Pultruded Fiber-reinforced Polymer Research Articles

Shear characterisation of pultruded superstructural FRP-concrete push-outs

In this paper, an investigation aimed at characterising the behaviour of headed shear studs in push-out testing is presented. The study aims to contribute to the limited knowledge of Pultruded Fibre Reinforced Polymer (PFRP)-concrete composites, highlighting the predominant failure mode and the underlying variables relevant for predictive analytical equations. Two phases of experimental push-out tests were carried out on composite slabs comprising of normal density concrete (NWC), and PFRP connected using steel headed studs. Phase one focused on studying the effects of headed shear stud configuration on the load capacity of the composite slabs, adopting 19 mm diameter studs. Phase two of the study was aimed at characterising the behaviour of the composite slab by varying the headed stud diameters. Two push-out test specimens adopted 12 mm diameter studs, and a third specimen within this phase adopted the 16 mm stud diameter. The dominant failure mode was bearing, net tension and shear out failures of the FRP plates. These modes of failure were distinctly different from those prevalent in the conventional steel-concrete composite, which is either stud shank failure or concrete pull out. The test investigation suggested a successive increase in shear capacity with increased stud sizes. Specimen with stud size of 16 mm attained higher shear strength per stud, approximately 29.4% in comparison to those with 12 mm diameter studs. The study observed that PFRP-concrete composites could mobilise between 40 and 50% shear resistances to that of their steel-concrete counterpart’s. However, the intensity of bearing failure increases with increase in stud size, thereby compromising the ductility of shear connection.

Review on pultruded FRP structural design for building construction

Fibre reinforced polymer (FRP) have been used in civil engineering for past few years. Researches often argue that available design standard practice are lack of practical design details to be used in structure design. This paper reviews the recent researches of pultruded FRP structural design in civil engineering focusing these fours aspects of area. The design consideration in these areas are relatively important for structural designer to focus. These consist of environments impact, dynamics responses, issue of connection, and buckling design. For environment impact, review focus on the severity of artificial ageing and natural ageing to material mechanical properties, as pultruded FRP structures are now used by industries which require serviceability for harsh environment. Due to the low weight stiffness ratio of FRPs structure, vibration effect is in large degree of extent. Unlike steel structures, pultruded FRP structures are using only the bolting connection. Hence, it is crucial to understand the bolting in detail. For buckling issue, studies of interaction of local and global buckling is often suggested by researches.

Characterisation of C-shape pultruded fibre reinforced polymer for bridge structures

The development of polymer technology has been increased for the past 20 years. Most of the polymer based product is available for aviation, automotive, industrial, and infrastructure purposes include bridges. But, information concern with the used of polymer materials for bridge structures are scattered. In this paper, characterisation was made to investigate the applicability of pultruded fibre reinforced polymer (PFRP) for bridges as structural elements. Several experiments test was then carried out to determine the physical and mechanical properties of PFRP. Some results are compared with the available pre-standard of PFRP for structures. Afterwards, an ageing test was undertaken to observe the effect of temperature on the mechanical properties of PFRP. Comparison with the pre-standard of PFRP for structures show that the physical characteristics are satisfied the minimum requirements. In the mechanical part, the tensile and flexural properties of tested PFRP are conform with the pre-standard of PFRP, whereas the compressive strength was below the recommendation of the pre-standard. From ageing test under high temperature, the PFRP strength is possible to increase or decrease. Enhancement of mechanical strength could be generated by polymer cross-linking reactions which takes place after the production of PFRP and accelerated by high temperature. While, the decreasing of strength is related to the delamination process of the fibre.

Influence of restraint thermal effects on the bond strength of externally bonded CFRP-concrete joints

Elevated temperatures lead to a reduction of the bond strength of FRP (fibre reinforced polymer) reinforcement glued on concrete by ambient cured epoxy adhesive. This degrading behaviour is mainly observed for exposure temperatures beyond the glass transition temperature of the epoxy (Tg ≃ 60–80 °C) which is usually 2–3 times lower than the Tg of the matrix of pultruded FRP reinforcement. Contrary, lap shear tests on FRP-concrete systems made with carbon fibre reinforced polymer (CFRP) revealed an increase of the bond strength at temperatures close to the Tg of the epoxy adhesive. Several explanations have been expressed for this unexpected trend. The most accredited hypothesis describes the increase of bond strength as a consequence of the induced restraint thermal effect between the CFRP and the concrete substrate, because of the different thermal elongation of the materials. In this work, the influence of the restraint thermal effect is investigated further in terms of influence on the ultimate load recorded by lap shear tests at elevated temperature and to understand better the underlying mechanism. The obtained outcomes have revealed that the evaluation of the restrained thermal action has to consider the influence of the bond length of the joint and the thermal degradation of the adhesive.

