Nonlinear behavior of FRP-reinforced concrete-filled double-skin tubular columns using finite element analysis

• Research addresses exhaustive study on CFDST columns circumscribed by FRP layers.
• Increasing FRP layers only from 2 to 6 induces a 45% increase in ultimate stress.
• Changing fibers from glass to carbon increases/decreases ultimate stress/strain.
• The ultimate effect of concrete strength is larger in hybrid than regular columns.
• A 0.25 increase in the hollow section ratio can lead to 70% ultimate load increase.

The literature lacks exhaustive study on CFDST hybrid columns circumscribed by FRP layers. Extended FEM analysis was carried out on 70 real-scale models with varying parameters including the material and number of FRP layers, concrete strength, length-to-diameter ratio (specific length), and hollow section ratio. Carbon fibers proved stronger than glass fibers, leading to higher ultimate stress associated with lower strain. Specimens with high specific lengths suffered from steel premature buckling, thus stiffened with steel plates. Specimens with various hollow section ratios were finally compared, showing an increase range of 70% between the maximum (0.75) and minimum (0.25) ratios.