E2 300 150 5 58。0 746 37。5 49。7 Slender 83。6 — — — — 0。53 20 0。133

E3 300 300 5 58。0 301 59。0 78。3 Compact 70。5 — — — — 0。26 40 0。133

E4 300 300 5 58。0 746 37。5 49。7 Compactd 70。5 60 5 301 30。0 0。49 40 0。133

E5 300 150 5 58。0 746 37。5 49。7 Compactd 83。6 60 5 301 30。0 0。55 20 0。133

aWidth-to-thickness ratio of the tube flange, where bt  ¼ B − 2tt。

bWidth-to-thickness ratio of the subpanel, where w ¼ B=2。

cAxial load contribution of the steel section δs  ¼ ðfy;tAs;t  þ fy;sAs;sÞ=ðfy;tAs;t  þ fy;sAs;s  þ 0。85fc0 AcÞ。

dw=tt  was considered。

The average compressive  strengths  of  concrete cylinders (100 × 200 mm) are presented in Table 1。 The concrete cylinders were tested on the 36th day after concrete casting。 The column specimens were tested on the 34 ∼ 36th days。 As mentioned, in square-section Specimens E1, E3, and E4, the compressive strength of the concrete was fc0 ¼ 70。5 MPa。 In the rectangular-section Specimens E2 and E5, the concrete strength was fc0  ¼ 83。6  MPa。