Flexural behaviour of spun-cast concrete-filled fibre reinforced polymer tubes for pole applications
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In this study, the feasibility of utilizing the spin casting technique with structural Fibre-Reinforced Polymer (FRP) tubes and eliminating steel reinforcement is explored for the first time. This would make spun-cast FRP tubes (SCFTs) desirable in pole applications, as they are relatively light-weight, protected from deicing salts and other elements by the tube, and have similar flexural resistance to the completely filled FRP tubes (CFFTs). This study evaluates the flexural and bond performances of SCFTs through experimental and analytical investigations. The experimental investigation included a total of nine beam specimens, approximately 330 mm in diameter and 2.85 m in length, tested in three and four-point bending. Glass-FRP (GFRP) tubes with different wall thicknesses and proportions of fibres in the longitudinal and hoop directions were used in eight specimens. One control specimen was cut from a conventional prestressed spun-cast pole and tested for comparison. Also, one specimen was essentially a control CFFT. The main parameters studied were tube laminate structure, concrete wall thickness, and the effect of additional steel rebar in SCFTs. The experimental investigation also included six push-off stub specimens tested to examine the bond behaviour of SCFTs. An analytical model predicting the flexural response of SCFT beams was developed, verified, and used in a parametric study to examine a wider range of tube laminate structures, concrete wall thicknesses and FRP tube thicknesses. The study demonstrated the feasibility of fabrication of SCFTs in conventional precast plants. SCFTs were shown to have similar flexural strength to conventional prestressed spun-cast poles of an equivalent reinforcement index but are less stiff due to the lower modulus of FRP and lack of prestressing. SCFTs with inner-to-outer diameter ratio (Di/Do) up to about 0.6 achieved the same flexural strength as the CFFT specimen. However, the parametric study showed that this optimum (Di/Do) ratio is dependent on tube thickness and laminate structure and is generally smaller in thicker tubes or tubes stiffer in the longitudinal direction.