Fiber Reinforced Polymer Members Research Articles

A novel ductile connection for FRP pultruded beam-to-column assemblies

The resistance, stiffness and ductility of the joints between Fibre Reinforced Polymer (FRP) members play a key role in ensuring the required structural performance of pultruded composite frames. Both bonded and bolted joints are characterised by poor mechanical performance due to brittle failure and low resistance respectively. Hybrid joints are stronger and more ductile, but are still affected by some criticisms such as (i) non-repairability, (ii) the presence of holes in the fibre-reinforced material, (iii) the difficulty of assembling a transverse beam into the joint, which is typically required for real 3D systems. To overcome such limitations, a novel ductile connection has been developed by combining ductile steel elements bonded to FRP members. The steel elements are bolted together and are designed to be weaker than the FRP profiles and adhesive. Experimental tests on beam-column assemblies have been carried out and the test results have shown that the investigated hybrid connection is characterised by adequate stiffness, resistance and high ductility. The damage is concentrated in the bolted steel elements, which can be easily replaced, confirming the repairability of the assembly.

Innovating arch structures with fiber-reinforced polymer composites: A review

Fiber-reinforced polymer (FRP) composites are a class of advanced non-metallic materials featuring advantages of high strength, light weight and excellent corrosion resistance. These advantages, in conjunction with the various methods available for making curved FRP members, create a wide range of possibilities for innovating arch structures with FRP composites. However, this subject has received inadequate research attention despite the exciting prospects demonstrated by pioneer studies. This paper provides a review on this subject with the aim to build a holistic picture and engage wider research participation. The paper begins with an overview of four feasible manufacturing/forming methods (vacuum infusion, filament winding, pultrusion and active bending), with an emphasis on their capability of creating curved FRP members and potential applications in arch structures. A review is next made on previous arch projects and relevant novel concepts, which are classified into two categories (all-FRP arches and FRP-incorporating hybrid arches) with distinct functionality and targeted areas of application. On the basis of this review, directions for future development of each of the two categories are highlighted, with a number of challenges and potential solutions discussed.

Study on Graphene-modified FRP Bars Used in the Process of Construction Health Management

The distributed long-gauge optical sensor on fiber reinforced polymer (FRP) bar cannot be manufactured through integrated production in current situation, which is hard for construction management. On the other hand, the point-sensing technology of the self-sensing bar will cause deviations in structural health monitoring (SHM). To solve these issues, applying the graphene/epoxy on FRP members is a feasible method for the piezoresistive characteristics of graphene. In this paper, basalt FRP (BFRP) bars with graphene/epoxy film were tested under repeated and cyclic loads and the resistance was measured at the same time until they were broken down. The results suggested that the test pieces can maintain stable sensing performance under repeated and cyclic loads. These facts indicated that the graphene-modified BFRP bars can well reflect the stress condition of the structural member within a safe range and can maintain stable self-sensing performance in the construction health management.

Study on Self-Sensing Performance of Graphene-Modified FRP Bars

At present, the distributed long-gauge optical sensor on fiber reinforced polymer(FRP) bar cannot be manufactured through integrated production. On the other hand, the point-sensing technology of the self-sensing bar will cause deviations in structural health monitoring (SHM). To solve these issues, applying the graphene/epoxy on FRP members is a feasible method for the piezoresistive characteristics of graphene. In this paper, basalt FRP (BFRP) bars with graphene/epoxy film were tested under static tensile load and the resistance was measured at the same time until they were broken down. The results suggested that the changing rate of resistance was linearly correlated to the strain. This fact indicated that the graphene-modified BFRP bar can well reflect the stress condition of the structural member within a safe range.

Structural performance of axially- and laterally-loaded cantilevers with thermally-improved detailing

Cladding details that span the building envelope are particularly susceptible to forming thermal bridges, where heat is transferred between interior and exterior, resulting in loss of energy. Steel buildings are particularly susceptible to forming thermal bridges due to the relatively high thermal conductivity of steel compared to that of other structural materials. To mitigate these thermal bridges, thermal breaks may be inserted in the cladding detail connection to the building interior, and have demonstrated promise in previous thermal modeling studies, with up to 65% reduction in thermal bridging. This paper summarizes recent work on the design, validation, and implementation of thermal break strategies that maintain structural integrity. Fiber-reinforced polymer (FRP) shims were used to provide thermal breaks in steel connections of cladding details. Partial replacement of steel structural members with FRP members was also explored. Shims were the focus of the work due to ease of installation, cross-section availability, and thermal performance. While several cladding details were examined in this research, this paper summarizes the cyclic performance of roof posts (under axial and cyclic lateral loads) and canopy beams (under cyclic lateral loads only), representing their anticipated performance during earthquakes and wind events. While roof posts and canopy beams exist in a range of applications in building construction, structural archetypes selected for this work represent lightly-loaded examples that are common in the field. The impact of adding FRP shims at the bolted base plate connection to the building interior is discussed. Recommendations for design and future research are also presented.

