New cross-sectional slenderness limits for stiffened rectangular concrete-filled steel tubes

Abstract

Rectangular concrete-filled steel tubes (RCFST) are efficient structural members that exhibit good strength, stiffness, and ductility. The mechanical properties of RCFST can be further enhanced by the addition of internal stiffeners which delay local buckling of the tube, improve load transfer, and can confine the concrete. Numerous experimental and analytical studies have been performed to characterize the behavior of stiffened RCFST. However, most studies focus on a single type of stiffener. Also, most major design standards do not provide guidance on how to account for the beneficial effects of the stiffeners. The objective of this work was to develop strength design recommendations for short stiffened RCFST columns and beam-columns that are applicable to a variety of stiffener types. A database of previously published experimental tests on stiffened RCFST members was compiled and the experimental results were compared to American, European, and Chinese design standards. Each of these standards employs the plastic stress distribution method for filled composite members that are not susceptible to local buckling as identified using cross-sectional slenderness ratio limits. The results indicate that neglecting the stiffeners is unnecessarily conservative. New cross-sectional slenderness ratio limits are proposed for stiffened RCFST, allowing a greater range of members to be assessed using the plastic stress distribution method. These results provide strong justification for changes to design standards to recognize the benefits of highly efficient stiffened RCFST members.