behavior. FRP structural members are usually pultruded with I, H, C, box or other thin-walled closed or open sections. The mechanical behavior of pultruded FRP members, having continuous unidirectional fibers embedded into a polymeric resin, can be described as transversely isotropic, where the plane of isotropy is perpendicular to the fibers. The static behavior of FRP pultruded profiles has been subject of numerous analytical and numerical investigations. Among the former, a common approach adopted in the past has been to extend to orthotropic materials the well-known theory for thin-walled beams developed by Vlasov and Timoshenko. In this paper, a different approach to the static analysis of FRP pultruded profiles is presented. The exact theory of thin-walled isotropic beams developed by Capurso in 1964 is generalized to the case of transversely isotropic materials and its predictions are analyzed. Such a theory eliminates the limitations related to St. Venant’s principle and thus allows determination of the state of stress in the proximity of restraints or concentrated loads, and the state of stress generated by arbitrary loads acting on the lateral surface of the beam. It is shown that, for transversely isotropic materials and within the range of mechanical properties of common FRP profiles, the discrepancy between exact and Vlasov formulations may be significantly larger than for isotropic materials. Hence, Vlasov theory may lead to significantly inaccurate predictions of the state of stress. A numerical example is presented for the I-profile.