Longitudinal Stiffeners in Concrete-Filled Tubes

To enhance the strength and constructability of rectangular (or trapezoidal) tubular compression members, reinforced or unreinforced concrete may be filled in the tube. Longitudinal stiffeners are often attached to increase the local buckling strength of the thin-walled skin. The effect of important design parameters on the minimum required stiffener moment of inertia was investigated numerically in this study by examining the residual stress distributions, initial imperfections, and elastic and inelastic buckling stresses of a number of hypothetical models. Because the thin-walled panel can only buckle (bulge) out from the concrete core, the buckling mode shape of a panel with multiple stiffeners resembles a waffle slab. A series of parametric studies was performed to characterize and quantify the analytically collected data. A new equation for the minimum required moment of inertia for the longitudinal stiffeners was derived. Through the evaluation of a few selected case studies and a design example, the validity and reliability of the proposed equation was demonstrated. DOI: 10.1061/(ASCE)ST.1943-541X.0000526. (C) 2012 American Society of Civil Engineers.