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

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.