Ultimate Capacity Estimate of Self-Compacting Concrete-Filled Small Diameter Steel Tubes under Axial Load

This study explores the effect of length to diameter (𝐿/𝐷) ratio on the axial load capacity of selfcompacting concrete-filled small diameter steel tube (SCFT) specimens. The SCFT specimens with 𝐿/𝐷 ratio of 2, 4, 6, 8, 10, 12 and 14 were tested. Two different cold-formed steel tubes were used in the construction of the SCFT specimens. For each 𝐿/𝐷 ratio, two specimens were tested. For tension tests, three specimens were tested for each type of unfilled steel tube. A total of 62 steel tube specimens were tested which included 6 specimens under axial tension and 56 specimens under axial compression. The experimental results of the SCFT specimens were compared with the estimates from three design standards: American Standard, Canadian Standard and European Standard (Eurocode 4). It was found that Eurocode 4 provided the best estimate, whereas American Standard provided the most conservative estimate. Also, when the 𝐿/𝐷 ratio of SCFT specimens increased from 2 to 8, the parameter related to the effect of confinement concrete (𝜂𝑐) which is calculated from Eurocode 4 decreased. Therefore, the decrease in 𝜂𝑐 resulted in a decrease in the concrete enhancement factor. For SCFT specimens with 𝐿/𝐷 ratio ≥ 10 the parameter 𝜂𝑐 was negligible and resulted in the concrete enhancement factor =1.