Experimental and statistical investigation on uniaxial compressive performance of hybrid double skin tubular slender columns

Double-skin tubular columns have emerged as preferable in the construction sector because of their distinguished ease of benefits over traditional concrete columns. The uniaxial compression behaviour of the novel hybrid GFRP-concrete-steel double-skin tubular columns for different orientations is tested experimentally with various slenderness ratios. The experimental phase tested twenty-seven specimens by considering the three parameters such as fibre orientations (± 0°, 0°/90° and ± 45°), infill of the concrete (NSC, HSC and GPC) and void ratio (0.58, 0.6 and 0.68). The effect of these parameters was based on the ultimate load capacity, axial load-strain, and lateral deflection of DSTCs. The experimental tests revealed that as the column specimen's height increased, the confinement action became less effective. The test variables evaluated the effect of the slenderness ratio, the axial load-carrying capacity, ultimate axial strain, hoop strain, energy dissipation and ductility index. The fibre in 0/90° showed a higher energy dissipation and ductility index than the 0° and ± 45°. The load-carrying capacity of HSC infill revealed a 16% - 28% increase over the NSC and GPC. The axial strain showed a non-linear behaviour after 75% of the ultimate load. This study aims to develop a mathematical expression that predicts and optimises using a response surface methodology approach. The generated models were validated using Yu et al's model by introducing the slenderness ratio and proposed a new equation that closely agrees with the experimental results.