Design of concrete-filled high-strength steel RHS and SHS tubes under bending

Concrete-filled steel tubular members have been widely used in construction industry in recent years, and high-strength steel (HSS) is gaining its popularity as a construction material. This paper presents a numerical investigation of concrete-filled high-strength steel tubular members subjected to bending. An extensive parametric study with 144 specimens covering a wide range of geometric parameters was performed. The specimens consisted of square hollow sections (SHS) and rectangular hollow sections (RHS) with high-strength steel grades of 700 MPa and 900 MPa, and filled with concrete of grades C40, C70 and C110. The numerical results, together with test results reported in literature, were compared with design strengths calculated by existing design rules. Reliability analysis was conducted to evaluate the suitability of different design rules for concrete-filled high-strength steel tubular beams. The American Specification was shown to provide very conservative predictions of moment capacities for slender sections. On the other hand, theoretical plastic moment and European Code 4 with plastic moment assumption provide better predictions. Finally, a design method that incorporated confinement effect between the two materials was proposed. It is shown that the proposed design method provides more accurate and less scattered predictions compared to the aforementioned design rules.