Table 1.

Main parameters of the specimens.

Group	Name	Shape	Quantity of Cavities	Cross-Sectional Area	Concrete Strength		Equivalent Steel Strength	Steel Plate Ratio		Steel-Bars Ratio
				A (m2)	fcu,m (Mpa)	fc,m (Mpa)	$\overline{f_{\mathrm{y}}}$ (Mpa)	ρ1 (%)	ρ2 (%)	ρ3 (%)
P	CFT1-P	Irregular pentagon	1	0.354	51.1	38.8	378.5	7.81	1.68	0.29
	CFT2-P		4				385.8	7.81	3.60	0
	CFT3-P		4				385.7	7.81	3.60	0.29
H	CFT1-H	Irregular hexagon	6	0.313	30.7	23.3	300.5	3.42	2.60	0.82
	CFT2-H		6		42.0	31.9	295.0	3.42	2.60	0
	CFT3-H		6		42.0	31.9	300.5	3.42	2.60	0.82

Note: f_cu,m is the tested average concrete cubic strength (150 mm × 150 mm × 150 mm); f_c,m = 0.76f_cu,m is the average concrete axial compressive strength [25]; $\overline{f_{\mathrm{y}}}=\frac{{\displaystyle \sum f_{\mathrm{y}i}{A}_{si}}}{{\displaystyle \sum A_{si}}}$ is the equivalent steel strength; ρ₁ is external steel tube steel plate ratio; ρ₂ is inner partition steel plate ratio.