Analytical modeling and axial load design of a novel FRP-encased steel–concrete composite column for various slenderness ratios

A novel composite column composed of steel, concrete and a fiber reinforced polymer (FRP) tube is presented in this paper. The confinement and composite action between the constituent materials result in enhanced compressive strength, ductility and energy dissipation capacity of the proposed composite column compared to a traditional reinforced concrete (RC) column. Due to the presence of the FRP tube, current design methods for concrete-filled steel tubes (CFSTs) or concrete-encased steel (CES) columns are not directly applicable. An analytical model was developed to predict the behavior of the composite column for various slenderness ratio values. Predicted values are found to be in good agreement with the experimental results from tests of six columns ranging from 500mm to 3000mm in height. A parametric study is conducted to investigate the influence of column diameter, FRP tube thickness, axial compressive modulus of the FRP tube and steel-to-concrete area ratio on the capacity relationships and slenderness limits. Finally, a simplified design equation is proposed to predict the compressive load capacity of this type of composite column.