Behaviour of bolted connection system in pultruded GFRP structures

The pultruded GFRP hollow sections, in particular, have received growing interest from the engineering community due to better torsional rigidity, effective resistance of out-of-plane forces, high load transfer and improved strength and stiffness of the minor axis. However, one of the significant issues that hinders the widespread use of pultruded GFRP hollow sections is the inadequacy or unpredictability of its connection system. In this study, the behaviour of pultruded GFRP truss structure using through-bolt connection system was investigated based on the current industrial practice in Australia. The through-bolt connection system is incorporated with an FRP mechanical insert as a filled-type connection element and currently, there is no scientific research focusing on joint behaviour of pultruded GFRP hollow profiles with mechanical inserts. This has been the key motivation for this research whereby the suitability and joint strength adequacy of bolted connection with insert for pultruded FRP, in particular, tubular profiles were examined. Therefore, the study ultimately investigated this particular jointing technique on pultruded GFRP trusses and aimed to understand how the loads are resisted, transferred, and distributed to each FRP component. The experimental data and theoretical predictions developed in this study are critical to produce a safe, reliable and adequate connection system for pultruded GFRP hollow sections. This thesis is presented as a compilation of technical papers. In the first paper, effects of threaded bolt with varying end distance to bolt diameter, laminate thickness, clamping pressure and laminate orientations (longitudinal and transverse) on the joint strength behaviour, joint efficiency and mode of failure were evaluated using a double lap joint test set-up configuration. The test results obtained from the effects of using threaded bolt were compared to that of plain bolt in order to assess the differences in joint behaviour and possible reduction in joint capacity. In this experiment, the joint was designed to promote bearing failure as it is preferable in composite joint due to its progressive nature of failure. From this study, approximately 30-40% reduction in joint strength was observed for specimens with longitudinal laminate orientation caused by laminate tearing of the bolt. In addition, under scanning electron microscope (SEM) imaging, this damaging effect was further observed to better understand its mechanism and how it affects the resulting mode of failures. In the second paper, the joint behaviour of pultruded GFRP hollow sections with a single all-threaded bolt and mechanical insert connection system was investigated under elevated in-service temperature. A comparison of different bolted joint configurations of pultruded GFRP hollow sections, namely joint without mechanical insert (N), joint with mechanical insert with tight-fit attachment (I) and joint with mechanical insert bonded with epoxy adhesive (G) was conducted and the effects on the joint strength and failure mechanism were evaluated. The results of this experimental work have demonstrated that the bolted joint with adhesively bonded mechanical insert sustained the highest load-carrying capacity across the elevated temperatures compared to other configurations. Also, the proposed joint strength prediction equation, which incorporates the strength reduction and modification factors based on different joint configurations involving mechanical insert, produced reasonable outcomes against experimental failure load. These results suggest that, the use of mechanical inserts to strengthen bolted connections system can be adopted in pultruded GFRP hollow sections and the joint performance of this configuration at a structural level was discussed in the next paper. In the third paper, the joint behaviour of through-bolt connection with mechanical insert under eccentric loading was investigated. The joint configuration was adopted in pultruded GFRP T-joints using both single and double bottom chords, with the former imbalanced configuration intended to impart load eccentricity. This eccentric condition can be found in composite truss bridges. The experimental results showed that, the presence of mechanical inserts in both single and double bottom chords of the T-joints had improved the joint strength and fixture stiffness when compared to their insert-less counterparts. It was found that the mechanical insert has prevented bolt flexure and contributed to the improvement in bending resistance when subjected to a couple moment developed due to eccentricity. In the last paper, the structural behaviour of double-chorded pultruded GFRP trusses connected using through-bolt with mechanical inserts under different load cases were investigated. The structural performance of the trusses was described in terms of load-midspan deflection response, force distribution of internal members and mode of failure. The results of this study indicate that the adopted through-bolt with mechanical insert connection system possess high joint load-carrying capacity and demonstrated effective transmissitheoretical strength limits of pultruded GFRP truss members in tension, compression and flexural according to ASCE pre-standard were in close agreement with the experimental results. Meanwhile, the prediction equation proposed in the second paper was used here to evaluate the joint load-carrying capacity of the pultruded GFRP trusses. A two-dimensional numerical model to simulate the behaviour of the pultruded GFRP trusses was constructed using Strand7 finite element analysis software. Satisfactory comparisons against experimental results were achieved and this demonstrates the validity of the Strand7 simplified numerical model. From this overall research program, it can be concluded that the combination of through-bolt and mechanical insert is a promising connection system for pultruded GFRP in truss application. The proposed factors and theoretical joint strength equations developed in this research can be important tools for practitioners to perform strength analysis of through-bolt with mechanical insert connection system, encouraging its acceptance and utilisation, especially in truss application.on of internal forces to other truss members. Th