Prediction of global buckling loads of doubly symmetric pultruded FRP columns subjected to concentric compression

AbstractThis paper presents an improved closed‐form solution to determine the global buckling capacity of axially loaded pultruded fiber‐reinforced polymer (PFRP) columns with doubly symmetry cross sections based on the original solution recommended by Eurocode 3 (EC3). In this improved solution, a new closed‐form equation to determine the reduction factor for global buckling of doubly symmetric PFRP members under axial compression is developed, based on the Ayrton–Perry formula and observed initial out‐of‐straightness of PFRP members measured by other researchers. Recognizing that data on initial imperfections may be unavailable, a second new empirical closed‐form equation is derived to predict the global buckling loads of doubly symmetric PFRP columns based upon the experimental data. Validation of the two explicit solutions taking into account the influence of geometric imperfections of doubly symmetric PFRP shapes is performed by both comparison to experimental data and comparison with validated numerical simulations. In addition, compared with the five closed‐form solutions available in the literature, the two proposed solutions exhibit higher accuracy in predicting the global buckling capacity of concentrically loaded PFRP columns with doubly symmetry cross sections. Parametric studies are further conducted, and the influences of the main parameters on the performance of corresponding solutions are discussed. The two proposed solutions can facilitate the global buckling analysis and design of doubly symmetric PFRP columns under concentric compressive loading.

A comparative study of pull-out performance of bolted joints in pultruded FRP with drilled holes or punched holes

In this study, we investigate the pull-out performance of bolted joints of pultruded fiber reinforced polymer (PFRP) profile specimens with drilled and punched holes, respectively, and investigate the effects of different resin matrices and different fiber directions on the pull-out performance of the bolted joints. The experiment results show that the pull-out performance of the bolted joints in the uni-axial polyurethane-based PFRP is better than that in the uni-axial unsaturated polyester resin-based PFRP. The pull-out capacity of bolted joints on the multi-axial PFRP specimens with drilled holes is better than that of bolted joints in the uni-axial PFRP specimens with drilled holes. The multi-axial fiber can effectively prevent longitudinal splitting of pultruded profiles and significantly improve their pull-out performance. The punching process has little impact on the pull-out performance of bolted joints in the uni-axial PFRP specimens. However, it greatly undermines the pull-out performance of the bolt hole of the multi-axial PFRP specimens. Finally, using the progressive damage analysis (PDA) model, and combined with the Hashin failure criteria, we establish a model by means of the C3D8R solid elements in ABAQUS to simulate the pull-out mechanical behavior of the bolted joints.

Axial compressive behavior of square concrete columns confined with CFRP strip ties using wet lay-up technique

Pultruded fiber-reinforced polymer (FRP) bars used as confining reinforcement in concrete columns provide limited ductility and confinement efficiency due to the drastic reduction of strength at bend portions and premature bond slip failure at overlapping regions. In this study, complete close-type CFRP strip ties (C-S) with rectangular cross-section and fabricated using wet lay-up technique were proposed to overcome the shortcomings of pultruded FRP ties. Ten square concrete columns (300 × 300 × 900 mm), longitudinally reinforced with steel bars and confined with different types of ties such as steel, pultruded CFRP (C-P), and CFRP strip (C-S) ties, were tested to investigate their axial compressive behavior. Test results depicted that the columns confined with C-S ties exhibited improved confined concrete strength and ultimate axial strain in comparison with the columns confined with steel and C-P ties. Confined concrete strength and ultimate axial strain were increased up to 1.16 times and 3.5 times, respectively, by the replacement of C-P ties with the equal volumetric ratio of C-S ties.