Classification and regression tree (CART) modelling for analysis of shear strength of FRP-RC members

The shear behaviour of concrete members that are reinforced with fibre-reinforced polymer (FRP) bars varies from that of steel reinforced concrete members. The use of non-parametric techniques, which can explain the relationship between different properties of FRP members in more detail, has not yet been well researched in this area. This study utilized a non-parametric technique, namely Classification and Regression Tree (CART) to predict the shear capacity of FRP reinforced concrete members. The members were only reinforced lengthways without vertical reinforcement. A total of 216 experimental results are used to train and test the CART model. The outcomes from CART were compared to traditional models and equations, as well as another non-parametric model from previous research. The comparison showed that CART has better accuracy than other models. It can therefore be used to develop guidelines for the design of FRP concrete members.

Mechanical Properties of Fibre Reinforced Polymers under Elevated Temperatures: An Overview

Fibre-reinforced polymer (FRP) composite is one of the most applicable materials used in civil infrastructures, as it has been proven advantageous in terms of high strength and stiffness to weight ratio and anti-corrosion. The performance of FRP under elevated temperatures has gained significant attention among academia and industry. A comprehensive review on experimental and numerical studies investigating the mechanical performance of FRP composites subjected to elevated temperatures, ranging from ambient to fire condition, is presented in this paper. Over 100 research papers on the mechanical properties of FRP materials including tensile, compressive, flexural and shear strengths and moduli are reviewed. Although they report dispersed data, several interesting conclusions can be drawn from these studies. In general, exposure to elevated temperatures near and above the resin glass transition temperature, Tg, has detrimental effects on the mechanical characteristics of FRP materials. On the other hand, elevated temperatures below Tg can cause low levels of degradation. Discussions are made on degradation mechanisms of different FRP members. This review outlines recommendations for future works. The behaviour of FRP composites under elevated temperatures provides a comprehensive understanding based on the database presented. In addition, a foundation for determining predictive models for FRP materials exposed to elevated temperatures could be laid using the finding that this review presents.

An investigation of the influence of the reduced elasticity modulus on strength of pultruded frp members in bending

The polymer composite known as Fibre Reinforced Polymer (FRP) has several advantages over conventional materials. It has been slowly incorporated into civil infrastructures, because the general regulations have not yet been officially introduced. Pultruded FRP manufactures have internal standards of organizations and Guidelines. Therefore, the design identifies issues that require clarification. This study presents influence of the reduced elasticity modulus on strength of pultruded FRP members in bending with a symmetrical cross-section. The position of the neutral line and calculation of strength and deflections with and without reduced modulus of elasticity are determined in the study. Comparison of the results of calculations showed that when taking into account the reduced modulus of elasticity, the deformability is reduced by up to 15 %. The significance of the results obtained for the construction industry consists in the possibility of a refined calculation of the flexural pultruded FRP members taking into account the reduced modulus of elasticity in order to effectively use the strength reserves and reducing material consumption.

Comparative study on calculation methods for local buckling critical stress of rectangular section FRP members

The prediction accuracy of the local buckling critical stress calculation formula of the existing FRP members is analyzed by the experimental data of the local buckling critical stress of the fiber reinforced polymer (FRP) members.Verification of the validity of the finite element model based on experimental data.The comparison results between the numerical simulation critical stress and the predicted value of the calculation formula after adjusting the size of the FRP member are obtained. The variation of the prediction accuracy of the existing calculation formula is studied.The research shows that the predictive value of the calculation method proposed by Strongwell in 1998 underestimated the database test data by 45.4%, and underestimated the finite element simulation result by 46.3%.It is the equation closest to the actual local buckling critical force of the PFRP member. As a general formula, predicting the local buckling critical stress of the PFRP member can improve the material utilization rate. After the research, it was found that the calculation formula proposed by Strongwell Company had a large error with the database test data, and there is still room for improvement.

Static performance of a new GFRP–metal string truss bridge subjected to unsymmetrical loads

A unique lightweight string truss deployable bridge assembled by thin-walled fiber reinforced polymer (FRP) and metal profiles was designed for emergency applications. As a new structure, investigations into the static structural performance under the serviceability limit state are desired for examining the structural integrity of the developed bridge when subjected to unsymmetrical loadings characterized by combined torsion and bending. In this study, a full-scale experimental inspection was conducted on a fabricated bridge, and the combined flexural–torsional behavior was examined in terms of displacement and strains. The experimental structure showed favorable strength and rigidity performances to function as deployable bridge under unsymmetrical loading conditions and should be designed in accordance with the stiffness criterion, the same as that under symmetrical loads. In addition, a finite element model (FEM) with a simple modeling process, which considered the multi segments of the FRP members and realistic nodal stiffness of the complex unique hybrid nodal joints, was constructed and compared against experiments, demonstrating good agreement. A FEM-based numerical analysis was thereafter performed to explore the effect of the change in elastic modulus of different FRP elements on the static deformation of the bridge. The results confirmed that the change in elastic modulus of different types of FRP element members caused remarkable differences on the bending and torsional stiffness of the hybrid bridge. The global stiffness of such a unique bridge can be significantly enhanced by redesigning the critical lower string pull bars using designable FRP profiles with high elastic modulus.

