Question: Where can I best obtain the axial compressive capacities of concrete-filled HSS columns?

Answer: The current design of composite members is prescribed by Chapter I of ANSI/AISC 360, which is a free download from www.aisc.org. Further information for designers is available from the current AISC “Steel Construction Manual”, also available from the AISC website. In STI Design Guide Volume 2, tables  outlining available strengths in axial compression (for both LRFD and ASD) for square, rectangular and round HSS to ASTM A500 Grade C, and ASTM A1085, filled with 4-ksi normal density concrete.