n0, as well as the measured Poisson’s ratio and tensile strength fu

as obtained from the coupon tests, are given in Table    2.

The CFSST specimens were all cast by using self-consolidating concrete (SCC). Two  types of concrete were prepared to fill    the

steel tubes, namely normal concrete and recycled aggregate con- crete (RAC). The mix proportions of the fresh concrete are pre-

where N0 = axial load applied to the composite column; and Nu = axial compressive capacity of  the column.  The value  of Nu   was

sented in Table 3. For RAC, 50% by weight of natural coarse aggregate was replaced by recycled coarse aggregate, which   was

Table 1. Summary of Specimen  Information

type label type (mm) N0  (kN) level n (kN) Kie ðkN · m2 Þ Kse ðkN · m2Þ coefficient (μ) Etotal  (kN · m)

Circular CN-0 Normal 120.0 × 4.0 16.1 0.02 61.5 596.9 553.1 >8.95 42.68

CN-3 Normal 120.0 × 4.0 241.7 0.3 61.1 992.2 664.2 5.28 33.84

CR-3 RAC 120.0 × 4.0 230.7 0.3 62.4 1,038.1 659.4 7.04 30.57

CN-6 Normal 120.0 × 4.0 483.3 0.6 54.3 1,724.0 912.6 4.58 23.35

CR-6 RAC 120.0 × 4.0 461.4 0.6 52.7 1,717.5 846.1 4.69 19.92

Square SN-0 Normal 120.0 × 4.0 27.6 0.02 140.1 1,094.1 980.0 >6.09 27.18

SN-3 Normal 120.0 × 4.0