Behaviour of GFRP Reinforced and GFRP Encased Square Concrete Members under Different Loading Conditions

The use of reinforcement with fibre reinforced polymer (FRP) composite materials have emerged as one of the alternatives to steel reinforcement for concrete structures prone to corrosion issues (ACI 440.1R–15 2015). However, the mechanical behaviour of FRP reinforcement is different from that of steel reinforcement. In general FRP bars have a higher strength-to-weight ratio, but lower modulus of elasticity as compared to steel. Furthermore, when subjected to tension, FRP bars do not experience any plastic behaviour before rupture. Also, the compressive strengths of FRP bars are relatively low compared to the tensile strengths and are subjected to significant variations. Therefore, due to the differences in properties, GFRP bars cannot simply replace steel bars (ISIS 2007). The level of understanding of the behaviour of FRP reinforced compression members has not reached a level where design standards are available for such members. Having said this, the current ACI 440.1R – 15 (2015) design guideline recommends neglecting the compressive contribution of FRP reinforcement when used as reinforcement in columns, in compression members, or as compression reinforcement in flexural members. Most of the findings of studies investigating FRP reinforced concrete columns have been reported based on testing under concentric loading with the behaviour of such members under eccentric axial loads not sufficiently addressed in the previous studies

Bond behaviour of composite sandwich panel and epoxy polymer matrix

Fibre composite sandwich panel made up with glass fibre reinforced polymer skins and phenolic foam core can be glued or cast together to produce a large structural beam section. To ensure the structural integrity and composite action, the sandwich panels should be effectively bonded with polymer matrix. However, the bond behaviour between sandwich panel and polymer matrix is not well understood. This paper experimentally investigated the effect of epoxy polymer matrix properties, bond length, bond thickness, and bond width on the bond behaviour, and evaluated the optimal parameters for effective bonding. The experimental program was designed by Taguchi method to reduce the number of experiments. Results showed that the polymer matrix consist with 40% filler and 60% resin (by volume) is the optimal binder. A bond length of at least 70 mm and bond thickness of 5 mm were found effectively to utilise the strength of the composite sandwich panel. The bond width however has insignificant effect on the bond strength

Behaviour of filled pultruded glass fibre reinforced polymer tubes under axial loading