Flexural Performance of a Hybrid Bridge Deck with Pultruded Fibre Reinforced Polymer Composite Sandwich Panels

Hybrid bridge decks with the pultruded fibre reinforced polymer have advantageous properties but easily crack because of their unsatisfactory transverse strength and shear strength. This study proposed a type of bridge deck composed of innovative pultruded fibre reinforced polymer composite sandwich panels. Using four-point bending tests, concentric wheelloading tests and eccentric wheel-loading tests combined with first-order shear deformation theory, this study investigated the failure mode, flexural capacity, deformation and ductility of hybrid bridge decks under different working conditions. Under four-point bending and concentric wheel loading, the primary failure modes for this hybrid bridge deck were shear failures along the fibre direction and buckling failure of the upper panel. Under eccentric wheel loading, the primary failure mode was a torsional failure due to the eccentric load. The bearing capacities of the hybrid bridge deck under the three working conditions were 3.8, 3.5 and 3.2 times the service load of a Class I vehicle load, respectively. Besides, the hybrid bridge deck remained in the linear elastic stress state at 2.6 times the service load, indicating that this hybrid bridge deck withstands relatively large vehicle overload without visible damage. The ductility values of this hybrid bridge deck under the three working conditions were 1.79, 2.09 and 2.00, respectively, which are higher than the values for an ordinary pultruded bridge deck. Therefore, the proposed design has the relatively good energy-dissipating capacity, which improves the emergency capacity of the bridge deck.

Numerical failure analysis of built-up columns composed of closely spaced pultruded FRP channels

The results of geometrically nonlinear analyses on 43 built-up Pultruded Fibre-Reinforced Polymer (PFRP) columns with closely spaced chords and intermittent interconnections are presented. A comparison between columns with the end sections entirely loaded and columns loaded at the end battens only is reported, showing no appreciable difference in the P-δ response. The effects due to variations of column length and battens spacing are then investigated. It is found that stocky columns with small battens spacing attain pre-buckling failure at the web-flange junctions of the chords for loads approximately equal to 70% of the crushing load. Slender columns fail by global buckling, whereas intermediate-slenderness columns may experience interaction between local and global buckling. A design method is finally proposed.

Testing and Characterization of Simply Supported Pultruded FRP Angle Beams Using Bending Tests

Structural performance and buckling behaviors of pultruded fiber-reinforced polymer (PFRP) angle profile beams under three-point bending tests are presented in this paper. The angle specimens were evaluated to investigate the effect of unbraced length of the beams on the buckling responses and critical buckling loads. In total, sixteen specimens, including eight span-to-width ratios (L/b) were tested. The dimension of the angle profile was commercially available 76x6.4 mm. The span-to-width ratios of the specimens were in the range of approximately 13 to 59. The constituent materials used for the angle profiles consist of unidirectional E-glass fibers and polyester resin. From the bending tests, the load-deformation relationships and failure modes of angle beams were reported. The experimental results indicated that the critical buckling load decreases as the span-to-width ratio increases. The degree of flexural-torsional buckling is directly related to span-to-width ratio. Furthermore, the comparison between the critical buckling loads obtained from experimental study and prediction using methods provided in AISC-LRFD design equation for PFRP angle profile beams showed an unsatisfactory correlation of the critical buckling loads.

Effect of bolt threads on the double lap joint strength of pultruded fibre reinforced polymer composite materials

The ability to provide effective and adaptable joints for pultruded fibre reinforced polymer (PFRP) is crucial for its widespread application in civil infrastructure. This experimental based study on 150 double lap joints specimens investigated the effects of threaded bolt and clamping pressure on the joint strength behaviour, failure mechanisms and joint efficiency of bolted joints in PFRP. Double lap joints in both longitudinal and transverse directions of the laminates and with different edge distance-to-bolt diameter (e/db) were prepared and tested in accordance with ASTM D5961 standards. The joint strength in the longitudinal laminates with plain bolt increased for e/db ratio for up to 4 and with no appreciable strength gain after exceeding this ratio. On the other hand, about 30%–40% reduction in joint strength was observed in the longitudinal direction due to the bolt thread tearing through the laminates. This leads to a recommendation of 0.6 reduction factor in preliminary design of PFRP bolted connections with bolt thread present. Meanwhile, only a marginal difference of 7% was observed in transverse direction. Furthermore, the introduction of lateral clamping pressure had increased the joint strength by 60%–90% and this has lessened the thread casualty effect on the pultruded composite joints.

Tensile and compressive modulus of elasticity of pultruded fiber-reinforced polymer composite materials

Many researches focused on the mechanical properties of steel and concrete have been carried out for applications in the construction industry. However, in order to clarify the mechanical properties of pultruded fiber-reinforced polymer (PFRP) structural members for construction, testing is needed. Deriving the mechanical properties of PFRP structural members through testing is difficult, however, because some members cannot be tested easily due to their cross-section dimensions. This paper reports a part of studies that attempt to present conservative results in the case of members that cannot be tested reasonably. The authors obtained and compared experimental and theoretical modulus of elasticity values. If the mechanical properties of PFRP members can be predicted using reasonable and conservative values, then the structure can be designed economically and safely even in the early design stages. To this end, this paper proposes a strain energy approach as a conservative and convenient way to predict the mechanical properties of PFRP structural members. The strain energy data obtained can be used to predict the mechanical properties of PFRP members in the construction field.

