Tests and Analysis of Cantilevered GFRP Tubular Poles with Partial Concrete Filling

In this study, six glass fiber-reinforced polymer (GFRP) cantilevered tubular poles were tested in flexure. Four poles were filled with varying amounts of concrete; within 13, 30, 51, and 72% of their lengths, from the fixed point. Two poles, namely, a hollow and a totally concrete-filled tubes, were also tested as control specimens. The filament-wound prismatic tubes were 3,660 mm long, including a 700 mm clamped length at the fixed end, with a 220 mm outer diameter, and 4.15 mm wall thickness. The study aims at increasing flexural strength of thin-walled GFRP tubular poles by using a small amount of concrete at the vicinity of maximum moment near the base. Test results showed that flexural strength increases as the length of concrete fill is increased, until it reaches a plateau corresponding to about double the strength of the hollow tube, when the concrete fill is about one third of the clear length. This is considered the optimal condition for this tube that provides the largest strength-to-weight ratio. Poles with a shorter filling length failed prematurely, by a combined local buckling and crushing of the hollow part, while poles with a longer filling length failed at the base by rupture of the tube in tension. An analytical model was developed, validated, and used in a parametric study. The correlations between the optimal filling length ratio and both “diameter-to-thickness” ratio, and laminate structure of the tube, have been demonstrated for both angle-ply and cross-ply tubes.