The use of fibre reinforced polymer (FRP) materials in civil engineering applications has been broadened as an alternative construction material due to their features such as high strength, stiffness-to-weight ratio and excellent durability characteristics in aggressive environments. They act as a non-corrosive reinforcement for concrete structures and as a permanent formwork. Pultruded FRP (PFRP) profiles are made in shapes similar to those are made of steel. The usage of pultruded FRP tube sections for column applications in civil infrastructure is not widespread. This is because their full capacity is not utilised due to low stiffness and buckling issues. To overcome this shortage in their axial compressive behaviour, it is necessary to study effects of tube shape, wall thickness, fibre orientation and layup using different sections. Examining effects of filler materials having different stiffness and simulate the axial behaviour using finite element method to study impacts of change in different parameters on the axial behaviour of pultruded FRP tubes are provided a comprehensive understanding about improving the stiffness and load capacity of pultruded FRP tube columns. Firstly, the mechanical properties of different pultruded FRP tubes were calculated by conducting material tests. The results show that the mechanical properties of the pultruded FRP tubes rely mainly on the percentage of the fibre content and fibre orientation. Moreover, it provides an enhancing approach to the axial behaviour of the FRP columns. The basis of this approach is selection the appropriate fibre orientation and layup for the targeted applications for the best structural performance. Secondly, the effect on the axial behaviour of PFRP tube columns due to different types of fillers was experimentally investigated. The results revealed that the stiffness and load carrying capacity of filled columns is increased as the modulus of infill concrete increases. It further shows that the degree of improvement depends on the properties of PFRP tube and concrete. The other important output is the axial behaviour after the peak load. The strength of the filled columns does not decrease sharply after the point of the peak load instead it declines gradually. The properties of infill concrete and transverse modulus of PFRP tube govern the rate of strength reduction in the post-peak region of the load deflection curves and capacity of the energy absorption. Thirdly, finite element simulation was performed to study the axial behaviour of the hollow and filled pultruded FRP columns. The simulation accuracy level was checked against the experimental results. The load-deflection curves, based on the lamina method, give a better agreement compared with the curves of the full-scale column tests. The numerical values of the load capacity also coincide well with those of the experimental tests. The importance of obtaining finite element model with adequate level of accuracy is important to investigate the effects of other parameters. Finally, the last part of this study is numerically examining the effect of different parameters using a parametric study. The parameters considered are wall thickness, fibre orientation and fibre concentration of the pultruded FRP tubes and properties of the infill concrete. The results show that the wall thickness impact positively on the stiffness and load capacity of the hollow square and circular columns. The stiffness of filled columns depends on the compressive strength of filler. The influence of fibre orientation on the performance of hollow circular columns is more significant than its influence on square columns. The significant outcomes of this study are advancing the knowledge of axial compressive behaviour of hollow pultruded FRP columns and establishing the effect of infill concrete on enhancing stiffness, load capacity and energy absorption capacity of filled pultruded FRP columns. Moreover, impacts of various parameters related to shape, dimensions, fibre structure and properties of the concrete filler material are also determined. This study outlines the importance of properties of FRP tube and filler material to enhance the axial behaviour of filled FRP tubes towards broadening their utilisation in civil infrastructure