Investigation of the thermal ageing process and mechanism of benzoxazine/bismaleimide/cyanate ester copolymer

Fibre-reinforced polymer (FRP) composites with thermosetting resin matrices are widely used in civil engineering (e.g. pultruded FRP plates and bars), and their thermal ageing behaviour is a concern when they are subjected to elevated temperatures (e.g. FRP chimney). In the present article, the effects of thermal ageing at 200°C and 250°C in air for up to 1000 h on mechanical properties and mechanism of the benzoxazine (Boz), bisphenol A dicyanate cyanate ester (BADCy), and 4,4′-bismaleimidodiphenyl methane (BMI) have been investigated. The effect of time in thermal ageing on structural and mechanical properties of the Boz/BMI/BADCy resin was deeply studied. The moisture absorption increases linearly with the square root of ageing time and it follows Fick’s second law. There are two main categories of reactions in thermal ageing: the first one is the post-curing process, which leads to a larger crosslinking density and a reduced interior stress; while the other is the formation of microcracks and thermal oxidation at the surface of the Boz/BMI/BADCy resin. The combination of the above factors leads to an increase–decrease variation in the mechanical properties. This work is believed to benefit the wide and safe application of a certain Boz/BMI/BADCy resin system in engineering application.

Global buckling capacity of pultruded FRP-I section columns under axial compression

This paper presents an improved closed-form solution to determine the global buckling loads of axially loaded pultruded fiber-reinforced polymer (PFRP) I-section columns based on the original solution recommended by Eurocode 3 (EC3). In this improved solution, a new closed-form equation to determine the reduction factor for global buckling of PFRP I-section members subjected to concentric compression is developed, based on the Ayrton-Perry formula and observed initial out-of-straightness of PFRP struts measured by other researchers. Recognizing that data on initial imperfections may be unavailable, a second new empirical closed-form equation is derived to predict the global buckling capacity of PFRP I-section columns based upon the experimental data. Validation of the two explicit solutions considering the influence of geometric imperfections of PFRP I-sections is performed by both comparison to experimental data and comparison with validated numerical simulations. In addition, compared with the five closed-form solutions available in the literature, the two proposed solutions display higher accuracy in predicting the global buckling loads of concentrically loaded PFRP I-section columns. Parametric studies are further conducted, and the influences of the main parameters on the performance of corresponding solutions are discussed. The two proposed solutions can facilitate the global buckling analysis and design of PFRP I-section members subjected to concentric compression.

Determination of critical loads for global buckling of axially loaded pultruded fiber-reinforced polymer members with doubly symmetric cross sections

This article proposes a new closed-form equation to determine the reduction factor for global buckling of concentrically loaded pultruded fiber-reinforced polymer struts based on the Ayrton–Perry formula and observed initial out-of-straightness of pultruded fiber-reinforced polymer members measured by other researchers, which makes the original solution recommended by Eurocode 3 easy to be used to predict the global buckling loads of doubly symmetric pultruded fiber-reinforced polymer members subjected to axial compression. The influence of the geometric imperfections of pultruded fiber-reinforced polymer profiles is considered in this new closed-form equation. Validation of the solution including the parameter of the reduction factor for global buckling of pultruded fiber-reinforced polymer columns is performed by comparison with published experimental evidence. In addition, compared with the five closed-form solutions available in the literature, this solution exhibits higher accuracy in predicting the global buckling capacity of concentrically loaded pultruded fiber-reinforced polymer struts with doubly symmetric cross sections. The solution implemented into the new reduction factor equation for global buckling of pultruded fiber-reinforced polymer members can be conveniently used by structural engineers at the preliminary engineering design stage for accurately assessing the reliability and safety of composite structures under concentric compressive loading.

