Numerical investigations on axial compression performance of square coral aggregate concrete-filled duplex stainless steel tube columns

Square coral aggregate concrete-filled duplex stainless steel tube (CACFDSST) columns combine the superior corrosion resistance of duplex stainless steel with the sustainable utilization of marine aggregates, offering promising prospects for marine island infrastructure. This study presents a comprehensive numerical investigation into the axial compressive behavior of square CACFDSST stub columns. A refined three-dimensional finite element (FE) model was established using ABAQUS, incorporating material, geometric, and contact nonlinearities, and was rigorously validated against experimental data concerning failure modes and load-deformation responses. Utilizing a “peeling method”, the study elucidates the internal force evolution and interaction mechanisms between the steel tube and concrete. The analysis reveals a non-uniform confinement distribution across the cross-section: strong confinement occurs at the corners, with effective confinement primarily concentrated within a region extending approximately one-tenth of the side length from the corners, whereas mid-edge regions experience weaker confinement. Attributed to the high porosity of coral aggregates, the core concrete undergoes significant densification following initial crushing, exhibiting a unique “secondary hardening” phenomenon. This mechanism facilitates stiffness recovery and sustains high residual strength during the post-peak stage. Results indicate that the width-to-thickness ratio is the critical parameter governing failure modes; a smaller ratio enhances confinement and delays local buckling, resulting in significant post-yield hardening, while a larger ratio induces premature buckling and rapid strength degradation. Finally, a simplified formula for calculating the axial compressive bearing capacity, accounting for local buckling, is proposed based on the superposition theory. The proposed formula exhibits high prediction accuracy, with a mean predicted-to-tested ratio of 1.0 and a standard deviation of 0.059, providing a reliable theoretical basis for the engineering design of this novel marine composite structure. • A refined FE model was developed and validated to simulate axial compression behavior. • The steel-concrete interaction mechanism and concrete secondary hardening were revealed. • Width-to-thickness ratio is identified as the critical parameter governing failure modes. • A simplified capacity formula considering local buckling was proposed with high accuracy.