This paper presents the experimental results and analytical modeling of the
axial compressive behavior of concrete cylinders confined by both glass fiber-reinforced
polymer (GFRP) tube and inner steel spiral reinforcement (SR). The concrete structure is
termed as GFRP–SR confined concrete. The number of GFRP layers (1, 2, and 3 layers) and
volumetric ratios of SR (1.5% and 3%) were the experimental variables. Test results indicate
that both GFRP tube and SR confinement remarkably increase the ultimate compressive strength,
energy dissipation capacity, and ductility of concrete. The volumetric ratio of SR has a more
pronounced influence on the energy dissipation capacity of confined concrete with more
GFRP layers. In addition, a stress–strain model is presented to predict the axial compressive
behavior of GFRP–SR confined concrete. Comparisons between the analytical results obtained
using the proposed model and experimental results are also presented.