Study of FRP bars under tension using acoustic emission detection technique

Acoustic emission (AE) signal has proved to be a useful tool for monitoring structures reinforced with FRP composites such as Fiber Reinforced Polymer (FRP) reinforced beams, carbon FRP (CFRP) sheets, or steel fiber reinforced concrete. This work focuses on studying the behavior of pultruded FRP bars, which have been manufactured using continuous fibers. Different configurations of CFRP and glass FRP (GFRP) bar specimens subjected to tensile load were monitored using AE technique. Several algorithms were used for signal processing to analyze AE signals in the time domain and in the time–frequency domain. The signal processing techniques extracted the amplitude, cumulative events, duration, energy, rise time, number of counts, cumulative counts, and frequency peaks of the acoustic signals. The frequency maxima were determined for different amplitude signals using short-time Fourier transform (STFT). Cumulative counts of AE signals showed significant changes in the slope during the tension test, while the stress–strain relationship of the FRP rods showed virtually no deviation from linearity. CFRP bars recorded higher amplitude signals and lower duration, than GFRP bars. The acoustic emission characteristics presented in this work show strong correlations with ultimate load and may prove useful for damage prediction.

Mechanical characterization of pultruded elements: Fiber orientation influence vs web-flange junction local problem. Experimental and numerical tests

Abstract Fiber Reinforced Polymers (FRP) material are proposed and implemented for civil engineering applications for both retrofitting of existing structures and building of new facilities. In new construction realizations, FRP elements are frequently manufactured using pultrusion that represents a high rate manufacturing method, however characterized by a prevalent longitudinal fiber orientation with consequently weakness along the directions different than the longitudinal one. The intrinsic orthotropy, the presence of defects due to the manufacturing processes and the brittle failure mechanisms are peculiarities that decelerate their wide applications, so that are an open issue to be solved. In this regard, the present work experimentally investigates the local behavior of a commercial Pultruded I-shaped Glass FRP (PGFRP) element, in order to: 1) evaluate the mechanical properties of the material according to different fiber orientations, 2) check the validity of the Tsai Hill Criterion and 3) investigate the capacity of the web-flange (WF) junction, that is a recognized weak point, through a novel and simple experimental test.

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.

Determination of critical load for global flexural buckling in concentrically loaded pultruded FRP structural struts

This paper presents a comprehensive test database of concentric compression experiments on pultruded fiber-reinforced polymer (PFRP) specimens that failed in a global flexural buckling mode published in literature between 1969 and 2016. A new closed-form equation to determine the reduction factor for global flexural buckling of PFRP structural struts under axial compression is developed on the basis of the Ayrton-Perry formula and observed initial out-of-straightness of PFRP members measured by other researchers. Recognizing that data on initial imperfections may be unavailable, a second new empirical closed-form equation is derived based upon the experimental database. Validation of the two explicit expressions is performed by both comparison to experimental data and comparison with validated numerical simulations. In addition, the accuracies of the two proposed equations are compared with those of five closed-form solutions available in the literature; both results in more accurate predictions than the extant equations. Both new proposed equations can be conveniently used by structural engineers at the preliminary engineering design stage for accurately assessing the reliability and safety of composite structures under concentric compressive loading.

Hygrothermal aging effects on axial behaviour of pultruded web–flange junctions and adhesively bonded build-up bridge members

Premature local failure of web/flange junctions of the majority of unstiffened commercially produced pultruded fiber-reinforced polymer composites profiles is inescapable due to lack of fiber continuity at the resin-dominated junction zones. This paper focuses on evaluating both short- and long-term behavior of such junctions when subjected to axial tensile stresses. In this study, the axial mechanical behavior of web/flange junctions of pultruded bridge deck components before and after hygrothermal aging effect is investigated. In the experimental phase, axial tensile tests were performed on six different types of pultruded web–flange junctions to assess axial characteristics of each web/flange junction type. In order to evaluate the hygrothermal behavior of such junctions, axial tensile tests were conducted on web/flange junction specimens that were exposed to both fresh water and artificial seawater environments at temperatures of 40℃, 60℃, and 80℃. Several controlling parameters affecting both strength and stiffness of pultruded fiber-reinforced polymer junctions were identified and discussed that include: (i) Junction's web and flange thicknesses, (ii) fillet radius, and (iii) variation of hygrothermal exposure environments. Results of this study indicated that the axial tensile capacity of a pultruded profiles is increased as the thickness of both web and flange increases. Also, it was found that the larger fillet radius of the pultruded fiber-reinforced polymer profile may contribute to a larger axial tensile capacity of pultruded profiles. However, due to variable size and geometry of the resin-rich junction zones and the common manufacturing defects in the form of folded fabric and other fibers misalignment effects, it is difficult to generalize the preceding results. Experimental results also showed that the degradation of web/flange junctions axial tensile strength increases when junctions are exposed to higher temperatures. Also, it was found that the axial tensile characteristics for junctions specimens exposed to freshwater environment are slightly different than those that were exposed to artificial seawater environments.