Development of prefabricated modular houses in pure composite sandwich panels

Tese de Doutoramento (Programa Doutoral em Engenharia Civil)In the scope of the ClickHouse R&D Project, a residential modular temporary building was proposed and developed to accommodate, in urgent situations, dislocated families due to e.g. the occurrence of natural disasters. Proposed building is composed of a frame structure, panels and a tailored connection system. The frame structure and connection are composed of glass fibre reinforced polymer (GFRP) pultruded tubular profiles. While for the panels, composite sandwich panels made of polyurethane foam (PU) core and GFRP skins, are utilized. A new connection system is defined for connecting adjacent members. This modular construction of temporary housing, should be capable of being prefabricated according to the pultrusion technology (for the case of frame and connection components), transported at low cost to the area of installation (due to the reduced weight and being packed), and being easily and quickly assembled. In the ambit of the present thesis, the following research programs, which contributed for the ClickHouse outcomes, were developed: (I) material testing program; (II) development/ characterization of a connection system for jointing composite panels, (III) evaluation of the mechanical performance of single panel, two jointed panels and three jointed panels under flexural loading; (IV) assessment of single and two jointed wall panel’s behaviour under axial loading; (I) performance/characterization of two floor modular prototypes. Phase I is comprising comprehensive material testing program for establishing constitutive relation of the constituent materials of the sandwich panel, namely the PU foam core, GFRP skins and the bond between these two materials. Furthermore, bearing strength behaviour of GFRP skin and pultruded profiles is subjected to study in this phase. In the phase II, a connection system is proposed for connecting floor and wall sandwich panels. Proposed connection is composed of two main parts namely as end integrated Ushape GFRP profile and two connected tubular square GFRP profiles. The end former working as a connector by interlocking inside the U-shape profiles. Two approaches are used to study mechanical behaviour of jointed panels: friction technique and hybrid technique. An experimental program is performed to study the mechanical response of this connection system in the longitudinal and transversal directions. Phase III is included a series of experimental tests are carried out on a single panel, on two and three jointed panels. Flexural responses of the panels, in short term, is analysed, including evaluation of the failure mechanism and the efficiency of the proposed connection system between panels in jointing sandwich panels. Additionally, the creep behaviour of the panels, which is a limiting factor for their serviceability design, is investigated. Numerical and analytical models are proposed and verified including capturing the local failure of the panel using experimental program. The proposed models are used to go further in-depth to understand capability of connection in jointing panels and influence of U-shape GFRP profiles in increasing flexural stiffness of the panels. Additionally, contribution of single sandwich panels components in total shear deflection is investigated. In the phase IV, the structural performances of the sandwich wall panels under axial loading condition are experimentally tested and thereafter analytically assessed in two cases: (i) single wall panels; (ii) two jointed wall panels. The influence of the proposed connection system on the axial load capacity of the jointed panels is analytically evaluated. In phase V, performances of the two floor prototypes to support typical load conditions of residential houses are also assessed. The experimental program is complemented with an extensive finite element modelling and analytical study to verify the experiments results and to obtain connection flexibility, load distribution factor and stress distribution within the floor modular components. Additionally, several parametric studies are developed using FEM models developed and validated by varying geometric aspect ratios and numbers of U-shape GFRP profiles to show potentiality of this structure to have more housing space and consequently to extend this concept for other markets.No âmbito do Projeto I&D ClickHouse, uma habitação modular temporária foi proposta e desenvolvida para acomodar, em situações de urgência, famílias deslocadas, devido à ocorrência de e.g. desastres naturais. A habitação proposta é composta por uma estrutura porticada, painéis sanduíche e um sistema de conexão. A estrutura porticada e ligações são em perfis tubulares pultrudidos em polímeros reforçados com fibra de vidro (GFRP). Por sua vez, os painéis de sanduíche compósitos são constituídos por uma espuma de poliuretano (PU) no núcleo e lâminas de GFRP nas extremidades. Um novo sistema de conexão é proposto para a ligação de elementos adjacentes. Esta construção modular de alojamento temporário, pré-fabricada de acordo com a tecnologia de pultrusão (no caso da estrutura porticada e conexões), pode transportada a baixo custo para a área da instalação (devido ao peso reduzido e sistema embalamento), e ser fácil e rapidamente montada. No âmbito da presente tese, os seguintes programas de investigação, que contribuíram para os resultados do ClickHouse, foram desenvolvidos: (I) programa experimental de caracterização dos materiais; (II) o desenvolvimento/caracterização do sistema de conexão, (III) a avaliação do comportamento mecânico de um painel isolado, dois painéis e três painéis ligados entre si sob cargas de flexão; (IV) a avaliação do comportamento mecânico de um painel isolado e dois painéis ligados entre si sob carga axial; (I) performance/caracterização de dois protótipos de piso modular. A fase I é composta por amplo programa de ensaios dos materiais para o estabelecimento de relações constitutivas dos materiais constituintes do painel de sanduíche, ou seja, o núcleo de espuma PU, as lâminas de GFRP e a aderência entre estes dois materiais. Além disso, a resistência ao esmagamento das lâminas e perfis de GFRP para o caso de ligações mecânicas é também estudada nesta fase. Na fase II, um sistema de ligação é proposto para ligar painéis sanduíche de piso e de parede. O sistema de conexão proposto é composto de duas partes principais, nomeadamente (i) perfis GFRP em “U” integrados no contorno dos painéis e (ii) perfis retangulares em GFRP. A ligação entre painéis é por encaixe, sendo que os elementos (ii) realizam a respetiva ligação. Duas abordagens são usadas para estudar o comportamento mecânico dos painéis ligados: encaixe (apenas por atrito) e técnica híbrida (atrito e mecânica). Um programa experimental é realizado para estudar a resposta mecânica deste sistema de ligação nas direções longitudinais e transversais Na fase III inclui-se série de ensaios experimentais realizados num painel isolado, em dois e três painéis ligados entre si. A resposta à flexão dos painéis, a curto prazo, é analisada, incluindo a avaliação dos mecanismos de rotura e a eficiência do sistema de ligação. Além disso, o comportamento de fluência dos painéis, o que é um aspeto condicionante no dimensionamento deste tipo de painéis, é investigada. Modelos numéricos e analíticos são propostos e validados com recursos aos resultados experimentais obtidos. Os modelos propostos são posteriormente usados na compreensão da capacidade da ligação entre painéis no aumento da rigidez à flexão dos painéis. Além disso, a contribuição da deformação por corte na deformação dos painéis sanduíche é também investigada. Na fase IV, o desempenho estrutural dos painéis sanduíche de parede é testado experimentalmente, sob condições de carga axial, e posteriormente avaliados analiticamente, em dois casos: (i) painéis de parede isolados; (ii) dois painéis de parede ligados entre si. A influência do sistema de ligação proposto na capacidade de carga axial dos painéis é avaliada analiticamente. Na fase V, o desempenho de dois protótipos modulares é avaliada para as condições de carga típicas de habitações residenciais. O programa experimental é complementado com uma extensa simulação numérica e analítica para verificar os resultados experimentais e obter a flexibilidade de ligação, o fator de distribuição de carga e a distribuição de tensões nos componentes modulares do piso. Além disso, vários estudos paramétricos foram desenvolvidos utilizando modelos FEM para mostrar a potencialidade do sistema ser aplicável a estruturas de vãos superiores e, consequentemente, estender este conceito para outros mercados

