Behavior of double-skinned composite tubes with inner CSP under bending

Abstract

To support the engineering application of double-skin composite tubular columns (DSCTCs), this study investigates their pure bending behavior through experiments and numerical analysis. Based on prior axial compression studies, bending tests were conducted with hollow ratio as the primary variable. The experimental work focused on mid-span moment–curvature responses, deflection profiles, and steel tube strain distributions. Finite element simulations using ABAQUS were performed to analyze the internal behavior, and a fiber model was developed to establish a design formula for flexural capacity. Experimental results revealed that the bending process consists of elastic, elastic–plastic, and plastic stages, with all specimens demonstrating good ductility. The confinement effect in the compression zone increased with loading, while it was negligible in the tensile zone. Lower hollow ratios led to higher post-yield stiffness. Specimens exhibited half-sine deflection shapes, and steel tube strains conformed to the plane section assumption. Finite element results closely matched the experimental data, showing that the troughs of corrugated steel plates provided strong confinement in compression zones, while peaks were more effective in tension zones. A parametric study using the fiber model yielded a reliable formula for predicting pure bending capacity, which showed good agreement with test results. This study provides both theoretical and practical guidance for the design and application of DSCTC members in structural engineering.