Finite element modeling of hollow and concrete-filled fiber composite tubes in flexure: Optimization of partial filling and a design method for poles

In this paper, the nonlinear finite element model developed and verified in the companion paper [Son J, Fam A. Finite element modeling of hollow and concrete-filled fiber composite tubes: Part 1 — model development and verification in flexure. Engineering Structures 2008;30(10):2656–66] has been used to study fiber-reinforced polymer (FRP) tubular poles partially filled with concrete in flexure. Partial filling is proposed as a low-cost alternative to using thicker-walled tubes, to enhance flexural strength and stability. The partial concrete fill length is optimized in cantilever-type mono-poles for tubes with different diameter-to-thickness (D/tD/t) ratios and different laminate structures. It was found that this optimum length is reduced in any one of the following conditions: as D/tD/t ratio becomes smaller, when fiber angles relative to the longitudinal axis in angle-ply tubes increases, when longitudinal fiber fraction in cross-ply tubes reduces, and when a laterally distributed load is applied instead of a point load at the tip. Simple expressions were established to calculate moment capacities of hollow and concrete-filled FRP tubes. They were then incorporated into a simple design approach developed to predict the optimum concrete fill length, on the basis of that failure occurs in the concrete-filled and hollow parts simultaneously. A procedure to account for tapered poles is also presented.