Design and Construction of 1 MW Class Floating PV Generation Structural System Using FRP Members

The paper investigates overview of construction process of a 1 MW class floating photovoltaic (PV) generation structural system fabricated with fiber reinforced polymer (FRP) members. The floating PV generation system consists of unit structures linked by a hinge type connection of which the effect of bending moment between the unit structures, induced by the unstable movement of the water surface, was minimized. Moreover, the unit structures were classified into three types of structures by combining the floating PV generation system and pontoon bridges, which are constructed to install the electrical equipment and a route of movement for workers. The structural safety of the connection system among the unit structures and/or the mooring system is confirmed by referring to the relevant design codes. In addition, structural analysis using the finite element method was performed to ensure the safety of the floating PV generation structure, and commercial viability evaluation was performed based on the construction cost. The FRP member shows superior performance in construction and cost effectiveness in a floating PV generation system.

Analysis of adhesive joints between fibre-reinforced polymer laminates and structural steel members

Over the past three decades, fibre-reinforced polymer (FRP) materials have gained a lot of attention in construction especially in the field of infrastructure. The attractiveness of FRP materials is mainly due to their superior mechanical properties such as high specific strength and stiffness, light weight and good fatigue and durability characteristics. The most common applications of FRP materials have been in strengthening and repair of existing structures. Using FRP composites for concrete strengthening and repair has been well researched and documented. However, when it comes to steel structures, the application of FRP materials is somewhat limited. One of the main reasons is the lack of accurate design models for adhesive joints between FRP and steel members. Issues such as the complexity of failure modes and the lack of knowledge of the force transfer mechanism are obstacles that contribute to the difficulty associated with developing accurate design models. This paper deals with analysis of adhesive joints used to bond carbon FRP laminates to steel substrates using a numerical and experimental approach. A numerical model of the studied joint configuration has been developed utilising the finite element method, while, an optic measurement technique has been used to experimentally verify the numerical results. Several classical failure criteria used for design of adhesive joints have been studied to examine their applicability and accuracy in predicting the failure load of the specimens. Different aspects of joint behaviour, such as strain distribution along the bond line and through the thickness of the adhesive layer and failure mechanisms are discussed and conclusions with regard to design of such joints are presented.

Analysis of Adhesive Joints Between Fibre-Reinforced Polymer Laminates and Structural Steel Members

Over the past three decades, fibre-reinforced polymer (FRP) materials have gained a lot of attention in construction especially in the field of infrastructure. The attractiveness of FRP materials is mainly due to their superior mechanical properties such as high specific strength and stiffness, light weight and good fatigue and durability characteristics. The most common applications of FRP materials have been in strengthening and repair of existing structures. Using FRP composites for concrete strengthening and repair has been well researched and documented. However, when it comes to steel structures, the application of FRP materials is somewhat limited. One of the main reasons is the lack of accurate design models for adhesive joints between FRP and steel members. Issues such as the complexity of failure modes and the lack of knowledge of the force transfer mechanism are obstacles that contribute to the difficulty associated with developing accurate design models. This paper deals with analysis of adhesive joints used to bond carbon FRP laminates to steel substrates using a numerical and experimental approach. A numerical model of the studied joint configuration has been developed utilising the finite element method, while, an optic measurement technique has been used to experimentally verify the numerical results. Several classical failure criteria used for design of adhesive joints have been studied to examine their applicability and accuracy in predicting the failure load of the specimens. Different aspects of joint behaviour, such as strain distribution along the bond line and through the thickness of the adhesive layer and failure mechanisms are discussed and conclusions with regard to design of such joints are presented.

Mechanical properties of pultruded carbon fibre-reinforced polymer (CFRP) plates at elevated temperatures

The use of fibre-reinforced polymer (FRP) composites is becoming increasingly widespread in civil infrastructure for strengthening and repair applications as well as whole FRP members and structures. A question which, however, continually arises from all stake-holders is the performance of FRP materials under elevated temperatures. An accurate understanding of the material properties and behaviour of FRP at such high temperatures is crucial, and they are necessary pieces of information that are surprisingly scarce in the literature. This paper therefore presents the mechanical properties of pultruded carbon fibre-reinforced polymer (CFRP) plates at elevated temperatures. More specifically, CFRP pultruded plate coupons were tested at steady and transient states for temperatures ranging from approximately 20 to 700 °C. The tests showed that, for the temperature ranges 20–150 °C and 450–706 °C, reductions of the tensile strength of the pultruded CFRP plate occurred. Between these temperature ranges, the tensile strength decreased by a small amount, while at 300 °C the ultimate strength was approximately 50% of the room-temperature strength. In addition, the tensile strength of the plate was as low as 7% of the room-temperature tensile strength at the approximate peak temperature of 700 °C. Finally, an equation that relates the tensile strength of the plate to the entire tested temperature range which has been calibrated with all the test data is proposed.

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.