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In this paper several design methods have been developed that can be used to conservatively estimate the strength of circular thin-walled concrete filled steel tubes under different loading conditions. The loading conditions examined include axial loading of the steel only, axial loading of the concrete only, and simultaneous loading of the concrete and steel both axially and at small eccentricities. Recent tests on circular concrete filled steel tubes have been used to calibrate and validate the proposed design methods. The test specimens were short with a length-to-diameter ratio of 3.5 and a diameter thickness ratio between 60 and 220. The internal concrete had nominal unconfined cylinder strengths of 50, 80, and 120 MPa. The bond (or lack of) between the steel and internal concrete was critical in determining the formation of a local buckle.
O’Shea et al. (Wed,) studied this question.