Abstract
Concrete filled double steel tubular members (CFDT) consist of two centric steel tubes and filled concrete between them. By the arrangement of the inner tube, own weight can be reduced in comparison with concrete filled steel tubular members. Four point loading tests on twelve specimens of CFDT were performed. Experimental parameters are inner-to-outer diameter ratios and outer tube's diameter-to-thickness ratios. The purpose of this study is to investigate effect of inner-to-outer diameter ratios on bending capacities. Experimental strengths were good agreement with bending strengths calculated using axial load (N)-bending moment (M) relation, where N was equal to zero. Failure modes were local buckling and fracture of outer tube. The larger inner-to-outer tube's diameter ratios, yield the smaller confinement strength.