Experimental investigations on continuous glass-GFRP beams: preliminary nonlinear numerical modelling

This paper describes results of experimental and numerical investigations about the structural behaviour of composite beams made of annealed glass panes and GFRP pultruded profiles. A brief description of flexural tests previously carried out on simply supported glass and glass-GFRP composite beams is first presented. Then, results of flexural tests on two-span glass-GFRP composite beams, bonded with three different structural adhesives, are described in detail. Finally, a preliminary numerical study of the glass-GFRP composite simply supported beams is presented. In this study, two-dimensional finite element models were developed in order to simulate and analyse the serviceability and post-cracking behaviour of those beams. Experimental and numerical results presented in this paper prove the advantages and technical viability of glass-GFRP composite beams

Evaluation on the axial compression mechanical properties of short BFRP laminated bamboo lumber columns

To investigate the effect of BFRP (basalt fiber) reinforced short laminated bamboo lumber (LBL) columns on axial compressive static performance, axial compression tests of twelve BFRP reinforced short LBL columns and three normal short LBL columns were conducted, and tensile tests of 13 BFRP were carried out. The test results show that the failure mode of BFRP reinforced short LBL columns was consistent with that of normal short LBL columns, buckling failure and adhesive layer failure. With the increase of BFRP cloth ratio, the bearing capacity of the columns increased. However, when the cloth ratio exceeded 2.3% (4 layers of BFRP), the average improvement of the load-bearing capacity was not obvious, and the reasonable cloth ratio was reached at 2.3%. The short LBL columns wrapped BFRP showed good compressive ductility, and the higher the cloth ratio of BFRP, the better the compressive ductility. Based on the suitable analysis of test data and referring to the relevant methods of fiber reinforced wood columns, the calculation model of axial compressive bearing capacity and stress-strain relationship model of BFRP reinforced short LBL columns were established. The comparison between theoretical calculation and experimental results verified the reliability and accuracy of the proposed bearing capacity calculation model and stress-strain model